UTILISATION OF SOLAR TUNNEL GREENHOUSE AS A SOLAR DRIER FOR DRYING SEEDLES GRAPES: I: THERMAL PERFORMANCE ANALYSIS OF SOLAR DRIER

In this research work an attempt has been made to analyse the thermal performance of solar tunnel greenhouse which can be utilised as a solar drier for seedless grapes. Three identical solar tunnel greenhouse driers (STGD) were used under the climatic conditions of El-Mansoura city, Egypt (latitude and longitude angles of 31.05ºN and 31.37 ºE, respectively), during August 2009. The thermal performance analysis of the solar driers (active or dynamic drier) based on the energy balance equations was evaluated. The three active solar driers were operated under three different mass flow rates of 0.122, 0.183, and 0.259 kg/s. The obtained results revealed that, the daily average solar energy available outside the solar driers was 16.727 kWh of which 12.572 kWh was available inside the drier with an average effective transmittance of 75.16%. The daily average solar energy available inside the three solar tunnel greenhouse driers during the experimental period was 12.572 kWh of which 6.993, 7.699, and 6.687 kWh, respectively, converted into useful heat gain. These solar energy available inside the three solar driers resulting in increase the inside air temperatures above the outside (31.6°C) by 21.9, 12.5, and 9.4°C, and reduce the air relative humidity under the outside (40.6%) by 9.0%, 3.1%, and 5.1%, respectively. The daily average overall thermal efficiencies of the three solar tunnel greenhouse driers during the experimental period were 55.62%, 61.24%, and 53.19%, consequently, 44.38%, 38.76%, and 46.81% of the solar energy available inside the solar driers was lost, respectively. The predicted heat energy for the three solar driers was validated well with that measured during the experimental period by 0.995, 0.991, and 0.998, respectively, which gave an excellent agreement.