Encyclopaedia Index

### TITLE : SFT analysis of Heat Exchangers

```
BY               : D.B. SPALDING and S.V.ZHUBRIN
FOR              : Technical-discussion meeting
DATE             : March, 1998
PHOENICS Version : 3.1
```

### PROBLEM :

Despite their great industrial importance, heat exchangers are still designed and analysed by techniques which are inferior to those of Computational Fluid Dynamics in several respects, including:-

• the flow distributions on the shell and tube sides are presumed rather than being computed from physical principles;
• steady-flow conditions are commonly presumed;
• the stresses in the tubes are computed, if at all, by separate algorithms and computer programs.

### SOLUTION :

The presentation will illustrate how it is possible to use a single computer program to calculate from the partial-differential equations governing relevant SFT ( Solid, Fluid and Thermal) processes the distributions of:-

• shell-side fluid velocity components for one or two phases;
• the corresponding temperatures and pressures;
• the tube-side fluid velocity components;
• the corresponding temperatures and pressures;
• the tube metal temperatures; and
• the stresses in the tubes and the shell.

### GENERAL IDEA :

The method adopted is a three-domain one. This implies that the computational grid covers the shell-and-tube space three times: once for shell-side simulation; once for the tube-side simulation; and once for metal simulation.

In the metal, it is displacements and dilatations which are computed rather than velocities and pressures.

All governing equations, formulated differently for each domain, are then assembled and solved simultaneously in one computational space.

The method is aimed to develop HEXAGON, a PHOENICS based, Heat EXchAnGer simulatiON, package .

### RESULTS :

What follows are the series of PHOTON plots illustrating the calculation results.

The fluid movements, temperature distributions and stresses in materials will be shown for a model heat exchanger.

The following picture depicts its lay-out.

The velocity vectors show the movement of tube fluid in the header, in the U-tube array and zigzag flow in baffled shell side.

Temperature distribution reflect the conjugate nature of the transfer processes which results in the followings:

### CONCLUSION :

The study has provided the first practical example of the Solid-Fluid-Thermal-in-single-operation analysis put forward recently by the first author.

HEXAGON multi-domain technique has been demonstrated as being practicable and simple.