Heat Pipe System Research Articles

An R1234ze(E) loop heat pipe with flat-plate evaporator for cooling electronic devices

With the development of high power electronic devices, the failure problem caused by the high temperature must be solved by a reliable cooling solution. A solution for cooling electronic equipment was proposed in this paper. Two loop heat pipe systems with flat-plate evaporator were designed. The effect of a new refrigerant, R1234ze(E), on the thermal performance of the loop heat pipe was investigated. Two cooling methods were designed to achieve different cooling requirements, namely liquid-condenser and air-condenser respectively. The reliability of the solution had been fully verified. When the temperature of the heat source was kept below 75 °C, the heat load that could be cooled by the two condensing methods is 150 W (9.8 W/cm2). The largest heat load of the liquid-condenser could even reach 270 W (16.9 W/cm2) under gravity assistance. For the air-condenser, the normal operating range was 10 W–150 W while the working power of the fan was 20 W. Under different operating conditions, the system responded quickly and without any failures. The minimum total thermal resistance of liquid-condenser LHP and air-condenser LHP was 0.307 °C/W and 0.135 °C/W, respectively. These two LHPs meet the cooling needs of electronic devices and can effectively alleviate the thermal problems of electronic devices.

Analysis of thermal performance a heat pipe for concentrated photovoltaic cooling

Heat pipes are used in this study for the concentrated photovoltaic (CPV) passive cooling. Investigations have been done in two steps: in the first step, the heat pipe's thermal performance in the horizontal position has been tested. Two sets cylindrical heat pipes with identical diameters (6 mm) but of different lengths (250 mm and 150 mm, respectively) were employed. Each set consists of three heat pipes. The results of the study showed that the heat pipe has a maximum operating point that is dependent on both the intensity of the incident light and the surrounding temperature. Moreover, this operating point could be determined. For high light intensity, a long heat pipe performs better than a short one, and vise versa. In the second step, a heat pipe passive cooled CPV system has been investigated for both long and short heat pipe systems. The performance of heat pipe cooled CPV system was compared to that of the traditional fins-cooled CPV system. Results showed that at light concentrations of 55 X, cooling a solar cell with a heat pipe enhances its maximum output power by 6% for a long heat pipe and by 7% for a short heat pipe, respectively. While at 210 X illumination concentration, long and short heat pipes, respectively, produced gains of 16 and 12% in the cell's maximum output power.

Experimental study of a photovoltaic solar-assisted heat pump/gravity-assisted heat pipe hybrid system

In the present study, a hybrid PV/T collector/evaporator was designed and manufactured. On this basis, a hybrid system named photovoltaic solar-assisted heat pump/gravity-assisted heat pipe system (PV-SAHP/GHP) was proposed. The proposed hybrid system can alternatively operate in GHP-PV/T mode and PV-SAHP mode. An experimental test platform was then constructed and a series of outdoor experiments were conducted to reveal and contrast the operating characteristics in different modes. Net yields and energy-saving factors were additionally employed to reveal the priority of different operating modes. The results indicated that the daily average energy efficiency and exergy efficiency of the GHP-PV/T mode were 36.87% and 7.09%, while that of the PV-SAHP mode were 51.39% and −6.34%. The fitting results of the thermal efficiency and overall efficiency of the PV-SAHP mode were higher than that of the GHP-PV/T mode. The GHP-PV/T mode though achieved a satisfactory energy-saving effect, its water temperature cannot meet the demand; while the PV-SAHP mode though met the temperature demand, and its energy conservation effect was unsatisfactory. Therefore, it is recommended to operate the GHP-PV/T mode during intense radiation and operate the PV-SAHP mode otherwise to balance the thermal performance and energy-saving benefits of the hybrid system.

Experimental Investigations of Heat Pipe Systems for Use in Electrical Engines

AbstractMit dem Ziel die Effizienz elektrischer Arbeitskraftmaschinen durch ein innovatives Kühlsystem zu erhöhen, wird ein Wärmetransportsystem auf Basis von Wärmerohren entwickelt und analysiert. Die Leistungsfähigkeit des Systems bei Variation des Temperaturbereichs und des zugeführten Wärmestroms sowie der Einfluss der Rotation werden experimentell untersucht. Der Wärmewiderstand des Systems wird im Vergleich zu reiner Wärmeleitung um 98 % reduziert. Die Rotation des Systems hat keinen signifikanten Einfluss auf den Wärmewiderstand, der bis zum Erreichen der Leistungsgrenze konstant ist. Die Leistungsgrenze ist temperaturabhängig und stimmt annähernd mit der Kapillarkraftgrenze überein.

An Innovative Design for a Solar Water Heating System Utilizing a Flat-Shaped Heat Pipe

Abstract In this work, an innovative design for a solar water heating system using a flat-shaped heat pipe as a heat transfer device is presented to pave the way for a substantial increase in the thermal performance of these systems. An analytical study is utilized to investigate the thermal performance of the solar water heating system. The analytical results of the flat-shaped heat pipe system are compared with the results of the evacuated tube solar water heating system with a U-tube, thermosyphon, and closed-loop pulsating heat pipe. It is found that the water temperature difference between the inlet and outlet of the flat-shaped heat pipe system is substantially higher than the U-tube, thermosyphon, and closed-loop pulsating heat pipe system by as much as 31.4, 22.5, and 18.5 °C, respectively, at a nominal 0.6 l/min mass flowrate. Furthermore, utilizing the flat-shaped heat pipe in the solar water heating system optimizes the thermal conductivity of the solar setup due to a reduction in the condenser section length. These reductions also lead to a large reduction in the weight and cost of the system.

Implementation of Artificial Intelligence in Modeling and Control of Heat Pipes: A Review

Heat pipe systems have attracted increasing attention recently for application in various heat transfer-involving systems and processes. One of the obstacles in implementing heat pipes in many applications is their difficult-to-model operation due to the many parameters that affect their performance. A promising alternative to classical modeling that emerges to perform accurate modeling of heat pipe systems is artificial intelligence (AI)-based modeling. This research reviews the applications of AI techniques for the modeling and control of heat pipe systems. This work discusses the AI-based modeling of heat pipes focusing on the influence of chosen input parameters and the utilized prediction models in heat pipe applications. The article also highlights various important aspects related to the application of AI models for modeling heat pipe systems, such as the optimal AI model structure, the models overfitting under small datasets conditions, and the use of dimensionless numbers as inputs to the AI models. Also, the application of hybrid AI algorithms (such as metaheuristic optimization algorithms with artificial neural networks) was reviewed and discussed. Next, intelligent control methods for heat pipe systems are investigated and discussed. Finally, future research directions are included for further improving this technology. It was concluded that AI algorithms and models could predict the performance of heat pipe systems accurately and improve their performance substantially.

Performance Study of Gravity-Type Heat Pipe Applied to Fuel Cell Heat Dissipation

A gravity-type heat pipe boiling characteristics test rig was constructed to solve the heat dissipation problem of fuel cells during operation. The boiling heat transfer characteristics of water in a parallel plate under negative pressure at different inclination angles and heat flow density input are investigated. The results show that: First, the gravity-type heat pipe can dissipate some heat and it is possible to use it for fuel cell heat dissipation. Second, with a certain range of heat flow density, the temperature of all parts of the plate is about 80 °C, with a small temperature difference, which is conducive to the safe operation of the fuel cell. Third, the heat flow density is in the range of 2222~3111 W·m−2, the temperature difference is large, and the outlet temperature is greater than 80 °C, which exceeds the operating temperature of the fuel cell, and the power-type heat pipe should be used for heat dissipation. Fourth, the average temperature of the plate placed at an inclination angle of 45°~60° is lower compared to other angles, and the temperature is evenly distributed. On the one hand, the conclusions reveal the characteristics of boiling heat exchange under negative pressure conditions of water inside the flat plate and, on the other hand, provide a reference for designing heat pipe systems for fuel cell heat dissipation.

EVALUATION OF A NOVEL TWO-PHASE CLOSED THERMOSYPHON SYSTEM UTILIZING NiFe2O4/DW, Fe3O4/DW, Fe2O3/DW MAGNETIC NANOFLUIDS

This study concentrates on investigating the implementation of a heat pipe system experimentally and theoretically by simulating a novel heat pipe model employing the MATLAB/Simulink® program, R2021a, using nanofluids obtained by adding 0.5 wt.% and 1 wt.% nickel ferrite, iron oxide, and ferric oxide magnetic nanoparticles to distilled water. A thermal-network dynamic representative was suggested to illustrate the thermal behavior of the heat pipe. The simulated system was capable to indicate the transient demeanour and steady-state temperature of the two-phase closed thermosyphon accurately. The experimental and simulated outcomes demonstrated that the best performance was accomplished using NiFe<sub>2</sub>O<sub>4</sub>/DW magnetic nanofluid with a proper deviation of ± 3.52%. Furthermore, the efficiency, thermal resistance, and Nusselt number of the system were boosted by approximately 22.24%, 9.3%, and 51.9% while utilizing NiFe<sub>2</sub>O<sub>4</sub> magnetic nanofluid corresponding to distilled water at 1 wt.%. A feedback control PID approach is assumed to perform a response within a fraction of a second as well as zero overshoot. The originality of the study is to experimentally and theoretically reveal the thermal behavior of NiFe<sub>2</sub>O<sub>4</sub> containing Ni and Fe and the thermal behavior of the only Fe-containing nanofluid compared to the nanofluids obtained with magnetic particles such as Fe<sub>2</sub>O<sub>3</sub> and Fe<sub>2</sub>O<sub>4</sub>

Novel Loop Heat Pipe System for EV Thermal Management of Batteries: Effects of Ambient Temperatures

Building from previous successful results from the Authors, a Loop Heat Pipe (LHP) based Battery Thermal Management System (BTMS) is investigated over a range of different ambient temperatures (from 20°C to 50°C), using a state-of-the-art environmental chamber. LHPs act as thermal vector from the bottom of the battery pack to a remote chiller, while graphite sheets allow to achieve a satisfactory level of temperature homogenization of the cells surface, with low added weight. This design was developed aiming to improve on fast charge timings, all-electric range, reduce costs and complexity, and decrease maintenance requirements. Preliminary studies showed the potential of this innovative BTMS to give better performances than standard active counterparts. The aim of this work is to extend the investigation towards a practical application, by matching experimental results obtained in the environmental chamber with a validated numerical Lumped Parameter Model and extend the results database to different geometries and material/fluid configurations, to support the adoption of this technology by automotive manufactures. Results showed a successful validation campaign, with average temperature discrepancy between the experimental results and the numerical prediction of 0.4°C. Further simulations results demonstrated how the proposed BTMS performs efficiently at higher temperatures, limiting cells maximum temperatures below 60°C even at ambient temperatures of 50°C, increasing safety.

Combining looped heat pipe and thermoelectric generator module to pursue data center servers with possible power usage effectiveness less than 1

With the rapid increase in the power consumption of global data centers, it is becoming more and more important to reduce the power usage effectiveness (PUE) value, which is a key metric for evaluating the energy efficiencies of data centers. The previously proposed advanced thermal management methods can make PUE values very close to 1. To further reduce the PUE of the air-cooled data center, a novel looped heat pipe (LHP) and thermoelectric generator (TEG) coupled system based on a series–parallel scheme was first proposed. Attributed to the passive heat dissipation apparatus with extremely low thermal resistance and high-efficiency thermoelectric power generation devices as adopted in this design, the power output, especially the net power output, could be greatly improved compared to the power outputs achieved in previous research, and an electrical power of more than several watts was obtained while cooling a server CPU, which enable servers possibly with PUE values less than one. The results showed that, under the condition that the junction temperature was below 85 °C, by using nine 40 mm TEGs, the minimum PUE of 0.997 was achieved at a Reynolds number of 930 and a heat load of 155 W.

Long Term Performance Assessment of a Residential PV/Thermal Hybrid System

The application of residential rooftop PV systems increased significantly in the last 10 years in many countries and became a major source of clean energy in dwellings besides traditional solar hot water technology. To optimise the performance of these green energy systems, the incorporation of PV/thermal hybrid systems is a future option for sustainable residential building designs. In this work, a novel design of PV/Thermal (PVT) hybrid panels, using heat pipe technology, is proposed with the aim of fulfilling the hot water and electricity demand of a house in Sydney. The heat pipe system is integrated into a traditional PV panel to transfer the heat stored within the PV panel material to a header that is connected to the household hot water cycle. A preliminary analysis of the test results for the proposed PVT system design under different weather conditions in Sydney is conducted, where the transient variation of the output water temperature as well as power production is investigated. The results show that the hot water temperature at the header outlet reaches around a maximum of 50 °C on a typical summer day and a minimum of 30 °C on a typical winter day. The daily heat delivered to the hot water tank is found to be in the range of 3.7–5.2 MJ per m2 of the PVT panel surface area. The results show that the energy efficiency of the adopted PVT panel design could reach more than 4 times higher than the traditional PV panel.

Development and assessment of a model predictive controller enabling anticipatory control strategies for a heat-pipe system

To support the reliable and resilient operation of modular reactors and microreactors, anticipatory control strategies have been proposed for achieving faster-than-real-time predictions and decision-making capabilities in anticipation of potential anomalies, including setpoint changes and cyber incidents. This work presents how anticipatory control strategies can be implemented via model predictive control (MPC) for a single heat pipe's temperature. Considering the uncertainty in developing and applying MPC, this work evaluates MPC performance given three different model forms: a linear response surface model, an artificial neural network (ANN), and an autoregressive model with exogenous input (ARX). This work also evaluates the impacts of different input biases and variance on MPC performance in order to account for potential sensor reading variations due to cyber incidents. We observe that the ANN and ARX result in more fluctuated control actions compared to the MPC with linear response surface model. However, when the cyber incidents are of large magnitudes, the linear response surface model produces smaller feasible regions than the ANN and ARX models under identical constraints.

Performance Analysis of Solar Water Heater with Various Working Fluids

Optimized design of a solar water heater for effective heat transfer and the performance analysis was carried out in the present study. An experimental and theoretical performance of the system with an integrated heat pipe is evaluated for the same. The system uses a heat pipe with a wick to transmit heat from evaporator to the tank. The thermal behaviour of different parts of the system is analyzed. A sequence of tests are done on the heat pipe solar water heating system and thermosyphon water heating system to stimulate better configuration. The thermal efficiency of the system is optimized for maximum heat transfer using analytical techniques. Results show good thermal performance characteristics. Computation of various design parameters of heat pipe system related to the collection and consumption of solar energy are also conducted. Further, the exergy analysis and comparison of performance analysis of solar heat pipe collector with flat plate collector is also done.

Analysis of an Evaporative Condensation System Coupled to a Microchannel-Separated Heat Pipe for Data Centers

In the age of the digital economy, the data center is the most crucial piece of infrastructure. The issue of the excessive power consumption of a data center’s cooling system needs to be addressed as the national objective of “peak carbon and carbon neutrality” is increasingly promoted. In this study, a microchannel-separated heat pipe-cooling system with evaporative condensation is introduced. The system may switch between three modes of operation in response to changes in outdoor air quality parameters, thereby maximizing the utilization of natural cooling sources while lowering data centers’ cooling costs. The purpose of this paper is to analyze the energy-saving potential of the hybrid system through experimental tests. The results show that 114.4% is the ideal liquid-loading rate for the heat pipe system. Under working conditions in Xi’an, the annual operating hours of the three modes accounted for 47.2%, 6.1%, and 46.7%. The hybrid cooling system may save 62.04% of the energy used annually compared to the standard cooling system and the cooling system in the server room thanks to its yearly average COP of 9.43.

Experimental Investigation on a Novel Necking Heat Pipe with Double-End Heating for Thermal Management of the Overload Operation

This work proposed a novel necking heat pipe with double-end heating for thermal management of the overload operation. The addition of another heat load was adopted to obtain a higher threshold critical power for the heat pipe system. The thermal performance of thermal switch heat pipe (TSHP) and traditional grooved heat pipe (TGHP) was investigated experimentally, including the threshold critical power, starting characteristic, recovery characteristic, surface temperature distribution, thermal resistance, etc. The optimized TSHP exhibited a larger threshold critical power range with low additional heat load input (from 55 W to 65 W, almost 20% increase), low starting additional heat load input (2 W), good recovery characteristic (less than 150 s from 75 °C to normal after overload), and low thermal resistance with additional heat load input (less than 0.13 °C/W). These results indicate that the optimized TSHP can offer great potential for the overload operation situation with the additional heat load. Such a novel necking heat pipe with double-end heating can be utilized in heat pipe systems to obtain different thermal performances for complicated working situations, especially for the overload operation situation.

The thermal performance and applicability analysis of the composite ventilation system with heat recovery in ultra-low energy buildings

By analyzing the energy transfer process of building ventilators with heat recovery, a novel building ventilator with exhaust air heat pump enhanced by pump-driven loop heat pipe system was proposed and experimentally compared with the dual-loop heat pump and traditional heat pump system. During the test, the thermal performance of the prototype under three different operating modes was comprehensively studied, and then the energy-saving potential and applicability of the heat recovery units in the ultra-low energy buildings (ULEBs) were analyzed by using the DEST and MATLAB tools. Results showed that compared with the heat pump system, the composite system presented the highest energy efficiency ratio (EER) in the whole year, at 12.6 for winter and 4.8 for summer conditions, respectively. What's more, the energy recovered by the composite system is in line with the fresh air load, which can solve the problem of energy recovery attenuation of traditional ventilators in cold climate conditions. In addition, the composite system had great applicability in ULEBs, and the energy-saving ratio was 35.3% and 14.5% in Harbin and Kunming, respectively. Future works are to improve the performance of the pump-driven loop heat pipe and heat pump unit under all operating conditions for better adaptability of the ventilators.

Thermal performance of a cryogenic parallel heat pipe system

In this study, we experimentally investigated the thermal behavior of a cryogenic parallel heat pipe system, which comprises a parallel arrangement of an N2-heat pipe and Ar-heat pipe or an N2-heat pipe and Ne-heat pipe. The heat pipes in the parallel system have common evaporator and condenser sections. We conducted preliminary experiments to investigate the individual thermal performance of heat pipes considering three working fluids, which formed the basis for analyzing the parallel heat pipe system. The experiments were performed at several condenser temperatures between 27 and 110 K for a wide range of heat loads considering various heat pipe operating states, such as the normal heat pipe operation, local dry-out, and locally frozen states. Although the tested heat pipes, manufactured by Fujikura Electronics (Thailand) ltd., were commercial heat pipes for room temperature applications, which use water as a working fluid, the working fluid was replaced with nitrogen, argon, or neon in the present experiments. The heat pipes used a composite wick comprising axial grooves and sintered metal powders. The experimental results verify that the heat pipe can be utilized even in the local dry-out state or locally frozen state. Moreover, the parallel heat pipe system can enhance the thermal performance with respect to the maximum heat transport capability, which was 29 W at an operating temperature of 87 K, and expand the operating temperature range to 24–150 K. The proposed parallel heat pipe system can be used to improve the cooling system of superconducting magnets and in other cryogenic applications.

A novel solar desalination system based on an evacuated tube collective condenser heat pipe solar collector: A thermo-economic and environmental analysis

Solar desalination has captivated consideration to overcome the problem of the scarcity of freshwater, with simple-design, economic, and environment-friendly solutions. This study navigates a novel solar-evacuated glass tube collector integrated with a collective condenser heat pipe system for solar desalination. A newly designed heat pipe array was represented in this work by affixing all the evaporator tube units of the heat pipes to a single condenser unit and was attached to the evacuated tube solar collector. The innovative assembly of the heat pipe provided uniform heating of water and rapid steam generation. The present system acts as a solar collector and as a stand-alone basin for freshwater formation. The performance assessment of the neoteric system was conducted based on half-filled and three-fourth-filled conditions of the water flow pipe kept within the collective condenser heat pipe. The maximum heat pipe temperature recorded during the half-filled state was 156.9°C and 151.48°C in the three-fourth-filled state. The half-filled state of the water flow pipe delivered a total distilled water content of 8,050 ml/day, whereas the three-fourth-filled state delivered 5,925 ml/day of distilled water. The maximum energy and exergy efficiency of the presented system was 19.27% and 3.92%, respectively. The economic minimum unit cost of freshwater by the present system is 4.27 INR, and the payback period is 2.9 years. The present eco-friendly energy system saves 4.25 kWh of electricity and 4.16 × 10−3 tons of CO2 equivalent per year.

Effectiveness prediction of CuO nanofluid heat pipe system using fuzzy neuro approach

Effectiveness prediction of CuO nanofluid heat pipe system using fuzzy neuro approach

Experimental investigation on the start-up performance of a loop heat pipe with three flat disk evaporators combined

To promote the heat transport applicability of the loop heat pipe(LHP) for high power and multi-heat sources, a multi-evaporator loop heat pipe(ME-LHP) system with three flat disk evaporators equipped with separate vapor lines was proposed and experimentally studied for the first time. The effects of the interaction between evaporators, the heat load distribution, and the gravity-assisted angle on the startup behavior of ME-LHP were investigated respectively. The results show that with the separated-vaporline structure, the adverse impact between evaporators was greatly reduced. The best performance appeared when all three evaporators were involved. At unequal heat load working conditions, the ME-LHP obtained the optimal startup performance when high heat load was applied on evaporators with a superior position in liquid separation. Besides, the outlet temperature of all evaporators tended to be consistent, even if multiple evaporators worked under unequal heat loads. The gravity-assisted angle affected the start-up process by changing the non-uniformity of liquid distribution. Compared with the gravity-assisted tilt θ = 10°, the highest performance was improved by 77 % for θ = 2°, and the peak load could reach 300 W. The present study may extend the application of the flat plane type of loop heat pipe for solving the multi-heat-sources dissipation problem.