Rate of Heat Transfer for an Engine
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The thermal characteristics of an engine are being monitored on a dynamometer. Analysis of the coolant water shows that after 30 minutes the engine has lost 36MJ of heat energy. The area of active heat transfer for the coolant side of the engine is 0.84m^2, the coolant temperature in the cylinder head is 102?C and the cylinder head temperature on the coolant side is 118?C.
1. Determine the rate of heat transfer for the engine.
2. Calculate the convection coefficient (h) for the transfer of heat from the cylinder head to the coolant water in the engine.
3. If the distance from the coolant to the combustion chamber of the engine is on average 23mm, the average surface area is 0.57m^2 and the conduction coefficient for the cylinder head material is 212W/mK, determine the average temperature of the walls of the combustion chamber.
4. If the cycle averages cylinder temperature is measured to be 440?C and the convective heat transfer area is 0.3m^2 determine the convection coefficient for the transfer of the heat from the combustion gasses to the cylinder walls.
5. If the engine was fitted with a steel head, k = 72W/mK, by how much would the coolant temperature of the engine be changed?
6. If the cylinder walls are coated in Zirconia, k = 1.3W/mK to a thickness of 0.5mm, what would be the new cylinder materials maximum temperature?
7. List and explain the assumptions you have made when carrying out these calculations.
8. There are two mechanisms of heat transfer considered in these calculations, discuss what part, if any, heat transfer through radiation plays in each of the scenarios considered above.
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The rate of heat transfer for an engine are examined.
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The thermal characteristics of an engine are being monitored on a dynamometer. Analysis of the coolant water shows that after 30 minutes the engine has lost 36MJ of heat energy. The area of active heat transfer for the coolant side of the engine is 0.84m^2, the coolant temperature in the cylinder head is 102?C and the cylinder head temperature on the coolant side is 118?C.
(Please remember temperature difference is same in 0C and K)
1. Determine the rate of heat transfer for the engine.
The rate of heat transfer is given by the heat transferred per unit time thus
∆Q/∆t=(36*〖10〗^6)/(30*60)=2*〖10〗^4 J/s =2*〖10〗^4 W
2. Calculate the convection coefficient (h) for the transfer of heat from the cylinder head to the coolant water in the engine.
When the heat is lost in a vast medium due to convection the rate of heat loss due to convection is given by
∆Q/∆t=h A ∆θ
Here h is the coefficient of convection, A is the area and is the temperature difference between the medium and source. thus substituting the values we get
2*〖10〗^4=h*0.84*(118-102)
Gives h=(2*〖10〗^4)/(0.84*(118-102))=1488 W/(m2K )
3. If the distance from the coolant to the combustion chamber of the engine is on average 23mm, the average surface area is 0.57m^2 and the conduction coefficient for the cylinder head material is 212W/mK, determine the average temperature ...
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