Understand the engineering model
What is Heat Exchanger LMTD and Effectiveness?
Thermodynamic calculations track energy, heat, work, temperature, phase change, resistance, and ideal limits under a declared system boundary and sign convention.
Provide both LMTD and effectiveness views while exposing crossed, impossible, or materially unreconciled terminal data instead of hiding it.
The relationship
Write the model before substituting values
Counterflow ΔT terms are T_h,in−T_c,out and T_h,out−T_c,in; parallel terms are inlet and outlet differences. LMTD=(ΔT₁−ΔT₂)/ln(ΔT₁/ΔT₂). Q_h=C_h(T_h,in−T_h,out), Q_c=C_c(T_c,out−T_c,in), Q_reconciled=(Q_h+Q_c)/2 only as a comparison estimate, and estimated effectiveness=Q_reconciled/(C_min(T_h,in−T_c,in)).
See the calculation
From measurement to engineering result
1System and state data2Energy or resistance model3Heat, work, or efficiency
Worked context
Read the output with its units
120→80 hot and 20→60 cold with equal 1,000 W/K capacity rates gives 40 kW balanced duty and a 40% reconciled effectiveness estimate.
Interpret with care
Important model boundary
This rating worksheet requires internally meaningful terminal temperatures and capacity rates. A mismatch warning means the average is only a reconciliation estimate, not an actual measured duty. Phase change, multipass correction factors, fouling, pressure drop, variable properties, leakage, and equipment selection are excluded.
A calculated value does not certify a component, material, installation, operating envelope, code requirement, or safety decision. Check measurements, signs, standards, uncertainty, and professional approval where consequences matter.
Browse Engineering & science for connected physical relationships.
Quick guide
How to use this calculator
- Choose the physical relationship and solve direction that match the known measurements rather than forcing unlike quantities into one formula.
- Enter every unit, sign, reference direction, geometry, material property, fluid property, temperature basis, coefficient, and idealization explicitly. The calculator normalizes compatible quantities internally and exposes intermediate values.
- Use reconciliation and companion outputs to catch entry mistakes, then retain the stated model boundary. A theoretical result is not a design approval, material certificate, equipment rating, or safety determination.
Calculation method
How the heat exchanger lmtd and effectiveness calculator works
Provide both LMTD and effectiveness views while exposing crossed, impossible, or materially unreconciled terminal data instead of hiding it.
Counterflow ΔT terms are T_h,in−T_c,out and T_h,out−T_c,in; parallel terms are inlet and outlet differences. LMTD=(ΔT₁−ΔT₂)/ln(ΔT₁/ΔT₂). Q_h=C_h(T_h,in−T_h,out), Q_c=C_c(T_c,out−T_c,in), Q_reconciled=(Q_h+Q_c)/2 only as a comparison estimate, and estimated effectiveness=Q_reconciled/(C_min(T_h,in−T_c,in)).
Worked example
Heat Exchanger LMTD and Effectiveness example
120→80 hot and 20→60 cold with equal 1,000 W/K capacity rates gives 40 kW balanced duty and a 40% reconciled effectiveness estimate.
Counterflow ΔT terms are T_h,in−T_c,out and T_h,out−T_c,in; parallel terms are inlet and outlet differences. LMTD=(ΔT₁−ΔT₂)/ln(ΔT₁/ΔT₂). Q_h=C_h(T_h,in−T_h,out), Q_c=C_c(T_c,out−T_c,in), Q_reconciled=(Q_h+Q_c)/2 only as a comparison estimate, and estimated effectiveness=Q_reconciled/(C_min(T_h,in−T_c,in)).
Supported inputs
Precision and limits
Engineering-model boundary
This rating worksheet requires internally meaningful terminal temperatures and capacity rates. A mismatch warning means the average is only a reconciliation estimate, not an actual measured duty. Phase change, multipass correction factors, fouling, pressure drop, variable properties, leakage, and equipment selection are excluded.
Units and precision
Calculations normalize compatible inputs to SI, retain working precision, and round only for display. Very small and large nonzero values use scientific notation; displayed digits cannot create accuracy beyond the entered measurements and properties.
Decision boundary
This page solves the declared idealized relationship only. Verify applicable material data, operating conditions, geometry, loads, coefficients, standards, codes, manufacturer requirements, uncertainty, and professional approval before consequential use.
Category ownership
Generic mechanics, materials, fluid, aerodynamic, wave, and thermodynamic relationships live here. Trade-specific pipe, HVAC, motor, electrical, construction, automotive, radiation, statistical, chemical, and astronomical workflows remain with their established categories.
Privacy
Entered values and results stay in this browser and are not sent to analytics or third parties.
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