Question

5-111 Consider a refrigerator whose outer dimensions are 1.80 m x 0.8 m × 0.7 m. The walls of the refrigerator are constructed of 3-cm-thick urethane insulation (k = 0.026 W m K and α = 0.36 × 10-6 m2/s) sandwiched between two layers of sheet metal with negligible thickness. The refrigerated space is maintained at 3°C and the average heat transfer coefficients at the inner and outer surfaces of the wall are 6 W/m2 K and 9 W/m2.K, respectively. Heat transfer through the bottom surface of the refrigerator is negligible. The kitchen temperature remains constant at about 25°C. Initially, the refrigerator contains 15 kg of food items at an average specific heat of 3.6 kJ/kg K. Now a malfunction occurs and the refrigerator stops running for 6 h as a result. Assuming the temperature of the contents of the refrigerator, including the air inside, rises uniformly during this period, predict the temperature inside the refrigerator after 6 h when the repair-man arrives. Use the explicit finite difference method with a time step of Δ 1 min and a mesh size of Δx-1 cm and disregard corner effects(i.e., assume one-dimensional heat transfer in the walls)

Answer 1

M03 + 1 O:0

n- nt m-1 nade), , and fa.vn / aa a上 nada_ | Alt dams

i+I m-I 2,+3 ろt, 2

and tine. ( inside-.0-La mass 91.3 m mass of e inSide ase 1-17kg 5.6135 m

t, is the eme 56135 m fa A 360 .145.5-55-17抓 る60 Tr - 25 с.