Performance evaluation of flattened tube in boiling heat transfer enhancement and its effect on pressure drop

An experimental investigation has been carried out to study heat transfer and pressure drop characteristics of R-134a flow boiling inside a horizontal plain tube and different flattened tubes. Round copper tubes with an inner diameter of 8.7 mm were flattened into an oblong shape with an internal height of 6.6 mm, 5.5 mm, 3.8 mm, and 2.8 mm. The test apparatus was basically a vapor compression refrigeration system equipped with all necessary measuring instruments. Analysis of the collected data showed that, by flattening the round tube, the heat transfer coefficient and pressure drop increased simultaneously. The performance of these tubes from the point of view of heat transfer enhancement and pressure drop increasing were evaluated. It was concluded that, the tube with an internal height of 5.5 mm has the best performance compared with the other flattened tubes. Finally, based on the present experimental pressure drop data, a correlation was developed to estimate the pressure drop in flattened tubes. This correlation predicts the experimental data of the present study within an error band of ± 20%.