Study Of Longitudinal Heat Transfer In Low Temperature Heat Pipes With Axial Grooves And Discrete Metal Fibres For Space Thermal Control Systems

Abstract

Development of space thermal control (TC) technique is tightly connected with achievements of heat pipe (HP) science and technology. The paper presents the experimental results of heat transfer for the following perspective HP designs with round cross section in wide range of operation parameters: saturation vapor temperature -70…+60 C, transferred heat power 0.5-100 W, axial heat flux density 10-250 W/cm2: a Copper – methanol HP with cooper discrete metal fiber capillary structure, external diameter 0.006 m, type – variable thermal conductance b Stainless steel – methanol HP with cooper discrete metal fiber capillary structure, external diameter 0.008 m, type- variable thermal conductance c Aluminum –ammonia HP with axial grooved capillary structure, external diameter 0.012 m, type- constant thermal conductance As characteristic parameter for comparison the ratio R=(T1-T2)/Q is used, where Q- transferred heat power, T1, T2 – averaged temperature of heat input and output zones of heat pipe. HPs “a” have shown essential impact of T2 of R, which varies from 60 K/W to 0.5 K/W. Physical basis of such behavior deals with changing of vapor flow regime in inner space and with the change of intensity of heat transfer by saturation vapor pressure. For HP “b” parameter R has variation from 90 K/W to 4 K/W. Physical basis of such behavior deals with creation of vapor –noncondensible gas boundary in coldest part of heat pipe and as the sequence, with variation of intensity of heat transfer. For HP “c” parameter R varies from 0.06 K/W to 0.045 K/W. Change of T2 has no essential impact of HP thermal resistance R. Comparison of longitudinal heat transfer characteristics of different types of heat pipes, obtained on representative quantity of tested units, allowed to define their functional abilities and duties in TC for different space applications.