Operational characteristics of oscillating heat pipe with long heat transport distance for solar energy application

In order to further understand the operational characteristic of long heat transport distance oscillation heat pipe (OHP) for solar energy application, an experimental investigation on the thermal performance of OHP with higher initial vacuum and pressure fluctuation behavior inside under two kinds of inner diameters, two kinds of working media, and different inclination angles and filling ratios (FR) were carried out. The main result shows that the OHPs exhibit excellent heat transfer performance. The effective thermal conductivity is about two orders of magnitude larger than that in the previous work and some other researchers' work. The start-up temperature of the OHP with 3 mm inner diameter increases from 45 °C to 58 °C with the growing of FR from 30% to 70% when injected with SRWF and placed vertically. The start-up temperature is inversely related to the inclination angle under the same condition. The working status of the OHP with 3 mm inner diameter and SRWF is hardly effected by the inner pressure. However, the effect is contrary for OHP with critical inner diameter. It can be inferred that the movement law of the liquid medium in the OHP is random and chaotic through the pressure frequency spectrum analysis.