Heat Exchanger LMTD Calculator

• •Use the Heat Exchanger LMTD Calculator when solving homework or exam problems that require quick numerical verification of your hand calculations — instant feedback helps identify arithmetic errors before they propagate.
• •Use it during the early design phase to rapidly iterate on parameters and narrow down feasible configurations before committing time to detailed finite element simulations or full design packages.
• •Use it when reviewing a colleague's calculation or checking a vendor's data sheet for plausibility — a quick sanity check can prevent costly downstream errors.
• •Use it to generate reference data for a technical report or presentation without manual computation, ensuring consistent, reproducible numbers throughout the document.
• •Use it in the field when a quick estimate is needed and a full engineering software package is not available.

The Heat Exchanger LMTD Calculator is a precision engineering calculation tool designed for students, engineers, and technical professionals. Calculate log-mean temperature difference and heat transfer rate for parallel and counter-flow heat exchangers All calculations are performed using established engineering formulas from the relevant scientific literature and standards. Inputs support both metric (SI) and imperial unit systems, with unit conversion handled automatically — simply select your preferred unit from the dropdown next to each field. Results are computed instantly in the browser without sending data to a server, ensuring both speed and privacy. This calculator is intended as a supplementary tool for learning and design exploration; always verify results against authoritative references for safety-critical applications.

The Log-Mean Temperature Difference (LMTD) method is the standard technique for heat exchanger analysis when the inlet and outlet temperatures on both sides are known. For a simple counter-flow or parallel-flow heat exchanger, the heat transfer rate is Q = U·A·ΔT_lm, where U is the overall heat transfer coefficient, A is the heat transfer area, and ΔT_lm is the log-mean temperature difference. For counter-flow arrangement: ΔT_lm = (ΔT_1 − ΔT_2) / ln(ΔT_1/ΔT_2), where ΔT_1 = T_h_in − T_c_out and ΔT_2 = T_h_out − T_c_in. For parallel flow, the formula is the same but with ΔT_1 = T_h_in − T_c_in and ΔT_2 = T_h_out − T_c_out. Counter-flow always gives a higher ΔT_lm than parallel flow for the same inlet and outlet temperatures, which is why counter-flow is preferred. For cross-flow and multi-pass configurations, a correction factor F is applied: Q = U·A·F·ΔT_lm,cf, where ΔT_lm,cf is the counter-flow value and F is read from correction charts (or computed from effectiveness-NTU methods). F values typically range 0.7-1.0 for practical heat exchangers; below 0.7 indicates severe temperature crossover or poor flow arrangement. LMTD method is most useful when inlet and outlet temperatures are known (typically from an energy balance or a design specification), and you need to find the required area or verify the performance. The method does not work directly if only the inlet temperatures and mass flow rates are known — in that case, ε-NTU is the preferred approach because it doesn't require knowing both outlet temperatures in advance.

• •Shell-and-tube heat exchanger sizing: given hot and cold stream flow rates and required temperatures, compute LMTD and use Q = U·A·F·ΔT_lm to find required area, then translate to tube count, length, and diameter.
• •Condenser and evaporator design: compute the LMTD between refrigerant (at phase change temperature) and heat sink (air or water) to size the heat transfer area.
• •Process heat recovery: in industrial plants, hot process streams are cooled using incoming cold process streams. LMTD analysis finds the heat transfer area required for a target recovery.
• •Chilled water cooling coil for HVAC: an air-side inlet and outlet temperature at design conditions plus chilled water inlet and outlet temperatures give all four points needed for LMTD calculation.
• •Educational problems: LMTD method is the traditional approach in undergraduate thermodynamics and heat transfer courses and appears in most standard problem sets.