ABSTRACT
Five small scale and two medium scale crop dryers with and without rockbed heat store well as a hybrid crop dryer, suitable for crop drying in different locations in savanna of Norther Nigeria were designed, constructed and lab-tested in IAR/ABU, Zaria The full capacity of the small scale dryers are 50kg of maize grain, 20kg of fresh tomatoes and 15kg of fresh okro The full capacity of the medium scale dryer fresh tomatoes and 30kg of fresh okro. The hybrid dryer is of capacity 600kg of unthreshed maize. The medium scale wood type, large scale metal type solar crop dryers were constructed the field, at Jere in Kaduna State, New-Wuse and Kwada in Niger State, The full capacity of the medium wood type dryer is 250kg of unthreshed fresh maize and 400kg of unthreshed fresh maize for each of the metal and mud type solar dryers. These dryers were built with the locally available and affordable materials. Laboratory and field tests were conducted on these dryers from May 1990 to June 1991. During the test 50 to 99% of savings in drying time were achieved with the natural convection solar dryers and the hybrid crop dryer when compared with the traditional open sun drying method. Up to 60% crop drying percentage cash flow gain over the traditional drying method was realised. Dryers cost analysis and their payback period showed that the designed dryers are within the farmers reach and that it is more economically profitable than the usual traditional open sun drying method. The nutrient value of vegetables and. fruits dried with the direct mode solar dryers having rockbed heat storage proved to the best when compared to the traditional drying method and the indirect mode solar crop dryer method. Data on the rate of crop drying are fully presented in Chapter five.