Assessment of Efficiency of Drying Grain Materials Using Microwave Heating

We present results of experimental work on studying the drying of a dense layer of grain using microwave heating. We investigated a series of techniques to supply heat to grain to assess energy efficiency of a microwave field. We studied the following ways of drying: a microwave method, a pulsating microwave method, a microwave-convective cyclic method with blow of a layer with heated air flow and air without preheating, simultaneous microwave-convective drying method.Studying the kinetics of drying in a microwave field showed that we can divide the process into heating periods (zero drying rate), constant (first drying rate) and falling (second drying rate). These periods are characteristic for drying of colloidal capillary-porous bodies at other methods of heat supply. We obtained empirical relationships for the drying rate and the average temperature of grain in the first period based on the generalization of experimental data on the study on drying of grain of buckwheat, barley, oats, and wheat. We presented kinetic dependences in a dimensionless form. They summarize data on the studied grains. The aim of comprehensive studies of various methods of heat supply during drying was determination of the optimal method and rational operational parameters, which ensure high intensity of the process and the required quality of the finished product with minimal energy consumption.All studies took place under identical conditions and for the same grain (oats) to ensure the accuracy of the comparison. We determined that the most preferable method is a simultaneous microwave-convective energy supply without air preheating, which minimizes specific energy consumption. Experimental studies on drying using a microwave field made possible to select the required process parameters: power, heating rate, mass, and form of loading. We plan to develop a technology for drying of grain using microwave energy based on the study dat

Assessment of Efficiency of Drying Grain Materials Using Microwave Heating

We present results of experimental work on studying the drying of a dense layer of grain using microwave heating. We investigated a series of techniques to supply heat to grain to assess energy efficiency of a microwave field. We studied the following ways of drying: a microwave method, a pulsating microwave method, a microwave-convective cyclic method with blow of a layer with heated air flow and air without preheating, simultaneous microwave-convective drying method.Studying the kinetics of drying in a microwave field showed that we can divide the process into heating periods (zero drying rate), constant (first drying rate) and falling (second drying rate). These periods are characteristic for drying of colloidal capillary-porous bodies at other methods of heat supply. We obtained empirical relationships for the drying rate and the average temperature of grain in the first period based on the generalization of experimental data on the study on drying of grain of buckwheat, barley, oats, and wheat. We presented kinetic dependences in a dimensionless form. They summarize data on the studied grains. The aim of comprehensive studies of various methods of heat supply during drying was determination of the optimal method and rational operational parameters, which ensure high intensity of the process and the required quality of the finished product with minimal energy consumption.All studies took place under identical conditions and for the same grain (oats) to ensure the accuracy of the comparison. We determined that the most preferable method is a simultaneous microwave-convective energy supply without air preheating, which minimizes specific energy consumption. Experimental studies on drying using a microwave field made possible to select the required process parameters: power, heating rate, mass, and form of loading. We plan to develop a technology for drying of grain using microwave energy based on the study dat

High-temperature drying of organically grown bread rye

Mycotoxin producing fungi are naturally occurring components in cereals. When produced, some of the mycotoxins are toxic to humans and animals. Heat treatment is a method to reduce fungal abundance on cereals. The objectives of this work have been to provide more knowledge on this topic, and specifically to optimise the drum drying technique with reference to reducing the dissemination and proliferation of fungi on organically grown rye without reducing the baking quality of the grain. The results show that drum drying can be a very efficient method in reducing fungi colonising on grain. For rye it is possible to achieve high effects on fungi without reducing the baking abilities. When drying at a constant maximum grain temperature of 64°C, the treatment resulted in less than 1% of the yeast propagules and less than 2% of the filamentous fungi, compared to what was found in the reference grain. As drying temperatures and time for the grain to be treated are essential, the drum drier must be equipped with an effective control unit. The experiments show that a control system using fixed constant maximum grain temperature is most suitable

EFFECTS OF DRYING AND ENSILING METHODS ON CYANIDES CONTENTS AND CHEMICAL COMPONENTS OF CASSAVA ROOTS AND STEMS

The objectives of this experiment was to compare the drying and ensiling methods to reduce cyanides contents in cassava, as well as related nutrient components. This experiment used roots and stems of cas-sava, fermented juice of epiphytic lactic acid bacteria (FJLB) and molasses. A completely randomized design was used in this experiment for 8 treatments. The treatments were 30 o C incubator, 50 o C incubator, 70 o C oven drying, freeze drying, 2 d incubator 30 o C ensiling, 2 d incubator 50 o C ensiling, 2 w incubator 30 o C ensiling and 2 w incubator 50 o C ensiling. The contents of HCN, acetone cyanohydrin, linamarin, proximate components and in vitro dry matter digestibility were determined in each treatment. The result of this experi-ment showed that the contents of HCN and linamarin in ensiled cassava roots were lower (p<0.01) than in dried cassava roots. There were no significantly different on residual HCN among treatments in cassava stems. The content of linamarin was higher in freeze drying than that in heat drying methods (p<0.05). There was an opposite pattern of acetone cyanohydrins and linamarin content of roots and stems. The content of dry matter (DM) in 30 o C ensiling was lower than in 50 o C ensiling (p<0.05). The content of ash increased in cassava roots silage (p<0.01), meanwhile the decreasing of ether extract content was occured in cassava stem silage (p<0.01). Ensiling method was more effective to reduce cyanide than the drying method, and cassava silage showed a proper qualification as feed. Keywords: Drying, Ensiling, Cyanides, Cassav

Drying of Heat Sensitive Materials of High Moisture Content in Mechanically Spouted Bed of Inert Particles

In drying operation the material characteristics such as heat sensitivity, moisture content and particle size are of great importance, which should be taken into account in selection of proper design and conditions for the process. Rigorous quality requirements, i.e. gentle drying of heat sensitive materials, stable, well-controlled and economic operation can be fulfilled by using Mechanically Spouted Bed (MSB) dryer with inert particles developed to eliminate some drawbacks of the conventional spouted bed dryers. In this paper the construction and the main features of MSB-dryer are presented. Different tasks with special quality demands, namely drying of bovine serum albumin and moisture removal from tomato pulp of thermoplastic behaviour, and a method to accomplish these requirements are shown

Micro-fabrication of Carbon Structures by Pattern Miniaturization in Resorcinol-Formaldehyde Gel

A simple and novel method to fabricate and miniaturize surface and sub-surface micro-structures and micro-patterns in glassy carbon is proposed and demonstrated. An aqueous resorcinol-formaldehyde (RF) sol is employed for micro-molding of the master-pattern to be replicated, followed by controlled drying and pyrolysis of the gel to reproduce an isotropically shrunk replica in carbon. The miniaturized version of the master-pattern thus replicated in carbon is about one order of magnitude smaller than original master by repeating three times the above cycle of molding and drying. The micro-fabrication method proposed will greatly enhance the toolbox for a facile fabrication of a variety of Carbon-MEMS and C-microfluidic devices.Comment: 16 pages, 5 figure

The effects of drying methods and storage conditions on pea seed (Pisum sativum L.) quality and the relationship between high temperature drying and maize seed (Zea mays L.) stress cracks : this thesis presented in fulfilment of the requirements for the degree of Master of Applied Science (Agricultural Engineering) in the Institute of Technology and Engineering, Massey University, New Zealand

High temperature and high relative humidity adversely affect the quality of seeds, and are features of tropical climate. Seed drying and storage are being used increasingly in developing countries to improve seed storage and quality. This study was undertaken to evaluate a range of seed drying methods and storage conditions with the view to selecting an appropriate method(s) for use in tropical countries. Pea (Pisum sativum L.) seeds at three initial seed moisture content (m.c.) of 23.8, 18.0 and 14.5% were dried to 10% seed m.c. before storage. The performances of four different drying methods: artificial dryer (Kiwi Mini) set at 30°C or 45°C, natural sun drying, and in-bin natural ventilation drying were evaluated. Natural sun drying, and in-bin natural ventilation drying were conducted from March to May, 1997, when mean temperature and relative humidity during sunny days were 17°C and 60% respectively. The dried seeds were stored under two conditions: open storage at 20.5°0 and 55% relative humidity (r.h.), and closed storage at 25°C and 90% r.h. for 20, 40, and 60 days. Time and energy consumed for drying by the different methods were determined to compare the drying efficiency when combined with quality of the seed. Deterioration of the seed due to storage conditions and drying methods used was determined by assessing their effects on seed germination, abnormal seedlings, dead seed, hollow heart percentages, and conductivity. Seed samples dried by the Kiwi Mini dryer set at 45°C took 7 hours and those set at 30°C took 17 hours. It took 54 hours with natural in-bin ventilation drying, while sun drying took 37 hours. However, energy consumed when drying seeds at 30°C was 17 kWh, which was more than twice that at 45°C. Seed germination was not significantly different between drying methods, but averaged only 75% because of sprouting damage of the crop prior to harvest. Germinations after open and closed storage for 20 days did not differ, although some differences appeared after 40 days of storage. However, open and closed storage for 60 days significantly reduced seed germination to 54 and 33% respectively. Because seeds are heat-sensitive, drying air temperature and drying rate are particularly important to avoid internal seed breakage, cracking and splitting, fungal growth, and loss of germination and vigour. Selected studies have shown that seed can be dried at high temperature for a short time, followed by tempering to re-distribute moisture and temperature inside the seed, thus reducing the percentage of cracking. Thus, a second experiment was conducted with maize (Zea mays L) to study the impact on seed viability of high temperature drying followed by tempering. Maize at 28.5% initial seed m.c. was dried at 60°C for short periods of 5, 10, 15, 20, or 25 minutes, followed by tempering for 45 minutes at either 30°C or 21°C. This cycle was repeated until maize seeds were dried to 13.0% m.c.. The percentage of cracked seeds, germination immediately after drying, and after an accelerated ageing test, did not differ between 30°C and 21°C tempering. Drying exposure times of up to 10 minutes per cycle at 60°C caused vertical cracks in up to 50% of seeds, but seed germination remained over 90% and seed vigour was also maintained. The percentage of seeds with stress cracks due to high temperature drying (5 - 25 minute cycles) at 60°C followed by tempering had polynomial relationships with seed germination and vigour. Seeds dried at the same temperature without tempering had their germination reduced from 99 to 20%

Effect of Distributed Superficial-Velocity in Deep-Bed Grain Drying

This paper deals with influence of velocity field distribution to heat and mass transfer process in deep bed grain dryers. Two-dimensional (2D) models of deep-bed grain dryers were built by considering simultaneously momentum, heat, and mass transfer in the drying air phase. The Navier-Stokes momentum equations are applied to simulate pressure drop and velocity field of the drying airflow. Effect of velocity distribution to the heat and mass transfer coefficient distribution were simulated along the height of grains bed. The dynamic equations are solved numerically by using finite difference method by utilization of alternating direction implicit method, while the momentum equations are solved numerically by utilization of SIMPLE algorithm. The simulation results showed that velocity distribution along the grains bed - 5 cm of bed height - did not so influenced to the heat and mass transfer coefficient. Further, the vector plot of drying air superficial velocity field and contour of pressure distribution along deep bed of grain was simulated

Solar timber kilns: State of the art and foreseeable developments

Analysis of the evolution in solar heated drying kilns in recent decades shows that there have been a series of modifications to optimize their thermal and drying efficiency. Using an analysis method based on product design, we report on existing solar timber kilns. The dryers and their component units are studied, developments are noted, focusing on changing trends in technological systems. As a result of this analysis we suggest some future adaptations