Guoyuan Ma

Experimental Study on a Pump Driven Loop-Heat Pipe for Data Center Cooling

AbstractAn experimental study on a pump-driven loop heat pipe (PLHP) charged with R22 for cooling a data center is reported in this paper. The PLHP had five tube-fin heat exchangers as evaporators and three tube-fin heat exchangers as condensers, a liquid reservoir, and a canned motor pump. The coefficient of performance of the unit was 3.75 when the indoor-outdoor temperature difference was 10°C, then increased to 9.37 when the temperature difference was 25°C. The mass flow rates of R22 increased from 200 to 1,100  kg/h with one evaporator and one condenser of the PLHP, and the heat transfer rates first increased and then decreased. When the vapor quality of R22 at the evaporator outlet was between 0.3 and 0.6, the mass flow rate affected the heat transfer rate slightly. As the increase of mass flow rate in the PLHP, the temperature difference between the evaporator inlet and outlet, and the sensible heat ratio were both rising. When the mass flow rate was about 1,400  kg/h and the indoor-outdoor tempera...

Study on Optimal Operating Mode of a Thermosyphon Heat Exchanger Unit in a Shopping Center

AbstractIn order to meet the operating requirements during both winter and summer, a thermosyphon heat exchanger unit used to recover energy from the exhaust air needs to be adjusted for its inclination angle by a regulation mechanism. In this paper, the factors that affect the heat transfer efficiency of the thermosyphon heat exchanger was analyzed and the unit practical operating data in a shopping center was studied. The unit optimal operating mode was acquired due to the influence of the unit inclination angle on the temperature effectiveness under a wide temperature change of the outdoor air. In addition, the inclination angle regulation mechanism uses a programmable logic controller (PLC) to control the unit to work at the optimal operating mode. The unit charged with R410A working fluid worked well and was highly effective.

Entropy generation rate analysis of a thermosyphon heat exchanger for cooling a telecommunication base station

Energy consumption can be reduced effectively if ambient energy is used to cool the telecommunication base station. A thermosyphon heat exchanger was adopted as a promising technique to utilise ambient energy. A prototype was developed, and the experimental system was constructed. Relations between dimensionless entropy generation rate, heat transfer rate and energy efficiency ratio of the thermosyphon heat exchanger were discussed theoretically and experimentally. Ambient temperature and facing air velocity were also examined. Results indicated that dimensionless entropy generation rate decreased by 8-9% when temperature difference increased by 3°C and increased by 8% when the ambient temperature increased by 3°C. The errors were in the range of 5.7-14.2%. When the facing air velocity increased from 2 m/s to 3.5 m/s, the test dimensionless entropy generation rate increased from 0.4 to 0.53 and the errors were 0.53-9.56%. Simulation and test results showed similar trends under different working conditions.

Numerical Investigation of a Novel Grooved Vapor Chamber

An effective thermal spreader can achieve more uniform heat flux distribution and thus enhance heat dissipation of heat sinks. Vapor chamber is one of highly effective thermal spreaders. In this paper, a novel grooved vapor chamber was designed. The grooved structure of the vapor chamber can improve its axial and radial heat transfer and also can form the capillary loop between condensation and evaporation surfaces. A two dimensional heat and mass transfer model for the grooved vapor chamber is developed. The numerical simulation results show the thickness distribution of liquid film in the grooves is not uniform. The temperature and velocity field in vapor chamber are obtained. The thickness of the liquid film in groove is mainly influenced by pressure of vapor and liquid beside liquid-vapor interface. The thin liquid film in heat source region can enhance the performance of vapor chamber, but if the starting point of liquid film is backward beyond the heat source region, the vapor chamber will dry out easily. The optimal filling ratio should maintain steady thin liquid film in heat source region of vapor chamber. The vapor condenses on whole condensation surface, so the condensation surface achieves great uniform temperature distribution. By comparing the experimental results with numerical simulation results, the reliability of the numerical model can be verified.Copyright