摘要:

A mathematical model for predicting three-dimensional, two-phase flow, heat and mass transfer inside fluidized-bed dryers has been developed. The model consists of the full set of partial-differential equations that describe the conservation of mass, momentum and energy for both phases inside the dryer, and is coupled with correlations concerning interphase momentum-, heat-, and mass-transfer.

ISSN:0737-3937    

DOI:10.1080/07373939708917295

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A non destructive method for surface strain measurements is proposed to quantify the wood drying quality during convective drying. This method uses a visible laser scan micrometer intercepting needles maintained vertical at the board surface with a special device, and then gives shrinkage values at several surface points. The results analysis is related to heal and mass transfer phenomena.

ISSN:0737-3937    

DOI:10.1080/07373939708917296

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Combined heat transfer and evaporation dynamics are analyzed during drying of a continuously moving, porous strip which is in direct contact with a heated plate. A transient, quasi-two-dimensional model of conjugate heat transfer between a hot massive externally /internally heated plate and wet porous strip moving along the plate is developed by accounting for evaporation dynamics. The model consists of four conjugate energy conservation equations with proper boundary/interface conditions which describe the heat transfer in four distinct zones (1-electrically or indirectly heated massive metal plate, 2-thin superheated vapor film resulting from vaporization of water in the porous strip that separates hot plate and porous strip, 3-dry region of the porous strip, and 4-wet region of the porous strip). The relevant dimensiouless parameters governing the problem are identified, and results of parametric calculations are reported to gain fundamental understanding of the process.

ISSN:0737-3937    

DOI:10.1080/07373939708917297

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We investigate experimentally the behaviour of the receding evaporation front during the drying of food products by measuring the temperature distribution profile within the potato slab. The effect of key process parameters on the receding speed of this evaporation front is investigated. We show that the square root of the drying time varies linearly with the transient position of the front. Also, the receding velocity of the front is seen to be related to the drying rate of the product as the front decelerates inward to the center of the material.

ISSN:0737-3937    

DOI:10.1080/07373939708917298

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Dryer design requires food properties, drying rate and mass-heat transfer coefficients. These values change continuously during drying due to changes in food fractions, particularly the water fraction. The high energy demand and costs allied to inefficient devices, creates a great need for new processing equipment. Along these guide-lines, several heat pump drying research projects were established at the Norwegian University of Science and Technology. The heat pump dryer provides high quality final product as its drying conditions can be controlled. Its efficiency and non-polluting operation come from closed air-refrigerant circuits and from its ability to fully recover the latent heat of moist air as it exits the drying chamber. Most of the above features are quite the opposite of the conventional dryer characteristics. Several experiments were made on heat pump drying of fruits and roots at temperatures from -22.5 to 40°C to obtain data and correlations on thermophysical properties, specific enthalpy and rehydration. Also, tests were done on drying rate, moisture content, drying constant, effective mass diffusivity and heat and mass transfer equations. The next important phase is the development of a simulation model to predict the performance and characteristics of the heat pump dryer plant. The objectives of the present work are to develop and lo test a heat pump dryer simulation model. The simulation provides results on the characteristics of both plant and components which are integrated by heat and mass transfer equations. The program has menus with click-on icons, input and output pop-up dialogue boxes. The usual commands such as, file-open, file-save, edit-delete are available in this program simply called Hpdryer. The model contains moist air psychrometric. natural and conventional refrigerant property libraries. Ammonia is a time-tested, self-alarming and natural refrigerant. It has been used extensively in the past, and it has better thermodynamic and transport properties than halocarbons. Safety is easily attained by design and its restrictive standards have helped increase its use in several countries. There are 36 ammonia installations in Norway and in the United Kingdom, including a drying plant. Ammonia has zero Odp, zero Gwp and the recent R&D has led to viable small-sale heat pump plants. Ammonia and dichlarodifluoromethane refrigerants were used in the test cases simulated by Hpdryer madel.

ISSN:0737-3937    

DOI:10.1080/07373939708917299

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Drying kinetics of four Fruits (namely, apple, pear, kiwi and banana) were studied by introducing an one-parameter empirical mass transfer model, involving a characteristic parameter (drying constant), as a function of process variables. The model was tested with data produced in a laboratory dryer, using non-linear regression analysis. The investigation involved a wide range of characteristic dimensions of samples and air conditions (temperature, humidity, and superficial velocity). The parameters of the model considered were found to be greatly affected by sample characteristic dimension and air temperature. The model also involved the equilibrium material moisture content which was formulated in the form of the GAB equation. Its parameters were evaluated by means of non-linear regression analysis to independent experiments covering two process variables (temperature and water activity of the surrounding air).

ISSN:0737-3937    

DOI:10.1080/07373939708917300

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Drying of red pepper under solar radiation was investigated, and a simple model related to water evaporation was developed. Drying experiments at constant laboratory conditions were undertaken where solar radiation was simulated by a 1000 W lamp.

ISSN:0737-3937    

DOI:10.1080/07373939708917301

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In part one, a simple drying model of red pepper related to water evaporation was developed. In this second part the drying model is applied by means of related experiments.

ISSN:0737-3937    

DOI:10.1080/07373939708917302

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

For a more accurate simulation of the moisture sorption process in wood, the precise separation of surface emission and diffusion coefficients is essential. In this paper, a non-linear simplex technique that was developed to obtain the optimum pair of the surface emission coefficient he, and the diffusion coefficient D from a single sorption curve is presented and tested with experimental data. An easy to use computer program was employed to carry out the evaluation. Data analysis showed that the new method resulted in a more statistically accurate calculation of bcand D than currently existing methods.

ISSN:0737-3937    

DOI:10.1080/07373939708917303

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The heat and mass transfer during freeze drying of raw beef by different heating methods is studied theoretically and experimentally. The difference between radiant heating and microwave heating in freeze drying process has been analyzed. The results obtained are important for the selection of the heating methods in practical freeze dryers.

ISSN:0737-3937    

DOI:10.1080/07373939708917304

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor