First Law of Thermodynamics—Flow Processes

Abstract

This chapter is confined to the application of the first law of thermodynamics to steady-flow processes, i.e. those processes defined by two fundamental principles:

• (a) Steady mass flow rate m = pAu (mass continuity)

  • where ρ = fluid density

  • A = duct area

  • u = fluid velocity

  • and $\dot m = steady mass flow rate = \left( {\frac{{dm}}{{dt}}} \right)$.

  • (This is usually recast as ṁv = uA since v = 1/ρ.)

• (b) Conservation of energy (the steady-flow energy equation or SFEE for short):

  $$_1{\dot Q_2}{ - _1}{\dot W_2} = \dot m\left[ {\left( {{h_2} - {h_1}} \right) + \frac{1}{2}\left( {u_2^2 - u_1^2} \right) + g\left( {{z_2} - {z_1}} \right)} \right]$$

  where z = height above datum (all other symbols as before).