Явище гістерезису при тепловіддачі кипінням у двофазних контурах теплоперенесення

Abstract

Systems for ensuring the thermal regime of ground and space applications with a capacity of more than 6 kW are rationally built on the basis of heat transfer circuits with a two-phase coolant. In such circuits, heat is transferred from the devices to the coolant in the heat sink (thermoplate) by heat transfer by boiling. When the device is switched on and heated up, there is a transition from single-phase convection to developed boiling in the evaporator channel of the Heat sink, which is sometimes accompanied by significant overheating of the device and a temperature drop. When the device is turned off, the temperature decreases smoothly, without a drop. This undesirable phenomenon, called "thermal load hysteresis", or "Hysteresis Phenomena at the Onset of Nucleate boiling" can affect the reliability of the device, and is the subject of study in this article. The problem of hysteresis has been studied by many authors at the local level both during boiling in a large volume and during the flow of coolant in the channels. It is associated with the need for some overheating of the wall to start boiling, the origin of vaporization centers. This article reviews the studies on the problem of hysteresis and describes a task for the experimental study of the phenomenon of hysteresis in the evaporator channel of a heat sink during the transition from single-phase convection to boiling. Tasks: it is necessary to consider the factors affecting hysteresis and to develop and test a methodology for conducting the experiment on the stand of simulation of heat transfer circuits with a two-phase coolant at the integral level. According to the results of the review, it was found that hysteresis is affected by various factors such as the properties of the coolant, surface roughness, flow parameters, etc. Usually, the study of hysteresis is conducted out at the local level, but engineering practice is interested in the phenomenon at the integral level, and what is the probability and magnitude of overheating of the device when it is turned on. However, if hysteresis exists at the local level, it is not obvious that hysteresis will appear at the device level. The authors obtained a "boiling curve" of ammonia on an experimental heat sink with a characteristic temperature drop of the device and showed that the phenomenon of hysteresis exists at the integral level. Conclusions. Considering the probabilistic nature of the phenomenon, many factors affecting the hysteresis, including the design features of the thermoplate, the authors propose to perform further studies using the "integral" methodology on standard coolants, with parameters close to the operating conditions of standard thermal control systems.