Experimental parametric study of the pressure drop characteristic curve in a horizontal boiling channel

•The working pressure has a determinant role on the existence of a negative slope.•The heating power seems to have a small influence on the negative slope.•The axial distribution of the heat flux has a large impact on the negative slope.•Decreasing heat profiles leads to steeper negative slopes, and vice versa. The main objective of this study is to provide experimental data with the aim of clarifying the behavior of the pressure drop of a boiling fluid through a horizontal heated pipe as a function of the mass flux. The steady-state pressure drop characteristic curve of a heated pipe is extremely important regarding stability issues. This characteristic curve can present a negative slope which is usually not desired. In this study, a systematic analysis on the influence of the different relevant parameters was conducted with R-134a boiling on a horizontal channel. The working pressure was found to have a determinant role on the existence of a negative slope in the two-phase flow outlet region. As the pressure is increased, this negative slope decreases. The inlet temperature has also a strong influence on the presence of the negative slope in the curve, with this slope increasing as the inlet temperature is decreased. The heating power seems to have a small influence on the negative slope, being proportional to it. Finally, the axial distribution of the heat flux has a large impact on the negative slope in the characteristic curve.