摘要:

Advances in dehydration techniques and development of novel drying methods have in recentyears enabled the preparation of a wide range of dehydrated products and convenience foods from fruits and vegetables meeting the quality, stability and functional requirements coupled with economy. This has been made possible by the sustained experimental studies over the years to understand the theoretical and fundamental aspects of the process and optimisation of the techniques to achieve a favourable combination of cost and quality. This paper reviews and highlights the developments in the dehydration of fruits and vegetables and their products during the last decade covering the oretical aspects and practical applications with major emphasis on techniques that have received the maximum attention.

ISSN:0737-3937    

DOI:10.1080/07373939208916413

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0737-3937    

DOI:10.1080/07373939208916411

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0737-3937    

DOI:10.1080/07373939208916412

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper presents a new contact heat transfer model for estimation of wallto-bed heat transfer rates based exclusively on information on particle flow andmixing within a stirred granular bed. The effects of solids flow ability, bedheight, blade rotational speed, size of the annular wall-to-blade clearance, vesseldiameter and aeration of the bed on the overall solids mixing patterns, particlerenewal rates and contact heat transfer in vessels agitated with flat paddles arepresented and discussed. The model is shown to yield satisfactory agreementWith expenrnental data.

ISSN:0737-3937    

DOI:10.1080/07373939208916414

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The extended thin film evaporation is analyzed during the constant drying rate period. The extended thin film is defined as the liquid film which the disjoining pressure dominates the fluid flow field and works as the driving force of replenishing the evaporating liquid. The results of the analysis show that the extended thin film evaporation can compensate the reduction of evaporation rate due to the increase of dry spots and keep the evaporation rate nearly constant. Experimental data in the literature are in good agreement with the results of this work. This implies that the extended thin film evaporation may be an important part of the mechanism for drying.

ISSN:0737-3937    

DOI:10.1080/07373939208916415

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The extent interline of evaporating region is analyzed for polar liquid film, with the disjoining pressure expressed by Pd= B ln(t) + A. An average effective evaporation is defined for this region and expressed as a simple equation. The results of analysis show that the average effective evaporation rate varies with the relative vapor pressure and so does the length of the interline evaporating region. The increase in relative vapor pressure will make the evaporation from the wetting film more significant.

ISSN:0737-3937    

DOI:10.1080/07373939208916416

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Stochastic analytical model was developed to describe the heat transfer in a thin layer of grain ventilated with ambient air. As an excitation to the drying system, a stochastic analytical model of ambient air temperature variations during the period of drying, based on a sine function, was used. Mean, correlation function, variance and the standard deviation were determined for air and grain temperature, both treated as random processes. The stochastic model of air temperature variation was fitted to the observed historical data. The effect of the standard deviation of air temperature of the three different climates (Canadian in Winnipeg, Polish in Poman and English in Weddington) on the standard deviation of grain temperature is shown.

ISSN:0737-3937    

DOI:10.1080/07373939208916417

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Cylinder-to-bed heat transfer in aerated vibrated beds was studied experimentally. Beds of various model particles were vibrated in the vertical direction with a frequency varying from 0–25 Hz and half-amplitude from 0–4 mm. Alumina and molecular sieve particles of sizes ranging from 27 μm to 1400 μm were used as the model particles. A single-orifice bottom plate was used to supply the air flow at rates varying from 0 to the minimum fluidizing velocity. For small-panicle beds which display resonant behaviour, the cylinder-to bed heat transfer coefficient remains close to the packed bed value as the frequency is increased. Close to the resonant frequency, it increases rapidly to reach a maximum at the resonant frequency. Thereafter, h decreases only gradually with further increase of frequency. The cylinder-to-bed heat transfer coefficients at resonance are much higher than those in packed beds (up to 19 times). The high heat transfer rates are due to particle mobility which reaches a maximum at the resonant point. Surface coverage is greatly affected by both the resonant frequency and aeration rates. It affects the heat transfer rate but is not rate limiting even at low bed bulk densities and surface particle coverage.

ISSN:0737-3937    

DOI:10.1080/07373939208916418

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Beds of alumina particles (dp= 27 μm and 100 μm) were vibrated in the vertical direction at frequencies frdm 0–25 Hz and half-amplitudes from 0–4 mm. Air flow rate through a single-hole or multiple-holes bottom plate varied from 0 to 2 times the minimum fluidizing velocity. The contact heat transfer coefficients at resonance are much higher than those in packed beds and in vibrated fluidized beds (up to 1.2 times). The high heat transfer rates are due to enhanced particle mobility which reaches a maximum at the resonant point. A simple semi-empirical correlation is developed for contact heat transfer which is based on particle mobility. Heat transfer coefficients are correlated with frequency using amplitude, bed height and particle size as adjustable parameters. The correlation is found explain the observed trends in the data reasonably well over the range of parameters studied.

ISSN:0737-3937    

DOI:10.1080/07373939208916419

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effective thermal conductivity of a number of paper sheets was measured at high temperatures and various water contents. This was done by enclosing a pile of sheets between brass plates which were subjected to a sinussoidally varying temperature. The temperature variations at two positions in the pile were measured using thermocouples. From amplitude ratio and phase shift the conductivity was calculated. At low water contents, conductivity was proportional to the density of the paper and independent on temperature. At intermediate water contents, the conductivity increased markedly with temperature, attaining values higher than for pure water.

ISSN:0737-3937    

DOI:10.1080/07373939208916420

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor