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A mathematical model of the plate-fin heat exchanger filled with catalyst (CFPFHX) is established to investigate the continuous cooling process coupled with ortho-para hydrogen conversion at 42–70 K. The flow and heat transfer performance and the efficiency of ortho-para hydrogen conversion in the CFPFHX are quantitatively evaluated, and the effects of the structural parameters on the flow and heat transfer coupled with ortho-para hydrogen conversion are analyzed. The results show that the Elovich model is the best existing kinetic models of ortho-para hydrogen conversion with an average relative deviation of 1.8%. The Colburn heat transfer factor (j factor) of the hot side of the CFPFHX is 4.3 times that of the plate-fin heat exchanger (PFHX), and the thermal enhancement factor (TEF) of the hot side is 37.7% of that of the PFHX. Meanwhile, for the CFPFHX, the j factor and the TEF of the hot side under different structural parameters are always about 8–10 times and 68%–93% of that of the cold side respectively. Therefore, the CFPFHX can ensure the flow and heat transfer performance and realize the ortho-para hydrogen continuous conversion. And a fin with the larger flow area (high fin height, wide fin spacing and small fin thickness) has a better flow and heat transfer performance and ortho-para hydrogen conversion. The outlet para-hydrogen ratio youtp-H2 and the mass space velocity vm in the CFPFHX have an approximate linear trend. When mass space velocity vm ≤ 0.6589 kg/(m3·s), the outlet para-hydrogen ratio youtp-H2 can meet the requirement at 42–70 K. Above all, the mechanism of flow and heat transfer coupled with ortho-para hydrogen conversion is revealed for the first time in this study, which can provide a theoretical guidance for the application of the integrated technology in large scale hydrogen liquefaction process.

This study investigates the issues involved in the design of a compact two-phase thermosyphon in which the locations of evaporator and condenser need a high degree of freedom. Enhancement of boiling heat transfer in the compact evaporator space was achieved by a microfabricated structure. Anticipating situations where gravity does not provide sufficient potential to drive the condensate, a pump-assisted circulation loop was studied. The relative height between the evaporator and condenser and the pumping rate were systematically varied by utilizing two thermosyphon loops. Close examination of the data suggests that there could be an optimum point in the parametric domain where the thermal resistance is minimized with least assistance from the pump.

Heat flux and heat transfer coefficient may either be measured by a single measurement process, or they may require the measurement of several quantities before they may be estimated. Of course, it is best if the required quantity is directly measurable. We will give as much detail as possible, keeping in mind the target reader of the book. Many techniques are beyond the scope of the book and require direct reference to the appropriate research literature.

This paper presents a derivation of design guidelines for plate heat exchangers used for evaporation of zeotropic mixtures in heat pumps. A mapping of combined heat exchanger and cycle calculations for different combinations of geometrical parameters and working fluids allowed estimating the trade-off between heat transfer area and pressure drops on the thermodynamic and economic performance indicators of the cycle. Compressor running costs constituted the largest cost share, and increased due to a steep decrease of the heat pump coefficient of performance at high refrigerant pressure drops. It was found that the pressure drop limit leading to infeasible designs was dependent on the working fluid, thereby making it impossible to define a guideline based on maximum allowable pressure drops. It was found that economically feasible designs could be obtained by correlating the vapour Reynolds number and the Bond number at the evaporator inlet as Re V − 0.42 Bd 0.26 ≈ 0.040 . The use of the proposed guideline was illustrated for the mixture Propane/Iso-Pentane (0.5/0.5), leading to evaporator designs with net present values deviating maximum −4.4% from the best value found in the mapping. The presented methodology can be applied in different scenarios to develop similar guidelines, thereby decreasing the cost of combined cycle and component optimizations.

The need for high performance heat exchangers has led to the development of many types of surfaces that enhance the rate of heat transfer. One of the heat exchanger types are the matrix heat exchangers. Matrix heat exchangers consist of a series of perforated plates, separated by a series of spacers. The present study experimentally investigates the overall heat transfer characteristics of flow through a perforated plate with 2 mm in diameter, the hole length to diameter ratio of 1 and 25.6% porosity. Numerical simulations were performed to determine the overall heat transfer in the function of geometric parameters. Reynolds numbers based on the perforated plate pitch were set in the range from 50 to 500. The results of the average Nusselt number prediction were compared with the related experimental correlations. The experimental data agreed on qualitatively with the results obtained using a CFD. Using these data, a Nusselt criterial equation was obtained.

The objective of this study is numerically to investigate the heat transfer characteristics of the integrated heating system considering the temperature of cabin and battery of an electric vehicle under the cold weather conditions. The integrated heating system consists of a burner to combust fuel, an integrated heat exchanger for CHE (coolant heat exchanger) and AHE (air heat exchanger). The heat transfer characteristics like the overall heat exchanger effectiveness, the heat transfer rate, the temperature distribution and the fluid flow characteristics like the pressure drop, velocity distribution of the investigated integrated heating system were considered and analyzed by varying the inlet mass flow rates and the inlet temperatures of the cold air and water, respectively. The average Nusselt numbers for the cold air side and the water side were increased 28.4% and 9.5%, respectively, with the increase of the cold air side Reynolds numbers from 15,677 to 72,664 and the water side Reynolds numbers from 4330 to 11,912. The numerical results showed good agreement within ±9.0% of the existed data and thus confirmed that the present model was valid. In addition, the proposed integrated heating system could be used as the thermal management of the cabin and the battery system of the electric vehicle under the cold weather conditions.

In this paper, a numerical simulation of heat transfer in a heat sink installed on the transistorized square chip of a computer was investigated. Thermal performance of mainboard chip is very important in this operation. Heat sink was an appropriate device for removing heat uses air cooling technique. The fourth order Runge-Kutta method was used to solve nonlinear heat transfer equation. This simulation analyzed a heat sink geometry made from different materials with various heights such as aluminum and copper. Thermal conductivity of heat sink materials was temperature dependent. The effect of internal heat generation and radiation from heat sink surface, was studied. The Nusselt number and heat transfer coefficient was obtained in different velocities of air flow. As a main outcome, the Nusselt number increased with the increase of the air flow velocity and it caused of an enhancement in heat transfer coefficient.

The membrane based heat exchangers are a promising technology in air conditioning and energy recovery domains, in which they recover both sensible heat and moisture. In this paper, a comparison between different forms of obstacles (rectangular, triangular and circular), inserted in the geometry of the proposed membrane based heat exchanger, is presented. In order to evaluate their impacts on the heat and mass transfer distributions, a numerical model including the momentum, heat and mass transport equations is solved. The impacts of height channels ratio (RH) on heat and mass transfer rates are also mentioned. The results show that the benefit of circular obstacles form is more important than that of other ones. In addition, a high height channels ratio (RH) leads to a large air temperature and humidity ratio values in the outlet fresh channel. Also, the three dimensional model of the membrane based heat exchanger hasn’t any effect on the air temperature and humidity distributions in the co-current and counter current flow arrangements.

Although R-1233zd(E) has been considered as an alternative to R-245fa used in the organic Rankine cycle (ORC), experimental studies on the heat transfer characteristics of R-1233zd(E) in plate heat exchangers are limited. In this study, the evaporation heat transfer coefficient and pressure drop of R-1233zd(E) in a brazed plate heat exchanger are measured with respect to the mass flux, heat flux, saturation temperature, and vapor quality. As a result of the experiment in this study, the heat transfer coefficient of R-1233zd(E) is strongly dependent on the mass flux and vapor quality, and not on the heat flux and saturation temperature because the flow is in the convective boiling regime. The frictional pressure drop of R-1233zd(E) shows a strong dependence on the mass flux, vapor quality, and saturation temperature. Moreover, the heat transfer coefficient and pressure drop of R-1233zd(E) are compared with those of R-245fa. Finally, empirical correlations for the heat transfer coefficient and friction factor of R-1233zd(E) are developed based on the measured data.

The paper investigates whether air-water heat exchanger with longitudinal fins along the air flow direction are an appropriate means to reduce pressure loss in mechanical ventilation systems, compared to conventional heating coils. To answer this question, theoretical calculations regarding pressure loss and heat transfer are performed and the results are checked by measurements. It is found that a longitudinal fin heat exchanger with 30 radially arranged fins and an overall length of 830 mm transfers the same heat flow as a conventional heating coil (∅ 125). The pressure loss only adds up to about 60% to 70%, so a reduction of 30% to 40% can be achieved. Additionally it is expected, that the longitudinal fin heat exchanger is more suitable for efficient low temperature heating systems, because of the counter-current heat transfer. The disadvantage of its increased length can be compensated by integrating the longitudinal fin heat exchanger in a duct silencer, which is required anyway. Hence, the energy efficiency of mechanical ventilation system can be increased.

In this paper, a numerical simulation model has been extended for analyzing the energy and exergy of direct-expansion geothermal heat pumps (DX-GHP) in domestic hot water and heating applications. Carbon dioxide (CO2) in transcritical cycle has been used as the refrigerant and the effects of the refrigerant pressure drop in the heat exchangers have been considered. The present numerical investigation gives the energy and exergy analysis under different operational conditions in two separate cases. In the first case, the ground heat exchanger loop length is considered to be constant and in the second case, the heating load is considered to be fix. With the aim of evaluation the system work performance, a detailed parametric investigation has been carried out on the effect of different parameters including the difference between soil temperature and the outlet temperature of the evaporator, the compressor speed, the temperature and the mass flow rate of inlet water to the gas cooler, the gas cooler length, the number of ground heat exchanger loops, and soil temperature. The results of this study include heating capacity, coefficient of performance (COP), exergy efficiency, ground heat exchanger loop length can be used for design and optimization of a DX-GHP.

Nanoparticles deposition is one of the most challenges for industrial use of nanofluids. In the present study, the heat transfer enhancement of Multi Wall Carbon Nano Tube, MWCNT-water nanofluid in a double pipe heat exchanger due to vibrating walls is examined for different mass fractions. This work is performed by a flexible double pipe heat exchanger made of PVDF. The forced vibration on the outer surface of the heat exchanger is imposed by electro-dynamic vibrators. Results demonstrate that imposing the vibrations increases the heat transfer coefficient remarkably, while decreases the nanoparticles deposition. Heat transfer increases by increasing the nanofluid temperature, mass flow rate, nano fluid mass fraction and vibtation level. The most increase in heat transfer coefficient is 100% which is obtained in the test of the lowest mass fraction (0.04%) with the highest vibration level (9 m/s2) in the experiment range.

A ground heat exchanger is an essential component of ground source heat pumps, which saves cooling and heating energy effectively. In this study, a branch tube type heat exchanger is suggested for a ground heat exchanger instead of commonly using the U-tube type for increasing heat transfer efficiency. The branch tube type heat exchanger has conjugate heat transfer including convective heat transfer between the walls of primary- and branch-tubes and internally circulating fluid, and conduction in the tube walls and grout. This conjugate heat transfer phenomenon is analyzed by steady 3-D numerical analysis using the finite volume method. In the analysis, temperature distribution, rate of heat transfer and pressure drop are compared for the branch tube type ground heat exchanger with 2, 4, 6, and 8 branch tubes together with a single U-tube type ground heat exchanger. Generally, the branch tube type shows better heat transfer performance compared to the U-tube type and the higher number of branch tubes give better heat transfer performance. Also, the branch tube type yields higher pressure drop than the U-tube type for the same mass flow rate of circulating fluid in the heat exchanger.

Energy efficiency evaluation of heat exchangers are crucial for energy saving in industrial applications. Currently, no energy efficiency evaluation is appropriate for the grading of energy efficiency of heat exchangers. In this paper, an energy efficiency index (EEI) is proposed to evaluate the energy efficiency of single-phase flow and heat transfer of plate heat exchangers. EEI is defined by k/∇pn, where k is overall heat transfer coefficient, ∇p is flow pressure gradient and exponent n is the indicator of the relative importance between heat transfer and flow resistance. EEI indicates the overall heat transfer coefficient per unit equivalent pressure drop. The recommended n is 0.31 for plate heat exchangers based on the data of 281 heat exchangers. We conclude a normal distribution function for the evaluation of energy efficiency of plate heat exchangers. The present method can quantitative evaluate the performance of plate heat exchangers and hence can grade them in terms of energy efficiency.

This paper involves an exhaust gas waste heat recovery system for vehicles, which uses thermoelectric modules and a heat exchanger to produce electric power. Based on summarizing the latest research of vehicle exhaust thermo-electric generator (TEG), it presents two new fin structures for the cylindrical heat exchanger in a TEG system. It mainly studies the thermal performance of two kinds of three-dimensional cylindrical heat exchanger models including spiral-fin heat exchanger with variable pitch in a computational fluid dynamics simulation environment. In terms of interface temperature and thermal uniformity and based on an evaluation method of the temperature uniformity for the heat exchangers, the thermal characteristics of heat exchangers with different pitch angle of the twisted fins, pitch of spiral fin, fin thickness and fin height are discussed. Two new fin structures are feasible to enhance the heat transfer performance of heat exchanger.

Thermosyphon heat exchangers were widely applied to recover exhaust heat, and the effectiveness-NTU method was proposed for their thermal performances. As the thermal resistances inside thermosyphon were neglected in that approach, the predicted effectiveness was overestimated and the outlet temperature of hot fluid underestimated compared with experimental data. In the present work, the comprehensive mathematic model, with the thermal resistances of vaporization and condensation inside thermosyphon taken into consideration, is proposed to accurately predict the thermal performance of thermosyphon heat exchanger. The numerical solution scheme is presented and the thermosyphon heat exchanger released in the literature is computed for the validation. With current model, the typical profiles of fluid temperatures are predicted. In addition, the fin spacings of evaporator and condenser are decreased to improve the thermal performances of concurrent and countercurrent thermosyphon heat exchangers. As the vapor temperature inside thermosyphon is coupled with working pressure and thus significant in optimal design, its profile and variation are systematically studied. The present work demonstrates that the current comprehensive model could predict the thermal performance of thermosyphon heat exchanger with a good accuracy, and the effects of heat transfer enhancement on the effectiveness and vapor temperature are both obtained.

Heat pipes are compact and efficient heat exchangers which are widely used in a large number of thermal devices. Researchers were attracted towards the application of nanofluids in heat pipes due to its superior thermo physical properties. They used nanofluids as working fluid in heat pipes and noticed significant changes in thermal performance. In present study authors summarize the research outcomes of various experimental and numerical studies. It also provides an overview of heat transfer mechanisms responsible for the change in thermal performance of heat pipes. Heat transfer mechanisms depend upon, type of heat pipes, nanofluids characteristics, design and operating parameters of heat pipes, etc. All the parameters have their own individual as well as the combined effect on thermal performance. Authors have drawn the attention of research community to explore the dependency of all parameters on each other.

The aim of this work is to experimentally evaluate three different compact branched heat exchangers, measuring, for every single device, the thermal efficiency and the pressure drop. The generality of the analysis of phenomena is enhanced by a comparison of the performance of different refrigerant fluids. In the first configuration, the channels have been designed, varying the inner diameter, to allow for an average constant flow speed throughout the exchanger. In the second one, the flow Reynolds number inside of the channels has been maintained constant. The last configuration is built according to the constructal diameter variation, as indicated in Bejan Constructal Theory. The exchanger manufacturing process is described in detail. The test bench has been assembled using a hot source (Heating Plate with a power of 500 W) and a submersible pump, needed for the fluid recirculation, coupled with flowmeters, to control the mass flow rate within a specific range. The data obtained from several comparative tests have been analyzed, to determine the optimal solution for each refrigerant among the different exchangers.

The charging and discharging processes of a latent heat thermal energy storage system assisted by a heat pipe network was experimentally studied. Rubitherm RT55 was chosen as the phase change material (PCM) and was enclosed within a vertical cylindrical container. A network of simulated heat pipes was embedded within the PCM to enhance the heat transfer. The heat pipe array consisted of a primary central heat pipe with an array of secondary heat pipes. The primary heat pipe transfers the thermal energy from the heat source to the heat sink while the secondary heat pipes transport the extra thermal energy into to the phase change material during the charging process or retrieve it from the phase change material during the discharging process. The heat pipe network was simplified by employing an arrangement of copper and acrylic pipes. Water was used as the heat transport fluid, which was circulated through the pipe network with a relatively high velocity to decrease the temperature drop, similar to what happens inside a real heat pipe. The effects of different heat transfer fluid flow rates and temperatures on the thermal performance of the latent heat energy storage system were studied. The results indicated that the heat transfer fluid flow rate and temperature have significant impacts on the total charging time of the system. It was also found that the while the flow rate of the heat transfer fluid has minimal effect on the discharging process, the temperature of the heat transfer fluid plays a significant role.

Heat sink has been widely used as a cooling device for electronic systems in recent years. Because of the considerable heat generated by electronic devices and low efficiency of conventional heat sinks, a large number of researches have been focused on the performance enhancement of these systems. Innovative heat sink in the presence of Al 2 O 3 -water nanofluid is experimentally investigated in this study. The effects of adding various volume fractions of nanoparticles on the convective heat transfer coefficient, pressure drop, thermal resistance and heat sink base temperature are investigated in different flow rates from 6.14 to 32.2 (cm 3 /s). The obtained results reveal that the convective heat transfer enhances 16% and thermal resistance reduces more than 15%. The innovative thermal energy absorption system in present research is a tangential heat sink with impinging liquid jet and elliptical cross section which is expected to be able to achieve significant enhancement in thermal energy removal as a cooling device, which is proposed as the novelty here. Also comparison between cylindrical and elliptical cross sections in this type of heat sink is carried out. The results disclose that using tangential heat sink with liquid jet impingement achieves convective heat transfer coefficient 2.26 times greater than conventional heat sink in the presence of pure water.

Heat exchangers are essential components of many systems and their use is extended to include various industrial, chemical, and automotive applications. Heat exchanger behavior affects the total performance of a thermal system. Enhancing this critical component leads to improving the system overall performance and thus its energy efficiency. Since a heat exchanger operates in conjunction with other process equipment, its evaluation under a transient condition is crucial. A transient response of heat exchangers is necessary to evaluate the exchanger performance when subjected to a change in its conditions. The scarcity of experimental data on a transient response of heat exchangers in general and minichannel exchangers in particular is the main motivation for this research. This work is an investigation of an experimental characterization of the transient response of a cross flow liquid-air heat exchanger subjected to step changes in liquid mass flow rate. Hot fluid mass flow rate step changes of 0.5, 0.8, 1.5, and 2.0 are considered and the liquid outlet temperature response time is presented. The results are compared with the limited experimental work from the literature. While the outlet temperatures of both fluids do not respond instantaneously to the step change in the primary fluid mass flow rate, the cold fluid exhibits a faster response time than that of the hot fluid. The step variation increases the Reynolds number which results in a longer hot fluid response time to reach the steady state. The outcome of this work is valuable in the design, selection, and analysis of heat exchangers. The experimental data provided in this work can be used to establish a database for future advances in research. It also provides an overview of the characteristic behavior of certain parameters such as fluid temperatures, response time, and residence time when the heat exchanger is subjected to a change in the hot fluid mass flow rate.

The heat exchangers used in thermoelectric power generation are required to achieve an optimal efficiency by comparing heat transfer that is related to the power generation into the consumption of pump power. The main objective of this study is to enhance heat transfer at a lower flow rate using a tangled channel. The newly introduced channel was designed to increase heat transfer through the entangled shape despite the low Reynolds numbers. Both experimental and numerical analyses were used to investigate the thermal–hydraulic characteristics of the present printed circuit heat exchanger (PCHE). The computational fluid dynamics analysis using ANSYS CFX 15.0 successfully predicted the experimental data with average errors of 1.25% and 4.51% for temperature and pressure differences between the inlet and the outlet, respectively. The present PCHE with a tangled channel showed the improvement of heat transfer when the Reynolds number ranges from 1000 to 3000. Based on the numerical calculation, the geometric effect was investigated by using the concept of temperature uniformity. The temperature uniformity in mixing zones might be a reason for the improvement in heat transfer at a relatively low range of Reynolds number.

The heat transfer in heat sinks of microelectronic components has been numerically analyzed for different heat sink geometries in tandem and staggered arrangements. The present numerical study addresses cooling of fins with forced air convection in single micro channel heat sink using Ansys FLUENT software. Maximum heat transfer flux with minimum flow resistance was considered as the selection criteria for different heat sinks. Standard and staggered fins of uniform thickness are considered for all the heat sinks to analyze heat transfer performance. Quality factors corresponding to different geometries were calculated and compared with experimental and numerical results available in open literature. The present numerical results ensure the better performance of staggered heat sinks over standard ones. It has been noticed that staggered fins with conic section provide enhanced quality factors at flow Reynolds number range of 450–900 whereas staggered fins with rounded leading edges provide better thermal performances for Reynolds number beyond 900.

In this paper, the influence of the addition of fins and the use of two different heat transfer fluids (water and a commercial silicone) have been experimentally tested and compared in four latent heat thermal energy storage systems, based on the shell-and-tube heat exchanger concept, using paraffin RT58 as phase change material. Three European institutions were involved under the framework of the MERITS project. A common approach (temperature and power profiles), and five different key performance indicators have been defined and used for the comparison: energy charged, average power, 5-min peak power, peak power to energy ratio, and time. For the same heat transfer fluid, results showed that finned designs (4.7-9.4 times more heat transfer surface) showed an improvement of up to 40%. On the contrary, for the same design, water (which has a specific heat 3 times higher and a thermal conductivity 4.9 times higher than silicone Syltherm 800), yielded results up to 44% higher. The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/2007–2013) under grant agreement No ENER/FP7/295983 (MERITS) and under Grant agreement N°PIRSES-GA-2013-610692 (INNOSTORAGE), and from the European Union's Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The work is partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER) and ULLE10-4E-1305). The authors would like to thank the Catalan Government for the quality accreditation given to the research group GREA (2014 SGR 123). Jaume Gasia would like to thank the Departament d’Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship (2017FI_B 00092).

As a novel solid desiccant component, solid desiccant coated heat exchanger (DCHE) is proposed by coating solid desiccant material to conventional sensible heat exchanger (SHE) surface. The idea of adopting a DCHE and an SHE operating in series is proposed and an experimental setup was built up to investigate its performance. Results show that with the use of an auxiliary SHE, the temperature variable rate increases, while about 4 °C lower outlet temperature can be obtained, the corresponding cooling power and COP increase by about 75% and 13% respectively. Besides, lower cooling water temperature is recommended to obtain enhanced system performance; system performance increases with increasing inlet air temperature and relative humidity ratio, the recommended air velocity is different with respect to different aims.

A three-dimensional computational fluid dynamics (CFD)-based simulation for the Intermediate Heat Exchanger (IHX) of a pool-type sodium-cooled fast neutron reactor has been performed in this paper, which investigates the flow-field and temperature distributions of liquid sodium on both primary and secondary sides at full power conditions. Typically, some simplifications are applied to reduce the difficulty of computation and render the problem more tractable. A proposed method is that treat a number of tubes as porous media that replicates the pressure loss and heat transfer characteristics of the detailed model. The heat exchanger model of the ANSYS FLUENT code is used to analyze the heat transfer phenomena inside of the IHX and the resistance coefficients of porous media have been predicted by empirical relationships which vary with height and flow directions. Two separate models, with different size of inlet and outlet area for shell-side sodium, have been developed in this paper. By comparing the results from the different simulations, the model with larger inlet area for primary and non-uniform inlet velocity distribution of secondary sodium satisfies the design requirements with respect to the permissible upper limit of temperature difference and local radial velocity.

This paper investigated the frost formation on louvered folded fins in microchannel type heat exchangers and the effects of frost accumulation on the time dependent air side convective heat transfer coefficients during transient heat and mass transfer processes. Seven fin geometries, which were commonly used in outdoor microchannel type heat exchangers of air-source heat pump systems, were investigated for a wide range of temperatures and humidity promoting frost growth. The air-side heat transfer coefficient was depended on the rate of frost growth and it sometimes increased during early frost formation and then it decreased sharply. Frost thickness on the fin leading edge, air face velocity, and corresponding heat transfer coefficients and pressure drops were measured and semi-empirical correlations were developed. The frost thickness and air face velocity were key variables for estimating a local time-dependent air-side Reynolds number and for describing the transient behaviour of the local air-side heat transfer coefficient of the fins. The newly developed correlations identified the main parameters that describe frost growth and heat transfer on louvered folded fins under frosting operating conditions and they agree with the experimental data of the present work and from the literature.

The evaporation processes at low temperatures are essential for the factories and thermal systems as the heat pumps by absorption. This paper shows the design, building and characterization about an evaporator of 2 kW with a steam generation at 323.15 K. Its geometry consists in three nested helical coils with different diameters. Every coil is connected in series and the heat interchange is given by means of pool boiling. The heat transfer coefficients are indicated considering different operating conditions. The sizing method was validated taking into account the theoretical and experimental overall heat transfer coefficient of 659.8 W/m2 K. The evaporator efficiency was up to 83% taking into account a steam of 7.1 × 10−4 kg/s with a heat source at 334.35 K and 0.11 kg/s.

The project reported in this paper used CFD as a tool to investigate the effect of multi-pass on the shell side heat transfer of a heat exchanger system. The heat exchanger system is equipped with six vertical thermosyphons transferring thermal energy from a heat source (air) to a heat sink (water). The CFD model has been experimentally validated. The two-phase change processes inside the thermosyphons were not modelled during the simulation. Instead, the thermosyphons were treated as solid rods with a constant thermal conductivity, which was calculated theoretically by applying the thermal resistance analogy with the aid of convection, boiling and condensation correlations found in the literature. The heat source consists of multiple air passes on the evaporator section of the thermosyphons and two water passes on the condenser section. Three different arrangements on the evaporator section were investigated with one, two or three shell passes and the thermal performance compared for the three configurations. The investigation was performed at various inlet conditions: a range of air inlet temperatures (100, 150, 200 and 250 °C) and mass flow rates (0.05, 0.08, 0.11 and 0.14 kg/s). The water inlet conditions were kept constant (a temperature of 15 °C and a mass flow rate of 0.08 kg/s). The overall rate of heat transfer was obtained by both CFD and a theoretical model, and the results lay within 15% of the experimental data. The numerical predictions demonstrated that the k − e Realizable turbulence model is a reliable tool for predicting heat transfer and fluid flow in such heat exchangers.

In this work, the heat transfer intensification in shell and helically coiled tube heat exchangers via installing annular fins on the outer surface of the helical coil, has been numerically investigated. Thirteen heat exchangers were designed for this purpose. All geometrical parameters of the heat exchangers are same except, fin's number or height. All of the heat exchangers have been studied at three different shell side Reynolds number (Re sh = 7500, 15,000 and 30,000). In order to validation of the numerical model two method has been used. In the first method, the calculated heat transfer has been compared with the approximate method which is based on the experimental correlations for both coil and shell side Nusselt numbers and consideration of the E-NTU relations of these types of heat exchangers. In the second method, the heat transfer coefficient of the shell side has been compared with the experimental heat transfer coefficients of the previous works. An acceptable agreement has been observed in these comparisons. Furthermore, the optimum cases and some correlations have been obtained for prediction of the heat transfer coefficient of the shell side. Results indicate that, in the range of 7500 ≤ Re sh ≤ 30,000, the heat transfer rate can increase up to 44.11%.

High temperature heat pipes offer an efficient way of heat removal in nuclear reactors under both normal operation and postulated accidental scenarios. Heat pipes with sodium as a working fluid has been proposed to be used in Compact High Temperature Reactor (CHTR), 233U-Thorium fuelled reactor being designed to operate at 1000 °C. High temperature heat pipes can also be used for decay heat removal from dump tanks of molten salt breeder reactor and heat removal from first wall of fusion reactors. High temperature heat pipes of special construction can also be used for heat removal from core without use of coolant. Thus, reliable and long term operation of heat pipes is essential for the safe working of the reactor. In this respect, computer codes have been developed for design and simulation of high temperature heat pipes. To assist in the design stages, codes have been developed, which incorporate performance limits based on correlations and having a user friendly GUI. For system level studies, simplified heat transfer model is developed using a FEM model. For a detailed study of the heat pipe, the vapour flow behavior and interface evaporation condensation phenomena using a full CFD analysis is essential. This has been done by using a commercial CFD code by incorporating user defined functions (UDFs) which address the saturated nature of the vapour phase and the vapour wick interface conditions. A three dimensional transient numerical model has been developed to predict the vapour core, wall temperatures, vapour pressure, and vapour velocity in the screen mesh wick of sodium heat pipe. The results have been compared using a sodium heat pipe developed in-house. This paper will give an outline of all the developed models and compared the predicted results against the experimental data.

Two-phase heat exchanger immersed in a passive containment cooling water storage tank (PCCWST) is a key component of the passive containment cooling system (PCCS) in light water reactors. Condensation and boiling heat transfer phenomena taking place on the inside and outside walls are crucial to the performance of the heat exchanger tube. The performances of such phenomena can be readily affected by the inclination angle of the heat exchanger tube under buoyancy-driven convection conditions in a PCCWST. However, to date no systematic examination of the effects of inclination angle on pool heat exchanger performance has been reported. This paper presents the results of numerical and experimental analyses of how inclination angle affects the performance of a single steam condensation tube immersed in a saturated water pool. To concurrently predict the two-phase heat transfer processes inside and outside the heat exchanger tube, an explicit heat structure coupling of two thermal-hydraulic codes was implemented using open media models. An experimental facility was also constructed to test a single-tube heat exchanger under the same conditions as the simulation. A comparison of simulation data and experimental results obtained for the reference case (tube inclination of 30°) confirmed that the coupled code could predict the heat transfer rate in the pool heat exchanger within the error limits of the experimental measurements. In light of this, additional simulations and experiments were conducted at varying inclination angles, from 3° to 90°. The results of simulations and experimental studies revealed that the heat transfer rate of a heat exchanger tube in a saturated pool is hardly influenced by tube inclination. Although an increase in inclination angle caused the vapor slug to spread around the heat exchanger tube surface, preventing liquid from getting to the surface of the tube, thereby decreasing boiling heat transfer coefficients, this was compensated for by an increase in condensation heat transfer coefficients as the inclination angle increased as a result of accelerated condensate liquid film in the tube. Thus, the overall effect of inclination angle on the thermal performance of a single-tube pool heat exchanger is inconsequential.

This paper numerically explores the heat transfer behaviors of cryogenic fluids in offset strip fin (OSF) channels considering the important effect of fin efficiency that combines the factors of low thermal conductivity of fin material at cryogenic temperatures and the fin geometry. A series of numerical simulations, which involve three kinds of fin materials with different thermal conductivities and the cryogenic fluids including both gases and liquids of nitrogen, normal hydrogen and classic helium 4, are carried out with well-validated 3D models. The results show that lower thermal conductivity of solid material at cryogenic temperature causes a considerable reduction in heat transfer performance of OSF fins especially for the liquids with high Prandtl number. Further analysis of the results reveals that for different cryogenic fluids, Nusselt number is strongly related to Prandtl number and fin efficiency. In particular, Nusselt number is proportional to the Pr 0.235 η f 0.9 in laminar region, regardless of Reynolds number and fin geometries. The results for different fin geometries suggest that larger fin thickness-to-length ratio can help to improve the heat transfer performance, while smaller fin thickness-to-height ratio and higher fin density no longer contribute to higher j factor (or Nusselt number) of OSF fin, especially in the case of lower thermal conductivity of fin material. There exist optimum fin thickness-to-height ratio and fin density that correspond to the maximum value of j factor for the cryogenic fluids.

The study presents the experimental information on heat transfer performance of jet impingement cooling on circular pin- fin heat sinks with/without a hollow perforated base plate. Smoke flow visualization is also used to investigate the behavior of the complicated flow phenomena of the present heat sinks for this impingement cooling. The effects of flow Reynolds numbers (3458≤Re≤11,526), fin height, the geometry of the heat sinks (with/without a hollow perforated base plate), and jet-to-test heat sink placement (1 ≤H/d≤16) are examined. In addition, empirical correlation to estimate the heat transfer coefficient was also developed.

The procedure for field testing of plate heat exchanger, considered as a black box, is presented in the paper. After the field measurements have been conducted, simple but unambiguous procedure has been used to establish heat performance parameters including the heat duty and fouling factor. Advantage of hereby presented method is that it can be used for analysis of any other similar heat transfer equipment.

In typical gas-to-liquid thermoelectric generators for waste heat recovery, the stream-wise gas temperature drop in the hot-side heat exchanger leads to the decrease of power output of the whole system. Denser fins are usually arranged on the downstream of the hot-side heat exchanger to improve the uniformity of temperature field and thus the total power output performance of thermoelectric generators when the steam-wise temperature drop is small, but it is not benificial when the steam-wise temperature drop is large. This work investigates the effect of configuration of winglet vortex generators on the performance of thermoelectric generator system. Three sets of hot-side heat exchangers, including a heat exchanger with smooth channel, a heat exchanger with uniform configuration of winglet vortex generators and a heat exchanger with non-uniform configuration of winglet vortex generators, are tested in a gas-to-liquid thermoelectric generators experimental system. The hot-side Reynolds number ranges from 3000 to 6400 and the hot-side inlet temperature is within 523–553 K. The experimental results show that the total and net power output of thermoelectric generator under matched load resistance with uniform heat exchanger can respectively outperform that with smooth heat exchanger by 97.5% and 77.7% in average, whereas that with non-uniform heat exchanger by 189.1% and 177.4% in average. Since the uniform and non-uniform heat exchangers have the same number but different configuration of winglet vortex generators, this kind of active cascade control of heat transfer enhancement elements is proved to be effective in improving the power output of thermoelectric generator system without increasing pumping power.

In this study, the heat and mass transfer characteristics of desiccant coated heat exchanger (DCHE) and conventional heat exchanger are compared by experiments. A general-purpose test platform is built to test and compare the characteristics above. Based on the designed experimental setup, two heat exchangers of different depths of fins conventional/desiccant coated are experimentally investigated and compared with the given performance evaluation standards. In addition, parametric influences of inlet air velocity, hot water temperature and cycle time are analysed. Experimental results show that compared with the conventional heat exchanger, the heat transfer capacity of DCHE is reduced by 30% because of the heat resistance produced by desiccant coating. Pressure drop and Euler number are both increased by 60% approximately for the same reason. Doubling the depth of fins increases the average moisture removal by 40% and COPth by 10%, without changing the other structure parameters.

The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis (CHFS) system to enhance the heat transfer and minimize the required length of the heat exchanger. For this purpose, numerous numerical simulations are performed to investigate performance of the system with porous media. First, the numerical simulation for the heat exchanger in CHFS system is validated by experimental data. Then, porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness, based on the minimum required length of the heat exchanger. Finally, by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate, the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed. The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%. The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness. Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.

The supercritical CO 2 Brayton cycle (SCO 2 -BC) is proposed to be used as the concept of fast cooled reactor (FCR), which is a typical application in the 4th generation reactors. The recuperator and cooler, which acted as important components in SCO 2 -BC, are required for long-term operation especially at the high pressure condition. However, the traditional shell-and-tube heat exchanger, which already has mature fabrication technology, is not appropriate in the developing miniaturized thermal system because of its low compactness. In the present paper, the compact printed circuit heat exchanger (PCHE) with straight ribs is manufactured by the photochemical etching technology and the diffusion bonding method independently. Then, the thermohydraulic performance of PCHE is tested on the SCO 2 -water experiment platform. Considering the difference of thermal properties of working fluid, the comparison of thermal and hydraulic performance between SCO 2 and water in the tested PCHE is studied at the same mass flow rate, which shows that the SCO 2 has better heat transfer capability than water fluid. Further, the heat transfer rate and pressure loss of PCHE are investigated at different SCO 2 operating pressure, which indicates that the PCHE has better comprehensive performance when it operates at higher pressure condition. Meanwhile, the extreme operating condition due to the pseudo-critical point of CO 2 working in the PCHE is analyzed comparing with the normal operating condition. The results show that the comprehensive performance of PCHE is significantly reduced nearly 17.6% when operates at the transcritical state. The heat transfer correlation of PCHE with straight ribs is fitted by experimental data in both the supercritical and transcritical states in order to simplifying design process.

In this study, the heat transfer characteristics of pilot wave heat exchanger for white smoke reduction system was investigated. The performance of the wave and honeycomb heat exchanger combined with the first stage, second stage and third stage was tested using a calorimeter. Air and water inlet/outlet temperature and flow rate, pressure drop and dehumidification amount were measured to compare the heat transfer performance according to the type and the combination of heat exchanger. The heat transfer rate and dehumidification amount of the wave heat exchanger were higher than that of the honeycomb heat exchanger, and the pressure drop was low. As the stage increased, the heat transfer rate and the increase of the dehumidification amount were more pronounced, and the pressure drop linearly increased. The wave heat exchanger had a lower flow resistance than the honeycomb heat exchanger with the honeycomb structure and had a higher heat transfer effect due to the convection, so the water outlet temperature was higher in the wave heat exchanger.

The effects of different plate-fin heat exchanger structures in high temperature gas-cooled reactors (HTGR) were studied numerically. Four fin structures and four working conditions were analyzed to scrutinize the plate-fin heat exchanger performance with detailed analyses of the velocity distributions, pressure distributions, temperature distributions and heat transfer. The results show that the velocity curves around staggered fins have two peaks with high velocity fluid near the fins. For the same average inlet velocity, the fluid temperature is more uniform with the staggered fins. The fluid temperatures are more stratified with the plain fins unlike the staggered fins periodically disrupt the boundary layer and mix the flow, so the boundary layer along the staggered fins is thinner than along the plain fin and the heat exchange rates are higher. However, the pressure drop with the staggered fins structure is also increased. The total heat transfer rates for Model 2 were 1.3–1.4 than for Model 1, with those for Model 3 1.4–1.5 and those for Model 4 1.5–1.6 times higher than those for Model 1 for all conditions. The total pressure drop with Model 2 was 1.5–1.8 times higher, Model 3 was 2.1–2.6 times higher and Model 4 was 2.8–3.7 times higher than for Model 1. The complete thermal-hydraulic evaluation indicates that the staggered fin structure with a modest fin length, approximately 3.5 mm, is the best choice.

In this paper, the study was focused on a double flow plate-fin heat exchanger (PFHE) whose heat transfer element was offset staggered fin. Numerical simulations have been carried out to investigate the thermodynamic characteristics of a full-size PFHE via the porous media approach. Based on the numerical model, the effects of the dynamic viscosity and the locations of the inlet and outlet tubes on flow distribution and pressure drop of the PFHE were studied. The results showed that flow distribution of the PFHE was improved by increasing the dynamic viscosity. Therefore, the relationship between flow distribution and pressure drop was analyzed under various inlet velocity, and a correlation among flow distribution, pressure drop, and Reynolds number was derived. Finally, the middle-based strategy was proposed and numerically verified to improve flow distribution of the PFHE.

Heat transfer and pressure drop of a fin-and-tube heat exchanger are studied by taking into account the conjugated heat transfer between the flow and the fin. The temperature distribution of the fin is calculated in respect to the convective heat transfer of the air flowing through the tube bank channel. Contemporary enhancement methods emphasize the importance of local turbulence augmentation which effects the convective heat transfer. In this paper, the importance of conjugated heat transfer, where the temperature of the flow and fin are coupled together is emphasized and compared with a constant surface temperature boundary condition simulation and experiment, which are found in the literature.

The application of a phase change material (PCM) as thermal energy storage observed unprecedented growth due to its large latent heat storage capacity at a constant temperature. However, the design...

Compact-sized organic Rankine cycle (ORC) power generators call for higher performance and down-sized heat exchangers. Heat exchangers in ORC systems, especially evaporators contribute to a big portion of the system size as well as the capital cost, and their price is also directly related to their size. Since the heat transfer area plays a direct role in the performance of heat exchangers, high-porosity metal foams are proposed for insertion into heat exchanger channels to enhance the heat transfer mechanism in evaporators. Their high surface area to volume ratio makes them a good candidate for manufacturing high-performance heat exchangers. The metalfoams are being considered to improve performance while keeping the size of heat exchangers small. In this experimental study, the performance of a 100 kW class heat exchanger with the channels brazed with nickel based metal foam and stainless steel sheets was investigated. A hot water loop was designed for heat input. The cold side of the heat exchanger works with R245fa as the working fluid. The phase-change heat transfer experiments were performed with different mass flow rates ranging from 0.32 to 0.51 kg/s while the operating pressure was at 10 to 13 bar with hot water inlet temperature was 133℃. Furthermore, the heat transfer performance is compared with a commercial plate heat exchanger (produced by Alfalaval, AC120EQ) which was custom-made as a 100kW class evaporator. In the comparison test, refrigerant side has 0.5kg/s of mass flow rate at 44℃ and heat source side has 1.23 kg/s mass flow rate at 132℃. Although the pressure drop in the metal foam plate heat exchanger is increased compared to that of the conventional plate heat exchanger, increase of the recovered waste heat from the heat source is much higher due to higher overall heat transfer coefficient. As a result, the energy density of the new heat exchanger is about 2.5 times higher than that of the conventional plate heat exchanger.

The combination of the rotating heat pipe with conventional air cooling technique can be considered as an emerging and effective cooling technique for gas turbine disk. Accordingly, the thermal steady and transient analysis of a simplified turbine disk integrated with heat pipes have been numerically investigated. The steady and transient temperature variations in the presence and absence of heat pipes were investigated for various parameter, such as the thermal conductivity of the disk, the convective heat transfer coefficient for both the air and heat pipes, the dimension of the disk, and the number of heat pipes. The thermal analysis were performed by using finite element (FE) modeling software ANSYS-17.2. The extensive numerical simulations showed that when the number of heat pipes equal to 32, the maximum temperatures at the disk edge can be decreased by more than 100 degree. Additionally, increasing the convective heat transfer coefficient of the working fluid inside the heat pipes up to 10,000 W/m 2 .°C, the maximum temperature at the disk rim can further be reduced by more than 280 degree. It has also been observed that the time required to achieve the minimum steady-state temperature was more sensitive to the air convective heat transfer coefficient.

The objective of this paper is to analyze the heat transfer characteristics of plate-fin radiator for the cold air heating system of a PEMFC engine and to find the optimal parameter combination in order to reduce the power consumption. The effect of the coolant mass flow and temperature on the heat exchange performance of the radiator was investigated based on 3D porous medium model. The results, including the amount of heat transferred and temperature change and heat exchanger effectivity with the increasing of the air flow rate at different coolant flow rate were obtained using CFD method. Good agreement is found by comparing the simulation values with the test data and the deviation is less than 7% which indicate simulation model validation and research method feasibility used in this study. The simulation results indicate that bigger coolant flow rate and temperature result in higher outlet air temperature and the amount of heat transferred. The variation of the heat exchanger effectivity is predicted for different working conditions. Based on the Taguchi method, the influence of structural parameters of the corrugated fins on the heat transfer and pressure drop of the radiator is analyzed qualitatively. It is shown that fin length has the greatest impact on the comprehensive heat transfer performance of the radiator. This research provides a guide for optimizing the air preheating system and improving the amount of heat transferred.

Pillow-plate heat exchangers (PPHE) represent a promising alternative to conventional equipment, e.g., in the process industries; however, the lack of published design methods still hinders their widespread application. The present work represents a first step towards investigation of a particular PPHE operation mode, which comprises process medium condensation between adjacent pillow plates and simultaneous cooling medium evaporation in the plates. An experimental set-up was built and used for heat transfer experiments, in which 1,1,1,2-tetrafluoroethane evaporated in both thermosyphon and forced-convection operation mode. The focus was on the investigation of heat transfer during the evaporation process in the wavy pillow-plate channel, and the (virtual) enthalpy of condensation was imitated using dissipation of electrical current in the walls of a single pillow plate. Along these lines, two-phase heat transfer coefficients for the evaporating fluid flow in the inner channels of the plates were determined. The results reveal a promising heat transfer performance, which can be utilised to increase energy efficiency in the process industries. A correlation proposed by Kandlikar for saturated two-phase flow boiling heat transfer inside tubes was found suitable for the prediction of heat transfer in pillow plates, with slight underestimation. The results of this study can further be applied for the description of a number of heating and cooling processes.

Micro heat exchangers are the integral part of advanced technologies such as space technologies. However, the cooling of these micro heat exchangers encounters various challenges due to large aspect ratios. Further, the conventional coolants could not dissipate the heat due to limited thermal conductivity and specific heat. Hence, suspension of nanoparticles in such coolants would increase the efficiency of micro heat exchanges. Nanofluids are widely used in biomedical applications, as coolants in transportation, industrial cooling, nuclear reactor cooling and defense applications due to their higher stability, higher heat transfer capabilities and reduced particle clogging. In the present work, the thermophysical properties of Al2O3, SiO2, SiC, CuO and TiO2 nanoparticles in Liquid Nitrogen (LN2) are studied with the volume concentration of 3%. It is observed that thermal conductivity of nanofluid is enhancing with the increase in volume concentration of nanoparticles which result in enhancing the heat transfer rate in micro heat exchangers. In order to confirm this fact, a computational investigation on pressure drop and heat transfer is performed with Liquid Nitrogen as a base fluid and CuO, SiO2, SiC, Al2O3 and TiO2 as nanoparticles. A computational geometry is developed in ANSYS® and the pressure drop and heat transfer analysis is done using FLUENT®. Relevant boundary conditions are applied to reflect the practical operating conditions of micro heat exchangers. It is observed from the results that the decrease in pressures drop with the suspension of CuO nanoparticle is low. Further, the heat transfer is observed to be increasing with the addition of Al2O3 and SiO2 nanoparticles with the concentration of 3% by volume. Finally, it can be concluded that the dispersion of the nanoparticles in Liquid Nitrogen (LN2) is beneficial to be used in micro heat exchangers.

Molten salt heat exchangers are key components in some advanced power systems. Two shell-and-tube molten salt heat exchangers are experimentally investigated, including a gas cooled one with finned tubes and a molten salt to salt one with segmental baffles in the shell side. Based on a nonlinear regression scheme, heat transfer coefficients in both the tube and shell sides are obtained. Heat transfer characteristics of molten salt in the tube side are discussed and compared with three empirical correlations. It is found that Wu’s Equation has better agreement with the experimental data than Gnielinski’s and Hausen’s Equations in transitional flow region. For the developing laminar flow in the tube side, the widely used Sieder–Tate correlation underestimates heat transfer coefficients of molten salt by up to 30%. Compared with oil and a chart method proposed from sufficient database, molten salt seems to have better heat transfer performance than other working fluids in the baffled shell side. Further researches on the heat transfer characteristics of molten salt in the shell side with baffles are needed and significant.