Transient characteristics of a loop heat pipe-based hydraulic temperature control technique

• Published in: International journal of heat and mass transfer 2016-12, Vol.103, p.125-132
• Main Authors: Joung, Wukchul, Kim, Yong-Gyoo, Lee, Joohyun
• Format: Article
• Language: English
• Subjects: Control gas pressure control; Hydraulic temperature control technique; Instability; Loop heat pipe; Pressure-controlled loop heat pipe
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2016.07.068

•Transient responses of the LHP-based hydraulic temperature control were investigated.•The optimum increase rate of the control gas pressure was obtained.•At the optimum pressure increase rate, a fast large-scale temperature increase was stably achieved.•The maximum temperature increase rate was measured to be around 2K/min at 50Pa/s.•A fast, precise, and stable hydraulic temperature control was attainable in any directions and scales. Recently, a new type of a hydraulic temperature control technique, which was based on thermo-hydraulic characteristics of a pressure-controlled loop heat pipe (PCLHP), was suggested and proved its effectiveness in terms of the stability, precision, and predictability. However, the hydraulic operating temperature control of a PCLHP showed a temporary operation failure when a large-scale temperature increase was attempted with a rapid increase in the control gas pressure due to a possible pressure inversion between the evaporator and the compensation chamber. Although the PCLHP was soon recovered from the temporary instability, an accompanied sudden temperature drop made the hydraulic temperature control inadequate for applications where fast, large-scale, yet stable temperature controls were required. In this work, transient responses of the PCLHP to various increase rates of the control gas pressure were tested to obtain an optimum increase rate of the control gas pressure at which a large-scale temperature increase could stably be achieved without any instabilities. The tested pressure increase rates were from 25Pa/s to 100Pa/s, and the obtained optimum rate was 50Pa/s for the tested PCLHP at 800W. At this optimum rate of the control gas pressure increase, the PCLHP showed stable temperature increases with maximum increase rates of around 2K/min whereas the control gas pressure increases at 100Pa/s consistently resulted in temporary operation failures. Details on the experiments and the analyses on the obtained results were provided.