: A liquid nitrogen storage dewar can be approximated by two concentric spheres, $8$ inches and $12$ inches in diameter, with the space in between them evacuated. Liquid nitrogen at $-320\mathrm{.}7$ o F is stored in a room so that the outer sphere is at $68$ o F$.$ a$.$ If the surfaces have been flashed with aluminum $($$=0\mathrm{.}03),$ what is the heat transfer to the inner vessel. b$.$ If the liquid air has a latent heat of vaporization of $85\mathrm{.}7$ Btu$/$lbm$,$ what is the vaporization rate of the liquid nitrogen in lbm$/$hr