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30 pages, 8665 KiB

Open AccessFeature PaperArticle

A 1D Reduced-Order Model (ROM) for a Novel Latent Thermal Energy Storage System

by Gargi Kailkhura, Raphael Kahat Mandel, Amir Shooshtari and Michael Ohadi

Energies 2022, 15(14), 5124; https://doi.org/10.3390/en15145124 - 14 Jul 2022

Cited by 3 | Viewed by 2038

Abstract

Phase change material (PCM)-based thermal energy storage (TES) systems are widely used for repeated intermittent heating and cooling applications. However, such systems typically face some challenges due to the low thermal conductivity and expensive encapsulation process of PCMs. The present study overcomes these [...] Read more.

Phase change material (PCM)-based thermal energy storage (TES) systems are widely used for repeated intermittent heating and cooling applications. However, such systems typically face some challenges due to the low thermal conductivity and expensive encapsulation process of PCMs. The present study overcomes these challenges by proposing a lightweight, low-cost, and low thermal resistance TES system that realizes a fluid-to-PCM additively manufactured metal-polymer composite heat exchanger (HX), based on our previously developed cross-media approach. A robust and simplified, analytical-based, 1D reduced-order model (ROM) was developed to compute the TES system performance, saving computational time compared to modeling the entire TES system using PCM-related transient CFD modeling. The TES model was reduced to a segment-level model comprising a single PCM-wire cylindrical domain based on the tube-bank geometry formed by the metal fin-wires. A detailed study on the geometric behavior of the cylindrical domain and the effect of overlapped areas, where the overlapped areas represent a deviation from 1D assumption on the TES performance, was conducted. An optimum geometric range of wire-spacings and size was identified. The 1D ROM assumes 1D radial conduction inside the PCM and analytically computes latent energy stored in the single PCM-wire cylindrical domain using thermal resistance and energy conservation principles. The latent energy is then time-integrated for the entire TES, making the 1D ROM computationally efficient. The 1D ROM neglects sensible thermal capacity and is thus applicable for the low Stefan number applications in the present study. The performance parameters of the 1D ROM were then validated with a 2D axisymmetric model, typically used in the literature, using commercially available CFD tools. For validation, a parametric study of a wide range of non-dimensionalized parameters, depending on applications ranging from pulsed-power cooling to peak-load shifting for building cooling application, is included in this paper. The 1D ROM appears to correlate well with the 2D axisymmetric model to within 10%, except at some extreme ranges of a few of the non-dimensional parameters, which lead to the condition of axial conduction inside the PCM, deviating from the 1D ROM. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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28 pages, 7146 KiB

Open AccessArticle

Steam Temperature Characteristics in Boiler Water Wall Tubes Based on Furnace CFD and Hydrodynamic Coupling Model

by Xin Guo, Liangwei Xia, Guangbo Zhao, Guohua Wei, Yongjie Wang, Yaning Yin, Jianming Guo and Xiaohan Ren

Energies 2022, 15(13), 4745; https://doi.org/10.3390/en15134745 - 28 Jun 2022

Cited by 10 | Viewed by 2924

Abstract

With the development of power plant units of higher capacity and with improved parameters, the proportion of high-capacity units for generating power has increased; this requires large capacity units to take responsibility for power-grid peak shaving. When the boiler operates at low loads, [...] Read more.

With the development of power plant units of higher capacity and with improved parameters, the proportion of high-capacity units for generating power has increased; this requires large capacity units to take responsibility for power-grid peak shaving. When the boiler operates at low loads, the working fluid in the boiler water wall tubes is subjected to high heat flux in the furnace, which can cause heat transfer deterioration, tube overheating or even leakage. Therefore, it is particularly important to study the reliability of the boiler hydrodynamic cycle during peak shaving (low load operation). This study takes a 1000 MW ultra-supercritical single-reheat Π type boiler with single furnace and double tangential firing as the research object. A furnace Computational Fluid Dynamics (CFD) and hydrodynamic coupling analysis model is established and verified according to the actual operating conditions on site. The calculation results show that the simulated value is in good agreement with the actual operating value. Therefore, the model established in this study can reflect the real situation of the on-site furnace to a certain extent, and has high reliability. Based on the fitting results, the causes of steam temperature deviation of the boiler water wall are analyzed, and measures to reduce the deviation are proposed to provide a necessary basis for power plant operation and boiler design. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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17 pages, 3746 KiB

Open AccessArticle

A New Simple Function for Combustion and Cyclic Variation Modeling in Supercharged Spark Ignition Engines

by Stefano Beccari and Emiliano Pipitone

Energies 2022, 15(10), 3796; https://doi.org/10.3390/en15103796 - 21 May 2022

Cited by 1 | Viewed by 1650

Abstract

Research in the field of Internal Combustion (IC) engines focuses on the drastic reduction of both pollutant and greenhouse gas emissions. A promising alternative to gasoline and diesel fuel is represented by the use of gaseous fuels, above all green hydrogen but also [...] Read more.

Research in the field of Internal Combustion (IC) engines focuses on the drastic reduction of both pollutant and greenhouse gas emissions. A promising alternative to gasoline and diesel fuel is represented by the use of gaseous fuels, above all green hydrogen but also Natural Gas (NG). In previous works, the authors investigated the performance, efficiency, and emissions of a supercharged Spark Ignition (SI) engine fueled with mixtures of gasoline and natural gas; a detailed research involving the combustion process of this kind of fuel mixture has been previously performed and a lot of experimental data have been collected. Combustion modeling is a fundamental tool in the design and optimization process of an IC engine. A simple way to simulate the combustion evolution is to implement a mathematical function that reproduces the mass fraction burned (MFB) profile; the most used for this purpose is the Wiebe function. In a previous work, the authors proposed an innovative mathematical model, the Hill function, that allowed a better interpolation of experimental MFB profiles when compared to the Wiebe function. In the research work presented here, both the traditional Wiebe and the innovative Hill function have been calibrated using experimental MFB profiles obtained from a supercharged SI engine fueled with mixtures of gasoline and natural gas in different proportions; the two calibrated functions have been implemented in a zero-dimensional (0-D) SI engine model and compared in terms of both Indicated Mean Effective Pressure (IMEP) and cyclic pressure variation prediction reliability. It was found that the Hill function allows a better IMEP prediction for all the operating conditions tested (several engine speeds, supercharging pressures, and fuel mixtures), with a maximum prediction error of 2.7% compared to 4.3% of the Wiebe function. A further analysis was also performed regarding the cyclic pressure variation that affects all the IC engines during combustion and may lead to irregular engine operation; in this case, the Hill function proved to better predict the cyclic pressure variation with respect to the Wiebe function. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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15 pages, 4259 KiB

Open AccessArticle

Typical Damage Prediction and Reliability Analysis of Superheater Tubes in Power Station Boilers Based on Multisource Data Analysis

by Guangkui Liu, Xu Yang, Xisheng Yang, Kui Liang, Dong An, Di Wu and Xiaohan Ren

Energies 2022, 15(3), 1005; https://doi.org/10.3390/en15031005 - 29 Jan 2022

Cited by 7 | Viewed by 2167

Abstract

The superheater and re-heater piping components in supercritical thermal power units are prone to creep and fatigue failure fracture after extensive use due to the high pressure and temperature environment. Therefore, safety assessment for superheaters and re-heaters in such an environment is critical. [...] Read more.

The superheater and re-heater piping components in supercritical thermal power units are prone to creep and fatigue failure fracture after extensive use due to the high pressure and temperature environment. Therefore, safety assessment for superheaters and re-heaters in such an environment is critical. However, the actual service operation data is frequently insufficient, resulting in low accuracy of the safety assessment. Based on such problems, in order to address the issues of susceptibility of superheater and re-heater piping components to creep, inaccurate fatigue failure fracture, and creep–fatigue coupling rupture in a safety assessment, their remaining life prediction and reliability, as well as the lack of actual service operation data, multisource heterogeneous data generated from actual service of power plants combined with deep learning technology was used in this paper. As such, three real-time operating conditions’ data (temperature, pressure, and stress amplitude) during equipment operation are predicted by training a deep learning architecture long short-term memory (LSTM) neural network suitable for processing time-series data and a backpropagation through time (BPTT) algorithm is used to optimize the model and compared with the actual physical model. Damage assessment and life prediction of final superheater tubes of power station boilers are carried out. The Weibull distribution model is used to obtain the trend of cumulative failure risk change and assess and predict the safety condition of the overall system of pressurized components of power station boilers. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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22 pages, 4105 KiB

Open AccessArticle

Numerical and Experimental Study of a Novel Additively Manufactured Metal-Polymer Composite Heat-Exchanger for Liquid Cooling Electronics

by Gargi Kailkhura, Raphael Kahat Mandel, Amir Shooshtari and Michael Ohadi

Energies 2022, 15(2), 598; https://doi.org/10.3390/en15020598 - 14 Jan 2022

Cited by 10 | Viewed by 2816

Abstract

In order to meet increasing power-dissipation requirements of the electronics industry, compact, low-cost, and lightweight heat exchangers (HXs) are desired. With proper design, materials, and manufacture, polymer composite heat exchangers could meet these requirements. This paper presents a novel crossflow air-to-water, low-cost, and [...] Read more.

In order to meet increasing power-dissipation requirements of the electronics industry, compact, low-cost, and lightweight heat exchangers (HXs) are desired. With proper design, materials, and manufacture, polymer composite heat exchangers could meet these requirements. This paper presents a novel crossflow air-to-water, low-cost, and lightweight metal-polymer composite HX. This HX, which is entirely additively manufactured, utilizes a novel cross-media approach that provides direct heat exchange between air and liquid sides by using connecting fins. A robust numerical model was developed, which includes the dimensional effects of additive manufacturing. The study consists of a simplified 3D CFD model based on ellipsoidal-shaped staggered tube banks for the laminar range. It then uses an analytical approach to compute entire HX performance. The model is validated experimentally within 8% for thermal performance, 12% for air-side impedance, and 18% for water-side impedance. Finally, HX is compared with a conventional CPU radiator and performs within 10% of the conventional unit for reasonable flow rates and pressure-drop ranges. Moreover, HX also provides added design and cost advantages over the conventional unit, which makes the HX a potential candidate for electronic cooling applications. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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23 pages, 6092 KiB

Open AccessArticle

Performance Improvement of a Double-Layer Microchannel Heat Sink via Novel Fin Geometry—A Numerical Study

by Yong-Dong Zhang, Miao-Ru Chen, Jung-Hsien Wu, Kuo-Shu Hung and Chi-Chuan Wang

Energies 2021, 14(12), 3585; https://doi.org/10.3390/en14123585 - 16 Jun 2021

Cited by 15 | Viewed by 2773

Abstract

This study proposes a novel design having dense fins with lesser thickness at the upper layer and comparatively spare fins with greater thickness in the lower layer to further improve the overall thermal performance of a double-layer microchannel heat sink. The design can [...] Read more.

This study proposes a novel design having dense fins with lesser thickness at the upper layer and comparatively spare fins with greater thickness in the lower layer to further improve the overall thermal performance of a double-layer microchannel heat sink. The design can effectively direct more low temperature fluid flow toward the lower layer to improve heat transfer while the sparse fin structure at low layer can ease pressure drop penalty. At the same time, the thicker fins at the lower layer ensure higher fin efficiency to facilitate high heat transfer. Parametric and detailed analysis is conducted for the proposed double-layer microchannel heat sink in comparison with the traditional one. After optimization, the thermal resistance of the proposed double-layer microchannel heat sink at the same pumping power is found to be reduced by 9.42% when compared to the traditional double-layer microchannel heat sink. Yet at the same Reynolds number, the Nusselt number of the proposed design exceeds the traditional value by 13%. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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20 pages, 8301 KiB

Open AccessArticle

Influence of Errors in Known Constants and Boundary Conditions on Solutions of Inverse Heat Conduction Problem

by Sun Kyoung Kim

Energies 2021, 14(11), 3313; https://doi.org/10.3390/en14113313 - 4 Jun 2021

Cited by 2 | Viewed by 1761

Abstract

This work examines the effects of the known boundary conditions on the accuracy of the solution in one-dimensional inverse heat conduction problems. The failures in many applications of these problems are attributed to inaccuracy of the specified constants and boundary conditions. Since the [...] Read more.

This work examines the effects of the known boundary conditions on the accuracy of the solution in one-dimensional inverse heat conduction problems. The failures in many applications of these problems are attributed to inaccuracy of the specified constants and boundary conditions. Since the boundary conditions and material properties in most thermal problems are imposed with uncertainty, the effects of their inaccuracy should be understood prior to the inverse analyses. The deviation from the exact solution has been examined for each case according to the errors in material properties, boundary location, and known boundary conditions. The results show that the effects of such errors are dramatic. Based on these results, the applicability and limitations of the inverse heat conduction analyses have been evaluated and discussed. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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16 pages, 778 KiB

Open AccessArticle

Organic Rankine Cycle Optimization Performance Analysis Based on Super-Heater Pressure: Comparison of Working Fluids

by Ana Fernández-Guillamón, Ángel Molina-García, Francisco Vera-García and José A. Almendros-Ibáñez

Energies 2021, 14(9), 2548; https://doi.org/10.3390/en14092548 - 29 Apr 2021

Cited by 8 | Viewed by 2874

Abstract

The organic Rankine cycle (ORC) is widely accepted to produce electricity from low-grade thermal heat sources. In fact, it is a developed technology for waste-heat to electricity conversions. In this paper, an ORC made up of super-heater, turbine, regenerator, condenser, pump, economizer and [...] Read more.

The organic Rankine cycle (ORC) is widely accepted to produce electricity from low-grade thermal heat sources. In fact, it is a developed technology for waste-heat to electricity conversions. In this paper, an ORC made up of super-heater, turbine, regenerator, condenser, pump, economizer and evaporator is considered. An optimization model to obtain the maximum performance of such ORC, depending on the super-heater pressure, is proposed and assessed, in order to find possible new working fluids that are less pollutant with similar behavior to those traditionally used. The different super-heater pressures under analysis lie in between the condenser pressure and 80% of the critical pressure of each working fluid, taking 100 values uniformly distributed. The system and optimization algorithm have been simulated in Matlab with the CoolProp library. Results show that the twelve working fluids can be categorized into four main groups, depending on the saturation pressure at ambient conditions (condenser pressure), observing that the fluids belonging to Group 1, which corresponds with the lower condensing pressure (around 100 kPa), provide the highest thermal efficiency, with values around

η = 23 - 25 %

. Moreover, it is also seen that R123 can be a good candidate to substitute R141B and R11; R114 can replace R236EA and R245FA; and both R1234ZE and R1234YF have similar behavior to R134A. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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13 pages, 1449 KiB

Open AccessArticle

A MCDM Methodology to Determine the Most Critical Variables in the Pressure Drop and Heat Transfer in Minichannels

by Eloy Hontoria, Alejandro López-Belchí, Nolberto Munier and Francisco Vera-García

Energies 2021, 14(8), 2069; https://doi.org/10.3390/en14082069 - 8 Apr 2021

Cited by 2 | Viewed by 1896

Abstract

This paper proposes a methodology aiming at determining the most influent working variables and geometrical parameters over the pressure drop and heat transfer during the condensation process of several refrigerant gases using heat exchangers with pipes mini channels technology. A multi-criteria decision making [...] Read more.

This paper proposes a methodology aiming at determining the most influent working variables and geometrical parameters over the pressure drop and heat transfer during the condensation process of several refrigerant gases using heat exchangers with pipes mini channels technology. A multi-criteria decision making (MCDM) methodology was used; this MCDM includes a mathematical method called SIMUS (Sequential Interactive Modelling for Urban Systems) that was applied to the results of 2543 tests obtained by using a designed refrigeration rig in which five different refrigerants (R32, R134a, R290, R410A and R1234yf) and two different tube geometries were tested. This methodology allows us to reduce the computational cost compared to the use of neural networks or other model development systems. This research shows six variables out of 39 that better define simultaneously the minimum pressure drop, as well as the maximum heat transfer, saturation pressure fluid entering the condenser being the most important one. Another aim of this research was to highlight a new methodology based on operation research for their application to improve the heat transfer energy efficiency and reduce the CO₂ footprint derived of the use of heat exchangers with minichannels. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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22 pages, 8156 KiB

Open AccessArticle

Passive Heating and Cooling of Photovoltaic Greenhouses Including Thermochromic Materials

by Javier Padilla, Carlos Toledo, Rodolfo López-Vicente, Raquel Montoya, José-Ramón Navarro, José Abad and Antonio Urbina

Energies 2021, 14(2), 438; https://doi.org/10.3390/en14020438 - 15 Jan 2021

Cited by 2 | Viewed by 2263

Abstract

The integration of photovoltaic technologies into greenhouse envelopes appears to be an innovative and environmentally-friendly way to supply their various energy demands. However, the effect on the inner growing conditions, especially on the temperature, must be assessed in order to effectively implement this [...] Read more.

The integration of photovoltaic technologies into greenhouse envelopes appears to be an innovative and environmentally-friendly way to supply their various energy demands. However, the effect on the inner growing conditions, especially on the temperature, must be assessed in order to effectively implement this solution. In this study, experimental temperature data were obtained over two years for four structures built with different photovoltaic technologies (mono-crystalline silicon, amorphous silicon, cadmium telluride, and an organic polymeric technology) and fitted to a thermal model in order to provide a comprehensive analysis of their potential utilization as a cover material in greenhouses. Additionally, the thermal effect of color in structures composed of several common construction materials (brick, wood, plasterboard and glass) was quantified and modelled, supplementing the thermal analysis of passive solutions for this application. In all cases, inner and ambient temperature differences of up to +20 °C, created by a passive heating effect during the day, and −5 °C, created by a passive cooling effect during the night, have been observed, suggesting the use of the photovoltaic modules with different degrees of structure coverage, complemented with the color tuning of the modules themselves as passive methods to control the temperature and light spectrum of greenhouses. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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21 pages, 7948 KiB

Open AccessArticle

Numerical Calculation and Uncertain Optimization of Energy Conversion in Interior Ballistics Stage

by Tong Xin, Guolai Yang, Liqun Wang and Quanzhao Sun

Energies 2020, 13(21), 5824; https://doi.org/10.3390/en13215824 - 7 Nov 2020

Cited by 7 | Viewed by 2717

Abstract

Gun firing is a process that converts propellant chemical energy to projectile kinetic energy and other kinds of energies. In order to explore the energy conversion process, firstly, the interior ballistics mathematical model and the barrel-projectile finite element model are built and solved. [...] Read more.

Gun firing is a process that converts propellant chemical energy to projectile kinetic energy and other kinds of energies. In order to explore the energy conversion process, firstly, the interior ballistics mathematical model and the barrel-projectile finite element model are built and solved. Then, the related variable values and energy values are obtained and discussed. Finally, for improving energy efficiency, the interval uncertainty optimization problem is modeled, and then solved using the two-layer nested optimization strategy and back-propagation (BP) neural network surrogate model. Calculation results show that, after optimization, the heat efficiency raises from 31.13% to 33.05% and the max rifling stress decreases from 893.68 to 859.76 Mpa, which would improve the firing performance and prolong the lifetime of the gun barrel. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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17 pages, 4814 KiB

Open AccessArticle

Hydrothermal Investigation of a Microchannel Heat Sink Using Secondary Flows in Trapezoidal and Parallel Orientations

by Safi Ahmed Memon, Taqi Ahmad Cheema, Gyu Man Kim and Cheol Woo Park

Energies 2020, 13(21), 5616; https://doi.org/10.3390/en13215616 - 27 Oct 2020

Cited by 16 | Viewed by 3048

Abstract

Thermal performance enhancement in microchannel heat sinks has recently become a challenge due to advancements in modern microelectronics, which demand compatibility with heat sinks able to dissipate ever-increasing amounts of heat. Recent advancements in manufacturing techniques, such as additive manufacturing, have made the [...] Read more.

Thermal performance enhancement in microchannel heat sinks has recently become a challenge due to advancements in modern microelectronics, which demand compatibility with heat sinks able to dissipate ever-increasing amounts of heat. Recent advancements in manufacturing techniques, such as additive manufacturing, have made the modification of the microchannel heat sink geometry possible well beyond the conventional rectangular model to improve the cooling capacity of these devices. One such modification in microchannel geometry includes the introduction of secondary flow channels in the walls between adjacent mainstream microchannels. The present study computationally models secondary flow channels in regular trapezoidal and parallel orientations for fluid circulation through the microchannel walls in a heat sink design. The heat sink is made of silicon wafer, and water is used as the circulating fluid in this study. Continuity, momentum, and energy equations are solved for the fluid flow through the regular trapezoidal secondary flow and parallel secondary flow designs in the heat sink with I-type, C-type, and Z-type inlet–outlet configurations. Plots of velocity contours show that I-type geometry creates optimal flow disruption in the heat sink. Therefore, for this design, the pressure drop and base plate temperatures are plotted for a volumetric flow rate range, and corresponding contour plots are obtained. The results are compared with corresponding trends for the conventional rectangular microchannel design, and associated trends are explained. The study suggests that the flow phenomena such as flow impingement onto the microchannel walls and formation of vortices inside the secondary flow passages coupled with an increase in heat transfer area due to secondary flow passages may significantly improve the heat sink performance. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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17 pages, 6277 KiB

Open AccessArticle

Mechanical Integrity Assessment of Two-Side Etched Type Printed Circuit Heat Exchanger with Additional Elliptical Channel

by Armanto P. Simanjuntak and Jae-Young Lee

Energies 2020, 13(18), 4711; https://doi.org/10.3390/en13184711 - 10 Sep 2020

Cited by 6 | Viewed by 2665

Abstract

Printed circuit heat exchangers (PCHEs) are often subject to high pressure and temperature difference between the hot and cold channels which may cause a mechanical integrity problem. A conventional plate heat exchanger where the channel geometries are semi-circular and etched at one side [...] Read more.

Printed circuit heat exchangers (PCHEs) are often subject to high pressure and temperature difference between the hot and cold channels which may cause a mechanical integrity problem. A conventional plate heat exchanger where the channel geometries are semi-circular and etched at one side of the stacked plate is a common design in the market. However, the sharp edge tip channel may cause high stress intensity. Double-faced type PCHE appears with the promising ability to reduce the stress intensity and stress concentration factor. Finite element analysis simulation has been conducted to observe the mechanical integrity of double-etched printed circuit heat exchanger design. The application of an additional ellipse upper channel helps the stress intensity decrease in the proposed PCHE channel. Five different cases were simulated in this study. The simulation shows that the stress intensity was reduced up to 24% with the increase in additional elliptical channel radius. Besides that, the horizontal offset channels configuration was also investigated in this study. Simulation results show that the maximum stress intensity of 2.5 mm offset configuration is 9% lower compared to the maximum stress intensity of 0 mm offset. This work proposed an additional elliptical upper channel with a 2.5 mm offset configuration as an optimum design. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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23 pages, 16957 KiB

Open AccessFeature PaperArticle

Nonlinear Optimization of Turbine Conjugate Heat Transfer with Iterative Machine Learning and Training Sample Replacement

by Sandip Dutta and Reid Smith

Energies 2020, 13(17), 4587; https://doi.org/10.3390/en13174587 - 3 Sep 2020

Cited by 6 | Viewed by 3600

Abstract

A simple yet effective optimization technique is developed to solve nonlinear conjugate heat transfer. The proposed Nonlinear Optimization with Replacement Strategy (NORS) is a mutation of several existing optimization processes. With the improvements of 3D metal printing of turbine components, it is feasible [...] Read more.

A simple yet effective optimization technique is developed to solve nonlinear conjugate heat transfer. The proposed Nonlinear Optimization with Replacement Strategy (NORS) is a mutation of several existing optimization processes. With the improvements of 3D metal printing of turbine components, it is feasible to have film holes with unconventional diameters, as these holes are created while printing the component. This paper seeks to optimize each film hole diameter at the leading edge of a turbine vane to satisfy several optimum thermal design objectives with given design constraints. The design technique developed uses linear regression-based machine learning model and further optimizes with strategic improvement of the training dataset. Optimization needs cost and benefit criteria are used to base its decision of success, and cost is minimized with maximum benefit within given constraints. This study minimizes the coolant flow (cost) while satisfying the constraints on average metal temperature and metal temperature variations (benefits) that limit the useful life of turbine components. The proposed NORS methodology provides a scientific basis for selecting design parameters in a nonlinear design space. This model is also a potential academic tool to be used in thesis works without demanding extensive computing resources. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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26 pages, 13705 KiB

Open AccessEditor’s ChoiceArticle

Development of a Variable Valve Actuation Control to Improve Diesel Oxidation Catalyst Efficiency and Emissions in a Light Duty Diesel Engine

by José R. Serrano, Francisco J. Arnau, Jaime Martín and Ángel Auñón

Energies 2020, 13(17), 4561; https://doi.org/10.3390/en13174561 - 3 Sep 2020

Cited by 11 | Viewed by 4481

Abstract

Growing interest has arisen to adopt Variable Valve Timing (VVT) technology for automotive engines due to the need to fulfill the pollutant emission regulations. Several VVT strategies, such as the exhaust re-opening and the late exhaust closing, can be used to achieve an [...] Read more.

Growing interest has arisen to adopt Variable Valve Timing (VVT) technology for automotive engines due to the need to fulfill the pollutant emission regulations. Several VVT strategies, such as the exhaust re-opening and the late exhaust closing, can be used to achieve an increment in the after-treatment upstream temperature by increasing the residual gas amount. In this study, a one-dimensional gas dynamics engine model has been used to simulate several VVT strategies and develop a control system to actuate over the valves timing in order to increase diesel oxidation catalyst efficiency and reduce the exhaust pollutant emissions. A transient operating conditions comparison, taking the Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC) as a reference, has been done by analyzing fuel economy, HC and CO pollutant emissions levels. The results conclude that the combination of an early exhaust and a late intake valve events leads to a 20% reduction in CO emissions with a fuel penalty of 6% over the low speed stage of the WLTC, during the warm-up of the oxidation catalyst. The same set-up is able to reduce HC emissions down to 16% and NO_x emission by 13%. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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18 pages, 8607 KiB

Open AccessArticle

Convective Drying of Ceramic Bricks by CFD: Transport Phenomena and Process Parameters Analysis

by Morgana de Vasconcellos Araújo, Balbina Raquel de Brito Correia, Vanderson Alves Agra Brandão, Iran Rodrigues de Oliveira, Rosilda Sousa Santos, Guilherme Luiz de Oliveira Neto, Leonardo Pereira de Lucena Silva and Antonio Gilson Barbosa de Lima

Energies 2020, 13(8), 2073; https://doi.org/10.3390/en13082073 - 21 Apr 2020

Cited by 13 | Viewed by 3853

Abstract

In the manufacturing process of ceramic brick, the step of drying needs the control of process variables to uniformly dry the porous material, producing a good end-product. The majority of numerical simulations involving drying of ceramic materials is performed considering only the solid [...] Read more.

In the manufacturing process of ceramic brick, the step of drying needs the control of process variables to uniformly dry the porous material, producing a good end-product. The majority of numerical simulations involving drying of ceramic materials is performed considering only the solid domain, resulting in a very simplified and limited study. This way, the objective of this work is the analysis of the drying process with hot air of an industrial hollow clay brick inside the oven at different temperatures by using computational fluid dynamic (CFD). The results of the temperature and water mass distribution inside the brick and of air in the oven at different times of the drying process are shown, analyzed and checked with experimental data, and it was obtained in a concordance with the data. An equation to calculate the brick water mass diffusivity depending on the drying air temperature was proposed. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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23 pages, 15242 KiB

Open AccessFeature PaperArticle

System Characteristics Analysis for Energy Management of Power-Split Hydraulic Hybrids

by Hyukjoon Kwon and Monika Ivantysynova

Energies 2020, 13(7), 1837; https://doi.org/10.3390/en13071837 - 10 Apr 2020

Cited by 11 | Viewed by 3718

Abstract

Hydraulic hybrid powertrains provide an opportunity for specific applications, such as heavy-duty vehicles based on high-power density, which has not been included in other types of hybrid powertrains. Among the various architectures of hybrid vehicles, power-split hybrids have a greater possibility of producing [...] Read more.

Hydraulic hybrid powertrains provide an opportunity for specific applications, such as heavy-duty vehicles based on high-power density, which has not been included in other types of hybrid powertrains. Among the various architectures of hybrid vehicles, power-split hybrids have a greater possibility of producing better fuel efficiency than other hybrid architectures. This study analyzed the possible energy-saving characteristics of power-split hydraulic hybrid vehicles (HHVs); this has not been comprehensively described in previous studies. A typical configuration of power-split HHVs was modeled with the FTP-72 driving cycle using a novel simulation method that considered the dynamic and thermal behaviors together. The characteristics were analyzed in comparison to a power-split hydrostatic transmission (HST), which is designed with the same conditions except for hydraulic energy storage. The power-split HHV not only has a better fuel efficiency, but it also shows system energy-saving characteristics. The power-split HHV has more chances for engine idling, which is directly related to fuel consumption savings due to engine stop. Additionally, more engine idling time enables the system to operate in a more efficient area on the engine map by load leveling. The results for the system temperature show that the power-split HHV offers the possibility to deliver better thermal management because it prevents the waste of braking power, which is especially crucial for hydraulic systems in comparison to other power systems such as electric or mechanical power systems. The ease of thermal management results in less energy consumption for cooling down the system temperature by minimizing the cooling system, as well as in a better thermal stability for the hydraulic system. The power-split HHV characteristics analyzed in this study can be used to design and organize the system control logic while developing power-split HHVs. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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26 pages, 4284 KiB

Open AccessArticle

Study of the Miller Cycle on a Turbocharged DI Gasoline Engine Regarding Fuel Economy Improvement at Part Load

by Xuewei Pan, Yinghua Zhao, Diming Lou and Liang Fang

Energies 2020, 13(6), 1500; https://doi.org/10.3390/en13061500 - 22 Mar 2020

Cited by 16 | Viewed by 4285

Abstract

This contribution is focused on the fuel economy improvement of the Miller cycle under part-load characteristics on a supercharged DI (Direct Injection) gasoline engine. Firstly, based on the engine bench test, the effects with the Miller cycle application under 3000 rpm were studied. [...] Read more.

This contribution is focused on the fuel economy improvement of the Miller cycle under part-load characteristics on a supercharged DI (Direct Injection) gasoline engine. Firstly, based on the engine bench test, the effects with the Miller cycle application under 3000 rpm were studied. The results show that the Miller cycle has different extents of improvement on pumping loss, combustion and friction loss. For low, medium and high loads, the brake thermal efficiency of the baseline engine is increased by 2.8%, 2.5% and 2.6%, respectively. Besides, the baseline variable valve timing (VVT) is optimized by the test. Subsequently, the 1D CFD (Computational Fluid Dynamics) model of the Miller cycle engine after the test optimization at the working condition of 3000 rpm and BMEP (Brake Mean Effective Pressure) = 10 bar was established, and the influence of the combined change of intake and exhaust valve timing on Miller cycle was studied by simulation. The results show that as the effect of the Miller cycle deepens, the engine’s knocking tendency decreases, so the ignition timing can be further advanced, and the economy of the engine can be improved. Compared with the brake thermal efficiency of the baseline engine, the final result after simulation optimization is increased from 34.6% to 35.6%, which is an improvement of 2.9%. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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28 pages, 5368 KiB

Open AccessArticle

Studying the Role of System Aggregation in Energy Targeting: A Case Study of a Swedish Oil Refinery

by Elin Svensson, Matteo Morandin, Simon Harvey and Stavros Papadokonstantakis

Energies 2020, 13(4), 958; https://doi.org/10.3390/en13040958 - 20 Feb 2020

Cited by 6 | Viewed by 2794

Abstract

The definition of appropriate energy targets for large industrial processes is a difficult task since operability, safety and plant layout aspects represent important limitations to direct process integration. The role of heat exchange limitations in the definition of appropriate energy targets for large [...] Read more.

The definition of appropriate energy targets for large industrial processes is a difficult task since operability, safety and plant layout aspects represent important limitations to direct process integration. The role of heat exchange limitations in the definition of appropriate energy targets for large process sites was studied in this work. A computational framework was used which allows to estimate the optimal distribution of process stream heat loads in different subsystems and to select and size a site wide utility system. A complex Swedish refinery site is used as a case study. Various system aggregations, representing different patterns of heat exchange limitations between process units and utility configurations were explored to identify trade-offs and bottlenecks for energy saving opportunities. The results show that in spite of the aforementioned limitations direct heat integration still plays a significant role for the refinery energy efficiency. For example, the targeted hot utility demand is reduced by 50–65% by allowing process-to-process heat exchange within process units even when a steam utility system is available for indirect heat recovery. Furthermore, it was found that direct process heat integration is motivated primarily at process unit level, since the heat savings that can be achieved by allowing direct heat recovery between adjacent process units (25–42%) are in the same range as those that can be obtained by combining unit process-to-process integration with site-wide indirect heat recovery via the steam system (27–42%). Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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28 pages, 8218 KiB

Open AccessArticle

Planned Heating Control Strategy and Thermodynamic Modeling of a Natural Gas Thermal Desorption System for Contaminated Soil

by Hui-Juan Xu, Yun-Ze Li, Li-Jun Gao and Xin Zhang

Energies 2020, 13(3), 642; https://doi.org/10.3390/en13030642 - 3 Feb 2020

Cited by 11 | Viewed by 2996

Abstract

This paper presents a planned heating control strategy applied for a natural gas thermal desorption system for polluted soil to achieve the dynamic adjustment of the heating time and energy consumption. A lumped-parameter model for the proposed system is established to examine effects [...] Read more.

This paper presents a planned heating control strategy applied for a natural gas thermal desorption system for polluted soil to achieve the dynamic adjustment of the heating time and energy consumption. A lumped-parameter model for the proposed system is established to examine effects of the natural gas mass flow rate and the excess air coefficient on the heating performance of the target soil. The control strategy is explored to accomplish the heating process as expected with constant temperature change rate or constant volumetric water content change rate at different phases by adapting the natural gas flow. The results demonstrate that the heating plan can be realized within the scheduled 36 days and the total natural gas consumption can be reduced by 24% (1487 kg) compared to that of the open-loop reference condition, which may be widely applied for other thermal remediation systems of the polluted soil. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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24 pages, 6559 KiB

Open AccessArticle

Thermo-Economic Analysis of a Hybrid Ejector Refrigerating System Based on a Low Grade Heat Source

by Gianluca Lillo, Rita Mastrullo, Alfonso William Mauro, Raniero Trinchieri and Luca Viscito

Energies 2020, 13(3), 562; https://doi.org/10.3390/en13030562 - 23 Jan 2020

Cited by 15 | Viewed by 3485

Abstract

The rising of the global energy demand requires the use of alternative energy conversion systems employing renewable sources. In the refrigeration and air conditioning fields, heat driven ejector systems represent a promising way to produce the cooling effect by using available low-grade temperature [...] Read more.

The rising of the global energy demand requires the use of alternative energy conversion systems employing renewable sources. In the refrigeration and air conditioning fields, heat driven ejector systems represent a promising way to produce the cooling effect by using available low-grade temperature sources. In this paper, a thermo-economic analysis of a waste heat recovery hybrid ejector cycle (WHRHEC) was carried out. A thermodynamic model was firstly developed to simulate a WHRHEC able to obtain chilled water with a cooling load of 20 kW, by varying the working fluids and the pinch point values in the heat exchangers. Specific single- and two-phase heat transfer correlations were used to estimate the heat transfer surface and therefore the investment costs. The operative ranges that provide a reasonable compromise between the set-up costs and the cycle performances were then defined and compared to the current waste heat-driven technologies, such as absorption chillers and organic Rankine cycles (ORCs) coupled with vapor compression cycles (VCCs). The last part of the paper presents an economic analysis providing the map of the design (plant size) and contingent (specific cost of energy, waste heat availability) variables that lead to the economic convenience of a WHRHEC system when integrated to a conventional VCC plant. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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28 pages, 2778 KiB

Open AccessArticle

Improvements of a Failure Database for Marine Diesel Engines Using the RCM and Simulations

by Francisco Vera-García, José Antonio Pagán Rubio, José Hernández Grau and Daniel Albaladejo Hernández

Energies 2020, 13(1), 104; https://doi.org/10.3390/en13010104 - 24 Dec 2019

Cited by 30 | Viewed by 4769

Abstract

Diesel engines are widely used in marine transportation as a direct connection to the propeller and as electrical principal or auxiliary generator sets. The engine is the most critical piece of equipment on a vessel platform; therefore, the engine’s reliability is paramount in [...] Read more.

Diesel engines are widely used in marine transportation as a direct connection to the propeller and as electrical principal or auxiliary generator sets. The engine is the most critical piece of equipment on a vessel platform; therefore, the engine’s reliability is paramount in order to optimize safety, life cycle costs, and energy of the boat, and hence, vessel availability. In this paper, the improvements of a failure database used for a four-stroke high-speed marine diesel engine are discussed. This type of engine is normally used in military and civil vessels as the main engine of small patrols and yachts and as an auxiliary generator set (GENSET) for larger vessels. This database was assembled by considering “failure modes, effects, and criticality analysis (FMECA),” as well as an analysis of the symptoms obtained in an engine failure simulator. The FMECA was performed following the methodology of reliability-centered maintenance (RCM), while the engine response against failures was obtained from a failure simulator based on a thermodynamic one-dimensional model created by the authors, which was adjusted and validated with experimental data. The novelty of this work is the methodology applied, which combines expert knowledge of the asset, the RCM methodology, and the failure simulation to obtain an accurate and reliable database for the prediction of failures, which serves as a key element of a diesel engine failure diagnosis system. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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16 pages, 3982 KiB

Open AccessArticle

An Energetic Model for Detonation of Granulated Solid Propellants

by Carmen López-Munoz, J.R. García-Cascales, F.J.S. Velasco and R.A. Otón-Martínez

Energies 2019, 12(23), 4459; https://doi.org/10.3390/en12234459 - 22 Nov 2019

Cited by 6 | Viewed by 2353

Abstract

Unexpected detonation of granular solid energetic materials is a key safety issue in the propellants manufacturing industry. In this work, a model developed for the characterization of the early stages of the detonation process of granular solid energetic materials is presented. The model [...] Read more.

Unexpected detonation of granular solid energetic materials is a key safety issue in the propellants manufacturing industry. In this work, a model developed for the characterization of the early stages of the detonation process of granular solid energetic materials is presented. The model relies on a two-phase approach which considers the conservation equations of mass, momentum, and energy and constitutive relations for mass generation, gas-solid particle interaction, interphase heat transfer, and particle-particle stress. The work considers an extension of approximated Riemann solvers and Total Variation Diminishing (TVD) schemes to the solid phase for the numerical integration of the problem. The results obtained with this model show a good agreement with data available in the literature and confirm the potential of the numerical schemes applied to this type of model. The results also permit to assess the effectiveness of different numerical schemes to predict the early stages of this transient combustion process. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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12 pages, 5479 KiB

Open AccessArticle

Fast Heating Model for the Aircraft Cabin Air

by Zhi Yang, Zhengwei Long and Guangwen Wang

Energies 2019, 12(18), 3565; https://doi.org/10.3390/en12183565 - 18 Sep 2019

Cited by 3 | Viewed by 3112

Abstract

Maintaining a suitable cabin air temperature distribution is essential for providing an acceptable thermal environment for passengers and crew. However, cabin air may be very cold for the first flight in winter morning. It could be difficult to heat quickly the cabin air [...] Read more.

Maintaining a suitable cabin air temperature distribution is essential for providing an acceptable thermal environment for passengers and crew. However, cabin air may be very cold for the first flight in winter morning. It could be difficult to heat quickly the cabin air and to maintain an acceptable temperature gradient before boarding with the existing environmental control system. This study developed numerical model for predicting the heating process that coupled airflow and heat transfer in a cabin. The model was validated by using the experimental data obtained from an MD-82 airliner. With the validated numerical model, this investigation proposed to use an electric blanket to heat cabin air quickly and to reduce the air temperature gradient. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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12 pages, 2250 KiB

Open AccessFeature PaperArticle

Analysis of Thermodynamic Models for Simulation and Optimisation of Organic Rankine Cycles

by Goran Durakovic and Geir Skaugen

Energies 2019, 12(17), 3307; https://doi.org/10.3390/en12173307 - 27 Aug 2019

Cited by 5 | Viewed by 3029

Abstract

Equations of state (EOSs) form the base of every thermodynamic model used in the design of industrial processes, but little work has been done to evaluate these in the context of such models. This work evaluates 13 EOSs for their accuracy, computational time [...] Read more.

Equations of state (EOSs) form the base of every thermodynamic model used in the design of industrial processes, but little work has been done to evaluate these in the context of such models. This work evaluates 13 EOSs for their accuracy, computational time and robustness when used in an in-house optimisation program that finds the maximum power output of an organic Rankine cycle. The EOSs represent popular choices in the industry, such as the simple cubic EOSs, and more complex EOSs such as the ones based on corresponding state principles (CSP). These results were compared with results from using the Groupe Européen de Recherches Gazières (GERG) EOS, whose error is within experimental uncertainty. It appears that the corresponding state EOSs find a solution to the optimisation problem notably faster than GERG without significant loss of accuracy. A corresponding state method which used the Peng–Robinson EOS to calculate the shape factors and a highly accurate EOS for propane as the reference EOS, was shown to have a total deviation of just 0.6% as compared to GERG while also being 10 times as fast. The CSP implementation was also more robust, being able to converge successfully more often. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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17 pages, 6281 KiB

Open AccessArticle

Diesel Mean Value Engine Modeling Based on Thermodynamic Cycle Simulation Using Artificial Neural Network

by Eunhee Ko and Jungsoo Park

Energies 2019, 12(14), 2823; https://doi.org/10.3390/en12142823 - 22 Jul 2019

Cited by 10 | Viewed by 4143

Abstract

This study aims to construct a reduced thermodynamic cycle model with high accuracy and high model execution speed based on artificial neural network training for real-time numerical analysis. This paper proposes a method of constructing a fast average-value model by combining a 1D [...] Read more.

This study aims to construct a reduced thermodynamic cycle model with high accuracy and high model execution speed based on artificial neural network training for real-time numerical analysis. This paper proposes a method of constructing a fast average-value model by combining a 1D plant model and exhaust gas recirculation (EGR) control logic. The combustion model of the detailed model uses a direct-injection diesel multi-pulse (DI-pulse) method similar to diesel combustion characteristics. The DI-pulse combustion method divides the volume of the cylinder into three zones, predicting combustion- and emission-related variables, and each combustion step comprises different correction variables. This detailed model is estimated to be within 5% of the reference engine test results. To reduce the analysis time while maintaining the accuracy of engine performance prediction, the cylinder volumetric efficiency and the exhaust gas temperature were predicted using an artificial neural network. Owing to the lack of input variables in the training of artificial neural networks, it was not possible to predict the 0.6–0.7 range for volumetric efficiency and the 1000–1200 K range for exhaust gas temperature. This is because the mean value model changes the fuel injection method from the common rail fuel injection mode to the single injection mode in the model reduction process and changes the in-cylinder combustion according to the injection timing of the fuel amount injected. In addition, the mean value model combined with EGR logic, i.e., the single-input single-output (SISO) coupled mean value model, verifies the accuracy and responsiveness of the EGR control logic model through a step-transient process. By comparing the engine performance results of the SISO coupled mean value model with those of the mean value model, it is observed that the SISO coupled mean value model achieves the desired target EGR rate within 10 s. The EGR rate is predicted to be similar to the response of volumetric efficiency. This process intuitively predicted the main performance parameters of the engine model through artificial neural networks. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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8 pages, 325 KiB

Open AccessComment

Comment on Hamayun et al. Evaluation of Two-Column Air Separation Processes Based on Exergy Analysis. Energies 2020, 13, 6361

by Miroslav Variny, Dominika Jediná and Patrik Furda

Energies 2021, 14(20), 6443; https://doi.org/10.3390/en14206443 - 9 Oct 2021

Cited by 1 | Viewed by 2290

Abstract

Oxygen production from air belongs to energy-intense processes and, as a result, possibilities for its decrease are a frequent topic of optimization studies, often performed with simulation software such as Aspen Plus or Aspen HYSYS. To obtain veritable results and sound solutions, a [...] Read more.

Oxygen production from air belongs to energy-intense processes and, as a result, possibilities for its decrease are a frequent topic of optimization studies, often performed with simulation software such as Aspen Plus or Aspen HYSYS. To obtain veritable results and sound solutions, a suitable calculation method hand in hand with justified assumptions and simplifications should form the base of any such studies. Thus, an analysis of the study by Hamayun et al., Energies 2020, 13, 6361, has been performed, and several weak spots of the study, including oversimplified assumptions, improper selection of a thermodynamic package for simulation and omission of certain technological aspects relevant for energy consumption optimization studies, were identified. For each of the weak spots, a recommendation based on good praxis and relevant scientific literature is provided, and general recommendations are formulated with the hope that this comment will aid all researchers utilizing Aspen Plus and Aspen HYSYS software in their work. Full article

(This article belongs to the Special Issue Modelling of Thermal and Energy Systems)

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