No abstract

No abstract

The authors use computer simulation and experiment to study thermal characteristics of a less expensive design of the air cooling system for transmit/receive modules based on the heat sink with the dimensions of 25×324×500 mm made of mass-produced heat sink profile. The total power of the 8 transistors in the transmit/receive module is 224 W. It is shown that the increase in air velocity in the heat sink channels from 1 to 30 m/s causes an approximately twofold drop in the maximum temperature of the mounting surface (from 78.45 to 38.70°C) and a decrease in thermal resistance of the cooling system by 3.16 (from 0.262 to 0.083°C/W). The air velocity range from 5 to 10 m/s proves to be the most rational option. For the inlet air temperature of 20°C, the temperature in the spots where the transistors are mounted remains below 56.3°C for the air velocity of 5.5 m/s in the heat sink channels and below 51.8°C for 10.5 m/s. A new original technical solution based on low-cost flat gravity heat pipes with a threaded evaporator will provide the efficiency of the cooling system at higher inlet air temperatures.

This paper considers the effect of structural parameters and saturation pressure on the intensity of heat transfer from boiling on porous structures made of copper metal fibers. The study involved changing the structural and geometric characteristics of porous samples and saturation pressure. The study regime parameters were chosen based on the conditions of operation of steam chambers, namely the horizontal orientation of the work area, the capillary transport of the heat carrier to the work area. It was determined that reducing saturation pressure from 0.1 MPa to 0.012 MPa leads to a reduction in heat transfer by 15‒20 % depending on the parameters of porous structures. This pattern has been explained in this paper by the increased detachable diameters of steam bubbles that thus overlap part of the capillary structure's vaporization area, which leads to a decrease in the values of the discharged heat flux at the same temperature gradient values. The influence of values of the porosity and diameters of fibers, which the samples of a capillary structure were made from, was ambiguous. The parameter chosen for generalizing the data obtained was an effective diameter of the samples' pores, which is a more general characteristic. The generalization of the experimental data has demonstrated that the efficiency of heat transfer increases with an increase in the effective diameter of pores in the examined range from 20 to 90 µm. Estimation dependences have been built to determine the intensity of heat transfer under sub-atmospheric pressures for metal-fibrous porous structures at a deviation of up to ±30 %. It turned out that the resulting dependences could be used to determine the intensity of heat transfer by the examined powder structures under the sub-atmospheric pressure conditions. Applying these dependences would make it easier to design thermal stabilization systems based on steam chambers.

No abstract