Влияние неконденсирующегося газа на диапазон регулирования тепловых труб переменной проводимости

Abstract

One of the important tasks to be solved in designing and manufacturing heat pipes (HP) is the determination of their thermal parameters, taking into account the specified geometry and coolant mass. The task becomes more complicated when in addition to the coolant, non-condensable gas (NG) appears in the heat pipe as a component forcedly introduced for control purposes. This generates the need to develop a model of transfer processes for the designs gas-controlled heat pipes (GCHP) based on widely used axial heat pipes (AHP), the body and the capillary structure of which are manufactured by extrusion as a whole, and to verify it with the developed structures. Options of simulating the operation of an HP with axial grooves for various masses of non-condensable gas with taking into account thermal conductivity and diffusion are considered. This approach made it possible not only to assess the adequacy of the 2D model of heat and mass transfer in the vapor-gas front for a particular GCHP design, but also the possibility of using the same GCHP geometry with various masses of NG to improve the control accuracy. The article presents a calculation for a GCHP with axial grooves, in which the reservoir volume and the evaporation and condensation zone lengths are predetermined. A procedure for testing an axial heat pipe filled with a coolant and non-condensable gas is described. The results on the distribution of temperature fields in the GCHP operation modes with the minimal (10 W) and maximal (100 W) thermal loads at various condensation zone temperatures are obtained. The test results are compared with the calculated data, and a good agreement between them is shown. Despite the fact that the correctness of the procedure has been confirmed, the test result in terms of requirements for the upper control temperature is negative. The required range is 15°C instead of its actual value equal to 32°C. A conclusion was drawn from this result that, given the existing external conditions, the considered pipe geometry cannot ensure the control range from 15 to 30°C. Based on this result, options with a larger reservoir volume without a significant change in the GCHP design and its external dimensions were proposed. It is shown that the GCHP design with axial grooves and a reservoir in the form of an extended casing cannot ensure a control range of more than 25°C even with a ten-fold increase in the NG volume in view of the influence the coolant vapor entering the reservoir has on the NG temperature. Methods for improving the control accuracy are proposed.