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STEADY FLOW ENERGY EQUATION (SFEE) | STUDY MECHANICAL | MECHANICAL PROJECTS





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ASSUMPTIONS MADE IN NUSSELT’S ANALYSIS OF FILM CONDENSATION | MECHANICAL PROJECTS | STUDY MECHANICAL

Nusselt’s analysis of film condensation makes the following assumptions : The film of the liquid formed flows under the action of gravity. The condensate flow is laminar, and the fluid properties are constant. The liquid film is in good thermal contact with the cooling surface and therefore, the temperature at the inside of the film is taken equal to the surface temperature T s . Further, the temperature at the liquid-vapor interface is equal to the saturation temperature T sat  at the prevailing pressure. Viscous shear and gravitational forces are assumed to act on the fluid; thus normal viscous force and inertia forces are neglected. The shear stress at the liquid-vapor interface is negligible. This means there is no velocity gradient at the liquid-vapor interface. The heat transfer across the condensate layer is by pure conduction and temperature distribution is linear. The condensing vapor is entirely clean and free from gases, air, and non-condensing i...
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HEAT EXCHANGER ANALYSIS | MECHANICAL PROJECTS | STUDY MECHANICAL

The flow in the heat exchanger is considered under steady-state and fully insulated at the outer surface. Consider an infinitesimal part of the heat exchanging tube of area dA, where temperatures of hot and cold fluid are T h and T c , respectively. The figure below shows the temperature profile along the direction of flow in parallel flow and counter flow heat exchangers. Figure 1: Temperature profiles in parallel flow and counter flow heat exchangers The profile of temperature variation depends upon the heat capacity of the fluid. The profiles are different for both types of heat exchangers, therefore, expressions of LMTD are also different, derived as follows. heat exchange from infinitesimal area dA at any point of the heat exchanger is given by dQ = U.dA(T h – T c ) Where ‘U’ is the overall heat exchanger coefficient and ‘A’ is the heat transfer area of the heat exchanger. this heat is taken from hot fluid and given to cold fluid. the temperature of...
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