Reference no: EM13880692

Liquid oxygen (LOX) for the Space Shuttle can be stored at 90 K prior to launch in a spherical container 4 m in diameter. To reduce the loss of oxygen, the sphere is insulated with superinsulation developed at the U.S. Institute of Standards and Technology's Cryogenic Division that has an effective thermal conductivity of 0.00012 W/(m K). If the outside temperature is 20°C on the average and the LOX has a heat of vaporization of 213 J/g, calculate the thickness of insulation required to keep the LOX evaporation rate below 200 g/h.

GIVEN

• Spherical LOX tank with superinsulation
• Tank diameter (D) = 4 m
• LOX temperature (TLOX) = 90 K
• Ambient temperature (T?^?) = 20°C = 293 K
• Thermal conductivity of insulation (k) = 0.00012 W/(m K)
• Heat of vaporization of LOX (hfg) = 213 kJ/kg
• Maximum evaporation rate ( mLox ) = 0.2 kg/h

ASSUMPTIONS

• The thickness is small compared to the sphere diameter so the problem can be considered one dimensional
• Steady state conditions prevail
• Radiative heat loss isnegligible