Heat Exchanger LMTD and Effectiveness-NTU
Log-mean temperature difference, heat duty, required UA, effectiveness, NTU.
Example
You enter
- Flow configuration counterflow
- Hot inlet (°F) 200
- Hot outlet (°F) 100
- Cold inlet (°F) 60
- Cold outlet (°F) 140
- Hot flow (GPM) 50
- Cold flow (GPM) 62.5
You get
- LMTD 49.33 F
- Heat duty 2500000
- Effectiveness 0.7143
- Number of transfer units NTU 2.027
Details, formula, and sources
Log-mean temperature difference, heat duty, required UA, effectiveness, NTU, and capacity-rate ratio for counter-flow or parallel-flow from four temperatures and the two flows. Per the TEMA standards and standard heat-transfer texts.
LMTD = (dT1 − dT2) / ln(dT1/dT2). Q = C × delta-T with C = GPM × fluid factor. UA = Q / LMTD. Effectiveness = Q / (C_min × (Th_in − Tc_in)). NTU = UA / C_min. Capacity-rate ratio Cr = C_min / C_max.
TEMA (Tubular Exchanger Manufacturers Association) standards by name; standard heat-transfer texts (Incropera, Cengel) by name.
TEMA standards TOC free at tema.org; texts licensed.
Estimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
Field names used by the API: config, th_in_F, th_out_F, tc_in_F, tc_out_F, hot_gpm, cold_gpm, lmtd_F, q_btu_hr, effectiveness, ntu
- LMTD limit as dT1 → dT2 the LMTD equals the common end differencecalculus limit of the LMTD expression
- Capacity rate C = GPM × fluid factor (BTU/hr-°F)first-principles fluid energy balance