Heat exchanger

01

Define the duty before choosing a type

Alfa Laval lists six parameters needed to solve a heat-exchanger problem: the heat load, the inlet and outlet temperatures on both sides, the maximum allowable pressure drop on both sides, the maximum operating temperature and pressure, and the flow rate on both sides. The heat load follows from P = m × cp × δt and must equal k × A × LMTD. [1]

LMTD, the logarithmic mean temperature difference, is (ΔT1 − ΔT2) ÷ ln(ΔT1 ÷ ΔT2), where ΔT1 is hot inlet minus cold outlet and ΔT2 is hot outlet minus cold inlet. For a fixed duty and heat-transfer coefficient, the area needed rises as LMTD falls. [1]

As a calculation example only, cooling 10 m³/h of water from 30 to 20 °C removes about 10,000 kg/h × 4.18 kJ/(kg·K) × 10 K ≈ 418,000 kJ/h, or 116 kW. If the cooling water enters at 15 °C and leaves at 25 °C, ΔT1 = 30 − 25 = 5 K and ΔT2 = 20 − 15 = 5 K, so LMTD = 5 K (when both end differences are equal, LMTD equals that difference). Use your own fluids, specific heats and temperatures.

Alfa Laval notes that area does not grow linearly as the approach tightens: the last few tenths of a degree are disproportionately expensive, and relaxing the approach by 0.1–0.2 °F can greatly reduce the size of a plate exchanger. Check whether your process really needs the closest approach requested. [2]

Send both sides' fluids, flows, inlet and outlet temperatures, allowable pressure drops and design pressure and temperature. An enquiry that gives only 'kW' or 'm²' cannot be sized or compared.

02

Choose the type from the fluids, pressure and cleaning

Suppliers linked to this page cover more than one distinct type. The right one depends on the two media, pressure and temperature, fouling and how the unit will be cleaned.

03

Set the fouling margin for the exchanger type

The Heat Exchange Institute defines fouling as the loss of heat transfer over time from deposits on the walls. Designers size with a fouled coefficient Uf rather than the clean value Uc, using a fouling factor (1/Uf = 1/Uc + ff), a fouling margin (Uf = Uc ÷ (1 + fm%)) or a cleanliness factor (Uf = Uc × cf). [3]

04

Trace the heat exchanger components

This is a functional reference built from the sources cited; it is not one maker's parts list. Components differ by type; materials and dimensions come from the data sheet of the unit you order.

05

Fill the specification fields with values for your duty

A heat-exchanger quotation needs duty-specific values. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send both sides of the duty together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Hot side: [fluid; flow; inlet and outlet temperature; allowable pressure drop; fouling tendency]
Cold side: [fluid; flow; inlet and outlet temperature; allowable pressure drop; fouling tendency]
Duty: [heat load; required approach temperature]
Design: [design pressure and temperature each side; test pressure; construction code]
Type: [plate gasketed/brazed/welded, shell-and-tube, spiral, finned or air-to-air; cleaning method]
Fouling: [fouling factor or margin and its basis; filtration; redundancy (2×100% or 3×50%)]
Materials: [plates or tubes; shell/frame; gaskets; corrosion allowance]
Connections: [sizes and standards; orientation]
Installation: [space; frame extension capacity; lifting; maintenance access]
Documents: [thermal data sheet with clean and fouled U; pressure-drop calculation; drawings; test certificates]

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