Heat Loss In Space
The problem of temperature regulation is most acute for the astronaut when he is outside his vehicle and therefore disconnected from the relatively bulky machinery which normally attends to his thermal needs. It is necessary to arrange that metabolic heat is transported from the skin surface to some device which will absorb it. Two heat exchangers are therefore required, one at the skin surface and one in the thermal pack, and the transport of heat from skin to absorbent must be effected optimally in terms of the weight and bulk of apparatus necessary.
The properties of an existing air ventilated clothing system have been investigated using a heated dummy whose regional “tissue conductance” has been matched to that of a thermally comfortable human subject. It was found that if the complex distributions of air flow and skin temperature were ignored, the results could be expressed in terms of the performance characteristics of a simple heat exchanger having its plate surface temperature equal to the mean skin temperature. The relation between mass flow and heat exchange coefficient at the skin surface was such as to suggest that suitable characteristics could be obtained by introducing air at the four extremities and removing it at the waist. The power required to ventilate existing suits was found to be many times the theoretical minimum, and considerable improvement in this respect appeared possible.
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