Heat transfer performance of a flexible looped heat pipe using R134a as a working fluid: Proposal for a method to predict the maximum heat transfer rate of FLHP

Abstract This paper presents the heat transfer performance of a Flexible Looped Heat Pipe (FLHP) using R134a as a working fluid. In our evaluation system, an evaporator and a condenser are connected by long flexible tubes with a diameter of 3 mm, and the total piping length of this looped heat pipe system is approximately 7500 mm. We selected porous Teflon with an effective pore diameter of 2 r cw = 1.2 µm to overcome high gravitational heads. Elevation of the evaporator above the condenser Δ H = H e − H c ) was changed in three conditions [ $\def\circle#1{{\ooalign{\hfil\raise.07ex\hbox{#1}\hfil\crcr\mathhexbox20D}}} \circle{1}$ Top heat mode (Δ H = +1 m), $\def\circle#1{{\ooalign{\hfil\raise.07ex\hbox{#1}\hfil\crcr\mathhexbox20D}}} \circle{2}$ Horizontal mode (Δ H = 0), $\def\circle#1{{\ooalign{\hfil\raise.07ex\hbox{#1}\hfil\crcr\mathhexbox20D}}} \circle{3}$ Bottom heat mode (Δ H = −1 m)] considering the terrestrial application and the influence of gravity on the FLHP performance was investigated. FLHP provided high thermal transport capacities over long distances through small cross‐sectional flexible tubes compared with conventional heat pipes. We also proposed an analysis method to predict the maximum heat transfer rate of FLHP. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 306–318, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10093