The potential of dielectric heating with microwaves at 2450 MHz for drying grapes into raisins was studied. Feasibility studies in a conventional microwave oven were successful. A new microwave drying system equipped with specialized instrumentation and data acquisition components and permitting full control of microwave power levels and duration of application was then developed and used for detailed experimental work. / It was found that when the grapes were dipped in surfactants, as is common practice in the raisin industry, microwave drying was not only faster than convective drying but also had a much lower specific energy requirement. However, it was also possible to obtain raisins of adequate quality without dippings. Good quality light coloured raisins were obtained without sulphur dioxide fumigation. Thus, microwave drying has potential in reducing both the quantity of chemicals entering at this point in the food chain and the energy consumed for food preservation. / The shrinkage and density of grapes were found to be linearly related to moisture content; initial size and method of drying had no influence. (Abstract shortened by UMI.)

No description available.

The influence of freezing rate, rate of heat input and drying chamber pressure on freeze-drying rate was studied to determine the thermal and physical properties of MacIntosh apple and Netted Gem potato tissue. The samples were frozen either by immersion in dry ice and ethanol (fast frozen) or by placement in a refrigerated cabinet maintained at a temperature between -10° and +5° F (slow frozen). The samples were suspended in a chamber maintained at a pressure of 550 or 1400 microns of mercury and surrounded by a constant temperature water bath which provided a radiant heat source of 86° or 104°F. The weight, and the surface and centre temperature of the sample were recorded continuously during freeze-drying. Vapor diffusion was the rate limiting factor for fast frozen samples while heat transfer was rate limiting for slow frozen samples. Chamber pressure had little influence on the freeze-drying rate of slow frozen samples. Potato tissue thermal conductivity varied from 0.66x10⁻² BTU/Hr.°F Ft. at a pressure of 550 microns to 0.78x10⁻² at 1400 microns. The thermal conductivity of apple tissue was 1.0 x 10⁻² BTU/Hr.°F Ft. at both pressures. The eutectic temperature of apple and potato tissue was found to be -10°F and -1°0F. respectively. / Land and Food Systems, Faculty of / Graduate

The purpose of this study was to evaluate the effectiveness of steam conditioning immediately after drying to reduce internal checking resulting from high-temperature drying of Pacific Coast hemlock lumber. Three different levels of conditioning time, 2, 4 and 6 hours, were carried out on 2 inches wide by 4 inches thick by 3 feet long (51 mm by 102 mm by 0.91 m) , and on 4 inches wide by 4 inches thick by 3 feet long (105 mm by 105 mm by 0.91 m), specimens. For comparison purposes, controls of both sizes of specimens were also high-temperature dried without conditioning. Analysis of the results indicated that internal checking was not significantly reduced by steam conditioning and was more likely to develop afterwards during storage at room temperature, and that total degrade observed in the "4x4" specimens was more excessive than that in the "2x4" ones. The defective "4x4" specimens were found over-dried (below the targeted 12% moisture content) with high core-shell moisture content differences. More internal checking was found when the specimens' final moisture content ranged from 7 to 8%. / Forestry, Faculty of / Graduate

No description available.

No description available.

Passive (static) and dynamic studies have shown aroma to be an important aspect of food quality, which can be used to differentiate, classify, and grade foodstuffs, and in some cases it can be used to predict other quality characteristics. Monitoring and control of food aroma changes during food processing can significantly improve the quality of the final product in terms of flavour, color, taste, and overall appearance. Hence, it is a prominent and urgent field of study in the post production systems. / Passive aroma detection of unprocessed foods and dynamic aroma detection during food processing was undertaken using a fast GC analyzer -- zNose. During the study on the passive aroma detection, the aroma of Chinese spirits (Fenjiu) and mango (Mangifera indica L.) fruits, (i.e., liquid and solid states, respectively) was analyzed. In the study of Chinese spirits, aroma profiles of Fenjiu liquor samples of different quality levels were acquired and used for quality classification and prediction. Measurements of dielectric properties of the samples were also conducted to estimate alcohol concentration. In the study of mango fruits, aroma changes of mango samples were monitored during their shelf life and used to evaluate mango quality. Ripening and rots were detected with 80% and 93% accuracy, respectively. / During the study of dynamic aroma detection, a real-time aroma monitoring and control system was developed for use during microwave drying. Aroma signals of a processed food item were detected with zNose and analyzed with a fuzzy logic algorithm to determine the optimal food drying temperature. Phase control was used to adjust the microwave power level to meet temperature requirements. Carrot (Daucus carota L.) and apple (Malus domestica Borkh) were selected as representatives of vegetables and fruits. In carrot drying, samples could be dried in a short time at high temperatures but the interior of some sample cubes was burnt. Drying at a lower temperature extended the drying process, but led to a great loss of aroma in the finished product.' The best results were obtained at 60°C. Based on these results, a fuzzy logic controller was designed and employed to control the drying process according to carrot aroma changes. To investigate the possibility of aroma improvement without zNose assistance, a linear control method was developed whereby a temperature control profile imitated the fuzzy logic control, but aroma control was not included. With these new control strategies, the carrot color and flavour were significantly improved and less time and power were consumed. Similar results were achieved when apple was microwave-dried. Apple aroma was monitored online during microwave drying processes and controlled with similar fuzzy and linear control strategies. Apple color, aroma, and overall appearance remained intact with the new strategies and less time and power were consumed. In contrast to the carrot drying, a different linear temperature profile was required for apple drying in terms of aroma retention.

The moisture contents of the final coal products from processing plants are often too high and do not meet the requirements of the client. In many cases, drying becomes a necessary step to control the moisture content. Conventional thermal drying is inefficient and is not environmentally friendly. This study investigates the application of microwaves as an alternative heat source for drying coal. The rate of drying was determined by the thermogravimetric analysis (TGA) technique. Several variables that have significant effects on the drying kinetics were investigated, including incident microwave power, initial moisture content and the sample mass. Microwave drying tests were performed under various conditions and the mass change was monitored continuously. The percentage mass loss, moisture fraction and drying rate were obtained for each experimental condition. The final temperature was measured and drying efficiencies were calculated. For comparison purposes, some conventional thermal drying tests were also carried out at temperatures ranging from 130 to 220oC and with coal masses ranging from 10g to 100g. The TGA results show that microwave drying has distinct advantages over conventional drying such as reducing the overall required time and increasing the drying efficiency. A multiple-regression analytical method was used for both microwave and conventional drying to find the best fit model among eleven different types. Finally, the sample mass, which proved to be the most dominant factor in microwave drying, was incorporated into the equation of the best fit model. / Thesis (Master, Mining Engineering) -- Queen's University, 2010-12-23 22:56:04.119

No abstract available. / Thesis (Ph.D.)-University of Natal, Durban, 1991.

Hog fuel is increasingly becoming an alternative to alleviate the energy problems associated with the use of fossil fuels. To make adequate use of hog fuel, its moisture content should be reduced prior to combustion either in an external dryer or in the initial stages of a hog fuel boiler. Therefore, this research project was undertaken to establish the factors which govern the drying rate of wet hog fuel particles. The convective drying of wood-waste on the slow moving bed of hog fuel boilers was simulated in a packed bed. The information which was obtained can also be applied to approximate the drying behaviour in external dryers. An apparatus was constructed to accommodate the use of hot air, flue gas, superheated steam and a mixture of them as drying media. Drying tests were carried out, over the temperature range of 125-245°C, on 1.1 to 4 kg batches of Western Hemlock hog fuel of thicknesses from 2 to 12 mm. The relative effects of velocity (V), temperature (T), nature of the drying gas, bed depth (L), and initial moisture content of the hog fuel samples (M₀) on the drying process were investigated using a mixture of several thickness fractions having an average (sauter mean) particle thickness (dp) of 6.3 mm. Drying rates were determined through measurement of the change either in humidity of the drying gas, or flow rate of the superheated steam across the bed of hog fuel. Gas humidity was measured using an optical dew point sensor and steam flow was monitored using an orifice plate connected to a massflow transmitter. Drying rates have been quantified as functions of hog fuel particle thickness, initial moisture content and bed depth. The effects of gas temperature, velocity and humidity have also been quantitatively established. The drying process was insensitive to CO₂ content of the drying gas. The existence of an inversion temperature above which drying rates increase with humidity of the drying medium was both experimentally and theoretically confirmed and the locus of inversion points was determined. Instantaneous normalized drying rates, ƒ, and characteristic moisture contents, Φ , have been determined and the existence of a unified characteristic drying rate curve was verified. Using a receding plane model, ƒ was formulated as a function of Φ, for dp = 6.3 mm and at L = 25 cm, for both superheated steam and relatively dry air. Pressure drop measurements were obtained for all the runs with the exception of the superheated steam ones. Application of an accepted pressure drop equation permitted the sphericity of the hog fuel particles to be approximated. A design equation for gas pressure drop in beds of hog fuel particles was investigated. The simultaneous heat and mass transfer processes in drying during the heat transfer controlled period was studied. Using the concept of volumetric evaporation, an empirical correlation for the overall heat transfer coefficient in a packed bed of hog fuel particles has been obtained. The effects of different parameters on both the particle residence time required for drying and the grate heat release rate in hog fuel boilers were determined. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate