Visualization the Distribution of Air-Water Mixtures Flow in Two Outlet Distributor

Transcription

1 Journal of Applied Science and Engineering, Vol. 18, No. 1, pp (2015) DOI: /jase Visualization the Distribution of Air-Water Mixtures Flow in Two Outlet Distributor Azridjal Aziz 1 * and Akio Miyara 2 1 Department of Mechanical Engineering, Riau University, Kampus Bina Widya, Km 12,5, Sp. Baru, Panam, Pekanbaru, 28293, Indonesia 2 Department of Mechanical Engineering, Saga University, 1 Honjomachi Saga-shi, , Japan Abstract This study presents an experimental investigation of air-water mixture distribution (gas and liquid phase) in a distributor. The distributor with one inlet and two outlet tubes branch, upper part and lower part is used with the aim that flow through it can be distributed evenly, particularly in two phase flow. The flow distribution was observed by a high-speed video camera and volumetric flow rates of air and water were measured for each outlet branches, respectively. Inclination angle effect of the distributor and flow rate of air and water flow pattern were investigated. It was found that through distributor, evenly distribution will occurs by the superficial velocity gas and liquid in large quantity. Water tends to flow out at the bottom, and air tends to flow out at the top of tube branch because effect of gravity and different fluid density. The distribution of two-phase flow through distributors tend unevenly flow distribution on the decrease of the angle of distributor, from vertical position to horizontal position. Key Words: Visualization, Two-Phase Flow, Distributor, Flow Pattern, Distribution 1. Introduction Uneven distribution in heat exchangers with parallel flow circuits reduce the thermal performance where the heat transfer occurs. Often, flow rates through the channels are not uniform and in the extreme case, there is almost no flow through some of them, which exhibits a poor heat exchanging performance. The situation becomes more complicated especially with two phase flows [1]. In evaporators, uniform distribution is essential to avoid dry-out phenomenon and the resulting poor heat exchange performance. In condensers, uneven distribution of liquid could create zones of reduced heat transfer due to high liquid loading. Thus, in the design and optimization of compact heat exchangers with parallel flow *Corresponding author. azridjal@yahoo.com technology, understanding of two phase distribution in the manifolds are of great importance [2,3]. Sang-Jin Tae and Keumnam Cho have investigated two phase flow distribution and phase separation through various types of branch tubes in single T-junction [4]. Mao-Yu Wen et al. [5], investigated how to improving two-phase refrigerant distribution in the manifold of the refrigeration system with three different distributor configuration. Many variables effect the distribution of twophase mixture, including geometric factors (manifold cross-section design, branch couplings, location and orientation of the tubes) and on the inlet flow conditions (flow rate, flow structure and vapor fraction and heat load on the tubes). Due to this complexity, no general physically based method has been developed to describe the flow conditions in heat exchanger manifolds and predict the two phase flow distribution. Nae-Hyun Kim and

2 34 Azridjal Aziz and Akio Miyara Tae-Ryong Sin [6] studied air and water two-phase flow distribution in a parallel flow heat exchanger. Due to complexity, only a limited number of studies have investigated the phenomenon that occur in two-phase flow distributors [7]. Recently, the use of heat exchanger for residential air conditioners with small tubes of the pipe diameter is becoming of interest in predicting the heat transfer performance. The diameter of the pipe tends to be smaller and now reaches almost 5 mm in upper diameter to reduce airside pressure drop and obtain a higher heat transfer coefficient of refrigerant flow. However, a small diameter tube also causes a large pressure drop of refrigerant flow, which leads to decrease in heat transfer performance [8]. Therefore, to reduce the pressure drop of the refrigerant flow and to achieve proper distribution from multiple numbers of parallel refrigerant passages, the liquid portion of the two-phase flow must be divided equally to each evaporator coil circuit using a distributor. The refrigerant distributor will distribute refrigerant flow equally from the thermostatic expansion valve (TEV) into each circuit of a multiple evaporator coil. The generally accepted flow patterns given by many researchers are dispersed bubble, slug, plug (elongated bubble), stratified, wavy, and annular flow [9 15]. Other flow patterns, such as, slug-wavy, slug-bubbly, wavyannular, annular-slug, bubbly-plug, slug-bubbly and semi slug, may be considered transitional flow patterns [16 19]. Mandhane et al. [20] and Baker [21] successfully presented a useful map by using superficial gas velocity (U G ) and superficial liquid velocity (U L ) as coordinates for fluid properties. The data base of this flow regime map is primarily air-water mixture. The flow pattern observed in this study for horizontal flow has been confirmed by map of Mandhane et al. [20] and Baker [21]. To keep the heat exchanger performance not decrease, refrigerant should be distributed equally through each of the pipe. However, the refrigerant flow through distributor is not easy flow divided equally, and the drift condition of the refrigerant flow will occur influenced by the shape and position of the distributor. Often, could be lead to decrease of heat exchanger performance. It is necessary to maintain the performance of the heat exchanger to minimize this drift [7]. This experimental research is aimed to clarify general characteristics of air-water two phase flows through the distributor. Air-water flow rate and the distributor inclination angle were investigated. The flow rates of each phase flowing in the outlet after distributor branches upper and lower were measured. To understand the two phase flow regime behavior in the distributor, flow distribution of air and water are observed by visualization technique. 2. Experimental Method and Apparatus Aziz et al. [7] has been explained in previous research paper the experimental method, apparatus, procedure and data reduction that explained again in this paper for understanding the experimental process. 2.1 Experimental Apparatus and Procedure The schematic diagram of experimental apparatus used in this study has shown in Figure 1. The experimental apparatus consists of air and water supply system, merging section, a distributor test section, gas-liquid separator, air measuring bath, and water measuring cylinder. Air flow rate and water flow rate before entering to test section is set up using a flow meter and air-water will mix in the merging section [7]. The test section consists of an entrance tube with diameter of 8 mm and a distributor with two outlet tube, upper and lower with diameter of 5 mm. The entrance tube has 400 mm tube length from the distributor inlet to ensure a fully developed flow. To investigate the slope effect of the distributor, the angle direction of the test section can changed to other angle. In the oulet tube the air will flow at the top and water will flow at the bottom because gravity and the difference of fluid density. The distributor made from transparent acrylic to conduct the flow visualization observation. The whole test section and the detail of the distributor are shown in Figures 2 and 3, respectively [7].

3 Visualization the Distribution of Air-Water Mixtures Flow in Two Outlet Distributor 35 Figure 1. Schematic diagram of experimental apparatus [7]. Figure 2. Test section [7]. Figure 3. Distributor [7]. In this study air and water were used as two phase flow working fluid. Water was supplied by water source in laboratory. Air was supplied by portable compressed air with set up pressure regulator. Both the air and water flow rate were measured by using calibrated rotameter with accuracy 6% before entering the merging section [7]. The experiments were conducted in different slope of the distributor from 0, 45 and 90 with varying air and water flow rates. The inclination angle 0 degree is used for horizontal position and 90 degree is used for vertical position. The measurements of air and water flow rates at each exit of distributor were taken after the gas-liquid separator. Air flow rate was measured by air measuring bath and water flow rate by water measuring cylinder. The data presented are average values of ten measurements. The error analysis was carried out using the method suggested by Bell [22] and Moffat [23]. The errors of the air and water flow rate measurements are considered to be acceptable and they are evaluated as 6.14% and 5.19%, respectively [7]. Visual observation for the two phase flow in a distributor were obtained using a high-speed camera and video recorder at shutter speed 1/30000 second. The picture frame rate at 500 fps and reproduction speed at 15 fps [7]. 2.2 Data Reduction In this experiment each fluid volumetric flow rate was taken after flow out from the gas-liquid separator. The volumetric flow rates of air in outlet 1 and outlet 2 are Q G1 and Q G2 and the volumetric flow rates of water are Q L1 and Q L2, respectively. The deviation ratio (R)defined with equation (1) and (2). The air deviation ratio is R G, and the water deviation ratio is R L (subscript G for gas or air and subscript L for liquid or water) [7]. (1) (2) R = 1 states that all fluid flow out at the upper outlet, R = 0 states that there is no deviation, and R = -1 states that all fluid flow out at the lower outlet [7]. The superficial velocity U for each phase is as the

4 36 Azridjal Aziz and Akio Miyara volumetric flow rate only that phase flowed in the flow passage, divided by flow area A, therefore: U G = Q G /A and U L = Q L /A [7]. 3. Results and Discussion Data taken in this experimental conditions for the gas superficial velocity are 0.06, 0.15, 0.70, 3.31 and m/s and for the liquid superficial velocity are 0.03, 0.06, 0.33, 0.82, 3.54 m/s, respectively. The flow regime map of Mandhane et al. [20,24]. with solid line and flow regime map of Baker [21,24] with dash line for cocurrent flow in horizontal pipes are displayed for one figure in Figure 4(a). The flow regime map of Sekoguchi [24] for upward, cocurrent vertical flow had shown in Figure 4(b). Figure 4 shows the flow pattern map of Mandhane-Baker and Sekoguchi, with three different mark shows the flow conditions for different experimental series varying the inlet superficial velocity at different angle condition, where in this paper point b, c, w,andtare discussed. The three marks are the angle slope of distributor in the experimental conditions. The black circle mark for 0, square mark for 45, triangle mark for 90 angle. In these conditions the flow regime after entrance of distributor are stratified flow, wavy flow, elongated bubble flow, dispersed flow, slug flow, bubble flow, annular flow. The flow regime is determined from flow rate through distributor. It is difficult to obtain data with the same volumetric flow rate in this study for a different angle. 3.1 Annular Flow (Wave) 0 Figure 5 shows the experimental result of distributor angle 0 at gas superficial velocity m/s and liquid gas superficial velocity 0.06 m/s (point t as shown in Figure 4). The flow regime in this condition is annular flow (wave) as shown in Figure 4 at point t. The flow behavior was visualized in Figure 6, from this photo- Figure 5. Deviation ratio and superficial velocity for the 0 degree of distributor position. Figure 6. Visualized image at U G = m/s and U L = 0.06 m/s as annular flow (wave) regime. Figure 4. The experimental condition on flow pattern map of Mandhane-Baker [20,21] in horizontal pipe (a) and Sekoguchi [24] flow pattern map in vertical pipe (b).

5 Visualization the Distribution of Air-Water Mixtures Flow in Two Outlet Distributor 37 graph, it can be confirmed that the flow regime is almost evenly distribution and the flow regime could be classified as annular flow (wave) regime. The deviation ratio in this condition for air is 0.11 and the deviation ratio for water is In this condition the flow tends to evenly distribution, but the low liquid flow rates and the influence of gravity cause fluid friction at the bottom of wall pipe so that the deviation in the liquid phase is greater than the gas phase. 3.2 Elongated Bubble Flow 45 Figure 7 shows the experimental result of distributor angle 45 at gas superficial velocity 0.67 m/s and liquid superficial velocity 0.03 m/s. The flow regime in this condition plotted at flow pattern map of Mandhane- Baker and Sekoguchi as shown in Figure 4 at point w. The flow regime from the flow pattern map in Figure 4 at point w is stratified flow. The flow behavior was visualized in Figure 8. From this photograph, it can be confirmed that the flow regime is almost evenly distribution and the flow regime could be classified as elongated bubble flow regime. In this condition, the deviation ratio for air is and the deviation ratio for water is -0.05, could be regarded no deviation. If the flow regime in Figure 8 was confirmed with point w position in Figure 4, the flow regime is difference. The visualization using video recording shown that the elongated bubbles some time look as stratified flow, but elongated bubbles flow regime more appropriate than stratified flow in this condition. The difference is actually due to subjective observation of the flow pattern. At this position, some elongated bubble flow may be regarded as wavy/stratified flow during observation. 3.3 Dispersed Flow 0 Figure 9 shows the experimental result of distributor angle 0 with deviation ratio at gas superficial velocity 0.14 m/s and liquid superficial velocity 3.80 m/s. The flow regime in this condition plotted at flow pattern map of Mandhane-Baker and Sekoguchi as shown in Figure 4 at point b. The flow regime at point b is dispersed flow. The flow behavior was visualized in Figure 10. From Figure 7. Deviation ratio and superficial velocity for the 45 degree of distributor position. Figure 9. Deviation ratio and superficial velocity for the 0 degree of distributor position. Figure 8. Visualized image at U G =0.67m/sandU L =0.03 m/s as elongated bubble flow regime. Figure 10. Visualized image at U G =0.14m/sandU L =3.80 m/s as dispersed flow.

6 38 Azridjal Aziz and Akio Miyara this photograph, it can be confirmed that the flow regime is almost evenly distribution and the flow regime could be classified as dispersed flow regime. If the visualization flow regime in Figure 10 was confirmed with point b position in Figure 4., the flow regime have the same pattern. In this condition, the deviation ratio for air is 0.04 and the deviation ratio for water is -0.05, could be regarded no deviation. 3.4 Dispersed Flow 45 Figure 11 shows the experimental result of distributor angle 45 with deviation ratio at gas superficial velocity 0.69 m/s and liquid superficial velocity 3.71 m/s. The flow regime in this condition plotted at flow pattern map of Mandhane-Baker and Sekoguchi as shown in Figure 4 at point c. The flow regime at point c is dispersed flow. The flow behavior was visualized in Figure 12. From this photograph, it can be confirmed that the flow regime is almost evenly distribution and the flow regime could be classified as dispersed flow regime. If the visualization flow regime in Figure 12 confirmed with flow map point c position in Figure 4, the flow regime have the same pattern. In this condition, the deviation ratio for air is 0.14 and the deviation ratio for water is -0.03, could be regarded no deviation. 4. Conclusions In this study the experiments was conducted to characterize the flow and diversion of gas-liquid two-phase flow through the distributor. The flow regime of this study was plotted on Mandhane-Baker flow map and the Sekoguchi flow map and through the observation of flow visualization was obtained using high speed cameras and video recorder shows that the flow regime plotted on the flow maps appropriate with result visualization. The distribution of two-phase flow through distributor tends unevenly flow distribution on the decrease of the angle of distributor, from vertical position to horizontal position. The two phase flow distribution tends evenly distributed through distributor on the large gas and liquid superficial velocity. The separated flow will occur at low liquid superficial velocity and high gas superficial velocity (stratified flow, wave flow and annular flow). The mixed flow will occur at high liquid superficial velocity and low gas superficial velocity (bubble flow, dispersed flow, annular flow). References Figure 11. Deviation ratio and superficial velocity for the 45 degree of distributor position. Figure 12. Visualized image at U G =0.69m/sandU L =3.71 m/s as dispersed flow. [1] Lee, J. K. and Lee, S. Y., Distribution of Two-Phase Annular Flow at Header-Channel Junctions, Experimental Thermal and Fluid Science, Vol. 28, No. 2 3, pp (2004). doi: /S (03) [2] Vist, S. and Pettersen, J., Two-Phase Flow Distribution in Compact Heat Exchanger Manifolds, Experimental Thermal and Fluid Science, Vol. 28, No. 2 3, pp (2004). doi: /S (03) [3] Marchitto, A., Devia, F., Fossa, M., Guglielmini, G. and Schenone, C., Experiments on Two-Phase Flow

7 Visualization the Distribution of Air-Water Mixtures Flow in Two Outlet Distributor 39 Distribution Inside Parallel Channels of Compact Heat Exchangers, International Journal of Multiphase Flow, Vol. 34, No. 2, pp (2008). doi: /j.ijmultiphaseflow [4] Tae, S. J. and Cho, K., Two-Phase Flow Distribution and Phase Separation through Both Horizontal and Vertical Branches, KSME International Journal, Vol. 17, No. 8, pp (2003). [5] Wen, M. Y., Lee, C. H. and Tasi, J. C., Improving Two-Phase Refrigerant Distribution in the Manifold of the Refrigeration System, Applied Thermal Engineering, Vol. 28, No , pp (2008). doi: /j.applthermaleng [6] Kim, N. H. and Sin, T. R., Two Phase Flow Distribution of Air-Water Annular Flow in Parallel Flow Heat Exchanger, International Journal of Multiphase Flow, Vol. 32, No. 12, pp (2006). doi: / j.ijmultiphaseflow [7] Aziz, A., Miyara, A. and Sugino, F., Distribution of Two-Phase Flow in a Distributor, Journal of Engineering Science and Technology, Vol. 7, No. 1, pp (2012). [8] Yoshioka, S., Kim, H. and Kazai, K., Performance Evaluation and Optimization of a Refrigerant Distributor for Air Conditioner, Journal of Thermal Science and Technology, Vol. 3, No. 1, pp (2008). doi: /jtst.3.68 [9] Wong, T. N. and Yau, Y. K., Flow Patterns in Two- Phase Air-Water Flow, International Communications in Heat and Mass Transfer, Vol. 24, No. 1, pp (1997). doi: /S (96) [10] Brennen, C. E., Fundamentals of Multiphase Flows, Cambridge University Press, UK, pp (2005). doi: /CBO [11] Wambsganss, M. W., Jendrzejczyk, J. A. and France, D. M., Two-Phase Flow Patterns and Transitions in a Small, Horizontal, Rectangular Channel, International Journal of Multiphase Flow, Vol. 17, No. 3, pp (1991). doi: / (91) L [12] Massoud, M., Engineering Thermo Fluids (Thermodynamics, Fluid Mechanics, and Heat Transfer), Springer-Verlag Berlin Heidelberg, Germany, pp (2005). [13] Ghiaasiaan, S. M., Two Phase Flow, Boiling and Condensation (In Conventional and Miniature Systems), Cambridge University Press, UK, pp (2008). doi: /CBO [14] Tong, L. S. and Tang, Y. S., Boiling Heat Transfer and Two-Phase Flow, 2 nd ed., Taylor and Francis, USA, pp (1997). [15] Kandlikar, S. G., Shoji, M. and Dhir, V. K., Handbook of Phase Change: Boiling and Condensation, Taylor and Francis, USA, pp (1999). [16] Theilacker, J. C. and Rode, C. H., An Investigation into Flow Regimes for Two-Phase Helium Flow, A Cryogenic Engineering Conference Publication,Springer US., Vol. 33, pp (1987). doi: / _48 [17] Ghajar, A. J. and Tang, C. C., Void Fraction and Flow Patterns of Two-Phase Flow in Upward and Downward Vertical and Horizontal Pipes, Advances in Multiphase Flow and Heat Transfer, Vol. 4, pp (2012). doi: / [18] Wongwises, S. and Pipathattakul, M., Flow Pattern, Pressure Drop and Void Fraction of Two-Phase Flow Gas-Liquid in an Inclined Narrow Annular Channel, Experimental Thermal and Fluid Science, Vol. 30, No. 4, pp (2006). doi: /j.expthermflusci [19] Azzopardi, B. J., Chemical Engineering and Chemical Process Technology, Multiphase Flow, Vol. 1, EOLSS Publishers, UK, pp (2010). [20] Mandhane, J. M., Gregory, G. A. and Aziz, K., A Flow Pattern Map for Gas-Liquid Flow in Horizontal Pipes, International Journal of Multiphase Flow, Vol. 1, No. 4, pp (1974). doi: / (74) [21] Baker, O., Design of Pipe Lines for Simultaneous Flow of Oil and Gas, Oil and Gas Journal, Vol. 53, No. 12, pp (1954).

8 40 Azridjal Aziz and Akio Miyara [22] Stephanie, B., A Beginner s Guide to Uncertainty of Measurement (Issue 2), National Physical Laboratory, UK, pp (2001). [23] Moffat, R. J., Describing the Uncertainties in Experimental Results, Experimental Thermal and Fluid Science, Vol. 1, No. 1, pp (1988). doi: / (88)90043-X [24] Ueda, T., Two-Phase Flow (in Japanese), Yokendo Co, Ltd, (1989). Manuscript Received: May 1, 2014 Accepted: Jan. 12, 2015