Models for the electrical heating of solid-liquid food mixtures

Zhang, L.; Fryer, P.J.

doi:10.1016/0009-2509(93)80132-a

Cited by 83 publications

(40 citation statements)

References 8 publications

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“…Despite this, Zhang and Fryer (1993) demonstrate that significant quality loss can still accumulate during cooling. It is thus vital to study the whole process.…”

Section: Food Sterilizationmentioning

confidence: 87%

“…It is assumed that in each section of the tube, heat generation rates in the solid and liquid, the temperatures of the phases, and velocities of the phases are uniform and known. Fryer et al (1993) show that uniform heating in the liquid is possible, and Zhang and Fryer (1993) show that a rotating particle can heat uniformly.…”

Section: Electrical Heating Modelmentioning

confidence: 98%

“…The current paths around objects may be complex, as demonstrated by de Alwis et al (1989) (for spheres) and de Alwis and Fryer (1992) (for more complex shapes); Zhang and Fryer (1994) demonstrate that circuit analysis models can be inaccurate in some situations. Zhang and Fryer (1993) describe a model which assumes that the food mixture is homogeneous, such that sections of the fluid can be modeled as representative of the whole. If the distribution of particles in the liquid is uniform, the system can be divided into a number of 'unit cells,' each containing a number of particles.…”

Section: Solution Of Laplace's Equation For Heat Generation Ratesmentioning

confidence: 99%

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Food sterilization by electrical heating: Sensitivity to process parameters

Zhang

Fryer

1994

AIChE Journal

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Food SterilizationThe aim of food sterilization is to produce a sterile product of the highest possible quality. The classical method is canning, in which the product is sealed and then processed until it has reached the correct level of sterility. This may result in a lowquality product; the kinetics of sterilization and quality loss reactions are such that a better product is obtained by heating to higher temperatures for shorter times. This is best done in a continuous process with three sections: (i) a heating section in which product is first heated to the required temperature; (ii) a holding section in which it is held at temperature long enough to ensure sterility; and (iii) a cooling section prior to packaging. The holding section is generally a horizontal or slightly inclined tube.Continuous processes are capable of producing a higherquality product than canning. It is possible to process liquids, using forced convective heat transfer, at much higher heating and cooling rates, on the order of l"C/s, than is possible in processes which rely on thermal conduction or natural convection in the can. A number of commercial food sterilization processes involve the transport and heating of solid-liquid food mixtures of high solids fractions (Holdsworth, 1993). These flows can consist of up to 50-60% solids, particle diameters up to 25 mm in diameter, and carrier fluids which are generally non-Newtonian. Fluid velocities are restricted by the requirement to cause as little damage as possible to the mixture. It is difficult to process solid-liquid mixtures rapidly as solids heating is thermal-conduction-controlled; however, new volumetric heating technologies, such as microwave (Ayappa et al., 1991) and electrical (ohmic) heating (Biss et a]., 1989; Parrott, 1992) allow solids to be heated at the same rates as liquids.Volumetric processes potentially remove heat-transfer limitations on processing particles during the heating stage. Despite this, Zhang and Fryer (1993) demonstrate that significant quality loss can still accumulate during cooling. It is thus vital to study the whole process. To design processes and confirm the sterility of the final product, the temperatures of solidliquid mixtures must be known. Little information is available on the heating rates of the particles and the liquid and of the flow patterns of the food mixture; the design of plant is thus largely empirical. Food will have a range of residence times in any flow situation, and so the process must be designed so that the fastest moving piece of fluid must be sterilized while the slowest moving part is not overcooked.The APV Baker ohmic heater forms the basis for the electrical heating system modeled here. As described by Parrott (1992), the heater consists of a vertical or near-vertical tube up to 10 m in length and 75 mm in diameter, containing a series of up to seven electrode housings, each containing a single cantilever electrode across the tube. Up to 3 ton/h of flood flow upward through the tube past the electrodes; current density ...

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“…Despite this, Zhang and Fryer (1993) demonstrate that significant quality loss can still accumulate during cooling. It is thus vital to study the whole process.…”

Section: Food Sterilizationmentioning

confidence: 87%

Section: Electrical Heating Modelmentioning

confidence: 98%

Section: Solution Of Laplace's Equation For Heat Generation Ratesmentioning

confidence: 99%

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Food sterilization by electrical heating: Sensitivity to process parameters

Zhang

Fryer

1994

AIChE Journal

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“…The problem was considered initially in [19] where the stability of models allowing for different types of flow is studied. More background on this type of process can be found in [5,4,9,20,22,24]. In [15] problem (1.1) is also studied and it is found that for f decreasing with for instance either f (s) = e −s or f (s) = (1 + s) −p , p > 1, satisfy (1.2).…”

Section: Introductionmentioning

confidence: 99%

Numerical Solution of a Nonlocal Problem Modelling Ohmic Heating of Foods

Nikolopoulos

2009

Comput. Methods Appl. Math.

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-An upwind and a Lax-Wendroff scheme are introduced for the solution of a one dimensional non-local problem modelling Ohmic heating of Foods. The schemes are studied regarding their consistency, stability and the rate of convergence for the cases that the problem attains a global solution in time. A high resolution scheme is also introduced and it is shown that it is total-variation-stable. Finally some numerical experiments are presented in support of the theoretical results.

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“…The controlling parameter is the electrical conductivity of the solid and liquid phases. More background of this process can be found in [1,2,3,7,8,9,10].…”

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confidence: 99%

Blow-up time estimates for a non-local reactive-convective problem modelling sterilization of food

Nikolopoulos¹,

Tzanetis²

2004

Nonlocal Elliptic and Parabolic Problems

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Abstract. We consider a non-local equation with initial and boundary conditions of the form2 , which models the temperature when an electric current flows through a moving material with negligible thermal conductivity and time-dependent velocity. The potential difference across the material is fixed but the electrical resistivity f (u) varies significantly with temperature. It is found that for f (u) decreasing with ∞ 0 f (s) ds < ∞, blow-up occurs if λ is too large for a steady state to exist or if the initial condition is large enough. On the other hand, if f (u) is decreasing with ∞ 0 f (s) ds = ∞, then it is proved that u(x, t) is a global-in-time and unbounded solution.

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Models for the electrical heating of solid-liquid food mixtures

Cited by 83 publications

References 8 publications

Food sterilization by electrical heating: Sensitivity to process parameters

Food sterilization by electrical heating: Sensitivity to process parameters

Numerical Solution of a Nonlocal Problem Modelling Ohmic Heating of Foods

Blow-up time estimates for a non-local reactive-convective problem modelling sterilization of food

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