Ammonia has drawbacks associated with combustibility and toxicity

and therefore

reducing the charge in ammonia refrigeration systems is of great importance. The application of small diameter tubes offer a higher surface coefficient of heat transfer

which has the potential to improve the compactness of the heat exchanger and reduce refrigerant charge. This study conducted experiments to investigate the characteristics of heat transfer and pressure drop for ammonia flow boiling in a horizontal plain tube with an inner diameter of 4 mm. The dependencies of the heat transfer and frictional pressure drop on vapor quality

mass flux

and heat flux are analyzed in detail. The experimental results show that the surface coefficient of heat transfer increases with vapor quality. In addition

an increase in the mass flux and heat flux can lead to a higher surface coefficient of heat transfer. In addition

the two-phase frictional pressure gradient also increases with increasing vapor quality. Further

at a certain vapor quality

the two-phase frictional pressure gradient increases with an increase in mass flux.