loop heat pipes
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2022 ◽  
Vol 92 (1) ◽  
pp. 22
Author(s):  
В.М. Кисеев ◽  
О.В. Сажин

Heat transfer in capillary pumped loops (CPL) is carried out by transferring the mass of the circulating coolant in the form of liquid and vapor. Therefore, the hydrodynamics of the phases in the CPL determines their heat transfer capacity (heat flow or the product of the heat flow by the heat transfer length). The influence of structural, hydraulic and thermo-physical properties of capillary structures used as capillary pumps in two-phase thermal control systems (Loop Heat Pipes - LHP) on their heat transfer capacity has been analyzed. Methods of increasing the heat transfer capacity of LHP, due to the use of anisotropic capillary structures with a decrease in pore sizes in the direction of the vaporization zone, have been determined. The conditions of LHP operability and the method of analytical calculation of the temperature field in anisotropic capillary structures for a model with pseudo-convection have been considered. The calculated and experimental data have been compared.


Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1374
Author(s):  
Pawel Szymanski

The focus of this review is to present the current advances in Loop Heat Pipes (LHP) with flat evaporators, which address the current challenges to the wide implementation of the technology. A recent advance in LHP is the design of flat-shaped evaporators, which is better suited to the geometry of discretely mounted electronics components (microprocessors) and therefore negate the need for an additional transfer surface (saddle) between component and evaporator. However, various challenges exist in the implementation of flat-evaporator, including (1) deformation of the evaporator due to high internal pressure and uneven stress distribution in the non-circular casing; (2) heat leak from evaporator heating zone and sidewall into the compensation chamber; (3) poor performance at start-up; (4) reverse flow through the wick; or (5) difficulties in sealing, and hence frequent leakage. This paper presents and reviews state-of-the-art LHP technologies; this includes an (a) review of novel manufacturing methods; (b) LHP evaporator designs; (c) working fluids; and (d) construction materials. The work presents solutions that are used to develop or improve the LHP construction, overall thermal performance, heat transfer distance, start-up time (especially at low heat loads), manufacturing cost, weight, possibilities of miniaturization and how they affect the solution on the above-presented problems and challenges in flat shape LHP development to take advantage in the passive cooling systems for electronic devices in multiple applications.


Author(s):  
Guangming Xu ◽  
Rongjian Xie ◽  
Nanxi Li ◽  
Cheng Liu

Abstract Two kinds of new refrigerant-R1234ze (E) and R245fa were discussed as substitutes or supplements to traditional working fluids of loop heat pipes based on their favorable thermophysical properties and characteristics such as being safe and environmentally friendly. Thermal characteristics of a loop heat pipe with sintering copper wick at different charging ratios were experimentally investigated under variable heat loads. The results showed that the optimal charging ratio in the loop heat pipe range from 65% to 70%, and at this charging level, the R1234ze(E) system had better start-up response, while the R245fa system presented a stronger heat transfer capacity. The characteristic temperature of R1234ze(E) system was below 35 °C, and the corresponding thermal resistance was 0.08 K/W ~ 1.62 K/W under heat loads ranging from 5 W to 40 W. The thermal resistance of the R245fa system was 0.18 K/W ~ 0.91 K/W under heat loads of 10 W ~ 60 W, and the operating temperature was below 60 °C. The loop heat pipes charged with the proposed new refrigerants exhibit superb performance in room temperature applications, making them beneficial for enhancing the performance of electronics, and could provide a distinctive choice for the cooling of small-sized electronics especially.


Author(s):  
Randeep Singh ◽  
Tien Nguyen

Abstract This present paper investigates the potential of loop heat pipe (LHP), with respect to technological merits and application niche, in automotive thermal management. Broadly, LHP design and applicability for hot spot cooling in electronics (local dissipation), and for heat transport over longer distances (remote dissipation) has been proposed and discussed in detail. The basic module in these applications includes loop heat pipe with different shapes and sizing factors. Two types of LHP design have being tested and results discussed. The miniature version, with 10 mm thick and flat evaporator, for cooling ECU with 70 W chipset while keeping source temperature below 100 °C limit was evaluated. Two larger versions with cylindrical evaporator, 25 mm diameter & 150 mm length, and heat transfer distances of 250 mm and 1000 mm respectively were tested for power electronics and battery cooling, with more than 500 W transport capabilities in gravity field. In conclusions, loop heat pipes will provide an energy efficient passive thermal control solution for next generation low emission automotive, particularly for electric vehicles which have high level electrifications and more definitive cooling requirements.


2021 ◽  
Vol 22 (1) ◽  
pp. 23-35
Author(s):  
Yu Wang ◽  
Oleg V. Denisov ◽  
Liliana V. Denisova

One of the key problems in the development of nanosatellites is to provide a given temperature range for the operation of the on-board computer. The constantly increasing information load leads to the need to use more advanced processors with high thermal design power (TDP). The indicated thermal regime of processors can be achieved using remote heat removal systems - miniature loop heat pipes. Using a model of nanosatellite as an example, a thermal control system with miniature loop heat pipes is designed. The simulation was carried out in the Siemens NX program in the elliptical and geostationary orbits of the Earth. The cooling schemes of the processor with a thermal power of 15 W using one and two loop heat pipes are considered. Calculations showed that the use of loop heat pipes can reduce the processor temperature to acceptable values. The anisotropy of the thermal conductivity coefficient in the reinforcement plane of the composite material of the nanosatellite case can have a significant effect on the temperature of the processor. This opens up prospects for the use of anisotropic composite materials to ensure the thermal regime of the nanosatellite.


Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1332
Author(s):  
Bing Cai ◽  
Weizhong Deng ◽  
Tong Wu ◽  
Tingting Wang ◽  
Zhengyuan Ma ◽  
...  

A pouring silicate wick was manufactured to explore the influence of process and physical properties on the production and performance of loop heat pipes (LHP). This paper theoretically analyzed the advantages of pouring porous wick and introduced the technology of pouring silicate directly on evaporator. Based on this, the heat transfer performance of copper-methanol LHP system with pouring porous wick was tested under different positions. The results showed that with the input of multiple heat sources, the LHP could start up and maintain a stable temperature from 40 W to 160 W. When the vapor grooves were located above the compensation chamber, it was difficult to start up positively. By adding gravity assistance, the system could obtain more stable liquid supply and vapor flow, so as to realize start up. In the variable heat load test, the LHP showed good adaptability to the change of heat load. The thermal resistance of the system decreased with the increase of heat load. The thermal resistance of the evaporator almost unchanged and was always lower than 0.05 °C/W, which indicated that the pouring porous wick in the evaporator had good heat load matching.


Author(s):  
Bingyao Lin ◽  
Nanxi Li ◽  
Shiyue Wang ◽  
Leren Tao ◽  
Guangming Xu ◽  
...  

Abstract In this paper, a thin film evaporation model that includes expressions for energy, mass and momentum conservation was established through the augmented Young-Laplace model. Based on this model, the effects of pore size and superheating on heat transfer during thin film evaporation were analyzed. The influence of the wick diameter of the loop heat pipe (LHP) on the critical heat flux of the evaporator is analyzed theoretically. The results show that pore size and superheating mainly influence evaporation through changes in the length of the transition film and intrinsic meniscus. The contribution of the transition film area is mainly reflected in the heat transfer coefficient, and the contribution of the intrinsic meniscus area is mainly apparent in the quantity of heat that is transferred. When an LHP evaporator is operating in a state of surface evaporation, a higher heat transfer coefficient can be achieved using a smaller pore size.


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