How to calculate the efficiency of a heat engine that is able to reuse latent heat of condensatiion

[haruosan]

In a Rankine Cycle, the latent heat of condensation cannot be redirected back into the cycle itself because the condensation process is not the hottest point in the cycle. In an Organic Rankine Cycle the waste heat is redirected to some external process that is able to generate electricity. If the latent heat of condensation could be reused for the thermodynamic cycle itself, how would the efficiency be calculated?

 

[1503-44]

Don't count the latent heat utilised as input. It's all generated inside the system boundary. Take the total power output and divide by only the energy/time that crosses the boundary as actually input.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[georgeverghese]

In a typical ORC, the latent heat of condensation of the closed loop work fluid is rejected to cooling water or air or something similar. If you could reuse this latent heat of condensation within this cycle itself, presumably it results in a higher work output from the ORC ( for example higher electrical power at the expander turbine driven power generator) - that seems to be obvious ??

Can you tell us how you recover this latent heat of condensation to generate more power ?

 

[haruosan]

The cycle I’m thinking creates cold vapor through a flash process. The cold vapor is heated on its way to the condenser. After condensing, the latent heat of condensation is the heat used to increase the temperature of the vapor. The flash vapor is the cold sink for the condenser. A bit of external heat must be added for the first cycle and to maintain the temperature above, at least 373K. Using this method latent heat of condensation can be reused.

I don’t know the power output, so it will have to be predicted based on amount of steam created. I’ve calculated that 160kW are needed for a pump and 100kW for additional heating to produce 3,600 kg of steam per hour.

 

[georgeverghese]

It sounds like this is an economiser, but a process sketch will makes things clearer - can you post one?