The recommended ejector HDV-E23 can therefore suck in 873 kg/h and deliver to an intermediate pressure that is 4 bar higher. Entrainment rate of the HDV-E23 ejector as a function of gas cooler outlet temperature for selected pressure lifts The HDV-E23 ejector pre-selected in the BITZER calculation tool has a mass flow ratio of 0.56 and a pressure stroke of 4 bar at a high pressure of 89 bar and a motive mass flow of 1572 kg/h. Due to the separation in the intermediate pressure vessel, the net mass flow that flows through the evaporator and is sucked in again by the ejector is the total mass flow minus the flash gas mass flow in this example, this is 1572 kg/h - 699 kg/h = 873 kg/h.īased on the mass flow that must flow through the evaporator to achieve the cooling capacity of 60 kW, the necessary delivery rate of the compressors can be determined via the mass flow ratio of the ejector. With these assumptions, the first step is to calculate the ejector's mass flow to be delivered to achieve the cooling capacity of 60 kW.
According to a first estimate, this corresponds to the pressure lift of the system with ejector. The intermediate pressure is selected approx.
Cooling capacity of the medium temperature compressor stage (Q o MT): 60 kW.Evaporation temperature in the medium temperature compressor stage (t o MT): -8☌.Gas cooler outlet temperature (t gc) at the design point: 35☌.In the following example, a single-stage system with one ejector is to be calculated: The intermediate pressure is determined by the suction pressure control of the compressor. The goal is to increase the pressure only to the extent allowed by the mass flow ratio of the pumping operation.įrom the characteristics of the selected ejector results the suction mass flow at the given high pressure, motive mass flow rate and intermediate pressure. The ejectors circulate the refrigerant in a similar way to a refrigerant pump.
In a low lift application, the mass flow ratio is the essential selection criterion.
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