The energy equation for general steady-state flow

2 The energy equation for general steady-state flow 

To develop the appropriate equations, we begin with the energy equation for a small element of pipe of length x from Chapter 3, Section 3.9  

The energy contained in the element will be unchanged with time in the steady state  

Further, the partial differential on the right-hand side of equation (3.62) may be expanded as 

The term f Sx/W is the heat flux into the small element per unit mass flow, or, alternatively, the heat input per unit mass of the passing fluid, in units of Joules per kilogram. As - 0. we may name this dq  

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We may appeal to the energy equation for general, steady-state flow to gain an insight into the variation in pressure through the valve ... 

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