Thermo-hydrodynamic performance and geyser boiling flows of a novel co-axial condensing heat pipe (CCHP) for low-grade green energy exploitations

Due to their excellent heat transfer efficiency, two-phase closed thermosiphons (TPCTs) are essential for solar applications and the cooling of electronics. In this research, a novel coaxial condensing heat pipe (CCHP) was proposed, which has a more compact structure compared to traditional heat pipe, given the same volume and heat transfer area. Numerical modeling and experimental investigation were fully utilized to examine the influences of heat inputs, inclination angles, liquid filling ratios, and working mediums on the heat transmission properties of CCHP. The vapor-liquid flow phenomenon along with the thermal and mass transmission mechanism of CCHP under various operating conditions were explored. Our findings demonstrated that CCHP exhibited optimal thermal transmission performance at the tilt angle of 60° when the filling rate is 50 % and the input power is 100 W, the minimum thermal resistance of CCHP is 0.284K/W. At the tilt angle of 60° and input power of 100 W, CCHP has the lowest thermal resistance of 0.267K/W. Besides, the utilization of ethanol as a working medium could simultaneously reduce the evaporator temperature and enhance the thermal properties of CCHP. Inside CCHP, "geyser boiling" phenomena was further observed. Our experimental findings and numerical ones agreed well for each other. This innovative heat pipe could be confident and robust applied in the solar energy collection and relevant heat transfer enhancement fields.