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Plate heat exchangers are realized by means of a heat transfer mechanism, in which heat is naturally transferred from the hot substance to the object with a lower temperature according to the laws of thermodynamics. Two liquids of different temperatures flow on the wall, heat transfer on the wall and convection of the liquid on the wall, thus promoting heat transfer between the two liquids. Under the same flow rate and power consumption conditions, its heat transfer coefficient is three times that of shell and tube heat exchangers, which is a key and efficient new equipment for effectively using effective resources and saving and developing new energy. However the heat supply plate heat exchanger has a tiny circulation surface and is easily obstructed. Regular maintenance and cleaning, troubleshooting, and plate replacement all necessitate frequent heat exchanger disassembly and installation. The requirements and challenges in dismantling and assembling the heat exchanger are very high, and manual disassembly is wasteful, making consistent force difficult to achieve. The current methods of disassembly and assembly are inefficient and incorrect. The intelligent mechanization of disassembly and assembly equipment is realized in this paper by driving, clamping, automatic control, distance measurement, sensing, and other systems. The problems of uneven force, low efficiency, and precision in plate heat exchanger disassembly and assembly are solved. Our power disassembly equipment for high efficiency heat transfer plate heat exchangers not only enhances disassembly efficiency and precision, but it also ensures the safe operation of the plate heat exchanger heating system, and the heat transfer efficiency and heat exchange efficiency are improved. Furthermore, it has a wide range of applications in the petroleum, chemical, and other industries. [ABSTRACT FROM AUTHOR]

An efficient and accurate method for optimizing capsule-type plate heat exchangers is proposed in this paper. This method combines computational fluid dynamics simulation, a backpropagation algorithm and multi-objective optimization to obtain better heat transfer performance of heat exchanger structures. For plate heat exchangers, the heat transfer coefficient j and friction coefficient f are a pair of contradictory objectives. The optimization of capsule-type plate heat exchangers is a multi-objective optimization problem. In this paper, a backpropagation neural network was used to construct an approximate model. The plate shape was optimized by a multi-objective genetic algorithm. The optimized capsule-type plate heat exchanger has lower flow resistance and higher heat exchange efficiency. After optimization, the heat transfer coefficient is increased by 8.3% and the friction coefficient is decreased by 14.3%, and the heat transfer effect is obviously improved. Further, analysis of flow field characteristics through field co-ordination theory provides guidance for the further optimization of plates. [ABSTRACT FROM AUTHOR]

This paper presents the results of an analysis of heat transfer in a cross-flow mini heat exchanger (CFMHE). The purpose of the paper was to analyze the results of the experimental measurements presented in the previous work in order to determine dimensionless correlations that allow for the calculation of heat transfer coefficients for the CFMHE. Analyzed CFMHE consisted of a brass cylindrical core, in which 2 mm circular holes were drilled. A method based on an optimization procedure was used to determine the correlations describing the heat transfer coefficients, allowing the correlations to be determined without the need of measuring the mini channel wall temperature. Overall heat transfer coefficients calculated using the proposed correlations typically did not deviate by more than ±10% from the corresponding experimental results, which was a significant improvement in the quality of the fit compared to the results presented in previous work. [ABSTRACT FROM AUTHOR]

The cross-wave primary surface recuperator (CW-PSR) is a dependable option as a recuperator for micro gas turbines (MGT). The micro CW-PSR studied in this paper is composed of 171 stacked curved plates, with each plate containing 33 micro heat transfer channels with equivalent diameters of less than 1 mm. In this study, the influence of bending curvature on the thermal performance of CW-PSR plates is investigated through three-dimensional numerical simulation with fluid–solid–thermal coupling. The results indicate that the variation in bending curvature studied can result in a noteworthy 8% difference in the total heat transfer coefficient of CW-PSR plates. A direct correlation between heat transfer capacity and secondary flow strength is derived mathematically, explaining the mechanism by which secondary flow enhances heat transfer. By employing this relationship, a comprehensive analysis of CW-PSR plates with diverse bending curvatures is conducted, effectively showcasing how curvature influences the secondary flow pattern and enhances the channel's heat transfer capacity. In addition, this paper considers the comprehensive influence of the size parameters of the heat transfer unit and the bending curvature of the heat transfer plate on the heat transfer and flow characteristics of the CW-PSR, and a dominant mathematical expression is obtained, which can be used for the design of similar heat exchangers of the same type. [ABSTRACT FROM AUTHOR]

In this paper, a micro‐bare‐tube heat exchanger structure with the tube bundle diameter varying gradually in the range of 1.0–0.4 mm is proposed. The airside friction and heat transfer performance correlations for this structure are given. This paper applies CFD simulation to develop and verify the correlation of the diameter gradually varied micro‐bare‐tube heat exchangers' performance. Compared with the traditional same diameter micro‐bare‐tube heat exchanger, the new structure not only reduces the pressure drop, but also improves the thermal hydraulic performance. The friction coefficient f is decreased by 8.59%, the pressure drop is reduced by 43.14%, the heat transfer coefficient j is increased by 12.07% compared to the constant diameter micro‐bare‐tube heat exchanger. At the same time, it reduces the void volume by 47.32% and the tube bundle manufacturing material by 28.57%. The proposed airside performance prediction equation can make the error of more than 70% source data within 10%, and the error of more than 90% source data within 20%. It is suggested to apply this empirical equation to 7–29 rows. [ABSTRACT FROM AUTHOR]

In this paper, a comprehensive analysis of the combined effect of major influencing parameters on heat transfer in a single U-tube BHE (sBHE) and a double U-tube BHE (dBHE) with two independent circuits was performed by using a validated numerical heat transfer model. Geometrical parameters, such as shank spacing (with maximum, average, and minimum values), borehole diameter (large, medium, and small borehole sizes), and borehole depth (shallow, average, and deep borehole depths) as well as the thermal conductivity of soil and grout, which ranges from minimum to high values, were considered. The combined impact of these parameters was included under the following four major cases: (1) the combined effect of borehole depth, borehole size, and shank spacing; (2) the combined effect of borehole depth and soil and grout thermal conductivity; (3) the combined effect of soil and grout thermal conductivity and borehole size; and (4) the combined effect of soil thermal conductivity, borehole size, and shank spacing. Each of these major cases has nine different design options for both sBHEs and dBHEs. A series of results of heat transfer per unit borehole depth were generated for all the considered various cases. With the given parameters, the BHE case that provides the highest heat transfer among the various cases of sBHEs and dBHEs were obtained. [ABSTRACT FROM AUTHOR]

Amidst the background of "double carbon", energy saving and emission reduction is a popular direction in the current refrigeration industry. Therefore, the research on the boiling heat transfer of gas–liquid two-phase flow is helpful to strengthen the heat transfer and design a more efficient heat exchanger. In this paper, a research method combining numerical simulation and experimental verification is adopted. Firstly, an experimental platform used for the subcooled flow boiling of refrigerant in casing tubes is introduced and experiments are carried out to obtain experimental data, which provides a theoretical basis for the development of numerical simulation and verifies the feasibility of numerical simulation. A numerical model of subcooled flow boiling in R22 was established and the grid independence test was carried out. Based on the simulation results, three factors affecting the boiling heat transfer of R22 are analyzed: First, the boiling heat transfer coefficient of R22 increases with the increase of the mass flow rate of R22, but the increase decreases when the mass flow rate increases from 0.018 kg/s to 0.020 kg/s. Second, the boiling heat transfer coefficient of R22 increases significantly with the increase of hot water flow rate. Third, the influence of R22 subcooling on boiling heat transfer is more complex. When the subcooling is 5 °C and 1 °C, heat transfer can be enhanced; high subcooling at 5 °C can enhance convective heat transfer and low subcooling at 1 °C can accelerate the arrival of saturated boiling. In this paper, three kinds of bubble behaviors affecting heat transfer in supercooled flow boiling, including sliding, polymerization, and bounce are also studied, which provides a basis for further research on heat transfer mechanism of supercooled flow boiling. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental investigation and the new statistical method for the determination of preliminary thermal characteristics of a prototype compact minichannel heat exchanger with laminar flows and significant heat transfer in the manifolds. The exemplary heat exchanger consists of 9 straight, parallel, square-shaped channels and two rectangular-shaped manifolds milled on both sides of the single aluminium plate. The design of the investigated heat exchanger is quite particular, as the heat transfer area of both pairs of manifolds provides almost 1/3 of the total heat transfer area. In the new statistical method presented in this paper, the manifolds' and channels' heat flows are considered separately. The heat exchanger's thermal characteristic was obtained statistically on the basis of the experimental results and is presented in the form of the overall heat transfer rate. The developed thermal characteristic model accounts for two effects, among many others, which may affect heat transfer in the exchanger, i.e. the heat loss to the ambient and the significant heat transfer in the manifolds. It is proved that the heat transfer to the surroundings was negligible due to the suitable thermal insulation. In order to demonstrate that the heat transfer in the manifolds is significant, two calculation variants are presented. The relative differences (residuals) between the experimental and statistically corrected heat transfer rates and the coefficient of determination R² are determined in both variants. In the first variant the heat transfer in the manifold pairs is neglected and in the second model it is included. It was observed that the lack of consideration of the heat transfer in the manifold pairs provides drastic dispersion between the experimental and statistical results. In turn, in the second model, where the manifolds are accounted for, a significant enhancement in the consistency of the results is noticed. The relative residuals are much lower, and the corresponding coefficient R² is improved from R² = 0.8827 in the first variant to R² = 0.9335 in the second one, respectively. [ABSTRACT FROM AUTHOR]

The printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm. Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features. The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleateboiling- like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed. In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover, heat transfer deterioration will always appear, since the supercritical flow will finally develop into a filmboiling- like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE. [ABSTRACT FROM AUTHOR]

In order to provide a more comprehensive depiction of the actual heat transfer process in energy piles, this research paper presents an approximate solution for a finite line heat source model operating under variable heat flow conditions. This solution is established by integrating the finite line heat source model and the superposition principle. Furthermore, the W-tube heat exchanger is divided into many segments, and a segmented superposition approach is used based on the thermal response. Consequently, a heat transfer model for a single-pile heat source is formulated, taking into consideration the heat exchange between the circulating water and the energy pile. Notably, the soil temperature predicted by this proposed model closely aligns with the results obtained from the FLUENT numerical model, thereby substantiating the accuracy of the proposed approach. Simultaneously, the heat transfer model is employed to analyze variations in temperature and heat flux density within the heat exchanger and to investigate the influence of parameters such as mass-flow rate, pile-soil heat transfer coefficient, pile-soil density, and pile-soil specific heat capacity on the heat transfer characteristics of energy piles. This model enables the determination of time-varying heat flux and precise outlet temperature, thereby facilitating a rapid assessment of the heat transfer efficiency of energy piles. [ABSTRACT FROM AUTHOR]

The efficiency of heat transfer in air-cooled heat exchangers of various industrial facilities depends on the flow rate of the coolant, its inlet temperature and ambient temperature. These parameters are transient and depend both on the features of the technological process and on weather conditions. One option for a compact design of heat exchangers is the use of close-packed coils with a small bending radius. In this case, heat transfer in the complex geometry of the annular space cannot be described by simple one-dimensional dependencies. To solve this problem, it is necessary to consider the three-dimensional spatial structure of the heat exchange surface. Since the size of the grid elements will be several orders of magnitude less than the size of the facility, the size of the computational grids for CFD modeling full-scale heat exchangers will be billions of finite volumes, and even on powerful supercomputers, the solution time will be about a month. One way to reduce computational costs is to use reduced order models, in which the computational domain is not modeled directly; instead, simplified models, such as a porous medium model, are used to describe it. However, such models require additional closing relations and coefficients that characterize the actual channel geometry. This paper presents a technique for creating a digital twin of a heat exchanger with small bend radius coils based on a porous medium model. The values of heat transfer coefficients and hydraulic resistance depend on the speed of air movement in the space between the coils. The calculated value of the thermal power obtained using the strengthened model was 529 kW, which corresponds to the passport data of 500 kW, with less than 6% deviation for the heat exchanger under study. This confirms the correctness of the calculation with accepted simplifications. The calculation time in this case was only a few minutes when using a personal computer. The developed numerical model allows for the resolution of performance characteristics based on the temperature of the cooled medium at the inlet, air temperature, and fan speed. Analyzing the different modes of turning on the cooling fans made it possible to determine the values of the thermal power when turning off the fans or reducing the number of revolutions. [ABSTRACT FROM AUTHOR]

The finned-tube heat exchanger is the core part of an air conditioning system. Its heat exchange performance directly affects the energy consumption and efficiency of the air conditioner. The shortage and rising price of copper have led to increasing replacement of copper tubes with aluminum tubes in finned-tube heat exchangers. This paper studies two kinds of such heat exchangers, one consisting of copper tubes and aluminum fins and the other consisting of aluminum tubes and aluminum fins. The influences of the different base tube materials on heat transfer are compared and analyzed in terms of heat transfer strength and cost per unit heat transfer. The results show that the heat transfer and heat transfer coefficient increase with increasing inlet wind speed. Under different inlet wind speeds, the heat transfer and heat transfer coefficient of the finned-tube heat exchanger with aluminum tubes are 4%–12% and 7%%–9% lower than those of an identically structured heat exchanger with copper tubes, respectively. The aluminum-aluminum exchanger achieves 67% higher heat transfer than that of the copper-aluminum exchanger at only 8% of the cost. These results are significant for guiding the development and application of finned-tube heat exchangers. [ABSTRACT FROM AUTHOR]

There are numerous reports and publications in reputable scientific and engineering journals that attribute substantial enhancement in heat transfer capabilities for heat exchangers once they employ nanofluids as working fluids. By definition, a nanofluid is a working fluid that has a small volume fraction (5% or less) of a solid particle with dimensions in the nanoscale. The addition of this solid material has a reported significant impact on convective heat transfer in heat exchangers. This work investigates the significance of the reported enhancements in many recent related publications. Observations on these publications' geographical origins, fundamental heat transfer calculations, experimental setups and lack of potential applications are critically made. Heat transfer calculations based on methodologies outlined in random selection of available papers were conducted along with a statistical analysis show paradoxically inconsistent conclusion as well as an apparent lack of complete comprehension of convective heat transfer mechanism. In some of the surveyed literature for example, heat transfer coefficient enhancements were reported to be up to 27% and 48%, whereas the recalculations presented in this work restrain proclaimed enactments to ~ 3.5% and − 4% (no enhancement), respectively. This work aims at allowing a healthy scientific debate on whether nanofluids are the sole answer to enhancing convective heat transfer in heat exchangers. The quantity of literature that confirms the latter statement have an undeniable critical mass, but this volition could be stemming from and heading to the wrong direction. Finally, the challenges imposed by the physical nature of nanoparticles, as well as economic limitations caused by the high price of conventional nanoparticles such as gold (80$/g), diamond (35$/g), and silver (6$/g) that hinder their commercialization, are presented. [ABSTRACT FROM AUTHOR]

This paper introduces an inverse study method applied to an experimental dataset of infrared temperature acquisitions to determine the local convective heat transfer coefficient of the turbulent flow inside a duct with corrugated surfaces. The study focuses on six tubes with different corrugation profiles: helical, transversal, and cross-helical. Previous research has shown that transversal corrugation generates the highest improvement in heat transfer performance, while helical corrugations are the easiest to manufacture. Consequently, the single helix solution is the preferred one in heat exchangers adopted in the food industry. A merger solution between them is represented by the cross-helix profile. The estimation process proposed in this study employs the external surface temperature of the tube, acquired with an infrared thermal camera, as starting data for the inverse heat conduction problem inside the pipe wall region. The calculation of its Laplacian was finally achieved by a filtering technique applied to the infrared temperature acquisitions. [ABSTRACT FROM AUTHOR]

Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how fast heat from an alternative energy source, such as the Sun, will be stored. For the design of adsorption heat accumulators, plate fin heat exchangers are mainly used. In this paper, the procedure for the estimation of the global heat transfer coefficient for the adsorber heat exchanger depending on its geometry is considered. The heat transfer coefficient for a LiCl/SiO2 sorbent flat layer under conditions of heat storage stage was measured. Based on these data, the global heat transfer coefficients for a number of industrial heat exchangers were theoretically estimated and experimentally measured for the adsorption cycle of daily heat storage. It was shown that theoretically obtained values are in good agreement with the values of the global heat transfer coefficients measured experimentally. Thus, the considered technique makes it possible to determine the most promising geometry of the plate fin heat exchanger for a given adsorption heat storage cycle without complicated experiments. [ABSTRACT FROM AUTHOR]

A gas cooler is one of the important parts of a carbon dioxide (CO2) heat pump water heater, and it must meet the needs of not only pressurization but also heat transfer. It is important to study gas coolers. In this paper, a heat exchanger with a spiral channel is studied. ANSYS CFX software was used to analyze the flow and heat transfer characteristics of the heat exchanger (single-plate model). The influences of the cooling pressure of CO2, the mass flux of CO2, the mass flux of water and the channel radius of CO2 are discussed. In this paper, the results show that the cooling pressure of CO2, the mass flux of CO2 and the channel radius of CO2 all have a large influence on the local heat transfer coefficient: with an increase in the cooling pressure of CO2, the peak value of the heat transfer coefficient of CO2 decreases and the average heat transfer coefficient decreases; with an increase in the mass flux of CO2, the peak value of the heat transfer coefficient of CO2 increases and the average heat transfer coefficient increases; and with a decrease in the channel radius of CO2, the peak value of the heat transfer coefficient of CO2 increases. The water mass flux has only a slight effect on heat transfer, and the lower cooling pressure of CO2 corresponds to a higher peak heat transfer coefficient, which can reach 27.5 kW∙m−2∙K−1 at 9 MPa. [ABSTRACT FROM AUTHOR]

The paper is concerned with water vapor condensation on vertical pipes. The vertical position of pipes in a condenser is not discussed very often. Its application has a number of particularities in terms of the numerical determination of heat transfer. In the first stage of this paper, the authors focus on the experimental identification of heat transfer during vapor condensation on vertical pipes with a diameter of 14.0 × 1.0 mm. The pipes are placed in a narrow channel and the steam flows around them in a perpendicular direction. Two channel widths were tested, i.e., 20.0 and 24.0 mm. In the second stage, numerical modelling (CFD) is used for a detailed identification of the vapor velocity fields near the pipes. In the third stage, the results of the experimental measurements and numerical modelling are compared with data published by various authors. There are studies in the literature dealing with axial flow around vertical pipes; however, the associated results are based on conditions which are distinct from those applied in our study. The outcome of this paper is the specification of the heat transfer coefficient and the calculation formulas precisely describing the studied condenser configuration. [ABSTRACT FROM AUTHOR]

This paper presents a preliminary study of a novel type of turbulizers based on the jet pump working principle and designed to intensify heat transfer in double-tube heat exchangers. To determine the potential for their use, Computational Fluid Dynamics (CFD) and realizable k-ε turbulence model were applied to four turbulizers differing in the angles and diameters of the nozzle and diffuser. During studies, a number of parameters were determined, including: (i) Euler number Eu, (ii) overall heat transfer coefficient kT and (iii) reduced ratio of heat duty to mechanical power 𝜀r; and then compared with data available for strip turbulizers. The tests yielded the following maximum values of: Eu - 1.5 times higher, kT - 2 times higher, and 𝜀𝑟 - 27 times higher than those obtained by classical strip turbulizers, which indicates the high potential of presented jet pump turbulizers and justifies their further development. [ABSTRACT FROM AUTHOR]

This article presents an in-depth analysis of internally finned tube heat exchangers, which are used in a broad variety of condensers and evaporators for air conditioners, as well as radiators for vehicles and solar air heaters, amongst other places. The growing need for cooling systems that are more efficient and heat exchangers that take up less space has inspired many studies in this area of expertise. This research uses both experimental and computational analysis to compare and contrast the efficacy of various heat transfer enhancement processes in internally finned tube heat exchangers concerning the impacts they each have and the operating parameters they each need. This study aims to investigate how altering the fins' design affects heat transfer and pressure drop under varying operational situations. This paper examines the ranges in which these correlations have been verified, as several correlations have been created to assist in estimating heat transfer and pressure drop characteristics on internally finned tube heat exchangers. This study extensively delves into various analytical approaches such as Log Mean Temperature Difference (LMTD), Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), and other methodologies specifically tailored to address the unique goals of the particular problem. To derive a conclusion with practical significance, we categorize these relationships into multiple groups and conduct a comparative analysis. [ABSTRACT FROM AUTHOR]

Because of their compact structure, ease of processing and higher heat transfer coefficient, curved-tube heat exchangers are widely applied in various industry applications, such as nuclear power systems, solar-powered engineering, aircraft engine cooling systems and refrigeration and cryogenic systems. Accurate knowledge about the heat transfer characteristics of the supercritical fluids in the tube is critical to the design and optimization of a curved-tube heat exchanger. The available literature indicates that the flow of supercritical fluids flowing in curved tubes affected by the dual effects of the buoyancy force and centrifugal force is more complex compared to straight tubes. Therefore, to obtain insight into their unique characteristics and further research progress, this paper presents a comprehensive review of available experimental and numerical research works on fluids at supercritical pressure flowing in curved tubes. Overall, the secondary flow caused by the curvature enhances the heat transfer and delays the heat transfer deterioration, but it also causes a non-uniform heat transfer distribution along the circumferential direction, and the strengthening performance of the curved tube is damaged. Compared with the more mature theories regarding straight tubes, the flow structure, the coupling mechanism of buoyancy and centrifugal force, and the general heat transfer correlation of supercritical fluids in a curved tube still urgently need to be further studied. Most importantly, studies on the suppression of heat transfer oscillations and heat transfer inhomogeneities specific to curved tubes are scarce. Considering the current status and shortcomings of existing studies, some study topics for supercritical fluids in a curved tube are proposed. [ABSTRACT FROM AUTHOR]

Flue gas after wet desulfurization contains a large quantity of water vapor, as well as a small amount of fine particulate matter, acid and other pollutants. Direct emissions will cause haze and environmental pollution. Flue gas condenser can effectively recover latent heat of vaporization and remove these pollutants. However, the traditional flue gas condenser has disadvantages such as large volume, low heat exchange efficiency and easy blockage. To overcome these problems, a new type narrow gap heat exchanger, which is easy to detach and clean, is proposed. Then, the flue gas condensation characteristic is experimentally investigated. The factors including velocity and temperature of flue gas, flow and temperature of cooling water are studied on heat transfer coefficient and the condensation rate. The results indicate that the overall heat transfer coefficient is seven times of convection heat transfer coefficient, and the condensation rate can reach more than 60%. As the cooling water temperature increases, the condensation rate and condensation heat transfer coefficient gradually decrease. With the increasing of the flue gas velocity, condensation rate gradually decreases and condensation heat transfer coefficient gradually increases. Finally, the dimensionless correlation of Nusselt number is carried out, and the error is within 10%. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model of heat pump exchangers and their thermal interaction with a fan for an air dryer. The calculation algorithm developed for the finned heat exchangers is based on the ε-NTU method, allowing the determination of air side and refrigerant side heat transfer coefficients, evaporator and condenser heat capacity and air parameters at the dehumidifier outlet with known exchanger geometries, initial air parameters and mass flow rate. The model was verified on an industrial dehumidifier test bench. This enabled the heat transfer coefficients for the exchanger to be calculated as a function of the speed and, therefore, the power of the fan's drive motor. An increase in fan performance on the one hand results in an increase in the heat transfer rate, but, on the other hand, it causes an increase in the total energy consumption of the motor. Thus, while it causes an increase in drying capacity, it also causes an increase in the energy consumption of the dehumidifier. In order to optimise the unit in terms of energy consumption, it is therefore necessary to determine a function that relates the amount of heat exchanged to the efficiency of the fan. [ABSTRACT FROM AUTHOR]

In typical turbulent flow problems, detailed heat transfer coefficient (h) maps obtained through short-duration experiments are based on inverse heat transfer methods that take the wall temperatures measured via liquid crystals or infrared thermography as input, and an error minimization routine is adopted to determine the best value of h that satisfies the wall temperature temporal evolution under a certain change in fluid temperature. A common practice involves modeling the solid as a one-dimensional semi-infinite medium by selecting the solid material that has low thermal conductivity and low thermal diffusivity. However, in certain flow scenarios, the neglection of the lateral heat diffusion may lead to significant errors in the deduced h values. It is imperative to understand the reasons behind large errors that may be incurred by using the 1D heat conduction assumption in order to accurately determine high-resolution h maps for better heat exchanger designs in a wide range of thermal management applications. This paper presents a computational heat transfer study on different jet impingement scenarios to demonstrate the errors incurred in the determination of h when calculated under the assumption of one-dimensional (1-d) heat conduction into a solid. To this end, three different cases are studied: (a) single jet, (b) array jet (theoretical distribution), (c) array jet (experimental distribution), along with three different mainstream temperature evolution profiles representing step change, moderately fast transient and slow transient nature of flow driving the heat transfer in the solid. A known distribution of heat transfer coefficient ("true h") for each of the three cases is considered, and three-dimensional transient heat diffusion equations were solved to populate temperatures of each node in the solid at every time step. It is found that stagnation zones' h1d calculations were lower than the "true h" while the low heat transfer zones exhibited significantly higher h1d compared to the "true h". For the array jet (experimental distribution) case, it was observed that errors can be as high as 10% in certain low heat transfer zones. Different data reduction procedures, configurations, and conditions explored in this study indicate that a suitable balance can be achieved if shorter time durations in transient experiments are used as a reference for tracking in h1d calculations to keep the deviations from the "true h" low. [ABSTRACT FROM AUTHOR]

Nanofluids are the combination of base fluid and nanoparticles which offer higher thermal conductivity resulting higher heat transfer. In this research article, soft computing tool is used to find the accurate Nusselt number of coiled tube heat exchanger handling Al2O3/H2O nanofluids at three different volume concentrations and at different mass flow rate in terms of Dean number. The input predictor variables used in this model are convective heat transfer coefficient, thermal conductivity of nanofluids, and Dean number and the output response variable is Nusselt number. Linear regression, generalized linear regression, and Lasso and elastic-net regularized generalized linear models methodologies are taken to predict the Nusselt number. It is observed that the linear regression method shows an accurate agreement with experimental data with root mean square error value of 0.05614 and regression coefficient value is 0.99. It is studied that the experimental data holds good accordance with the predicted data given by the trained network. The average relative errors in the prediction of Nusselt number and heat transfer coefficients are found to be 0.3% and 0.2%, respectively. [ABSTRACT FROM AUTHOR]

This paper considers the main parameters of the solar collector with thermosyphon circulation for the solar heat supply system. There was developed a flat solar collector construction with thermosyphon circulation wherein the heat transfer coefficient is increased by removing the additional partitions between a panel and heat insulation. The solar collector's efficiency reached by the availability of a tank and thermal pump in the construction where a condenser and evaporator executed the form of a heat exchanger of «spiral in spiral» type and heat exchanger pipe connections are one above another, which allows increasing the square and heat exchange intensity. The outcome of the study is a description of the mathematical analysis of the heat transmission process in the tank accumulator. We have shown a heat carrier thermophysical parameter dependence on the temperature. [ABSTRACT FROM AUTHOR]

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The paper investigates the heat transfer characteristics of the heat exchanger under two different configurations namely taper helical tube and spiral tube type heat exchanger. The working fluid is water which flows in tubes kept horizontally and the mass flow rate ranges from 0.04 kg/s to 0.16 kg/s. The effect of tube configuration parameters and Reynolds number on heat transfer coefficient and Nusselt number were studied. Regression equations have been developed for both the configurations under horizontal orientation using various process parameters and regression tools available in Minitab Software. A comparison has been made between the theoretical results and the results obtained from simulation gives an error of 15% which is well within the permissible limit. The result indicates that the highest value of Nusselt number is greater by 21% than taper helical tube heat exchanger which is attributed to better heat transfer characteristics of spiral tube heat exchanger and hence the former is thermally superior over the latter. In this study, temperature and velocity contour have been developed for both the configurations which clearly indicates that, when heat transfer is considered, spiral configuration should be preferred over taper helical configuration. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation to determine the air-side heat transfer and the pressure drop characteristics of a flat tube heat exchanger with offset strip fin. The effects of the fin bending ratio such as 29%, 36%, 44%, 50%, and the fin spacing such as 2.10 mm, 2.35 mm, 2.60 mm on the performance of the heat exchanger are studied by using a commercial CFD software. The air having constant viscosity, thermal conductivity, and density enters the heat exchanger at 298 K and the wall temperature of the strip fins is considered as constant at 314 K. Variations of the heat transfer coefficient and the pressure drop in the airside are presented with respect to the frontal air velocity while Colburn j-factor and the friction factor f are presented with respect to the airside Reynolds number ranging from 200 to 1200. Finally, the thermal-hydraulic performance of all investigated cases is compared by using the volume goodness factor, j/f1/3. The results show that the air-side heat transfer coefficient and the pressure drop increase when the frontal air velocity ascends. The air-side heat transfer coefficient decreases with the increase of fin spacing. The fin bending ratio does not have a significant effect on the pressure drop in the considered fin spacing. Both the Colburn j-factor and friction factor reduce with the increment of Reynolds number and fin spacing [ABSTRACT FROM AUTHOR]

This paper aims to numerically investigate the thermal enhancement of a latent thermal energy storage component with mini-channels as air passages. The investigated channels in two sizes of internal air passages (channel-1 with dh = 1.6 mm and channel-2 with dh = 2.3 mm) are oriented vertically in a cuboid of 0.15 × 0.15 × 0.1 m3 with RT22 as the PCM located in the shell. The phase change is simulated with a fixed inlet temperature of air, using ANSYS Fluent 19.5, with a varying number of channels and a ranging air flow rate entering the component. The results show that the phase change power of the LTES improves with by increasing the number of channels at the cost of a decrease in the storage capacity. Given a constant air flow rate, the increase in the heat transfer surface area of the increased number of channels dominates the heat transfer coefficient, thus increasing the mean heat transfer rate (UA). A comparison of the channels shows that the thermal performance depends largely on the area to volume ratio of the channels. The channel type two (channel-2) with a slightly higher area to volume ratio has a slightly higher charging/discharging power, as compared to channel type one (channel-1), at a similar PCM packing factor. Adding fins to channel-2, doubling the surface area, improves the mean UA values by 15–31% for the studied cases. The variation in the total air flow rate from 7 to 24 L/s is found to have a considerable influence, reducing the melting time by 41–53% and increasing the mean UA values within melting by 19–52% for a packing factor range of 77.4–86.8%. With the increase in the air flow rate, channel type two is found to have considerably lower pressure drops than channel type one, which can be attributed to its higher internal hydraulic diameter, making it superior in terms of achieving a relatively similar charging/discharging power in exchange for significantly lower fan power. Such designs can further be optimized in terms of pressure drop in future work, which should also include an experimental evaluation. [ABSTRACT FROM AUTHOR]

This paper presents an experimental analysis on the heat transfer and pressure drop enhancement of oil nanofluid flow. In this analysis, the first method has used the helically coiled tube and shell, the oil nanofluids were employed instead of the base fluid (oil) in the second process. the two techniques were used to improve the heat transfer and pressure drop. Nanofluid oil concentrations utilized within range from 1 to 5 percent vol. This paper applied two forms of nanoparticles: copper (Cu (20 nm)) and zirconium oxide (ZrO2 (40 nm)) and base fluid (oil). The influence on the heat transfer coefficient for different factors such as the flow number of Reynolds, the temperature of the nanofluid oil, the concentration and shape of the nanoparticle, and the pressure gradient of the flow have examined. The results indicated that the value of a 40.35 percent in the heat transfer coefficient for Cu + oil and 28.42 percent for ZrO2 + oil increased compared with the base fluid (oil) at 5 percent vol concentration. Using oil nanofluids (Cu, ZrO2 - oil) instead of the base fluid (oil) led to increasing in the heat transfer coefficient and decreasing the pressure. In addition, the result showed that the heat transfer efficiency has enhanced using the helically coiled tube and shell, as well as increasing in the pressure drop was due to the curvature of the tube. Baes on the relationship between viscosity and shear intensity, the oil nanofluid behaviors were similar to the standard Newtonian fluids. Moreover, the related flow and heat transfer methods are used to present the output index. The exergy inflow, exergy destruction and exergy efficiency of oil nanofluid (Cu +oil) were greater than the oil nanofluid (ZrO2 +oil) and oil. The exergy inflow, exergy destruction, and exergy efficiency for the two type of oil nanofluid increased with increasing of nanoparticles concentration. [ABSTRACT FROM AUTHOR]

Gathering of fouling on the heat transfer surfaces, both on the water side and the steam side of heat exchangers of the ship steam systems leads usually to the loss of their heat transfer capacities. This loss appears owing to the high value of the fouling heat resistance and is called the thermal degradation process. It is linked to falling the heat flux transported by a heat exchanger and decreasing total efficiency of the heat unit as well as increasing costs of operation and freight costs after all. The loss of thermal power of a heat exchanger does not only depend on the fouling thermal resistance but is also strictly correlated with the thermal quantities of a given heat exchanger, among others its overall heat transfer coefficient values at various operating modes. The paper presents the aforementioned phenomena and results of the author's own experimental studies, as well. [ABSTRACT FROM AUTHOR]

Energy is a key aspect of any country's economic development. Improving heat transfer performance leads to saving energy. Nanotechnology has a key role to play in optimizing heat exchangers. Fluids containing nanosized particles are called nanofluids. Nanofluids have higher thermal conductivity than typical liquids. This paper outlines current research on convective heat transfer performance, thermophysical properties, particle size, and volume concentration effects in nanofluid studies. Measurement methods for thermal conductivity and correlations used by earlier researchers to determine thermal conductivity are also encompassed. The main applications of nanofluids as lubricants and radiator systems to improve the efficiency of heat removal from vehicle engines have also been emphasized. Results suggest that by using a larger size of particle some drawbacks include particle sedimentation, clogging, erosion, stability, and increasing pressure drop. Enhancing thermal conductivity with optimum volume concentration. Improving the efficiency of heat exchange systems is one of the possible ways to reduce energy consumption. The need for optimum concentration of nanofluids is required. The Problem of stability, corrosion, and erosion arrived by increasing the volume concentration of nanoparticles in a nanofluid. [ABSTRACT FROM AUTHOR]

Cardiac surgeries that involve cardiopulmonary bypass technique require a stable temperature maintenance for oxygenated blood or the cardioplegia solution. For this purpose, the heat exchangers are used. Nowadays, these exchangers consist of stainless steel tubes or bellows in a plastic shell. The blood is then warmed or cooled by water flowing in the shell around these structures. In the paper, the thermal specifications of two commercially used cardioplegia heat exchangers Capiox Cardioplegia and MYOtherm XP were evaluated and compared. For this purpose, a water was used as a substitution for blood. Both components were tested for varying flow rates in the pipes in the range 20-150 l/h and fixed flow rate 700 l/h in the shell. The thermal performances of both devices resulted similarly (up to 2.4 kW) at maximal flow rate. The performance factors for low flow rates approached values close to 0.98 and with increasing flow rate decreased down to 0.50. MYOtherm XP shows lower pressure drop than Capiox Cardioplegia due to more optimal construction. The major difference between the heat exchangers was observed in overall heat transfer coefficients at maximal flow rate and resulted in 2191.3 W/m²K or 1760.2 W/m²K for MYOtherm XP or Capiox Cardioplegia, respectively. [ABSTRACT FROM AUTHOR]

The aim of the paper is to fulfill the parametric analysis on the heating performance of a compact automotive radiator using computational fluid dynamics. The analysis has been carried out at different air velocities with different fins modeling as real fins and as porous media. SC-Tetra computational fluid dynamics software was used for this study. The fluids are incompressible; the flow was three-dimensional and turbulent. The geometry of the fins has a high impact to the heat transfer coefficient and the heat performance, so the shape, the size and the thickness of the fins are compared to each other. The results show that the ratio of the fin pitch, the wall thickness of the fins, the number of the fins, the flow depth and the geometry of the tube are the main factors of the heat transfer. The main goal is to find a dependable Nu-number correlation for this type of heat exchanger. Furthermore with the usage of this function the goal is to find the optimal shape of the radiator, which can decrease the temperature of the cooling liquid to the necessary value and has the smallest weight. [ABSTRACT FROM AUTHOR]

Summary: This paper numerically investigates the first and second law efficiencies of transient crossflow over tube banks. A significant number of simulations were performed using a commercial computational fluid dynamics (CFD) tool, ANSYS Fluent 18.2, with varying inlet temperature, Reynolds number, pitch ratio (PR), number of inline cylinders, and heat transfer coefficient defining a heat leakage on the system. Numerical results compare favorably with published data in terms of Nusselt number and pressure drop. Five hundred seventy‐six simulations were performed, and energy efficiencies ranged from 72% to 99%, while exergy efficiencies ranged from 26% to 70%. No discernable, universal trends were observed across all data sets, but the staggering amount of results spans a wide range of operational characteristics for tube bundle waste heat recovery. To illustrate the insight such data can provide, we consider four sample cases for analysis: well‐insulated low‐grade heat recovery, poorly insulated low‐grade heat recovery, well‐insulated high‐grade heat recovery, and poorly insulated high‐grade heat recovery. Low‐ and high‐grade heat recovery cases were simulated with differing inlet heat transfer fluid (HTF) values, and heat leakage was introduced as a source term in the 2D energy equation. Detailed descriptions of the efficiencies of all cases are described, with references to the immense body of simulation data included in the appendix. Overall, the highest efficiencies of the first and second laws were obtained in domains that have three cylinders and inlet temperature of 500 K and eight cylinders and an inlet temperature of 400 K, respectively. The main findings of this study could be beneficial in designing a highly efficient waste heat recovery system, especially when source temperatures vary. [ABSTRACT FROM AUTHOR]

The double helix coil heat exchanger, which has high heat transfer performance, has been increasingly used in heat transfer systems. In this paper, a 3D numerical model is established to simulate heat transfer performance of the double helical coil. Then, the Box-Behnken design method and response surface method (RSM) are used to establish response surface models of the input parameters (internal coil pitch, external coil pitch, internal helix diameter, external helix diameter, and coil diameter), which are used to evaluate the interaction of input parameters and objective functions (overall heat transfer coefficient and pressure drop). Finally, the multi-objective genetic algorithm (MOGA) is used to optimize the design parameters of double helix coil heat exchangers, and the optimized double helix coil heat exchanger with high heat transfer coefficient, low exergy loss and pressure drop are obtained. Compared with the original design, the pressure drop decreases by 19.98 %, the exergy loss decreases by 8.7 %, and the overall heat transfer coefficient increases by 5.34 %. • BBD method and RSM are adopted to establish the prediction model for double helix coil heat exchangers performance. • MOGA is used to optimize the design parameters of double helix coil heat exchangers. • An optimized double helix coil heat exchanger with high heat transfer coefficient, pressure drop performance is obtained. [ABSTRACT FROM AUTHOR]

The purpose of this study is to experimentally enhance the heat exchange rate of the shell and helical coil tube heat exchanger by mixing water with aluminum oxide (Al2O3) nanoparticles, as well as to explore the effect of inlet thermal parameters on the performance of the heat exchanger. A test rig was constructed to investigate the influence of particle concentration, and inlet temperatures on the performance of nano-fluid. Parameters such as Nusselt number, pressure drop, performance evaluation criteria (PEC) are considered to rate the performance of the nano-particle with the heat exchanger. In this study a wider range of particle concentration is considered, which varies from 0.0%-0.75%. Experiments with and without nanoparticles are carried out under identical working conditions. By analyzing the experimental data, it was found that nanoparticles significantly improve the coefficient of heat transfer inside the helically coiled tube. From sensitivity analysis, it is obseerved that there is a slight decrease in Nusselt number of the nano-fluid with increase in inlet temperatures of the nano-fluid and the cooling water. Furthermore, it is concluded that an 8.5% increase in PEC value is observed with increase in particle concentration from 0.15% to 0.75%. [ABSTRACT FROM AUTHOR]

This article addresses the design of a compact heat exchanger for the cooling of electronic systems. The Quality Function Deployment (QFD) method is used to identify crucial product features to improve device performance and key customer requirements. The QFD simplifies management processes, allowing modifications to device components, such as design parameters (dimensions and materials) and operating conditions (flow type and preferred temperature range). The study was applied to analyse the fundamental features of a compact heat exchanger, assessing their impact on enhancing heat transfer intensity during fluid flow through mini-channels. The thermal efficiency of the compact heat exchanger was tested experimentally. The results allow to verify the results obtained from the numerical simulations due to Simcenter STAR-CCM+. Consequently, the experimental part was reduced in favour of numerical simulations conducted using this commercial CFD software version 2020.2.1 Build 15.04.01. The numerical simulations performed with the aid of CFD showed increases in the heat transfer coefficient of up to 180% compared to the case treated as a reference. The application of the QFD matrix significantly reduces the time required to develop suitable design and material solutions and determine the operating parameters for the cooling of miniature electronic devices. [ABSTRACT FROM AUTHOR]

The paper presents an experimental investigation of a silicone based heat exchanger, with passive heat transfer intensification by means of surface enhancement. The main objective of this paper was to experimentally investigate the performance of a heat exchanger module with the enhanced surface. Heat transfer in the test section has been examined and described with precise measurements of thermal and flow conditions. Reported tests were conducted under steady-state conditions for single-phase liquid cooling. Proposed surface modification increases heat flux by over 60%. Gathered data presented, along with analytical solutions and numerical simulation allow the rational design of heat transfer devices. [ABSTRACT FROM AUTHOR]

A numerical simulation of global heat transfer process in three types of micro-channel heat exchangers was investigated in this paper: spiral double-pipe micro-channel heat exchanger (DPHE), cross-plate micro-channel heat exchanger (CPHE), and shell and tube micro-channel heat exchanger (STHE). The inner tubes of all three heat exchangers have a diameter of 1 mm and are charged with CO2 as refrigerant. A detailed analysis of the heat exchanger's global heat transfer process was carried out, which is entirely different for different structures. The heat transfer characteristics of supercritical CO2 were analyzed by considering the operating pressure, the refrigerant mass flux, the cooling water mass flux, and the heat exchanger refrigerant inlet temperature. The relationship between the CO2 heat transfer coefficient (hCO2) and CO2 bulk temperature (Tb,CO2) was analyzed in detail. The pseudo-critical temperature (Tpc) mainly determines where the peak CO2 heat transfer coefficient occurs. When Tb,CO2 < Tpc, the rise in Tb,CO2 is accompanied by an increase in the heat transfer coefficient, which reaches a maximum when Tb,CO2 is a little bit higher than the pseudo-critical temperature, the heat transfer coefficient curve begins to decline as Tb,CO2 continues to rise. Higher peak heat transfer coefficients can be achieved at higher pressures. Increased refrigerant mass flux always results in larger heat transfer coefficients. The influence of the refrigerant inlet temperature of the heat exchanger in the Tb,CO2 < Tpc region on the heat transfer coefficient is more significant than expected. In this study, different flow patterns on heat transfer due to different structures were compared. The best heat transfer was achieved using a spiral double-pipe micro-channel heat exchanger (DPHE). It consistently reaches the highest heat transfer and the lowest outlet temperature under the same operating conditions‎. [ABSTRACT FROM AUTHOR]

In this paper, heat transfer analysis for an air-air heat exchanger was experimentally carried out to find its thermal performance and effectiveness. Air-air heat exchanger equipped with finned heat pipes was considered for the experimentation. Mass flow rate of air was considered in between 0.24 to 0.53 kg/s. The temperature at the condenser side of the heat pipe heat exchanger was kept constant at around 23 °C and at the evaporator part it was varied from 88 to 147 °C. The performance of heat pipe heat exchanger was evaluated at different mass flow rate of air, in terms of effectiveness and compared with its corresponding value found by theoretical analysis. [ABSTRACT FROM AUTHOR]

The present paper, for the first time, examines the influences of utilizing oil-ZnO nanofluid with different volume fractions φ = 0.5 %, 1 %, and 2 % in alternating flattened tubes (AFTs) with different alternating pitch angles of 30°, 45°, 60°, and 90° on the performance of a dual-tube heat exchanger (DTHE). This work is conducted experimentally and numerically for the Reynolds number (Re) range of 300 < Re < 1900 for oil-ZnO nanofluid and Re = 2000 for water. Based on the experimental results, the optimal case is selected for the numerical simulations of AFTs. The performance evaluation criterion (PEC) is defined for the simultaneous evaluation of pressure drop (Δp) and heat transfer coefficient (HTC). The results demonstrate that the overall heat transfer coefficient (U) and Δp are augmented with the inlet flow rate and the alternating angle between the pitches. Therefore, the maximum heat transfer (HT) and Δp correspond to the AFTs with the angle of 90° (AF4) at Re = 1900. The PEC amount of AF4 shows a 56 % enhancement compared to the circular tube. It is also observed that using copper oxide nanoparticles inside the oil improves the HT rate and Δp in the heat exchanger. Besides, an increment in φ increases U and Δp; however, the values of PEC show that the positive effects of the nanofluid are larger than their negative impacts in such a way that the PEC is improved by 64 % when the nanofluid with φ = 2 % is utilized in AFTs compared to the circular tube. [ABSTRACT FROM AUTHOR]

To enhance the heat transfer, an innovative origami channel heat exchanger is proposed and its performance is studied experimentally and numerically. The experimental results show the maximum temperature on the origami channels' pipe wall is 2.8 °C lower than that on the flat channel with the same the heat flux of 9500 W/m2. Additionally, the temperature difference across the pipe wall of the origami channel shows a reduction of 5.7 °C compared with that across the flat channel. The simulation results show the mean heat transfer coefficient of the origami channel increases by up to 331% compared to the flat channel with the 0.012 kg/s mass flow rate. Nevertheless, the origami channel leads to an extra energy consumption penalty. To evaluate overall performances of the origami channel, this paper introduces three dimensionless efficiency factors to quantify relevant costs in terms of energy, volume and mass. It is found that the origami channel achieves much higher dimensionless mass efficiency and volume efficiency but less dimensionless energy efficiency than the flat channel. The comprehensive evaluation, which considers all the three factors, reveals that the combined efficiency factor of origami channels with folding angles ranging from 65° to 75° improves by 80% to 95% compared to the flat channel. [ABSTRACT FROM AUTHOR]

• Supercritical CO 2 heat transfer in lattice structure channel is numerically studied. • Effects of key parameters of lattice on flow and heat transfer are evaluated. • Buoyancy effect and flow acceleration affected by lattice structure is analyzed. • Vortices induced by lattice structure can suppress the heat transfer deterioration. This study numerically explores the fluid flow and heat transfer features of supercritical carbon dioxide (CO 2) in lattice structure array channel. The mitigation mechanism of the miniature cylindrical lattice structure array on heat transfer deterioration (HTD) of supercritical CO 2 in vertically upward heated channel is studied. This paper evaluates the effect of several key influential parameters (length, diameter, pitch and number) of cylindrical lattice structure array on fluid flow field involving vortex structures, heat transfer coefficient, buoyancy effect and accelerated effect. The results indicate that the lattice structure can effectively suppress the HTD by generating the vortex structure which promoting the turbulent mixing effect and enhancing the turbulent kinetic energy (TKE) of the fluid. Compared with the smooth channel, the peak wall temperature of the lattice structure channel is reduced by about 50 °C, with a corresponding increase in the heat transfer coefficient of about 140 %. The average heat transfer coefficient of the channel is increased by more than 1/3. Furthermore, by increasing lattice length can reduce flow layer stratification and by increasing lattice diameter can creating a composite vortex, which enhance flow mixing strength. The larger the lattice pitch, the worse the overall suppression effect. A denser lattice arrangement produces more temperature valleys, thereby increasing the heat transfer coefficient. The conclusions in this study could provide the main theory support for security and stability of supercritical CO 2 heat exchangers in power system. [ABSTRACT FROM AUTHOR]

• An enhanced heat transfer structure is proposed, which can improve efficiency by 29 %. • The performance of the new structure was investigated by numerical simulation. • Experimental tests were conducted to prove the effectiveness of the new structure. To enhance the heat transfer efficiency of the helically coiled tubes heat exchangers, this paper proposes a double shell-passes structure designed for a multi-layer helically coiled tubes heat exchanger. Numerical simulation is employed to investigate the performance of the Double Shell-passes Multi-layer Helically Coiled Tubes Heat Exchanger (DSMHCTHE). Furthermore, an experimental test system is constructed to validate the simulation results, exploring the performance under different operating conditions. A comparative analysis is conducted with the traditional Multi-Layer Helical Tube Heat Exchanger (MHCTHE). The results indicate that, under identical experimental conditions, the heat transfer rate and thermal effectiveness of DSMHCTHE increased by 5.1 % to 12.9 %. The overall heat transfer coefficient showed an improvement ranging from 21.5 % to 29.0 %, while the shell-side heat transfer coefficient increased by 36.2 % to 47.5 %. However, the shell-side pressure drop increased by 60.7 % to 83.4 %. Utilizing the heat exchanger's comprehensive performance as the evaluation criterion, it was observed that DSMHCTHE exhibited superior comprehensive performance. In comparison to MHCTHE, the comprehensive performance of DSMHCTHE improved by 12 %. The design of the double shell-passes configuration has shown significant enhancements in both convective heat transfer and overall performance, highlighting the superior application potential of DSMHCTHE. [ABSTRACT FROM AUTHOR]

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Double-layer heat tubes have been designed to effectively reduce the occurrence of heat pipe rupture accidents. However, inter-tube thermal contact resistance can decrease heat transfer efficiency, thus hampering the heat dissipation in the primary loop system of lead-bismuth reactors. Therefore, optimizing the design of double-layer heat tubes is necessary. This work focuses on the double-layer heat exchanger of a lead-bismuth reactor and utilizes gallium-based graphene nanofluids as a thermal interface material to fill the gap between the heat tubes. Furthermore, the impact of the length, wall thickness, outer diameter, and spacing of heat tubes on the heat transfer performance of the double-layer heat exchanger with and without the nanofluids has been analyzed. The study aims to optimize the JF factor and cost-effectiveness ratio (CER). Genetic algorithms are employed to optimize and evaluate the heat transfer performance of the main heat exchanger based on the four aforementioned parameters. Consequently, a new design scheme is obtained for the double-layer heat exchanger, which increases the optimized overall heat transfer coefficient of the main heat exchanger by 5.79%, pressure drop in the primary loop by 2.32%, JF factor by 5%, and CER by 24.62%. These results demonstrate that the gallium-based graphene nanofluids can effectively enhance the heat transfer performance of the double-layer heat exchanger while reducing the likelihood of steam generator tube rupture accidents. [ABSTRACT FROM AUTHOR]

The potential use of carbon steel in CO2-saturated brine is studied for its potential use in heat exchangers in geothermal applications. A dedicated setup, including a double-pipe heat exchanger, is developed to study the relation between corrosion and the thermohydraulic behavior inside heat exchangers. Hot brine flows inside the inner carbon steel tube, thus corroding the inner surface of this tube. The thermohydraulic behavior of the heat exchanger, i.e., the pressure drop over the pipe and the heat transfer rate through the pipe, are continuously monitored. On the other hand, weight-loss experiments and microscopic analyses are performed on samples that are periodically removed from the setup. The corrosion rate is studied as a function of temperature, i.e., the entrance vs. the exit of the heat-exchanging section, and flow. Therefore, an experiment with static brine and a uniform temperature is used as a reference. The corrosion rate is generally higher in dynamic compared to static conditions. Furthermore, the corrosion rate increases with increasing temperature in dynamic conditions, whereas it decreases with increasing temperature in static conditions. These observations might be explained by the different corrosion products that formed. The corrosion products have no significant effect on the pressure drop over the pipe, but clear fluctuations in the heat transfer coefficient are observed. The origin of these fluctuations should be further studied before the observed heat transfer coefficient can be used as a measure for corrosion. [ABSTRACT FROM AUTHOR]