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Pressure drop directly impacts the performance of the refrigeration loop, as illustrated in Figure 4, all heat exchangers (both for CO2 and R410A) are modelled with fixed pressure drops (Ξππ ). Because ex and is particularly important when modelling low pressure systems (Blanco et al., 2012). In this study, the COP for a refrigeration loop depends not only on the size of the exchanger pressure drops, but also the pressure drop profile in each exchanger, a linear pressure drop profile has been assumed where Ξππ β ππ, where ππ is the amount of heat transferred in the exchanger. Equation (3) illustrates how the pressure drop profile for βGas Cooler Cβ is calculated. 3 ex h4βh3 3 4 Ejector Performance Modelling 2.1.1 ππ=ππβΞππ οΏ½hβh3οΏ½forhβ₯hβ₯h. (3) The layout of the components between points 7 and 1 are changed if an ejector is included. The ejector system design studied in this article is shown in Figure 4, which also illustrates a CO2-based process in a logarithmic ph diagram. Figure 4. Left: flow diagram of a CO2 heat pump with an ejector modification (ABC + ejector). Right: example of a CO2 process with ejector having 35 % efficiency, where all exchangers have 0.5 bar pressure drop. The performance of the heat pump depends on the efficiency of the ejector. Several methods can be (2008), which relates the actual work rate recovered by the ejector ππ = ππΜ (h β h ) to the used to describe ejector efficiency, and this study applies the definition described by Elbel and Hrnjak maximum work rate recovery ππrec,max: ππejec = ππrec = ππΜ 0οΏ½h0,isβππ8βh0οΏ½, rec 0 0,isβππ8 0 οΏ½ respectively, to the ejector outlet pressure (ππ ). The steady-state mass flows used in this definition (4) ( 5 ) (6) ππrec,max ππΜ 7οΏ½h7βh7,isβππ where h and h are the enthalpies obtained by isentropic processes from point 0 and 7, 0,isβππ 7,isβππ 88 8 8 are related through the 1st law of thermodynamics, e.g. by defining a control volume around both the ejector and the receiver: ππΜ h + ππΜ h = ππΜ h + ππΜ h , 77007109 and a control volume around the ejector: ππΜ h +ππΜ h =ππΜ h , 770088 where ππΜ 8 = ππΜ 7 + ππΜ 0, i.e., neglecting heat loss and changes in potential and kinetic energies. The ejector efficiency for a given design case, ππ, with an ejector outlet pressure, ππ8, is calculated by creating a custom made function ππejec,ππ = ππ(ππ8, ππ) in MATLAB release 2018a (MathWorks, 2018). In the 6PDF Image | CO2 Heat Pump Performance
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