Heat Pipe Array Research Articles

Optimization of a cold thermal energy storage system with micro heat pipe arrays by statistical approach: Taguchi method and response surface method

Optimization of a cold thermal energy storage system with micro heat pipe arrays by statistical approach: Taguchi method and response surface method

Heat transfer performance and startup characteristics of separated gravity heat pipe

Separated gravity heat pipes, with distinct arrangements of evaporating and condensing sections, offer low thermal resistance, high heat transfer efficiency, and a simple structure, making them suitable for passive cooling of spent fuel pools through gravity-driven processes. In this study, a steady-state, one-dimensional, two-phase flow model is developed to analyze phase change heat transfer in a separated gravity heat pipe. The research investigates the impact of liquid filling rate and vacuum level on heat pipe operation. The findings reveal a notable increase in pressure drop inside the tube with higher liquid filling rates, which diminishes the adaptability of the heat pipe as pressure rises, resulting in a narrower range of effective liquid filling rates. Specifically, the liquid filling rate of the heat pipe ranges from 38 % to 72 % at P = 13.75 kPa and from 44 % to 68 % at P = 15.75 kPa. Additionally, a startup prediction model is formulated based on a thermal resistance network model using the ideal gas assumption. Two startup states—namely, the initial startup state and the subsequent startup state—are proposed for large-scale separated gravity heat pipe arrays. The heat pipe achieves the large-temperature-difference initial startup state at a 50 % liquid filling rate within 7 min before transitioning to the subsequent startup state. The vapor mass, heat transfer coefficient, and working fluid temperature initially increase and then decrease over time, with varying peak times. As the liquid filling rate increases, the maximum vapor mass also increases. The heat transfer coefficient peaks at a 60 % liquid filling rate before subsequently declining. The optimal liquid filling rate of 60 % is identified based on startup time, heat transfer coefficient, and overall heat transfer efficiency.

Performance analysis and optimization of insulation layers on a novel building-integrated photovoltaic system

Conventional photovoltaic-thermoelectric generator (PV-TEG) systems are hindered by significant heat transfer losses, which impair power generation throughout the year. Addressing this challenge, a novel PV-MCHP-TEG system is proposed, integrating photovoltaic (PV) cell, microchannel heat pipe (MCHP) array, and thermoelectric generator (TEG) module components with strategically placed insulation layers to facilitate year-round, day-and-night power generation. This study primarily investigates the impact of insulation layers on heat transfer processes, employing a comprehensive analysis and optimization approach. Utilizing Simulink software, the multifaceted influence of insulation layer variables, including locations, thicknesses, and materials, on TEG efficiency across various conditions was examined. Further, a comparative analysis was undertaken to evaluate the dynamic payback period across different modes. The optimization of these insulation parameters revealed that incorporating Polyisocyanurate Foam (PIR) as the insulation material in the optimized PV-MCHP-TEG system achieved an efficiency of 19.32 %, marking a 2.41 % improvement over conventional PV-TEG systems without insulation. Furthermore, the dynamic payback period was reduced to 11.34 years, representing a decrease of 1.05 years compared to conventional PV-TEG systems. These findings underscore the potential of our proposed system to outperform existing solutions by optimizing thermal management through insulation, thereby offering a promising avenue for enhancing photovoltaic-thermoelectric energy conversion.

Simulation and optimization on a novel air-cooled photovoltaic/thermal collector based on micro heat pipe arrays

To further enhance the performance of an air-cooled photovoltaic/thermal (PV/T) system, this study integrates micro heat pipe arrays (MHPAs) and serrated fins as the primary heat dissipation components. The lumped-parameter method was utilized to establish a mathematical model for the previously proposed PV/T system based on MHPAs. The model reliability was validated with the test data (errors within ± 10 %). Subsequently, the influence of solar irradiance, ambient temperature, airflow velocity inside the duct, and component structure on the air-cooled PV/T system performance was analyzed and optimized using the method of controlling variables. The impact of varying the condensing section length of the MHPA from 4 to 28 cm on the system performance was analyzed, and it was found that the condensing section length had a relatively small effect on the system thermoelectric performance. When the optimal comprehensive performance was achieved with fin heights ranging from 6 to 18 mm, heat collecting efficiency remained stable at around 19.5 %. When the cross-sectional dimension of the duct was 25 cm, the power generation efficiency reached its maximum value of 12.59 %. Such research findings provide data support for the promotion, development, and wider applications of air-cooled PV/T systems in energy utilization.

Multi-objective optimization of a novel phase-change thermal storage unit based on theoretical modeling and genetic algorithm

Phase-change thermal storage technologies are becoming increasingly indispensable in the field of renewable energy, and researchers have been striving to achieve high thermal storage performance in storage devices. To enhance the application potential of phase-change thermal storage units based on micro heat pipe arrays, theoretical analysis is applied to optimize the operating parameters and the fin structure, addressing the research gap caused by insufficient theoretical analysis. Therefore, an accurate thermal resistance network model is developed, and machine learning algorithms are employed for the multi-objective optimization of the fin structure. The optimal heights, widths, and thicknesses in two directions of the fins are 42.2, 3.7, 0.3, and 0.8 mm, respectively, resulting in a 15.8 % increase in charging power compared to the initial structure without increasing metal consumption. Additionally, it is recommended that the design flow rate be increased by 26 kg/h for each additional thermal storage unit connected in series. Finally, a phase-change thermal storage device is designed for a solar water heating system, and its applicability is simulated and analyzed. This study provides design guidance for this novel thermal storage device and promotes its application in the field of renewable energy.

A hybrid battery thermal management system composed of MHPA/PCM/Liquid with a highly efficient cooling strategy

Hybrid battery thermal management system (BTMS) has received a lot of attention lately because of its excellent heat dissipation. However, the performance of hybrid BTMS is impacted by several elements, including basic technologies, structural design, and control methods. To improve the temperature and temperature uniformity of prismatic batteries, a novel hybrid BTMS composed of the U-shaped micro heat pipe array (U-MHPA) and the liquid cold plate filled with composite phase change material (cPCM) was proposed. Furthermore, a performance evaluation method and delayed cooling strategy were proposed and used to optimize the hybrid BTMS. Results showed that adhering a U-MHPA to the surface of the battery can effectively mitigate temperature non-uniformity in the prismatic battery. The cold plate filled with cPCM addressed the issue of significant temperature gradients parallel to the long flow direction of the cold plate. Compared to the single liquid cooling, the hybrid BTMS exhibited outstanding cooling performance under extreme operating conditions, reducing the Tmax of the battery module by 4.2 °C and the ΔTmax by 8.39 °C. The delayed cooling strategy based on the principles of phase change reduced the energy consumption of the hybrid thermal management system by 41.7%.

Thermal characteristics of solid-state battery and its thermal management system based on flat heat pipe

Solid-state batteries (SSBs) offer promising potential for commercial applications due to their high energy density and elimination of the flammability associated with conventional liquid electrolyte batteries (LBs). Taking into account both experimental and simulated outcomes, the SSB generates more heat than LB, which leads to a higher temperature rise. To effectively address this issue, a hybrid battery thermal management system (BTMS) with micro heat pipe array (MHPA) and air-cooling was developed in this work for the solid-state battery pack (SSBP). In parallel, an electro-thermal coupling model at the pack level considering parallel branch current distribution and an equivalent thermal resistance-based MHPA model were developed. The models were verified by comparing the experimental and simulated results on the 2-parallel and 1-series connected (2P1S) battery pack and the BTMS. A maximum average absolute error (AEave) of 1.11 °C, an average relative error (REave) of 1.62 %, and a root mean square error (RMSE) of 0.88 °C were considered. The simulations were conducted to compare the temperature rise of the battery pack with MHAP and aluminum plate cooling. In the 35 °C-35 °C-6 m/s cooling condition and at 1.5C discharge, the pack temperature reached 52.21 °C with aluminum plate cooling, 8 °C higher than that with MHPA. Moreover, the simulations predicted the temperature, current, and state of charge distributions of 3P4S connected SSBP and LB pack (LBP) based on the hybrid BTMS at different cooling conditions. The results showed that the temperatures of SSBP and LBP were controlled within 43 °C even at 35 °C ambient temperature. Reducing the air temperature had a stronger cooling capacity than increasing the air speed. However, the temperature gradient was exacerbated to 3.29 °C and 1.54 °C in the SSBP and LBP. The impact of temperature difference on the resistance worsened the current inhomogeneity in the parallel branch and led to a maximum state of charge (SOC) difference of 5.59 % within the SSBP and 0.56 % in the LBP. Thus, to achieve an efficient cooling of SSBPs with higher heat loads, a more balanced consideration of the induced thermal-electrical homogeneities is required.

Performance analysis of a battery thermal management system based on phase change materials with micro heat pipe arrays

Lithium-ion battery packs generate high-level heat under harsh and rigorous conditions. The inadequate heat dissipation results in high pack temperature above the safe operating range. This study investigates an efficient and cost-effective battery thermal management system based on phase change materials and a micro heat pipe array. The battery is treated as a single domain. A battery pack with six series stacked batteries is analyzed using the Newman-Tiedemann-Gu-Kim model. The thermal performance of a battery thermal management system is analyzed using phase change materials with various melting temperature values, ambient temperature, and convective heat transfer coefficients of micro heat pipe arrays. Results show that the maximum temperature of the cooling system with micro heat pipe arrays and phase change materials is 33.8 °C, which is reduced by 22.3 % and 7.8 % compared to the air-cooled and cooling system with micro heat pipe arrays. At forced convection of 50 W·m−2·K−1, the maximum battery temperature values for the phase change material RT31, RT35, and RT42 are reduced by 11.8 %, 8.9 %, and 5.4 % compared to those at forced convection of 5 W·m−2·K−1. Under short-circuit conditions, the cooling system with micro heat pipe arrays and cooling system with micro heat pipe arrays − phase change materials reduce the maximum battery temperature by 12.4 % and 29.9 % compared to the air-cooled system. Results show that the developed model for the battery thermal management system provides a reference for designing phase change materials with micro heat pipe arrays.

Performance investigation of a novel flat-plate solar air collector with L-shaped dual micro heat pipe arrays

To improve the thermal performance of solar air collectors by reducing heat leakage and fully transporting the heat absorbed in the evaporation section, this paper proposes a structural innovation based on previous research, that is, L-shaped dual micro heat pipe arrays integrated with a flat-plate solar air collector with a double glazing cover. Experiments are conducted to investigate the thermal performance of the proposed collector. The effects of solar irradiation, ambient temperature, and air flow rate on thermal performance are reported. Thermal resistance is analyzed theoretically. The application performance of the collector is evaluated based on a typical rural building heating model. The results show that the average heat collection efficiency is 49.72 %, 55.69 %, 59.37 %, and 61.48 % for air flow rates of 80, 120, 160, and 200 m3/h, respectively. The evaporation section temperature is reduced by a maximum of 25.28 °C under flow rates of 200 m3/h. The performance of the solar collector is more significantly influenced by solar irradiance than by ambient temperature. The average thermal efficiency is linearly related to the normalized temperature difference. The CO2 reduction over the lifetime of the device is 15040.09, 19287.80, and 5662.95 kg compared with the use of conventional bulk coal, electricity, and natural gas, respectively.

Thermal performance of flat plate heat pipe array with surface wettability modification: An experimental and simulation study

Surface wettability has a significant effect on the heat transfer characteristics of the flat plate heat pipe array (FPHPA). In this study, an aluminum based FPHPA measuring 250 × 100 × 3 mm3, comprising of 9 independent channels, was developed to investigate the impact on wettability segmented modification through experiment and simulation. After chemical etching, the micro-nano structure of the surface can produce a hydrophilic effect, while hydrophobic effect can be achieved after spraying polydimethylsiloxane mixture, and the two modification methods passed the heat resistance and durability tests. The FPHPA, equipped with a hydrophilic evaporator, a hydrophobic adiabatic, and a condenser, exhibited enhanced heat transfer characteristics, lower wall temperature, a higher heat transfer limit, and reduced sensitivity to inclination angle. Simulation results revealed that the hydrophilic surface promoted bubbles to break away from the wall surface and improved the critical heat flux of the evaporator, while the hydrophobic surface had a faster droplet return rate and a thinner liquid film thickness, which improved the convective heat transfer coefficient of the condenser. Compared to conventional flat heat pipes, hybrid wetting modified FPHPA shows a higher overall effective thermal conductivity at thermal powers above 90 W. The findings from this study contribute to a better understanding of the heat transfer mechanism following surface modification and offer a practical method for modifying FPHPA.

Experimental study on 18650 lithium-ion battery-pack cooling system composed of heat pipe and reciprocating air flow with water mist

Lithium-ion batteries (LIBs) are critical power sources for portable devices, electric vehicles, power grids, and energy-storage systems. Effective thermal management is mandatory for achieving optimal battery performance. Although the air-cooling method has been investigated extensively owing to its simple structure, convenient maintenance, and low cost, it is insufficient for cooling large-scale battery packs because of its limited air-cooling capacity and unsatisfactory temperature uniformity. Thus, a reciprocating spray cooling system comprising a reciprocating air flow channel, heat pipe array, and spray nozzle is proposed herein for the efficient cooling of 18,650 LIB packs. The effects of the inlet air speed, spray frequency, and spray duty cycle on the cooling performance of the reciprocating mist cooling system and the corresponding optimal operating parameter range are analyzed. Additionally, the competitive mechanism between forced air convection and evaporative cooling is discussed. The results indicate that, compared with the case of natural convection cooling, the temperature increment of the battery pack decreases by 32.1 % under reciprocating mist cooling. Meanwhile, the maximum temperature difference reduces to approximately 3.41 °C with 3C of discharge. The spray frequency minimally affects the overall heat dissipation but induces surface temperature fluctuations in individual batteries. Increasing the spray duration per 10 s in a single spray duty cycle can reduce the average temperature of the battery pack by approximately 2 °C. Additionally, the power-allocation scheme affects the heat dissipation of the system. Decreasing the flow rate of spray cooling water and increasing the inlet air speed promote the evaporation of water mist inside the system, thus further improving heat dissipation. This study provides new insights into the design of air-cooled thermal management systems for battery packs.

Cooling performance of a mhpa@mof based hybrid passive battery thermal management system for a module with large-capacity prismatic lithium-ion battery

Metal-organic frameworks are beginning to be employed in the thermal management system of lithium-ion batteries because of its high water absorption and enthalpy of phase change. However, its cooling performance is only preliminarily explored used in small cylindrical cells or a single large cell. The effect on multiple large-capacity cells has not be verified yet. In this study, a micro heat pipe arrays@MIL-101(Cr) hybrid battery thermal management system is proposed, and its cooling performance of different number of battery modules at different discharge rates is studied. Experimental results show that MIL-101(Cr) is evenly distributed, and the water vapor adsorption capacity reached 1.65 g/g. The maximum temperature of the micro heat pipe arrays@MIL-101(Cr) group was 36.42?C in the experiment of the four-cell battery pack at 1C discharge rate, which was 12.98?C lower than that of the natural cooling group and 3.05?C lower than that of the micro heat pipe arrays group. With the increase of the number of cells, the maximum temperature of the battery pack rises from 43.12?C to 47.37?C, and the temperature difference rises from 1.53?C to 5.57?C at 2C discharge rate. As the discharge rate increases, the maximum temperature of the battery consisting of four cells rises from 36.42?C to 47.37?C, and the maximum temperature difference rises from 2.87?C to 5.57?C, which suggests that the current micro heat pipe arrays@MOF based battery thermal management system be combined with an active thermal management system to ensure temperature control in high-rate and multi-battery modules.

An Effective Cooling Scheme Using Micro Heat Pipe Array for Electrical Machines with Distributed Windings

An Effective Cooling Scheme Using Micro Heat Pipe Array for Electrical Machines with Distributed Windings

Experimental research on thermoelectric characteristics of a thermoelectric generator with external influencing factors optimization

The external influencing factors, the thermal interface material, load-bearing brick weight, and temperature difference, of a thermoelectric generator (TEG) device were experimentally examined. The micro heat pipe array (MHPA), as one novel thermal interface material, was investigated. The multi-variable coupling approach is used to analyze the intrinsic coupling correlation of the external influencing factors. The dimensionless synthesis economic factor index was proposed to analyze the improvement of thermoelectric characteristics, which can quickly assess the contact thermal resistance of different thermal interface materials. The results showed that the load power and load voltage generally increase with increased temperature differences. The contact thermal resistance decreases with increased load-bearing brick weight, but the decrement gradually decreases. The thermal interface material plays an important role in thermoelectric characteristics. The load-bearing brick weight performs little impact on the non-thermal interface material (NTIM) scheme. The two thermal conductive silicone grease schemes noticeably reveal better thermoelectric characteristics than those of the graphite paper schemes, although the thermal conductivity of thermal conductive silicone grease are much lower than that of graphite paper. The MHPA scheme exhibit the best thermoelectric characteristics, and its dimensionless synthesis economic factor index can be up to 371.81 %.

Study on the performance of oil fume heat recovery heat exchanger based on micro heat pipe array

In China, the utilization of high-temperature flue gas waste heat recovery has been widely studied and developed, while the large number of low-temperature flue gas waste heat recovery has not been fully developed. Therefore, research has been conducted on the heat transfer characteristics of plate heat exchangers for low-temperature oil fume. The heat exchanger were 28–44 ℃ at the hot end and − 10 to 5 ℃ at the cold end. The outlet temperature, wind speed, etcetera were measured and recorded by changing indoor and outdoor temperature, variable flow rate and variable fin size. The impact of different working conditions on heat transfer and heat transfer efficiency of the heat exchanger was analyzed. The result showed that within the range of effective experimental test temperature, the variation trend of Nu and h was the same for heat exchangers with different finned fins and heat pipes with a different liquid-filled working medium The Nu value increased linearly with the increase of the Reynolds coefficient (Re), and the heat transfer coefficient presented a quadratic curve and increased with the increase of Re. Smaller fins had a higher efficiency and higher heat transfer. The heat exchange efficiency was stable between 0.75 and 0.97, which was higher than the value required by the national standard. At the same time, the heat exchanger also met the demand for high-efficiency heat recovery at low outdoor temperature, which has a wide application prospect.

Characteristics of heat, power generation, and energy efficiency study on a novel air-cooled PEMFC stack based on micro heat pipe arrays

This study introduces a novel kilowatt-scale air-cooled proton exchange membrane fuel cell stack utilizing micro heat pipe arrays (MHPA-PEMFC stack). This innovative stack design addresses issues commonly associated with conventional air-cooled fuel cell stacks, such as low heat transfer efficiency, suboptimal performance, and safety concerns, especially during high-load operations. In addition to the output performance of the stack, this study investigates the heat and power generation performance limits, operational security, and energy utilization efficiency of the MHPA-PEMFC stack under high power output and varying flow rates. The study introduces two novel evaluation indexes, namely, relative load gain (RLG) and relative safety gain (RSG), to provide a comprehensive evaluation. These indexes are utilized to link energy efficiency and exergy efficiency to the performance of the MHPA-PEMFC stack. The results show that the MHPA-PEMFC stack exhibits superior heat dissipation performance, uniform temperature distribution, and enhanced load capacity and safety compared with conventional PEMFC stacks. The maximum RLG and RSG achieved by the MHPA-PEMFC stack are 100% and 7.53, respectively. The energy efficiency of the MHPA-PEMFC stack surpasses 29% while maintaining a guaranteed maximum RLG. Notably, a higher RSG leads to a sacrifice in both energy and exergy efficiency.

Performance simulation of novel heat pipe type phase change thermal storage device

Given that the performance of the phase change thermal storage device (PCTSD) is limited by the low thermal conductivity of the phase change material, more effective heat transfer structures should be developed to improve the thermal storage rate. In this paper, a novel micro heat pipe array (MHPA)–PCTSD with a highly rational heat transfer structure is proposed to understand the influence mechanism of the relative positions of the MHPA and heat transfer channel. The arrangement of the heat transfer fluid (HTF) channels on both sides of the MHPA (Type A) and the arrangement of the MHPA on both sides of the HTF channel (Type B) are numerically modeled in three dimensions, and the thermal storage performance is analyzed. Results show that Type B has a significant advantage over the traditional heat pipe PCTSD and Type A, which can obtain better temperature uniformity and more reasonable thermal resistance distribution. Moreover, its total thermal resistance and melting time are 17.4% and 21% lower than those of Type A, thus confirming its higher optimization potential.

A numerical study on the effect of condenser fin in micro heat pipe array based evacuated tube collector for water heating

A numerical study on the effect of condenser fin in micro heat pipe array based evacuated tube collector for water heating

Experimental investigation on the optimization of different filling ratios for large-size flat plate heat pipe array

To meet the increased heat dissipation demands of 5G base stations, a flat plate heat pipe array (FPHPA) of 500 × 200 × 3 mm3 comprising of 19 independent channels is developed. To investigate the thermal performance of the FPHPA under different filling ratios (FR) and heat powers (30–300 W), a multi-channel independent filling system is designed to conduct two experimental cases: uniform or asymmetric filling of all channels. Results indicate that 30 %–70 % FR exhibits better thermal performance and can replace the aluminum plate over a broader heat power range. Furthermore, separate tests are conducted to evaluate the heat transfer and start-up performance of the FPHPA. The optimal filling ratio interval of single channel at different heat fluxes is derived through asymmetric filling. Subsequently, a mixture model is proposed and compared with the uniform filling ratio case, resulting in optimized heat transfer performance. The optimized FPHPA provides better heat transfer performance, effectively reducing the area averaged wall temperature and ensuring the normal operation of the 5G base station.

Performance of a BAPVT modules coupled TEHR unit fresh air system based on micro heat pipe array

Energy consumption for heating and cooling fresh air has become a major component of building energy consumption, and there is a growing focus on highly-efficient and energy-conserving fresh-air treatment technology. This paper presents a new fresh-air system based on a high-efficiency heat transfer element, the micro heat pipe array (MHPA). It consists of a novel air-cooled building attached to a photovoltaic/thermal module (MHPA-BAPVT) and a thermoelectric heat recovery unit (MHPA-TEHR). The system uses solar energy, photovoltaic power generation, and waste heat for fresh air preheating. A series of fresh-air systems were designed, constructed, tested, and analyzed. The results reveal that on sunny winter days, the temperature of fresh air flowing through MHPA-BAPVT modules can increase by 22.15 °C. The average thermal and electric efficiency of the MHPA-BAPVT modules was 12.16% and 7.10%, respectively, and MHPA-TEHR could exceed the upper limit of passive heat recovery technology, which could generate 1.25 kW of heat per 1 kW of input electric power. The maximum ratio of total heating power to the total power consumption of the fresh-air system reached 14.94. During a typical day in the winter season, solar preheating exceeded the fresh air heat requirement by 24.34%, and the excess heat provided 292.92 MJ for building heating demand. Comparing the electric heating fresh-air unit with conventional heat recovery, the former achieved nearly zero energy consumption during the winter season. During the transitional season, the system could provide 711.82 MJ of solar energy, which improved the indoor temperature. Finally, using the experimental data and meteorological parameters of Zibo, the annual heat and electricity benefits and reduced carbon dioxide emissions of the fresh-air system were calculated. The fresh-air system in this study can fully utilize solar energy for heat collection and power generation to reduce building energy consumption and can be applied widely.