Analysis Of Heat Transfer Performance Research Articles

Heat transfer performance analysis of medium - deep coaxial borehole heat exchanger (CBHE): combination of heat extraction operation test and numerical simulation

Abstract Geothermal energy is a clean and renewable energy source that can effectively reduce carbon emissions. Coaxial borehole heat exchanger (CBHE) is a crucial component of the geothermal mining system. To understand the heat transfer mechanism of a CBHE and to design its construction, this paper analyzes the geotechnical thermal response characteristics of CBHE under constant power conditions. COMSOL was used to simulate the performance of the heat exchanger during intermittent operation in both summer and winter. The results indicate that the inlet water temperature and the thermal conductivity of the grouting material have a weak impact on the energy efficiency coefficient of the heat exchanger. The energy efficiency coefficient can increase by about 22% when the inner pipe's thermal conductivity is lower. The temperature difference between the medium flowing into the inner pipe at the bottom of a shallow cased buried pipe and the medium flowing out of the inner pipe defines the thermal short circuit value. The influence on the thermal short circuit value is on the order of the inner pipe thermal conductivity, grouting material thermal conductivity, and the inlet water temperature. The fluctuation of soil temperature in the summer is greater than that in the winter, the soil temperature of shallow-buried pipes is easier to recover in the winter. The characteristic law obtained in this paper provides a valuable reference for the scientific design of CBHE.

A novel compact supercritical CO2 solar receiver based on impinging jet: Heat transfer performance and thermal stress analysis

The compact solar receiver can withstand high temperature and high pressure, which provides promising solutions for direct supercritical CO2 (S-CO2) solar receiver applications. However, it still suffers from local high temperature and large thermal stress due to the non-uniform heating boundary condition. The impinging jet method can significantly enhance the local heat transfer coefficient, holding significant potential in reducing the local high temperature of the compact S-CO2 receiver. Inspired by this, a novel design for a compact S-CO2 receiver using the impinging jet was proposed in this work. The heat transfer performance and stress behavior of the jet channel within the receiver were numerically investigated. The results showed that the jet channel has a significantly higher heat transfer performance than the rectangular channel, and the shorter flow path of the jet channel also effectively reduces the pressure loss. Meanwhile, the jet pattern significantly enhances the temperature uniformity, thereby reducing the thermal stress. In addition, increasing the channel aspect ratio improves the thermo-hydraulic performance, but increase the stress at the same time. The increase in the number of jet holes and the jet hole diameters not only enhance the thermo-hydraulic performance, but also reduce the stress of the jet channel.

Comparative analysis of heat transfer performance in cavities with varied wall conditions and nano encapsulated phase change material–water

This numerical study investigates convective flow within a square cavity subjected to a temperature gradient established between hot and cold walls. The cold wall is subjected to three different conditions: standard, elastic, and open boundary. The cavity is filled with an advanced nanofluid comprising water and nano encapsulated phase change material (NEPCM). The NEPCM feature a polyurethane shell encapsulating a nonadecane core, known for its phase transition capabilities and efficient storage or release of substantial latent heat. Numerical solutions for the momentum and energy equations are obtained for the three wall types, considering variations in the volume fraction of NEPCM (0.0≤ϕ≤0.05), Rayleigh number (105≤RaH≤106), and the fusion temperature of the core (0.1≤θF≤0.3). The results reveal that the type of wall in the cavity (standard, elastic, or open) has a significant impact on the flow patterns and heat transfer characteristics. The open wall, in particular, showed a distinct behavior with a lower mid-region temperature and a higher heat transfer rate at lower NEPCM concentrations compared to the standard and elastic walls. Adjusting the concentration from 1% to 5% increases the heat transfer rates by 44, 49, and 37 percent for standard, elastic, and open wall conditions, respectively.

Heat and mass transfer performance analysis of a vertical tubular ammonia/water bubble absorber based on CFD modeling

Bubble absorbers are highly efficient in mass transfer processes, but their popularization is limited by the risks associated with too much ammonia charging. In order to reduce the ammonia charge, it is essential to optimize the heat and mass transfer performance in the absorber. Existing models provide in-depth analysis of bubble motion and morphology, but insufficient attention has been paid to the concentration distribution and interfacial heat and mass transfer resistance. In this study, a two-dimensional axisymmetric vertical tubular ammonia/water bubble absorber was modeled based on Fluent and phase equilibrium, absorption heat data based on Aspen was imported. The relative deviations were 9%, 0.45%, and 4.1% in terms of the completely absorbed height, the liquid phase ammonia mass fraction, and the outlet temperature, respectively. The results showed that the mass transfer deterioration point was at the gas column closure and the heat transfer deterioration point was at the gas column contraction. Variable parameter studies have shown that turbulence effects at the gas–liquid interface can lead to enhancement and deterioration of local heat and mass transfer, which in turn cause local oscillations in the concentration and temperature profiles. While increasing the interphase mass transfer driving force promotes the interphase mass transfer process, it hinders the diffusion mass transfer process within the liquid phase. This effect is particularly pronounced in the absence of intense cooling, leading to an increase in the complete absorbed height.

Numerical investigate on the heat transfer performance and mechanical analysis of a water sublimator

Water sublimators play a critical role in efficiently managing the high thermal load of spacecraft in a vacuum environment, ensuring their proper functioning. This article focuses on a novel cold plate water sublimator driven by a porous sublimation tube structure, which is still in the theoretical research stage. Numerical methods are employed to study the evaporation, freezing, and sublimation processes, with validation against experimental data. The average absolute error of the four operating conditions is 1.33 K, and the ice layer thickness error is 8.33 %. Additionally, a method to calculate the effective thermal conductivity of porous aluminum foam is proposed, with a model error of 9 %. The sublimator's heat transfer characteristics are significantly influenced by the porosity of the aluminum foam and sublimation tubes. The impacts on temperature behavior, ice thickness, feed water pressure, and stress are carefully examined. Results reveal aluminum foam porosity of 0.7 and sublimation tube porosity of 0.3. Moreover, the study explores how different heat loads affect the sublimator's operation mode. Heat loads above 2 W/cm2 cause evaporation and dryness within the sublimation tube, while excessively small heat loads lead to ice formation and increased stress on the aluminum foam structure. These findings provide valuable insights for water sublimator design.

Structure Design and Heat Transfer Performance Analysis of a Novel Composite Phase Change Active Cooling Channel Wall for Hypersonic Aircraft.

Efficient and stable heat dissipation structure is crucial for improving the convective heat transfer performance of thermal protection systems (TPSs) for hypersonic aircraft. However, the heat dissipation wall of the current TPS is limited by a single material and structure, inefficiently dissipating the large amount of accumulated heat generated during the high-speed maneuvering flight of hypersonic aircraft. Here, a convection cooling channel structure of TPS is proposed, which is an innovative multi-level structure inspired by the natural honeycomb. An active cooling channel (PCM-HC) is designed by using a variable-density topology optimization method and filled with phase change material (PCM). Numerical simulations are used to investigate the thermal performance of the PCM-HC wall, focusing on the influence of PCM properties, structural geometric parameters, and PCM types on heat transfer characteristics. The results demonstrate that the honeycomb-like convection cooling channel wall, combined with PCM latent heat of phase change, exhibits superior heat dissipation capability. With a heat flux input of 50 kW/m2, the maximum temperature on the inner wall of PCM-HC is reduced by 12 K to 20 K. Different PCMs have opposing effects on heat transfer performance due to their distinct thermophysical properties. This work can provide a theoretical basis for the design of high-efficiency cooling channel, improving the heat dissipation performance in the TPS of hypersonic aircraft.

Experimental and numerical convective heat transfer performance analysis of a confined impinging round jet with triangular tabs under crossflow influence

In this study convective heat transfer performance of a confined impinging round jet with/without nozzle tabs under channel crossflow is investigated experimentally and numerically for a wall mounted heated module. Numerical investigations are carried out for different jet to crossflow velocity ratios (Vr) and compared to experimental data. Four different Vr values (5,6,8, and 10) are tested for single target plate distance to jet nozzle diameter ratio (H/D=8). ANSYS Fluent software is used for numerical simulations while infrared thermography is utilized for experimental investigations. Surface temperature values of the wall mounted module are obtained and presented along with complex flow structures obtained via numerical simulations. Results show that crossflow has decisive effect on temperature distribution on the component. By inserting triangular tabs to the nozzle exit, it is possible to further decrease the surface temperature of the module and minimize the crossflow caused jet deflection. The addition of triangular tabs resulted in a significant increase of up to 10% in the mean Nusselt number on the top surface of the module at Vr=10.

Sensitivity Analysis and Optimization of Heat Transfer Performance of Ultra-Thin Vapor Chamber With Composite Wick

Abstract An ultra-thin vapor chamber (VC) with the composite wick formed by four spiral woven meshes (SWMs) and a copper mesh was proposed to solve the heat dissipation problem in miniaturized electronic equipment because of its sufficient heat transfer capability under limited thickness. However, the influence factors on the thermal performance of the VC with composite wick are more than that of the VC with a single type of wick. In this study, in order to investigate the thermal performance of the VC with composite wick, a theoretical model was developed to calculate the maximum heat transfer capacity. Besides, a three-dimensional numerical model for the heat transfer characteristics was established, and the simulation results have a good match with the experimental results. The orthogonal test method was adopted to determine that both the width of the vapor channel (wv) and the thickness of the vapor channel (tv) have a significant effect on the maximum heat transfer capacity and thermal resistance, while the porosity of the mesh (εmesh) has a prominent effect on the maximum heat transfer capacity, but has little effect on the thermal resistance. Further optimization of the sensitive factors for VC heat transfer performance was achieved to enhance the maximum heat transfer capacity.

Numerical simulation and analysis of heat transfer performance of new airfoil fin printed circuit heat exchangers

The airfoil fin printed circuit heat exchanger (PCHE) is very suitable for use as the heat exchangers in the supercritical CO2 Brayton power generation cycle due to its multiple advantages. However, in most previous studies, the new fin designs have complex curved surface geometries, which would bring difficulties in their manufacturing. Therefore, in this study, some simple fin structures based on the modification of traditional NACA0018 airfoil fin are proposed to enhance the heat transfer performance of PCHE. The influence of different structure modification shapes, size and positions on the overall PCHE performance are examined by numerical simulation. The results revealed that setting concave with a radius of 0.3 mm in the flow boundary zone (i.e. Type-VI) can significantly improve the thermal hydraulic performance of the fin channels. By comparing the local thermal hydraulic performance with the prototype fin, the Type-VI fin shows the advantages of reducing the fluid pressure difference resistance near the fin wall and increasing the impact area of the fluid on the fin, resulting in its j factor can be increased by 4.37 % to 7.16 %, f factor reduced by 0.45 % to 1.77 %, and η increased by 5.20 % to 9.10 %.

Analysis of heat transfer performance and system energy efficiency of catalytic combustion heaters for low calorific value waste gas application to oil shale in-situ conversion

In this study, we explore the utilization of low calorific value waste gas for in-situ conversion mining of oil shale. Through simulation, we analyze the effects of variations in the parameters of the catalytic combustion heater's independent variables on the exhaust gas temperature, methane conversion rate, and system energy efficiency (dependent variables). The results demonstrate that larger values of the pore radius, gas injection flow rate, and pulsation flow rate parameters lead to reductions in the corresponding dependent variables. The system's energy efficiency remains stable between 21.94% and 22.46% with increasing gas injection temperature. Furthermore, an increase in the oxygen molar fraction results in elevated methane conversion rates from 0.64% to 58.2% and system energy efficiency from 0.4% to 21.51%. Conversely, an increase in the methane molar fraction causes a decrease in methane conversion from 76.17% to 7.18% and a decline in system energy efficiency from 32.83% to 7.18%. Notably, gas flowback occurs at downhole pressure conditions of 2 MPa. The variation in pressure stabilizes the system's energy efficiency between 21% and 22.10%. The simulation and analysis findings of this study provide significant reference value for subsequent practical testing efforts.

Heat transfer and energy performance analysis of photovoltaic thermal system using functionalized carbon nanotubes enhanced phase change material

The photovoltaic thermal system (PVT) is an emerging technology that simultaneously generates both electrical and thermal energy from solar energy, aiming to improve solar energy utilization. However, significant technological issues with these systems obstruct their large-scale operation. The major drawback of the cooling fluid-based PVT systems lies in operation during sun-shine hours only. To address this issue, the present research endeavors a comparative study on with and without nano-enhanced phase change materials (NePCM) integrated PVT system. In this study, the performance evaluation of four configurations was analyzed with a flow rate varying from 0.4 to 0.8 litter per minute. From this, the experimental analysis was performed on two systems, including a photovoltaic and a PVT system. The simulation was performed using TRNSYS simulation on the phase change materials integrated photovoltaic thermal system, and NePCM integrated photovoltaic thermal system. The results indicates that increasing the flow rate by 2.2 times leads to a 4.9-fold increase in pressure drop, while the friction factor decreases with rising mass flow rate. Notably, the NePCM-integrated PVT system exhibited a substantial reduction in cell temperature and increased electrical power output at higher flow rates. At a flow rate of 0.4litter per minute, a significant heat gain was achieved with an impressive energy-saving efficiency of 75.67 %. Furthermore, the total efficiency of the PVT system, phase change materials integrated PVT system, and NePCM integrated PVT system were determined to be 81.9 %, 84.5 %, and 85.05 %, respectively. These findings underscore the potential of NePCM-integrated PVT systems for enhancing performance and expanding their practical application.

Analysis of flow and heat transfer performance of different types of flow channels in printed circuit heat exchangers for pre-coolers

The shape of fins in flow channels of printed circuit heat exchangers (PCHE) significantly affects the heat exchanger performance. In the pre-cooler condition of the marine supercritical CO2 Brayton cycle power generation system, this study focuses on three typical discontinuous flow channel printed circuit heat exchangers. The investigation involves a numerical analysis of flow and heat transfer performance using CFD method. The comparative consequences illuminate that the rectangular fin channel exhibits the optimal heat transfer performance, and temperature drops are 1.18 times and 1.23 times, exceeding those of airfoil and rhombic fin channels, respectively. All three flow channels show different degrees of temperature drop reduction along the direction of fluid-flow. However, the rectangular fin channel demonstrates the worst flow performance, as pressure drops are 16.6 times and 17.8 times, higher than those of airfoil and rhombic fin channels, respectively. By calculating the values of Nu/f and Q/?p, the comprehensive performance of each flow channel is ranked from high to low airfoil fin channel, rhombic fin channel, and rectangular fin channel. This research provides guidance for optimizing the design and applying PCHE in engineering for marine supercritical CO2 Brayton cycle pre-coolers.

Simulation Analysis of Heat Transfer Performance of Falling Film Evaporative Cooler

Simulation Analysis of Heat Transfer Performance of Falling Film Evaporative Cooler

Analysis of vortex shedding characteristics and heat transfer performance of staggered tube bundle system

Tube bundle systems' heat transfer is unclear due to complex flow channels and turbulent fluctuations, affecting energy efficiency. This study simulates 2D staggered 18-row tube bundles at Reynolds numbers 3,100-50,000. 3D cylinders are simplified to 2D tubes, with grid independence and model validation. Flow, temperature fields, and synergy angles are analyzed for positions, Reynolds numbers, and spacings. High vortex shedding frequency in front tubes with multiple subfrequencies at different amplitudes. Asymmetric solutions emerge due to turbulent fluctuations. At high Reynolds, vortex shedding patterns complexify and frequencies rise. Nusselt number and synergy angle trends similar at low Reynolds, but diverge at high Reynolds. Small tube spacings significantly impact heat transfer; large spacings have weaker effects.

EXPERIMENTAL ANALYSIS OF HEAT TRANSFER AND THERMAL PERFORMANCE OF PARABOLIC TYPE SOLAR COLLECTOR WITH RIBBED SURFACE TEXTURE FOR CLEAN ENERGY EXTRACTION

This paper examines the performance of a parabolic type solar collector (PTSC) that uses both plain tube and ribbed surface textured tube channels for elevating the water temperature used for various applications. The performance of a solar water heater is evaluated experimentally. During the experiment, the solar radiation intensity and the feed water flow rate of 1.0 kg/min to 5.0 kg/min in steps of 1 kg/min are taken into consideration for analyzing the effect of ribbed textured tubes on the thermal effectiveness, frictional factor, convective transfer of heat, Reynolds number, and the Nusselt number of the PTSC. Furthermore, the overall performance of the PTSC is analyzed considering the above thermo-physical parameters. Based on the result of this study, at a flow rate of 3.0 kg/min, the thermal efficiency is found to be enhanced by about 28.25%, the friction factor is augmented by about 0.23%, the convective heat transfer coefficient is improved by 24.22%, and the Nusselt number is increased by about 26.32%. On average, an overall improvement in the performance of 8.25% is observed for the ribbed textured tube than that of the plain tube. The experimental error analysis shows that the standard deviation for both plain and ribbed textured tubes is in the range of 3.2, which is in the acceptable limit.

Experimental and ensemble machine learning analyses of heat transfer, friction factor and thermal performance factor of rGO/water nanofluids in a tube

This paper explains about the experimental evaluation of thermophysical properties, heat transfer coefficient, Nusselt number, friction factor, and thermal performance factor of water-based reduced graphene oxide (rGO) nanofluids passes through a tube under turbulent flow conditions. The rGO nanoparticles in this study was prepared based on the Hummer's procedure. The thermophysical properties were estimated at different volume loadings from 0.5 % to 2.0 % and at different temperatures from 20 °C to 60 °C, respectively, similarly, the heat transfer and friction factor experiments were conducted in the Reynolds number ranging from 1800 to 21,000. The obtained data of heat transfer coefficient, Nusselt number, friction factor and thermal performance factor was predicted based on the advanced machine learning algorithms of boosted regression tree (BRT), and extreme gradient boosting (XGB), respectively. Results indicated that, at 2.0 % vol. of rGO/water nanofluid the thermal conductivity is raised by 26.95 % at a temperature of 60 °C, viscosity is raised by 63.29 % at a temperature of 20 °C, over base fluid. Moreover, the results are further shown that, at 2.0 % vol. of nanofluid the Nusselt number, heat transfer coefficient, factor in friction, drop in pressure, and pumping power raise of 34.80 %, 44.19 %, 16.73 %, 10.48 %, and 4.55 % at a Reynolds number of 13,705, against water. The correlation coefficient (R2) results predicted from BRT and XGB models for Nusselt number data is 0.9831 and 0.994, respectively. It is understood that the XBG algorithm predicts very accurate values compared to BRT algorithm with a less mean square error. The overall performance of the system was raised by 1.28 -folds than water. Using the experimental data, new Nusselt number and friction factor correlations were proposed.

Heat transfer performance and entropy generation analysis of Taylor–Couette flow with helical slit wall

The turbulent flow between concentric cylinders and its heat transfer performance is studied by the large eddy simulation. The models with longitudinal slit and helical slit spacing in the range from 168 to 672 mm on the outer cylinder are investigated to compare their heat transfer ability. Further, the notion of field synergy and entropy formation serves as the foundation for evaluating heat transfer qualities. According to the results, the enhancement effect of helical slits on heat transfer is better than that of longitudinal slits. Helical slits are more effective in promoting fluid mixing at different temperatures within the annulus. In terms of field synergy, the helical slit models exhibit a smaller field synergy angle compared to the longitudinal slit model at various Reynolds numbers from 3061 to 4592. Results of using helical slits indicate an improved coordination between the velocity and temperature fields. Thermodynamic analysis reveals that the helical slit models have lower entropy generation as compared to the longitudinal slit models. Higher efficiency in energy utilization and superior heat transfer properties of the helical slit models are noticed. Findings of this study provide valuable insights for the optimal design of various rotating machinery applications.

Quantification and correlation analysis of bubble characteristics and heat transfer performance in direct contact heat exchanger

In this work, a combination of morphological processing and watershed algorithm is proposed to measure bubble size, based on which an improved frame difference method is proposed to obtain bubble velocities with an F1 score of 0.96. Empirical equations for the boiling properties of flow in immiscible fluids and their influencing factors are developed. Correlation equations for the Nusselt (Nu) number and Colburn (j) factor are developed, with mean deviations of 5.42% and 5.47%, respectively. The results show that the increase in bubble rise rate and the trend of bubble growth become slower with the increase in the flow rate of the dispersed phase. In contrast, the temperature of the continuous phase has a negative correlation on the bubble growth and almost no effect on the bubble velocity. In addition, the heat transfer coefficient, which increases with the increase of the flow rate of the dispersed phase, has a negative correlation with the initial temperature difference. The main objective of this study is to provide a new method for measuring bubble parameters during direct contact boiling heat transfer and to provide new ideas for studying direct contact boiling heat transfer.

Analysis of heat transfer performance and thermo-hydraulic characteristics of graphene nanofluids: impact of sedimentation effects

This study investigates the heat transfer performance and thermo-hydraulic characteristics of nanofluids containing graphene nanoparticles in a water and ethylene glycol mixture. Results show that both nanofluid samples, with concentrations of 0.15% and 0.10% by volume, experience increased heat transfer coefficients (h) compared to the base fluid under various operating conditions, with average reductions of approximately 21% and 26%, respectively. Additionally, the nanofluids exhibit higher friction losses and pressure drops compared to the base fluid. The friction factor and head loss increased by 8.7% and 7.7% for the 0.15% concentration sample and 12.7% and 12.4% for the 0.10% concentration sample. These findings indicate that the thermo-hydraulic performance of the nanofluids is unsatisfactory, offering limited advantages over the base fluid. Surprisingly, the sedimentation of nanoparticles in the test section leads to unexpected results. Contrary to typical observations, the higher concentration sample shows a lower head loss. This discrepancy is attributed to nanoparticle sedimentation, increasing friction factors, and pressure drops. The study also examines the thermal conductivity and viscosity of the nanofluids. It is found that even at low concentrations, graphene nanofluids exhibit higher thermal conductivity than the base fluid. The dynamic viscosity slightly increases with concentration, aligning well with theoretical models. Further research is needed to optimize nanofluid performance and address these issues in practical applications.

Entropy generation and heat transfer performance analysis of a non-Newtonian NEPCM in an inclined chamber with complicated heater inside

The present research deals with thermic energy storage structures based on nano-encapsulated phase change material with a complicated charger inside the storage system. Flow structures, heat transfer, and entropy generation performance are studied using the partial differential governing equations based on non-Newtonian nature of the working medium. Analysis has been performed numerically using the finite element method. Effects of the cavity inclination angle, inner charger structure, power-law index for non-Newtonian nature of the working liquid, Rayleigh number, and nanoparticles volume fraction on flow structures, entropy generation fields and temperature fields have been studied. It has been found that the considered dilatant working fluid is not effective for the heat transfer applications, because Nusselt number decreases with a growth of the power-law index. At the same time, the cavity inclination angle and inner heater structure can be effective parameters to manage the heat transfer and entropy generation.