A single, straight-tube pulsating heat pipe (examination of a mechanism for the enhancement of heat transport)

Heat transport in a pulsating heat pipe consisting of a single, straight tube with an open end (SST-PHP) is investigated experimentally. Periodic oscillation of a vapor plug with a large amplitude is excited in a horizontal orientation and continues for a long period of over 8000 s without ceasing. The heat transport rate and the effective thermal conductivity increase with heating power up to approximately 75 W and 40 kW/(m K), respectively. The heating section, the inner diameter of which is slightly larger than that of the heat transport tube, is maintained at approximately the saturation temperature of the working liquid throughout the succession of oscillation. Liquid is supplied to the heating section due to the inflow of liquid film from the heat transport tube each time the vapor plug shrinks. The postulated mechanism of the heat transport can be characterized by three factors: (a) latent heat transport due to the condensation of vapor onto the liquid film, (b) enhanced heat diffusion induced by oscillating motion of the liquid plug in the heat transport tube, and (c) liquid exchange due to oscillating motion between the heat transport tube and the cold liquid reservoir. In order to examine the contribution of each factor, the effective thermal conductivity is measured for several types of heat transport tubes, each of which is partially different in structure from the SST-PHP, so that some of these factors will be excluded. Based on these results, the mechanism for the enhancement of heat transport in the SST-PHP compared to that for forced oscillatory liquid flow is discussed.