Figure 1 - uploaded by Maogang He
Content may be subject to copyright.
Source publication
The effects of liquid supply method on falling-film transitions between horizontal tubes are experimentally studied. Several different liquid supply designs are considered, including variations in orifice size and arrangement, and experiments are conducted with ethylene glycol, water, and a mixture of ethylene glycol and water at 30°C and 40°C. It...
Contexts in source publication
Context 1
... flow patterns are referred to as the falling-film modes. There are three main falling-film modes: the sheet mode, jet (column) mode, and droplet mode; they have been defined in detail in prior work [4][5][6], and are illustrated in a general sense in Figure 1. In addition to the main modes discussed already, there are mixed modes that reflect com- bined features of two main modes concurrently. ...
Context 2
... all experiments, the distance between adjacent horizon- tal tubes, S in Figure 1 Table 1 Fluid properties and test uncertainty Dynamic Viscosity Density Surface Tension Galileo Test fluids Temperature and temperatures allowed experiments to be conducted over a wide range of Ga. The properties of the liquids in this experi- ment were obtained according to the temperature, as shown in Table 1. ...
Context 3
... effects of feeding method are explored in detail in Fig- ures 10 and 11, where transitional Re is plotted against (l o - d o )/λ d . Most notable is that the transition thresholds for all flow modes with H = 20 mm are larger than those with H = 1.6 mm. ...
Context 4
... data for Ga 0.25 = 128, 165, 548, and 658 at H = 1.6 mm and 20 mm are plotted in Figures 12 and 13, which show the transitional Re of for the jet/jet-droplet transition and the jet- droplet/droplet transition against distribution diameter (l o -d o ) over the wavelength of the fastest growing disturbance (λ max ). In Figure 12, it can be found that the transitional Re increases slowly with parameter (l o -d o )/λ max with H = 1.6 mm, while it increases much faster for H = 20 mm. ...
Context 5
... data for Ga 0.25 = 128, 165, 548, and 658 at H = 1.6 mm and 20 mm are plotted in Figures 12 and 13, which show the transitional Re of for the jet/jet-droplet transition and the jet- droplet/droplet transition against distribution diameter (l o -d o ) over the wavelength of the fastest growing disturbance (λ max ). In Figure 12, it can be found that the transitional Re increases slowly with parameter (l o -d o )/λ max with H = 1.6 mm, while it increases much faster for H = 20 mm. This is more obvious for jet-droplet/droplet transitions in Figure 13; there it is seen that the rate of change ∂ Re/∂((l o − d o )/λ max ) is greater than that in Figure 12 for H = 20 mm. ...
Context 6
... Figure 12, it can be found that the transitional Re increases slowly with parameter (l o -d o )/λ max with H = 1.6 mm, while it increases much faster for H = 20 mm. This is more obvious for jet-droplet/droplet transitions in Figure 13; there it is seen that the rate of change ∂ Re/∂((l o − d o )/λ max ) is greater than that in Figure 12 for H = 20 mm. ∂ Re/∂((l o − d o )/λ max ) is smaller and almost equal to zero for H = 1.6 mm. ...
Context 7
... Figure 12, it can be found that the transitional Re increases slowly with parameter (l o -d o )/λ max with H = 1.6 mm, while it increases much faster for H = 20 mm. This is more obvious for jet-droplet/droplet transitions in Figure 13; there it is seen that the rate of change ∂ Re/∂((l o − d o )/λ max ) is greater than that in Figure 12 for H = 20 mm. ∂ Re/∂((l o − d o )/λ max ) is smaller and almost equal to zero for H = 1.6 mm. ...
Context 8
... Re/∂((l o − d o )/λ max ) is smaller and almost equal to zero for H = 1.6 mm. Comparing Figure 12 to Figure 13, it can be found that the effect of liquid distributing The effects of the feeding parameters on the falling-film transitions appear to have several aspects. First, the orifice de- sign parameters certainly affect the uniformity of the original liquid distribution, and apparently uniformity decreases transi- tional Re. ...
Context 9
... Re/∂((l o − d o )/λ max ) is smaller and almost equal to zero for H = 1.6 mm. Comparing Figure 12 to Figure 13, it can be found that the effect of liquid distributing The effects of the feeding parameters on the falling-film transitions appear to have several aspects. First, the orifice de- sign parameters certainly affect the uniformity of the original liquid distribution, and apparently uniformity decreases transi- tional Re. ...
Context 10
... detailed comparison of the transitional Re from curve fit and experiment for different falling-film transitions with differ- ent fluids is provided in Figure 14, in which four transitions for three fluids at two different temperatures with eight differ- ent distributing methods are considered. It can be seen that all measured data are in reasonable agreement with the curve fit. ...
Context 11
... ethylene glycol has the lowest Galileo number of the fluids used, and its transitional Reynolds numbers are lowest, giving rise to higher uncertainties. The experimental conditions with the largest relative uncertainties are those with the largest RMS relative deviations, just as shown in Figures 14c and d for the jet/jet-droplet and jet-droplet/droplet transitions at Ga 0.25 = 24 and 35. Another reason for the higher RMS relative deviation at certain Ga 1/4 may be the limited data in this study. ...
Context 12
... order to further explore the effects of orifice config- uration on the flow, the jet mode was examined in more Figure 16 Each panel shows jet diameter data at three vertical locations (top, middle, and bottom are at 3.6 mm, 6.3 mm, and 9.0 mm below the orifice, respectively). The width ratio (%) is the sum of all liquid jet diameters in the field of view divided by the total horizontal length of the field of view. ...
Context 13
... liquid distribution in the intertube space was stud- ied, with a focus on the jet shape. Jet shapes with different orifice configurations at Re = 20, H = 20 mm are shown in Figure 15 Figure 15d, the liquid jets are of nearly uniform diameter from the top to the bottom, while in Figure 15f, the liquid jets have a large diameter at the top and are nar- row at the bottom. Image processing was used to quantify this behavior. ...
Context 14
... liquid distribution in the intertube space was stud- ied, with a focus on the jet shape. Jet shapes with different orifice configurations at Re = 20, H = 20 mm are shown in Figure 15 Figure 15d, the liquid jets are of nearly uniform diameter from the top to the bottom, while in Figure 15f, the liquid jets have a large diameter at the top and are nar- row at the bottom. Image processing was used to quantify this behavior. ...
Context 15
... liquid distribution in the intertube space was stud- ied, with a focus on the jet shape. Jet shapes with different orifice configurations at Re = 20, H = 20 mm are shown in Figure 15 Figure 15d, the liquid jets are of nearly uniform diameter from the top to the bottom, while in Figure 15f, the liquid jets have a large diameter at the top and are nar- row at the bottom. Image processing was used to quantify this behavior. ...
Context 16
... order to improve the data accuracy, the diameter of all jets in the sam- pled image was added and the ratio of the sum of jet diameters to the entire sampled image width was calculated. The results are shown in Figure 16. The locations top jet, middle jet, and bottom jet indicate position 3.6 mm from the bottom of the up- per tube, 6.3 mm, and 9.0 mm, respectively. ...
Context 17
... locations top jet, middle jet, and bottom jet indicate position 3.6 mm from the bottom of the up- per tube, 6.3 mm, and 9.0 mm, respectively. From Figure 16 it can be seen that the orifice design has more effect on the shape near the top of the jets than at the middle or bottom of the jets. The jet diameter increases with orifice diameter and decreases with orifice spacing. ...
Context 18
... jet diameter increases with orifice diameter and decreases with orifice spacing. The range of width ratio at dif- ferent jet locations is from about 42% to 22% for the feeding height of H = 1.6 mm in Figure 16a, and from about 45% to 19% for the feeding height of H = 20 mm at Re = 20 in Fig- ure 16c. Thus, variations in jet shape are larger for the larger feeding height (the same trend is reflected in Figures 16b and 13d at Re = 13). ...
Context 19
... jet diameter increases with orifice diameter and decreases with orifice spacing. The range of width ratio at dif- ferent jet locations is from about 42% to 22% for the feeding height of H = 1.6 mm in Figure 16a, and from about 45% to 19% for the feeding height of H = 20 mm at Re = 20 in Fig- ure 16c. Thus, variations in jet shape are larger for the larger feeding height (the same trend is reflected in Figures 16b and 13d at Re = 13). ...
Context 20
... range of width ratio at dif- ferent jet locations is from about 42% to 22% for the feeding height of H = 1.6 mm in Figure 16a, and from about 45% to 19% for the feeding height of H = 20 mm at Re = 20 in Fig- ure 16c. Thus, variations in jet shape are larger for the larger feeding height (the same trend is reflected in Figures 16b and 13d at Re = 13). Therefore, the jet for the large feeding height has a wider top and thinner bottom, which may explain the increased instability of the flow with large feeding height; for a very large feeding height the jet will manifest a Rayleigh instability. ...
Similar publications
A novel design of log-periodic dipole array (LPDA) for high-frequency direction finding (DF) is presented. The traditional Carrel method employs fixed values of scale factor and spacing factors in LPDA designs. Here, we propose a design method which uses the continuous change of both the scale factor and the spacing factor so that the length of the...
Citations
... With the gradual development of falling film technology, the types of heat exchange tubes have developed from plain tubes to three-dimensional (3D) finned tubes with more robust heat transfer performance. For the study of the falling film mode between the plain tubes, Armbruster and Mitrovic [14], Hu and Jacobi [15,16], Roques et al. [17], Gstöhl and Thome [18], Wang et al. [19], Qu et al. [20] and Bustamante and Garimella [21] conducted their own experiments to obtain the Reynolds number (Re) of different falling film transition modes. Not only that, the tube spacing is another important factor affecting the falling film mode between tubes. ...
... The prediction model is Re = AGa b , where A and b are empirical constants, and Ga is the modified Galileo number. The subsequent plain tube prediction model takes into account the tube spacing, tube diameter and distributor size based on the Hu and Jacobi's prediction model [19,23,27,29,32]. The prediction model of Wang et al. [19] is applied to the plain tube, and the model mainly considers the effect of tube diameter and liquid distributor device height on the falling film transitional Re and does not consider the effect of tube spacing. ...
... The subsequent plain tube prediction model takes into account the tube spacing, tube diameter and distributor size based on the Hu and Jacobi's prediction model [19,23,27,29,32]. The prediction model of Wang et al. [19] is applied to the plain tube, and the model mainly considers the effect of tube diameter and liquid distributor device height on the falling film transitional Re and does not consider the effect of tube spacing. The prediction models of Wang et al. [23], Chen et al. [29] and Wang and Jacobi [32] consider the effect of tube spacing on the falling film transitional Re. ...
To investigate the effect of different falling film modes on the heat transfer performance of three-dimensional (3D) finned tubes in a falling film heat exchanger, the falling film transition modes are experimentally investigated by observing the flow modes on 3D finned tubes and determining the Reynolds numbers of flow transition modes. A test facility, which contains an array of three horizontal test tubes, is constructed to study the effect of tube spacing and fin structure on the falling film Reynolds number (Re). The results show that tube spacing and fin structure significantly affect the Re and observed mode. With the increase in tube spacing, the Re overall shows an increasing trend for the four transition modes, especially for the transition between the column and the column–sheet mode. With the increase in the ratio for fin structure parameters, the Re overall shows a downward trend, and this phenomenon is more evident with the increase in the tube spacing. Machine learning methods are utilized to predict the Re, considering the effects of tube spacing and fin structure. Both this method and the linear regression method are used to predict the Re of the literature and this experiment, and the results indicate that machine learning has a lower prediction deviation.
... The distributor type, distributor height, and orifice spacing all had a strong influence on the inter tube flow regimes and their characteristics (Wang et al. 2013;Qu et al. 2019). Mohamed (Mohamed 2007) conducted experiments to investigate the effect of the test tube rotational speed on flow pattern transformations. ...
The coverage of the liquid film over the horizontal tubes, particularly the wetting ratio, is important for gravity-driven evaporators and absorbers to achieve a better heat transfer mechanism. A 2D, two-phase CFD model was developed to examine the falling-film hydrodynamics and transient film coverage for Reynolds numbers ranging from 100 to 500, static contact angles spanning from 0°/30°/60°/90°, and tube-to-tube distance of 10 mm. The VOF method is used in this article to capture the liquid–gas interface. The findings showed that the complete spreading of the liquid film is difficult at low Reynolds numbers and high contact angles. The formation of dry regions on the tube wall as a result of insufficient liquid supply, liquid film breakage, and liquid film shrinkage. Furthermore, as the Reynolds number increases and contact angle decrease, the wetting ratio over the tube surface increases. It is worth noting that each contact angle must have a minimum Reynolds number in order to keep the surface completely wet. The research also revealed that for higher Reynolds numbers, the influence of contact angle on wettability of tube wall can be ignored. For the same Reynolds number, the liquid propagation time required to wet the tube surface increases as the contact angle value increases.
Graphical Abstract
... Hu and Jacobi [1] proposed transition relation of falling film mode is related to the Reynolds number (Re) versus the Galileo number (Ga), and provided a mathematical relationship between Re and Ga (Re = AGa b ), where A and b are empirical constants in the formula. This formula is widely used to determine the falling film mode between the plain tubes and the enhanced tubes, and the effect of the tube spacing, tube diameter and liquid distribution structure are considered [16][17][18][19][20][21]. ...
... Hu [11], Ding [25], Zhang [26] and Karmakar [27] conducted numerical simulation and experimented with analyzing the effect of instability wavelength on the falling film mode between the plain tubes and corrugated tube. Wang [18], Qu [20] and Ruan [28] designed different liquid distributors to achieve liquid distribution conditions on the plain tube surface. Roques [16], Gstöhl [29], Zavaleta-Aguilar [30] and Sun [31] used water, ethanol, ethylene glycol, refrigerant and ammonia-water mixtures as test liquid to analyze the evolution of flow mode transitions between plain tubes. ...
... Because of the above two points, a prediction model considering tube material and tube spacing is proposed for tube material and tube spacing. To enhance the extensibility of this model, literature data [1,16,18,20] are considered in this prediction model. For the factor of tube material, the contact angle, which characterizes the degree of Table 4 Correlation coefficients and application range of prediction model Content courtesy of Springer Nature, terms of use apply. ...
A falling film flow test facility is designed and constructed to investigate the effect of tube spacing and tube material on the falling film transition mode. In the experiment, water is used as the falling film working liquid, copper and fluoroplastic are used as the tube materials, the tube spacing is set to 14 mm and 20 mm, and the diameter of the test tube is 20 mm. The analysis of the four observed transition modes and Reynolds number (Re) shows that the column modes in droplet to droplet-column and droplet-column to column transition modes are stretched, and the sheet modes in the column to column-sheet transition modes have gaps after the tube spacing increases. The Re of the two tube spacings is similar for droplet to droplet-column (D-DC) and droplet-column to column (DC-C) transition modes. For column to column-sheet (C-CS) and column-sheet to sheet (CS-S) modes, the Re of the tube spacing of 20 mm is higher than that of the tube spacing of 14 mm. After the copper tube is replaced with a fluoroplastic tube, the falling film flow rate distribution is uneven, and the columnar mode in the column to column-sheet (C-CS) transition mode and the partial sheet mode in the column-sheet to sheet (CS-S) transition mode deviated from one side of the fluoroplastic tube surface. For D-DC and DC-C transition modes, the Re of copper tube and fluoroplastic tube is similar. For C-CS and CS-S transition modes, the Re of fluoroplastic tube is higher than that of the copper tube. In order to facilitate the subsequent study of tube spacing and tube materials, a new prediction model of transition mode is established, and the literature data is considered to introduce the prediction model to enhance the application range. The Re prediction deviations of the model for the four transition modes are within ± 20%. This work provides a new research idea for the subsequent study of falling film flow with different tube materials and tube spacing.
... The ow regimes between the tubes and its characteristics were strongly in uenced by the distributor type, height of the distributor, and ori ce spacing [17,18]. Mohamed [19] carried out experiments to analyze the in uence of the rotational speed of the test tube on ow pattern transformations. ...
... 17 and 18 demonstrate the propagation time for the stabilizing tube and test tube, as well as the time taken into account for the inter tube commuting of liquid lm. The propagation time in this study is de ned as the time required for the liquid lm to completely wet the stabilizing tube and test tube in one cycle. ...
... The propagation time in this study is de ned as the time required for the liquid lm to completely wet the stabilizing tube and test tube in one cycle. Another concern highlighted by Figs.17 and 18 is that the propagation time required to wet the tube surface increases as the Ψ value for the same Re. Furthermore, as Re increases, the wetting time decreases. ...
The coverage of the liquid film over the horizontal tubes, particularly the wetting ratio, is important for gravity-driven evaporators and absorbers to achieve a better heat transfer mechanism. A 2D, two-phase CFD model was developed to examine the falling-film hydrodynamics and transient flow mechanism for Reynolds numbers ranging from 100-500, static contact angles spanning from 0°/30°/60°/90°, and tube-to-tube distance of 10 mm. The VOF method is used in this article to capture the liquid-gas interface. The findings showed that the complete spreading of the liquid film is difficult at low Reynolds numbers and high contact angles. The formation of dry regions on the tube wall as a result of insufficient liquid supply, liquid film breakage, and liquid film shrinkage. Furthermore, as the Reynolds number increases and contact angle decrease, the wetting ratio over the tube surface increases. It is worth noting that each contact angle must have a minimum Reynolds number in order to keep the surface completely wet. The research also revealed that for higher Reynolds numbers, the influence of contact angle on wettability of tube wall can be ignored. For the same Reynolds number, the liquid propagation time required to wet the tube surface increases as the contact angle value increases. Fouling over the tubes can be aided by the formation of air voids near the lower stagnation zone.
... The flow regimes between the tubes and its characteristics were strongly influenced by the distributor type, height of the distributor, and orifice spacing [17,18]. Mohamed [19] carried out experiments to analyze the influence of the rotational speed of the test tube on flow pattern transformations. ...
The coverage of the liquid film over the horizontal tubes, particularly the wetting ratio, is important for heat transfer mechanism of gravity-driven evaporators and absorbers. A 2D, two-phase CFD model was developed to examine the falling-film hydrodynamics and transient flow mechanism for Reynolds numbers ranging from 100-500, contact angles spanning from 0°/30°/60°/90°, and inter tube spacing of 10 mm. The VOF method is used in this article to capture the gas-liquid interface. The findings showed that the complete spreading of the liquid film is difficult at low Reynolds numbers and high contact angles. The formation of dry regions on the tube wall as a result of insufficient liquid supply, liquid film breakage, and liquid film shrinkage. Furthermore, as the Reynolds number increases and contact angle decrease, the wetting ratio over the tube surface increases. It was worth noting that each contact angle must have a minimum Reynolds number in order to keep the surface completely wet. The research also found that for higher Reynolds numbers, the influence of contact angle on wettability of tube wall can be ignored. The liquid propagation time required to wet the tube surface increases as the contact angle value increases for the same Reynolds number. Fouling over the tubes can be aided by the formation of air voids near the lower stagnation zone.
... It is worth noting that the liquid distributor height is the vertical distance between the liquid exit from the bottom of the distributor and the top point on the external perimeter of the first horizontal tube (see [1] ). The liquid distributor height is also known as the feeding height (see [48] ); 16. The around-tube film thickness depends only on flow rate; fluid properties; and tube geometry, and thus this thickness is identical for the droplet and jet modes at the transitional Reynolds number; Fig. 2 ). ...
... Other aspects of the distribution system design have been reported in the literature to have impact on the prevailing flow mode. For example, Wang et al. [48] reported an increase in the transitional Re with the flow nonuniformity, where they represented the flow nonuniformity as the difference between the distributor orifice spacing and the orifice diameter divided by the most dangerous Taylor instability wavelength. They [48] also reported an increase in the transitional Re with the distributor/feeding height, H . ...
... For example, Wang et al. [48] reported an increase in the transitional Re with the flow nonuniformity, where they represented the flow nonuniformity as the difference between the distributor orifice spacing and the orifice diameter divided by the most dangerous Taylor instability wavelength. They [48] also reported an increase in the transitional Re with the distributor/feeding height, H . More recently, Bustamante and Garimella [59] investigated eight distributor designs and reported a significant influence of the distributor design on the flow morphology (including flow mode, droplet size, jet diameter, and departure site spacing). ...
The objective of this paper is to propose and validate a model for predicting the transitional film Reynolds number between the droplet and jet modes of falling film flows. The proposed model relies on thermodynamic availability with no fitting to mode transition data. The model directly predicts the numerical values of the transitional film Reynolds numbers at different operating conditions. The results of the model are validated against 43 experimental data points from the literature, which cover 10 working fluids and a wide range of tube geometries. The accuracy of the proposed model in predicting the validation data is -on average- more than 20 % better than that of the widely used Re=a(Ga)b and Re=a(Ga)b(S/ξ)c models. The model also achieves low computation time (less than 30 seconds for the 43 validation data points). The model presented in this paper has the potential of integration with heat transfer, mass transfer, and pressure drop models for optimizing the design and operation of falling film heat and mass exchangers.
Gravity-driven horizontal falling-film flow phenomenon is a ground-breaking technology that has been actively used in a wide range of industrial applications, including desalination, petroleum refineries, food processing industries, and refrigeration, among others. A series of experiments and a 2-D two-phase model were developed to investigate falling-film flow regimes, microscopic flow mechanism, and finer flow parameter details. The experiments focused primarily on axial inter-tube flow modes, and circumferential flow parameters were evaluated using numerical simulations. A high-speed digital photographic device was used to capture and visualize the flow pattern. The VOF method is used to capture the liquid–gas interface. The Reynolds number ranged from 41 to 1000, the tube spacing was 10/20/30/40 mm, and the contact angle was 0°. According to the findings, droplet flow has three important phases, detached spherical flow pattern, discrete spherical flow pattern, full neck formation by linked droplets, and droplet flow before reaching column flow. The Reynolds numbers 166, 208, and 250 have departure-site spacing values of approximately 23.84 mm, 18.16 mm, and 14.52 mm, respectively. The flow parameters such as radial film thickness and vortices beneath the tube increase with increasing Reynolds number. As Reynolds number increases, the departure-site spacing and liquid film inter-tube propagation time decrease. The thinnest film zone appeared between 90°and 140°. The velocity magnitude of the liquid film over the test tube is greater than that of the stabilizing tube, despite being close to the distributor. Furthermore, the film velocity on the lower half of the tube wall is slightly higher than that on the upper half of the tube wall.
This study helps to predict the effect of open ratio (OR), current collector roughness (CCR) and compression on the equivalent mass transport resistance (EMTR) as a result passive DMFC performance analytically. This study gives the analytical result of gas diffusion layer (GDL) compression due to the CCR. Here, the simple mathematics is used to solve the equation and to estimate the other parameter. 1D model has been developed to calculate percentage increase in EMTR. CCR, OR and compression have significantly affected the EMTR of passive direct methanol fuel (DMFC) performance.
In order to avoid the formation of dry spots, the liquid film hydrodynamics over the tube surface take an influential role in falling film-type condensers and evaporators. One of the fundamental flow patterns seen in many industrial heat exchanger units is the droplet flow regime between horizontal tubes. The present study explored the distinct phases of the droplet regime and droplet impact modes between inline horizontal tubes experimentally. The flow patterns were captured using a Phantom V440L high-speed camera device for a Reynolds number ranging from 41 to 250 and a tube-to-tube distance of 10 mm. To detect the edges, the Sobel edge detection technique was used, and flow parameters were quantified using MATLAB image analysis. The photographic pieces of evidence revealed that the distinct phases in the droplet flow regime can be broadly classified as primary droplet development, secondary droplet formation, columnar droplet, neck break, and retraction. The droplet impact modes were found to be different as the Reynolds number varied. The outcomes can be used to model the heat transfer correlations for the various droplet impact modes.
