🔥 Heat Exchanger Design Calculator

Variable Definitions

• Th,in / Th,out: Hot stream inlet/outlet temperature.
• Tc,in / Tc,out: Cold stream inlet/outlet temperature.
• ṁh, ṁc: Mass flow rates of hot/cold streams.
• Cp,h / Cp,c: Specific heats at operating temperature (use average if Cp varies).
• U_clean: Clean overall heat-transfer coefficient (user estimate/vendor typical).
• R_f: Lumped fouling resistance (overall), entered as fouling factor.
• U_design: Overall U including fouling, computed by resistance-in-series.
• Q: Heat duty (hot-side and cold-side energy balances).
• ΔT_m: Mean temperature difference (LMTD for parallel/counter; AMTD screening for cross-flow).
• A: Required heat-transfer area from Q = U·A·ΔT.
• C: Heat-capacity rate C = ṁ·Cp; C_min is the smaller of hot/cold.
• NTU: Number of transfer units NTU = U·A / Cmin.
• ε: Effectiveness ε = Q / Qmax, where Qmax = Cmin·(Th,in − Tc,in).

Formulas / Logic (Screening)

• Energy balance (SI internal basis):
  Hot side: Qh = ṁh·Cp,h·(Th,in − Th,out)
  Cold side: Qc = ṁc·Cp,c·(Tc,out − Tc,in)
• Design duty: Qdesign = min(|Qh|, |Qc|) (conservative when inputs are inconsistent).
• Heat balance error: |Qh − Qc| / Qdesign × 100%.
• Mean temperature difference:
  • Parallel: ΔT1 = Th,in − Tc,in, ΔT2 = Th,out − Tc,out
  • Counter: ΔT1 = Th,in − Tc,out, ΔT2 = Th,out − Tc,in
  • LMTD: ΔTm = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2) (if both ΔT1 and ΔT2 are positive)
  • Cross-flow: uses AMTD as a quick estimate: (ΔT1+ΔT2)/2. For detailed design, apply a correction factor/F-chart.
• Fouling in series: 1/Udesign = 1/Uclean + Rf.
• Area: A = Qdesign / (Udesign·ΔTm) (with Q in W).
• Effectiveness–NTU check (screening): computes ε from duty and NTU from UA/Cmin to sanity-check the sizing. Detailed ε–NTU correlations depend on flow arrangement.

Assumptions / Notes

• This is a preliminary sizing tool. Final exchanger design should follow TEMA practices and vendor thermal ratings.
• Cross-flow is treated as a screening estimate without explicit LMTD correction factor F. Use vendor rating software or published correction charts for multi-pass/cross-flow cases.
• Uses constant Cp and single-phase sensible heat only (no phase change). For condensation/boiling, use latent heat methods and appropriate U values.
• Enter U_clean and fouling consistent with service; fouling factors are commonly selected per TEMA/industry practice and company standards.
• Temperatures must avoid “temperature cross” such that terminal ΔT values remain positive for LMTD calculations.
• Plate HX (screening): typically counter-current with high U for clean services; final sizing requires vendor plate geometry and allowable pressure drop.
• Air-cooled HX (screening): overall U is dominated by the air side and fin efficiency; final sizing should follow API 661 and vendor fan/bundle rating.