Film Flow Rate Research Articles

Falling film evaporation in a triangular tube bundle under the influence of cross vapor stream

Abstract The falling film evaporation and the effect of cross vapor stream in falling film evaporator with triangular tube bundle using R123 was experimentally investigated. The variations of local and bundle average heat transfer coefficients were described. The tube bundle consisted of 4 × 3 (column × row) of triangular horizontal copper tubes. The tests without vapor effect were conducted with nominal heat fluxes of 20 to 60 kWm–2, saturation temperatures of 6 to 16 °C and film flow rates of 0.016 to 0.18 kgm–1s–1. Cross vapor stream effect experiments were operated at three heat fluxes of 20, 30 and 40 kWm–2 and two film flow rates of 0.035 and 0.07 kgm−1s−1, and the vapor velocity at the narrowest interstice in the tube bundle varies from 0 to 5.0 ms−1. It is indicated that the heat transfer is seriously influenced by the bundle effect while less affected by changing of saturation temperature. With the increase in vapor velocity, the heat transfer performance is generally weakened; the cross vapor stream has a strong influence on falling film evaporation of R123.

Modeling of the plywood making process glued with thermoplastic polymer

A promising variety of the wood composite materials is plywood glued with thermoplastic polymers. However, making such a wood composite requires adjustment of the pressing modes, because there is a slightly difference between the hot method of the veneer packages pressing glued with thermoplastic films and the method of the veneer packages pressing glued with thermosetting adhesives. Among the main processes that occur in the gluing plywood process are heat and mass transfer. The availability of the thermoplastic film between the veneer sheets is going to change the thermal conductivity of the package, and therefore will affect the pressing duration. If suppose, that the package has a plate appearance, which is located between heated to the certain temperature pressed plates, then the known Fourier-Kirchhoff thermal differential equation can be applied. The basis for the model development of the warming package veneer process glued with thermoplastic film are laid methods of nonlinear programming, uniform search and conjugate gradient. On the offered mathematical model basis, the temperature field change in the package thickness during the plywood gluing with plastic film is calculated, the calculation of the warming duration indicators of the package veneer is done and this indicator dependence on the thermoplastic film flow rate and the pressing temperature is established. The duration of the warming package veneer glued with thermoplastic film depends on the temperature at which the thermoplastic polymer will change from a highly elastic to the viscous state. The transition of the thermoplastic film LDPE to the viscous state begins at 125оС and lasts up to 240 оС. With increasing of the press temperature plates from 140 to 180оС the duration of warming up the middle of the package to 125оС decreases by 89% for all investigated polymer costs is established. Changing the polymer content in the package does not significantly affect the duration of its warming. With increasing of the thermoplastic film flow rate from 130 g/m2 to 190 g/m2, the duration of warming up the middle of the veneer package to 125оС increases slightly from 3,8 to 4,2% depending on the pressing temperature. Suggested mathematical model allows to set the material parameters and plywood pressing mode influence on the duration of the warming package veneer while plywood making glued with the thermoplastic film LDPE.

A Comparative Study of the Oil-Free Centrifugal Water Chillers with the Flooded or Falling Film Evaporator—A Case Study

A comparative study regarding the performance of real-scale oil-free centrifugal chillers having the flooded evaporator or falling film evaporator was conducted in this study. The nominal capacity for the test chillers was around 200~230 USRT (US refrigeration ton) (703~809 kW). The compressors of the two chillers were identical and R-134a was used as the working fluid. Both evaporators employed the same enhanced tubes (GEWA-B) to fulfill phase change. Tests were conducted in full, 75%, 50%, and 25% loading. Test results indicate that both chillers contained a comparable system performance with an integrated part-load value of around 8.62~8.63. The overall heat transfer coefficient for the flooded evaporator was appreciably higher (20~40%) than the falling film evaporator. This is because the falling film flowrate was below the threshold value and the heat transfer was dominated by evaporation mode. Yet, the heat transfer performance for the falling film evaporator was further jeopardized due to starvation of the film flowrate (partial dry-out), especially in the middle or bottom of the tube bundle. This phenomenon became even more pronounced at partial loading (25%), whereas the flooded evaporator did not reveal such a performance dip at partial loading.

CFD modeling of liquid film reversal of two-phase flow in vertical pipes

The phenomenon of two-phase flows is characterized by its wide range of presence in nature and industrial applications. In gas and oil production, the simultaneous two-phase flow of gases and liquids often occurs in gas wells. The produced gases flow rate decreases over the years until reaching a critical flow rate when they lose their ability to lift the associated liquids upward and the liquid film reverses direction, which triggers liquid loading. Liquid loading causes the produced liquids to accumulate in the bottom of the wellbore, which causes a high back pressure that reduces the well production rate till production is ceased eventually. The critical gas velocity exists in the churn flow regime which is mainly characterized by the oscillatory behavior of the liquids flow field. This study employs CFD techniques to model the churn flow in a 3-inch-diameter vertical pipe near the critical gas flow rate for different liquid flow rates. This work utilizes the two-fluid Eulerian model along with the RNG (Re-Normalization Group) k-ε turbulence model to investigate the behavior of the flow field in a two-dimensional axisymmetric computational domain. Simulations were carried out using the commercial software ANSYS Fluent 18.2 with air and water as the two working fluids. The model results showed a good agreement with the experimental data and proved the mesh and time independence of the model. Oscillatory behaviors of the liquid film flow rate, shear stress, and pressure were observed along with the formation of interfacial waves. Detailed information about the velocity, shear stress, and pressure behaviors is presented. Accordingly, recommendations are suggested for future considerations.

Thermohydraulics of the liquid films in rotating heat pipes

Purpose In this study, closed-form solutions are presented to investigate thermohydraulics of liquid films in a rotating heat pipe. The film thickness is expressed as a function of flow rate. Design/methodology/approach Further, sensitivity of both film thickness and flow rate to the length of the rotating heat pipe can now be investigated using the explicit expressions presented here. Findings To make it easier for practical application, an approximate solution is presented on top of the exact solution. Originality/value Both approximate and exact solutions are then applied to note that results are in good agreement when compared to those available in the literature.

흡수식 냉동기의 증발기에 사용되는 전열촉진관에서 물의 유하 액막 증발 열전달에 대한 실험적 연구

Thin film evaporation of water using enhanced tubes is one of the most common mode of heat transfer in absorption chillers evaporators. Proper design of the evaporators require adequate knowledge of evaporation heat transfer coefficient. In this study, seven enhanced tubes with different enhancement geometries were tested at a saturation temperature of 12℃, 15℃ tube-side water inlet temperature and a film flow rate of . The results indicated that the evaporation heat transfer coefficient of the Floral tube was lower than that of the smooth tube, while the Corrugated tube yielded almost the same heat transfer coefficient as the smooth tube. Notched Floral tube yielded a heat transfer coefficient of 72%, which is higher than that of smooth tube. It was found that Notched geometry was better than the End-cross geometry. Moreover, addition of Floral and Corrugated geometry formations to tubes having threedimensional protrusions, such as Notched or End-cross tubes further enhanced the evaporation heat transfer. As for the overall heat transfer coefficient, which accounts for both evaporation and tube-side heat transfer, End-cross Corrugated tube yielded the highest heat transfer coefficient at 57% as compared to smooth tube.

Application of different advanced oxidation processes for the removal of chloroacetic acids using a planar falling film reactor

Advanced oxidation processes (AOPs) are considered as an effective and promising method for the degradation and mineralization of aqueous recalcitrant organic pollutants. In this study, application of ozonation and various types of AOPs including photocatalysis, Fenton alone and their combinations were investigated and compared for the degradation and mineralization of chloroacetic acids (CAAs) in aqueous solutions, using a planar falling film reactor. CAAs are widely available in water treated by chlorination processes and are resistance against ozonation in the darkness. The results of the present work showed that the plain ozonation was inefficient method for the destruction of the CAAs as only about 2% degradation was observed after 90 min treatment. However, the best results were achieved by ozone in combinations with other oxidation processes. Furthermore, a synergistic effect on the removal rate was observed when these processes were exposed to the UVA light. Among the examined processes, combination of photo-Fenton with ozonation was found to be the fastest one for CAAs degradation. The effects of different parameters such as initial concentration of Fe2⁺, H₂O₂ and CAAs in photo-Fenton combined with ozonation were investigated. The optimum ratio of 0.12 of Fe2⁺/H₂O₂ concentration was found to give the best result for CAAs degradation. The degree of CAAs mineralization, measured by the total organic carbon removal, as well as the effect of falling liquid film flow rate on the removal of CAAs were also studied and discussed.

Heat transfer correlations of refrigerant falling film evaporation on a single horizontal smooth tube

Falling film evaporation heat transfer of R134a and its potential substitutes R290 and R600a outside a single horizontal plain tube is experimentally investigated, and the effects of the saturation temperature, film flow rate and heat flux on heat transfer coefficient are studied. Heat transfer performance of R290 is slightly superior than that of R134a, while R600a is inferior than that of R134a. The threshold film Reynolds number is determined to separate the variation trend of HTC with film Reynolds number into full wetting and partial dryout regimes. Increase of heat flux benefits the heat transfer in both full-wetting and partial dry-out regimes. New heat transfer correlations based on the present data and data for R32 and R1234ze(E) in the authors’ group are suggested for two regimes. The correlation for full wetting regime fits 96.7% of the total 542 correlated data within ±30% while fits 73.4% of the total 289 data in references from −30% to +15%, the correlation for partial dryout regime fits 97.5% of the total 162 correlated data within ±30% while fits 76.8% of the total 95 data from references within ±30%.

The Role of Substrate Roughness in Superfluid Film Flow Velocity

It is known that the apparent film flow rate $j_0$ of superfluid $^4$He increases significantly when the container wall is contaminated by a thin layer of solid air. However, its microscopic mechanism has not yet been clarified enough. We have measured $j_0$ under largely different conditions for the container wall in terms of surface area (0.77-6.15 m$^2$) and surface morphology using silver fine powders (particle size: $0.10$ \mu m) and porous glass (pore size: 0.5, 1 \mu m). We could increase $j_0$ by more than two orders of magnitude compared to non-treated smooth glass walls, where liquid helium flows down from the bottom of container as a continuous stream rather than discrete drips. By modeling the surface morphology, we estimated the effective perimeter of container $L_{\mathrm{eff}}$ and calculated the flow rate $j~(= j_0L_0/L_{\mathrm{eff}})$, where $L_0$ is the apparent perimeter without considering the microscopic surface structures. The resultant $j$ values for the various containers are constant each other within a factor of four, suggesting that the enhancement of $L_{\mathrm{eff}}$ plays a major role to change $j_0$ to such a huge extent and that the superfluid critical velocity, $v_{\mathrm{c}}$, does not change appreciably. The measured temperature dependence of $j$ revealed that $v_{\mathrm{c}}$ values in our experiments are determined by the vortex depinning model of Schwarz (Phys. Rev. B $\textbf{31}$, 5782 (1986)) with several nm size pinning sites.

Spatiotemporally resolved heat transfer measurements in falling liquid-films by simultaneous application of planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography

We present an optical technique that combines simultaneous planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography for the space-and time-resolved measurement of the film-height, 2-D velocity and 2-D free-surface temperature in liquid films falling over an inclined, resistively-heated glass substrate. Using this information and knowledge of the wall temperature, local and instantaneous heat-transfer coefficients (HTCs) and Nusselt numbers, Nu, are also recovered along the waves of liquid films with Kapitza number, Ka=180, and Prandtl number, Pr=77. By employing this technique, falling-film flows are investigated with Reynolds numbers in the range Re = 18–66, wave frequencies set to fw=7, 12 and 17 Hz, and a wall heat flux set to q̇=2.5 W cm−2. Complementary data are also collected in equivalent (i.e., for the same mean-flow Re) flows with q̇=0 W cm−2. Quality assurance experiments are performed that reveal deviations of up to 2–3% between PLIF/PTV-derived film heights, interfacial/bulk velocities and flow rates, and both analytical predictions and direct measurements of flat films over a range of conditions, while IR-based temperature measurements fall within 1 °C of thermocouple measurements. Highly localized film height, velocity, flow-rate and interface-temperature data are generated along the examined wave topologies by phase/wave locked averaging. The application of a heat flux (q̇=2.5 W cm−2) results in a pronounced “thinning” of the investigated films (by 18%, on average), while the mean bulk velocities compensate by increasing by a similar extent to conserve the imposed flow rate. The axial-velocity profiles that are obtained in the heated cases are parabolic but “fuller” compared to equivalent isothermal flows, excluding any wave-regions where the interface slopes are high. As the Re is reduced, the heating applied at the wall penetrates through the film, resulting in a pronounced coupling between the HTC and the film height in thinner film regions. When the imposed wave frequency is increased, a narrower range of HTCs is observed, which we link to the evolution of the film topology and the associated redistribution of the fluid flow upstream of the imaging location, as the liquid viscosity decreases. The local and instantaneous Nu is strongly coupled to the film height and experiences variations that increase as fw is reduced.

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films.

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.

Experimental study on heat and mass transfer of falling liquid films in converging-diverging tubes with water

To improve the heat and mass transfer performances of falling films and develop a new type of falling film evaporator, the heat and mass transfer characteristics of falling film evaporation and sensible heating in four different sizes of converging–diverging (CD) tubes were experimentally explored in this study. By analyzing the relationship between the heat transfer coefficient and the falling film flow rate, it was found that the CD tube is suitable for falling film evaporation and sensible heating with a large Reynolds number. For different sizes of tubes, the key factor affecting the heat transfer performance in falling film evaporation and sensible heating is the rib height. At the same rib height and rib pitch, the longer the converging segment of the CD tube, the better the heat transfer performance. According to the comparative analysis on heat and mass transfer performances of falling film evaporation and sensible heating inside the four CD tubes, the CD tube 3# is the best. The evaporation heat transfer coefficient (when the Reynolds number of the liquid films is 2356), evaporation mass transfer rate (when the perimeter flow rate of the liquid films is 0.173 kg/(m·s)), and sensible heating heat transfer coefficient (when the Reynolds number of the liquid films is 1635) of CD tube 3# are 62%, 38% and 63% higher than that of the smooth tube, respectively. For the same CD tube, the evaporation heat transfer coefficient is greater than the sensible heating heat transfer coefficient, but both increases as the flow rate increases. The heat transfer correlations of falling film evaporation and sensible heating in the experimental range were obtained. It will provide a useful reference for future engineering design and industrial applications.

Experimental investigation of R410A and R32 falling film evaporation on horizontal enhanced tubes

In this study, heat transfer performance on horizontal copper tubes of high pressure refrigerants R32 and R410A was investigated. An integrated fin (condensation enhanced) tube and three boiling enhanced tubes with 3-D different enhancement structures were tested. A plain tube was also tested for comparison. Effects of film flow rate, saturation temperature and heat flux on the falling film heat transfer coefficients were investigated. A tube bundle comprised of 6 enhanced boiling tubes was also tested to find the bundle effect. Experiments were carried out at saturation temperatures of 6, 10 and 16 °C, heat fluxes from 20 to 150 kW·m−2 and film flow rates from 0.01 kg·m−1·s−1 to 0.14 kg·m−1·s−1. It is found that the effect of film Reynolds number on HTCs of enhanced tubes can be separated into two regimes, a quasi-plateau regime and a sharp decrease regime. HTCs increase with heat flux. Increase of saturation temperature has negligible effect on enhanced tubes as well as the tube bundle. The integrated fin tube performs best among the tubes tested. As a whole, R410A is inferior than R32. Tubes positioned below the top row possess the similar variation trend of HTCs with that of the first row but suffer an earlier dryout.

Effect of downward vapor stream on falling film evaporation of R134a in a tube bundle

The influence of downward vapor stream on the falling film evaporation with nucleate boiling outside a horizontal enhanced tube bundle arrayed in a vertical column is experimentally investigated. The variations in local and bundle averaged heat transfer coefficients with vapor velocity are presented. To simulate the practical condition in a falling film evaporator, the flow passages of the liquid/vapor are constructed using two quartz glass sheets and two columns of dummy half tubes. The test ranges are saturation temperature of 6 °C, film flow rate of 0.035–0.1 kgm–1s–1, heat flux of 20, 30, 40 kWm–2. It is found that (1) the downward vapor effects are either positive or negative depending on the tube position, film flow rate, heat flux and vapor velocity; (2) the bundle effect becomes stronger under the effect of downward vapor stream; (3) the downward vapor has a significant effect on the heat transfer of the lower tubes than the upper tubes; and (4) the vapor stream effect on the bundle averaged heat transfer coefficient varies with the levels of film flow rate and heat flux. The experimental results provide significant guidance in the design of the vapor escape channel in a falling film evaporator.

Safety and stability of two kinds of ship rotor bearing system under rolling condition

Rolling condition, the bearing load is changed with time, which is bound to affect the safety and stability analysis results of the rotor-bearing system. Only through the steady state analysis that is difficult to guarantee the security and reliability of the support bearing. In this paper, using a rotor-bearing system dynamic characteristics analysis software DLAP (dynamic lubrication analysis program) developed by the lubrication theory and Bearing Research Institute of Xi’an Jiao Tong University, solution of the Reynolds equation and the temperature viscosity equation. The key operating parameters of the elliptic and offset bearing such as the minimum oil film thickness, maximum oil film pressure, temperature rise, power dissipation and flow rate are obtained. At the same time, the axis orbit and the oil film pressure of the two kinds of bearings are compared and analyzed under rolling condition. In addition, based on the assumption of piecewise linearization of bearing stiffness and damping, the rotor-bearing model with different rolling angles was established. Coupled solution of the two kinds of rotor-bearing system dynamics model was presented. By means of eigenvalue and eigenvector, unbalance response analysis, stability analysis and transient dynamic analysis, the stability and safety of the rotor-bearing system are studied in detail. Finally, the dynamics characteristics of rotor system supported by ellipse and offset bearings under rolling conditions were obtained.

Hydrodynamic behaviors of the falling film flow on a horizontal tube and construction of new film thickness correlation

The laminar liquid film falling on a horizontal smooth tube is studied numerically. The instantaneous hydrodynamic characteristics of falling film flow, the importance of surface tension in calculation and the effects of film flow rate, tube diameter, liquid distributor height and inlet liquid temperature on the flow field and film thickness are elucidated. The results indicate that: (1) The surface tension is important in the calculations of falling film flow on a horizontal tube; (2) The film falling on a circular tube has obvious instantaneous behaviors; (3) The film thickness increases with increase of film flow rate, while decreases with increase of the tube diameter, liquid distributor height and liquid temperature, respectively; (4) The film distribution along the peripheral angle is unsymmetrical, and the minimum thickness appears in 110–150° of peripheral angle depending on the working conditions. Furthermore, new correlations of falling film thickness on a horizontal tube based on the present data are established, which fit 97% of 84 data in θ = 2–15° within ±20%, 90% of 632 data in θ = 15–165° within ±20%, and 73% of 112 data in θ = 165–178° within ±30%.

Falling Film Evaporator for Desorption of Basic Aluminum Sulfate SO2-Rich Solution and Enhancement of Heat and Mass Transfer

This study was aimed to improve the SO2 desorption effect of basic aluminum sulfate SO2-rich solution. Based on the desorption mechanism, we first used a falling film evaporation method to intensify heat transfer and mass transfer. Based on the falling film desorption heat and mass transfer model, we analyzed the falling film evaporation and desorption of basic aluminum sulfate SO2-rich solution inside the converging–diverging tube and the smooth tube and investigated the heat and mass transfer rules under different conditions. It was found as the quantity of SO2-rich solution increased, the heat transfer coefficient and mass transfer coefficient of falling film evaporation both increased, but the SO2 desorption efficiency decreased. With the rise of the heating temperature, the three indices all increased. With the rise of the inlet sulfur concentration, the three indices all increased. With the rise of the aluminum concentration, the three indices all gradually declined. With the rise of the alkalinity, the three indices all gradually declined. Comparative analysis showed the heat transfer coefficient and mass transfer coefficient of falling film evaporation and SO2 desorption efficiency were 17%–29%, 33%–69%, and 6.7%–16.3% larger inside the converging–diverging tube than the smooth tube, respectively, indicating the basic aluminum sulfate SO2-rich solution significantly outperforms inside the converging–diverging tube in terms of heat transfer and mass transfer. At the heating temperature of 108 °C, liquid film flow rate of 0.005 kg/s, sulfur concentration of 0.06 mol/L, aluminum concentration of 20 g/L, and basicity of 20%, the SO2 desorption efficiency inside the converging–diverging tube could reach a high level 94.2%, compared with only 83.7% inside the smooth tube. Moreover, correlations were obtained to predict the heat and mass transfer coefficients.

A comprehensive numerical study on the subcooled falling film heat transfer on a horizontal smooth tube

The effects of film flow rate, heat flux, inlet liquid temperature, tube diameter and liquid distributor height on subcooled falling film heat transfer outside a horizontal smooth tube are numerically studied, and a heat transfer correlation based on the current data is developed. Comparisons between the predicted results and the published experimental data in the literature are also conducted. The calculation ranges are: film flow rate from 0.025 to 0.284 kg m−1 s−1, heat flux from 1.0 to 100 kW m−2, inlet liquid temperature from 2 to 104 °C, tube diameter from 6.35 to 50.8 mm and liquid distributor height from 3.0 to 50.8 mm. The results indicate that: (1) the numerical results of the local heat transfer coefficient are in good agreement with the experimental data in the literature; (2) the surface tension plays an important role in the calculations of heat transfer in two stagnation zones, (3) the heat transfer coefficient shows four distinct zones along with peripheral angle: stagnation zone, impingement zone, thermal layer development zone and departure zone; (4) the heat transfer coefficient increases with increase in film flow rate, tube diameter or liquid distributor height, while keeps constant with increasing heat flux; (5) the correlation predicts 92% of the total 141 calculated data with deviations within ±10%, and predicts 78% of 284 data available in literature with deviations within ±30%.

Experimental study of the local and average falling film evaporation coefficients in a horizontal enhanced tube bundle using R134a

The falling film evaporation with nucleate boiling in a horizontal enhanced tube bundle arrayed in a vertical column is experimentally investigated. And the influences of film flow rate, heat flux, saturation temperature and bundle depth on the local and average heat transfer coefficients are discussed. The tests are performed at saturation temperatures of 6, 10 and 16°C, film Reynolds number from 254 to 3700 and heat flux from 20 to 80kWm−2. To simulate the actual condition of the falling film evaporator, the passages of liquid/vapor flows are constructed using quartz glass panels and dummy tubes. The results indicate that: the film flow rate, heat flux, saturation temperature and bundle depth have significant effects on the falling film evaporation in the tube bundle; as the film flow rate decreases, the local heat transfer coefficients firstly keep at a plateau and then decrease rapidly and the average heat transfer coefficients firstly keep at a quasi-plateau and then drops sharply; the falling film heat transfer performance becomes worse with increase in heat flux, but becomes better with increase in saturation temperature.