Experimental Investigation of Two-Phase Flow Distribution with Different Vertical Header Configurations

Abstract

In this study, we investigated the behavior of two-phase flow distribution inside a vertical header of a microchannel heat exchanger (MCHX) that functions as an evaporator of a heat pump system. In general, the two-phase flow distribution behavior of the refrigerant differs depending on the target application, which ranges from small-scale automobile air-conditioners to large-scale building heat pump systems. Particularly, it is reported that the distribution characteristics in the vertical header of the MCHX vary extensively according to the inlet flow conditions of the refrigerant and the physical profile of the header. In this study, the physical configurations (header height, branch tube diameter) of four types of vertical headers were considered. Thereafter, the operating conditions in an experimental device that simulates an MCHX with a vertical header were selected. The experiment was performed under R410A as the working fluid, with a saturation temperature of 15 °C, inlet mass flow rate of 50–150 kg h−1 (mass flux of 908–2723 kg m−2 s−1), and an inlet vapor quality of 0.1–0.2. The liquid and vapor flow ratios and the relative standard deviation were adopted as metrics to characterize the uniformity of flow distribution. The distribution characteristics were subsequently described according to Reynolds and Froude numbers. The larger the Reynolds number and the smaller the Froude number, the more uniform the two-phase flow distribution becomes. A correlation was proposed as a function of the Reynolds and Froude numbers to predict the flow distribution characteristics for the considered vertical headers.

Experimental study of the two-phase flow distribution in helical-structured vertical headers

“…The spacing between the five outlets was designed to be 105 mm, matching the pitch of the helical-structured channel. Furthermore, the distance between the first and fifth outlets was 420 mm, consistent with the configuration employed in our previous work [ 19 ]. Considering the pitch of the channel, the distance between the first outlet and the header inlet was 105 mm.…”

“…1 shows the helical-structured vertical header. The parallel tube connected to the header outlet was simplified to a smooth tube with a pressure control valve to directly compare with the findings with those of our previous work [ 19 ]. Fig.…”

“…The cross-sectional geometry of the helical-structured channel (see Fig. 1 (d)) is identical to that of the simple straight vertical header employed in our previous study [ 19 ]. The inlet and outlet of the vertical header were oriented in the same direction.…”

“…Higher mass flow rates and lower vapor qualities effectively produced uniform flow distribution. Regarding the combination of structural design and operating conditions, Kim et al [ 19 ] demonstrated that a reasonable flow distribution can be achieved by considering the physical configuration of the vertical header (cross-sectional area, height, and outlet bore) and operating conditions (mass flow rate, vapor quality, and temperature). Furthermore, Fei and Hrnjak [ 20 ] highlighted the importance of flow patterns, influenced by the mass flux and working fluid properties, particularly in horizontal headers under the influence of gravity.…”

“…In this study, experimental measurements were conducted under three mass flow conditions (50, 100, and 150 kg h −1 ) and two inlet vapor quality conditions (0.1 and 0.2). The flow distribution characteristics obtained from the helical-structured vertical header were compared to those obtained from a previous study [ 19 ] using a header with the same height and cross-sectional geometry but lacking the helical structure. Additionally, dimensionless numbers were analyzed to gain insights into the behavior of the two-phase flow through the helical structure.…”