Heat Exchanger

About

Two streams exchange heat: one cools, the other warms by the same amount. Give the duty, or one outlet temperature, and it finds the rest — and refuses a pairing that would need heat to flow backwards.

What This Models

A hot stream and a cold stream flowing past each other and exchanging heat — a shell-and-tube unit, a plate exchanger, any device where the two never mix. Whatever heat the hot stream gives up, the cold stream takes on: no loss to the surroundings is modelled, so the duty on one side always equals the duty on the other.

Key Relations

Q = ṅ_hot·(h_hot,in − h_hot,out)     heat the hot stream gives up
Q = ṅ_cold·(h_cold,out − h_cold,in)  heat the cold stream picks up

The same Q both ways, by construction — no separate closure to check. Each Δh comes from the same relation the Heater case uses on its one stream, Δh = ∫Cp dT + Σ L_tr (sensible heat plus any latent heat crossed), run once per stream. Whichever you give — the duty, or one stream's own outlet — the other three unknowns follow from these two equations together.

Counter-Current

The two streams are assumed to flow in opposite directions through the unit, the usual arrangement and the more efficient one. That choice only matters for the feasibility check below — the energy balance itself is the same either way.

Inputs

The form is grouped Hot stream, Cold stream and Duty. Each stream asks for the same things the Heater case asks for a single stream, given twice:

• Substance, a chemical or a mixture built the same way as on the Property tab. The defaults are hot carbon dioxide and cold nitrogen, echoing a calciner giving up heat. Air is a blend with no heat-capacity data of its own, so use nitrogen and oxygen instead.
• Flow given as, one of Mass flow, Molar flow, Volumetric flow or Normal Volumetric Flow, then the value. Only rates are offered: a batch heat exchanger is not a standard concept. Each stream has its own basis. The default is 1000 kg/h.
• Inlet temperature, 900 °C for the hot stream and 20 °C for the cold, and Pressure, 1.01325 bar, held constant through the exchanger on each side.

Specify then chooses what you know:

• Duty — find both outlet temperatures. Enter one Duty; it is always positive, since which stream is hot already says which way the heat goes.
• Hot stream's outlet temperature — find the duty and the cold outlet. The outlet must be cooler than the hot inlet.
• Cold stream's outlet temperature — find the duty and the hot outlet. The outlet must be warmer than the cold inlet.

Press Calculate. Editing any input, or changing a unit, clears the answer.

What comes back

A Duty line, then a group each for the Hot stream and the Cold stream: inlet and outlet temperature, initial and final phase, a Melting point or Boiling point line for each transition crossed, and when the phase changes the duty split into of which sensible and of which latent. Then the stream's mass flow, molar flow and volumetric flow at inlet conditions.

Grey notes say that flow is assumed counter-current with no heat loss, so both sides carry the same duty, and that this is the energy balance only. If either stream changes phase, a note warns that the feasibility check below cannot see a pinch at the plateau. A failure inside one stream, such as a duty beyond what it can absorb, names the stream, so you are not left checking both.

When It Refuses

Heat only flows from hot to cold.

T_hot,out ≥ T_cold,in
T_cold,out ≤ T_hot,in

In a counter-current unit those are the two ends where the streams pair up — asking for a pairing that breaks either one is refused rather than answered with a duty that would require heat to run backwards.

That check only looks at the four inlet/outlet temperatures, not the shape of the temperature profile in between. If a stream changes phase partway through, the closest approach between the two streams can actually occur at that phase change rather than at either end — sizing an exchanger for that case needs the fuller method below, not this check alone.

What This Does Not Do Yet

This is the energy balance only: how much heat moves, and what temperature each stream leaves at. It does not size the exchanger — no heat-transfer area, no tube count, no pressure drop, no fan or pump power, and no cost. Sizing needs the temperature profile along the unit and a heat-transfer coefficient, both a separate calculation from the one here.