Separated Generator

Heat and mass transfer separated: external heating + vapour released in a separate chamber · Framework page · worked examples in preparation

The construction

The solution is first heated — without boiling — in an external heat exchanger, then enters a separate chamber at generator pressure, where part of the refrigerant flashes off (or is desorbed across a sprayed film) and leaves as vapour. No heating surface does duty inside the separation chamber.

How the account differs

Two books instead of one. The heat input is booked in the external exchanger by its own UA / Δt account; the chamber is booked as an equilibrium flash: mass, species and energy balances over the chamber alone, with no K·F·Δt_m term for the generator itself.
The coupling is the state line. The two books meet at the chamber inlet state (temperature and concentration after heating); the flash fixes the vapour rate and the outlet concentration together.
The vapour-enthalpy question survives the move. The flashed vapour is still formed at solution temperature, above the saturation temperature at its pressure — whether a model books it as superheated or saturated changes Q by the same order of Δh as in the built-in family (67–142 kJ/kg over the typical grid, see the built-in page).

Worked example (draft)

Draft: the flowsheet and the notation are published first; the balance equations, the enthalpy basis and the source are to be added once checked.

Separated generator flowsheet fragment: generator heat exchanger, generator, condenser — Flowsheet fragment (GHX–Gen–Cond): drive heat enters the generator heat exchanger (GHX) at DE and leaves at DL; rich solution, preheated in the GHX, enters the generator (Gen) as SGR, and weak solution leaves the generator bottom as SGP; vapour passes to the condenser (Cond), the heat sink enters at KE and leaves at KL, and the refrigerant liquid leaves the condenser bottom as ROC.

Notation (fixed terms; SHX and GHX are two different exchangers):

Tag	Meaning
SHX	solution heat exchanger
GHX	generator heat exchanger (the external heating surface of this family)
DE / DL	drive heat entry / leave
SGR	rich solution entering the generator
SGP	weak solution leaving the generator
SHXRO	rich solution outlet of the solution heat exchanger
KE / KL	sink entry / leave (condenser cooling water)
ROC	refrigerant at the condenser outlet
SE / SL	source entry / leave (evaporator side; not in this fragment)

Calculation table (draft)

Inputs (four givens): the generator outlet flow ṁ_sgp, the outlet concentration ξ_sgp, the condensing temperature T_cond, and the vapour flow ṁ_v,gc. Every other quantity is computed from the books in the table (marked “solve”); the numerical values of temperatures and enthalpies await the property basis. The relations between the state quantities — the flash equilibrium, how each enthalpy is taken and on what basis, the heat-transfer constraints on the two utility sides — are exactly the basis this table is missing; each will be filled in as the books are checked.

Tag	Stream	ṁ (kg/s)	T (℃)	ξ (%)	h (kJ/kg)	Basis
DE	drive heat, in	solve	solve	—	solve	to follow
DL	drive heat, out	solve	solve	—	solve	to follow
SHXRO	rich solution, out of the SHX	solve	solve	solve	solve	to follow
SGR	rich solution, into the generator	solve	solve	solve	solve	to follow
SGP	weak solution, out of the generator	given	solve	given	solve	to follow
—	refrigerant vapour, generator → condenser (flow ṁ_v,gc)	given	solve	—	solve	to follow
ROC	refrigerant liquid, out of the condenser	solve	solve	—	solve	to follow
KE	heat sink, in (cooling water)	solve	solve	—	solve	to follow
KL	heat sink, out (cooling water)	solve	solve	—	solve	to follow

One book per component (no heating inside the chamber; the heat input is booked on the GHX):

GHX: Q_g = ṁ_sgr·(h_sgr − h_shxro) = ṁ_d·(h_DE − h_DL)

Gen (flash chamber): ṁ_sgr = ṁ_sgp + ṁ_v,gc, ṁ_sgr·ξ_sgr = ṁ_sgp·ξ_sgp, ṁ_sgr·h_sgr = ṁ_sgp·h_sgp + ṁ_v,gc·h_v,gc

Cond: Q_cond = ṁ_v,gc·(h_v,gc − h_roc) = ṁ_k·(h_KL − h_KE)

Note: the high-side pressure is fixed by T_cond, P_gen = Pref(T_cond). One condition is still missing to close the GHX book and fix Q_g: either the drive side (ṁ_d with T_DE, T_DL) or the SHXRO temperature — one of the two, to be decided.

Status

Worked examples are being collected from the published models in this family and will be added case by case, each with its balance boundary, enthalpy basis and accounting side stated.

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