Quiet power-free cooling system enabled by loop heat pipe

Abstract

Loop heat pipe (LHP) is a quite promising two-phase heat transfer device, holding significant application potential in the modern electronics cooling. In this work, a LHP-based cooling system has been developed, which features no power consumption and no noise, taking full advantage of LHP's efficient longdistance heat transport capability. The heat source was simulated by a film electric resistance heater, which was connected to the cylindrical evaporator of the LHP through an aluminum saddle. The condenser line was embedded into the bottom surface of a fin radiator with a relatively large volume, where heat dissipation to the ambient was completely in the form of air natural convection. Extensive experiments on this cooling system were conducted, mainly focusing on its startup and system thermal resistance. Experimental results show that this cooling system can successfully realize the startup with a very small heat load. With the film heater temperature not exceeding 80 , this cooling system can dissipate a heat load up to 150 W to the ambient at a temperature about 24 , corresponding to a system thermal resistance about 0.30 /W. In addition, this cooling system exhibited very strong anti-gravity capability. With an adverse elevation of 0.5 m, the cooling system can realize normal operation, and no obvious performance decay was observed except an increased operating temperature at small heat loads.

Startup characteristics of an ammonia loop heat pipe with a rectangular evaporator

“…According to Ref. 22, since FLHP has no evaporator core inside the evaporator, there will be only two startup scenarios, i.e., the situations 1 and 2. When vapor exists in the vapor grooves, FLHP will start up immediately; whereas an obvious superheat is required to initiate the nucleate boiling for a startup when the vapor grooves are filled by liquid.…”

“…However, the thermal contact surface of electronic equipment is generally flat, and in practical applications, a saddle is necessarily employed outside the cylindrical evaporator of the LHP to ensure its interaction with the electronic devices [19,20]. The saddle is usually made of metal materials with high thermal conductivity [21,22]. The thermal resistance of the system would increase due to the existence of the thermal contact resistance between the evaporator casing and the saddle.…”

Comparative study of two loop heat pipes using R134a as the working fluid

“…Compared with traditional heat pipe, significant structural improvement has been made for LHP, mainly including the local installment of porous wick, the employment of inverted evaporator as well as the separation of liquid/vapor transport lines. These structural improvement effectively overcomes the inherent drawback of conventional heat pipe such as small heat transfer capacity, weak antigravity capability and unfavorable flexibility in installment, enabling LHP to be a more universal and advanced heat transfer device [10][11][12][13][14][15]. Its long distance heat transport capability and flexibility in packaging as well as strong antigravity operation show obvious advantages over traditional heat pipes [16][17][18][19][20][21][22][23][24][25][26][27].…”

Experimental study on a dual compensation chamber loop heat pipe with dual bayonet tubes

“…That is because in the terrestrial surroundings, once the CC is located below the evaporator, liquid working fluid will accumulate in the CC due to the gravity effect. It will cause a difficulty in the liquid supply to the evaporator wick, and under which condition the normal operation of the LHP will be disrupted, leading to an operating failure of the LHP [15][16][17][18]. Although sometimes the employment of a secondary wick hydrodynamically connecting the primary wick and the CC can help guarantee the liquid supply to the evaporator in an adverse attitude, because the liquid flow resistance in the secondary wick is relatively large, it will inevitably result in a considerable reduction in the heat transport capability.…”