Comparative analysis for the general operational properties of advanced actuating media for open systems of low-temperature heat release in space

Аuthors

Bondareva N. V.^*, Koroteev A. A.^*, Samsonov A. B.^*

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: chkt@yandex.ru

Abstract

The aim of this paper is to make comparative analysis for the basic performance characteristics of advanced working media potentially applicable for the open systems of low-temperature heat release in space. Primary requirements to such heat-transfer media include:

• extremely low vapor pressure for reaching the lowest rate of evaporation in space;
• broad operating temperature range;
• immunity to extraneous influencing factors, significant irradiation doses including, during the deep-space operation;
• bioinertness;
• high enough flowability.

The so-called ultrahigh-vacuum fluids (UHVF) offer a combination of such properties. Results of comparative analysis for their basic performance characteristics are presented in this paper as applied to different temperature ranges of the liquid droplet radiator (LDR) operation.
High-temperature LDRs are characterized by the top («hot») temperature of droplets near the generator of about 1000К. Liquid metals, tin in particular, may be used as a working medium in them due to the low saturated vapor pressure. Advantages of high-temperature radiators include: a possibility to reach high density for the released heat flow at the compact shroud sizes; practically total absence of the outer solar or planetary radiation influence on the efficiency of radiational cooling of droplets. And still the liquid-metal coolant application requires attacking many complicated problems related to the necessity for the structure thermostatting, chilled coolant transfer, development and operation of sophisticated shutoff and control equipment, etc.
Operating temperature range of the low-temperature radiators is 300430К. The organosilicon fluids may be used as coolants in them. Such substances are characterized by the specific set of properties that can not be attributed to any other organic compound: low temperatures of glass-transition and slump loss meshed with the high thermal and thermo-oxidative stability (up to 250 °С and higher), very low saturated vapor pressure, low fugacity, and high resistance to radiation. As compared to the high-temperature radiators, the influence of outer solar radiation on the radiator performance appears to be rather high. This results in the necessity for some radiating area increase or proper consideration for the problem of optimum shroud orientation.
Medium temperature range is characterized by operational temperatures from 450 K up to 650 К. Within this range it is possible to manage work process of relatively compact LDR with the heat output of 25 MW. The potentialities to use ion liquids for such radiators are being considered currently. Their basic advantages include practically total lack of evaporability in vacuum and capacity for increasing operational temperature up to 650 К.

Keywords:

liquid droplet radiator, working media, ultra-high vacuum liquid, physical and chemical properties

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