Test of the operating characteristics and energy saving performance of a container cooling system that reduces the operating energy of a refrigeration system using a loop thermosyphon heat exchanger that removes heat by temperature difference between outdoor and indoor was performed. As a result of the experiments, when the loop thermosyphon and the refrigeration system were operated simultaneously, the refrigeration system operated intermittently by reducing the heat load. As the temperature difference between indoor and outdoor increased, the operating time of the refrigeration system decreased and the energy efficiency rate increased. Energy efficiency rate showed a tendency to increase with increasing temperature difference, and the predicted correlation of energy efficiency rate using the performance of the loop thermosyphon heat exchanger and the refrigeration system was relatively consistent with the experimental value.
Experiments were conducted to evaluate the performance factors such as type of working fluid, flow direction, arrangement and stage of loop thermosyphon heat exchanger for ESS battery container cooling. Pentane showed slightly better performance of the heat exchanger than R-134a as a working fluid. Driving the fan in the suction direction showed improved performance compared to the blowing direction. The two-stage heat exchanger increased the heat transfer rate by more than 30% at the same temperature difference compared to the single-stage heat exchanger. Also, the counterflow flow showed better performance than the parallel flow in the two-stage heat exchanger.
Experiments were conducted on the operating characteristics and performance of various types of working fluid, filling amount and heat flow rate of a loop thermosyphon for cooling ESS battery container. As results of performance test on various working fluids, HFE-7100 and R-134a as a working fluids showed unstable operating and low performance due to vapor pressure drop, and performance was improved by increasing the number of vapor lines for reducing a pressure drop. In this study, n-pentane was more stable and showed better thermal performance among various working fluids.
This study presents design, construction and testing of a immiscible two working fluids thermosyphon with water and FC-40 to prevent freezing of vehicle starting up at temperatures below freezing point of water. The two working fluids thermosyphon was experimentally investigated on the startup characteristics at low temperatures below 0°C and then the thermosyphon was stable during startup and operated reliable at temperature of –30°C. The testing also showed that the performance and characteristics of the two working fluids thermosyphon differ from the charging ratio and mixture ratio of the two working fluids.
The frozen start up characteristics of the two phase closed thermosyphon using water and FC 40 as working fluid to prevents dry out by freezing of water at the condenser when below zero operation condition has been tested and studied. The experimental data showed that the thermosyphon using immiscible 2 fluids thermosyphon start up successfully at a -30℃ cooling condition as melted water by inflow 2nd working fluid to the condenser.
The experimental study for an operational characteristics and performance of the sodium heat pipe were carried out. For an experiment, the heat pipe which is 1000mm length and 25.4mm diameter of stainless steel container with 50 mesh of screen wick using sodium as a working fluid is manufactured and tested as functions of heat flow rate, inclined angle and operating temperature. The test results are as follows. During the start-up, frontal start up was observed because of the vapor density increasing as increased the hot zone. Also, the heat pipe showed uniform temperature over than 420℃ of the operating temperature. The average heat transfer coefficient increased as the heat flux and the vapor temperature increase, and the range of the total thermal resistance was 0.075～0.04℃/W at the 12～53.55kW/m2 of heat flux and 500～750℃ of operating temperature. The maximum heat flow rate was 750W at the 10 degree of top heating mode.
The loop thermosyphon has been designed and tested for cooling several hundreds watt of heat. This cooling system is consisted of copper block, condenser which is fabricated with tubes and fins and transport lines. In this research, operational characteristics and limitation of the loop thermosyphon were investigated as a function of fill charge ratio, thermal load, vapor temperature and effective head. The experimental results shows that the heat transfer limitation is dominated by vapor temperature and effective head. Also, the correlation for the heat transfer limitation is presented and showed good agreement. The evaporating heat transfer coefficient is affected by vapor temperature and heat flux, but the fill charge ratio and liquid head are minor factor.
A heat pipe heat sink which is possible to frozen start up at the lower than -20℃ by using a VCHP was designed, manufactured and tested. The VCHP uses water and nitrogen gas as the working fluid and non-condensable gas. The test results showed that the VCHP heat sink started up successfully at the range of -20 to -30℃ of the ambient temperature and 1000 to 2600W of the heat flow rate. The thermal resistance of the VCHP heat sink decreased as increased the heat flow rate and the ambient temperature since the active zone of VCHP increased.
The operational characteristics of a VCHP in the various operation conditions were investigated. A water heat pipe including nitrogen gas as a non-condensable gas was designed and manufactured using a copper tube with 12.7㎜ diameter and 480㎜ length. Experimental data showed that the length of non-active zone mostly depend on the temperature of the vapor and the non-condensable gas. And the heat flow rate was negligible parameter at the same vapor temperature in the range of the experiment. As the vapor temperature increase and the non-condensable gas temperature decrease, the non active zone was increased. The calculated data by using the flat front model and the experimental results showed same tendency.