| 1. |
- Ashar, Mohamed, 1979, et al.
(author)
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Single droplet breakup in a rotor-stator mixer
- 2018
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In: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 181, s. 186-198
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Journal article (peer-reviewed)abstract
- This study presents measurements of droplet transport inside a rotor-stator mixer under turbulent flow conditions and contributes to the understanding of the droplet breakup phenomenon. The measurements contain unique information on droplet breakup down to the limit of equilibrium droplet size. The experimental setup includes a custom-built rotor-stator mixer that provides optical access to the mixing region. High-speed camera imaging is used to study droplet stability and breakup due to turbulent inertial stress at different operating conditions. The analysis reveals when, where, and how the droplets break up inside the rotor-stator mixer. Analysis of the breakup location reveals that droplet breakup mainly occurs in the downstream region of the stator and inside the emanating jets. Prediction of the flow field and turbulent kinetic energy dissipation rate from CFD simulations explains the propensity of droplet breakup at different locations in the rotor-stator. It is found that both the average time for droplet-vortex interaction and the distribution increases with the size of mother droplets, and a model is proposed that explains the results fairly well. Measurement of the breakup probabilities reveals a monotonically increase from zero probability at a low We-number to approximately 50% probability at We > 4. The number of fragments formed upon breakage depend on how far the droplets are from equilibrium size and it is found that the probability for multiple fragmentation dominates even close to the equilibrium size.
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| 2. |
- Deshmukh, K. P., et al.
(author)
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Cleaning of simple cohesive soil layers in a radial flow cell
- 2022
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In: Food and Bioproducts Processing. - : Elsevier BV. - 0960-3085. ; 136, s. 84-96
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Journal article (peer-reviewed)abstract
- A radial flow cell (RFC, inlet tube radius 0.95 mm and gaps of 1–4.2 mm) was used to investigate the removal of two thin (80–230 µm thick) model soil layers from glass and 304 stainless steel substrates by the flow of water at 20 °C. Under the flow conditions employed (Reynolds numbers 200–1400), inertial effects give rise to recirculation zones and regions of high shear stress on the bottom, soiled plate. The soils were dried layers of (i) instant coffee and (ii) a domestic abrasive cleaning suspension comprising fine particulates in a soluble matrix. Cleaning data exhibited a constant local erosion rate which varied strongly with radial position. For both soils, cleaning involved the growth of a circular cleaned region and redeposition of particulate matter in a ring at locations close to the foot of the secondary recirculation zone predicted by 2D axisymmetric CFD simulations. Removal beyond this location was observed with the coffee layers, indicating that cleaning for this soil was controlled primarily by simple diffusion mechanisms. The effect of channel aspect ratio and flow rate on the location of recirculation zones and shear stress distributions was investigated. The local cleaning rate in these steady flows was not linked simply to local wall shear stress.
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| 3. |
- Gourdon, Mathias, 1980, et al.
(author)
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Heat transfer for falling film evaporation of industrially relevant fluids up to very high Prandtl numbers
- 2016
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In: Waerme-Stoffuebertrag Thermo-Fluid Dyn. - : Springer Science and Business Media LLC. - 0042-9929 .- 1432-1181. ; 52:2, s. 379-391
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Journal article (peer-reviewed)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
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| 4. |
- Gourdon, Mathias, 1980, et al.
(author)
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Qualitative investigation of the flow behaviour during falling film evaporation of a dairy product
- 2015
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In: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777. ; 60, s. 9-19
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Journal article (peer-reviewed)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.
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| 5. |
- Innings, F, et al.
(author)
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Visualization of the drop deformation and break-up process in a high pressure homogenizer
- 2005
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In: Chemical Engineering & Technology. - : Wiley. - 1521-4125 .- 0930-7516. ; 28:8, s. 882-891
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Journal article (peer-reviewed)abstract
- For the creation of sub-micron emulsions in fluids of low viscosity the high pressure homogenizer (HPH) is usually chosen. One way of obtaining deeper knowledge of exactly what happens in the active region is to visualize it. In this work, a drop deformation and break-up visualization system based on a modified Particle Image Velocimetry (PIV) system is described. The system reproduces the gap in a HPH and has been used with pressures up to 18 MPa and drops as small as 5 mu m. The optics of the system are analyzed taking into account limiting factors such as the lens resolving power, the focal depth, and the duration of the laser pulses. It is shown that it is possible to resolve drops down to a few mu m moving in excess of 100 m/s, and that the main limitations are the resolving power and in the focal depth of the objectives. Examples are shown from capillary drop creation and from the deformation and break-up of drops in a HPH. It can be concluded that in a HPH, the drops are only deformed to a limited extent in the inlet of the gap, and that all drop break-up occurs far downstream of the gap.
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| 6. |
- Malafronte, Loredana, 1986, et al.
(author)
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Exploring drying kinetics and morphology of commercial dairy powders
- 2015
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In: Journal of Food Engineering. - : Elsevier BV. - 0260-8774 .- 1873-5770. ; 158, s. 58-65
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Journal article (peer-reviewed)abstract
- Understanding the effect of the initial composition of a liquid feed on the spray drying process and morphology of powders is important in order to reduce the time and costs for process design, and ensure the desired properties of the final product. In this work, seven commercial dairy products with different fat content were selected. The effect of initial composition on drying time during single drop experiments was studied. The morphology of powder particles and the influence of morphology changes on the drying rate were investigated in order to assess the effect of fat content on the effective diffusivity of water in dairy products. Results show that fat content influences drying time and morphology of powder particles. The higher the fat content the longer the drying time and particles appear to be less shrivelled. Changes in morphology and the drying rate seem to be related. Two falling drying periods were observed for most of the products. During the first period the drops shrink spherically, while during the second period shrivelling occurs. The effective diffusivity of water shows that high fat contents lead to a lower diffusivity of water in the products.
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| 7. |
- Malafronte, Loredana, 1986, et al.
(author)
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Prediction of regions of coalescence and agglomeration along a spray dryer-Application to skim milk powder
- 2015
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In: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 104, s. 703-712
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Journal article (peer-reviewed)abstract
- Spray drying is a well-established method used in the food industry for production of powders, such as dry milk, coffee, tea, and soup. The operating conditions of spray dryers depend on the product and chamber design. Thus scaling up the process is complex, and simulation tools are needed to reduce time and cost, and to enhance quality of the final product. In this study a validated distributed-parameter model for predicting drying of single particles was combined with a CFD simulation model of an eight-meter pilot dryer to investigate drying kinetics of skim milk powders. A qualitative assessment of the effect of water diffusivity values on preconditions for agglomeration and a multi-scale analysis of coalescence and agglomeration regions were performed. Results showed that accurate water diffusivity values and sticky conditions have to be implemented when modelling spray drying to investigate preconditions for coalescence and agglomeration. The results also showed the need to simulate surface conditions of particles during spray drying to predict probable regions of coalescence and agglomeration. In conclusion, the applied methodology allows understanding of the stickiness ability of a product and size of the chamber. The methodology can be used to support preliminary design of spray dryers.
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| 8. |
- Mirzaei, Maryam, 1982, et al.
(author)
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Large Eddy Simulation of the flow and heat transfer in a half-corrugated channel with various wave amplitudes
- 2014
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 76, s. 432-446
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Journal article (peer-reviewed)abstract
- Large Eddy Simulation (LES) of turbulent flow and convective heattransfer over a half-corrugated channel is presented in this paper. Simulationsare performed for various ranges of the normalized wave amplitudes,AM = 0 − 0.15 (the ratio of wave height to wave length). The Reynoldsnumber based on the bulk velocity is chosen as Reb = 10 000 and thePrandtl number is Pr=0.71. A comparison between the DNS and LESresults of a plane channel (AM = 0) at Re = 395 is also performed.The obtained results indicate that the region of recirculating flow dependsstrongly on the wave amplitude. This study shows that the Nusseltnumber (Nu) increases by increasing the wave amplitude until a specificvalue then it remains approximately constant. The thermal performanceparameter (JF) is used as a measure for the heat transfer enhancementrelative to the pressure drop and it is found that the maximum values ofNu and JF appear at AM = 0.1, which hence correspond to the optimumvalue of the wave amplitude.
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| 9. |
- Mirzaei, Maryam, 1982, et al.
(author)
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The effect of corrugation on heat transfer and pressure drop in channel flow with different Prandtl numbers
- 2013
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In: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 66, s. 164-176
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Journal article (peer-reviewed)abstract
- Large Eddy Simulation and Direct Numerical Simulation are applied to study the turbulent flow field in a wavy channel at two Prandtl numbers, Pr = 0.71 and Pr = 3.5, and Reynolds number Re b = 10,000. The characteristics of the separated shear layer and the near wall recirculating zone are discussed in relation to the turbulent heat transfer. Special attention is paid to the behavior of the flow and thermal boundary layers and various turbulent characteristics and their effects on the distribution of the Nusselt number and friction coefficient in the separation and reattachment regions. The results indicate that the thickness of the thermal boundary layer rather than the turbulent fluctuations has a significant effect on the local variation of the averaged Nusselt number. The results are compared with Direct Numerical Simulation results of a plane channel at the same Reynolds number. © 2013 Elsevier Ltd. All rights reserved.
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| 10. |
- Mura, Ernesto, 1974, et al.
(author)
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Effect of Co-flowing Vapor during Vertical Falling-film Evaporation
- 2016
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In: Experimental Heat Transfer. - : Informa UK Limited. - 0891-6152 .- 1521-0480. ; 29:4, s. 561-575
-
Journal article (peer-reviewed)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.
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