| 1. |
- Gourdon, Mathias, 1980, et al.
(författare)
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Performance evaluation of falling film evaporators in the dairy industry
- 2017
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Ingår i: Food and Bioproducts Processing: Transactions of the Institution of of Chemical Engineers, Part C. - : Elsevier BV. - 1744-3571 .- 0960-3085. ; 101, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- Falling film evaporators constitute an essential part of dairy powder production facilities. Evaporation belongs to the thermal separation processes; consequently, the evaporation plant is fundamentally energy intensive. Hence, improvements to its operation can have a significant impact on the energy usage. A simulation tool that is based on experimental correlations developed at conditions similar to the industrial scale is presented to provide insight into the fundamental mechanisms occurring along the heat transfer surface of industrial evaporators. The model includes the complex interaction between the produced vapor and the liquid flow. The results demonstrate that the pressure drop, through its influence on the saturation temperature, is of high importance in the performance of evaporators. The tool can be used to investigate different design configurations, and it exemplifies how a change in the tube diameter for the same temperature difference and length of the surface will affect the maximum heat load per area as well as the pressure drop.
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| 2. |
- Mura, Ernesto, 1974, et al.
(författare)
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Effect of Co-flowing Vapor during Vertical Falling-film Evaporation
- 2016
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Ingår i: Experimental Heat Transfer. - : Informa UK Limited. - 0891-6152 .- 1521-0480. ; 29:4, s. 561-575
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Mura, Ernesto, 1974, et al.
(författare)
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Experimental Study of the Heat Transfer in a Falling Film Evaporator: Influence of the Co-Flowing Vapor
- 2014
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Ingår i: 10th International Conference on Heat Transfert, Fluid Mechanics and Thermodynamics - HEFAT 2014. 14-16July 2014. Orlando, Florida, USA.. ; , s. 1938-1944
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Konferensbidrag (refereegranskat)abstract
- A large number of industrial processes are based on the concentration of liquid products by means of falling-film evaporation. In the dehydration of dairy products, concentrating a fluid by evaporating represents one of the most important steps of the whole drying process. Among the advantages of this technology is that it is possible to operate within small temperature differences which results in low heat consumption. In this sense, it is necessary to increase the amount of removed water during the falling-film evaporation to reduce the energy cost of the overall process. However, reducing the fraction of the solvent leads to an increase in viscosity of the product which can show non-Newtonian features. This aspect significantly affects the heat transfer, that is to say, the higher the solid content, the lower the heat transfer coefficient. One of the possible solutions to this drawback consists in drawing maximum benefit from the interaction between the fluid film and the co-flow of the gaseous phase resulting from the evaporation process. Unfortunately, accurate studies of the effect of co-flow on evaporative falling films are very rare and difficult to perform because of the high costs of the implementation of a suitable experimental apparatus.In this work, the experimental study of the influence of the co-flow on the heat transfer coefficient is presented as a function of both the solid content and the mass flow rate of the feed. The experimental set-up, consisting in a unique industrial pilot scale evaporator, provides the possibility to obtain results useful for realistic industrial conditions. Tests were conducted with varying dry solid content from 10 to 50%.The results show that the co-flow has the effect to decrease the potential for fouling/poor wetting. Above this, the influence on the heat transfer is not as large as expected because of the dominant influence of the viscosity.
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| 4. |
- Mura, Ernesto, 1974, et al.
(författare)
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Interfacial shear stress, heat transfer and bubble appearance in falling film evaporation
- 2016
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777. ; 79, s. 57-64
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Tidskriftsartikel (refereegranskat)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
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| 5. |
- Mura, Ernesto, 1974, et al.
(författare)
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Pressure drop in dairy evaporators: Experimental study and friction factor modelling
- 2017
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Ingår i: Journal of Food Engineering. - : Elsevier BV. - 0260-8774. ; 195, s. 128-136
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Tidskriftsartikel (refereegranskat)abstract
- The pressure drop that occurs during the falling film evaporation of dairy products is related to the downward co-flowing vapour and directly affects the saturation temperature of the product, resulting in a non-constant thermal driving force of the process along the evaporator. Frictional forces are the major contributor to the pressure drop, and the friction factor is a crucial parameter in reliably estimating the pressure drop. In the present study, the absolute vapour flow pressure losses during falling film evaporation of dairy products were measured using an experimental internal tube evaporator set-up. To simulate real industrial conditions, experiments were conducted by varying the co-flow inlet velocity (from 0 to 37 ms(-1)) over a wide range of product dry solid content DC (from DC = 0%-50%). Results obtained at DC = 0% show that the experimental approach is consistent when measurements are compared to the well-known Wallis correlation. A large number of experimental data has been obtained for DC between 13 and 40% for which the pressure losses have a strong dependence from the co-flowing vapour rate; in some specific cases, the influence of the surface bubbling phenomena has been put in evidence. The presented results, have been used to calibrate a new accurate correlation for the friction factor (4f(tv)) coefficient showing a squared residual of R-2 = 0.93.
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| 6. |
- Tarlet, D., et al.
(författare)
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Distribution of thermal energy of child-droplets issued from an optimal micro-explosion
- 2014
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 77, s. 1043-1054
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Tidskriftsartikel (refereegranskat)abstract
- The micro-explosion phenomenon is involved in emulsified fuel droplets placed in a hot atmosphere, such as spray combustion. Droplets of water-in-sunflower oil emulsion are used, since they are representative of a class of emulsions used in practical applications of biofuels. Once the micro-explosion is triggered after a short delay, the rapid (<= 1 ms) vaporization of the inside water droplets and the subsequent disintegration of the emulsion droplet blow the fragmented droplets away. These fragmented droplets are called "child-droplets", and they are too small and fast for an on-the-fly infra-red imaging thermal characterization. The present study focuses on the thermal reaction of a thin plate when impacted by them. Thorough and detailed tests are carried out, to make sure that the plate and the acquisition system are collecting a data that is actually representative of the child-droplets thermal energy. A quantitative post-processing is applied to the transient temperature field on the plate. It leads to the thermal energy of the whole plate, and of representative samples of individual child-droplets. The results show that their thermal energy is governed by a log-normal distribution.
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