Query re. Expansion Nozzle
Query re. Expansion Nozzle
(OP)
I'm busy doing an analysis on our R22 fridge plant and am
having difficulty understanding which parameters control which.
Firstly: With a expansion nozzle, if the pressure drops, the temperature remains relativley constant, and its isenthalpic, where does that energy go??
Secondly: We seem to have a constant discharge pressure on the compressors, with a slide valve to control compressor output. Is the suction pressure dependant on pressure in the evaporator, which is in turn dependant on our (R22/glycol evaporator) glycol inlet temperature, or is it primarily more dependant on condenser pressure, which is turn is controlled by cooling water.
Thirdly: How does the expansion nozzle control refrigerant flow, and what variable does it look at??
having difficulty understanding which parameters control which.
Firstly: With a expansion nozzle, if the pressure drops, the temperature remains relativley constant, and its isenthalpic, where does that energy go??
Secondly: We seem to have a constant discharge pressure on the compressors, with a slide valve to control compressor output. Is the suction pressure dependant on pressure in the evaporator, which is in turn dependant on our (R22/glycol evaporator) glycol inlet temperature, or is it primarily more dependant on condenser pressure, which is turn is controlled by cooling water.
Thirdly: How does the expansion nozzle control refrigerant flow, and what variable does it look at??





RE: Query re. Expansion Nozzle
Secondly: Suction pressure is directly dependent on the saturation temperature of the refrigerant in the evaporator. As you state, that temperature is most likely affected by the heat exchange process in your scenario, and the resulting temperatures. Head pressure is directly affected by condenser pressure/temperature.
Thirdly: The most common refrigerant expansion valve is a thermostatic expansion valve. A thermostatic expansion valve measures temperature at the evaporator outlet to maintain a pressure that guarantees some amount of superheat (setpoint TBD). This in turn guarantees that the evaporator coil is completely filled with refrigerant with no danger of liquid carryover into the compressor.
RE: Query re. Expansion Nozzle
rmw
RE: Query re. Expansion Nozzle
RE: Query re. Expansion Nozzle
There are refrig systems that depend entirely on gas expansion to do cooling, in which the pressure change is effected at a ture Delaval type critical flow nozzle.
There are arrangements that use geometry much like a venturi to effect refrigerant recirculation, some called Inductors and others Eductors.
And certain systems use a fixed, formed plate type of a nozzle, as per the ANSI test orifices.
Besides TXV's (thermostatic expansion vlaves) there are AXV's Subcooling COntrol valves, Float Valves and so on...Some of which are active in establishing the machine's Suction Pressure.
And most slide valve machine's are controlled off suction pressure; some are controlled from a process variable (for instance, a brine temperature).
Maybe we can offer more if you describe this thing in a little greater detail?