12-09-2014, 09:55 AM
EXPERIMENTAL STUDIES OF SECONDARY WICK FOR LOOP HEAT PIPE
EXPERIMENTAL STUDIES.ppt (Size: 1.11 MB / Downloads: 10)
Introduction
Satellites are built for multi purpose application
Increased number of electronic packages.
Compaction of electronics resulted in sharp rise in heat flux.
Internal thermal dissipation in the near future communication spacecrafts will be of the order of 10 to 15kW
Two-phase heat transfer technologies have the potential to transport large amounts of heat over long distances
a) Heat Pipes b) Loop Heat pipes (LHP)
Concept of heat pipe
A heat pipe is a device that efficiently transports thermal energy from its one point to the other
heat pipe consists of a sealed container, a wick structure, a small amount of working fluid
The length of the heat pipe can be divided into three parts viz. evaporator section, adiabatic section and condenser section
Concept of loop heat pipe
Loop Heat pipe is improved version of the basic Heat pipe that aims to increase performance by keeping the liquid and gas phases apart.
LHPs were independently developed in Russia in the 1970s. Active development of LHPs began in the late 1970s. The first LHP flight test was performed aboard the Russian spacecraft Granat in 1989
Comparison
Heat pipe is a single tube within which both evaporation and condensation occurs where as in LHP both evaporation and condensation takes place separately.
Heat transport capability of heat pipe is less than LHP. Heat pipe can handle only 180W of heat where as LHP is tested and its working is satisfactory so far till 1200W.
Wick is arranged on the circumference of the heat pipe tube where as in LHP both primary and secondary wicks are separately manufactured and installed in loop.
Fluid in excess is stored in reservoir and is supplied depending on the heat load where as in heat pipe with the increase in heat load evaporation and condensation rate does not match to the need
Conclusion
From this study, the proposed configuration of secondary wick is adequate based on two criteria outlined below:
1) Heat transport capability (36 W at 5mm adverse tilt)
2) Blockage of wick: While there is significant blocking of wick, it is concluded that the heat transfer coefficient is still adequately large enough to allow fluid flow to the primary wick.