Effectiveness NTU Calculator
Calculate heat exchanger effectiveness and number of transfer units (NTU) for thermal engineering design.
Heat Exchanger Effectiveness and NTU
The effectiveness–NTU method sizes heat exchangers without knowing outlet temperatures in advance. Effectiveness \(\varepsilon\) is the ratio of actual heat transfer to the maximum possible transfer, while NTU (number of transfer units) measures the exchanger's size relative to flow capacity.
Counterflow Formulas
$$\text{NTU} = \frac{UA}{C_{\min}}$$ $$C_r = \frac{C_{\min}}{C_{\max}}$$ $$\varepsilon = \frac{1 - e^{-\text{NTU}(1-C_r)}}{1 - C_r}$$\(UA\) is overall conductance in W/K, and \(C_{\min}\), \(C_{\max}\) are the smaller and larger heat capacity rates \(\dot{m}c_p\) in W/K. When \(C_r = 1\), use \(\varepsilon = \text{NTU}/(1 + \text{NTU})\).
When to Use This Method
The \(\varepsilon\)-NTU approach is standard in thermal engineering for rating counterflow, parallel-flow, cross-flow, and shell-and-tube exchangers. Counterflow gives the highest effectiveness for a given NTU.
Frequently Asked Questions
What is NTU?
Number of transfer units: NTU = UA/C_min. It compares heat exchanger conductance to the minimum fluid heat capacity rate.
What is heat capacity rate C?
\(C = \dot{m} c_p\) in W/K. It is the rate at which a fluid stream can absorb or release heat per degree of temperature change.
Why counterflow specifically?
Counterflow is the most efficient flow arrangement. This calculator uses the counterflow effectiveness correlation.
What happens when C_r approaches 1?
The denominator \(1 - C_r\) goes to zero. Use the limiting form \(\varepsilon = \text{NTU}/(1 + \text{NTU})\) instead.
Can effectiveness exceed 100%?
No. Effectiveness is bounded between 0 and 1 (0% to 100%) by definition of maximum possible heat transfer.
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