جستجوی مقالات مرتبط با کلیدواژه « Coefficient of performance » در نشریات گروه « مکانیزاسیون کشاورزی »

This study evaluated the performance of a thermal dryer with a closed air circulation system equipped with a metal-organic framework (MOF) system. Dryer sections included: product drying chamber, the MOF containing chamber nano-absorbents, measurement and control systems. Dryer yield on mint was compared at three temperature levels (40, 50, and 60 °C). Finally, the energy consumption and drying mint leaves was evaluated. The results showed that the closed air circulation system reduces the dry time by 27% to 50%, the penetration coefficient of mint leaves increased with increasing temperature. Its values in cases of not using and using nano-absorbent plates were determined respectively (4.05690×10-11) and (2.8215×10-10) m2/s. The activation energy in two methods of not using and using the nano-absorbents was 45.72 and 51.96 kJ/mol, respectively, which is consistent with the researchers' results. Also, the coefficient of performance, the rate of moisture evaporation, and the rate of specific moisture evaporation showed the effectiveness of using nano-absorbent in the dryer system and reducing energy consumption. The total color index (ΔE) did not change much with increasing temperature from 40 to 50 °C, but from 50 to 60 °C, the increased total color index. There wasn't a clear difference in total color index between the two methods of using and not using nano-adsorbent.

Fluidized bed dryers have not yet been used for drying products such as mint leaves. This could be due to high porosity and low mechanical resistance resulting in poor quality of fluidization. Applying vibration has been recommended to overcome problems such as channeling and defluidization, and hence improving the fluidization quality. In this research, a laboratory scale vibro-fluidized bed heat pump dryer was designed and constructed for drying mint leaves. The experiments were conducted at vibration frequency of 80 Hz and amplitude of 3 mm. The velocity and temperature of the inlet air was controlled by an automatic control system. Experiments were carried out at 40, 50 and 60 °C, and two heat pump drying (HPD) and non-heat pump drying (NHPD). The results revealed that drying process primarily occurred in the falling rate period. Effective moisture diffusivity of the samples increased with increase in drying air temperature and varied from 4.26656×10-11 to 2.95872×10-10 m2 s-1 for the HPD method, and 3.71918×10-11 to 1.29196×10-10 m2 s-1 for the NHPD method and was within the reported range of 10-9 to 10-11 m2 s-1 for drying of food materials. The activation energy was determined to be 84 kJ mol-1 for the HPD and 54.34 kJ mol-1 for the NHPD, both have very good agreement with the results of other investigators. The coefficient of performance and specific moisture evaporation rate showed the acceptable performance of the heat pump system. Moreover, the energy consumption of the dryer for the NHPD method was more than the HPD method.