SINGLE EFFECT ANALYSIS Overall material balance.
Assuming no leaks in the system, S=C F=P+V Where each letter represents a flow rate (kg/s) : S = steam, C = condense, F = feed, P = product, V = vapour Solid mass balance FXf = PXp Using X to represent the fraction of solids (in %)
Energy (entalphy) balance: • Heat lost ( or supplied by steam) = heat gained by the feed.
Shs + Fhf = Php + Vhv + Chc • Where h represents the enthalpy per unit mass (kJ/kg). The enthalpies are best calculated using the steam tables for pure water components (S, V and C). The food component enthalpies (F and P) can be estimated using: hf = CfTf hp = CpTp
• C is specific heat or heat capacity (J/kgoC) that can be obtained from literature values, models or direct measurement.
HEAT TRANSFER EQUATION a)
Q=UA
T
b) Q = heat transferred from steam to food (in Joule/sec or Watts), c)
U = overall heat transfer coefficient (W/m2oC),
d) A = effective surface area (m2) (for a pipe, this is the log mean area of the inside and outside of the pipe surfaces,
e) TIn is the log mean temperature difference (LMTD) over the length of the pipe
f) In the absence of heat losses from the system, the heat transferred is related to the change in heat content of the steam and of the feed as follows:
g) Heat supplied by steam = sensible heat of product + latent heat by vaporization