Heat Loss

[ermorgan]

Hello,

I'd like to prescribe heat loss from a compressor or turbine. Is there a way to add a negative energy stream from the compressor or turbine?

On a related note, is there a way to find heat loss to the environment from a compressor, or other unit given a solved flowsheet?

Thanks,

Eric

[jasper]

Define heat loss? Is that (F_out * H_out - F_in * H_in ) - work? In this case, heat loss is zero; these devices operate adiabatically.

[jasper]

(if you double click the unit you can get the enthalpy balance, this should equal the energy production or energy demand parameter on these devices)

[ermorgan]

I was hoping to calculate heat transfer from a compressor to the surroundings, or at least add it using an (negative) energy stream. I'm just trying to determine total entropy generation from a device: Sgen = m(se-si)-Q/T. Being able to add some heat transfer to the surroundings changes conditions within the compressor, generating more entropy.

BTW, I submitted a journal article entitled "A Steady-State Simulation of a CO2-Based Methanol Synthesis Device using COCO Freeware". I'll let you know if it gets published.

eric

[jasper]

Very nice.

But the "heat loss" of these devices is not to the surroundings, but rather to the product stream. Again I would like to ask which heat loss to the surroundings you mean.

[jasper]

Total entropy generation is easy. It is the product entropy minus the feed entropy. Well - that part is easy. You still need to add the entropy it took to generate the power to run a pump or compressor, or subtract the entropy change resulting from whatever you do with the generated power of a turbine or expander.

[ermorgan]

By "heat loss to the surroundings" I mean heat transfer from the shell of the device to the ambient environment. That is, a compressor will heat the room that it's in - Q/T. I only ask because I'd like a clean way to calculate the entropy generation from all devices. At the moment, I can do as you suggested: "product entropy minus the feed entropy" for each device. However, in doing so, I get negative S values. I'd like add heat transfer to the surroundings directly to make the S terms all positive.

Thanks,

Eric

[jasper]

The negative entropy is due to the fact that you put in power. There where power was generated entropy must have been generated as well. You can calculate how much, if you assume the source of power generation. For example, you can calculate how much methane you need to burn to generate the required energy, and assume an efficiency which with methane is converted to power. But this depends on the source of power of course.