摘要:

Residence time distributions (RTDs) of water as influenced by particle concentration and mutator speed (SSHE only) were investigated in a holding tube and a horizontal scraped surface heat exchanger (SSHE). Liquid mean residence times (LMRTs) were not significantly influenced by particle concentrations up to 30% in the holding tube. Variance, on the other hand, was significantly higher without particle loading, indicating a broader distribution. About 20% particle loading significantly reduced the LMRTs regardless of the mutator speed. In addition, an increase in the mutator speed significantly increased the variance regardless of the particle concentration, indicating a broader distribution. the variance in SSHE was not significantly influenced by the particle concentration, unlike the holding tube. the LMRTs calculated from volumetric flow rates were lower than those from pulse input experiments for both holding tube and SSHE.

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1995.tb00359.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The sizing of holding tubes for continuous sterilization of foods containing large particles is affected by the flow behavior of the suspensions. Velocities of carrier fluid and model food particles in holding tube flow were numerically simulated through an iterative solution of the Navier‐Stokes equations and particle dynamic equations in three dimensions. the Lagrangian approach was used to predict the individual particle trajectories under multiparticle tube flow. the physical domain included two straight tubes connected with a 180° bend. the system had an upward inclination of 1.194° (0.25 in./ft of straight run). the assumptions considered included Newtonian carrier, spherical and neutrally buoyant particles, and 10% v/v particle loading. the results indicate that the particles have a significant back‐influence on the fluid flow field. the 180° bend strongly affected both fluid and particle flow fields, which further reinforced the interaction of the two phases. the fastest particle velocities were less than the fluid streamline velocities passing through the particles' center. the radial positions of the particles on the cross section of the holding tube changed very little in the first straight section, but experienced a significant shifting in the bend and second straight‐tube sections due to secondary flow. the residence times of particles under secondary‐flow effect are therefore different from those obtained under straight tube

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1995.tb00360.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A semi‐analytical (concerning the particle temperature) semi‐numerical (concerning the fluid temperature) solution to the differential equations governing heat transfer to axially rotating liquid/particulate canned foods was obtained using Duhamel's theorem and a numerical 4th‐order Runge‐Kutta scheme. This solution avoids some of the shortcomings of earlier solutions such as the requirement for constant heating medium temperature, the need for empirical formulas, or the use of unrealistic assumptions regarding the fluid temperature. the agreement between the proposed solution and limiting case analytical results was very good. A maximum fluid temperature difference of less than 2C was momentarily observed at the beginning of heating; differences between particle surface temperatures were even smaller. Comparison between predicted values and experimental data from the literature showed good agreement only as far as the fluid temperature was concerned; particle surface temperatures deviated signif

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1995.tb00361.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Osmotic dehydration rates were determined for coconut over a range of osmotic solution concentration (40–70°B) and temperature (25–45C). A semi‐empirical relation for kinetics of osmotic dehydration has been proposed, which indicates the moisture diffusion as a function of concentration of osmotic solution and its temperature. Good agreement was observed between the observed and predicted values (correlation coefficient 0.90). the effective diffusion coefficients of water in coconut during osmotic dehydration were estimated and also the activation energy of the osmotic dehydration process of coconut was found as 1.75 × 104J/

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1995.tb00362.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A mathematical model was developed to predict the frequency distribution of steady‐state O2partial pressures in modified‐atmosphere packages of fresh and minimally processed fruits and vegetables. Variation in O2uptake was predicted to have relatively larger influence on the package O2distribution than variation in film permeability to O2. the model also predicted that the range of O2partial pressures in the packages would be larger for the products with lower K1/2(a constant in product O2uptake equation) values. the percent deviation of package O2partial pressures from [O2]medincreased with [O2]medup to about 3 kPa and gradually decreased thereafter. Package O2distribution was symmetrical at higher [O2]medbut became gradually asymmetrical with decreasing [O2]medfrom 6 kPa. the model was used to predict target [O2]medfor the design of modified‐atmosphere packages for different probability levels of having package O2being equal to or less than a minimum tolerable level of the pr

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1995.tb00363.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Drainage of curd is the separation of solid curd grains and whey, an essential process step in making cheese. It is difficult to model this process by use of current consolidation theories, mainly because of the considerable loss of whey by the curd grains themselves during the expulsion of whey from pores between the curd grains. As an alternative we have studied a model that takes the expression of a single curd grain as a starting point. By analyzing experimental results of a column filled with uniform curd grains drained in radial direction while being under axial external pressure, we study the question to which extent this model might be used to predict the change of porosity with time. It appeared that the model gives reasonable results at low external pressures. At high external pressures the model proves to be inadequate. In the intermediate pressure range the model predicts too fast an expression of the curd grains, although a liquid pressure gradient between the center and the outside of the curd column could not be detected. This suggests the existence of isolated pores, or a geometric limitation of the deformation of curd grains in a curd bed.

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1995.tb00364.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY