What does a warning from PROII mean? !
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** Warning: Controller unit 8, ‘cn3’, is using a vary command to control stream ‘compin’, which is a product of unit 2, ‘cooler’. Therefore, attempting to control the properties of this stream is invalid. -------------------------------------------------------------- It is said that “attempting to control the properties of this stream is unfounded”. Is this flow a circulating flow? Can’t it be controlled? Please ask an expert for guidance. Please see the attachment. PROII version: 9.4
What this means is that you use a variable to control a flow of material, and this flow is the product of unit 2, the ‘cooler’. Since it’s a product, it cannot be changed, so your control is ineffective; what you need to control is the feed to unit 2, the ‘cooler’
** Warning: Controller unit 8, ‘cn3’, is using a vary command to control the stream ‘coolerin’, which is a product of unit 5, ‘v1’. Therefore, attempts to control the properties of this stream are invalid. ------------------------------------- I set it to feed mode, and the above message appeared; this fluid is a circulating stream, serving both as feed and as discharge! As shown in the figure.
You’d better explain your design approach – what are the given conditions? What is used to control what?
This process is low-temperature evaporation of a heat pump. The four blocks on the right side represent the heat pump cycle, while the one on the left is the evaporator; the vapor exiting from it exchanges heat with the cooler of the heat pump, transferring heat to the cooler. A heat pump is a cyclic process, so it serves as both the inlet and the outlet.
@zhxbkofkyo
You’re talking about the principle of heat pumps; there’s no need for you to explain that. What I mean is, what are your variables? In the first step, which variable is used to control which other variable? In the second step, again, which variable is used to control which variable, and what is the desired goal at the end? You should explain your control strategy
The evaporation rate for low-temperature evaporation is 200 L/h, the evaporation pressure is 6 KPa (absolute pressure), and the circulation volume of the heat pump is determined based on this value. Refrigerant R134a, compressor outlet 85 degrees. It’s about calculating the circulation flow rate of the heat pump.
Only the relevant circulating streams have been considered; according to the design specifications, the temperature at the compressor outlet is 85°C. For the amounts related to non-relevant streams, relevant design specifications should be added separately