Evaporation Heat Transfer Coefficient in a Capillary Pumped Loop for Different Working Fluids
Abhijit A. Adoni1,a, V. S. Jasvanth1,b, Amrit Ambirajan1,c, Dinesh Kumar1,d, D. R. Bhandari1,e,
K. Badarinarayana1,f and Pradip Dutta2
1Thermal Systems Group, ISRO Satellite Centre, Bangalore, Karnataka 560 017, India.
aabhijit@isac.gov.in
bjasvanth@isac.gov.in
cambi@isac.gov.in
ddkumar@isac.gov.in
ebhandari@isac.gov.in
fkbn@isac.gov.in
2Department of Mechanical Engineering, Indian Institute of Science, Bangalore, Karnataka 560 012, India.
pradip@mecheng.iisc.ernet.in
ABSTRACT
Capillary pumped loop (CPL) and Loop Heat Pipe (LHP) are passive two-phase heat transport devices. They have been gaining importance as a part of the thermal control system of spacecraft. Their working principle is similar to that of the heat pipe, however the wick is localized to the evaporator wherein heat is applied. The liquid and vapour lines (smooth tubes) connect the evaporating and condensing region. The flow is sustained by surface tension in the pores of the wick. CPLs and LHPs differ based on the location of the two-phase reservoir — the reservoir in an LHP is thermally and hydraulically linked to the evaporator, whereas the reservoir in a CPL is plumbed to the liquid line (or the evaporator as in three port CPL) with just a hydraulic link between them.
The evaporation heat transfer coefficient at the tooth-wick interface has a significant impact on the evaporator temperature in CPLs and LHPs. It is also the main parameter in sizing of a CPL or LHP. Experimentally determined evaporation heat transfer coefficients from a three-port CPL with tubular axially grooved (TAG) evaporator and a TAG LHP with Acetone, R-134A and Ammonia as working fluids are presented in this paper. The experimental data was generated using a test rig at ISRO Satellite centre. The influence of working fluid, hydrodynamic blocks in the core, and evaporator configuration (LHP or CPL) on the heat transfer coefficient are presented.
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