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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J: Thermal Management".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 36409

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Special Issue Editors

Dr. Pouyan Talebizadeh Sardari

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Power Electronics, Machines and Control (PEMC) Research Institute, University of Nottingham, Nottingham NG8 1BB, UK
Interests: computational fluid dynamics (CFD); heat and mass transfer; turbulence; thermal energy storage; multiphase flows; aerosols transport and deposition phase change materials; photovoltaic/thermal systems
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Prof. Dr. Goodarz Ahmadi

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Department of Mechanical and Aeronautical Engineering, Clarkson University, Potsdam, NY 13699-5725, USA
Interests: computational fluid dynamics (CFD); turbulence; multiphase flows; aerosols transport and deposition; respiratory flows; heat and mass transfer
Special Issues, Collections and Topics in MDPI journals

Dr. Kiao Inthavong

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Guest Editor

School of Engineering, RMIT University, Bundoora, VIC 3083, Australia
Interests: computational and experimental fluid dynamics (CFD, EFD); respiratory flows; multiphase flows; aerosol science; spray atomization; heat and mass transfer

Special Issue Information

Dear Colleagues,

The Guest Editors would like to invite you to submit a paper to the Special Issue of Energies on the subject area of “Computational Heat Transfer and Fluid Mechanics”.

With the advances in high-speed computer technology, complex heat transfer and fluid flow problems can be solved computationally with high accuracy. Computational modeling techniques have found a wide range of applications in diverse fields of mechanical, aerospace, energy, environmental, as well as numerous industrial systems. Computational modeling has also been used extensively for optimization of performance of a variety of engineering designs.

This Special Issue would welcome papers in various aspects of innovative computational heat transfer and fluid flows, including both fundamental and practical applications of single and multiphase flows, turbulent flows, energy storage, heat exchangers, respiratory flows and heat transfer, and biomedical applications.

Dr. Pouyan Talebizadeh Sardari
Prof. Dr. Goodarz Ahmadi
Dr. Kiao Inthavong
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

Computational fluid dynamics (CFD)
Heat and mass transfer
Fluid mechanics
Aerospace
Laminar and turbulent flows
Multiphase flows
Energy storage
Optimization
Aerosols transport and deposition
Nanofluids
Porous media
Heat exchanger
Combustion
Respiratory systems
Biomedical applications
Spray atomization

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Published Papers (13 papers)

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Research

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23 pages, 4589 KiB

Open AccessArticle

Solidification Enhancement in a Triple-Tube Latent Heat Energy Storage System Using Twisted Fins

by Xinguo Sun, Jasim M. Mahdi, Hayder I. Mohammed, Hasan Sh. Majdi, Wang Zixiong and Pouyan Talebizadehsardari

Energies 2021, 14(21), 7179; https://doi.org/10.3390/en14217179 - 1 Nov 2021

Cited by 33 | Viewed by 2941

Abstract

This work evaluates the influence of combining twisted fins in a triple-tube heat exchanger utilised for latent heat thermal energy storage (LHTES) in three-dimensional numerical simulation and comparing the outcome with the cases of the straight fins and no fins. The phase change material (PCM) is in the annulus between the inner and the outer tube, these tubes include a cold fluid that flows in the counter current path, to solidify the PCM and release the heat storage energy. The performance of the unit was assessed based on the liquid fraction and temperature profiles as well as solidification and the energy storage rate. This study aims to find suitable and efficient fins number and the optimum values of the Re and the inlet temperature of the heat transfer fluid. The outcomes stated the benefits of using twisted fins related to those cases of straight fins and the no-fins. The impact of multi-twisted fins was also considered to detect their influences on the solidification process. The outcomes reveal that the operation of four twisted fins decreased the solidification time by 12.7% and 22.9% compared with four straight fins and the no-fins cases, respectively. Four twisted fins improved the discharging rate by 12.4% and 22.8% compared with the cases of four straight fins and no-fins, respectively. Besides, by reducing the fins’ number from six to four and two, the solidification time reduces by 11.9% and 25.6%, respectively. The current work shows the impacts of innovative designs of fins in the LHTES to produce novel inventions for commercialisation, besides saving the power grid. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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16 pages, 2924 KiB

Open AccessArticle

Numerical Investigation of Microchannel Heat Sink with Trefoil Shape Ribs

by Sadiq Ali, Faraz Ahmad, Kareem Akhtar, Numan Habib, Muhammad Aamir, Khaled Giasin, Ana Vafadar and Danil Yurievich Pimenov

Energies 2021, 14(20), 6764; https://doi.org/10.3390/en14206764 - 17 Oct 2021

Cited by 14 | Viewed by 2632

Abstract

The present study investigates the thermo-hydraulic characteristics of a microchannel sink with novel trefoil Shaped ribs. The motivation for this form of rib shape is taken from the design of lung alveoli that exchange oxygen and carbon dioxide. This study has been conducted numerically by using a code from the commercially available Fluent software. The trefoil shaped ribs were mounted on the centerline of different walls of the microchannel in three different configurations. These consisted of base wall trefoil ribs (MC-BWTR), sidewall trefoil ribs (MC-SWTR), all wall trefoil ribs (MC-AWTR) and smooth channel (MC-SC) having no ribs on its wall. The streamline distance between the ribs was kept constant at 0.4 mm, and the results were compared by using pressure drop (∆p), Nusselt number (Nu), thermal resistance (R_th) and thermal enhancement factor (η). The results indicated that the addition of trefoil ribs to any wall improved heat transfer characteristics at the expense of an increase in the friction factor. The trends of the pressure drop and heat transfer coefficient were the same, which indicated higher values for MC-AWTR followed by MC-SWTR and a lower value for MC-BWTR. In order to compare the thermal and hydraulic performance of all the configurations simultaneously, the overall performance was quantified in terms of the thermal enhancement factor, which was higher than one in each case, except for MC-AWTR, in 100 < Re < 200 regimes. The thermal enhancement factor in the ribbed channel was the highest for MC-SWTR followed by MC-BWTR, and it was the lowest for MC-AWTR. Moreover, the thermal enhancement factor increases with the Reynolds number (Re) for each case. This confirms that the increment in the Nusselt number with velocity is more significant than the pressure drop. The highest thermal enhancement factor of 1.6 was attained for MC-SWTR at Re = 1000, and the lowest value of 0.87 was achieved for MC-AWTR at Re = 100. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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18 pages, 5890 KiB

Open AccessArticle

Numerical Study of Heat Transfer Intensification in a Circular Tube Using a Thin, Radiation-Absorbing Insert. Part 1: Thermo-Hydraulic Characteristics

by Piotr Bogusław Jasiński

Energies 2021, 14(15), 4596; https://doi.org/10.3390/en14154596 - 29 Jul 2021

Cited by 2 | Viewed by 1925

Abstract

The presented paper, which is the first of two parts, shows the results of numerical investigations of a heat exchanger channel in the form of a cylindrical tube with a thin insert. The insert, placed concentrically in the pipe, uses the phenomenon of thermal radiation absorption to intensify the heat transfer between the pipe wall and the gas. Eight geometric configurations of the insert size were numerically investigated using CFD software, varying its diameter from 20% to 90% of the pipe diameter and obtaining the thermal-flow characteristics for each case. The tests were conducted for a range of numbers Re = 5000–100,000 and a constant temperature difference between the channel wall and the average gas temperature of ∆T = 100 °C. The results show that the highest increase in the Nu number was observed for the inserts with diameters of 0.3 and 0.4 of the channel diameter, while the highest flow resistance was noted for the inserts with diameters of 0.6–0.7 of the channel diameter. The f/f_s(Re) and Nu/Nu_s(Re) ratios are shown on graphs indicating how much the flow resistance and heat transfer increased compared to the pipe without an insert. Two methods of calculating the Nu number are also presented and analysed. In the first one, the average fluid temperature of the entire pipe volume was used to calculate the Nu number, and in the second, only the average fluid temperature of the annular portion formed by the insert was used. The second one gives much larger Nu/Nu_s ratio values, reaching up to 8–9 for small Re numbers. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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12 pages, 609 KiB

Open AccessArticle

Improvement of Mathematical Model for Sedimentation Process

by Ivan Pavlenko, Marek Ochowiak, Praveen Agarwal, Radosław Olszewski, Bernard Michałek and Andżelika Krupińska

Energies 2021, 14(15), 4561; https://doi.org/10.3390/en14154561 - 28 Jul 2021

Cited by 8 | Viewed by 2475

Abstract

In this article, the fractional-order differential equation of particle sedimentation was obtained. It considers the Basset force’s fractional origin and contains the Riemann–Liouville fractional integral rewritten as a Grunwald–Letnikov derivative. As a result, the general solution of the proposed fractional-order differential equation was found analytically. The belonging of this solution to the real range of values was strictly theoretically proven. The obtained solution was validated on a particular analytical case study. In addition, it was proven numerically with the approach based on the S-approximation method using the block-pulse operational matrix. The proposed mathematical model can be applied for modeling the processes of fine particles sedimentation in liquids, aerosol deposition in gas flows, and particle deposition in gas-dispersed systems. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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18 pages, 4791 KiB

Open AccessArticle

Numerical Study of Heat Transfer Intensification in a Circular Tube Using a Thin, Radiation-Absorbing Insert. Part 2: Thermal Performance

by Piotr Bogusław Jasiński

Energies 2021, 14(15), 4533; https://doi.org/10.3390/en14154533 - 27 Jul 2021

Cited by 2 | Viewed by 1659

Abstract

This article is the second part of the work under the same title, which is based on the results of the research presented in the previous article: “Numerical study of heat transfer intensification in a circular tube using a thin, radiation-absorbing insert. Part 1: Thermo-hydraulic characteristics”. Part 1 presents an analysis of pressure drops and heat transfer intensification in a round tube with an insert, using the phenomenon of radiation absorption. In this paper, an analysis of the tested insert’s thermal performance (PEC) is presented, taking into account the criterion of equal pumping power. The tests were carried out for the range of Re = 5000–100,000 numbers, for various insert diameters (from 20% to 90% of the pipe diameter) and a constant temperature difference between the wall and the gas ∆T = 100 °C. The highest Nu numbers were observed for inserts with dimensionless diameters of 0.3 and 0.4, while the highest flow resistance was observed for inserts with diameters of 0.6 and 0.7 of the channel diameter. The thermal efficiency was calculated in two ways, as was the associated Nu number. These results significantly differed from each other: the maximum PEC values for method (I) reached 2, and for method (II) to 8. The common feature for both calculation methods was the fact that the maximum values of the Nu number and the thermal efficiency were observed for small Re numbers; however, as the Re number increases, PEC and Nu number decrease strongly. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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24 pages, 16042 KiB

Open AccessArticle

Particle-Resolved Computational Fluid Dynamics as the Basis for Thermal Process Intensification of Fixed-Bed Reactors on Multiple Scales

by Nico Jurtz, Urvashi Srivastava, Alireza Attari Moghaddam and Matthias Kraume

Energies 2021, 14(10), 2913; https://doi.org/10.3390/en14102913 - 18 May 2021

Cited by 15 | Viewed by 2733

Abstract

Process intensification of catalytic fixed-bed reactors is of vital interest and can be conducted on different length scales, ranging from the molecular scale to the pellet scale to the plant scale. Particle-resolved computational fluid dynamics (CFD) is used to characterize different reactor designs regarding optimized heat transport characteristics on the pellet scale. Packings of cylinders, Raschig rings, four-hole cylinders, and spheres were investigated regarding their impact on bed morphology, fluid dynamics, and heat transport, whereby for the latter particle shape, the influence of macroscopic wall structures on the radial heat transport was also studied. Key performance indicators such as the global heat transfer coefficient and the specific pressure drop were evaluated to compare the thermal performance of the different designs. For plant-scale intensification, effective transport parameters that are needed for simplified pseudo-homogeneous two-dimensional plug flow models were determined from the CFD results, and the accuracy of the simplified modeling approach was judged. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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30 pages, 3443 KiB

Open AccessArticle

State-of-the-Art Review of Effervescent-Swirl Atomizers

by Krystian Czernek, Michał Hyrycz, Andżelika Krupińska, Magdalena Matuszak, Marek Ochowiak, Stanisław Witczak and Sylwia Włodarczak

Energies 2021, 14(10), 2876; https://doi.org/10.3390/en14102876 - 16 May 2021

Cited by 5 | Viewed by 3550

Abstract

This paper presents issues in the field of theory, construction, calculations, as well as the design of effervescent-swirl atomizers. The results of experimental studies of spraying liquids with different physico-chemical properties for this type of atomizers are discussed. Effervescent-swirl atomization is a complex process and its mechanism is not fully understood. Therefore, the purpose of the manuscript is the complexity of the atomization process and its mechanism as well as the influence of individual parameters on its efficiency were thoroughly analyzed. The analyzed parameters include: atomizer design, outlet shape, gas and liquid flow rate, injection pressure, physicochemical properties of the atomized liquid, pressure drop, outflow coefficient, spray angle, quantitative droplet distributions, and average droplet diameter. Moreover, in the work, on the basis of the literature review, the results of the research related to, inter alia, the phenomenon of air core formation and the influence of a number of parameters on the efficiency of the atomization process are analyzed. The literature review included in the work makes it possible to better understand the atomization process carried out in effervescent-swirl atomizers, and also provides better design criteria and analysis of the efficiency of the tested devices. The article presents correlation equations covering the basic features of the atomization process, which relate a large number of parameters influencing the efficiency of this process and the character of the sprayed liquid, which may be useful in design practice. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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18 pages, 6850 KiB

Open AccessArticle

Investigation of Thermal-Flow Characteristics of Pipes with Helical Micro-Fins of Variable Height

by Piotr Bogusław Jasiński, Michał Jan Kowalczyk, Artur Romaniak, Bartosz Warwas, Damian Obidowski and Artur Gutkowski

Energies 2021, 14(8), 2048; https://doi.org/10.3390/en14082048 - 7 Apr 2021

Cited by 6 | Viewed by 3081

Abstract

The results of numerical investigations of heat transfer and pressure drops in a channel with 30° helical micro-fins are presented. The main aim of the analysis is to examine the influence of the height of the micro-fins on the heat-flow characteristics of the channel. For the tested pipe with a diameter of 12 mm, the micro-fin height varies within the range of 0.05–0.40 mm (with 0.05 mm steps), which is equal to 0.4–3.3% of its diameter. The analysis was performed for a turbulent flow, within the range of Reynolds numbers 10,000–100,000. The working fluid is water with an average temperature of 298 K. For each tested geometry, the characteristics of the friction factor f(Re) and the Nusselt number Nu(Re) are shown in the graphs. The highest values of Nusselt numbers and friction factors were obtained for pipes with the micro-fins H = 0.30 mm and H = 0.35 mm. A large discrepancy is observed in the friction factors f(Re) calculated from the theoretical relationships (for the irregular relative roughness values shown in the Moody diagram) and those obtained from the simulations (for pipes with regular roughness formed by micro-fins). The PEC (Performance Evaluation Criteria) heat transfer efficiency analysis of the geometries under study is also presented, taking into account the criterion of the same pumping power. The highest PEC values, reaching 1.25, are obtained for micro-fins with a height of 0.30 mm and 0.35 mm and with Reynolds numbers above 40,000. In general, for all tested geometries and for large Reynolds numbers (above 20,000), the PEC coefficient reaches values greater than 1, while for lower Reynolds numbers (less than 20,000), its values are less than 1. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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17 pages, 6378 KiB

Open AccessArticle

Conical Two-Phase Swirl Flow Atomizers—Numerical and Experimental Study

by Marek Ochowiak, Daniel Janecki, Andżelika Krupińska, Sylwia Włodarczak, Tomasz Wilk and Radosław Olszewski

Energies 2021, 14(6), 1745; https://doi.org/10.3390/en14061745 - 21 Mar 2021

Cited by 2 | Viewed by 2024

Abstract

This paper presents the results of numerical simulations for the developed and discussed conical two-phase atomizers with swirl flow, differing in the ratio of the height of the swirl chamber to its diameter. Experiments were carried out for SAN-1 with H_S/D_S = 1 and SAN-2 with H_S/D_S = 4 atomizers. The study was conducted over a range of Reynolds number for liquid Re_L = (1400; 5650) and for gas Re_G = (2970; 9900). Numerical calculations were performed with the use of computational fluid dynamics (CFD), which were verified on the basis of experimental data. Based on the analysis of experimental studies and simulations results the influence of operational parameters and changes of the atomizer geometry on the generated spray was demonstrated. As the gas flow rate increased and the swirl chamber height decreased, the spray angle increased. Higher velocity values of the liquid and greater turbulence occur in the center of the spray. The flow inside the atomizer determines the nature of the spray obtained. The geometry of the swirl chamber influences the air core formed inside the atomizer, and this determines the atomization effect. The results of numerical simulations not only confirm the results of experimental studies, but also provide additional information on internal and external fluid flow. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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20 pages, 6317 KiB

Open AccessArticle

Simulation of a Fast-Charging Porous Thermal Energy Storage System Saturated with a Nano-Enhanced Phase Change Material

by Mohammad Ghalambaz, S.A.M. Mehryan, Hassan Shirivand, Farshid Shalbafi, Obai Younis, Kiao Inthavong, Goodarz Ahmadi and Pouyan Talebizadehsardari

Energies 2021, 14(6), 1575; https://doi.org/10.3390/en14061575 - 12 Mar 2021

Cited by 4 | Viewed by 2181

Abstract

The melting of a coconut oil–CuO phase change material (PCM) embedded in an engineered nonuniform copper foam was theoretically analyzed to reduce the charging time of a thermal energy storage unit. A nonuniform metal foam could improve the effective thermal conductivity of a porous medium at regions with dominant conduction heat transfer by increasing local porosity. Moreover, the increase in porosity contributes to flow circulation in the natural convection-dominant regimes and adds a positive impact to the heat transfer rate, but it reduces the conduction heat transfer and overall heat transfer. The Taguchi optimization method was used to minimize the charging time of a shell-and-tube thermal energy storage (TES) unit by optimizing the porosity gradient, volume fractions of nanoparticles, average porosity, and porous pore sizes. The results showed that porosity is the most significant factor and lower porosity has a faster charging rate. A nonuniform porosity reduces the charging time of TES. The size of porous pores induces a negligible impact on the charging time. Lastly, the increase in volume fractions of nanoparticles reduces the charging time, but it has a minimal impact on the TES unit’s charging power. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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24 pages, 67762 KiB

Open AccessArticle

Numerical Study on the Cavitation Flow and Its Effect on the Structural Integrity of Multi-Stage Orifice

by Gonghee Lee, Myungjo Jhung, Juneho Bae and Soonho Kang

Energies 2021, 14(6), 1518; https://doi.org/10.3390/en14061518 - 10 Mar 2021

Cited by 6 | Viewed by 2184

Abstract

Flow leakage due to cavitation erosion occurred at the socket welding part downstream of the multi-stage orifice installed in the auxiliary feedwater (AFW) pump recirculation line of the domestic nuclear power plant (NPP). To assess the adequacy of the changed operating flow rate proposed by a domestic NPP operator as the corrective measure concerning the flow leakage in the AFW pump recirculation line, the pattern of the cavitation flow in the eight-stage orifice and the connecting pipe depending on the magnitude of the operating flow rate was predicted by using ANSYS CFX R19.1. Additionally, using ANSYS Mechanical, the structural analysis was conducted under the same operating flow rate condition used for the flow analysis, and the structural integrity was evaluated for the allowable stress. Based on the flow analysis results, it was found that the operating flow rate was the main factor to influence the cavitation behavior inside the multi-stage orifice, and cavitation flow still happened even in the vicinity of the corrected operating flow rate, so it should be necessary to fundamentally review the adequacy of the multi-stage orifice design. On the other hand, the geometric dimensions and arrangement of orifice hole position at the individual stage of the multi-stage orifice may have a significant influence on the characteristics of pressure drop and flow patterns (including cavitation). Therefore, these effects were examined by simulating an analysis model in which the hole diameter of the eighth-stage orifice was changed under the design flow rate condition. As a result of flow analysis, it was found that reducing the hole diameter in the eighth stage orifice resulted in increasing the pressure drop. In relation to the structural integrity of the eight-stage orifice and the connecting pipe, it was found that its integrity could be maintained under the design and operating flow rate conditions. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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Review

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34 pages, 6637 KiB

Open AccessReview

Heat Transfer Characteristics of Conventional Fluids and Nanofluids in Micro-Channels with Vortex Generators: A Review

by Mushtaq T. Al-Asadi, Hussein A. Mohammed and Mark C. T. Wilson

Energies 2022, 15(3), 1245; https://doi.org/10.3390/en15031245 - 8 Feb 2022

Cited by 7 | Viewed by 3686

Abstract

An effective way to enhance the heat transfer in mini and micro electronic devices is to use different shapes of micro-channels containing vortex generators (VGs). This attracts researchers due to the reduced volume of the electronic micro-chips and increase in the heat generated from the devices. Another way to enhance the heat transfer is using nanofluids, which are considered to have great potential for heat transfer enhancement and are highly suited to application in practical heat transfer processes. Recently, several important studies have been carried out to understand and explain the causes of the enhancement or control of heat transfer using nanofluids. The main aim upon which the present work is based is to give a comprehensive review on the research progress on the heat transfer and fluid flow characteristics of nanofluids for both single- and two- phase models in different types of micro-channels. Both experimental and numerical studies have been reviewed for traditional and nanofluids in different types and shapes of micro-channels with vortex generators. It was found that the optimization of heat transfer enhancement should consider the pumping power reduction when evaluating the improvement of heat transfer. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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16 pages, 2299 KiB

Open AccessReview

Investigation of the Photon to Charge Conversion and Its Implication on Photovoltaic Cell Efficient Operation

by Vasileios Kapsalis, Grigorios Kyriakopoulos, Miltiadis Zamparas and Athanasios Tolis

Energies 2021, 14(11), 3022; https://doi.org/10.3390/en14113022 - 23 May 2021

Cited by 10 | Viewed by 3004

Abstract

Efficient photon to charge (PTC) transfer is considered to be the cornerstone of technological improvements in the photovoltaic (PV) industry, while it constitutes the most common process in nature. This study aims to investigate the parameters that impact efficient PV-cell photon to charge conversion in two ways: (a) providing a brief research analysis to extract the key features which affect the electrical and optical performance of PV cells’ operation, and (b) investigating the dependance of these characteristics on the photon to charge mechanisms. The former direction focuses on the latest advances regarding the impacts of the microenvironment climate conditions on the PV module and its operational performance, while the latter examines the fundamental determinants of the cell’s efficient operation. The electrical and optical parameters of the bulk PV cells are influenced by both the external microenvironment and the intrinsic photon to charge conversion principles. Light and energy harvesting issues need to be overcome, while nature-inspired interpretation and mimicking of photon to charge and excitation energy transfer are in an infant stage, furthering a better understanding of artificial photosynthesis. A future research orientation is proposed which focuses on scaling up development and making use of the before mentioned challenges. Full article

(This article belongs to the Special Issue Computational Heat Transfer and Fluid Mechanics)

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