3 replies to this topic

[sunflower]

I am encountering a problem with my compressors. They have negative efficiency. I specified temperature, pressure, composition for my inlet and outlet, and when I connected these inlet + outlet to the compressor, it said I overspecified something. So I deleted the adiabatic efficiency (left it blank). But once I left blank the adiabatic efficiency, I got a negative efficiency value. I think I have made no mistake in inputting the values, what is really going on here? Does it have anything to do with the fluid package??

[ankur2061]

sunflower,

You cannot specify the outlet or discharge temperature temperature. It needs to be calculated by simulation. That is the reason that you are getting an over specification error. Specify the adiabatic efficiency as 75% (a very common figure for the purpose of compressor calculations) and run the simulation. You should get your simulation right.

Regards,
Ankur.

[pavanayi]

sunflower,

Adding to what ankur said,
the simulation will calculate the temperature rise due to compression. Now, for you to get to the conditions that you wanted, add a cooler and specify the outlet temperature (The one which you specified as the outlet temperature of the compressor in the first place)

[Padmakar Katre]

Hi,
Far basic in Hysys the compressor operation needs a converged inlet streams and to converge the compressor you need,
1. Outlet stream Pressure as Input or
2. Compressor Duty as Input
Out of these two above inputs you need one to be specified.

Now when it comes outlet temperature calculations, Hysys considers adiabatic efficiency of 75% as a default input. If you have the field measure value of temperature then you simply delete the efficiency and input the outlet temperature to get the efficiency. Efficiency more than 100% or negative efficiency means that the outlet temperature value is unrealistic or wrong corresponding to the specified discharge pressure value or compressor duty.