Design And Manufacturing Of Anti-gravity Loop Heat Pipe And Study On Its Composite Porous Wick

Loop Heat Pipes (LHPs) are highly efficient passive phase-change heat transfer devicesdeveloped for aerospace applications in1972. LHPs has several advantages such as large heatflux transport capability, fast response, low heat resistance and long distance heat transfer andmain area of application of LHPs is space technology at present. Recently, with the fast risingheat flux of chips and reduction of dissipating space in the microelectronic field, traditionalcooling methods have shown several restrictions and LHPs have became a promising solutionfor heat dissipation problem in electronics and computers on the ground.In the terrestrial application, it is normal to have the heat source above the cold source.When a LHP is operating at this orientation, the evaporator is placed above the condenser andheat is transferred toward the direction of the gravitational field. This orientation is called theanti-gravity orientation. It is generally believed that the LHP has the capability to operateefficiently without any restrictions of orientation in the gravity field. However, recent studiesshow that gravity does affect the thermal performance of the conventional LHP/CPL on theground. To solve this problem, this paper presents an anti gravity loop heat pipe with acontinuous graded pore-size wick. The distinctive continuous graded pore-size wick consistsof two sections with different capillary pore sizes, and these two sections are filled in theevaporator and the liquid line respectively.The main contents are as follows:An Anti-gravity loop heat pipe with a continuous graded pore-size wick was developed.The continuous graded pore-size wick consists of two sections with different capillary poresizes and permeability, and these two sections are filled in the evaporator and the liquid linerespectively. The wick inside evaporator provides high capillary force to pump the workingfluid againet gravity, and the wick inside vapor line has high permeability to minimize thefluid resistance. The fabrication process of anti-gravity loop heat pipe was introduced,especially the solid-phase sintering of the continuous graded pore-size wick. Severaltechnology problems were solved, including thin-walled tube bending and forming ofcomplex shape wick. The theoretical model and thermal resisitance model of anti-gravity loop heat pipe model were established. The capillary heat transfer limit of anti-gravity loop heatpipe was calculated.Sintered composite porous material was developed for the wick structure insideanti-gravity loop heat pipe. Two different design were introduced, the sintered mixed metalpowder and sintered composite material of metal foam and powder. The propertis of greencopper powder were investigated and the influence of loose packing porosity was discussed.The solid-phase sintering process of these two composite porous material was studied. Thegeometric sintering shrinkage model of two designs were introduced. Effect of sinteringparamters on the performance of sintered composite porous material were studied, such assintering shrinkage, sintered density, capillary pore size, porosity and permeability. Theoptimal sintering parameters was introduced.The corresponding test system of the anti-gravity loop heat pipe was developed, and thestart-up characteristics and heat transfer performance at heat loads below100W wereinvestigated experimentally. The transient thermal response patterns and steady-state responsepatterns of anti-gravity loop heat pipe were investigated and discussed. The capillary transferthermal limits of the anti-gravity loop heat pipe was tested. The effect of different parameterson the performance of anti-gravity loop heat pipe were studied, such as the sinteringparameters, wick paremeters and working fluid filling ratio. The failure characteristics ofanti-gravity loop heat pipe were analyzed under different conditions. A RRU simulationmodule with anti-gravity loop heat pipe was developed and its thermal performance wastested.