Investigation of thermal characteristics of a loop heat pipe in a wide range of external conditions

Abstract

A study has been made of thermal characteristics of an ammonia loop heat pipe (LHP) with an effective length of 421 mm equipped with a cylindrical evaporator 10 mm in diameter in a wide range of external conditions. The slope angle was varied from −90° to +90°, the temperature of the liquid cooling the heat sink from 0 to +60 °C, and the liquid flow rate from 0.1 to 4 L/min. It is shown that the most favorable position an LHP is the horizontal one. At a cooling temperature of 0 °C and a flow rate of 4 L/min the maximum heat load reached 500 W. In this case the thermal resistance of the “heat source – cooling liquid” system was 0.147 °C/W. It is also shown that changes in the value of the maximum heat load at all slope angles did not exceed 19% of the maximum value. The greatest effect on the LHP maximum heat load, operating temperature and thermal resistance was exerted by the heat sink temperature and the efficiency of its cooling. LHPs tests in a real cooling system of 1U computer server demonstrated energy savings of 8%.