Visual study of flow patterns during evaporation and condensation of R-600a inside horizontal smooth and helically dimpled tubes

Abstract

In this paper, flow patterns and their transitions for the refrigerant R-600a during flow boiling and condensation inside a helically dimpled tube and a smooth tube were observed and analysed. The inner surface of the helically dimpled tube was enhanced by a modified pattern consisting of both shallow and deep protrusions. For evaporation, the experiments were performed for refrigerant mass velocities in a range of 155 kg/m 2 s to 467 kg/m 2 s, all at an average saturation temperature of 56.5℃ with the vapour qualities up to 0.8. Stratified-wavy, intermittent, and annular flows were observed for the smooth tube; for the dimpled tube, the stratified-wavy flow was not seen. For condensation, all tests were conducted at vapour qualities up to 0.8, and average saturation temperatures ranging between 38℃ and 42℃. The refrigerant mass fluxes varied in the range of 114-368 kg/m 2 s. Annular, intermittent, and stratified-wavy flows were recognized for the plain tube, but there was no stratified-wavy flow in the flow pattern visualization of the dimpled tube. The investigation clearly shows that the dimples in both evaporation and condensation have a significant impact on the two-phase flow pattern. Inside the helically dimpled tube, the transition from intermittent to annular (or vice versa) occurred at a lower vapour quality value than for the smooth tube.

Research on prediction model of forming mechanical behavior of the dimpled tube based on the response surface methodology

“…However, the factors DP and PR have p-values greater than 0.1, which indicate that the DP and PR are insignificant according to the p-value, and should be removed from the developed empirical relationships. Therefore, the prediction model for the stress can be described by equation (4).…”

“…Their results showed that the dimpled helical coiled tube increased the heat transfer coefficient by 32-48% compared with the smooth helical coiled tube. Mashouf et al 4 performed flow visualization during evaporation and condensation in helically dimpled tubes. They found that the flow in the dimpled tube transitioned more easily from intermittent to annular at a lower vapor quality value than in the plain tube.…”

Flow Boiling Heat Transfer Characteristics in Horizontal, Three-Dimensional Enhanced Tubes

“…The earlier transition of flow regimes in the micro-fin tube is mainly due to the liquid droplet entrainment effect of spiral mini-channels on the inner wall. Mashouf et al [32] carried out a visualization study to observe evaporation flow patterns of R600a in horizontal dimpled and smooth tubes. At the same mass flux, the flow pattern transition in the dimpled tube occurred at a lower vapor quality in comparison with the equivalent smooth tube.…”

Análisis numérico de los mapas de patrones de flujo del refrigerante R600a en un colector/evaporador de una bomba de calor asistida por energía solar

“…Mashouf et al [10] realizaron una investigación trabajando con tubos horizontales y el refrigerante R600a; presentaron diferentes patrones de flujo a velocidades de masa entre 114 y 368 kg•m −2 •s −1 , con temperatura de saturación entre 38 y 42°C y calidad de 0,8 para el proceso de ebullición del refrigerante. Los resultados obtenidos fueron un flujo intermitente y anular en un tubo con hoyuelos, mientras que, para un tubo liso se observó un flujo intermitente, anular y estratificado ondulado.…”