Variable-density method for multi-layer insulation
AssigneeCryogenic Technical Services, Inc.
InventorGlen E. McIntosh
Life of this patent
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Abstract
A variable-density MLI-insulation employs unbonded, glass paper to separate radiation barriers. A layer-by-layer heat balance is conducted to determine the thickness of the various separation layers which vary from relatively thin at the warm wall to relatively thick at the cold wall.
Claims5
A method of insulating a multi-layer insulation (MLI) structure which includes a relatively cold wall, a relatively warm wall, an evacuated space therebetween, a plurality of radiation barriers located in said evacuated space and a plurality of separators located between substantially all adjacent radiation barriers, said separators having a thickness to provide a distance between said radiation barriers, said method comprising the steps of:
- conducting a heat balance at selected locations between said warm and said cold walls in said evacuated space to determine the portion of the overall thermal conductivity value (k.sub.t) that is attributable at each said selected location to radiation (k.sub.r) and solid conduction (k.sub.s);
- and
- establishing the thickness of said separators at said selected locations and thusly the distance between said radiation barriers at said selected locations in accordance with the values of k.sub.t and k.sub.r at said selected locations, wherein said heat balance is conducted substantially in accordance with the equations:
- k.sub.t =k.sub.r +k.sub.g +k.sub.s ;
- and, ##EQU2## Where, .sigma.=Stephan-Boltzmann constant=5.675E(-8) W/m.sup.2 .multidot.K.sup.4
- T.sub.w =temperature of the warm surface, K
- T.sub.c =temperature of the cold surface, K
- .di-elect cons..sub.w & .di-elect cons..sub.c are the warm and cold surface emissivities
- C=a factor of the separated material and density
- k.sub.g =C.sub.1 .multidot.P.multidot..varies.
- Where,
- k.sub.g =gas conduction, W/m.sup.2 .multidot.K
- P=gas pressure, Pa
- .varies.=accommodation coefficient
- C.sub.1 =[(.gamma.+1)/(.gamma.-1)].multidot.[R/8.pi..multidot.M.multidot.T].sup.1/ 2 and,
- Where,
- .gamma.=C.sub.p /C.sub.v
- R=gas constant, 8.31441 J/mol.multidot.K
- M=molecular wt of gas, kg/mol
- T=temperature of vacuum gauge, normally 300K;
- and,
- k.sub.s =C.sub.2 .multidot.f.multidot.K/.DELTA.X
- Where,
- k.sub.s =the solid conductivity per unit thickness, W/m.sup.2 .multidot.K
- C.sub.2 =an empirical constant
- f=relative density of the separator compared to solid material
- k=separator material thermal conductivity, W/m.multidot.K, and
- .DELTA.X=actual thickness of separator between reflectors, m.
Dependencies are inferred from the claim text.