In this research, convective and microwave drying characteristics, energy requirement and color changes of nettle leaves (Urtica diocia L.) were reported. Samples of freshly harvested nettle leaves were dehydrated under three air temperatures of 50 &deg;C, 60 &deg;C and 70 &deg;C and at three microwave power levels of PL-1, PL-2 and PL-3. Selected drying air velocity was 0.30 m/s for all temperatures. This is coming from the fact that it was understood from the preliminary studies that the temperature less than 50 &deg;C and the air speed more than 0.30 ms-1 increase the drying time and energy requirement, extremely for these products. Nettle leaves were dehydrated from the initial moisture content of 320 (percentage dry basis) to a final moisture content of 7 % to 9 %. During convective drying experiments, product were weighted automatically by the balance per (5 to10) min. Data were transferred to the computer and processed by a software. During microwave drying, the product were weighted and data recorded manually per (15 to 60) min. The influence of drying method, drying air temperature and microwave power level have also been studied. Hunter L, a, b values system was also used to evaluate changes in total color difference (DE) on dried products. The results showed that convective drying air temperature and microwave oven power levels influenced the total drying time, total energy requirement, specific energy requirement and color difference for nettle leaves. The minimum specific energy requirement were determined as 6.95 kWhkg-1 and 23.63 kWhkg-1 for 70 &deg;C and PL-2 respectively. 70 &deg;C drying air temperature and PL-3 was found to yield better quality product in terms of color retention of Hunter L, a, b and &nbsp;DE. As a result, to reduce drying energy consumption and to keep better color retention, convective drying can be recommended for this application.

Convective and microwave drying characteristics, energy requirement&nbsp;and color retention of dehydrated nettle leaves (Urtica diocia L.)&nbsp;

Background: Muga is an exclusive golden-colored silk produced by the Antheraea Assamensis silkworm species in North-east India. In the silk processing stage, drying of Muga silkworm cocoon is essential to prevent the pupa from emerging from the shell and to preserve the cocoons for a longer period (3-6 months). It is necessary to reduce the potentially harmful high moisture level in the cocoon shell and pupa body to an optimum or safe level of moisture content (6-12%). In India, the natural sun drying method is the most common method to preserve Muga cocoons for a longer period. Considerably losses may occur using the sun-drying method due to various effects such as rodents, insects, rain, microorganisms, excessive temperature, etc. To address this issue the study was conducted to improve the quality of Muga silk yield using a comparative study between Convection and IR heating methods for cocoon drying.&nbsp; 
 
Methods: In this study, Muga cocoons were dried properly at optimum temperature (50-100&deg;C) to obtain a safe moisture level for getting quality Muga silk. The drying of the Muga cocoon is processed using convection (1 kw) and Infrared (650 watts) modes of heating for the same duration of time. Muga cocoons were placed in a drying chamber initially at a high temperature (100&plusmn;5&deg;C) using both convection and Infrared heating methods separately to maintain the moisture content to an optimum level. It took approximately 75 minutes to obtain the temperature 100 from room temperature and every 15 minutes temperature measure was recorded for both methods and compared. The parameters studied were temperature, time, cocoon weight, shell weight, shell ratio and moisture content. These parameters were examined, evaluated and compared for both the Convection and IR heating methods.&nbsp; 
 
Result: The comparative study results indicated that the performance of the studied cocoon parameters namely temperature, cocoon weight, shell weight, shell ratio and moisture content are approximately similar for both convection and IR heating methods. Moisture content was maintained at the optimum range (6-12%) for both the convection and IR methods. The study provided a better performance using the IR heating method as compared to convection heating concerning energy consumption and safety for the same duration of time. Energy consumed by a 1 kW convection heater is 1.25 kWh, whereas energy consumption in a 650-watt IR heater is 0.8125 kWh.&nbsp;

A Comparative Study of Drying of Muga Cocoons using Convection and Infra-red Heating Method

The application of solar drying technology for fruits, vegetables and other crops is one of the most attractive, cost-effective and eco-friendly. Many types of solar dryers have been designed and developed in different parts of the world, having different degrees of technical performance. There are four types of solar dryers: (1) direct solar dryers, (2) indirect solar dryers, (3) mixed-mode dryers and (4) hybrid solar dryers. A synthesis view of the classification of solar energy dryers is also presented. Two groups of solar energy dryers can be identified: Passive or natural-circulation solar energy dryers and active or forced convection solar energy dryers. This paper is a review of all these types of solar dryers, including aspects of the various designs, details of construction and operational principles. Therefore, the selection of dryers for a particular situation is primarily based on what is available and the types of dryers currently used are widely based on available circumstances. Some recent developments in solar drying technology and the appropriateness of each design type for application by farmers in developing countries are also discussed.

Convective and microwave drying characteristics, energy requirement and color retention of dehydrated nettle leaves (Urtica diocia L.)

A Comparative Study of Drying of Muga Cocoons using Convection and Infra-red Heating Method

Solar Drying Technology for Agricultural Products: A Review