Heat Pipe Technology Research Articles

A Review on Cooling Systems for Portable Energy Storage Units

Achieving the global electricity demand and meeting the United Nations sustainable development target on reliable and sustainable energy supply by 2050 are crucial. Portable energy storage (PES) units, powered by solid-state battery cells, can offer a sustainable and cost-effective solution for regions with limited power-grid access. However, operating in high-dust and high-temperature environments presents challenges that require effective thermal management solutions. This paper is a comprehensive review of thermal management systems for PES units, with a specific focus on addressing the challenge of overheating in airtight designs. The review of various active and passive cooling systems is conducted through extensive study of the relevant literature, which is significant in providing insights into the operation, performance parameters, and design options for different cooling system technologies. The findings from this review show heat pipe (HP) technologies as key cooling-system solutions for airtight PES units. Specifically, loop and oscillating HPs, as well as the vapour chamber, offer desirable features such as compactness, low cost, and high thermal conductivity that make them superior to other alternatives for the cooling systems in PES. The insights and knowledge generated via this review will help facilitate the design and development of innovative, efficient, and reliable PES units, thereby contributing to the advancement of off-grid renewable energy applications and enabling sustainable power solutions worldwide. Furthermore, an appropriate design of PES units can help in reducing capital and maintenance costs.

Analysis and design of air-heat pipe composite cooling of high power density motor

High power density and short-term high overload performance motor is an important part of the aircraft's electric propulsion system. The efficient heat dissipation system can effectively control the temperature rise of the motor, which provides the possibility to improve the power density of the electric propulsion system.An air-heat pipe composite cooling system was designed by using heat pipe technology and the application environment of aviation motors. Firstly, a new composite cooling system was designed based on the structure and loss distribution characteristics of a 34 kW external rotor aero-motor; then four different U-shaped heat pipes were designed and fabricated. In order to select the optimal heat pipes to ensure the efficient performance of the composite cooling system, a test platform was built to carry out experimental research on the thermal conductivity of the heat pipes and the variation laws of thermal conductivity. Then the performance of the composite cooling system is evaluated and verified based on a combination of simulation and experiment. The results show that the cooling effect is better by arranging the heat pipes at the bottom of the stator slot of the motor, which can reduce the stable temperature rise of the motor winding by 19 K and prolong the overload operation time of the motor by 12.7 %. The high efficiency of the composite cooling system can effectively improve the power density of the motor.

Experimental study of boiling heat transfer characteristics of forced flow in annular tube under negative pressure

In order to investigate the recycling technology for efficiently recovering low-temperature wastewater waste heat from industrial production, we built an experimental device for forced boiling heat transfer in an annular tube. This paper takes a ring casing evaporator with an inner tube diameter of 30 mm, a length of 1450 mm, a wall thickness of 0.8 mm, and an outer tube diameter of 14.2 mm, which was used as the main object of study. We conducted experimental research on heat transfer in single-phase liquid flow and two-phase boiling phase change within annular tubes by varying the inlet circulating hot water temperature (60–85 °C), the mass flow rate of the circulating mass (0.85, 1.27, 1.69 kg m−2 s−1), and the inclination angle (0°–90°). The research results indicate that the heat transfer coefficient of boiling phase change within annular sleeves is significantly enhanced compared to convective heat transfer of single-phase liquid flow within annular tubes. This signifies that employing heat pipe technology for waste heat recovery can achieve highly efficient heat transfer processes. This study also reveals that with an increase in the inclination angle, the heat transfer coefficient on the boiling surface follows a trend of initial increase followed by a decrease. Near an inclination angle of 30° within the annular jacket tube, the heat transfer coefficient of two-phase boiling phase change reaches its maximum value. The findings of this study provide certain theoretical guidance for the application of heat pipe energy-saving technology in the field of medium- and low-temperature waste water recovery and utilization.

Optimization Design of an Intermediate Fluid Thermoelectric Generator for Exhaust Waste Heat Recovery

The intermediate fluid thermoelectric generator (IFTEG) represents a novel approach to power generation, predicated upon the principles of gravity heat pipe technology. Its key advantages include high-power output and a compact module area. The generator’s performance, however, is influenced by the variable exhaust parameters typical of automobile operation, which presents a significant challenge in the design process. The present study establishes a mathematical model to optimize the design of the IFTEG. Our findings suggest that the optimal module area sees substantial growth with an increase in both the exhaust heat exchanger area and the exhaust flow rate. Interestingly, the optimal module area appears to demonstrate a low sensitivity to changes in exhaust temperature. To address the challenge of determining the optimal module area, this study introduces the concept of peak power deviation. This method posits that any deviation from the optimal module area results in an equivalent power deviation. For instance, with an exhaust heat exchanger area of 1.6 m2, the minimum peak power deviation is 27.5%, corresponding to a design module area of 0.124 m2. As such, the actual output power’s deviation from the maximum achievable output power will not exceed 27.5% for any given set of exhaust parameters. This study extends its findings to delineate the relationship between the optimal design module area and the exhaust heat exchanger area. These insights could serve as a useful guide for the design of future power generators.

A Comprehensive Review and Experimental Investigation on Heat Pipes Application in Electrical Machines

The rapid development of transportation electrification brings unprecedented opportunities and challenges as well to the technological improvement of high-power density motors. As the major restriction of the motor performance, thermal issues attract more attentions recently and the heat pipe (HP), due to its high thermal conductivity and lightweight characteristics, is identified as a promising solution. Though HPs have been attempted in cooling systems of electrical machines, their thermal benefits still need to be fully understood. This article provides a comprehensive review and performs a series of experimental investigations to fill the technology gaps for the HP application in electrical machines. Firstly, the HP technology is briefly introduced, followed by a detailed review on its applications in different locations of electrical machines with corresponding thermal improvements reported. Then, experimental tests are conducted to investigate the correlation between the HPs’ parameters and their cooling effectiveness, including cross-sectional shape, bending angle, fins arrangement and inclination angle. The obtained results and conclusions could provide a guideline for the promotion of HPs in next generation electrical machines for future transportation.

Study on carnauba wax as phase-change material integrated in evacuated-tube collector for solar-thermal heat production

Abstract The evacuated-tube collector (ETC) for solar heat production is one of the most efficient systems to convert Sun energy into usable energy. Unfortunately, some technological barriers are still present in solar-thermal heat systems that limit the use of these technologies to decarbonize processes. An important obstacle is the requirement for heat at stable temperatures, which is not always achievable by solar fields, e.g. variable sky. For that reason, in this work, we studied the phase-change materials embedded in the ETC to keep stable the water temperature for a short period (minutes, hours). In this study, carnauba wax was used as a sustainable phase-change material (PCM), to avoid the use of PCM based on hydrocarbon waxes. The PCM has been packaged using a polyethylene bag inserted into an ETC with heat-pipe technologies and tested. The collector has been tested outdoors under solar irradiation and under shading conditions. The experimental results show that is possible to detect a sensible effect of the PCM on the temperature using 4 kg of carnauba wax while there is an important effect on the temperature stabilization using 9 kg of PCM. Using 9 kg of the PCM, we observed a stability of the outlet water temperature at 65°C for 30 minutes under shading conditions.

High-Fidelity Modeling and Experiments to Inform Safety Analysis Codes for Heat Pipe Microreactors

Heat pipe microreactors are reactor designs that primarily use liquid-metal heat pipes to cool the core. The main interest in heat pipes is the fact that they can remove heat passively. This, along with the use of liquid metal, allows the reactor to operate at higher temperatures. Although the use of heat pipes in nuclear reactors is new, liquid-metal heat pipe technology is mature. Nevertheless, experimental data on heat pipes are scarce, and very little is known about their behavior during abnormal operations and close to their thermal limits. Therefore, new experiments and accurate heat pipe simulations are needed to develop reliable closure models. This work describes a joint experimental and numerical investigation into heat pipes that attempts an initial closure of this gap. The numerical and experimental efforts are currently proceeding in parallel, aimed at different aspects of heat pipes. The numerical part is focused on gaps in local closures, and the experiments capture the overall heat pipe behavior.

An internal cooling grinding wheel: From design to application

The cooling and lubrication conditions during the grinding process significantly impact the nickel-based superalloy's final service performance. The existing jet cooling and heat pipe technology can solve the heat conduction problem in the grinding process of superalloy. Still, managing cooling, lubrication, and chip removal are difficult. This paper describes the design and fabrication of a novel central fluid-through internal cooling slotted grinding wheel with an ordered grain pattern to improve the grinding machinability of a nickel-based superalloy. The pressurized grinding fluid was ejected into the grinding zone via the pipe and tool holder from the lower-end face of the inner cooling wheel. The structure of the grinding wheel was optimized using computational fluid dynamics (CFD). The flow field in the grinding area achieved the highest overall flow rate, distribution homogeneity, and effective exit flow when the internal flow channel had four through-holes. The exit for the inner runner is located at the abrasive edge and diamond staggered pattern. Single-layer brazing was used to create cubic boron nitride (CBN) abrasive rings with various abrasive patterns. The internal cooling wheel matrix and various components were prepared according to the optimized grinding wheel geometry model. A grinding test bench was built to conduct an experimental study of grinding the nickel-based alloy GH4169. The results show that, under the same conditions, a diamond-shaped staggered pattern obtains lower grinding temperature, lower surface roughness, better surface morphology, and more significant residual compressive stress distribution than an abrasive cluster diagonal circular staggered pattern or disordered pattern. The average effective flow rate calculated by CFD is increased by 42.3% when compared to the disordered pattern. In the experiment, compared to the disordered arrangement, with the increase of grinding wheel’s rotating speed and coolant pressure, the average grinding temperature of abrasive grain with diamond-interleaved arrangement decreases by 58.2% and 51.7% respectively, and its surface hardening degree decreases by 11.1% and 11.7% respectively.

A new two-phase passive temperature control system for a wine fermenter

Thermal control of a fermenter tank is fundamental to guarantee a high-quality final product, especially in wine-making processes. Indeed, temperature is a crucial parameter for alcoholic fermentation in the production of wine, since it could modulate the generation of secondary products of fermentation in specific aromatic compounds. Fermentation is an exothermic process, and an efficient refrigeration system in fermenter tanks is necessary. Usually, to achieve this aim in fermentation tanks for wine-making processes, an external shell is implemented where a cooling fluid, normally water, flows. The circulation of the service fluid is triggered only when the temperature in the fermenter overcomes a critical value; however, this classical system could generate oscillation and stratification of the must temperature, reducing the goodness of the fermentation process. In this work, a substitutive cooling system based on heat pipe technology is proposed, and its feasibility is studied. It presents the benefit of always working and, for this reason, keeping a more constant and uniform value of temperature in the fermenter for the entire process duration. Additionally, the presented solution is completely passive, lowering energetic and economical costs. The obtained outcomes proved that the practical adoption of the proposed cooling system is achievable and that it constitutes an encouraging option.

Review of the State of the Art for Radial Rotating Heat Pipe Technology Potentially Applicable to Gas Turbine Cooling

Improvements in the efficiency of gas turbine engines over the decades have led to increasing turbine inlet temperatures. This, in turn, has resulted in the need to cool the turbine blades themselves to avoid damage to them. While air-cooling and film-cooling methods have been adopted as the primary methods of gas turbine blade cooling, the heat pipe cooling method shows greater potential in terms of temperature uniformity, maximum allowable gas temperature, reliability, and durability. This paper reviews the state-of-the-art research activities on the radial rotating heat pipes (RRHP) potentially applicable to gas turbine cooling. The emergence of the heat-pipe-cooled turbine blade concept, designs, and variants will be described at the beginning. Then the paper will review the literature addressing the heat transfer performance of RRHPs, and the effects on them of rotational forces, working fluid properties, and geometry, as well as operational limits they may be subject to. Additionally, the effects of secondary flow and numerical simulation of RRHPs will be reviewed and discussed. It can be concluded that fundamental studies are still needed for the understanding of the RRHP, as well as the improvement of numerical models.

Numerical Investigation on Internal Structures of Ultra-Thin Heat Pipes for PEM Fuel Cells Cooling

Proton exchange membrane fuel cell (PEMFC) powered propulsion has gained increasing attention in urban air mobility applications in recent years. Due to its high power density, ultra-thin heat pipe technology has great potential for cooling PEMFCs, but optimizing the limited internal cavity of the heat pipe remains a significant challenge. In this study, a three-dimensional multiphase model of the heat pipe cooled PEMFC is built to evaluate the impact of three internal structures, layered, spaced, and composite, of ultra-thin heat pipes on system performance. The results show that the heat pipe cooling with the composite structure yields a lower thermal resistance and a larger operating range for the PEMFC system compared to other internal structures because of more rational layout of the internal cavity. In addition, the relationship between land to channel width ratio (LCWR) and local transport property is analyzed and discussed based on composite structural heat pipes. The heat pipe cooled PEMFC with a LCWR of 0.75 has a significant advantage in limiting current density and maximum power density compared to the LCWRs of 1 and 1.33 as a result of more uniform in-plane distributions of temperature and liquid water within its cathode catalyst layer.

Heat pipes for PEM fuel cell cooling: State of the art review

The enormous usage of fossil fuels has caused a major shift in the scientific community's focus on hydrogen energy in the 21st century. Due to numerous appealing characteristics and excellent energy efficiency, proton exchange membrane (PEM) fuel cells are now the most popular hydrogen fuel cell type. PEM fuel cells have a high power generation efficiency, but they also produce 50% heat as a by-product, that must be evacuated from the stack for proper functioning during the electrochemical reaction. The current review paper tends to focus on the work of international researchers exploring the possibilities of passive cooling of a PEM fuel cell employing heat pipe technology to improve performance and durability in stationary and portable applications.

Investigation of calibration equations for NTC thermistors utilized in the deep-ocean temperature range

Deep-ocean temperature measurement demands sub-millikelvin precision over the range of 1–3 °C. Performance of a thermometry system using negative temperature coefficient thermistors is highly dependent on calibration methods and equations. Six pre-aged thermistors were calibrated in a water bath utilizing heat pipe technology. The primary standard triple point of water validated the thermistor stability. The performance of five calibration equations was evaluated by comparing fitting curves and interpolation residuals. The fitting curve deviation of all the equations was within 0.23 mK, excluding the Basic equation that reached 0.65 mK. The average interpolation residuals for the Hoge-1 and Basic equations were 0.15 mK and 0.35 mK, respectively. The Hoge-1 and Basic equations were shown to be sufficient and the third (or fourth) order equations were unnecessary for deep-ocean temperature measurements. Both the Hoge-1 and Basic equations demonstrated capacity to extrapolate by 0.5 K within 1 mK error.

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.

Numerical study on power battery thermal management system based on heat pipe technology

In the present work, a power battery pack and a novel thermal management system (TMS) based on the tubular heat pipe (THP) technology are designed according to the parameters of a pure electric light truck and battery. The TMS consists of THPs, power batteries, cooling plates, fins, and equivalent thermal conductivity is used to characterize the excellent thermal conductivity of THP. The heat generation rate of the battery at different discharge rates is obtained by establishing a multi-scale electrochemical–thermal coupling model, which accuracy is verified by the experiment. A multi-physics field coupling model is built to the thermal management system designed for the study. The results show that the battery temperature is higher when the battery is far from the THP in the cooling plate, and the maximum temperature reaches 35.6 °C at 1 C. Furthermore, the temperature difference between batteries is proportional to the discharge rate, and the maximum temperature difference reaches 7 °C at 2 C. The change in inlet temperature and wind speed can only restrain the temperature rise, while the temperature difference of the battery module is always 3.2 °C. When a fin spacing of 3 mm is chosen, the best temperature uniformity of the battery module is achieved at this time. The use of the multi-scale multi-physics field coupling analysis method in BTMS with heat pipes can be used as a reference for future numerical simulations of the same type.

Advances in heat pipe technologies for different thermal systems applications: a review

Advances in heat pipe technologies for different thermal systems applications: a review

Exergy-rational utilization of solar energy with advanced PVT systems and heat pipe technology in 100% renewable cities

This paper responds to the EU goals of decarbonization with solar energy leading to fifth-generation district energy systems (5DE). The dilemma of low-exergy (low-temperature) district heating systems with renewable and waste thermal sources and the temperature-incompatibility of the current comfort heating equipment demanding higher supply temperatures is addressed. Until innovative, low-exergy equipment and higher-exergy solar photo-voltaic-heat systems are developed, various methods of optimum temperature peaking and existing equipment oversizing are presented. Central temperature peaking at the plant site and the individual prosumer buildings are compared. A case study is presented, which involves an individually optimized solar prosumer building with an optimum mix of heat pump oversizing and commercial radiator oversizing. Results show that CO2 emissions responsibility-based optimum mix compared to economy-based optimum mix reduces the responsibility by 30%. This analysis was repeated by cascading two smaller heat pumps instead of a larger one to increase the overall COP. This change further improved the solution by 4% points. Results have also been compared to a modified case where cascaded heat pumps are coupled with low-exergy heat pipe radiators. This coupling resulted in much more improvement by an additional 52% points. The paper concludes that the key is low-exergy heating and cooling equipment. Then the fifth-generation district energy systems with supply temperatures as low as 320 K (47°C) and return temperatures as low as 300 K (27°C) will be possible with renewable and waste energy sources if the one-way distance between the plant and the district is not more than 1.6x10-5 km/kW times the thermal capacity of the district raised to a power of 1.5.

Model Development of a Thermosyphon Heat Pipe for the Temperature Management in a Wine Fermenter Tank

The grape must temperature management in a fermenter tank is fundamental to guaranty a high-quality wine. The fermentation is an exothermic process and a good cooling system in fermenter tanks is required. However, for reducing costs and increasing the efficiency of the cooling operation, a passive device based on the heat pipe technology was proposed. Since its thermal sizing must necessarily be accurate to allow a correct temperature of the product during fermentation, in this paper a thermal model of the proposed device was proposed and experimentally validated.

Operational characteristics of oscillating heat pipe charged with R-134a for heat recovery at low temperature

The oscillating heat pipe could transport heat quickly using rapid self-excited two-phase flow oscillation within very simple structure than any other conventional heat pipe technologies, thus it can cause significant improvement of heat exchange performance specially for waste heat recovery at low temperature. In the present study, the thermal performance of the oscillating heat pipe heat exchangers under temperature-controlled mode was experimentally and theoretically investigated. The oscillating heat pipe with 5-turns and 20-turns were manufactured using a copper meandering tube with inner diameter of 2 mm and R-134a was used as the working fluid due to its superior heat transfer performance at low temperatures. It is found that the smaller inclination angles cause the delay of the start-up and performance degradation for oscillating heat pipe with 5-turns. However, the oscillating heat pipe with 20-turns represents the same start-up operation and thermal performance regardless of inclination angles. The suggested theoretical model well predicts the thermal performance of the oscillating heat pipe heat exchangers with 5-turns and 20-turns under conditions in which the oscillating heat pipe operates normally with high thermal performance.

A review on data centre cooling system using heat pipe technology

Heat pipe, a high efficient, cost effective and reliable device, is considered one of the most promising passive technologies for cooling data centres. Aiming to provide comprehensive information and focused perspective on heat pipe system for cooling data centres, the literature reviewed in this review is obtained from the Web of Science by searching the topic “heat pipe” and “data centre” conducted on Sep. 1, 2019 for the decade from 2009 to 2018. In this paper, a comprehensive review on heat pipes for use in data centre cooling systems will be carried out, starting from the working principle, heat transfer analysis and applications. The review works will be analysed in terms of the system research methodology, energy performance evaluation, and IT tasks. From the system research methodology, the heat pipe structure, simulation and testing analyses were conducted. From the energy performance evaluation, the energy consumption, energy recovery and energy saving analyses were studied. From the IT tasks, the avoidance of hot spots and thermal management in the data centres were analysed. The opportunities for further works are revealed including: developing new and efficient data centre cooling systems employing advanced technology; optimising the heat pipe structure for the data centre cooling systems; testing the data centre cooling systems under actual conditions; and evaluating the economic feasibility and market potential of the data centre cooling systems. This review provides the guidelines for the development of data centre cooling system based on the heat pipe.