ANALYSIS OF BATCH DRYING DATA USING SAS

An analysis technique is described which uses the nonlinear curve fitting capabilities of the Statistical Analysis System (SAS) to analyze batch drying data. The technique does not require any apriori assumptions about whether a constant rate period exists. Rather, the only assumptions necessary are the possible forms of the equations which can be used to describe the drying phenomenon. The program will then determine, based upon statistical techniques, where each equation should be used during the drying process in order to best describe the overall drying process. Two examples are given; the first analyzes the drying of. sand, a material having a constant rate period; the second analyzes the data describing the drying of French fried potato pieces.     

DRYING CHARACTERISTICS OF THE HAZELNUT

Abstract

Equilibrium moisture content isotherms for Spanish hazelnut (Corylus avellana L.) at different temperatures (30°C-80°C) were determined using static gravimetric method. Thin layer drying experiments were done with forced air circulation and were conducted with different operating conditions to determine the drying characteristics of hazelnuts. The effect of air temperature (30°C-70°C), air velocity (0.5 m/s - 2 m/s) and drying bed loading density (50 kg/m² - 150 kg/m²) on drying of unshelled and shelled hazelnuts was studied. Six mathematical models were used to fit the experimental equilibrium moisture content data, from which the G.A.B. model was found to give the best fit. Diffusion coefficients were determined by fitting experimental thin-layer drying curves to the Fick's diffusion model. Variation of the effective diffusion coefficient with temperature was of the Arrhenius type. The Page equation was found to describe adequately the thin layer drying of hazelnut. Page equation drying parameters k and n were correlated with air temperature and relative humidity.     

A REVIEW OF THE FIELD DRYING OF GRASS

This paper reviews the data and models used to simulate the field drying of grass in swaths. The main factors influencing the drying rate are solar radiation, vapor pressure, rain, the swath structure and the thin layer drying rate of the grass. Most models consider these factors to some extent. The simulation of swath drying is well developed, with some models considering the heat and mass transfer processes in the swath. But the modelling of swath structure and the effect of rain have received less attention. The models agree on the effect, on the drying rate, of all weather factors except wind speed. Some models predict that more wind is beneficial, others say the opposite. This problem has not been resolved experimentally.     

QUANTITATIVE ANALYSIS OF DRYING BEHAVIOUR OF FRUITS AND VEGETABLES

ABSTRACT

In this study, the drying characteristics of seven vegetables (garlic, potato, bean. ginger, leek, onion, and carrot) and five fruits (avocado, banana, sultana, kiwi fruit and apple) were studied under idealised ‘constant’ controlled drying conditions using an automatic thermogravimetric analyser. Drying-rate curves were constructed and quantified in a systematic way using the least-squares method. This allowed the drying behaviour of each product to be expressed in terms of three variables; gradient of the “constant rate” stage, gradient of the falling rate stage and critical moisture content (CMC)

The drying curves of fruits and vegetables were found to vary greatly indicating the nature of foodstuffs to have a strong effect on the drying kinetics. The gradient of the constant rate period was not truly constant but had an average gradient of 3.1 × 10^?4 per second with bean having the lowest gradient (1.9 × 10 ^?4/) and garlic having the highest gradient (5.3 × 10^?4/s). This was expected as bean had the highest moisture content (93% wet basis) and was able to feed the surface with sufficient water to maintain a near constant rate of evaporation

The falling-rate period ranged from 10 × 10^?4 per second with avocado and garlic having the lowest gradient while apple had the highest gradient of 30 × 10^?4 per second. The CMC for most of the fruits and vegetables studied was about 1 kg/kg dry mass. This means that, at the CMC, the mass of water was the same as the mass of dry matter but with a spread in values from 0.7 for a fruit like banana to 1.8 for avocado.     

QUANTITATIVE ANALYSIS OF DRYING BEHAVIOUR OF FRUITS AND VEGETABLES

In this study, the drying characteristics of seven vegetables (garlic, potato, bean. ginger, leek, onion, and carrot) and five fruits (avocado, banana, sultana, kiwi fruit and apple) were studied under idealised 'constant' controlled drying conditions using an automatic thermogravimetric analyser. Drying-rate curves were constructed and quantified in a systematic way using the least-squares method. This allowed the drying behaviour of each product to be expressed in terms of three variables; gradient of the “constant rate” stage, gradient of the falling rate stage and critical moisture content (CMC)

The drying curves of fruits and vegetables were found to vary greatly indicating the nature of foodstuffs to have a strong effect on the drying kinetics. The gradient of the constant rate period was not truly constant but had an average gradient of 3.1 × 10^-4 per second with bean having the lowest gradient (1.9 × 10 ^-4/) and garlic having the highest gradient (5.3 × 10^-4/s). This was expected as bean had the highest moisture content (93% wet basis) and was able to feed the surface with sufficient water to maintain a near constant rate of evaporation

The falling-rate period ranged from 10 × 10^-4 per second with avocado and garlic having the lowest gradient while apple had the highest gradient of 30 × 10^-4 per second. The CMC for most of the fruits and vegetables studied was about 1 kg/kg dry mass. This means that, at the CMC, the mass of water was the same as the mass of dry matter but with a spread in values from 0.7 for a fruit like banana to 1.8 for avocado.     

HANDBOOK OF INDUSTRIAL DRYING

Papermaking is a massive dehydration operation. Thermal removal of moisture which can not be removed mechanically is a key process stage in papermaking. It is well known that it is a highly energy intensive step. However, it is less readily recognized that it also influences some of the most important physical, optical or functional properties of the product. With the advent of new drying technologies- some already commercialized while some still at pilot or laboratory stage - it is increasingly important to devote attention to the interaction between the drying conditions and the final product quality as measured by generally accepted standard test results. Aside from the drying parameters one must also examine paper/pulp parameters in the hope of achieving in the long term some predictive capability as well as drying-quality effects. This bibliography is selective in coverage and is compiled to ease the task of the interested reader in locating appropriate references covering his/her areas of interest.. Some general observations are made on the basis of the literature cited.

important problem.This is influenced by the composition and characteristics of the coating colour and raw stock and also by the type and rate of drying.

The following selected bibliography covers the effect of drying on pulp, paper and paperboard properties. Some available literature on coated paper drying is also included. It is encouraging to note a trend towards considering the effect of drying on the product quality as an integral part of drying R&;D projects. Earlier, the drying work was confined to optimising only the heat and mass transfer parameters. It should be noted also that this bibliography includes a substantial number of publications which are not in english. The availability of their translations into english is not known to the authors.

It is noteworthy that an international symposium - The Helsinki Symposium on Alternate Drying Technologies will be held in Helsinki in June 1991 to discuss the competing new drying technologies from the papermakers viewpoint.     

浅析影响原丝烘干的因素

概述湿纱含水对增强型玻璃纤维的重要性,影响原丝烘干的因素。主要介绍干燥过程的几个阶段,相对湿度,固含量及几个工艺参数对原丝烘干的影响,尤其减少原丝含水率可提高产品质量降低能耗,其中,提高固含量,减少原丝含水的影响最为有效。     

STATE ESTIMATION IN THE BATCH DRYING OF FOODS

ABSTRACT

Measurement of material moisture content is necessary for the control of product quality in batch drying. However, this variable cannot be measured on-line, and state estimation techniques are proposed. A non-linear dynamic model is developed for batch drying of foods. Process disturbances and measurement errors are modeled as stochastic processes and a hybrid extended Kalman filter is employed for state estimation. This filter is based on the local linearization of the process model around the suboptimal filter estimates. The moisture estimation approach was applied to experimental points obtained in a laboratory dryer with quite satisfactory results.     

THERMAL ANALYSIS AND DRYING KINETICS OF OLIVE BAGASSE

ABSTRACT

The slow thermal decomposition of olive bagasse at temperatures ranging from 25 to 900° C, with particular stress on the moisture evaporation phenomena, is analyzed making use of thermogravimetry, derivative ihermogravimelry and differential scanning calorimetry. The results obtained demonstrate that Thermal Analysis techniques contribute for the characterization of iniernai moisture transfer processes. “ Drying curves” obtained from Thermal Analysis experiments were compared with thin-layer drying curves of olive bagasse at relatively high temperatures. The existence of a critical moisture content, which distinguishes two types of water liaisons, was demonstrated, and its value quantified at 17-18%.     

COMPARISON Of STRATEGIES FOR AMBIENT-AIR DRYING OF LARGE ROUND BALES

ABSTRACT

A comparison of the drying efficacy of ambient-air drying of large forage bales was made between positive and negative pressure systems. Both systems effectively dried the bales to the desired average moisture content, but regions of higher moisture content within the bales were measured with the two systems. Energy consumption as expressed as the ratio of the energy consumed/weight of moisture removed was similar for both drying systems. Final configuration of the drying system will depend on whether heat is required to speed the drying process in order to meet the capacity of the harvesting system.     

DRYING KINECTICS OF PADDY USING THERMOGRAVIMETRIC ANALYSIS

The thermogravimetry (TG) and derivative thermogravimetry (DTG) were used to study the drying kinetics of the paddy. TG experiments were carried out at different heating rates (1, 3, 10 K/min) to study the drying kinetics. The Activation energy and pre exponential factors from the Arrhenious equation were calculated for the drying curves using ASTM and OZAWA-FLYNN WALL analysis. The results showed that the drying reaction was the second order reaction and the activation energy values changing with the partial mass loss representing that the drying reaction was of complex type of reaction. The isothermal drying curves predicted from the dynamic curves showed reasonably high mass loss occurred at moderate range of temperatures of 60-100°C.     

DRYING OF PARTICULATE SOLIDS: DETERMINATION OF THE CHARACTERISTIC CURVE OF BROWN COAL.

ABSTRACT

Variation on the rate of drying of brown coal powder as a function of environmental and intrinsic properties has been studied in a gravimetric laboratory-scale drier.

Raw data have been treated to correlate the constant rate of drying and the equilibrium moisture content as a function of flow rate and temperature of the gas phase, particle size and surface additives. The characteristic drying curve occurs when the reduced rate of drying is plotted as a function of a dimensionless moisture potetial.     

EVALUATION OF DIFFERENT METHODS OF DRYING ON THE QUALITY OF OYSTER MUSHROOM (Pleurotus sp)

ABSTRACT

Mushrooms are extremely perishable and have a short shelf life period. To increase the post harvest lives, different methods of drying viz., sun diving, fluidized bed drying and thin layer drying with potassium metabisulphite (KMS) and blanching was done. The quality of mushroom dried in fluidized bed condition at 50°C for 80-120 minutes with 0.5 KMS was found to be superior to other drying methods. Rehydration ratio was also maximum in KMS treated mushroom and no significant difference at higher concentration. The treatment with KMS and blanching reduces the nutritive quality but improves the colour of the mushrooms when compared with sun dried samples. Storage of mushrooms after treatment with KMS at higher concentration (1.5%) reduces the microbial spoilage.     

ADSORPTION DRYING OF CORN IN ZEOLITE GRANULES USING A ROTARY DRUM

ABSTRACT

This study was conducted to evaluate the potential of a natural zeolite (chabazite) as the particulate medium for grain drying. The granular zeolite was heated in an electric oven and mixed with grain corn. Drying experiments were conducted in a rotary batch dryer equipped with a computer and a data acquisition and control unit simulating an adiabatic process. Five initial medium temperatures (140, 160, 180, 200, and 220 °C) were used. Drying curves for grain corn and the values of effective diffusivity are reported. The amount of moisture removed and     

BATCH DRYING OF SHELLED CORN IN TWO-DIMENSIONAL SPOUTED BEDS WITH DRAFT PLATES

ABSTRACT

Geometrically similar spouted beds with draft plates were used to obtain the drying characteristics of freshly harvested shelled corn with 0.28 to 0.31 kg/kg initial moisture content at different air inlet temperatures and bed heights. Thermal equilibrium between air and grains was achieved at minimum spouting conditions. The drying kinetics of shelled corn in a drafted two-dimensional spouted bed was found to be of the "thin layer" type. Expressions for the model parameters in Page's equation accounting for the bed geometry, grain moisture content, and drying conditions were developed.     

EFFECT OF A TEMPERING PERIOD ON DRYING OF CARROT IN A VffiRO-FLUlDIZED BED

ABSTRACT

Drying of diced carrot in a vibrofluidized bed was studied experimentally for various air temperatures, bed heights and size of the cubes. Effect of a tempering period that mav be implemented into ¦ drying cycle was examined with respect to drying kinetics and energy consumption. Although two stage drying with a tempering period increases the overall drying time, it shortens the drying time in a VFB dryer thus reduces energy consumption     

STUDIES ON STIFLING AND DRYING OF COCOONS FOR LONGER STORAGE

ABSTRACT

Long term storage of stifled cocoons is an important problem during unfavourable seasonal conditions. Cocoons could be stifled within 20 minutes by using steam al 90°C. The shade drying of steam stifled cocoons in thin layers reduced the moisture content from 228 per cent (db) to 3 1.7 per cent (db) within 10 days. By hot air conditioning method the cocoons could be stifled and dried simultaneously. Using hot air at 90°C the cocoons could be stifled within 10 minutes, and dried to the equilibrium moisture content within 2 hours. The cocoons stifled by the hot air conditioning method could be reeled even just after stifling.     

A STUDY OF TEMPERATURE AND SAMPLE DIMENSION IN THE DRYING OF POTATOES

Abstract

It is common knowledge that sample size and drying temperature are two of the most important factors affecting the drying rate and quality of food. However, what is less commonly known are how these two factors interact relative to each other and their effects on the drying behaviour of potato. These effects were evaluated under controlled drying conditions using a thermogravimetric analyser. The least-squares method was used to fit a model to the experimental data and the response variables (slope of the first drying stage, transition moisture content and slope of the second drying stage) were determined systematically. Central composite design was applied for response surface modelling of the factors and regression methodology was used to analyse the results. The results showed that both temperature and sample dimension have significant (P=0.01) effect on drying behaviour of potato. Sample dimension significantly affected the transition moisture content, whilst both temperature and sample dimension significantly affected the slopes of the first and second stage of drying.     

PRACTICAL APPLICATIONS OF USING SOLAR COLLECTORS FOR DRYING PURPOSES IN AGRICULTURE

The main application for solar collectors in agriculture are drying of agricultural crops. Different types of active air type solar collectors have been examlned In small scale experiments and in full scale trials. This report deals with practical applications OF solar collectors for dryers. The investigations have shown that solar collectors can replace conventional heating units based on 011, electricity etc. for the heating. The most economical and practical solution is received lf the collector is integrated in the roof or a wall of a farm building. The report gives recommendations for the construction and For the choice of materials. Design dates and operation schedules are also presented.     

DYNAMIC OPTIMAL CONTROL OF BATCH RICE DRYING PROCESS

The drying of paddy rice may result in quality degradation, expressed as a head kernel yield, leading to significant commercial depreciation of the product. A mathematical model of the drying and of the quality degradation process was combined with a dynamic optimization algorithm to determine the drying conditions (air temperature and relative humidity as functions of time) that ensured the highest possible final product quality for a specified drying time and a specified final moisture content. The robustness of the optimal drying strategy with respect to the initial state of the product, to the model parameters and to the initialization of the optimization algorithm was verified. The compromise between the highest achievable final quality and the allowed total drying time was studied. The combination of simulation and optimization yielded a new insight in the rice drying process and in the quality preservation strategies.