Fix recuperator effectiveness for real-gas fluids#71
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The bisection observer assumed positive residual on model failure, telling the solver the pinch point hadn't been reached yet. For real-gas fluids (CoolProp), model failures near the upper bracket mean the cold outlet temperature violates the second law — the solver should treat that as negative (past the pinch). The inverted sign collapsed the bracket toward q_actual, producing effectiveness of 1.0 regardless of the actual min ΔT.
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Fix recuperator effectiveness returning 1.0 for real-gas fluids (CoolProp) even when min ΔT is well above zero.
The bug
The bisection observer in
effectiveness::computeassumed positive residual on model failure, telling the solver "min ΔT is still above zero, keep pushing." For real-gas fluids near the critical point, model failures at high cold outlet temperatures mean the second law has been violated — the solver should treat that as negative (past the pinch). The inverted sign collapsed the bracket towardq_actualinstead ofq_max, givingq_actual / q_max ≈ 1.0.Visible on the dashboard with default sCO₂ conditions: effectiveness showed 1.000 while min ΔT was 7.8 K.
The fix
One-line change:
assume_positive()→assume_negative()in the bisection observer.Test
Added
effectiveness_consistent_with_min_delta_tcovering both PerfectGas and CoolProp. Asserts that effectiveness < 1.0 whenever min ΔT > 1 K.With the fix, CoolProp returns effectiveness ≈ 0.97 for the dashboard defaults — consistent with the 7.8 K min ΔT.