Shell and tube heat exchangers: design, operation and use

A shell and tube heat exchanger transfers heat between two media that are separated only by the wall of a tube bundle. The design is widespread in plant engineering and industry wherever oils or steam are involved.

How is a shell and tube heat exchanger built?

The unit consists of a cylindrical shell holding the tube bundle. One medium flows through the tubes (tube side), the other flows around them in the shell space (shell side). Both spaces are sealed from one another by tube sheets; the heat passes exclusively through the tube wall.

Large conventional units run the tubes end to end from one tube sheet to the other. Our units use a coiled bundle throughout: thin-walled stainless steel tubes wound helically around a core. This packs a lot of heat transfer area into a slim shell, and the coil absorbs the different thermal expansion of tube and shell instead of passing it into the welds as stress. The hot medium flows through the coil, the cold one through the shell.

The heat transfer area follows from the number of tubes, the tube diameter and the tube length. Larger duties are reached with larger sizes - or with several units in parallel, where pressure drop or available space limits the single unit.

How does the heat transfer work?

On both sides a boundary layer forms at the tube wall. For liquids, its heat transfer depends on the mass flow and on the fluid properties - density, heat capacity, thermal conductivity and viscosity; with condensing steam it is governed by the condensate film, calculated from the inlet temperature and the temperature difference. Tube side and shell side sit in series with the conduction resistance of the tube wall; together they give the overall heat transfer. The driving force is the logarithmic mean temperature difference between the two media.

Viscous media such as oils form thick boundary layers and transfer heat poorly - which is exactly why sizing an oil cooler is more demanding than sizing for water, and why a catalogue of measured sizes beats a purely formula-based calculation.

When is this design the right choice?

Shell and tube heat exchangers come into their own when at least one of these applies: oils or other highly viscous media, or condensing steam. In the welded ranges there is no gasket between the two media that could age or would need replacing.

For pure water-to-water duties with limited space, a plate heat exchanger is often the more compact solution - the design comparison places both side by side.

How do you get from the operating point to the right unit?

It starts with the process data: media, temperatures, mass flows or duty. From there follows the energy balance, then the selection of a size from the catalogue - explained step by step in the guide sizing a shell and tube heat exchanger. In our configurator the energy balance follows along as you type; the sizing runs on our server against the size catalogue, and our team reviews it or does the sizing itself where the calculation model ends.