Experimental investigation of cryogenic oscillating heat pipes

Abstract

A novel cryogenic heat pipe, oscillating heat pipe (OHP), which consists of an 4 × 18.5 cm evaporator, a 6 × 18.5 cm condenser, and 10 cm length of adiabatic section, has been developed and experimental characterization conducted. Experimental results show that the maximum heat transport capability of the OHP reached 380W with average temperature difference of 49 °C between the evaporator and condenser when the cryogenic OHP was charged with liquid nitrogen at 48% (v/v) and operated in a horizontal direction. The thermal resistance decreased from 0.256 to 0.112 while the heat load increased from 22.5 to 321.8 W. When the OHP was operated at a steady state and an incremental heat load was added to it, the OHP operation changed from a steady state to an unsteady state until a new steady state was reached. This process can be divided into three regions: (I) unsteady state; (II) transient state; and (III) new steady state. In the steady state, the amplitude of temperature change in the evaporator is smaller than that of the condenser while the temperature response keeps the same frequency both in the evaporator and the condenser. The experimental results also showed that the amplitude of temperature difference between the evaporator and the condenser decreased when the heat load increased.

Fig. 1

Test section (OHP): (a) OHP photograph and thermocouples location, and (b) schematic of OHP operation and dimensions.

Fig. 2

Schematic of experimental system.

Fig. 3

Temperature responses in the evaporator and the condenser versus heat load: (a) heat load change from 22.5 to 380 W, and (b) heat load 86.7W(I) unsteady state (II) transient state (III) new steady state.

Fig. 4

Temperature response in the evaporator and condenser reach steady state at Q = 86.7 W.

Fig. 5

Performance of cryogenic OHP with liquid nitrogen as working fluid: (a) temperature difference versus heat load input, and (b) average temperature difference versus heat load input at steady state.

Fig. 6

Average thermal resistance versus heat load input at steady state.

Fig. 7

Heat load effect on the amplitude of temperature difference at steady state: (a) heat load Q = 40.5 W, (b) heat load Q = 203 W, and (c) heat load Q = 350.5 W.