Surface Condenser

[wmconlon]

I would like to model a surface condenser for a Rankine Cycle. It appears the approach is to is to assign the condensing vapor to input 1 of the HeatExchanger UnitOp and specify the amount of subcooling as the outlet of temperature stream 1 in the GUI. Condensing pressure is then controlled by setting the outlet pressure of the Expander UnitOp.

q1. Is this the preferred way to achieve this?
q2. Is there a cookbook that shows preferred patterns for solving problems (a la Alexander's 'A Pattern Language')?

TIA

[jasper]

There is no cookbook, but this example may be relevant to your problem:

Note that on a closed recycle you probably want to include a flow controller unit operation to keep the flow rate fixed. If you have more than one compound, the composition also needs to be fixed, which you could do with a small custom unit that would output a constant composition (e.g. an Excel Unit Operation).

You did not include the flowsheet, so it is hard to interpret what you mean by stream 1.

[wmconlon]

@Jasper. Sorry about not including a flowsheet. Stream 1 is assigned when connecting to the Heat Exchanger UnitOP.

Also thank for pointing out the CHP example, which uses a Heater/Cooler instead of a Heat Exchanger, and specifies the outlet temperature of the condensing stream. I am also interested in the cascade, i.e. the effect on the cooling stream, so I want to use the Heat Exchanger.

In my case, the cooled stream is superheated as it enters the Heat Exchanger, and as a result encounters a pinch point at the condensing temperature. This prevented the Heat Exchanger from meeting my desired constraint of specified exit temperature for the condensing stream.

Accordingly I used two Heat Exchangers. One to de-superheat, with the temperature of the cooled stream (Stream 1) specified to be at the condensing temperature. The second Heat Exchanger constrains the subcooling of the cooled stream (Stream 1).

[jasper]

What is exactly the reason for the superheated stream not to be able to be cooled in a single heat exchanger? Insufficient heat capacity of the cold stream?

[wmconlon]

[jasper]

If by subcooled you mean a vapor that is not in phase equilibrium (and would form a liquid), this is not possible in COFE; all streams will be in phase equilibrium.

The exit temperature spec should be honoured by the heat exchanger, unless there is not sufficient heat capacity in the other stream to reach the specified temperature. This is what the second message indicates.

[wmconlon]

[wmconlon]

My previous post illuminated my problem: The mass flow of the heated stream was insufficient to bring the cooled stream down to the specified temperature. Once I adjusted the flow rate, I could achieve the desired sub-cooling.

[jasper]

[wmconlon]