Heat Exchanger Calculator
The Heat Exchanger Calculator determines heat transfer performance using LMTD and NTU-effectiveness methods. Enter inlet/outlet temperatures, flow rates, specific heats, and U-value to get heat duty (Q), LMTD, required surface area, NTU, and effectiveness — with interactive temperature profile charts for counterflow, parallel, and crossflow. Free, no signup.
Scenario Presets
Flow Arrangement
Hot Side
Cold Side
Overall U-Value (W/m²·K)
Results
Heat Duty (Q)
251.16 kW
251160 W
LMTD
40.00 °C
Required Area
6.2790 m²
F = 1.00
Correction Factor (F)
1.00
Effectiveness (ε)
42.9%
NTU
0.7500
Hot Capacity Rate
8372 W/K
Cold Capacity Rate
8372 W/K
Capacity Ratio (Cr)
1.0000
Temperature Profile
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What is a Heat Exchanger Calculator?
A Heat Exchanger Calculator determines the thermal performance and sizing of heat exchangers using two primary methods: LMTD (Log Mean Temperature Difference) and NTU-effectiveness. The LMTD method uses Q = U × A × LMTD × F, where Q is heat duty (watts), U is the overall heat transfer coefficient, A is surface area, and F is a correction factor for flow arrangement. The NTU method relates effectiveness (ε = Q/Q_max) to the Number of Transfer Units (NTU = UA/Cmin). Counterflow exchangers are most efficient, achieving higher effectiveness than parallel flow for the same NTU.
How to Use This Calculator
- Enter hot side inlet/outlet temperatures and flow rate (or select a scenario preset)
- Enter cold side inlet/outlet temperatures and flow rate
- Select fluid specific heats from presets (water: 4186, oil: 2090 J/kg·K) or enter custom values
- Choose overall U-value from presets or enter a custom value
- Select flow arrangement (counterflow, parallel, or crossflow) and view results
Frequently Asked Questions
What is LMTD and how is it calculated?
Log Mean Temperature Difference (LMTD) is the effective average temperature driving force for heat transfer. For counterflow: LMTD = (ΔT₁ - ΔT₂) / ln(ΔT₁/ΔT₂), where ΔT₁ = T_hot_in - T_cold_out and ΔT₂ = T_hot_out - T_cold_in. For parallel flow, both ΔTs use the same end (inlet-inlet, outlet-outlet). LMTD is always larger for counterflow than parallel flow, meaning less surface area is needed.
Why is counterflow more efficient than parallel flow?
In counterflow, the cold fluid exits near the hot fluid entrance, maintaining a more uniform temperature difference along the exchanger length. This allows the cold outlet to approach the hot inlet temperature (thermodynamically impossible in parallel flow). For the same heat duty, counterflow requires 20-40% less surface area, making it the standard choice for most industrial applications.
What determines the overall heat transfer coefficient U?
The U-value combines all thermal resistances: 1/U = 1/h_hot + t/k + 1/h_cold + R_fouling, where h is the convective coefficient, t/k is wall conduction resistance, and R_fouling accounts for deposits. Typical values range from 25 W/m²·K (gas-to-gas) to 2500 W/m²·K (steam condensation). Fouling can reduce U by 20-50% over time, which is why heat exchangers are oversized by 10-25%.