Compute the effectiveness (ε) of a heat exchanger by the ε-NTU method. C*=C_min/C_max (0..1), NTU=U·A/C_min, q_max=C_min·(T_h,in-T_c,in), and ε=q_actual/q_max. Supports four arrangements: Parallel flow ε=[1-exp(-NTU(1+C*))]/(1+C*); Counter flow ε=[1-exp(-NTU(1-C*))]/[1-C*·exp(-NTU(1-C*))], or NTU/(1+NTU) when C*=1; Shell-and-tube 1-2 ε=2/[1+C*+√(1+C*²)·(1+exp(-NTU√(1+C*²)))/(1-exp(-NTU√(1+C*²)))]; Crossflow (both unmixed) ε=1-exp{(NTU^0.22/C*)·[exp(-C*·NTU^0.78)-1]}. When C*=0 (phase change on one side, boiler/condenser) every arrangement gives ε=1-exp(-NTU). Optionally supply T_h,in and T_c,in to recover the actual heat-transfer rate q=ε·q_max and both outlet temperatures. Temperatures are used only as differences: Δ°C=ΔK and Δ°F×5/9=ΔK.
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Key facts
Category
Math & Numbers
Input types
select, number
Output type
json
Sample coverage
4
API ready
Yes
Overview
Calculate heat exchanger effectiveness with the ε-NTU method for parallel-flow, counter-flow, shell-and-tube 1-2, or crossflow arrangements. Enter both heat-capacity rates, the overall heat transfer coefficient, and heat transfer area to obtain C*, NTU, and ε; optionally add inlet temperatures to calculate heat-transfer rate and outlet temperatures.
When to use
Estimate heat exchanger effectiveness when inlet and outlet temperatures are not yet known.
Compare parallel-flow, counter-flow, shell-and-tube 1-2, and crossflow arrangements using the same operating data.
Calculate actual heat transfer and both outlet temperatures when hot- and cold-side inlet temperatures are available.
How it works
1Enter the hot-side capacity rate C_h, cold-side capacity rate C_c, overall coefficient U, and heat transfer area A.
2Select the exchanger arrangement; the calculator determines C_min, C_max, C*=C_min/C_max, and NTU=U·A/C_min.
3The appropriate ε-NTU relation is applied to calculate heat exchanger effectiveness.
4Optionally provide both inlet temperatures to calculate q_max, actual heat transfer q, and the hot- and cold-side outlet temperatures.
Use cases
Thermal design checks for process, HVAC, and energy systems.
Early comparison of heat exchanger flow arrangements.
Estimating heat duty and outlet temperatures from capacity rates and inlet conditions.
Examples
1. Counter-flow effectiveness estimate
Thermal design engineer
Background
An engineer is checking the effectiveness of a counter-flow heat exchanger before completing a detailed thermal design.
Problem
Determine C*, NTU, and effectiveness from the capacity rates, overall coefficient, and heat transfer area.
How to use
Select Counter Flow and enter C_h=1000 W/K, C_c=1500 W/K, U=500 W/(m²·K), and A=10 m².
The calculator returns C_min=1000 W/K, C_max=1500 W/K, C*=0.6667, NTU=5, and effectiveness ε≈0.928. Without inlet temperatures, heat-transfer rate and outlet temperatures are not calculated.
2. Crossflow heat duty and outlet temperatures
Heat exchanger analyst
Background
An analyst has equal hot- and cold-side capacity rates and measured inlet temperatures for an unmixed crossflow exchanger.
Problem
Calculate effectiveness, actual heat transfer, and both outlet temperatures.
How to use
FAQ
What inputs are required?
Enter C_h, C_c, U, and A. The exchanger type is selectable, with counter flow used by default.
Which exchanger arrangements are supported?
The calculator supports parallel flow, counter flow, shell-and-tube 1-2, and crossflow with both fluids unmixed.
What does NTU mean?
NTU is the number of transfer units, calculated as U·A/C_min.
Are inlet temperatures required?
No. They are optional. Provide both inlet temperatures to calculate actual heat transfer and outlet temperatures.
Which temperature units can I use?
Use Kelvin, Celsius, or Fahrenheit. The calculation uses temperature differences, with Δ°C=ΔK and Δ°F×5/9=ΔK.