The Impact of Variation in Filling Ratios, Evacuation Pressure, and Heat Input on Thermal Performance of Pulsating Heat Pipe

Abstract

The reliability and computational speed of modern electronic systems have a significant dependence on the methods of heat management. In present scenario, passive cooling methods based on two-phase flow, such as heat pipes, have emerged as a preferred option for electronic thermal management. The pulsating heat pipe (PHP) is an ideal device for handling low and high heat fluxes due to its simple construction and compactness. The impact of some construction parameters on the thermo-hydrodynamics of PHP is still unresolved. Hence, to characterize the effects of construction parameters, simultaneous pressure, temperature measurement, and visualization experiments have been conducted under different heat inputs and evacuation pressure. Additionally, the flow patterns, effective thermal conductivity, and resistance have been mapped to correlate the flow characteristics and the thermal performance. A closed-loop two-turns semitransparent PHP test section of hydraulic diameter 2.3 mm was constructed having four 202 mm long adiabatic channels. The experiments were performed using partially filled degassed pure water as the working fluid up to 70% by volume in vertical orientation and bottom heating mode. The unstable oscillations of evaporator wall temperature occur until a pseudo-steady-state is achieved for different heat inputs. The thermal performance was enhanced and successful flow transitions occurred at an optimum filling ratio (FR), low pressure, and high heat input. Low evacuation pressure, 60% FR, and 25 W heat input were found to be efficient working conditions and optimum for maximum performance in this study.