What Size Heat Exchanger Do I Need? How Sizing Works

Heat exchanger size is determined by the thermal duty — how much heat must be transferred — not by the pipe diameter. To size a unit you need both stream media, inlet and outlet temperatures, flow rate, allowable pressure drop, and design pressure and temperature. From these, an engineer calculates the required surface area and selects a plate count or tube bundle.

1) Hot- and cold-side medium. 2) Inlet and outlet temperatures on each side. 3) Flow rate or mass flow. 4) Allowable pressure drop. 5) Design pressure. 6) Design temperature. With any five of these plus the duty, the sixth can usually be derived. The smaller the temperature approach you require, the more surface area — and the larger the unit.

A common mistake is selecting a heat exchanger by matching its connections to the pipe diameter. Connection size only limits flow velocity and pressure drop; it says nothing about how much heat the unit transfers. A correctly sized unit is driven by surface area for the duty, then checked against pressure drop and connection velocity.

Real services foul over time, so the design adds a fouling factor — extra surface area so the unit still meets duty when partially fouled. Too little margin means performance drops between cleanings; too much means an over-sized, low-velocity unit that fouls faster. A correct fouling allowance matched to the service is part of good sizing.

Shanghai Jiangxing's engineering team performs a free thermal sizing from your process conditions and returns a plate count or tube selection with indicative pricing, usually within one to two business days. Send your media, temperatures, flow and pressure to Evan, jxmike@shheatex.com, or WhatsApp +86 173 1725 8304.