Abstract
The results of flow studies of moist vapour in Laval-liked vapour channels of short linear heat pipes (HPs) are presented. The increase in heat transfer coefficient of short linear HPs, intended for creation the cooling systems of heat-stressed designs of spacecraft is carried out by making the HPs vapour channel forms of the Laval-liked nozzle. Comparison of the heat transfer coefficients of short HPs with the standard cylindrical vapour channel and the channel, made in the Laval nozzle form with the equality of all dimensions, flat evaporator shows that the HPs with the Laval-liked nozzle vapour channel exceeds the heat transfer characteristics of the standard HPs with a cylindrical vapour channel under high thermal loads. The study of the flow and condensation in such shaped vapour channels of the short HPs at high thermal loads gives an opportunity to analyze in detail the advantages of using such HPs. Capacitive sensors are additionally installed in cooled top covers of the HPs, and electromagnetic pulses with a frequency of 100 kHz were supplied to them from the external generator. At heating the HPs 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 and its discontinuous distribution. An analytical and numerical evaluation are applied to study the duration of the occurring pulsations, and the analytical results are compared with numerical and experimentally obtained values of the pulsations periods.
Highlights
The increase in heat transfer coefficient of short linear heat pipes (HPs) is a very important task when designing a spacecraft with a rigid regulation of take-off weight
The application of the linear HPs is justified in the case of the structural impossibility of placing a loop HPs and to improve long-term reliability of the cooling systems, which are distributed inlet and outlet closed lines of the loop HPs
The heat is transferred by the latent heat transfer liquid-vapour- liquid like in other types of heat pipes, and by conductive heat transfer of the hot oscillating liquid plugs for cold walls in the condensation zone of loop HPs. This phenomenon is the reason of high heat transfer coefficient of loop HPs in comparison with other types of HPs [4,5,6,7,8,9,10,11]
Summary
The increase in heat transfer coefficient of short linear HPs is a very important task when designing a spacecraft with a rigid regulation of take-off weight. The application of the linear HPs is justified in the case of the structural impossibility of placing a loop (contoured) HPs and to improve long-term reliability of the cooling systems, which are distributed inlet and outlet closed lines of the loop (contour) HPs. Pulsating (or oscillating) loop HPs - siphons, was invented in 1990 by Akachi [1]. The amplitude of oscillations is quite strong and the liquid plugs penetrate into both condenser and evaporator. This phenomenon is the reason of high heat transfer coefficient of loop HPs in comparison with other types of HPs [4,5,6,7,8,9,10,11]
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