Abstract A thermal control device utilizing the heat pipe principle. Heat receiving and heat rejecting surfaces are spaced from each other along the length of the heat pipe. In a preferred form, a radioisotope fuel capsule is in thermal conducting relationship with the heat receiving surface and a noncondensible gas is mixed with the working fluid of the heat pipe. A noncondensible gas automatically expands as the threshold temperature of the system drops to block off more of the heat rejecting surface. In other alternate preferred embodiments, a nonvaporizable liquid is utilized in lieu of a noncondensible gas to reduce the area of the heat receiving surface as the threshold temperature of the system drops or a second material is mixed with the working fluid which changes to a solid phase to block the flow of the working fluid between the heat rejecting and heat receiving surfaces as the threshold temperature of the system drops.
A completely passive, substantially isothermal heat transfer system comprising: a heat receiving surface; a heat rejecting surface; an enclosure connecting said surfaces; means for insulating said enclosure and said heat receiving surface from ambient while exposing said heat rejecting surface thereto; a working fluid including a mass of non-condensible gas carried within said enclosure having liquid and gaseous phases in equilibrium, said fluid tending to vaporize when in contact with said heat receiving surface and to condense when in contact with said heat rejecting surface whereby heat is transported from said heat receiving surface to said heat rejecting surface by said working fluid; means for varying the mass rate of flow of one phase of said working fluid between surfaces as a function of threshold temperature of said system, capillary means for returning said condensed working fluid from the heat rejecting surface to the heat receiving surface, and a radioisotopic fuel capsule thermally coupled to said heat receiving surface and means to pass helium into the enclosure so that said mass of noncondensible gas comprises helium produced in the alpha decay of said radioisotopic fuel.
Claim 2
Dependent Claim
185 words
A completely passive, substantially isothermal heat transfer system comprising: a heat receiving surface; a heat rejecting surface; an enclosure connecting said surfaces; means for insulating said enclosure and said heat receiving surface from ambient while exposing said heat rejecting surface thereto; a working fluid including a mass of non-condensible gas carried within said enclosure having liquid and gaseous phases in equilibrium, said fluid tending to vaporize when in contact with said heat receiving surface and to condense when in contact with said heat rejecting surface whereby heat is transported from said heat receiving surface to said heat rejecting surface by said working fluid; means for varying the mass rate of flow of one phase of said working fluid between surfaces as a function of threshold temperature of said system, capillary means for returning said condensed working fluid from the heat rejecting surface to the heat receiving surface, and a radioisotopic fuel capsule thermally coupled to said heat receiving surface and means to pass helium into the enclosure so that said mass of noncondensible gas comprises helium produced in the alpha decay of said radioisotopic fuel.