High-efficiency Heat Exchangers Research Articles

Numerical simulation on flow boiling heat transfer characteristics of R513A in the horizontal microfin tubes

To address the growing demand for high-efficiency heat exchangers in refrigeration, air conditioning, and heat pump systems, this study investigates the boiling heat transfer performance of R513A (an environmentally friendly azeotropic refrigerant) in horizontal microfin and smooth tubes with a 5.89 mm ID. Using 3D transient simulations, the tubes were analyzed under operating conditions of a mass flux of 50 kg/(m2·s) and a saturation temperature of 5 °C. The simulation results were validated against experimental data within a ±10 % error margin, confirming the reliability of model. At the constant mass flux, both the microfin and smooth tubes exhibited predominantly wavy-stratified flow, where surface tension dominated bubble flow. Gravity effects became more pronounced in slug, plug, and wavy-stratified flows. Structural parameters of microfin tubes, such as helical angle, fin height and number of fins, significantly affected flow boiling heat transfer. Increasing the helical angle had limited effect on enhancing boiling heat transfer performance. Microfin tube 4# (helical angle of 28°) exhibited an 11.27 % reduction in the boiling heat transfer coefficient compared to microfin tube 2#, due to the uneven distribution of liquid droplets in the vapor phase further reduced liquid film continuity and thickness. Microfin tube 5# (fin height of 0.30 mm) achieved an average mainstream velocity 1.36 times that of tube 2# (fin height of 0.17 mm), enhancing heat transfer. Conversely, microfin tube 6# with 54 fins showed local drying, negatively impacting its heat transfer efficiency.In summary, microfin tube 5# exhibited the optimal heat transfer characteristics.

Exploration and numerical study of new structures for high-efficiency and low-resistance vehicle-mounted plate-fin heat exchanger based on the three-field synergy principle

Exploration and numerical study of new structures for high-efficiency and low-resistance vehicle-mounted plate-fin heat exchanger based on the three-field synergy principle

Mathematical modeling of gas-phase mass transfer in hydrous materials for a total heat exchange ventilator

Total heat exchange ventilation systems are effective in achieving energy savings by reducing the ventilation load in buildings, while maintaining a certain amount of fresh outdoor air intake. As the system's elemental materials exchange both latent and sensible heat, hydrophilic chemical compounds may be exchanged simultaneously. Proper control of the exchange of hazardous chemicals and pollutants via these heat exchange elements is an important issue in the development of total heat exchange ventilation systems. In this respect, the development of a numerical model that facilitates repeated sensitivity analysis is important in the development of a new total heat exchanger that has high heat exchange efficiency and suppresses the exchange of polluting chemicals. This study proposes new hygrothermal and chemical compound transfer models for paper-based hydrous materials, which are the main components of total heat exchangers in indoor ventilation systems. Through a series of numerical analyses and experimental measurements, the prediction accuracy of the mathematical model was compared with experimental results for the gas transfer rate in hydrous materials and a building-sized total heat exchanger. The results demonstrated that an increase in water content in hydrous material has a significant impact on the permeability of water-soluble gases, with NH3 and HCHO permeability coefficients increasing by factors of 250 and 20 respectively. Conversely, for low-solubility gases such as CO2, the permeability coefficient only slightly increased at low humidity and remained largely unaffected thereafter. These findings contribute to the advancement of more efficient and safer total heat exchange ventilation systems.

Adaptability analysis of flow and heat transfer multi-scale numerical method for printed circuit heat exchanger

The printed circuit heat exchanger (PCHE) is a high-efficiency and compact mini-channel heat exchanger. Due to the large number of fine channels, it is difficult to conduct the flow and heat transfer numerical simulation of the entire heat exchanger based on the actual channels, which requires a lot of computational resource and time. In this paper, a simplified multi-scale numerical method with a non-equilibrium porous media model (NOPM) is proposed to study the flow and heat transfer performance of PCHE at high temperature and pressure. The pressure field, velocity field and temperature field of NOPM and actual multi-channel model (MC) under different working conditions are compared to study the adaptability of NOPM for the PCHE. The results indicate that the NOPM can accurately predict the flow and heat transfer performance under PCHE configurations with a large number of channels. However, as the channel number decreases, the relative errors in the temperature and pressure prediction significantly increase due to the increased flow maldistribution. Similarly, the NOPM can well predict the overall temperature distribution of the PCHE solid when the channel number is numerous. This work could support accurate thermal design, and provide accurate temperature field for the thermal stress analysis of PCHE.

Numerical and experimental investigation of additive manufactured heat exchanger using triply periodic minimal surfaces (TPMS)

With the increasing demand for high-efficiency compact heat exchangers in automobiles and spacecraft, lighter and more efficient metamaterials hold promise as advanced materials for cooling applications but remain beyond reach. Triply Periodic Minimal Surface (TPMS) structures, characterized by their smooth surfaces and significantly huge volumetric surface area, represent ideal internal structures for heat exchangers, and the development of additive manufacturing has made their design and production possible. This study focuses on designing heat exchangers based on seven TPMS structures (Fischer-Koch S, Gyroid, SplitP, Diamond, I-WP, F-RD, Primitive) and prints the finished heat exchangers using AlSi10Mg material based on numerical investigation results. Comprehensive evaluation metrics are used to rank the results. The findings reveal that the internal interleaved channels have varying effects on different structures, with Fischer-Koch S exhibiting the highest heat transfer capability of up to 269 W/K. Gyroid and I-WP demonstrate the best fluidity, with resistance only 23.44 % of Primitive’s. Gyroid has the best overall evaluation metrics, with a 54 % efficiency improvement over traditional plate heat exchangers. Additionally, this study proposes the use of the Voronoi algorithm to handle the channels of TPMS and identifies the asymmetric characteristics of heat exchangers on both sides, and it is believed that there is still greater optimization potential for the performance of TPMS heat exchangers.

Liquid-solid interface polymerization: A simple approach for efficient polyamide/polyethylene thin film composite total heat exchange membranes construction

A simple liquid-solid interface polymerization (LSIP) strategy was developed to prepare high performance polyamide (PA) based thin film composite (TFC) total heat exchange membranes (THEMs) to avoid the use of organic solvents and surfactant during the inverse phase interface polymerization processes between piperazine (PIP) and 1,3,5-benzenetricarbonyl trichloride (TMC) on porous polyethylene (PE) substrates. The non-polar organic solvent in the TMC organic phase coated on the surface of the PE surfaces was completely removed beforehand by evaporation to form polar TMC solid coating on the PE surfaces and facilitate the quick spreading of lately added aqueous PIP solutions, forming dense and highly cross-linked PA separation layers with superior total heat recovery efficiency and CO2 barrier property. The effects of TMC loading level, PIP concentration, and LSIP reaction time on the structure and performance of PA/PE-TFC THEMs were systematically investigated, leading to the formation of THEMs 0.20P-0.10T-6 with ultra-low CO2 permeance of 0.9 GPU, and high sensible heat exchange efficiency of 94.3 %, water vapor flux of 2128 g m−2·24 h−1, and enthalpy exchange efficiency of 76.8 %.

Numerical study flow and heat transfer characteristics of superhydrophobic single tube bundle surface and wake flow

Regarding the design optimization of the heat exchanger, the traditional method of changing the size of the macroscopic structure can no longer meet the increasing demand for heat exchange performance. The superhydrophobic surface can significantly reduce the flow resistance, which is expected to be a new method for the optimal design of heat exchanger. However, when the superhydrophobic effect is applied to a specific type of heat exchanger, its flow and heat transfer performance is not clear. In this paper, the flow and heat transfer model of the traversing superhydrophobic tube bundle is studied. Combined with the FLUENT 18.0 software, the slip boundary conditions of the superhydrophobic surface are deduced, and the flow and heat transfer characteristics of the superhydrophobic tube bundle surface and the wake are numerically analyzed, the influence mechanisms of slip effect on flow and heat transfer characteristics were obtained. Overall, as Ls increases, the comprehensive Nu, also known as heat transfer performance, on the cylindrical surface gradually increases, while the comprehensive Cf, also known as frictional resistance, on the cylindrical surface gradually decreases, indicating that superhydrophobic performance is expected to achieve heat transfer enhancement. The above conclusions can provide a theoretical basis for the optimal design of high-efficiency compact heat exchanger, and have important engineering application significance.

Vibration-Free 40-80K Turbo-Brayton Cryocooler and its Very High Efficiency Recuperator for Earth Observation Instruments

Several studies have demonstrated that Reverse Turbo-Brayton cryocoolers could be the next space cryogenic revolution, thanks to their capability to provide vibration-free remote cooling in the temperature range of 4 to 150K and for medium to high cooling powers. With this motivation, Absolut System developed a very low vibration 40-80K Reversed Turbo-Brayton cooler, work performed under the ESA Technical Program Technical Research Program - 4000113495/15/NL/KML. The cooler is based on two turbo-compressor stages, a high efficiency recuperator and a cryogenic turbo-expander, for operation between 300 and 40K. Following the fabrication of the cooler, we performed tests on both individual components, compressors, expander and recuperator as well as on the complete cooler. The turbomachines use aerodynamic bearings, i.e. contactless bearings, generate very little vibrations and exhibit no wear over time. The characterizations performed during the project concern exported micro-vibration behaviors of the compressors and the expander, operating respectively up to 250,000RPM and 150,000RPM, and thermodynamic performance of the different elements. The cooler was tested down to its minimum temperature and required the development of specific operating procedures for the conditioning of the circuit. We report here in a first part the main results and observations stemming from the test campaigns carried out during the project. This work showed the necessity of putting additional effort into the recuperator, one of the most critical components of the cooler. Absolut System is thus also working in parallel on developing a very high efficiency and compact heat exchanger, which we report in a second part, for the specific needs of Turbo-Brayton Coolers in response to the ESA Proposal ESA-TDE-TECMTT-SOW-023649. The technology selected for this is based on the common tube and shell but using very thin tubes of small diameters (<1mm). The challenge of this exchanger is not only the manufacturing, but also the very stringent requirements. Obtaining an efficiency higher than 97.5% in a very small mass while maintaining very low pressure drops, makes for a very challenging project. We have performed the design phase, tested, and validated different aspects of the assembly. The design for the first breadboard model has been validated numerically and is in the fabrication process. Testing the exchanger will then take place to characterize the performances of the recuperator and allow for a comparison between experimental results and analytical and CFD models. This effort participates in placing the Turbo-Brayton cryocoolers at the forefront of space coolers and pushing Europe even further in State of Art advancements for space to bring us closer to fulfill future Space Explorations and Earth Observation missions.

Investigating the coupling effect of ventilation and GHEs on temperature distribution and heat transfer characteristics

Tunnel lining geothermal heat exchangers (GHEs) offer numerous advantages, including small area, cost-effectiveness and high heat exchange efficiency. It is a good equipment to utilize geothermal energy in tunnels. However, few research has been conducted on the combined impact of tunnel lining GHEs and ventilation on the temperature field of the surrounding rock. In this study, laboratory test model of combined impact of heat transfer between ventilation and GHEs was established, the effects of different flow rates and wind speeds on temperature field and heat exchange characteristics of the rock were investigated, and the changes in heat transfer under different operational conditions were analyzed. The findings reveal that tunnel ventilation initially enhances the heat transfer efficiency of GHEs, but subsequently decreases the overall heat transfer. Moreover, higher wind speeds exacerbate this negative impact. The radius of the heating ring decreases with increased heat transfer, and the temperature of the surrounding rock rises with heightened heat exchange at same locations within the heating ring. There are reasonable ranges of wind speed and GHEs flow rate, which are 1.5 m/s–2 m/s for wind speed and 0.4 m/s–0.6 m/s for flow rate, respectively. These results are important for the evaluation of thermal effect of tunnel lining GHEs and ventilation design.

Study on Heat Transfer Synergy and Optimization of Capsule-Type Plate Heat Exchangers

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.

Heat Transfer Performance of a 3D-Printed Aluminum Flat-Plate Oscillating Heat Pipe Finned Radiator.

As electronic components progressively downsize and their power intensifies, thermal management has emerged as a paramount challenge. This study presents a novel, high-efficiency finned heat exchanger, termed Flat-Plate Oscillating Heat Pipe Finned Radiator (FOHPFR), which employs arrayed flat-plate oscillating heat pipes (OHP) as heat dissipation fins. Three-dimensional (3D)-printed techniques allow the internal microchannels of the FOHPFR to become rougher, providing excellent surface wettability and capillary forces, which in turn significantly improves the device's ability to dissipate heat. In this study, the 3D-printed FOHPFR is compared with traditional solid finned radiators made of identical materials and designs. The impacts of filling ratio, inclination angle, and cold-end conditions on the heat transfer performance of the 3D-printed FOHPFR are investigated. It is demonstrated by the results that compared to solid finned radiators, the FOHPFR exhibits superior transient heat absorption and steady-state heat transfer capabilities. When the heating power is set at 140 W, a decrease in thermal resistance from 0.32 °C/W in the solid type to 0.11 °C/W is observed in the FOHPFR, marking a reduction of 65.6%. Similarly, a drop in the average temperature of the heat source from 160 °C in the solid version to 125 °C, a decrease of 21.8%, is noted. An optimal filling ratio of 50% was identified for the vertical 3D-printed FOHPFR, with the minimal thermal resistance achieving 0.11 °C/W. Moreover, the thermal resistance of the 3D-printed FOHPFR is effectively reduced compared to that of the solid finned radiator at all inclination angles. This indicates that the FOHPFR possessed notable adaptability to various working angles.

Identifying regularities of fluid throttling of an inertial hydrodynamic installation

The article presents the results of experimental research conducted on a specially designed setup for pressurizing various types of fluids through throttle orifices. To determine the optimal operating mode of the thermal system, throttle nozzles of different diameters, specifically 1.5 mm, 2 mm, and 3 mm, were utilized. One of the primary advantages of vortex heaters is their high heat exchange efficiency. This is attributed to the vortical motions and turbulence generated within the device, which promote more vigorous fluid mixing, thus enhancing heat transfer efficiency. However, vortex heaters do have certain drawbacks. Vortical components may experience wear and require regular maintenance and replacement. Subsequently, during the course of experimental work, an alternative inertia-based hydrodynamic system for heating heat carriers was developed and installed in a laboratory experimental facility. The research focus was on technical water. The results indicated that the static pre-pressure generated by the supply of water from the water main into the system decreases as the rotor's angular velocity increases. Experimental investigations demonstrated that rotor rotation leads to a redistribution of flow characteristics in throttle orifices for both static and dynamic inertial fluid discharge. Given that any static column of liquid results in level flow through throttle orifices, their flow static parameters were established. Furthermore, the research revealed that with the increase in rotor angular velocity, the fluid pressure at the throttle orifices rises, while the share of fluid discharge from the initial static pressure decreases in the overall fluid flow

Transfer learning model to predict flow boiling heat transfer coefficient in mini channels with micro pin fins

Flow boiling in mini channels with micro pin fins is a promising heat sink technique to achieve high-efficient aircraft thermal management. The accurate prediction of its heat transfer coefficient is critical for the practical design of two-phase heat exchanger based on mini channels with micro pin fins. Previous investigation shows that heat transfer coefficient prediction accuracy of the machine learning method is generally better than that of conventional empirical correlations. However, the machine learning method cannot guarantee its prediction accuracy among different data domains. To extend the application region of the conventional machine learning method, a transfer learning framework was proposed in present study. First of all, an experimental system was built to acquire test data from different sample domains (i.e., the diamond pin fins with different geometries). Then a conventional machine learning model was developed based on the deep learning method. Furthermore, the developed deep learning model was adjusted with transfer learning process, and the performance of these two kinds of models (i.e., conventional machine learning model and transfer learning model) was comprehensively evaluated. Results showed that the conventional machine learning model had a good prediction accuracy with an overall deviation of 4.11 % but was only confined in the same data domain as training data. Differently, the transfer learning model with 70 % data set from the new domain can achieve appropriate prediction in the new domains with deviation of 4.28 %. The results of this paper demonstrated that the conventional machine learning model can extend into different domains with reasonable prediction accuracy through transfer learning frameworks. It will benefit the practical design of high-efficiency heat exchangers for aircraft thermal management.

Research and analysis of the thermal and control characteristics of the plate-type fuel assembly for the supercritical CO2 reactor

Small nuclear reactors can be applied to micro grid power generation, island and space nuclear power systems. The plate-type fuel assembly has a compact design structure, low fuel core temperature, large heat exchange area, and high heat exchange efficiency, which is widely used in small nuclear reactors. To supplement the lack of research in S-CO2 small nuclear reactor, The Brayton cycle reactor system analysis program of S-CO2 plate-type fuel assemblies (BRESA-PFA) is developed, and the reactor control system program is developed to simulate the transient condition in this paper. This article establishes a fuel assembly flow and heat transfer model and a control rod control model using Modelica language, achieving physical and thermal coupling and power control of the reactor. The steady-state operating parameters of the developed program BRESA-PFA were studied, and the flow distribution, coolant and fuel temperature distribution of BRESA-PFA were obtained. The flow distribution conforms to the experimental parameters of CARR, and the fuel assembly radial temperature distribution is high at the center and low at the edge. After verification, the maximum fuel temperature did not exceed the limit value and met the design requirements. Transient characteristic analysis was conducted to study the rod lifting strategy during the startup process, the start-up and rod lifting process of BRESA-PFA is N2-N1-G2-G1, using the logic of step control. Research on reactor control system response under loss of coolant accident, after the accident, the coolant flow suddenly decreased to 65 % of the rated value, and the reactor power also decreased to 65 % FP, G2 and G1 control rods were inserted downwards, the coolant temperature fluctuates by 1 %∼2%. The reactor control system was able to respond quickly, ensuring the stability of coolant temperature, proving the safety and reliability of BRESA-PFA, and providing theoretical reference and scheme support for the research of S-CO2 small nuclear reactors.

A frequency domain dynamic simulation method for heat exchangers and thermal systems

Dynamic simulation of thermal systems is crucial for their optimal control but facing the challenge of balancing calculation accuracy and efficiency, where numerically high-efficient and accurate heat exchanger (HX) modeling is a key. Herein, we propose a frequency domain model for HXs' dynamic simulation in the to meet this challenge. The governing equations of HXs are first converted to frequency domain through Fourier transform, and the analytical solution of the converted equations yields the frequency domain HX model in the form of transfer matrix that connects the inlet temperature variations and outlet temperature responses. Furthermore, integrating transfer matrices of HXs into the system's transfer matrix enables a high-efficiency thermal system simulation. Numerical cases of a single HX, a HX network, a district heating network, and a thermodynamic cycle are used to validate the developed method and demonstrate its efficacy by comparing it against finite difference/volume method. Results show that the proposed method could reduce the calculation time by 2–3 orders of magnitude, and the maximum deviation of node temperature is around 1 K. The proposed method can be a powerful tool for the analysis of thermal systems and potentially integrated energy systems.

Additive manufacturing of complex structures and flow channels using wire-arc thermal spray

The development of a cost-effective additive manufacturing method for millimeter-scale metal structures is essential for the fabrication of novel, high-efficiency heat exchangers and heat sinks. The millimeter-scale fluid channels produced by these structures provide a large surface area to promote heat transfer while minimizing system volume and mass. Traditional additive manufacturing methods are limited by their high cost, high energy consumption, and long processing times. This study presents an efficient additive manufacturing method by using wire-arc thermal spray through a polymer mask. Aluminum and copper structures with arbitrary shapes and a height of 1.3 mm were deposited on a plate 74 mm × 51 mm in size in 30 min and 15 min, respectively. Masks were fabricated by 3D-printing with a high-temperature photopolymer resin. All fabricated structures exhibited a dense center region, a porous side wall region, and a porous satellite particle region between deposited structures. The development of the deposited structures throughout the process is investigated for aluminum (having a low density, surface tension, and melting temperature) and copper (having a high density, surface tension, and melting temperature). The influence of the distance between the mask and the substrate on structure geometry and porosity is studied. The fabrication steps of a liquid-cooled mini-channel heat sink containing an enclosed flow channel are demonstrated using the proposed additive manufacturing method. The results suggest that using wire-arc thermal spray through a polymer mask can be used as a cost-efficient method to additively manufacture metal structures on the millimeter scale.

Research on shell-side heat and mass transfer with multi-component in LNG spiral-wound heat exchanger under sloshing conditions

The spiral-wound heat exchanger (SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop. These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.

Flow and heat transfer performance of bionic heat transfer structures with hybrid triply periodic minimal surfaces

Efficient energy conversion technologies are essential for mitigating the environmental impact of industrial activities. The development and application of high-efficiency heat exchangers are key components in this endeavor. Heat exchangers based on triply periodic minimal surfaces (TPMS) are widely acknowledged for their exceptional thermal-hydraulic performance. However, current research mainly focuses on the design and optimization of heat exchangers with standard TPMS structures. In this study, a hybrid process is utilized to construct ten novel heat exchangers, followed by comprehensive investigations of their internal flow fields using three-dimensional numerical simulations. In order to establish a baseline, five standard TPMS structures are also introduced as reference cases. The results reveal that complex secondary flow distributions and velocity variations are critical factors influencing the thermal-hydraulic performance. Moreover, the influence of different standard TPMS cells on the flow and heat transfer characteristics varies during the hybridization process. Specifically, the inclusion of the Schwarz cell generally leads to an improvement in heat transfer, while the presence of the Lindinoid cell may result in a deterioration of heat transfer. The Diamond and Lindinoid cells have an adverse impact on the flow characteristics, while the Gyroid and Neovius cells enhance the flow characteristics. To evaluate the overall thermal-hydraulic performance of different channels, a comprehensive performance assessment is introduced. The Diamond channel and the Gyroid-Neovius channel show superior overall performance in their respective Reynolds number regions, with the former exhibiting better flow characteristics and the latter has outstanding heat transfer performance.

Numerical study on the heat transfer characteristics of a microchannel heat exchanger with liquid lead–bismuth eutectic and supercritical CO2 as working fluids

The Lead-cooled Fast Reactor (LFR) is a promising option for fourth-generation nuclear energy systems, with the supercritical carbon dioxide (sCO2) Brayton cycle being the preferred power cycle for future nuclear energy systems. Lead-bismuth eutectic (LBE) is a more suitable reactor coolant than lead due to its lower melting point. High-efficiency microchannel heat exchanger (MCHE) may be an ideal choice for the intermediate heat exchanger (IHX) in liquid lead–bismuth fast reactors. To prevent the channels of MCHE from being blocked by liquid LBE, a new structure of MCHE is proposed, in which the liquid LBE flow channel has a large equivalent diameter and corresponds to two sCO2 microchannels. In this study, the heat transfer characteristics of conventional and new structures of MCHE were investigated using numerical simulation. The results indicate that the temperature change at the inlet of the liquid LBE channel enhances the heat transfer of both liquid LBE and sCO2. Under constant temperature and pressure, the velocity of sCO2 has a significant effect on the convective heat transfer of sCO2, but has little effect on liquid LBE. Based on the reliability of equipment operation, this study recommends the use of the heat exchanger form in case 5. Compared with case 3, altering the velocity of liquid LBE results in a 7.1–8.3% increase in the convective heat transfer coefficient of liquid LBE, and a ∼38% increase in the convective heat transfer coefficient of sCO2. Similarly, changing the velocity of sCO2 leads to a 6.1–7.5% increase in the convective heat transfer coefficient of liquid LBE, and a 32.8–38.0% increase in the convective heat transfer coefficient of sCO2. For sCO2 heat transfer calculation, Yoon's heat transfer correlation is recommended, while Kirillov's heat transfer correlation is suggested for liquid LBE heat transfer calculation. The deviation between numerical calculation results and correlations is less than 18.1% and 12.7%, respectively.

A Modified Correlative Model for Condensation Heat Transfer in Horizontal Enhanced Tubes with R32 and R410A Refrigerants

An experimental study was performed that compared tube side condensation heat transfer characteristics of enhanced tubes (hydrophobic surface tubes (HYD), herringbone micro fin tube (HB), and a composite hydrophobic/herringbone (micro fin) tube (HYD/HB)) to the performance of a smooth tube (ST). The condensation heat transfer coefficient (HTC) was calculated from data that were recorded for smooth and enhanced tubes that had an outer diameter (OD) of 12.7 mm. Data were collected (as a function of mass flow rate) using a couple of refrigerants (R410A and R32), for saturated temperatures of 35 °C and 45 °C, with vapor qualities that ranged from 0.8 to 0.2. Several previously reported smooth tube HTC models were used to calculate values that could be compared to experimentally obtained HTC values. The correlation model that demonstrated the best accuracy (for the conditions considered) was then modified for use with the enhanced tubes from this study. Results from the modified correlation show differences with experimental values that ranged from −10% to +17%; the new modified correlation demonstrates high prediction accuracy. An accurate correlation allows the evaluation of enhanced heat transfer tubes for use in high-efficiency heat exchanger systems. The development of this new model is significant in the study of enhanced heat transfer.