Heat Transfer in Condensers
The overall heat-transfer coefficient can be determined after estimating the individual resistances.
The heat transfer in a water-cooled condenser is described by the Equation given below
where U is the overall heat transfer coefficient based on the surface area A of the condenser and Δt is the overall temperature difference. Figure shows the
components of the heat-transfer resistance in a water-cooled condenser, viz., the outside refrigerant film, metal wall, scaling on water-side surface and insidewater film. The overall resistance is obtained by adding all the resistances which are in series.
Figure : Thermal Resistance in Water-Cooled Condenser
U0 = Overall heat-transfer coefficient based on the outside surface area
h0= Condensing film coefficient of heat transfer
A0 = Outside or refrigerant-side area
k = Thermal conductivity of the tube material
Am = Mean tube surface area
hf = Coefficient of heat transfer through the scale
Ai = Inside or water-side area
hi= Water-side coefficient of heat transfer.
Thus the overall heat-transfer coefficient can be determined from the above Equation after estimating the individual resistances.