Parametric experiments on a miniature loop heat pipe with PTFE wicks

Abstract

A miniature loop heat pipe (LHP) with polytetrafluoroethylene (PTFE) wicks was fabricated and its evaporator thermal performance was investigated with parametric experiments. The variables considered were the clearance between the cylindrical evaporator casing and the wick, the working fluid inventory, the properties of the working fluids, and the sink temperature. Micro-gaps between the outer surface of the wick and inner surface of the evaporator casing were included in the experiments with variables of clearance to investigate their effect on the evaporator heat-transfer coefficient. Ethanol, acetone, and R134a were charged in the LHP to evaluate the effect of the properties of the working fluids. The LHP tests were conducted with several W/cm 2 of applied heat flux to the evaporator under controlled sink temperature. The clearance seriously affected the evaporator heat-transfer coefficient, with a gap of 20 μm between the wick and casing having the best effect on the evaporator heat transfer across a range of tested heat fluxes. The effects of the working fluid inventory and fluid properties on the evaporator heat transfer were also clarified.Finally, the developed LHP was tested using ethanol as a working fluid under a stepwise heat load and sink temperature.

Numerical Study of Thermal Performance of a Capillary Evaporator in a Loop Heat Pipe with Liquid-Saturated Wick

“…In the PNM, characteristics of the porous structure can be established by setting dimensions for voids-the radius of each pore pore r , the radius of each throat th r , and the length of each throat th l (see Figure 1(c)) -which control the porosity, permeability, and pore radius distribution, respectively. In this study, a polytetrafluoroethylene (PTFE) wick [16], for which the porosity and permeability are 0.34 and 2.0 × 10 −14 m 2 , respectively, is modeled. The mode and maximum pore radius were 1.2 and 2.1 μm, respectively.…”

“…This approach has been addressed in [14]. In our previous study, polytetrafluoroethylene (PTFE) wicks, with a bulk thermal conductivity of 0.25 W/m•K, were applied in an attempt to decrease heat leaks to the CC [8] [15] [16]. Moreover, there is a requirement also for the evaporator to transfer the maximum heat load.…”

A thermosiphon loop for high heat flux removal using flow boiling of ethanol in OMM with taper

“…They are preferred where device compactness is desired and the condensing surfaces can be placed in close proximity of the evaporator surface. Nishikawara and Nagano [6] carried out a parametric study and investigated the effect of gap between wick and the evaporator, filling ratio, temperature of heat sink and working fluid properties on performance of heat pipe. R134a, acetone and ethanol were chosen as working fluids in their study.…”

Development and Investigation of a Miniature Copper-Acetone Loop Heat Pipe with a Flat Evaporator

“…References [13]- [16] present the results of investigations of LHPs with working fluids that are alternatives to water, namely, acetone, ethanol, methanol and R 134. Thus, in particular, in [13] an LHP equipped with a cylindrical evaporator 12 mm in diameter and a wick made of PTFE demonstrated serviceability in a horizontal position in the range of heat loads from 4 W to 40 W at heat sink temperatures varying from 0˚C to 75˚C.…”

“…Thus, in particular, in [13] an LHP equipped with a cylindrical evaporator 12 mm in diameter and a wick made of PTFE demonstrated serviceability in a horizontal position in the range of heat loads from 4 W to 40 W at heat sink temperatures varying from 0˚C to 75˚C. A minimum value of thermal resistance of 0.30 K/W was achieved at a heat load of 30 W and a heat sink temperature of 75˚C.…”