Two phase flow heat transfer

Background

Evaporation is a very effective heat transport mechanism due to the latent heat transfer. An evaporating fluid extracts this heat from its surroundings. The flow behavior has a strong influence on the two phase flow heat transfer and pressure drop. In compact fin and tube heat exchanger the refrigerant flows through a tube which is folded up in to a series of hairpins. Very little is known about the influence of these hairpins on the flow behavior. Most known correlations and models for the two phase heat transfer and pressure drop are only valid for undisturbed flow in straight tubes. Yet, qualitative studies have shown that the effect of the bends could significantly affect the flow behavior.

Scope of research

This research aims to investigate the effect of the geometry on the two phase flow behavior. The evolution of the flow behavior and the pressure drop through a hairpin is studied. The research is solely experimental. In previous research a capacitive sensor was developed to study the flow behavior is straight tubes. In this work the flow behavior is studied with this capacitive sensor and with flow visualizations. The flow behavior is studied to acquire more insight on the mechanisms causing the evolution of the pressure drop in a hairpin. These insights together with the pressure drop measurements are then used to develop a more accurate model for the two phase flow pressure drop in a hairpin. Using this model the effect of the hairpins can better be accounted for in the heat exchanger design. This improved design will reduce the oversizing of the heat exchanger and increase the coefficient of performance.

Two phase flow in hairpin.
Two phase flow in hairpin.