During a cold winter day, wind at 42 km/h is blowing parallel to a 6-m-high and 10-m-high wall of a house. if the air outside is at 5 degrees c and the surface temperature of the wall is 12 degrees c, determine the rate of heat loss from that wall by convection. what would your answer be if the wind velocity was doubled?

9.08KW and 16.21KW

Explanation:

The convection over a flat surface with a length of 10 m and a width of 6m.

The mean temperature is (5oC + 12oC)/2 = 8.5oC.

Then find the following properties of air at this temperature from Table A-15:

k = 0.02428 W/m(oC, v= 1.413x10-5 m2/s, and Pr = 0.7340.

find the Reynolds number. Re= VL/v

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This means that the flow becomes turbulent over the plate and we can use the Nusselt number equation for combined laminar and turbulent flow.

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We then use this Nusselt number to find the heat transfer coefficient and the heat transfer.

Check the screen shot for the calculation

Ans

9.08 kW

Then if the wind velocity were doubled, the Re number would be doubled and we would repeat the calculations above, starting with this revised Reynolds number..

Ans

16.21 kW

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .