Experimental investigation of drying characteristics of lima beans with passive and active mode greenhouse solar dryers

摘要

In the study, the thermal performance of the even span and parabolic roof type solar greenhouse dryers is investigated under the active and passive modes under the same operating conditions. Dryers were covered with the 200-mu m UV stabilized polyethylene sheets to enhance the solar insolation effect. The performance of these dryers is evaluated for drying lima beans (Phaseolus lunatus). The moisture content of Lima beans was reduced from 75% (w.b.) to 11% (w.b). For both of active and passive mode conditions, the parabolic dryer could dry in 28 and 32 hr, respectively and that for the even span dryer, it could achieve the same state in 32 and 36 hr, respectively. The open sun drying took as high as 40 hr to dry time for the lima beans. The highest thermal efficiency of the dryers was estimated to be 14.7% for the active mode parabolic dryer and the minimum as 12.03% in the passive mode even span dryers. The nutrition retainment was the highest for parabolic active mode dryer with the payback period as 2.15 years, as against 10 years of expected solid life span and strong suggestion is made for the use of the small scale needful farmers.Practical Applications Drying is an energy consuming processes, and industries require more amount of energy for drying a food grain. In the current scenario, more attention is toward for usage of the Solar based dryers for the abundance of availability of solar energy which makes cost effective. However, the popularly available conventional method of open Sun drying of lima beans resulted in contamination of product from external dirt, degradation due to direct heating, existence of uncontrolled dry rate and additional dry time. To solve the above constraints, in open sun drying and to improve the dried product quality, the author constructed a simple, compact and economically modified greenhouse solar dryer. The quality of dried lima beans under active mode convection parabolic roof was superior. The much needed carbohydrate and protein values, of dried lima beans of 100 g sample for forced convection parabolic roof greenhouse solar dryer had shown the increase of 2 and 10% than open sun dry sample. Among various seeds used to making food stuff, the lima beans are one of the choices for people.