Design and performance of single loop pulsating heat pipe capable of working in horizontal position

Abstract

Pulsating Heat Pipe (PHP) is a promising device for heat transfer and became popular in last two decades. Heat transfer in PHP is a combination of sensible and latent energy exchange. Interfacial processes like bubble nucleation, pumping, agglomeration, and collapse under strong thermo-hydraulic coupling characterize the flow behavior inside the PHP. PHP’s have strong dependence on operating parameters, geometrical details and thermo-physical properties of the fluid. The complex physical phenomenon and involved dependence of constraints of PHP are still intriguing the researchers. The wickless structure of PHP provides a remarkable simplicity in its design. The circulation is aided by both gravity and the pressure difference between different parts of the loop which essentially needs a narrow cross-section. It has been a constant endeavor of the researchers to make the design operate independent of gravity. Reasonable success has been achieved by increasing the number of loops or turns. However, design of a PHP with limited number of turns yet independent of its orientation is still an open question. Present research proposes a unique design of a single loop PHP capable of working even in a horizontal position. Acknowledging the importance of gravity, operation of single loop PHP with “Source and Sink” at same elevation is attempted by providing gravitational assistance in the evaporator and the condensing sections. Gravity head is altered by varying the flow path of the PHP. Cooper tube is bent to form a closed loop of desired shape, in line with the aim of present study. Distilled water is used as a working fluid. PHP is experimented for varying fill ratios at different heat fluxes. Results shows that the proposed PHP shape works as a heat transfer device, transferring heat between “Source and Sink” at same elevation. High fill ratio and high threshold heat flux seems essentials for the PHP operation, gravity being a low head. Unidirectional flow, in line with the effect of gravity on the system, is achieved throughout the operation. Knowledge obtained from present thermal-hydraulic study can be used for commercial development of efficient PHP.