[FEATURE] Add separate inlet for drains into humid heater #564
Description
What is your precise need ?
In NPPs, actual humid heaters have separate condensing zones and subcooling zones. The extraction steam of a heater enters the top and passes through both, but the drains from the upstream heaters often enter lower down in the heater and only pass through the subcooling zones. However, our current humid heater model forces both the extractions and drains to pass through both zones.
This matters for the following reasons:
- The current heaters likely underpredicts W_cond, since W_cond is calculated as the difference between the hotside inlet enthalpy and the liquid saturation enthalpy at the inlet pressure (multiplied by flow rate). If you mix the drains at the heater inlet, that will lower the inlet enthalpy compared to what it actually is. In some cases, heat exchange in the condensing region could happen in the opposite direction, thus potentially causing convergence issues, if the enthalpy of the extraction steam and drains mixed together is lower than the saturated liquid enthalpy at that pressure.
- If there are changes in upstream drain flow that in reality only affect the subcooling dury W_subc, the model would still have it affecting both W_cond and W_subc. This may affect the calibrations of Kth_cond and K_th subc and make it more difficult to accurately detect faults that affect mostly the drain lines
What solution do you see ?
Add a separate hotside inlet port to the component that only passes that liquid through the subcooling region, not the deheating or condensing region
Do you see any other alternative ?
Model the humid reheater as a dry reheater followed by a liq-liq HX right below it, but this is not ideal since it's in fact one component