9.21 a household oven door of 0.5-m height and 0.7-m width reaches an average surface temperature of 32℃ during operation. estimate the heat loss to the room with ambient air at 22℃. if the door has an emissivity of 1.0 and the surroundings are also at 22℃, comment on the heat loss by free convection relative to that by radiation.

Q convection = 11.361 W

Q radiation = 21.438 W

Explanation:

Given data:

Pr = 0.7

Isobaric volume expansion is calculated as

L = 0.5 m Since door is vertical

grasshoff number is

Gr = 1.79\times 10^8

Rayleigh number

Ra = GrPr

therefore given flow is laminar

Nusselt number is

Nu = 62.4223

Heat transfer coefficient

h = 3.246 W/m^2 K

convection heat transfer

Q = 11.361 W

Radiation heat transfer

answer:

the average distance would be 20ly

Explanation:

100,000ly times 5,000ly=20ly