Energy Equation of the Boundary Layer

The foregoing analysis considered the fluid dynamics of a laminar-boundary-layer flow system. We shall now develop the energy equation for this system and then proceed to an integral method of solution. 

Consider the elemental control volume shown in Frg. 5-6. To simplify the analysis we assume 

Constant viscosity, thermal conductivity, and specific heat 

Negligible heat conduction in the direction of flow (jc direction) 

for the element shown, the energy balance may be written 

---