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Calculate the rate of heat flow through the wall of a refrigerated van of 1.5 mm of steel sheet at outer surface, 100 mm plywood at the inner surface and 2 cm of glass-wool in between, if the temperatures of the inside and outside surfaces are 15°C and 24°C respectively. Take thermal conductivities of steel, glass-wool and plywood as 23.2 W/m°C, 0.014 W/m°C and 0.052 W/m°C respectively.
Asked by ogatheo2000 | 08 Mar, 2023, 08:59: PM
Figure shows the insulation arrangement made by plywood , Glass-wool and steel sheet in a referegirated van.

Ambient temperature is 24o C and maintained temperature inside van is 15o C inside van.

Let T1 be the temperature at plywood-Glasswool interface and T2 be the temperature at Glasswool-steel interface .

At steady state , heta flux per unit area is written as

where ks , kg and kp are thermal conductivities of steel, glasswool and plywood respectively

If we consider heat flow through plywood and glasswool , we get

8.428 T1 - T2 = 7.428 × 15 =  111.4 ..................................(1)

If we consider heat flow through plywood and glasswool , we get

From above expression , we get T2 ≈ 24oC

If we substitute T2 = 24o C in eqn.(1) , we get T1 = 16oC

if Rate of heat flow per unit area  Q/A , then we get

Answered by Thiyagarajan K | 09 Mar, 2023, 09:21: AM
NEET neet - Physics
Asked by anjanakurup728 | 18 Oct, 2019, 10:06: AM