Number Of Heat Pipes Research Articles

Heat pipe for thermally coupled fuel cell and metal hydride as well as for cooling metal hydride hydrogen charging

ABSTRACT In this paper, a metal hydride (MH) canister and a PEM fuel cell are coupled using heat pipes to study the minimum number of heat pipes required, the operating range of the fuel cell, and the temperature change patterns of the MH. We account for temperature difference limitations between the fuel cell and the MH (∆T = 35–55 K) on the heat pipe dynamics, which has been neglected in previous similar studies. Since the hydrogen absorption rate of the MH canisters exhibits an initial increase followed by a decrease with increasing temperature, an analysis was conducted to select the appropriate heat pipe under different hydrogen filling pressures. This analysis ensured that the MH canisters remained at the optimal charging temperature (326 K) and achieved the maximum charging rate (6.64 slpm).

Heat Pipe-Based Cooling Enhancement for Photovoltaic Modules: Experimental and Numerical Investigation

High temperatures in photovoltaic (PV) modules lead to the degradation of electrical efficiency. To address the challenge of reducing the temperature of photovoltaic modules and enhancing their electrical power output efficiency, a simple but efficient photovoltaic cooling system based on heat pipes (PV-HP) is introduced in this study. Through experimental and numerical investigations, this study delves into the temperature characteristics and power output performance of the PV-HP system. Orthogonal tests are conducted to discern the influence of different factors on the PV-HP system. The experimental findings indicate that the performance of the PV-HP system is superior to that of the single system without heat pipes. The numerical simulation shows the effects of system structural parameters (number of heat pipes, angle of heat pipe condensation section) on system temperature and power output performance. The numerical simulation results show that increasing the angle of the heat pipe condensation section and the number of heat pipes leads to a significant drop in system temperature and an increase in the efficiency of the photovoltaic cells.

Numerical study of a novel battery thermal management system coupled with heat pipe and cold plate

This study addresses the critical issue of thermal management in lithium-ion batteries, presenting an innovative battery thermal management system that integrates heat pipes and a cold plate (IHPCP). Effective thermal management is crucial for enhancing the performance and longevity of lithium-ion batteries. Using three-dimensional numerical simulations, the study evaluates the impact of various parameters, including the number of heat pipes, the ratio of the plate runner’s width to the heat pipe’s thickness (ω), and the ratio of the cold plate’s thickness to the battery’s thickness (ζ), on battery temperature regulation. The results demonstrate that incorporating heat pipes significantly reduces the maximum battery temperature and improves temperature uniformity. Optimal heat transfer efficiency was achieved with seven heat pipes, resulting in a 21.7% reduction in maximum dimensionless temperature and a 16.4% decrease in temperature variance at a Reynolds number of 100. The Performance Evaluation Criterion (PEC) reached 3.1, indicating superior thermal management performance. This work surpasses previous efforts in the literature by demonstrating the enhanced thermal regulation capabilities of the IHPCP system, offering a compact and efficient solution for battery thermal management.

Influence of Channel Orientation in Air Coolers on the Efficiency of Heat Removal from Powerful Semiconductor Devices

The results of the study of air-cooled coolers with natural and forced heat removal from such powerful semiconductor devices as processors are presented. Experiments were performed in the SOLIDWORKS Flow Simulation software environment to assess the influence of the orientation of the formed thermal channels on the efficiency of heat removal from the surface of a heat-loaded element. Three-dimensional models of tower heatsinks with an installed fan and a supporting structure in the form of heat pipes penetrating fins that form horizontal (model No 1) or vertical (model No 2) air channels have been developed, which made it possible to determine the efficiency of heat removal from the processor during natural and forced convection. The developed model No 1 was rotated by 90°, which may be due to design requirements in the development of technical means. This led to a change in the movement of warm air during natural and forced convection along the vertically directed channels with an analysis of the effectiveness of passive and active cooling. The number of heat pipes has been changed from six to two for previously developed types of radiators (models No 1 and 2), only with active cooling. This made it possible to experimentally establish the influence of design solutions (the number and orientation of heat pipes) in the production of modern air-cooled coolers on the efficiency of heat removal.

Theoretical thermal performance of cross-flow finned heat pipe heat exchanger used for air conditioning in surgery rooms

The thermal efficiency of heat exchangers was applied for theoretical analysis of the thermal performance of a finned heat pipe heat exchanger (FHPHE) used as an auxiliary device to control the temperature and quality of the air conditioning in operating rooms. The theoretical analysis performed is punctual and distributed. It is divided into three aspects: analysis of the evaporator section, analysis of the condenser section, and analysis of the heat exchanger in terms of overall performance. The distributed procedure contrasts with the theoretical-experimental study, which uses the concept of thermal effectiveness (ε-NTU) for global heat exchanger analysis. The developed approach considers the number of heat pipes, the number of fins, and the flow rate variation at the inlet of the heat exchanger as fundamental parameters for determining the thermophysical quantities of interest. Theoretical values were determined for the average velocities, Nusselt numbers, thermal effectiveness, heat transfer rates, and exit temperatures. The localized theoretical-experimental comparisons are consistent, and the absolute relative error for the global heat transfer rate ranges from 0.5% to 35%.

Performance evaluation of a solar desalination-hot water system using heat pipe vacuum tube parabolic trough solar collector – An experimental study with Taguchi analysis

The utilization of renewable energy to generate hot water and distilled water can considerably reduce pollution. This study looked at a hybrid system that used a parabolic-trough heat pipe solar collector to generate hot water while also providing drinking water. The system is constructed in two stages, the first producing distilled water and the second producing hot water. A concave mirror increases the temperature of a vacuum tube heat pipe's evaporator area and the condenser of the heat pipe, which is directly connected to the desalination system's saltwater tank. To improve the amount of drinking water generated and to transfer thermal energy to the hot water generation system, a condenser region at the top of the saltwater tank, as well as multiple heat pipes, were employed. The effect of the water flow rate (200, 300, 400 and 500 ml/min), number of heat pipes (0, 1, 2 and 4), and the filling porous medium (0, 0.3, 0.6 and 0.9 m) of the vacuum tube on the system performance were evaluated. In addition, Taguchi-Based design of experiments was used to determine the effect of independent input parameters on the energy and efficiency of the system. The results showed that the effects of water flow rate, porous medium length, and number of heat pipes on the energy efficiency were approximately 50.89%, 26.53%, and 20.6%, respectively. Furthermore, the cost of distilled water and the cost of hot water were approximately 0.0380 $/L and 1.01 $/m3, respectively. Additionally, the highest daily productivity of the system (4940 ml/day) was obtained with a water flow rate of 200 ml/min, a length of porous media of 0.6 m, and four heat pipes. The CO2 emission reduction based on the environmental and enviroexergoeconomic parameters of the proposed systems ware improved by 37.5% and 268.4%, respectively, resulting in returns of approximately $358.1 and $260.5, respectively.

Study on the temperature control performance of photovoltaic module by a novel phase change material/heat pipe coupled thermal management system

High photovoltaic (PV) module temperature leads to the degradation of electrical efficiency, and passive PV thermal management systems, such as phase change materials (PCMs) and heat pipes (HPs), have been widely adopted to address this challenge. Due to the low thermal conductivity of PCM and the limited heat exchange capacity in the HP condensation section, this paper proposes a novel configuration for a PV thermal management system utilizing a phase change material/heat pipe coupled module (PV-PCM/HP). The experimental results showed that the performance of the coupled PCM/HP system was superior to that of the single system. A numerical model was developed to simulate and analyze the temperature variation and coupled heat transfer characteristics of the PV-PCM/HP system. The main components of heat transfer gradually change from PCM (PCM-dominated) to HP (HP-dominated), and PCM even plays a negative role during the solidification stage, which means that the coupled thermal management depends on HP only. Four design parameters (the number of HPs, PCM thermal conductivity, PCM phase change temperature, and PCM thickness) of the PV-PCM/HP system are discussed to investigate the effects on the performance of the PV-PCM/HP thermal management system. This shows that the increase in the number of heat pipes and PCM thickness can effectively improve the performance, but they should be determined according to technical and economic analysis. When the PCM thermal conductivity is >2.7 W/(m·K), it has little effect on thermal management performance under the conditions described in this paper. The value of the PCM phase change temperature should be determined according to actual weather conditions, and the purpose is to make the PCM melting period coincide with the period of higher solar radiation and lower phase change temperatures.

Optimization design and performance analysis of ammonia heat pipe air heater under low ambient temperature conditions

In coal-fired power plants, steam-based air heaters consume high-quality steam and are easily damaged due to water freezing under low ambient temperature conditions. In this paper, we propose an ammonia heat pipe air heater design with hot water in power plants as the heat source, which can eliminate the risk of freezing and save high-quality steam. Based on distributed parameter model and hybrid genetic particle swarm optimization algorithm, an ammonia heat pipe air heater with one-pipe diameter is designed and optimized. The results show that the optimal one-pipe diameter design consumes much less power and owns less weight than the normal empirical design. A new and optimal two-pipe diameter design (i.e., multi-scale design) is further proposed, which drops the power consumption by 10.1% and the weight by 9.4% compared to the optimal one-pipe diameter design. The two optimal designs require different geometrical parameters, especially the pipe diameter(s), the pipe length, the number of heat pipes, and the air side longitudinal pitch. In addition, the two optimal designs provide slightly higher outlet air temperature uniformity than the non-optimal design. Of the three working fluids, i.e., ammonia, methanol, and ethanol, the ammonia heat pipe air heater performs best.

Effect of Heat Pipe’s Configuration in Managing the Temperature of EV Battery

Because of their high energy density and long cycle life, lithium-ion batteries are commonly employed in electric cars. As battery performance and life are highly dependent on temperature, it is critical to maintain the optimum temperature range. A battery thermal management system (BTMS) is critical for controlling the thermal behaviour of the battery. Air cooling, liquid cooling, direct refrigerant cooling, phase change material (PCM) cooling, and heat pipe cooling are all BTMS strategies. Heat pipes come in a variety of sizes and configurations that can be employed in the BTMS and many studies have proven the feasibility of using heat pipe as the electric vehicles’ BTMS. However, there are many aspects of the design and configuration of the heat pipe that could affect the overall thermal performance of the heat pipe BTMS such as its length, diameter, evaporator and condenser lengths, tilt angle, types of heat pipes and working fluids. In this work, a numerical study was conducted to investigate the effect of heat pipe’s diameter, number of heat pipes and the types of heat pipes on the thermal performance of the heat pipe BTMS. The diameter of the heat pipe varies between 6 – 12 mm, the number of heat pipes varies from 2 – 10 and the type of heat pipe considered in this work is straight heat pipe. The thermal performance of the heat pipe is measured by the maximum battery temperature and the thermal resistance at different battery heat generation rate in the range of 10 - 30W. The simulation model was validated against experimental data and results indicate excellent agreement between simulation and experimental data. Simulation results shows that the greater the diameter, the lower is the battery temperature. By increasing the heat pipe’s diameter, the battery temperature can be reduced by at least 10% or 3.4°C. Temperature reduction of at least 12.7% was observed when the number of heat pipes used in the BTMS increases.

Improving thermal performance of battery at high current rate by using embedded heat pipe system

This study establishes a resistance-based thermal model for the battery cooled by the heat pipe. Unlike the traditional thermal model, the proposed battery thermal model includes the influence of the battery temperature, state of charge (SOC) and current on the heat generation in the battery body. Moreover, it also integrates the heat generation inside the tabs to improve its prediction accuracy. The heat pipe model is developed based on the thermal resistance of its components, and this model is integrated with the battery thermal model to form the thermal model of the BTMS based on the embedded heat pipe system. Experiment are carried out to verify the prediction precision. At the level of the battery unit, the prediction error is within 1 °C. Then, the different heat pipe number, fin number and heat transfer coefficient at the condensation section of the heat pipe are used for the embedded heat pipe system in order to improve its cooling performance. According to the research results, increasing the heat pipe number can reduce the battery temperature and its difference. However, when the heat pipe number is over a certain threshold, both the battery temperature and temperature difference change little. Although the heat transfer coefficient has limited influence on the battery thermal behavior, increasing the heat transfer coefficient and fin number at the same time can reduces the battery temperature a lot. In addition, comparative studies show that the embedded heat pipe system significantly outperforms the bar-type heat pipe and flat heat pipe at an extreme high current rate.

Optimization of a heat pipe-radiator assembly coupled to a recuperated closed Brayton cycle for compact space power plants

• Analysis of recuperated closed Brayton cycle conditions is carried out. • Brayton cycle and heat pipe-radiator models are numerically coupled. • Heat source and cold heat exchanger inlet temperatures are optimized. • The specific mass minimization is used as the objective variable. • Optimization provides cycles with specific masses ranging from 40 to 50 kg/kW. Compact and efficient energy conversion systems for space applications enable the appearance of new mission opportunities and technological discoveries resulted from space exploration. Besides energy availability, another crucial factor of any energy conversion system for space purposes is its total mass and size. Focusing on a recuperated closed Brayton cycle (CBC), thermodynamic modeling of a CBC is proposed. Moreover, a thermal model is carried out to predict the overall properties of the cold side of the system (i.e., heat pipes and radiator) for different CBC conditions. Both models are coupled and their conjunct solution provides operational data for the design of the heat rejection system, such as the number of heat pipes (HP), total assembly mass, length, and second-law efficiency. Furthermore, by means of this coupling, the heat source temperature and the cold heat exchanger (CHE) inlet temperature are defined, using an optimization procedure where the specific mass (i.e., radiator mass to cycle power ratio) is minimized. Based on this objective variable, the optimized heat source temperature of 1200 K is achieved, while the CHE inlet temperature of 513.2 K is obtained. Such temperature conditions ensure the future design of a space energy conversion system that aligns good efficiency and compactness.

Parametric study of photovoltaic/thermal wickless heat pipe solar collector

Wickless heat pipes are an effective passive heat transfer device that, due to their improved heat transfer capabilities, can enhance photovoltaic system efficiency. A new photovoltaic-thermal acetone wickless heat pipe solar panel (PVT/WHP) is described in this study. The main parameters affecting the thermal and electrical efficiency of the solar panel, such as wind velocity, incident radiation, water inlet temperature, heat pipe number, and collector surface area, as well as inner heat pipe behavior and operating limits, are studied using a mathematical model. According to the reduced temperature simulation results, the theoretical PVT/WHP module's average electrical, thermal, and overall efficiency were approximately 12.52%, 43.75%, and 56.27%, respectively. The study is being used to assess the thermal efficiency of PVT/WHP under Tunisian climatic conditions, and the simulation results show that PVT/WHP outperforms conventional PVT water-based systems with a maximum thermal and electrical efficiency gain of approximately 21.9% and 14.2% respectively. The current parametric study provided a framework for assessing such a system's behavior and providing useful flexibility to achieve the best possible system performance.

Study the heat dissipation performance of lithium‐ion battery liquid cooling system based on flat heat pipe

SummaryThis paper improves the thermal management system of lithium‐ion battery through the high thermal conductivity flat heat pipe, and attempts to improve its performance. The adoption of flat heat pipes reduces the problem of poor heat dissipation in the direction of the coolant flow when the liquid cooling plate is used alone, and increases the heat conduction in the longitudinal direction of the battery. A three‐dimensional simulation model is established to study the influence of the number and width of flat heat pipes on the maximum temperature rise and temperature difference of lithium‐ion batteries at a certain discharge rate. It is found that after adding flat heat pipes, the maximum temperature rise and temperature difference of the battery decreased. The heat dissipation performance reaches the best when the flat heat pipe number is 11 and the maximum temperature difference can be controlled below 5°C at 3 C discharge rate with 11 flat heat pipes.

Experimental study of Thermal performance on heat pipe radiator

The heat pipe radiator has become an effective way to solve the heat dissipation problem of electronic components due to its advantages of good reliability and high-heat dissipation efficiency. So it is necessary to explore the thermal performance of heat pipe radiators.In this paper,gravity radiators with two,four,and six heat pipes are used as the research object.The thermal performance of the three heat pipe radiators with different numbers of heat pipes is compared and analyzed through experiments.It mainly includes the influence of a different number of heat pipes on the heat dissipation power, thermal resistance,temperature uniformity, start-up time and other parameters of the radiator.Research shows that the number of heat pipes is one of the main factors affecting the thermal performance of a radiator. The more heat pipes,the better the thermal performance.

Experimental and numerical investigating a new configured thermal coupling between metal hydride tank and PEM fuel cell using heat pipes

This paper presents an experimental investigation of a fuel cell coupled with the metal hydride (MH) tank to study the effects of heat pipe number, wire number and the type of heat pipes with and without fin. The effect of the number of heat pipes and fins, as well as the number of copper wires as a wick layer, has not been investigated in previous similar studies. The computational fluid dynamics (CFD) calculations were carried out using the finite element method (FEM) in COMSOL. Some parameters including condenser length, adiabatic length, evaporator length, heat pipe diameter and heat pipe power were optimized. In the experiments, 30 and 40 strands of copper wire were selected as the wick layer and experiments were repeated for 5 and 10 finned heat pipes. Experimental results also compared with simulation data and it was found that results were consistent with little deviation. By using the relative deviation method, the deviations amounting to 7.45% and 6.76% were obtained in adsorption and desorption step, respectively. Also, sensitivity analysis of the capillary limit and wire diameter of heat pipes were carried out and results illustrated that the reduction of boiling limit has a more significant impact on the heat pipes thermal power than the capillary limit and wire diameter. Response surface methodology was used which showed that the best performance of the desorption process at 25 bar is achieved using 4 heat pipes covered by 10 fins.

Finding the Thermal Characteristics of a Heat Pipe using Hybrid Nano Fluid

In this experiment, work was carried out to infer the thermal characteristics of a heat pipe containing nano fluid inside in it. Various Parameters were considered in this experiment, some of them are inlet temperature at one end, mass flow rate (mfr) to evaporator section and inclination angle of heat pipe. In this work three numbers of heat pipes were used and hybrid nanofluid of Al2O3 – TiO2 has been used as cooling fluid in all three heat pipes. The thermal efficiency of the usage of hybrid nanofluidic working system is found to be highest and also this makes the system to get worse in terms of thermal resistance. The flow rate of condenser section was modified to the various ratios from 1:1 to 1:3 as that of evaporator section. To find the thermal characteristics of the heat pipe, many experiments have been carried out by considering many operating conditions. Evaluation on the heat pipe effectiveness was made on basis of gravity assistance to the condenser. The better productiveness of heat pipe when using the hybrid nanofluid has attained when Ch/Cc = 2 and 100 LPH for all operating conditions.

Experimental and Theoretical Study of the Performance of Solar Water Heaters with Gravity-Assisted Heat Pipes

The objective of this work is to study the performance of solar water heaters using heat pipes for heat transfer, from absorber plate to water tank, with two different types of working fluids (Ethanol and Acetone) and different numbers of heat pipes. Additionally, a theoretical investigation is conducted to predict the performance of the solar water heaters. These systems have been designed and fabricated with the same dimensions and materials. The hourly variation of the absorber plate temperature, the water storage tank temperature and solar radiation intensity are measured. Accordingly, the stored energy and the efficiency has been calculated. The results showed that, a good agreement has been achieved between the experimental and theoretical results. The operation point of the conventional system begins at the operating start while the operation point of the thermosyphon systems starts when the absorber plates temperatures reaches the boiling point of the working fluid. The maximum water temperatures gained of the forced convection system and thermosyphon system charged with ethanol and acetone were 66 C, 67.8 C, and 64.6 C, respectively while those of theoretical calculations were around 69.2 C, 69 C and 69.3 C, respectively. In addition, the maximum value of the actual efficiency of conventional system was ranged between 47~53% while that of theoretical calculation was between 50~53%. The experimental maximum efficiency of thermosyphon systems was around 55% at the case of installing 14 heat pipes charged with acetone and theoretical efficiency was 55% for same the case. The thermosyphon system gives better performance than forced convection system, because thermosyphon system does not consume electricity. Performance of the thermosyphon system using acetone as working fluid was better than the performance of the thermosyphon system using ethanol and the increase of the heat pipes number improves performance.

Assessment of the cost reduction potential of a novel loop-heat-pipe solar photovoltaic/thermal system by employing the distributed parameter model

A novel micro-channel loop-heat-pipe solar photovoltaic/thermal (LHP- PV/T) system is developed employing the co-axial tubular heat exchanger as the condenser and upper-end liquid header with tiny holes as the liquid feeder. The design facilitates an easier connection among the solar modules. It creates the improved condensation and separate evaporation effects within the LHP. A reduced evaporator area will thereby have a minor impact on the overall heat transfer performance, leading to significant potential for cost reduction. A distributed parameter model is established and validated by experimental data. The model is then applied to analyse the cost reduction potential of the LHP- PV/T via the optimization of geometrical and structural parameters. The impact of the area reduction on the LHP evaporator differs from that on the traditional integral heat pipe PV/T. The decrements in thermal and electrical efficiencies of the LHP- PV/T are 2.47% and 0.03% respectively when the width of heat pipes in the evaporator decreases from 26 to 10 mm. When the number of heat pipes decreases from 30 to 6, the decrements in thermal and electrical efficiencies are 4.63% and 0.12%, whilst the overall system cost drops by 28.58%, thus the cost-effectiveness of the system can be improved.

Experimental, study and design sensitivity analysis of a heat pipe photovoltaic/thermal system

Gravity-assisted heat pipe (HP) is usually introduced to overcome the freezing and corrosion problems associated with the traditional water-based photovoltaic/thermal (PV/T) solar collector. This study presents the design, construction and experimental study of a HP-PV/T system. A transient model for the proposed system is also developed and validated on a sunny day and a cloudy day, respectively. Based on the validated model, a design sensitivity analysis, including the effects of mass flow rate, dimensions of the heat pipe evaporator and condenser sections, the width of header pipe and the types of heat pipe working fluid, is conducted. The results indicate that the mean deviation between the simulation results and the experimental data is no more than 4.5%. The photothermal and photovoltaic efficiencies increase with increasing the water mass flow rate, the diameter of heat pipe condenser section and the number of heat pipes; however, the growth gradients become smaller when these three variables are respectively bigger than their respective specific values. Photothermal efficiency increases first and then decreases with increasing the length of heat pipe condenser section, suggesting an optimal length of 12 mm. Increasing the width of header pipe decreases both the photothermal and photovoltaic efficiencies. For the working fluid of heat pipe, H2O is suggested for mild climatic regions while R134a is suggested for cold climatic regions.

Experimental study on transient performance of heat pipe-cooled passive residual heat removal system of a molten salt reactor

Abstracts A heat pipe-cooled passive residual heat removal system (PRHRS) of a molten salt reactor (MSR) is proposed by employing high-temperature heat pipe technology. This system can significantly improve the passive safety of an MSR during abnormal transients. In the study, an experimental system is constructed to verify the feasibility of using a PRHRS in molten salt reactors. A eutectic salt mixture of 46.5 mol%LiF-42 mol%KF-11.5 mol%NaF composition, termed as FLiNaK, is selected as the working fluid because it has similar thermo-physical properties to real salt 67 mol% LiF-33 mol%BeF2, termed as FLiBe. The transient responses of the designed PRHRS for an MSR are studied from the following two aspects. 1) The temperature distribution of molten salt in the drain tank with different heat pipe cooling schemes during transients is analyzed. 2) The effect of key parameters such as height of the air stack, number of heat pipes, initial salt temperature, and different decay power on the transient performance of the PRHRS is investigated. Experimental results indicate that the heat pipe system significantly removes the residual heat of molten salt in the drain tank, although part of the heat pipes does not operate normally. The residual heat is released in 5–10 h until the molten salt reaches its freezing point, thereby indicating the feasibility of the designed PRHRS for an MSR. The study provides valuable experimental data and suggestions for the design and analysis of a PRHRS for an MSR.