The feasibility of solid sorption heat pipe for heat transfer

A novel type solid sorption heat pipe (SSHP) is developed for continuous heat transfer. In contrast to conventional heat pipe (HP), SSHP utilizes the composite sorbent-sorbate as working media to replace the wick structure inside HP. Such a technology is expected to alleviate the heat transfer limits of conventional HP. NaBr is chosen as the sorbent, and the expanded natural graphite treated with sulfuric acid serves as the matrix. A certain molar amount of the sorbate (NH3) is complexed with the composite sorbent. The desorption, condensation and chemisorption processes of NaBr-NH3 working pairs are investigated for both vertical and horizontal placed SSHP. The results show that the desorption process of NaBr-NH3 solid-gas reaction can be carried out while the heating temperature reaches up to 60 °C or above. The highest radial heat flux in both vertical and horizontal placed SSHP is around 22.1 and 12.4 kW/m2, respectively, while the axial heat flux for both SSHPs is not less than 400 kW/m2. It can be concluded that the SSHP is characterized by the non-isothermal heat transfer performance and verified to be available for continuous heat transfer. The vertical SSHP has a better overall heat transfer performance than horizontal SSHP under the same condition and NaBr-NH3 working pairs applied in SSHP is suitable for low-grade thermal energy transfer above 60 °C.