Warmtewisselaars met gekromde buizen

Ultra High Temperature (UHT) sterilisation is a commonly applied technique to preserve liquid food products. Stork Food & Dairy Systems has marketed coiled tubular UHT-sterilisers. For viscous and especially for gelatinising foods (e.g. custard and pudding) spiral sterilisers bring superior performance. Heat transfer greatly increases and required temperatures are attained faster, thus reducing processing time. Coiled sterilisers are therefore shorter and more compact, minimising the loss of quality factors due to the heat treatment. Finally, gelatinisation occurs rapidly and uniformly, and de reduced thermo-mechanical stresses enable a potentially lower amount of starch needed to obtain a target consistenc

Membrane emulsification with vibrating membranes: A numerical study

Membrane emulsification of oil in water may be enhanced by mechanically exciting the membrane, thereby enabling the formation of smaller droplets of a narrower size distribution, combined with higher specific production rate. To evaluate this potential, a force balance model was developed that includes the additional forces induced by the transversal membrane movement. This model yielded the ranges of interest of the excitation amplitude A and frequency f. In these ranges of interest, 3D transient simulations were carried out to predict the 3D droplet formation and detachment on a single pore under constant cross-flow. For conditions without membrane excitation, the force balance model agreed satisfactorily with experimental results reported in the literature and with the current 3D computations. The model also predicts a non-linear dependence of the droplet size on the pore diameter. However, under membrane excitation the extended force balance model does not seem to give reliable results. This is probably due to the simplifications in this model, which does not include the effects of the dispersed phase flux and viscosity, and the strongly non-spherical droplet geometry upon detachment. Moreover, for large vibration-induced forces coalescence occurred in the 3D model, which leads to much larger droplets. Thus, fully transient 3D CFD simulations appear to be required for reliable predictions. Ideally these should account for surfactant dynamics and a variable surface tension coefficient. The simulations show that membrane excitation potentially has a strong effect on the average droplet size in membrane emulsification, but that successful exploitation will require careful design of membrane and process. First estimates seem to indicate that systems with lower excitation frequency and larger excitation amplitude may perform better, but this will require experimental verification

Starch gelatinization in coiled heaters

A gelatinizing model food derived from a 5% wt./wt. cross-linked waxy maize starch suspension was simulated in coiled heaters to assess the impact of centrifugal forces on flow and heat transfer. For four coil diams. (D = 0.25, 1, 2.5, and ... m) and three flow rates (.hivin.w = 0.5, 1, and 2 m/s), heat transfer, viscous development, and the severity of channeling were evaluated. Increasing curvature proved to suppress channeling as a result of more uniform heating and gelatinization. The max. attainable viscosity was also higher, implying a lower starch consumption for a target viscosity. Higher flow rates necessitated longer heaters, and the max. viscosity decreased. Moderate product velocities are therefore recommende

Aseptic processing of liquid foods containing solid particles

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Optimising the thermal processing of liquids containing solid particulates

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Experimental and theoretical study of the flow in the volute of a low specific-speed pump

The flow in the volute of a low specific-speed pump was studied both experimentally and numerically near its design point. Measurements included time-averaged values of velocity and static pressure at a large number of locations in the volute. The numerical computations were based on the unsteady three-dimensional potential flow model for the core flow. Viscous losses were quantified using additional models that use the potential flow as input. It is shown that near the design point of this pump, the core flow behaves like a potential flow, provided that no boundary layer separation occurs. Explanations are given for the presence of local deviations due to secondary flow. These local deviations do not influence the overall potential flow characteristics significantly