Background

The request was made to look at the thermal efficiency of a small, aluminum multivoid tube as shown in the picture below. This tube was approximately one inch wide and a tenth of an inch thick. It was used in various heat exchangers such as automotive air conditioners and home heat pumps.

The customer provided drawings of the tube, and wished to know the temperature drop during service. A small temperature drop through the wall of the tube indicates an efficient design.

Description

Since the tubes would typically be very long, a two dimensional model was sufficient. The customer specified a working fluid inside the tube at 120 F and ambient conditions at 72 F.

When the computer run was complete, the results for the entire tube appeared as shown immediately below. Higher temperatures are shown as red while lower temperatures are blue.

A closeup view of the cross section is shown here. It can be seen that the voids on the ends are smaller. This is done to prevent a rupture when the tube is under pressure.

Conclusions

The maximum temperature difference in this tube is less than 0.3 F. The small temperature difference indicates very good heat transfer. Later designs included textured or rippled surfaces to improve heat transfer even more.

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