Browsing by Author "EL-Mesery, Hany S."

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    Comparison of a gas fired hot-air dryer with an electrically heated hot-air dryer in terms of drying process, energy consumption and quality of dried onion slices
    (Academic Journals, 2012-08-14) Gikuru, Mwithiga; EL-Mesery, Hany S.
    Onion slices were dried in either a gas-fired hot air dryer or an electrically heated hot air dryer at air temperatures of 50, 60 or 70°C, and at air flow velocities of 0.5, 1.0 or 2.0 m/s. Records of the drying rates and energy consumption were kept by using electronic weighing balances and an electric metering device. The results showed that the drying rate and final product quality in the two dryer were not significantly different at P < 0.05 level for the same setting of air flow and air temperature, and all dried products were of acceptable quality in terms of rehydration ratio and appearance. The specific energy consumption was found to decrease with increase in temperature but to increase with increase in air velocity in both dryers and for all conditions within the range of these experiments. The thermal efficiency of the gas dryer was between 54.87 to 69.52% while that of the electrically heated dryer was between 31.27 to 53.84%. The thermal efficiency of both dryers increased with increase in temperature and decreased with increase in air velocity. However, there was considerable difference in the energy consumption and efficiency of the two dryers, with the gas-fired dryer being more efficient at all settings.
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    Specific Energy Consumption of Onion Slices During Hot-air Convection, Infrared Radiation and Combined Infrared-Convection Drying
    (AENSI Journals, 2014) Gikuru, Mwithiga; EL-Mesery, Hany S.
    Total energy requirement and specific energy consumption for drying of onion slices were evaluated using various drying methods including hot-air convection, infrared radiation and hot air convection-infrared combination drying. Onion slices with initial moisture content of 7.31 g water/g dry solids, were dried to a final moisture content of 0.07 g water/g dry solids. Energy and specific energy consumption under the different drying conditions of the onion slices were compared. In particular, the experiments were carried out in convective dryer at three air temperature levels of 50, 60 and 70 oC and three air velocity levels of 0.5, 1.0 and 2.0 m/s. Experiments in the infrared dryer were done at three air velocity of 0.5, 0.7 and 1.0 m/s. For combination of infrared and hot-air convection drying, there were three air temperature levels of 40, 50 and 60 oC and three air velocity levels 0.5, 0.7 and 1 m/s while the infrared intensity was set at 0.15, 0.20 and 0.30 W/cm2. Results of data analysis showed that the lowest and highest energy consumption levels in drying onion slices were associated with the hot air convection-infrared combination (IR-HA) and convection (HA) dryers, respectively. Specific energy consumption in the hot air dryer showed a downward trend with increasing air temperature and an upward trend with increasing air velocity. In infrared (IR) drying, it was observed that increasing the air velocity increases the drying time and consequently the amount of energy consumed. However, a reduction in energy IRHA was noted with increasing infrared intensities under combination drying relative to infrared drying alone. Therefore, IR-HA drying of onion slices proved to have the lowest specific energy consumption and therefore the most efficient.