The Study of Condensation Processes in the Low-Temperature Short Heat Pipes with a Nozzle-Shaped Vapour Channel

Abstract

The results of researches of condensation processes in the vapour channel similar to the Laval nozzle of short linear heat pipes are presented. Capacitive sensors are additionally installed in cooled top covers of the heat pipes, and electromagnetic pulses were supplied to them from the external generator. At heating the heat pipe evaporator, starting from a certain thermal power threshold value, electromagnetic pulses became modulated. It is related with the formations of the boiling process in the capillary-porous evaporator and large amount of vapour over it. Boiling process results in rapid increase of the pressure under which the average temperature of the evaporator occurs to be less than the boiling temperature of the working fluid under increased pressure. Considering condensation of excess vapour, this leads to repeated initiation and extinction of the boiling process in the evaporator, which reflects in pressure pulsations in the vapour channel. Pressure pulsations cause modulating effect on electromagnetic impulses. Pulsations frequencies are measured as well as their dependence from overheating of the evaporator. Using the capacitive sensors and a special electronic equipment we measured the local thickness of the working fluid at the condensing surface inside the heat pipes. Time-averaged values of the condensate film thickness are measured, depending on the heat load on the capillary-porous evaporator. The measurement error does not exceed 2 × 10 −3 mm. It is demonstrated that the condensate film thickness lessens sharply with the increase of the heat load on the evaporator of a Laval-like low-temperature heat pipe, while the heat resistance of the film on the condensing surface reaches 60% of the total heat resistance of heat pipe with the capillary-porous evaporator.

Numerical Modeling of the Vapour Vortex Formation in the Short Heat Pipes

“…In the equations for the momentum conservation of the vapour moving (7) and (8), the projection of the radial and tangential friction stress τ s on the condensate film surface must be determined. To do this, we use the Prandtl hypothesis [17]…”

“…Measurements of the film flow rate were carried out earlier [7] [8], the solution of this equation is as follows:…”

“…The temperature of the HP's condensing surface in the flow vortex calorimeter is 295 ± 0.03 K (22˚C ± 0.03˚C). 1-solid line, the vapour density in the Laval-liked vapour channel at a pressure P = 6.13 × 10 5 Pa; 2-dotted line, the vapour density in the HP's with cylindrical vapour channel.From this relation, taking into account the density ρ vp from(7) and(8), an equation can be obtained to estimate the radial velocity in the core of the vapor flow at the inlet to the vapour toroidal ring vortex:…”

The study of condensable vapour vortex flow in short low temperature heat pipes

“…Проведение измерений и обсуждение полученных результатов толщины пленки конденсата диэтилового эфира внутри ТТ, в зависимости от температурного напора на испаритель ТТ, детально приведены в [16][17][18].…”

“…Целью данного исследования явилось сопоставление результатов, ранее проведенного в работах [16][17][18] изучения толщины пленки конденсата диэтилового эфира, в зависимости от тепловой нагрузки на испаритель с полученными расчетными значениями и аналитическими оценками.…”