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The main incentive in processing fruits such as apple is reduction of losses and gaining added value. In this research, drying kinetics and drying efficiency of Golden Delicious apple slices are investigated using hot air flow and uniform microwave drying. Microwave power levels, 500, 1,000, 1,500, and 2,000 W, air temperatures, 40, 50, 60, and 708C and air velocities, 0.5, 1, 1.5, and 2 ms 21 were selected. Results revealed that microwave dehydration is highly time-efficient with 80% reduction of processing time, compared to hot air method. Highest value of drying efficiency was found in microwave method and it was reduced by 99% in the case of hot air drying.Energy costs to cover the drying process were decreased by 60% when the microwave method was used. Technically speaking, microwave drying resolves insufficiency of hot air method along with a significant enhancement of drying rate, drying efficiency and energy economy. Practical applicationsDrying of agricultural commodities is known as a main challenge in the processing industry regarding the waste reduction, longer shelf time, easier transportation, and storage. The main technique in this regard is currently hot air convection method which suffers energy consumption and surface hardening. Reduction of drying time and energy consumption with simultaneous enhancement of drying efficiency and energy economy are well known features in modern drying technologies such as microwave method. However, microwave systems are rarely utilized in industry, because of lack of operating information and high-tech hardware issues. Application of microwave technology in dehydration of apple fruits can result in significant improvement in the processing economy. Volumetric and uniform heating as the primary benefit of microwave drying can be mentioned as an undeniable incentive to producers, processors and industrialists. Additionally, investigation of kinetics of drying is the first step for dryer design or scale-up. K E Y W O R D Sapple, drying economy, drying efficiency, microwave | INTRODUCTIONOptimizing moisture content of products is a highly effective way to reduce agricultural product wastes and prevent them from postharvest rotting and spoilage. High content of moisture within the product prompts the growth and activity of microorganisms and enzymes, and causes undesirable chemical reactions which leads to reduce the product durability and shelf time. As an effective method for preservation of agricultural products, drying occurs by evaporation or sublimation, which is characterized by phase shift. Reduction in product moisture content causes a reduction in the rate of adverse chemical reactions such as browning and oxidation and, consequently, product appearance is preserved. Thus, foodstuffs can be stored in productive seasons to be supplied in low seasons or be sold in other areas (Goksu et al., 2005).During the drying, constant and precise process control is required.Application of inappropriate methods leads not only to a sharp drop in the quality of final produ...

High energy and time consumption in the dehydration of sugar cubes hinder its industrial commercialization. Microwave is employed to overcome the drawbacks of hot air drying. For microwave power 880 W, pulsing ratios 1.5, 2.5, 4.5, and 10 were applied to prevent thermal runaway and probable melting and caramelization. In order to monitor the spatial thermal variation of sugar cubes, thermal imaging was performed. Maximum effective diffusivity was measured to be 9.0905 × 10−8 m2/s, which belongs to pulsing ratio 2.5 and is 16 times larger than when hot air is used. Furthermore, the minimum specific energy consumption and minimum energy cost were calculated to be 314,192.45 J/g H2O and 0.179 × 10−3 $/g, respectively, which found in pulsing ratio 2.5. Technically speaking, regarding the critical temperatures of sugar cubes and energy economy, the study suggests pulsing ratio 2.5 for sugar cube dehydration using microwave power 880 W. Practical applications Sugar cube production line consists of several unit operations. Dehydration is the last operation commonly known as the major concern in industry due to high level of quality issues and energy aspects. At present, hot air drying is the common method in plants and is highly dependent on thermal conductivity of cubes which is very low. This method exerts notable costs to producers. Microwave technology as a solution is investigated in this research. Influencing parameters such as diffusivity, energy consumption, economy of energy, and kinetics are experimentally assessed and described. Based on the results obtained, the industry would have a full perception of using microwave radiation as a substitute for conventional hot air drying in order to resolve the challenges of energy, time, and costs.

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