Validation

The Multi-Stream Heat Exchanger unit operation has been validated through two complementary test suites:

Validation Type	Description	Result
2-Stream Validation	8 test cases comparing MSHX against analytical e-NTU solutions for counterflow and co-current configurations	8/8 PASS
3-Stream Validation	3 test cases verifying energy balance, physical feasibility, and UA/MITA constraint matching for multi-stream configurations	3/3 PASS

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Test Infrastructure

All tests are executed headlessly via the DWSIM Automation API (no GUI required):

• Python with pythonnet for .NET interop
• DWSIM.Automation.dll with Automation3 class
• Base flowsheet with MSHX unit, inlet and outlet material streams
• Fluid: Water at 10 atm (1,013,250 Pa) to remain liquid
• Property package: Raoult's Law
• Results validated programmatically with automatic PASS/FAIL reporting

Acceptance Criteria

Metric	Tolerance	Rationale
Outlet temperature	< 5%	Accounts for real Cp(T) vs constant Cp in e-NTU reference
Heat duty (Q)	< 5%	Same as above
UA vs specification	< 3%	Numerical integration vs analytical
MITA vs specification	< 0.5 K	Bisection convergence tolerance
Physical feasibility	Must pass	Hot streams must cool, cold streams must heat
Temperature crossover	MITA > 0	Second Law of Thermodynamics
Energy balance	< 1%	Thermodynamic consistency