Electrical work is supplied to the air as it flows in a hair dryer. The mass flo

Question

Electrical work is supplied to the air as it flows in a hair dryer. The mass flow rate of air and the volume flow rate at the exit are to be determined. Assumptions 1 This is a Steady-flow process since there is no change with time. 2 Kinetic and potential energy changes are negligible. 3 Heat loss from the dryer is negligible. Properties The gas constant of argon is 0.287 kPa.m /kg.K. The constant pressure specific heat of air at room temperature is cP = 1.005 kJ/kg degree C (Table A-2a). Analysis (a) We take the pipe as the system, which is a control volume. The energy balance for this steady flow system can be expressed in the rate form as

Explanation / Answer

First law of thermodynamics
dE/dt = m_dotin(hin +0.5v2)- m_dotout(hout+0.5v2) = 0

m_dotin=m_dotout = m_dot (by conservation of mass)

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