High-efficiency Heat Exchangers Research Articles

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.

Modeling and Optimizing Automotive Waste Recovery for Optimal Performance

Abstract: It is vital to explore an effective way to capture waste heat from modern automobiles. This research outlines the current methods to harness that excess heat from the exhaust system and a proposal to use a high-efficiency printed-circuit heat exchanger (PCHE) to harness the heat. The research also revealed a unique iteration process that encompasses testing of the exchanger in a closed-loop steam system which would serve as the basis for future experiments. In lieu of experiments, data was collected from peer-reviewed research of other scientists to approximate the effectiveness and efficiency of the system. The following facts were theoretically revealed by the derived model. The theorized heat exchanger was found to have a maximum transfer rate of 510 kW while the maximum heat supplied by the exhaust is around 100 kW. The exchanger is sufficiently designed to capture energy wasted by the engine through the tail pipe. With a mass of 5.169 kg for the exchanger alone and the estimated amount of fluid, turbine, generator, and piping to be no more than 50 kg, the vehicle will experience very little mass increase.

Numerical Simulation Study of Geothermal Energy Extraction in Medium-deep Formation

Geothermal energy is a kind of renewable energy with rich content, relatively low cost and wide distribution. China is rich in geothermal reserves and urgently needs efficient heat extraction technology. Closed cycle heat extraction technology is a new geothermal development model that is suitable for medium-deep geothermal reservoir and has high heat exchange efficiency without taking water. In this system, the circulating working fluid is pumped into the annulus from the ground, and the heat is extracted from the formation through heat conduction, and then returned to the ground through the central pipe. In this paper, the heat recovery capacity of the heat extraction system is numerically simulated. The research results show that the coaxial borehole heat exchanger technology has a good heat recovery capacity, and the designed thermal insulation structure has a positive effect on heat extraction and heating, and the heat extraction 100 days can stably produce 360 Kw of heat.

Cost of Using Laser Powder Bed Fusion to Fabricate a Molten Salt-to-Supercritial Carbon Dioxide Heat Exchanger for Concentrating Solar Power

Advances in manufacturing technologies and materials are crucial to the commercial deployment of energy technologies. We present the case of concentrating solar power (CSP) with molten salt (MS) thermal storage, where low-cost, high-efficiency heat exchangers (HXs) are needed to achieve cost competitiveness. The materials required to tolerate the extreme operating conditions in CSP systems make it difficult or infeasible to produce them using conventional manufacturing processes. Although it is technically possible to produce HXs with adequate performance using additive manufacturing, specifically laser powder bed fusion (LPBF), here we assess whether doing so is cost-effective. We describe a process-based cost model (PBCM) to estimate the cost of fabricating a MS-to-supercritical carbon dioxide HX using LPBF. The PBCM is designed to identify modifications to designs, process choices, and manufacturing innovations that have the greatest effect on manufacturing cost. Our PBCM identified HX design and LPBF process modifications that reduced projected HX cost from $750 per kilo-Watt thermal (kW-th) ($8/cm3) to $350/kW-th ($6/cm3) using currently available LPBF technology, and down to $220/kW-th ($4/cm3) with improvements in LPBF technology that are likely to be achieved in the near term. The PBCM also informed a redesign of the HX design that reduced projected costs to $140–160/kW-th ($3/cm3).

LNG 운반선 PCHE 열교환기 내 상변화에 대한 수치해석

In this study, we studied the ice accretion that occurs in the next-generation heat exchanger, the PCHE(Printed Circuit Heat Exchanger) channel. PCHE heat exchanger is called the next-generation heat exchanger, and it has the advantage of being able to reduce the heat exchange efficiency by less than 1/10 compared to the existing heat transfer tube type method along with high heat exchange efficiency of more than 90%. Three CFD(Computational Fluid Dynamics) analysis were conducted prior to modeling and analysing PCHE heat exchanger through Ansys Fluent and Fensap-Ice. Through the established interpretation methodology, simulated heat exchange and phase changes caused by temperature differences between fluids through Hot Water and LNG(Liquified Natural Gas) flowing into the PCHE channel. First, setting the temperature of Hot Water to 10℃ to 80℃, and identified the heat exchange according to each temperature through CFD simulation. Next setting the temperature of Hot Water to 10℃, 50℃ and 90℃ and identified the ice accretion in the channel according to each temperature through CFD simulation.

Deep convolutional surrogates and freedom in thermal design

A deep learning approach is presented for heat transfer and pressure drop prediction of complex fin geometries generated using composite Bézier curves. Thermal design process includes iterative high fidelity simulation which is complex, computationally expensive, and time-consuming. With the advancement in machine learning algorithms as well as Graphics Processing Units (GPUs), parallel processing architecture of GPUs can be used to accelerate thermo-fluid simulation. In this study, Convolutional Neural Networks (CNNs) are used to predict results of Computational Fluid Dynamics (CFD) directly from topologies saved as images. A design space with a single fin as well as multiple morphable fins are studied. A comparison of Xception network and regular CNN is presented for the case with a single fin design. Results show that high accuracy in prediction is observed for single fin design particularly using Xception network. Xception network provides 98 percent accuracy in heat transfer and pressure drop prediction of the single fin design. Increasing the design freedom to multiple fins increases the error in prediction. This error, however, remains within three percent of the ground truth values which is valuable for design purpose. The presented predictive model can be used for innovative BREP-based fin design optimization in compact and high efficiency heat exchangers.

Modeling and optimization of the parameters of the heat accumulator of the combined livestock-heliogreenhouse complex

In the article, the heat exchange process in the water tank battery, which acts as a wall between the livestock building and the solar greenhouse, is studied. The division consists of parallelepiped-shaped tanks, between which the coefficients of heat transfer in charge and discharge mode are determined, taking into account the different temperatures and speeds of the air in the livestock building through the air-moving corridors. A mathematical model of the temperature regime was developed based on the balance equation of the water tank accumulator. The geometric dimensions of the water tank accumulators are optimized based on the criterion equations. A computer model was created using the COMSOL Multiphysics software tool and thermal efficiencies were determined. Based on the results of the conducted research and numerical calculations, it is based on the high heat exchange and energy efficiency when the size of the water tank accumulator is 40x60x25 cm.

Computational fluid dynamics calculations of high efficiency heat exchangers operating in laminar motion consisting of extruded plastic profiles with inserts

Computational fluid dynamics calculations of high efficiency heat exchangers operating in laminar motion consisting of extruded plastic profiles with inserts

Investigations of protracted finned double pipe heat exchanger system for waste heat recovery from diesel engine exhaust

The need for energy and material savings, as well as environmental concerns, have helped to increase the demand for high efficiency heat exchangers in the modern era. In practice, a heat exchanger or the direct ejection of the hot working fluid is used to recover the waste heat from a heat engine or thermal power plant into the environment. Waste heat of a heat engine or power plant is recovered to the environment via a heat exchanger or by direct ejection from the hot working fluid. In many situations, waste heat recovery removes or greatly reduces the necessity for additional fuel energy input to achieve this goal. The double pipe heat exchanger equipment is taken in this research, heat from engine exhaust recovers due to its superior qualities. The design characteristics of the heat pipe will be changed in order to increase overall efficiency by studying the concepts of various authors. Different design parameters for a double pipe heat exchange system as well as different working fluid-flow rates are tested with the suggested device. Additionally, ANSYS performs CFD for the proposed heat exchanger system in order for the results to support the experimental findings.