Condenser and evaporator models
The condenser and the evaporator are modeled by means of the є-NTU method for counter-flow heat exchangers. The heat exchanger is subdivided into 3 zones, each of them being characterized by a heat exchange coefficient U. Figure 4 shows the 3-zones heat exchanger in the case of an evaporator.
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Tsf, ex, ev T Sf |
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,ex, ev, tp |
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Tsf, su, ev, tp Tsfsue |
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Tr. su. ev Tr. su. ev. tp - Tev Tr ex. ev. tp Tr. ex. ev Figure 4 Three zones moving boundary evaporator model |
The AU heat transfer coefficient is calculated by considering two resistances in series (secondary fluid and refrigerant sides). The nominal heat transfer coefficients are identified for a nominal flow rate.
The coefficients are then obtained by: h = h ■ M 0,8
n n
This relationship can be justified by the Reynold’s analogy for a turbulent flow through a pipe [2] by assuming that the fluid properties, not included in this expression, remain unchanged.
Pump model
The pump is modeled by its swept volume, its isentropic efficiency (nPP, s) and its motor efficiency (nPP, m)- The two latter are supposed to be constant. The pump electrical consumption and the fluid flow rate are given by :
sh, pp
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Л pp, m Л pp, s.^ pp, m
