PhD Thesis - Energy Systems Research Unit - University of Strathclyde

equation (3.2), (3.4) and (3.6), the partial differential equations of the modelledchiller, using the numerical approximation process mentioned in Section 3.3.4.1.3.3.4.3 Finding the state points within the chillerIn order to obtain Q i , Q j and Q g , the net energy flows into and out of Node i, Node jand Node g respectively, the individual state points within the chiller’sthermodynamic cycle are calculated as follows:Equations and assumptions used to find Q iRecall from equation (3.3) that:Assuming that the refrigerant exits the evaporator as saturated vapour (the amount ofsuperheating in the evaporator of an absorption chiller is insignificant [28]), h 10 canbe considered to be the specific enthalpy (in kJ/kg) at dry conditions of p low , the lowpressure inside the evaporator-absorber. Also, assuming adiabatic expansion in theexpansion valve implies that h 9 is equal to h 8 , the specific enthalpy (in kJ/kg) at wetvapour conditions of p high (the amount of sub-cooling in the condenser of anabsorption chiller is insignificant [28]), the high pressure inside the condensergenerator.The low pressure, p low , and the high pressure, p high , are calculated usingempirically calibrated data as explained in Section 3.3.5.1.Considering the fact that in most chillers the condenser-generator and the evaporatorabsorberassembly are built into two separate shells, a reasonable assumption is thatno pressure loss occurs between the condenser and the generator and between theevaporator and absorber, and that pressure changes are only due to the pump andexpansion valve [28].The refrigerant mass flow rate, in kg/s, is found using equation (3.8).- (3.8)111