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.

Effect of Increasing Wick Evaporation Area on Heat Transfer Performance for Loop Heat Pipes

2013 ◽  
Vol 711 ◽  
pp. 223-228 ◽  
Author(s):  
Shen Chun Wu ◽  
Jhih Huang Gao ◽  
Zih Yan Huang ◽  
Dawn Wang ◽  
Cho Jeng Huang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Surface Area ◽  
Heat Transfer Performance ◽  
Heat Pipes ◽  
Loop Heat Pipe ◽  
Transfer Performance ◽  
Loop Heat Pipes ◽  
Heat Transfer Capacity

This study investigates the effects of increasing the evaporating area of wick in a loop heat pipe (LHP). This work attempts to improve the performance of the loop heat pipe by increasing the number of grooves and thereby the surface area of the wick. The number of grooves is increased from eight to twelve. Experimental results show that increasing the number of grooves not only increases the surface area of the wick but also enhances LHP performance. When the evaporating surface area increases by 50%, which corresponds to increasing the number of grooves from eight to twelve, the heat transfer capacity increases from 310W to 470W and the thermal resistance is reduced from 0.21°C/W to 0.17°C/W. According to preliminary measurements, increasing the number of grooves in the loop heat pipe is highly promising for improving the heat transfer performance.

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.

Response of Loop Heat Pipes to Transient Heat Loads

1999 ◽  
Author(s):  
J. B. Long ◽  
J. M. Ochterbeck
Keyword(s):  
Heat Pipe ◽  
Control Systems ◽  
Heat Pipes ◽  
Thermal Control ◽  
Loop Heat Pipe ◽  
Loop Heat Pipes ◽  
Power Inputs ◽  
Cyclic Heat ◽  
Lower Limits ◽  
Heat Loads

Abstract Loop heat pipes currently are being used in the thermal control systems for satellites. To expand possible loop heat pipe applications, information regarding response to transient heat inputs is required. In this investigation, two loop heat pipes with dual compensation chambers were subjected to heat inputs of varying magnitude, frequency, and waveform (square and sinusoidal). The performance of each loop heat pipe under these conditions was evaluated in different gravitational orientations. The upper and lower limits of heat transport also were assessed. A principle finding was that cyclic heat loads tended to aid startup of the loop heat pipes at the low power inputs.

Experimental Investigation of the Miniature Loop Heat Pipe With Flat Evaporator

2005 ◽  
Author(s):  
Randeep Singh ◽  
Aliakbar Akbarzadeh ◽  
Masataka Mochizuki ◽  
Thang Nguyen ◽  
Vijit Wuttijumnong
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Thermal Control ◽  
Capillary Forces ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Wick Structure ◽  
Flat Evaporator ◽  
Heat Loads

Loop heat pipe (LHP) is a very versatile heat transfer device that uses capillary forces developed in the wick structure and latent heat of evaporation of the working fluid to carry high heat loads over considerable distances. Robust behaviour and temperature control capabilities of this device has enable it to score an edge over the traditional heat pipes. In the past, LHPs has been invariably assessed for electronic cooling at large scale. As the size of the thermal footprint and available space is going down drastically, miniature size of the LHP has to be developed. In this paper, results of the investigation on the miniature LHP (mLHP) for thermal control of electronic devices with heat dissipation capacity of up to 70 W have been discussed. Copper mLHP with disk-shaped flat evaporator 30 mm in diameter and 10 mm thickness was developed. Flat evaporators are easy to attach to the heat source without any need of cylinder-plane-reducer saddle that creates additional thermal resistance in the case of cylindrical evaporators. Wick structure made from sintered nickel powder with pore size of 3–5 μm was able to provide adequate capillary forces for the continuos circulation of the working fluid, and successfully transport heat load at the required distance of 60 mm. Heat was transferred using 3 mm ID copper tube with vapour and liquid lines of 60 mm and 200 mm length respectively. mLHP showed very reliable start up at different heat loads and was able to achieve steady state without any symptoms of wick dry-out. Tests were conducted on the mLHP with evaporator and condenser at the same level. Total thermal resistance, R total of the mLHP came out to be in the range of 1–4°C/W. It is concluded from the outcomes of the investigation that mLHP with flat evaporator can be effectively used for the thermal control of the electronic equipments with restricted space and high heat flux chipsets.

scholarly journals Experimental Set up of Two Closed Loop Pulsating Heat Pipe (CLPHP) with Water base Fluids

2019 ◽  
Vol 8 (12S) ◽  
pp. 715-719
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Dissipation ◽  
Heat Pipes ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Water Mixture ◽  
Working Fluids ◽  
Pure Fluids ◽  
Acetone Water

Heat pipes are deliberated to be effective heat dissipation devices compared to other types of heat sinks due to their high effective thermal conductivity. Because of the flexibility in the design and layout of heat pipe turns along the heat source, pulsating heat pipes have gained popularity. One of the parameters that have the mainimpact on the presentation of CLPHP is the thermo physical properties of the working fluid. The properties of the working fluid affect the temperature difference between the evaporator and the condenser which in turn affect the thermal resistance of the CLPHP. In this connection, the influence of different working fluids is experimentally investigated on a two loop CLPHP, varying the evaporator heat flux. Pure fluids, viz., water, acetone, benzene and binary mixture, viz., Acetone-water and Benzene-water are utilized on working fluids. The heat input considered at the evaporator is 32W, 48W and 60W. The filling ratio is kept as 50 %. The results show that among the working fluids considered for the study, acetone exhibits least thermal resistance among the pure fluids at all heat fluxes considered in the analysis, while Acetone-water mixture has exhibited least thermal resistance among the water based mixtures.

Study on the Thermal Characteristics of Heat Pipes with Water-Based MWCNT Nanofluids

2011 ◽  
Vol 110-116 ◽  
pp. 1879-1885
Author(s):  
Hyo Jun Ha ◽  
Ji Hun Park ◽  
Seok Pil Jang
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Volume Fraction ◽  
Thermal Characteristics ◽  
Heat Pipes ◽  
Multiwalled Carbon ◽  
Evaporation Temperature ◽  
Water Based

In this paper, thermal characteristics of miniature heat pipes with grooved wick and water-based multiwalled carbon nanotubes(MWCNT) nanofluids(0.1, 0.2, and 0.5 vol.%) as working fluids are experimentally investigated. The thermal conductivity and thermal resistances are measured and compared with those of DI water. The thermal conductivity of water-based MWCNT nandfluids is enhanced by up to 29% compared with that of DI water. Experiments are performed under the same evaporation temperature condition. The thermal resistance of heat pipe is reduced from 30% to 35.2% as the volume fraction of nanoparticles inceasing from 0.1% to 0.5%. Finally, based on the experimental results, we present the reduction of the thermal resistances of the heat pipes compared with conventional heat pipes cannot be explained by only the thermal conductivity of water-based MWCNT nanofluids.

Loop Heat Pipes for Thermal Management of Electric Vehicles

2021 ◽  
pp. 1-12
Author(s):  
Randeep Singh ◽  
Tien Nguyen
Keyword(s):  
Heat Pipe ◽  
Thermal Management ◽  
Electric Vehicles ◽  
Hot Spot ◽  
Heat Pipes ◽  
Thermal Control ◽  
Loop Heat Pipe ◽  
Basic Module ◽  
Loop Heat Pipes ◽  
High Level

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.

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.

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