Experimental performance investigation of natural convection solar drying system

The aim of this study is to dry red peppers grown abundantly in the Şanlıurfa province under sanitary conditions and in a shorter time compared to traditional drying methods. In order to achieve this a natural convection solar dryer (NCSD) consisting of a natural convection solar air collector (NCSAC), and an integrated drying cabinet has been designed and manufactured. In the design of the NCSD and the planning of the study, local insolation duration, the geographical conditions, and the contribution of the red peppers produced to the regional economy were taken into consideration.The drying performance of the NCSD was investigated in two separate experiments conducted for 11 hours in a day in June 2021. Open sun drying experiments were also carried out on the same dates for comparison. It was measured the daily mass (moisture) losses of the samples in the experiments, besides the temperatures at different points of the NCSD were measured hourly. Moreover, the thermal performance test of the NCSD (NCSAC) was carried out in October 2021. In addition to the previous experiments, the air velocity at the NCSAC inlet was also measured in this experiment. The solar radiation fluxes and wind speeds used in the thermal calculations of NCSAC were obtained from the ġanlıurfa Meteorology Regional Directorate.The moisture content of the samples dried in the NCSD decreased to the desired final moisture content (below 4.3% on a wet basis and 7% on a dry basis on average) for the red peppers at the end of the 4th day. The moisture content of the open sun-dried samples could only be reduced to the desired final moisture content (below 8.1% on a wet basis) at the end of the 7th day. NCSD both reduced the final moisture content (~2.5% on a wet basis) of the red peppers and shortened the drying time (about 1/3) compared to open sun drying. The effects of spoilage (extreme shrinkage and color changes) and undesirable foreign materials (such as dust, insects, feathers, etc.), which are seen in open sun dried red peppers, were not encountered in NCSD application. In the experiments, calculations were carried out for theoretical thermal efficiencies for NCSAC, effective diffusion coefficients of red peppers, dimensionless moisture ratios, drying rates, energy and drying efficiencies, specific energy consumption and specific moisture extraction rates of the NCSD. The average theoretical and experimental thermal efficiencies of NCSAC are %44 and %40, respectively based on the experiment conducted in October 2021. As a result of the performance experiments, it was evaluated that the design changes that would enhance the natural air flow in NCSD would improve the thermal efficiency and drying performance