Modeling and Analysis of Supercritical Startup of a Cryogenic Loop Heat Pipe

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Lizhan Bai ◽  
Guiping Lin ◽  
G. P. Peterson ◽  
Dongsheng Wen
Keyword(s):  
Mathematical Model ◽  
Parametric Study ◽  
Heat Load ◽  
Heat Pipes ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Modeling And Analysis ◽  
Loop Heat Pipes ◽  
Network Method ◽  
Startup Performance

Supercritical startup of cryogenic loop heat pipes (CLHPs) has been investigated both analytically and experimentally. Mathematical model of the supercritical startup has been established using the nodal network method, and parametric study is conducted where the effects of working fluid charged pressure, parasitic heat load from the ambient, etc., on the supercritical startup characteristics are incorporated and evaluated. The result improves understanding of the effects of these parameters on supercritical startup and identification of those conditions under which supercritical startup can and will occur. In addition, the modeling effort has led to an enhanced understanding of supercritical startup performance.

scholarly journals Experimental Study on Thermal Performance of a Loop Heat Pipe with Different Working Wick Materials

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2453
Author(s):  
Kyaw Zin Htoo ◽  
Phuoc Hien Huynh ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Stainless Steel ◽  
Heat Pipes ◽  
Working Fluid ◽  
Stable Operation ◽  
Loop Heat Pipe ◽  
Heater Surface ◽  
Loop Heat Pipes ◽  
Limited Temperature ◽  
Sintered Stainless Steel ◽  
Continuous Heat

In loop heat pipes (LHPs), wick materials and their structures are important in achieving continuous heat transfer with a favorable distribution of the working fluid. This article introduces the characteristics of loop heat pipes with different wicks: (i) sintered stainless steel and (ii) ceramic. The evaporator has a flat-rectangular assembly under gravity-assisted conditions. Water was used as a working fluid, and the performance of the LHP was analyzed in terms of temperatures at different locations of the LHP and thermal resistance. As to the results, a stable operation can be maintained in the range of 50 to 520 W for the LHP with the stainless-steel wick, matching the desired limited temperature for electronics of 85 °C at the heater surface at 350 W (129.6 kW·m−2). Results using the ceramic wick showed that a heater surface temperature of below 85 °C could be obtained when operating at 54 W (20 kW·m−2).

Minimizing the Wick Thickness in a Planar Microscale Loop Heat Pipe Using Efficient Thermodynamic Design

2011 ◽  
Author(s):  
Navdeep S. Dhillon ◽  
Jim C. Cheng ◽  
Albert P. Pisano
Keyword(s):  
Heat Flow ◽  
Heat Pipe ◽  
Thermal Characteristics ◽  
Heat Pipes ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Loop Heat Pipes ◽  
Evaporator Section ◽  
Compensation Chamber

Theoretical and numerical thermodynamic analysis of the evaporator section of a planar microscale loop heat pipe is presented, to minimize the permissible wick thickness in such a device. In conventional cylindrical loop heat pipes, a minimum wick thickness is required in order to reduce parasitic heat flow, and prevent vapor leakage, into the compensation chamber. By taking advantage of the possibilities allowed by microfabrication techniques, a planar evaporator/compensation chamber design topology is proposed to overcome this limitation, which will enable wafer-based loop heat pipes with device thicknesses on the order of a millimeter or less. Thermodynamic principles governing two-phase flow of the working fluid in a loop heat pipe are analyzed to elucidate the fundamental requirements that would characterize the startup and steady state operation of a planar phase-change device. A three dimensional finite element thermal-fluid solver is implemented to study the thermal characteristics of the evaporator section and compensation chamber regions of a planar vertically wicking micro-columnated loop heat pipe. The use of in-plane thermal conduction barriers to reduce parasitic heat flow into the compensation chamber is demonstrated.

The Effect of CuO-Water Nanofluid and Biomaterial Wick on Loop Heat Pipe Performance

2014 ◽  
Vol 875-877 ◽  
pp. 356-361 ◽  
Author(s):  
Nandy Putra ◽  
Wayan Nata Septiadi ◽  
Rosari Saleh ◽  
Rardi Artono Koestoer ◽  
Suhendro Purbo Prakoso
Keyword(s):  
Heat Pipe ◽  
Pure Water ◽  
Sol Gel ◽  
Heat Pipes ◽  
Cuo Nanoparticles ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Gel Method ◽  
Loop Heat Pipes ◽  
Copper Pipe

The determinants of heat pipe performances are its wick and working fluid, instead of controlled by the material, dimension, and the shape of heat pipe. This study aimed to determine the effect of using nanofluid on the performance of Loop heat pipes (LHP) with CuO-water nanofluid that using biomaterials wick. LHP was made of 8 mm diameter copper pipe, with the diameter of evaporator and the condenser was 20 mm respectively and the length of the heat pipe was 100 mm. The wick was made of biomaterials Collaria Tabulate and the working fluid was CuO-water nanofluids where the CuO nanoparticles were synthesized by sol-gel method. The characteristic of the Tabulate Collaria biomaterial as a wick in LHP was also investigated in this experiment. The results of the experiments showed that the temperature differences between the evaporator and condenser sections with the biomaterial wick and CuO-water nanofluid were less than those using pure water. These results make the biomaterial (Collar) and nanofluids are attractive both as wick and working fluid in LHP technology. Keywords: loop heat pipe, wick, biomaterial, nanofluid.

Operational Limitations of Heat Pipes With Silver-Water Nanofluids

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Lazarus Godson Asirvatham ◽  
Rajesh Nimmagadda ◽  
Somchai Wongwises
Keyword(s):  
Silver Nanoparticles ◽  
Heat Pipe ◽  
Heat Load ◽  
Operating Temperature ◽  
Particle Diameter ◽  
Heat Pipes ◽  
Working Fluid ◽  
Limit Value ◽  
Capillary Limit ◽  
Nanoparticles Concentration

The paper presents the enhancement in the operational limits (boiling, entrainment, sonic, viscous and capillary limits) of heat pipes using silver nanoparticles dispersed in de-ionized (DI) water. The tested nanoparticles concentration ranged from 0.003 vol. % to 0.009 vol. % with particle diameter of <100 nm. The nanofluid as working fluid enhances the effective thermal conductivity of heat pipe by 40%, 58%, and 70%, respectively, for volume concentrations of 0.003%, 0.006%, and 0.009%. For an input heat load of 60 W, the adiabatic vapor temperatures of nanofluid based heat pipes are reduced by 9 °C, 18 °C, and 20 °C, when compared with DI water. This reduction in the operating temperature enhances the thermophysical properties of working fluid and gives a change in the various operational limits of heat pipes. The use of silver nanoparticles with 0.009 vol. % concentration increases the capillary limit value of heat pipe by 54% when compared with DI water. This in turn improves the performance and operating range of the heat pipe.

Experimental investigation of a loop heat pipe with R245fa and R1234ze (E) as working fluids

2021 ◽  
pp. 1-17
Author(s):  
Guangming Xu ◽  
Rongjian Xie ◽  
Nanxi Li ◽  
Cheng Liu
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Characteristic Temperature ◽  
Thermal Characteristics ◽  
Heat Pipes ◽  
Loop Heat Pipe ◽  
Working Fluids ◽  
Loop Heat Pipes ◽  
Heat Transfer Capacity ◽  
Heat Loads

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.

Steady State Parametric Modeling of Non-Conventional Loop Heat Pipes

2013 ◽  
Author(s):  
Karthik S. Remella ◽  
Frank M. Gerner ◽  
Ahmed Shuja
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Thermal Energy ◽  
Heat Pipes ◽  
Parametric Model ◽  
Parametric Modeling ◽  
Working Fluid ◽  
Loop Heat Pipes

Loop Heat Pipes (LHPs) are used in many thermal management applications, especially for micro-electronics cooling, because of their ability to passively transport thermal energy from a source to a sink. This paper describes the development of a parametric model for a non-conventional LHP operating in steady state, employed to cool Light Emitting Diodes (LEDs). This device is comprised of a flat evaporator, and a finned circular loop wherein condensation and sub-cooling of the working fluid takes place. Unlike a conventional LHP, this device has no compensation chamber. In the mesh screen of the evaporator, the vapor flow entrains liquid and hence the quality of the two-phase mixture leaving the evaporator (xevap) is less than unity (unlike in a conventional LHP where saturated vapor leaves the evaporator). Since this lower quality (approximately 0.2) results in a smaller ratio of latent energy to sensible energy being removed by the condenser and sub-cooler respectively; the ratio of the length of the sub-cooler to condenser length is significantly larger. This results in more stable and controlled operation of the device. Mathematical models of the evaporator, the condenser and the sub-cooler sections are developed, and two closure conditions are employed in this model. For consistency and accuracy, some parameters in the model, such as the natural convection heat transfer coefficient (h o) and a few thermal resistances in the evaporator, are estimated empirically from test data on the device. The empirically obtained value of the heat transfer coefficient is in very good agreement with correlations from the literature. The parametric model accurately predicts the LED board temperature and other temperatures for a specific amount of thermal energy dissipated by the LEDs.

Improvement of Heat Transfer Performance of Loop Heat Pipe for Electronic Devices

2011 ◽  
Author(s):  
Tomonao Takamatsu ◽  
Katsumi Hisano ◽  
Hideo Iwasaki
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Thermal Energy ◽  
Heat Load ◽  
Cooling System ◽  
Electronic Devices ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Reserve Area ◽  
Heat Transport Capability

In this paper is presented the results on performance of the cooling model using Loop Heat Pipe (LHP) system. In recent years, ever-ending demand of high performance CPU led to a rapid increase in the amount of heat dissipation. Consequently, thermal designing of electronic devices need to consider some suitable approach to achieve high cooling performance in limited space. Heat Pipe concept is expected to serve as an effective cooling system for laptop PC, however, it suffered from some problems as follows. The heat transport capability of conventional Heat Pipe decreases with the reduction in its diameter or increase in its length. Therefore, in order to use it as cooling system for future electronic devices, the above-mentioned limitations need to be removed. Because of the operating principle, the LHP system is capable of transferring larger amount of heat than conventional heat pipes. However, most of the LHP systems suffered from some problems like the necessity of installing check valves and reservoirs to avoid occurrence of counter flow. Therefore, we developed a simple LHP system to install it on electronic devices. Under the present experimental condition (the working fluid was water), by keeping the inside diameter of liquid and vapor line equal to 2mm, and the distance between evaporator and condenser equal to 200mm, it was possible to transport more than 85W of thermal energy. The thickness of evaporator was about 5mm although it included a structure to serve the purpose of controlling vapor flow direction inside it. Successful operation of this system at inclined position and its restart capability are confirmed experimentally. In order to make the internal water location visible, the present LHP system is reconstructed using transparent material. In addition, to estimate the limit of heat transport capability of the present LHP system using this thin evaporator, the air cooling system is replaced by liquid cooling one for condensing device. Then this transparent LHP system could transport more than 100W of thermal energy. However, the growth of bubbles in the reserve area with the increase in heat load observed experimentally led to an understanding that in order to achieve stable operation of the LHP system under high heat load condition, it is very much essential to keep enough water in the reserve area and avoid blocking the inlet with bubbles formation.

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