Multistream exchanger: one core, three streams, one free outlet

A cryogenic cold box is not a network of two-stream exchangers — it is one brazed-aluminium core with several streams exchanging heat simultaneously, and the multistream exchanger models it as such. Three streams share this core: 300 mol/s of 300 K feed gas being chilled, 250 mol/s of 190 K residue gas being rewarmed, and 60 mol/s of 200 K cold liquid. You specify outlet temperatures for all but one — 225 K for the feed gas, 280 K for the residue — and the remaining stream is the free one: its outlet, 230.1 K, is not specified but SOLVED, because it is what closes the adiabatic energy balance across the core. That is the correct number of degrees of freedom for an adiabatic exchanger, and specifying all three would over-specify it. The 1.08 MW duty and a composite-curve pinch check against a 3 K minimum approach come with it, so a specification that would need heat to flow the wrong way is rejected rather than reported. Bounded: this is a thermal feasibility and duty model, not a mechanical design. There is no core geometry, no layer stacking, no fin type, no per-stream pressure drop from passage dimensions — a real cold box datasheet needs all of those, and a vendor computes them from proprietary correlations.