Improved Heat Transfer Research Articles

Study on heat transfer characteristics and enhancement mechanism of supercritical carbon dioxide in adaptive channels

Supercritical CO2 power cycles have promising applications in many fields, the heat transfer of supercritical CO2 is critical to the efficiency and safe operation of cycle system. The adaptive channel was previously proposed by our group to improve heat transfer of supercritical CO2, the performance of heat exchanger with adaptive channel was experimentally studied. Whereas the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism remain unclear. In this study, the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism are analyzed numerically based on a single channel, the effect of structure on heat transfer is analyzed through the maximum wall temperature and average heat transfer coefficient under the same length and heat transfer area. The results reveal adaptive channel is effective at alleviating heat transfer deterioration with no local peak in wall temperature distribution. The channel variation length of adaptive channel need to be increased from 0.4 to 0.8 with the aggravation of heat transfer deterioration in order to eliminate local wall temperature peak. For the heat transfer deterioration conditions, the maximum wall temperature lowers first and then increases as channel variation length increases, there is a length that makes the maximum wall temperature lowest, which is lowered by more than 40 °C compared with straight channel. The average heat transfer coefficient can be increased by 1.1 ∼ 1.5 times as channel variation length increases. For the no heat transfer deterioration conditions, the maximum wall temperature increases about 30 °C whereas average heat transfer coefficient can be increased by 58 %∼76 % with channel variation length increasing. The mechanism of adaptive channel alleviating heat transfer deterioration is as follows: the fluid velocity always presents an inverted U-shaped distribution along the radial direction in adaptive channel, the radial density difference is less and buoyancy effects heat transfer weakly. The turbulent kinetic energy is kept at high, so the heat near the wall is transferred to the main flow timely.

Potential application of graphene-based nanofluid for improving heat transfer characteristics: a review

Potential application of graphene-based nanofluid for improving heat transfer characteristics: a review

Performance analysis and optimization of solar air heater with double-pass configuration using perforated blocks and semi-circular tubes as artificial roughness

The low heat transfer and thermal efficiency of the solar air heater are primarily caused by the formation of a thermal boundary layer along the absorber plate, which contributes to the low convective heat transfer coefficient between the absorber and air. The use of different artificial roughness geometries enhanced the turbulence that help to supress region of hot spot on the absorber plate more effectively and reduce the thermal boundary layer on the absorber for improved heat transfer. In light of this, the present study explores the double-pass configuration of solar air heater equipped with perforated blocks and semi-circular tubes together as artificial roughness on the performance metrics. The mathematical modeling is performed to evaluate the effect of design parameters: tube amplitude ratio (at/Hd), open area ratio (β) and blockage height ratio (eb/Hd), on thermal and effective efficiency at different Reynolds numbers (Re) and solar irradiation (I). Among the parameters studied, the maximum thermal efficiency is found to be 85.36 %, at eb/Hd of 0.8, at/Hd of 0.3, β of 30 %, Re of 19,000 and I of 1000 W/m2. The maximum effective efficiency has been evaluated, which is found to be 81.89 %, at at/Hd of 0.3, eb/Hd of 0.4, β of 30 %, Re of 11,000 and I of 1000 W/m2. In addition, novel correlations have been established for thermal and effective efficiency, showing absolute percentage errors of 0.2 % and 2.2 % respectively. The results indicate enhanced performance in terms of both thermal and effective efficiency, outperforming earlier designs.

Numerical investigation of electrically conducting thin film flow and heat transfer improvement for various shaped $$Sn-PG$$ and $$W-PG$$ nanofluids over an unsteady curved stretching surface

Numerical investigation of electrically conducting thin film flow and heat transfer improvement for various shaped $$Sn-PG$$ and $$W-PG$$ nanofluids over an unsteady curved stretching surface

Computational study of magnetohydrodynamic mixed convective flow in a nanofluid-filled cavity with diagonally moving lid

This study examines the phenomenon of uniform magnetohydrodynamic mixed convective flow in a cavity filled with nanofluid. The research focuses on analyzing the mixed convection induced by a uniformly heated lid-driven cavity with diagonal motion. The fluid and heat transport equations are solved using the finite volume method. Numerical simulations are conducted for various parameters including Richardson number (Ri) ranging as 0.1, 1 & 10, Hartmann number (Ha) 0, 10, 25 & 50, angle of inclination (γ) 0°, 30°, 45°, 60° & 90°, and solid volume fraction from 0.0 to 0.05. The results are presented in terms of flow and thermal fields. It is observed that higher Hartmann numbers and inclination angles of the magnetic field lead to a suppression of convection, favoring a dominant conduction mode and reducing the overall heat transfer rate. Specifically, the study highlights a significant enhancement in the heat transfer rate in a nanofluid-filled cavity with a diagonally moving wall. The movement’s of diagonal wall has significant power consumption, the tool may be used in an industrial process that improves heat transfer, offers flexibility, and raises the quality of the finished product. Additionally, the correlations that were found are a useful tool for heat exchanger design.

Investigation of a dual-spiral flat plate solar water heater under natural convection: an experimental study

In residential and industrial areas, a flat plate solar collector (FPSC) is an important technology that allows for direct solar energy utilisation for heating water. Conventional FPSCs have relatively low efficiency. More study is needed to increase the efficiency of FPSC by using novel designs. Modifications to the design of solar collectors are always a viable option for improving thermal efficiency significantly. In this study, dual spiral-shaped flow tubes were constructed instead of the usual flat plate solar collector's number of riser tubes and headers and tested with three different mass flow rates (0.0058, 0.0083, and 0.0117 kg/s). The optimum instantaneous efficiency achieved is 70.8% at a flow rate of 0.0117 kg/s, representing a 13.7% improvement in efficiency compared to the conventional collector. The modified collector achieves its highest instantaneous efficiency when the outlet water temperature is measured at 53.4°C. The modified collector improves heat transfer by increasing surface contact area of water and increasing the flow residence time. This results in a higher absorption of heat by the water, leading to a significant enhancement in the efficiency. When all other parameters are kept the same as in a conventional design, highly encouraging results in modified solar collector have been recorded.

Thermal performance enhancement of borehole heat exchanger by thermally induced groundwater convection in fractured rock

Thermal performance enhancement of Borehole Heat Exchanger (BHE) was a key to sustain the high effectiveness of this technology. Many measures have been taken to improve heat transfer efficiency of BHE in the past decades. However, all these changes leaded to slight thermal improvement due to restriction of heat conduction dominated heat transfer process in subsurface. To achieve an alternatively higher heat transfer mode of BHE, this study proposes a novel approach to induce groundwater thermal convection in fractured rock. A borehole was backfilled by gravels to sustain free groundwater flow in fracture network. A series of Thermal Response Tests (TRTs) show the fluid temperature of a gravel-filled BHE is 2.0–––2.4 °C lower than a sand-bentonite mixture grouted BHE, indicating the higher cooling efficiency. Two main factors including fracture dip angle and aperture, determine the flow behavior of a fracture network. The flow speed increases linearly with enlarging dip angle and shows a cubic polynomial relation with fracture aperture. Physical model tests show that the BHE induces groundwater convection flow by forming a circuit which couples with heat convection, mitigates the thermal stagnation around a borehole. As a result, thermal performance of a BHE was improved effectively.

Effect of an Adiabatic Obstacle on the Symmetry of the Temperature, Flow, and Electric Charge Fields during Electrohydrodynamic Natural Convection

This study explores the impact of an adiabatic obstacle on the symmetry of temperature, flow, and electric charge fields during electrohydrodynamic (EHD) natural convection. The configuration studied involves a square, differentially heated cavity with an adiabatic obstacle subjected to a destabilizing thermal gradient and a potential difference between horizontal walls. A numerical analysis was performed using the finite volume method combined with Patankar’s “blocked-off-regions” technique, employing an in-house FORTRAN code. The study covers a range of dimensionless electrical Rayleigh numbers (0 to 700) and thermal Rayleigh numbers (102 to 105), with various obstacle positions. Key findings indicate that while the obstacle reduces heat transfer, this can be counterbalanced by electric field effects, achieving up to 165% local heat transfer improvement and 100% average enhancement. Depending on the obstacle’s position and size, convective transfer can increase by 27% or decrease by 21%. The study introduces five multiparametric mathematical correlations for rapid Nusselt number determination, applicable to numerous engineering scenarios. This work uniquely combines passive (adiabatic obstacle) and active (electric field) techniques to control heat transfer, providing new insights into the flow behaviour and charge distribution in electro-thermo-hydrodynamic systems.

Thermo‐hydraulic analysis of wavy microchannel heat sinks with porous fins based on field synergy principle

AbstractIn order to enlarge the area and intensity of convective heat transfer among the coolant and heated surface, the vertical fins of microchannel heat sinks (MCHSs) with microencapsulated phase change material slurry (MPCMS) as coolant are arranged into wavy porous channels to realize more heat being dissipated to the outside. The phase transition of microencapsulated particles in laminar flow state is described, and the Brinkman–Forchheimer–Darcy model based on volume average approach and the energy equation for local heat equilibrium are adopted to portray flow and heat transfer in porous medium. The impacts of geometrical parameters on flow and heat transfer behaviour of wavy porous MCHS are numerically analyzed, and performance evaluation factor (PEF) is defined to estimate the thermo‐hydraulic capability of heat exchanger. The numeric outcomes match well with the experiments. Results indicate that MPCMS has a significant heat transfer improvement in the newly designed channel configuration compared with the coolant fluid flowing in the straight microchannel. Based on field synergy principle, the comprehensive capability enhancement mechanism of MPCMS in new MCHS is explored, and its superior thermal performance can be attributed to the improvement of the synergistic degree among flow and temperature fields, and its reasonable structural design can effectively improve the heat rejection capacity in the limited space.

A novel composite bionic leaf vein and honeycomb microchannel heat sink applied for thermal management of electronic components

Based on the bionic concept and fractal theory, a composite bionic microchannel radiator based on veins and honeycombs is designed in this work to address the problem of heat dissipation in electronic components. The convective heat transfer within the novel microchannel structure is numerically investigated, and the effects of the coolant (Fe3O4-water nanofluids) and the surface bump structure on the overall performance of the microchannel are explored. Compared to the traditional ordinary leaf vein-shaped fractal microchannels, the proposed microchannel heat sink in this work demonstrated a significant heat dissipation effect, with an optimal increase in the Nusselt number of 64.5%. The best microchannel heat dissipation was achieved using Fe3O4-water nanofluids with a mass fraction of 0.5%. Additionally, changing the height and arrangement of the bump structure allows for improving heat transfer by a maximum of 8% compared to microchannels without the bump structure. Furthermore, the novel bionic microchannel heat sinks are evaluated, and the resulting optimized microchannel structure has a comprehensive performance index of 1.11. Overall, the study results provide useful information and serve as a reference for designing new bionic heat sinks for the thermal management of electronic components.

Flow boiling characteristics in a microchannel heat sink with a condensing cover plate

Flow patterns and heat transfer characteristics during flow boiling in a microchannel heat sink with a condensing cover plate have been numerically investigated. The phase-field model is used to analyze the effects of different thermal conditions of the condensing cover plate on the bubble dynamics and heat transfer characteristics. Further, the effects of the wettabilities of the cover plate and the heating surface on the bubble evolution have been studied for different values of coolant mass flux. The condensing cover plate maintained at 50 °C significantly improves heat transfer performance with an enhancement of 23.97 % compared to the condenser plate maintained at 80 °C and a 27.35 % improvement compared to an insulated cover plate. The hydrophobicity of the condensing cover plate facilitates vapor bubble evacuation from nucleation sites, producing maximum heat transfer at a contact angle of 130°. Heat transfer performance decreases beyond the 130° contact angle due to the bubble attachment to the condensing cover plate and impeding subsequent nucleation from the cavity. The maximum heat transfer is observed for the heating surface with a contact angle of 60°. The heat transfer in the microchannel is deteriorated below and above this contact angle. At low coolant mass flux, the heat transfer is controlled by bubble nucleation. After reaching a steady state, the combined effects of bubble nucleation and liquid inertia affect the bubble generation frequency and heat transfer in the microchannel.

Numerical assessment of thermomagnetic convection of ferrofluid in a porous cavity employing a local thermal nonequilibrium model

Utilizing a two-temperature model, this study investigates the thermomagnetic convection of a ferrofluid within a porous cavity. The cavity is heated from the bottom and cooled from the sides to establish thermo-gravitational convection, whereas the thermomagnetic convection is induced by permanent magnets. The equations that govern flow and heat transfer are discretized using the finite volume method and the SIMPLE algorithm. The first part of the study evaluates the impact of the permanent magnet’s position on the flow pattern and ferrofluid and solid temperature fields. The results showed that positioning the magnet at the bottom of the cavity enhances heat transfer rate. The second part investigates the impact of the distance between two magnets at different magnetic, Rayleigh, and Darcy numbers, as well as the conduction ratio. The numerical findings exhibit that the heat transfer rate attains a peak at a certain distance between the magnets, depending on the Rayleigh number. With increasing Rayleigh number and conduction ratio, or decreasing Darcy number, the role of the magnetic field in improving heat transfer becomes less important. It is observed that thermomagnetic convection is replaced by thermo-gravitational one at high conduction ratios. The study emphasizes the need to use a local thermal non-equilibrium model in porous media with high magnetic and Darcy numbers, as well as large conduction ratios, to accurately capture the heat transfer phenomenon. It is observed that by placing two magnets at an appropriate distance, the heat transfer rate could be augmented by more than 136 %.

Experimental and numerical analysis of heat sink using various patterns of cylindrical pin-fins

The increasing heat generated by electronic devices requires effective dissipation methods. This research proposes a unique pin-fin (PF) design inspired by cylindrical pin-fins, including three patterns: cross-pin-fins (CPFs), parallel-pin-fins (PPFs) and double-cross-pin-fins (DCPFs). The study examines the hydrothermal performance of these designs within Reynolds numbers of 4500 to 18,000 and heat fluxes of 445 W/m² to 2281 W/m². The PF design aims to maximise performance by increasing surface area and airflow turbulence. Experimental data confirmed the computational results for the PF and CPF heat sinks, exhibiting significant agreement. A numerical study evaluated the hydrothermal performance, revealing that DCPFs deliver a superior performance. As the diameter expands, the Nusselt number (Nu) rises significantly across each design, with increases of 100 %, 162 % and 328 % for the PPFs, CPFs and DCPFs, respectively. Each configuration achieved a Heat Transfer Performance Factor (HTPF) exceeding 1, indicating improved heat transfer efficiency over the friction factor. The heat sink comprising the DCPFs achieved a high HTPF of approximately 2, irrespective of the Reynolds numbers and heat fluxes, demonstrating its effectiveness in heat dissipation compared to other designs.

An assessment of the performance of heat transfer enhancement for optimizing high-temperature thermal energy storage

Background: High-temperature phase change materials (PCMs) are increasingly recognized for their potential in applications such as solar energy utilization, industrial waste heat recovery, and power load regulation. These materials can store and release significant amounts of latent heat, making them highly efficient for thermal energy storage. Purpose: This study aims to propose and analyze a novel structure to enhance latent heat energy storage using a graphite sheet combined with a PCM (KNO3-NaNO3) with a melting point of 220 K. The focus is on improving heat transfer efficiency and understanding the parameters affecting the exothermic process. Research Design: A numerical simulation approach was employed, using Fluent 7.1 software to analyze the exothermic process. The simulation method was validated with two examples before being applied to study the energy storage system incorporating graphite sheets. Study Sample: The study analyzed the performance of a high-temperature thermtotal energy storage (HTTES) system using graphite sheets of varying thicknesses, tube spacing, tube temperatures, and PCM thermal conductivities. Data Collection and/or Analysis: The study utilized numerical simulations to examine how different parameters i.e. thickness of graphite sheets, spacing between tubes, tube temperatures, and the thermal conductivity of PCM—affect heat transfer efficiency and exothermic time. Results: The integration of graphite sheets with a thickness of 2 mm was found to significantly improve heat transfer efficiency. The results indicated that increasing the spacing between graphite sheets and tube diameter influenced the total exothermic time. A logarithmic relationship was observed between the thermal conductivity coefficient and exothermic time, suggesting diminishing returns beyond 3.5 W/(m·K). Additionally, increasing the quantity of graphite sheets enhanced heat transmission and overall system efficiency. Conclusions: The study provides valuable insights into the performance of HTTES systems, demonstrating that incorporating graphite sheets can significantly enhance heat transfer and system efficiency. These findings guide the design of more effective thermal energy storage systems, supporting the broader adoption of HTTES technologies and contributing to the transition toward sustainable energy solutions. Further research and development in this field are essential to drive advancements and promote the widespread implementation of high-temperature thermal energy storage systems. Practical applications The enhanced heat transfer techniques developed in this research offer practical applications across various sectors. These techniques, utilizing PCMs and innovative graphite structures, enhance the efficiency and reliability of high-temperature thermal energy storage systems. This advancement enables continuous power generation in concentrated solar power (CSP) plants, optimizes energy utilization in district heating and cooling systems, and improves industrial waste heat recovery. By implementing these techniques, energy costs can be reduced, system performance can be optimized, and greenhouse gas emissions can be lowered, contributing to a more sustainable energy future.

The significance of quadratic thermal radiative scrutinization of a nanofluid flow across a microchannel with thermophoretic particle deposition effects

Abstract The investigation of thermal radiation and thermophoretic impacts on nano-based liquid circulation in a microchannel has a significant impact on the cooling of microscale equipment, microliquid devices, and many more. These miniature systems can benefit from the improved heat transfer efficiency made possible by the use of nanofluids, which are designed to consist of colloidal dispersion of nanoparticles in a carrier liquid. Understanding and precisely modeling the thermophoretic deposition (TPD) of nanoparticles on the channel surfaces is of utmost importance since it can greatly affect the heat transmission properties. This work examines the complex interaction between quadratic thermal radiation, magnetohydrodynamics, and TPD in a permeable microchannel. It aims to solve a significant knowledge gap in microfluidics and thermal and mass transport. The governing equations are simplified by applying suitable similarity restrictions, and computing solutions to the resulting equations is done using the Runge‒Kutta Fehlberg fourth‒fifth-order scheme. The results are shown using graphs, and significant engineering metrics are analyzed. The outcomes show that increased Eckert number, magnetic, and porous factors will improve the thermal distribution. Quadratic thermal radiation shows the greater thermal distribution in the presence of these parameters, while Linear thermal radiation shows the least thermal distribution. The rate of thermal distribution is higher in the linear thermal distribution case and least in the nonlinear thermal radiation case in the presence of radiation and solid fraction factors. The outcomes of the present research are helpful in improving the thermal performance in microscale devices, electronic devices cooling, health care equipment, and other microfluidic applications.

Numerical investigation on the thermal performance of perforated and non-perforated twisted fins at different twisting angles

The present study numerically investigated the effect of variations in the twisting angle and perimeter of diamond-shaped perforation on the heat transfer of twisted fin heat sinks. The study showed a possible configuration of a heat sink design, aiming to improve heat transfer and the hydrothermal performance factor (HTPF). ANSYS/FLUENT computational fluid dynamics software was used to perform the simulations, and the Reynolds-averaged Navier–Stokes-based k−ε turbulence model was used. Results revealed that a maximum of 46 % enhancement in the Nusselt number and a 25 % increase in (HTPF) could be attained with a twisting angle of 540° in comparison with conventional cylindrical fins. Furthermore, the variation in perforation perimeter at a twisting angle of 540° resulted in a maximum of 28 % enhancement in the Nusselt value and a 36 % enhancement in HTPF in comparison with the twisted fins with no perforations. Therefore, this configuration is recommended as the optimal heat sink configuration.

Enhancing optical and thermohydraulic performance of linear Fresnel collectors with receiver tube enhancers: A numerical study

Linear Fresnel collector system is a type of solar thermal utilization installation. It is mainly used to focus solar radiation on the receiver tube to generate high temperature thermal energy which can be applied in many aspects. This study investigates five different types of receiver tube models using water as the flowing medium, which leads to improving heat transfer performance by means of being equipped with enhancers. The optical results and thermohydraulic performance of the Linear Fresnel collector system are evaluated through Monte Carlo Ray Tracing and Computational Fluid Dynamics (CFD) simulation methods. The obtained optical results reveal that the distribution of energy flux density concentrating on the receiver tube surpasses that of the parabolic trough collector system. In order to maintain an energy reception rate of 90.0% or higher, the installation height range of the receiver tube should be between 1468–1532 mm. When the sun-tracking error increases from 0.0° to 1.0°, the overall optical efficiency of the Linear Fresnel collector system decreases from 98.9% to 79.7%. The thermohydraulic performance shows that the enhancers can generate a swirling flow as its main feature, which effectively promotes the homogenization of the temperature field and destroys the boundary layer near the receiver tube wall, thus greatly improving the convective heat transfer in the receiver tube. However, the introduction of the enhancers also means that the pressure drop loss of the receiver tube increases. Furthermore, the impact of the Kenics mixer's enhancer on heat transfer and flow characteristics is further amplified as the rotation rate decreases, owing to its alternating and complex structure. Through a comparative analysis of the influence of different receiver tube models on Nusselt number (Nu), Frictional resistance coefficient (f) and comprehensive evaluation criterion (PEC) under four rotation rate conditions (y = 6.3, 8.1, 11.34, 18.9), the conclusions present that the receiver tube with an enhancer at a low rotation rate has a larger Nu than that at a high rotation rate, while the Frictional resistance coefficient changes little at different rotation rates. Therefore, the PEC is higher when the receiver tube is equipped with a low-rotation-rate enhancer. Moreover, the receiver tube equipped with a Kenics mixer at a rotation rate of 6.3 was found to be the overall optimum case, with the PEC value varying from 1.47 to 1.73.

Effects of vibration on natural convection in a square inclined porous enclosure filled with Cu-water nanofluid

PurposeThe purpose of this paper is to investigate the effects of gravitational modulation on natural convection in a square inclined porous cavity filled by a fluid containing copper nanoparticles.Design/methodology/approachThe present study uses a system of equations that couple hydrodynamics to heat transfer, representing the governing equations of fluid flow in a square domain. The Boussinesq–Darcy flow with Cu-water nanofluid is considered. The dimensionless partial differential equations are solved numerically using finite difference method based on alternating direction implicit scheme. The cavity is differentially heated by constant heat flux, while the top and bottom walls are insulated. The authors examined the effects of gravity amplitude (λ), vibration frequency (σ), tilt angle (α) and Rayleigh number (Ra) on flow and temperature.FindingsThe numerical simulations, in the form of streamlines, isotherms, Nusselt number and maximum stream function for different values of amplitude, frequency, tilt angle and Rayleigh number, have revealed an oscillatory behavior in the development of flow and temperature under gravity modulation. An increase of amplitude from 0.5 to 1 intensifies the flow stream (from |ψmax| = 21.415 to |ψmax| = 25.262) and improves heat transfer (from Nu¯ = 17.592 to Nu¯ = 20.421). Low-frequency vibration below 50 has a significant impact on the flow and thermal distributions. However, once this threshold is exceeded, the flow weakens, leading to a gradual decrease in heat transfer rate. The inclination angle is an effective parameter for controlling the flow and temperature characteristics. Thus, transitioning the tilt angle from 30° to 60° can increase the flow velocity (from 22.283 to 23.288) while reducing the Nusselt number (from 16.603 to 13.874). Therefore, by manipulating the combination of vibration and inclination, it is founded that for a fixed frequency value of σ = 100 and for increased amplitude (from 0.5 to 1), the flow intensity at inclination of 60° is boosted, and an increase of the heat transfer rate at inclination of 30° is also observed. Convective thermal instabilities may arise depending on the different key factors.Originality/valueTo the best of the authors’ knowledge, this study is original in its examination of the combined effects of modulated gravity and cavity inclination on free convection in nanofluid porous media. It highlights the crucial roles of these two important factors in influencing flow and heat transfer properties.

Improved heat transfer mathematical model forpyramid shaped seasonal heat storage water pit and the influence of boundary conditions

Seasonal heat storage can make use of urban waste heat for low-carbon heating throughout the year. Previous models for pyramid shaped water pit have limited adaptability and ignore the impact of soil temperature in the early stages of operation on the performance of water pits. This article combines two classic mathematical models to establish a mathematical model that can adapt to various sizes of inverted pyramid shaped water pits. The validation of this model was conducted using experimental data from 60000 m3 water pit of Dronninglund, and the influence of boundary conditions for this module were calculated and discussed. The results showed that the root mean square errors of the simulated top, bottom, and average temperature of the water pit were 3.07 °C, 2.39 °C, and 1.37 °C, with relative deviation ratios of 4.25 %, 2.27 %, and 6.62 %, respectively. Furthermore, it was found that for every 5 °C increase in the set average soil temperature, the storage efficiency of the water pits increases by 0.4 %∼0.5 %. In the case of common top insulation of the water pit, the total heat loss at the top, side walls, and bottom are 66.83 %, 31.8 %, 1.37 %. While considering comprehensive insulation in all directions, the heat loss rate for the top, side walls, and bottom are similar with the former, being 67.84 %, 30.79 %, and 1.37 %, respectively. The proposal and findings of this article provide a basis for simplified optimization planning and design of large-scale seasonal heat storage systems.

The influence of turbulators on the flow and heat transfer characteristic of helium-xenon mixture inside the tight lattice rod bundles

The gas-cooled nuclear reactor combined with the closed Brayton cycle is the ideal choice for future high-power space missions. The helium-xenon mixture is a suitable working medium for the reactor due to its good compressibility and heat transfer capacity. For the further development and application of a more lightweight compact reactor, the influence mechanism of turbulator structures with different angles and layouts on the heat transfer enhancement of a helium-xenon mixture in the sub-channel of a gas-cooled nuclear reactor is numerically studied. The results show that the heat transfer is effectively enhanced due to the vortex and secondary flow induced by the turbulator, leading to periodic fluctuations in the Nusselt number. When comparing the results at different angles, it is observed that the heat transfer enhancement from the turbulator at a 90° angle is relatively small, while the pressure drop is significant. Due to the secondary flow in a narrow triangular space induced by a turbulator with a 45° angle, the mixing between high and low-temperature fluids is effectively enhanced, leading to a more significant improvement in heat transfer. The heat transfer performance and thermal efficiency index of different turbulator layouts are summarized and compared, providing a reference for the heat transfer design of gas-cooled nuclear reactors.