Explanation Write the formula to calculate the density of the air ( ρ ) from ideal gas relation. ρ = P R T (I) Here, gas constant of air is R , pressure of air is P and temperature of air is T . Write the formula to calculate the mass flow rate of air ( m ˙ ) from volumetric flow rate. m ˙ = ρ V ˙ (II) Here, volumetric flow rate is V ˙ . Write the energy rate balance equation for a control volume. E ˙ in − E ˙ out = d E ˙ system / d t = 0 ( For steady state ) Here, the total energy rate at inlet is E ˙ in , the total energy rate at outlet is E ˙ out , and the change in net energy rate is d E ˙ system / d t . Rewrite the energy balance Equation for electronic devices mounted on cold plates. E ˙ in = E ˙ out Q ˙ in + m ˙ h 1 = m ˙ h 2 Q ˙ in = m ˙ c p ( T 2 − T 1 ) (III) Here, specific enthalpy of water at state 1 is h 1 , specific enthalpy of water at state 2 is h 2 , rate of heat transfer is Q ˙ in , mass flow rate of air is m ˙ , specific heat constant of air at room temperature is c p , temperature of air at inlet is T 1 , and temperature of air at exit is T 2 . Write the formula to calculate the heat transfer from the outer surfaces of the duct ( Q ˙ external ) . Q ˙ external = Q ˙ total − Q ˙ in (IV) Here, total heat transfer through the duct is Q ˙ total . Conclusion: Refer Table A-, “Gas constants of ideal gases”, obtain the gas constant ( R ) of air as 0.287 kJ / kg ° C . Refer Table A-2, “Ideal gas specific heats of various common gases”, obtain the constant pressure specific heat of air ( c p ) as 1.005 kJ / kg ° C . Substitute 101 .325 kPa for P , 0 .287 kPa ⋅ m 3 / kg ⋅ ° C for R , and 30°C for T in Equation (I)

8th Edition

ISBN: 8220102809444

Author: CENGEL

Publisher: YUZU

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Work and Heat Transfer

It is generally related to thermal engineering which tells about the use, creation, conversion and transfer of heat energy between the systems. It is also considered that to transfer heat from one source to another, transfer of masses is also required. T…

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Chapter 5.5, Problem 95P

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The rate of heat transfer from the outer surface of the duct.

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Chapter 5.5, Problem 94P

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