Air Cooled Heat Exchanger Calculator

Calculator Inputs

Hot fluid mass flow, kg/s

Hot fluid heat capacity, kJ/kg.C

Hot inlet temperature, C

Hot outlet temperature, C

Air heat capacity, kJ/kg.C

Air inlet temperature, C

Air outlet temperature, C

Air density, kg/m3

Overall heat transfer coefficient, W/m2.C

LMTD correction factor

Fin efficiency

Design margin, percent

Fan static pressure, Pa

Fan efficiency

Number of fans

Available surface per bay, m2

Formula Used

The process heat duty is calculated as:

Q = m × Cp × (Th,in - Th,out)

Air mass flow is calculated as:

mair = Q / [Cpair × (Ta,out - Ta,in)]

The log mean temperature difference is:

LMTD = (DT1 - DT2) / ln(DT1 / DT2)

Here, DT1 equals hot inlet minus air outlet. DT2 equals hot outlet minus air inlet.

Corrected LMTD equals LMTD multiplied by the correction factor.

Heat transfer area is calculated as:

A = Q / (U × corrected LMTD × fin efficiency)

Fan power is estimated as:

Power = air volume flow × static pressure / fan efficiency

How to Use This Calculator

Enter the hot fluid mass flow and heat capacity.
Add hot inlet and outlet temperatures.
Enter air inlet and target outlet temperatures.
Set air density, coefficient, correction factor, and fin efficiency.
Add design margin, fan pressure, fan efficiency, and fan count.
Press Calculate to view duty, airflow, area, and fan load.
Use CSV or PDF buttons to save the same result.

Example Data Table

Case	Hot Flow kg/s	Hot In C	Hot Out C	Air In C	Air Out C	U W/m2.C	Margin %
Base	12	145	95	35	52	55	15
High Duty	16	160	100	36	55	58	20
Low Approach	10	130	85	38	50	50	18

Air Cooled Heat Exchanger Design Guide

Overview

An air cooled heat exchanger removes process heat by moving ambient air across finned tubes. It is common in refineries, gas plants, power units, and utility systems. The design is attractive because it uses little water. It also reduces water treatment work. Good sizing still needs careful checks. The heat load must match the process duty. The airflow must carry the same duty. The temperature approach must also stay practical.

Key Inputs

The main process inputs are mass flow, heat capacity, inlet temperature, and outlet temperature. These values define the heat duty. Air inputs include inlet temperature, outlet temperature, density, and heat capacity. A larger air temperature rise lowers airflow. It may also increase approach risk. The overall coefficient links duty, area, and temperature difference. Fin efficiency adjusts the useful surface. A correction factor adjusts the log mean temperature difference.

Practical Sizing Notes

The calculator estimates thermal area from the corrected temperature difference. It also adds a design margin. This margin helps cover fouling, seasonal changes, and early data uncertainty. Fan power is estimated from air volume flow, static pressure, and fan efficiency. The result is a first pass estimate. Final equipment design should include vendor geometry, tube layout, noise limits, motor margins, vibration checks, and plot constraints.

Interpreting Results

High required area may mean the approach is too tight. It can also mean the assumed coefficient is low. High fan power often points to high air volume or pressure drop. A low corrected temperature difference can make the design large and costly. Compare several cases before choosing a basis. Try different outlet air temperatures, design margins, and coefficients. This improves the early design decision.

Why This Tool Helps

Manual heat exchanger sizing can be slow. Many values interact with each other. This tool keeps the main equations visible. It returns duty, airflow, area, fan load, and bay estimate in one place. It also supports exports for notes and reviews. Use it during concept design, study estimates, or classroom checks. For purchase design, confirm results with detailed thermal software and manufacturer data. Always review ambient design temperature. Check recirculation risk near walls. Confirm maintenance space, winter operation, and acceptable outlet process temperature before approval.

FAQs

What is an air cooled heat exchanger?

It is equipment that transfers heat from a process fluid to air. Fans move air across finned tubes. The process fluid cools without direct water cooling.

What does this calculator estimate?

It estimates heat duty, air mass flow, air volume flow, LMTD, required surface area, bay count, and fan power. It is useful for early sizing and comparison.

Why is LMTD important?

LMTD represents the effective temperature driving force. A small LMTD means heat transfer is harder. That usually increases required surface area.

What is the correction factor?

The correction factor adjusts ideal LMTD for real flow arrangements. Use a value from design charts, vendor data, or a conservative engineering assumption.

Why include fin efficiency?

Fins do not transfer heat perfectly across their full surface. Fin efficiency corrects the effective area and gives a more realistic estimate.

How is fan power calculated?

Fan power is based on air volume flow, static pressure, and fan efficiency. Higher flow or pressure increases estimated power demand.

Can this replace vendor design?

No. It gives a practical first estimate. Final design should include vendor geometry, noise checks, vibration review, materials, and operating limits.

Why add a design margin?

A margin covers fouling, ambient variation, uncertain data, and early design changes. It helps prevent undersized equipment during preliminary selection.