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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 April 2022) | Viewed by 31925

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Special Issue Editors

Prof. Dr. Andrej Kitanovski

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Guest Editor

Laboratory for Refrigeration and District Energy, University of Ljubljana, Ljubljana, Slovenia
Interests: refrigeration; heat pump; heat transfer; heat exchanger; thermal physics; thermal control; thermal management

Dr. Jaka Tušek

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Guest Editor

Special Issue Information

Dear Colleagues,

Over the last decade, important improvements have been achieved in terms of design, new materials or composites, surface treatment and topology, improved heat transfer, and/or the associated performance of different types of heat exchangers in cooling and heating technology. These include single-phase or phase-change fluids or suspensions, new materials and their composites, advanced topology and improved heat transfer surface, new or improved types of heat exchangers and manufacturing technologies, and new design tools.

For all of the above topics as well as others, summary information on advances in heat exchangers that could provide the reader with the most important and latest knowledge and achievements is missing. This information can undoubtedly promote new ideas for the reader and help researchers to find solutions that can be transferred from one topic to another, making this Special Issue a relevant milestone for any engineer working with heat exchangers in various fields of cooling, heating or process engineering.

Prof. Dr. Andrej Kitanovski
Assist. Prof. Dr. Jaka Tušek
Guest Editors

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Keywords

heat exchanger
enhanced heat transfer
energy efficiency
composites
advanced energy materials
working fluid
nanofluid
regenerator
recuperator
evaporator
condenser
additive manufacturing

Published Papers (13 papers)

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Research

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16 pages, 7349 KiB

Open AccessArticle

Numerical Improvement Using Flow and Heat Transfer Calculations of the Zigzag Geometry for Carbon Dioxide PCHEs

by Bo Wang, Jiafei Shen, Jindong Cheng and Yaliang Wang

Energies 2022, 15(8), 2831; https://0-doi-org.brum.beds.ac.uk/10.3390/en15082831 - 13 Apr 2022

Cited by 4 | Viewed by 1621

Abstract

A printed circuit heat exchanger (PCHE) is an efficient and compact heat exchanger that can work under high temperature and high pressure. For Z-shaped channel PCHEs, the corner structure could enhance heat transfer at the expense of increasing the flow resistance. In order to optimize the structural design and control the pressure loss caused by the corner, a three-dimensional numerical simulation using ICEM and Fluent is conducted to study the flow and heat transfer characteristics of carbon dioxide in a PCHE by inserting straight sections (offset distance 0.5–4 mm) or arc segments (radius of curvature 0.5–4 mm) at the zigzag corners of conventional Z-shaped channels. The overall performance of the PCHEs with different structures was compared based on the comprehensive evaluation factor. The results show that the pressure loss of the PCHE can be significantly reduced by inserting straight sections and arc segments at the zigzag corners, with the mass flow rate varying from 100 to 400 kg/(m² s). The greater the offset distance of the straight sections or curvature radius of the arc segments are, the more significant the effect is, but the heat transfer performance will be weakened at the same time. The comprehensive performance of the PCHE was the best when the curvature radius of the arc segment inserted at the zigzag corner was 4 mm. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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30 pages, 5527 KiB

Open AccessArticle

A Flexible Top-Down Numerical Modeling of an Air-Cooled Finned-Tube CO₂ Trans-Critical Gas Cooler

by Angelo Maiorino, Ciro Aprea and Manuel Gesù Del Duca

Energies 2021, 14(22), 7607; https://0-doi-org.brum.beds.ac.uk/10.3390/en14227607 - 14 Nov 2021

Cited by 2 | Viewed by 1373

Abstract

Carbon dioxide trans-critical refrigeration systems have been deeply investigated over the last years, with the aim to improve their performance by using several possible technical solutions. However, most of them lead to a more complex and expensive system, and therefore a trade-off is always needed to identify the best viable solution. Therefore, many efforts have also been focused on the study of a critical component of the basic carbon dioxide trans-critical cycle, which is the gas cooler, especially by numerical simulations. This work shows a new flexible approach to numerically model an air-cooled finned-tube CO₂ trans-critical gas cooler integrating a Top-Down methodology with a Finite Difference Method to solve the governing equation of the thermodynamic processes involved. The model was developed to reproduce the behavior of an experimental CO₂ refrigeration system, which provided the experimental data used for its validation. In detail, the model showed a good agreement with the experimental data, with average deviations of 1 K (0.3%), 0.9 bar (1%) and 0.15 kW (2.8%) regarding the refrigerant outlet temperature, the refrigerant outlet pressure and the rejected heat, respectively. The Top-Down numerical approach slightly outperformed the performance of previous numerical models available in the literature. Furthermore, the analysis of the refrigerant temperature and pressure along the tubes and rows also shows that the model can reproduce their behavior consistently and accordingly to data reported in the literature. The proposed approach can be used for detailed thermo-economic analysis of the whole refrigeration system, with the aim to optimize the design of the gas cooler. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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18 pages, 3190 KiB

Open AccessArticle

Evaporation Heat Transfer and Pressure Drop of Low-Global Warming Potential Refrigerant HFO-1234yf in 6.95-mm Horizontal Smooth Tube

by Chang-Hyo Son, Nam-Wook Kim, Jung-In Yoon, Sung-Hoon Seol and Joon-Hyuk Lee

Energies 2021, 14(19), 6325; https://0-doi-org.brum.beds.ac.uk/10.3390/en14196325 - 03 Oct 2021

Cited by 1 | Viewed by 1526

Abstract

This study investigated the evaporative heat transfer coefficient and pressure drop characteristics of R-1234yf in a horizontal tube with an inner diameter of 6.95 mm under various experimental conditions. The heat transfer coefficient increased with an increase in quality but showed a sharp decrease in the high-quality area. In addition, the heat transfer coefficient increased as the mass flux, heat flux, and saturation temperature increased. Although R-1234yf and R-134a presented similar heat transfer coefficients, that of R-134a was higher. The pressure drop increased with an increase in the quality and mass flux but decreased with an increase in the saturation temperature. The pressure drop of R-134a was larger than that of R-1234yf. In light of the flow pattern diagram by Taitel and Dukler, most of the experiments were included in the annular flow region, and some regions showed intermittent and stratified corrugated flow regions. Kandlikar’s heat transfer coefficient correlation provided the best prediction for the experimental database, with approximately 84% of the predicted data within ±30%. Moreno Quibén and Thome’s equation for pressure drop predicted approximately 88.71% of the data within ±30%. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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28 pages, 9211 KiB

Open AccessArticle

Performance of the Condensation Process for Water Vapour in the Presence of a Non-Condensable Gas on Vertical Plates and Horizontal Tubes

by Primož Poredoš, Nada Petelin, Tilen Žel, Boris Vidrih, Pero Gatarić and Andrej Kitanovski

Energies 2021, 14(8), 2291; https://0-doi-org.brum.beds.ac.uk/10.3390/en14082291 - 19 Apr 2021

Cited by 7 | Viewed by 2443

Abstract

The condensation of humid air is a crucial step in air conditioning and process engineering. However, the models that describe the condensation of vapour in the presence of a non-condensable gas require time-consuming numerical calculations that go beyond the Nusselt film theory. Only a small number of publications exist, where simple and computationally effective correlations for the condensation of water vapour in the presence of air are presented for specially designed condenser heat exchangers. Therefore, the objective of this paper is to extend the existing semi-empirical correlations for different geometries and process parameters. For the purpose of the study, an experimental setup with two different condenser heat exchangers based on vertical plates (height 74 mm) and horizontal tubes (3 tubes, diameter 40 mm and 7 tubes, diameter 15 mm) was built. Additionally, based on existing correlations, we developed two semi-empirical models that predict the condensation mass flux for the proposed geometries. Here, we report that the agreement between the experimental and theoretical values predicted by the new, semi-empirical correlations is excellent, with an average uncertainty of less than ±6%. Their usability was demonstrated by a possibly significant performance improvement of the condenser inside a condensation-type tumble dryer. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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17 pages, 8514 KiB

Open AccessArticle

Performance Assessment of Double Corrugated Tubes in a Tube-In-Shell Heat Exchanger

by Kristina Navickaitė, Michael Penzel, Christian R. H. Bahl and Kurt Engelbrecht

Energies 2021, 14(5), 1343; https://0-doi-org.brum.beds.ac.uk/10.3390/en14051343 - 01 Mar 2021

Cited by 3 | Viewed by 2103

Abstract

In this article, the performance of double corrugated tubes applied in a tube-in-shell heat exchanger is analysed and compared to the performance of a heat exchanger equipped with straight tubes. The CFD (computational fluid dynamics) analysis was performed considering a turbulent flow regime at several mass flow rates. It is observed that the double corrugated geometry does not have a significant impact on the pressure drop inside the analysed heat exchanger, while it has the potential to increase its thermal performance by up to 25%. The ε–NTU (effectiveness–number of transfer units) relation also demonstrates the advantage of using double corrugated tubes in tube-in-shell heat exchangers over straight tubes. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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19 pages, 5525 KiB

Open AccessArticle

Numerical Analysis of Liquid–Liquid Heat Pipe Heat Exchanger Based on a Novel Model

by Qilu Chen, Yutao Shi, Zhi Zhuang, Li Weng, Chengjun Xu and Jianqiu Zhou

Energies 2021, 14(3), 589; https://0-doi-org.brum.beds.ac.uk/10.3390/en14030589 - 24 Jan 2021

Cited by 3 | Viewed by 1950

Abstract

Heat pipe heat exchangers (HPHEXs) are widely used in various industries. In this paper, a novel model of a liquid–liquid heat pipe heat exchanger in a countercurrent manner is established by considering the evaporation and condensation thermal resistances inside the heat pipes (HPs). The discrete method is added to the HPHEX model to determine the thermal resistances of the HPs and the temperature change trend of the heat transfer fluid in the HPHEX. The established model is verified by the HPHEX structure and experimental data in the existing literature and demonstrates numerical results that agree with the experimental data to within a 5% error. With the current model, the investigation compares the effectiveness and minimum vapor temperature of the HPHEX with three types of HP diameters, different mass flow rates, and different

H^{*}

values. For HPs with a diameter of 36 mm, the effectiveness of each is improved by about 0.018 to 0.029 compared to HPs with a diameter of 28 mm. The results show that the current model can predict the temperature change trend of the HPHEX well; in addition, the effects of different structures on the effectiveness and minimum vapor temperature are obtained, which improve the performance of the HPHEX. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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18 pages, 6766 KiB

Open AccessArticle

Structural Design Simulation of Bayonet Heat Exchanger for Sulfuric Acid Decomposition

by Qunxiang Gao, Ping Zhang, Wei Peng, Songzhe Chen and Gang Zhao

Energies 2021, 14(2), 422; https://0-doi-org.brum.beds.ac.uk/10.3390/en14020422 - 14 Jan 2021

Cited by 8 | Viewed by 2048

Abstract

The heat generated in a high-temperature gas-cooled reactor can be used to drive the iodine-sulfur cycle to produce hydrogen. However, the sulfuric acid decomposition step requires a sophisticated sulfuric acid decomposer to increase the decomposition rate. The decomposition of sulfuric acid mainly occurs in the catalytic zone, and the optimization of its structure is very important for increasing the decomposition rate. This study focuses on the structural design of the catalytic zone of the sulfuric acid decomposer unit. The structure with double inner tubes is designed to analyze the influence of the inner tube heat transfer area and the catalytic volume of the annulus region on the decomposition rate. The species transport model is used to predict the proportion of products followed by analysis of the key factors affecting the decomposition rate of the catalytic domain. The results reveal that the new design attains the decomposition temperature requirements and increases the fluid velocity of the inner tube. This in turn promotes the heat transfer effect. The decomposition rate is negatively correlated with the flow rate. Nonetheless, a structure with double inner tubes which have the same total area of inner tube as a structure with a single inner tube has a better optimization effect than a structure which has the same annulus catalytic volume as a structure with single inner tube. It increases the decomposition rate by up to 6.1% while a structure which has the same annulus catalytic volume as a structure with a single inner tube does the same by up to 1.7%. The decomposition rate can be maintained at a relatively high level when the inlet velocity of the current structural design is about 0.2 m/s. This study provides a reference for the engineering design of sulfuric acid decomposer based on the heat exchange area and catalytic volume. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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13 pages, 9703 KiB

Open AccessArticle

Numerical Study on Novel Design for Compact Parallel-Flow Heat Exchanger with Manifolds to Improve Flow Characteristics

by Byunghui Kim, Kuisoon Kim and Seokho Kim

Energies 2020, 13(23), 6330; https://0-doi-org.brum.beds.ac.uk/10.3390/en13236330 - 30 Nov 2020

Cited by 4 | Viewed by 2478

Abstract

Parallel flow heat exchangers with manifolds are widely used in various industries owing to their compact size and ease of application. Research has been conducted to understand their flow characteristics and improve flow distribution and pressure drop performance; however, it is difficult to derive generalized improvements under different conditions for each application. This study proposes a novel design to improve the flow characteristics of a compact heat exchanger with a sudden expansion area of a dividing manifold and uses computational fluid dynamics simulation to verify it. The abrupt cross-sectional area change in the dividing manifold induces a jet flow near the entry region, which causes the flow maldistribution of the first few parallel tubes. To improve the efficiency of the dividing manifold, simple and novel designs with a converging-diverging area in the manifold header have been proposed. Parametric studies on the novel designs show improvements of up to 37.5% and 52.0% flow uniformity and 2.65% and 0.74% pressure drop performance for U- and Z-types, respectively, compared to the base model. Thus, the simple and easily fabricated quadrilateral shape can improve the flow maldistribution and pressure drop caused by a dividing manifold with a sudden area expansion. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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19 pages, 3600 KiB

Open AccessFeature PaperArticle

A Novel Analytical-ANN Hybrid Model for Borehole Heat Exchanger

by Anjan Rao Puttige, Staffan Andersson, Ronny Östin and Thomas Olofsson

Energies 2020, 13(23), 6213; https://0-doi-org.brum.beds.ac.uk/10.3390/en13236213 - 26 Nov 2020

Cited by 9 | Viewed by 1903

Abstract

Optimizing the operation of ground source heat pumps requires simulation of both short-term and long-term response of the borehole heat exchanger. However, the current physical and neural network based models are not suited to handle the large range of time scales, especially for large borehole fields. In this study, we present a hybrid model for long-term simulation of BHE with high resolution in time. The model uses an analytical model with low time resolution to guide an artificial neural network model with high time resolution. We trained, tuned, and tested the hybrid model using measured data from a ground source heat pump in real operation. The performance of the hybrid model is compared with an analytical model, a calibrated analytical model, and three different types of neural network models. The hybrid model has a relative RMSE of 6% for the testing period compared to 22%, 14%, and 12% respectively for the analytical model, the calibrated analytical model, and the best of the three investigated neural network models. The hybrid model also has a reasonable computational time and was also found to be robust with regard to the model parameters used by the analytical model. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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28 pages, 8209 KiB

Open AccessArticle

Research on the Thermal Hydraulic Performance and Entropy Generation Characteristics of Finned Tube Heat Exchanger with Streamline Tube

by Zuoqin Qian, Qiang Wang and Song Lv

Energies 2020, 13(20), 5408; https://0-doi-org.brum.beds.ac.uk/10.3390/en13205408 - 16 Oct 2020

Cited by 4 | Viewed by 1910

Abstract

Thermal hydraulic performance of the fin-and-tube heat exchanger is presented in this paper. The purpose of this investigation was to investigate the heat transfer mechanism and flow characteristics in the finned tube heat exchanger with streamline tube. The streamline tube in this paper had the streamline cross section which was composed of a semicircle and a half diamond. Three-dimensional numerical simulation was presented and validated by the experiment and the other numerical simulation from public articles. The present simulation had good agreement with the experimental results. The difference of the j factor and f factor between the experimental results and present simulation results by k-ε-enhance model was less than 7.6%. The geometrical parameters were considered as every single variable to investigate the thermal hydraulic performance. The results showed that smaller transversal and larger tube pitch provided greater compactness and better thermal performance. Moreover, a larger angle was not only beneficial to enhance the thermal performance, but also helpful to improve the overall performance. Secondly, the effects of angle on the heat transfer performance and fluid flow characteristics were investigated as the perimeter kept constant. It was shown that the overall performance of the streamline tube was better than the circular tube. Lastly, the entropy generation including frictional entropy generation and the thermal entropy generation were analyzed. It can be concluded that by using the streamline tube, the wake region can be obviously reduced, and thermal performance can be improved. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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18 pages, 12196 KiB

Open AccessArticle

Numerical Study on the Influence Mechanism of Crosswind on Frozen Phenomena in a Direct Air-Cooled System

by Wei Yuan, Fengzhong Sun, Yuanbin Zhao, Xuehong Chen, Ying Li and Xiaolei Lyu

Energies 2020, 13(15), 3831; https://0-doi-org.brum.beds.ac.uk/10.3390/en13153831 - 25 Jul 2020

Cited by 1 | Viewed by 1562

Abstract

The frozen phenomenon is unfavorable for the direct air-cooled condensers (DACCs) in a very cold area. The effect of crosswind on frozen phenomena in DACCs at the representative 2 × 350 MW thermal power units was investigated numerically. Results showed that when the crosswind velocity was 4 m·s⁻¹, the number of frozen air-cooled units reached a maximum of six. The increase of vortex range in the air-cooled unit was one of the important reasons to restrain the formation of frozen phenomena at a crosswind velocity from 4 m·s⁻¹ to 12 m·s⁻¹. The frozen phenomena in the DACC disappeared when the crosswind velocity was 12 m·s⁻¹. As the crosswind velocity continued to increase to 28 m·s⁻¹, the frozen region mainly appeared at the position of column 1 row 4, where the airflow rate was the maximum and the inlet air temperature was the minimum among all air-cooled units. This phenomenon occurred because there existed a relatively high-pressure zone near the inlet of each frozen air-cooled unit. In addition, although the frozen area increased from one-third of the air-cooled unit surface to half with the crosswind velocity from 20 m·s⁻¹ to 28 m·s⁻¹, the flow characteristics and the size of vortices in the air-cooled unit were similar in the above two crosswind conditions. Therefore, the key influencing factor became the airflow rate and the inlet air temperature of the air-cooled units under strong crosswind conditions. This study has important guiding significance for the antifreezing design and operation of DACCs. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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Review

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23 pages, 5656 KiB

Open AccessReview

Evaporator Frosting in Refrigerating Appliances: Fundamentals and Applications

by Christian J. L. Hermes, Joel Boeng, Diogo L. da Silva, Fernando T. Knabben and Andrew D. Sommers

Energies 2021, 14(18), 5991; https://0-doi-org.brum.beds.ac.uk/10.3390/en14185991 - 21 Sep 2021

Cited by 6 | Viewed by 4017

Abstract

Modern refrigerators are equipped with fan-supplied evaporators often tailor-made to mitigate the impacts of frost accretion, not only in terms of frost blocking, which depletes the cooling capacity and therefore the refrigerator coefficient of performance (COP), but also to allow optimal defrosting, thereby avoiding the undesired consequences of condensate retention and additional thermal loads. Evaporator design for frosting conditions can be done either empirically through trial-and-error approaches or using simulation models suitable to predict the distribution of the frost mass along the finned coil. Albeit the former is mandatory for robustness verification prior to product approval, it has been advocated that the latter speeds up the design process and reduces the costs of the engineering undertaking. Therefore, this article is aimed at summarizing the required foundations for the design of efficient evaporators and defrosting systems with minimized performance impacts due to frosting. The thermodynamics, and the heat and mass transfer principles involved in the frost nucleation, growth, and densification phenomena are presented. The thermophysical properties of frost, such as density and thermal conductivity, are discussed, and their relationship with refrigeration operating conditions are established. A first-principles model is presented to predict the growth of the frost layer on the evaporator surface as a function of geometric and operating conditions. The relation between the microscopic properties of frost and their macroscopic effects on the evaporator thermo-hydraulic performance is established and confirmed with experimental evidence. Furthermore, different defrost strategies are compared, and the concept of optimal defrost is formulated. Finally, the results are used to analyze the efficiency of the defrost operation based on the net cooling capacity of the refrigeration system for different duty cycles and evaporator geometries. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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31 pages, 1897 KiB

Open AccessReview

Application and Design Aspects of Ground Heat Exchangers

by Luka Boban, Dino Miše, Stjepan Herceg and Vladimir Soldo

Energies 2021, 14(8), 2134; https://0-doi-org.brum.beds.ac.uk/10.3390/en14082134 - 11 Apr 2021

Cited by 23 | Viewed by 4419

Abstract

With the constant increase in energy demand, using renewable energy has become a priority. Geothermal energy is a widely available, constant source of renewable energy that has shown great potential as an alternative source of energy in achieving global energy sustainability and environment protection. When exploiting geothermal energy, whether is for heating or cooling buildings or generating electricity, a ground heat exchanger (GHE) is the most important component, whose performance can be easily improved by following the latest design aspects. This article focuses on the application of different types of GHEs with attention directed to deep vertical borehole heat exchangers and direct expansion systems, which were not dealt with in detail in recent reviews. The article gives a review of the most recent advances in design aspects of GHE, namely pipe arrangement, materials, and working fluids. The influence of the main design parameters on the performance of horizontal, vertical, and shallow GHEs is discussed together with commonly used performance indicators for the evaluation of GHE. A survey of the available literature shows that thermal performance is mostly a point of interest, while hydraulic and/or economic performance is often not addressed, potentially resulting in non-optimal GHE design. Full article

(This article belongs to the Special Issue Heat Exchangers: Cooling and Heating Systems)

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