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Mathias Gourdon - One of the best experts on this subject based on the ideXlab platform.

  • interfacial shear stress heat transfer and bubble appearance in Falling Film Evaporation
    Experimental Thermal and Fluid Science, 2016
    Co-Authors: Ernesto Mura, Mathias Gourdon
    Abstract:

    In the Falling Film Evaporation of dairy products, the phase change process occurs via two major phenomena: surface convective Evaporation and boiling Evaporation. Previous studies have shown that under certain conditions, the heat transfer mechanism can be greatly improved when the Evaporation is dominated by the presence of bubbles or foam clusters. In the present work, the influence of the surface bubbling phenomenon on the heat transfer coefficient has been studied. The effect of the co-flowing vapor rate inside the evaporative tube has been experimentally related to the presence of the surface bubbles for dairy products characterized by different dry solid contents (DC = 0%, 13%, 30%, 40%, 51%). The results show that at low dry solid contents (DC <= 30%), the co-flowing vapor negatively affects the heat transfer when the structure and the dimension of the bubbles are modified or inhibited by the action of the co-flow. At high dry solid contents (DC = 40%, 51%), the sweeping effect of the co-flow plays a positive role on the heat transfer coefficient by promoting a more even circumferential distribution of the Falling Film and by increasing its velocity.

  • effect of co flowing vapor during vertical Falling Film Evaporation
    Experimental Heat Transfer, 2016
    Co-Authors: Ernesto Mura, Fredrik Innings, A Jongsma, Lennart Vamling, Anders Akesjo, Mathias Gourdon
    Abstract:

    A large number of industrial processes use Falling-Film Evaporation to concentrate liquid products. This technology allows for small temperature differences during operation and is often significantly more energy efficient than other techniques. When processing dairy products, a reduction in the solvent fraction results in an increased product viscosity and may thus result in non-Newtonian features. The interaction between a co-flowing vapor that is produced during the Evaporation process and the Falling Film is an important feature of the process. Few studies have accurately studied the effect of co-flow on evaporative Falling Films at high solid contents. In this work, an experimental study of the influence of co-flowing vapor on the heat transfer coefficient for a dairy product is presented as a function of both the solid content (from 10 to 50%) and the mass flow rate of the feed. The experimental set-up, consisting of a unique industrial pilot-scale evaporator, provides the possibility of obtaining results useful for realistic industrial conditions. An analytical approach that enables the simultaneous evaluation of heat transfer in every experimental condition, e.g., for Newtonian or non-Newtonian fluids and with or without co-flowing vapors, is presented.

  • Heat transfer for Falling Film Evaporation of industrially relevant fluids up to very high Prandtl numbers
    Heat and Mass Transfer, 2016
    Co-Authors: Mathias Gourdon, Fredrik Innings, Erik Karlsson, Alfred Jongsma, Lennart Vamling
    Abstract:

    In many industrial applications, Falling Film Evaporation is an attractive technique for solvent removal due to high heat transfer and low residence times. Examples are the powder production in the dairy industry and in kraft pulp production process to remove water from so called black liquor. Common for both applications is that the fluids exhibit high viscosities in industrial practice. In this paper, results from experimental studies on both black liquor and a dairy product are reported for Prandtl numbers up to 800. The results are compared with several existing correlation in literature, and the need for a modified correlation is recognized especially to cover higher Prandtl-numbers. The following correlation for the turbulent flow region with 3 

  • qualitative investigation of the flow behaviour during Falling Film Evaporation of a dairy product
    Experimental Thermal and Fluid Science, 2015
    Co-Authors: Mathias Gourdon, Fredrik Innings, A Jongsma, Lennart Vamling
    Abstract:

    Falling Film Evaporation is an important technology in the dairy industry for producing powders. In this paper, flow details of liquid Falling Films have qualitatively been investigated using a pilot evaporator, and in particular using a high-speed camera. Variations with different dry solids contents, flow rates and driving temperature differences were investigated. The flow characteristics were seen to be considerably affected by all three variables. Two of the main observations were the formation of bubbles under evaporative conditions and that the flow, bubble formation and evaporative heat transfer coefficient was observed to be heat flux dependent.

  • heat transfer for Falling Film Evaporation of black liquor up to very high prandtl numbers
    International Journal of Heat and Mass Transfer, 2013
    Co-Authors: Erik Karlsson, Mathias Gourdon, Lars Olausson, Lennart Vamling
    Abstract:

    In this study, heat transfer measurements for Falling Film Evaporation were performed up to very high Prandtl numbers, from 10 to 2800. Black liquor, a residual stream from the pulping process, was used as an example of a fluid that can have very high Prandtl numbers. To overcome the problem with fouling, which can be severe for black liquor due to crystal formation at higher concentrations, a new measurement method has been successfully developed which enables reliable measurements. Viscosity was clearly the most important parameter for the heat transfer coefficient, while the specific mass flow rate had a weak and positive dependence. The results were compared with existing heat transfer correlations, but none of them were able to capture the heat transfer behavior of black liquor throughout the whole range of Prandtl numbers.

Ziqian Chen - One of the best experts on this subject based on the ideXlab platform.

  • study on a multi effects regeneration and integral type solar desalination unit with Falling Film Evaporation and condensation processes
    Solar Energy, 2006
    Co-Authors: Hongfei Zheng, Yinjun Yang, Ziqian Chen
    Abstract:

    Based on the analysis of the mechanism of Falling Film Evaporation and condensation, a new solar desalination unit with three effects regeneration was designed. The performance of the unit was tested through in-door experiments, using an electric heater as heat source. The results indicate that the unit has relatively high performance ratio because of a considerable fraction of the latent heat of condensation and the sensible heat of the warm condensate being successfully utilized three times to preheat and evaporate the feedstock. The unit has also excellent transient-state performance because of using the thin layer Evaporation and Falling Film condensation which are the most effective processes for heat and mass transfer. When the operation temperature is over 90 °C and the inner pressure is below 15 kPa, the performance ratio of the unit can reach about 2.35 and its yield ratio can reach about 135 kg/h. The main factors influencing the performance of the unit were researched and analyzed. The reasonable ranges of some parameters were presented.

Wenquan Tao - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of the Falling Film Evaporation coefficients of r290 in a horizontal enhanced tube array
    International Journal of Heat and Mass Transfer, 2020
    Co-Authors: Ibrahim Mostafa, Puhang Jin, Zhuo Zhang, Wenquan Tao
    Abstract:

    Abstract In this study, the Falling Film Evaporation heat transfers of R290 on an array composed of five enhancement horizontal tubes (groove tubes) are studied. The tests are performed at constant saturation temperatures 5.5 °C with change of heat flux from 10 to 40 kW/m2. The Film Reynolds number ranges from 200 to 2200 and the Film flow rate of refrigerant is between 100 and 660 kg/h. The results show that the Film flow rate and heat flux have significant effects on R290 Falling Film Evaporation heat transfer coefficients (HTCs) of the tubes in the tube array. With decreasing the Film flow rate on the five tubes the tube HTCs display two stages, a plateau stage and a sharp drop stage. The heat transfer coefficients firstly keep more or less constant at the plateau stage and then decreasing rapidly. At the same nominal Film Reynolds number the tube averaged heat transfer coefficients of tube No. 1 to tube No. 5 decrease in order of the increasing tube number from top to bottom of the array. The Falling Film Evaporation HTC of R290 on single enhanced tube is about 4.5 times of single smooth tube HTC, and the HTCs of the enhanced tube array is higher than single smooth tube by more than 2.5 times. In addition, the R290 HTCs of the tube array are higher than those of R134a for the same tube array in the plateau region by about 25%. It is found that at high heat flux of 30–40 kW/m2, the heat transfer coefficient variation with Film Reynolds number of the lower enhanced tubes in the tube array exhibits severe undulating characteristics.

  • Falling Film Evaporation in a triangular tube bundle under the influence of cross vapor stream
    International Journal of Refrigeration-revue Internationale Du Froid, 2020
    Co-Authors: Chuangyao Zhao, Puhang Jin, Jufang Fan, Shun Yoshioka, Wenquan Tao
    Abstract:

    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.

  • experimental study of Falling Film Evaporation in tube bundles of doubly enhanced horizontal tubes
    Applied Thermal Engineering, 2020
    Co-Authors: Puhang Jin, Chuangyao Zhao, Ibrahim Mostafa, Zhuo Zhang, Wenquan Tao
    Abstract:

    Abstract Falling Film Evaporation (FFE) involves complicated physical phenomena and mechanisms such as wavy liquid Film, bubbly flow, capillary-driven Evaporation and nucleate boiling. FFE heat transfer characteristics in four doubly-enhanced tube bundles were investigated experimentally with R134a. For single tube, heat transfer coefficient (HTC) first increases then decreases with increase in heat flux, the turning points occurs around 20 kW/m2. Tubes with different positions in tube bundle own similar HTCs when tested individually. In tube bundle, with decreasing Film Reynolds number (ReΓ), HTC firstly keeps a quasi-plateau stage (increasing or keeping constant for upper tubes, decreasing for lower tubes), then after a certain threshold Film Reynolds number, HTC decreases sharply with ReΓ. At lower heat fluxes (10 kW/m2 and 20 kW/m2), tubes with different positions exhibit similar HTCs and threshold ReΓ. At higher heat fluxes (30 kW/m2 and 40 kW/m2), bottom tubes own much smaller HTCs and larger threshold ReΓ than upper ones due to partial dryout occurrence. The tube bundle with top plate exhibits higher HTCs and lower threshold ReΓ than those of the open-ended tube bundle indicating that counter-current vapor flow can deteriorate the heat transfer of FFE. Effect of heat flux on the bundle-averaged HTC increases with tube pitch.

  • heat transfer correlations of refrigerant Falling Film Evaporation on a single horizontal smooth tube
    International Journal of Heat and Mass Transfer, 2019
    Co-Authors: Puhang Jin, Chuangyao Zhao, Ibrahim Mostafa, Zhuo Zhang, Wenquan Tao
    Abstract:

    Abstract 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%.

  • Effect of downward vapor stream on Falling Film Evaporation of R134a in a tube bundle
    International Journal of Refrigeration-revue Internationale Du Froid, 2018
    Co-Authors: Chuangyao Zhao, Puhang Jin, Shun Yoshioka, Wenquan Tao
    Abstract:

    Abstract 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.

Hongfei Zheng - One of the best experts on this subject based on the ideXlab platform.

  • study on a multi effects regeneration and integral type solar desalination unit with Falling Film Evaporation and condensation processes
    Solar Energy, 2006
    Co-Authors: Hongfei Zheng, Yinjun Yang, Ziqian Chen
    Abstract:

    Based on the analysis of the mechanism of Falling Film Evaporation and condensation, a new solar desalination unit with three effects regeneration was designed. The performance of the unit was tested through in-door experiments, using an electric heater as heat source. The results indicate that the unit has relatively high performance ratio because of a considerable fraction of the latent heat of condensation and the sensible heat of the warm condensate being successfully utilized three times to preheat and evaporate the feedstock. The unit has also excellent transient-state performance because of using the thin layer Evaporation and Falling Film condensation which are the most effective processes for heat and mass transfer. When the operation temperature is over 90 °C and the inner pressure is below 15 kPa, the performance ratio of the unit can reach about 2.35 and its yield ratio can reach about 135 kg/h. The main factors influencing the performance of the unit were researched and analyzed. The reasonable ranges of some parameters were presented.

  • experimental study on a horizontal tube Falling Film Evaporation and closed circulation solar desalination system
    Renewable Energy, 2003
    Co-Authors: Lianying Zhang, Hongfei Zheng, Yuyuan Wu
    Abstract:

    A specifically designed solar desalinization system with a solar collector (about 2.01 m2 in area) has been developed and tested under practical weather conditions. In this system, a considerable fraction of the latent and sensible heat is successfully recycled and utilized for preheating the feedstock and recycling air via a condensation cavity and heat exchangers. The thermal performance of the system is greatly improved because of the Falling Film Evaporation technology used. As a result, the yield is about two to three times more than that of a conventional single basin type solar still under the same conditions. The transient-state performance of the system, the relationships with the solar radiation, the operating temperature, the feedstock flow rate and the productivity are presented. Other factors influencing the freshwater are also discussed.

Chuangyao Zhao - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of Falling Film Evaporation in tube bundles of doubly enhanced horizontal tubes
    Applied Thermal Engineering, 2020
    Co-Authors: Puhang Jin, Chuangyao Zhao, Ibrahim Mostafa, Zhuo Zhang, Wenquan Tao
    Abstract:

    Abstract Falling Film Evaporation (FFE) involves complicated physical phenomena and mechanisms such as wavy liquid Film, bubbly flow, capillary-driven Evaporation and nucleate boiling. FFE heat transfer characteristics in four doubly-enhanced tube bundles were investigated experimentally with R134a. For single tube, heat transfer coefficient (HTC) first increases then decreases with increase in heat flux, the turning points occurs around 20 kW/m2. Tubes with different positions in tube bundle own similar HTCs when tested individually. In tube bundle, with decreasing Film Reynolds number (ReΓ), HTC firstly keeps a quasi-plateau stage (increasing or keeping constant for upper tubes, decreasing for lower tubes), then after a certain threshold Film Reynolds number, HTC decreases sharply with ReΓ. At lower heat fluxes (10 kW/m2 and 20 kW/m2), tubes with different positions exhibit similar HTCs and threshold ReΓ. At higher heat fluxes (30 kW/m2 and 40 kW/m2), bottom tubes own much smaller HTCs and larger threshold ReΓ than upper ones due to partial dryout occurrence. The tube bundle with top plate exhibits higher HTCs and lower threshold ReΓ than those of the open-ended tube bundle indicating that counter-current vapor flow can deteriorate the heat transfer of FFE. Effect of heat flux on the bundle-averaged HTC increases with tube pitch.

  • Falling Film Evaporation in a triangular tube bundle under the influence of cross vapor stream
    International Journal of Refrigeration-revue Internationale Du Froid, 2020
    Co-Authors: Chuangyao Zhao, Puhang Jin, Jufang Fan, Shun Yoshioka, Wenquan Tao
    Abstract:

    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.

  • heat transfer correlations of refrigerant Falling Film Evaporation on a single horizontal smooth tube
    International Journal of Heat and Mass Transfer, 2019
    Co-Authors: Puhang Jin, Chuangyao Zhao, Ibrahim Mostafa, Zhuo Zhang, Wenquan Tao
    Abstract:

    Abstract 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%.

  • Falling Film Evaporation and nucleate pool boiling heat transfer of R134a on the same enhanced tube
    Applied Thermal Engineering, 2019
    Co-Authors: Wentao Ji, Chuangyao Zhao, Er-tao Zhao, Hu Zhang
    Abstract:

    Abstract Falling Film Evaporation and pool boiling of R134a outside a typical reentrant enhanced tube was investigated with an experimental approach. Experimental data from literature with other refrigerants were also compared. The saturation temperature was 11 °C. It was found that the overall heat transfer coefficient for the enhanced tube was as much as 3 times higher than smooth tube. Shell-side Falling Film Evaporation heat transfer coefficient increased by a factor of 2.1–4.9. Pool boiling yielded a higher heat transfer coefficient at higher heat flux for the same enhanced tube. The dependence of Falling Film Evaporation heat transfer coefficient on the heat flux was also different from pool boiling for the same tube. Although the bubbles in pool boiling were pushed up by buoyancy and in Falling Film evaporating were driven by the flow of Films, the transmission of energy were both dominated by the phase change heat transfer. The contribution of forced convection to Falling Film Evaporation heat transfer coefficient is weak compared with phase change heat transfer.

  • cross vapor stream effect on Falling Film Evaporation in horizontal tube bundle using r134a
    Heat Transfer Engineering, 2018
    Co-Authors: Chuangyao Zhao, Wentao Ji
    Abstract:

    AbstractThe Falling Film Evaporation of R134a with nucleate boiling outside a triangular-pitch (2-3-2-3) tube bundle is experimentally investigated, and the effects of saturation temperature, Film flow rate and heat flux on heat transfer performance are studied. To study the effect of cross vapor stream on the Falling Film Evaporation, a novel test section is designed, including the tube bundle, liquid and extra vapor distributors. The measurements without extra vapor are conducted at the saturation temperature of 6, 10 and 16°C, Film Reynolds number of 220 to 2650, and heat flux of 20 to 60 kWm−2. Cross vapor stream effect experiments are operated at three heat fluxes 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 smallest clearance in the tube bundle varies from 0 to 2.4 ms−1. The results indicate that: Film flow rate, heat flux and saturation temperature significantly influence the heat transfer; the cross vapor stream either promote or inhibit th...