Visual observation of two-phase flow pattern of R-22, R-134a, and R-407C in a 6.5-mm smooth tube

Two-Phase Flow Boiling Heat Transfer for Evaporative Refrigerants in Various Circular Minichannels

“…The Wang et al (1997) map showed a better prediction of the flow pattern of the current experimental data for the beginning of annular flow than the Wojtan et al (2005) map; however, the Wang et al (1997) map could not show the prediction for dry-out conditions. The flow pattern prediction of the current test results for the all test conditions with the Wang et al (1997) flow pattern map was for the intermittent, stratified wavy and annular flow. The stratified wavy flow appeared earlier for higher mass fluxes and its regime was longer for the low mass flux condition.…”

“…The present experimental results were mapped on Wang et al (1997) and Wojtan et al (2005) flow pattern maps, which were developed for diabatic two-phase flows. The Wang et al (1997) flow pattern map is a modified Baker (1954) map, developed using R-22, R-134a, and R-407C inside a 6.5mm horizontal smooth tube. Therefore, they claim that their flow pattern map is better for prediction of flow patterns in small tubes.…”

“…Therefore, they claim that their flow pattern map is better for prediction of flow patterns in small tubes. The Wang et al (1997) study showed that the flow transition for a mixture refrigerant showed a considerable delay compared with that of pure refrigerants. For R-410A, at the initial stage of evaporation, R-32 evaporated faster than R-125.…”

“…For the other working refrigerants, the physical properties of the refrigerant such as density, viscosity and surface tension have a strong effect on the flow pattern. The predicted flow pattern for the selected current experimental data according to the existing flow pattern maps of Wojtan et al (2005) and Wang et al (1997) can be seen in Figs. 4(a) -(f) and 5(a) -(f), respectively.…”

Pressure drops of single and two-phase flows through T-type microchannel mixers

“…Another deviation is seen from these figures that Lockhart and Martinelli correlation fails to describe the dependence of C value on X and j L , i.e., the present N 2 -water two-phase flow in microchannels exhibits significant mass flux effect, as already proved by other authors for air-water two-phase flow in mini rectangular channels [36,45] and for two-phase flow of refrigerants in a mini tube [46]. Thus a modification of C value in Eq.…”