Convective Flat-plate Solar Heat Collector for Cauliflower Drying

• DOI: 10.1016/j.biosystemseng.2005.11.012
• Publication Date: 2006-01-24T09:15:36Z
• Authors: Dattatreya M. Kadam; D.V.K. Samuel
• Keywords: Thermosiphon

A forced convective, flat-plate, solar heat collector has been developed and tested for drying cauliflower. Its main components were galvanised iron sheet with black paint, transparent glass over it and a closed duct. Four panels were arranged in parallel to each other and the hot air was transferred to drying chamber by means of forced air blower. Solar time (14:363 h), standard time (+5:30 h), solar declination angle (−7·15°), total sunshine duration (11:48 h) and solar heat collector thermal efficiency were calculated using solar collector theory. Ambient and collector outlet air temperature as well as relative humidity (RH) were measured at an interval of 1 h for 28-day experimental period. The temperature rise of the drying air ranged from a minimum of 1·7 °C to a maximum of 13·5 °C and the RH reduction was from a minimum of 1·59% to a maximum of 10·5% by passing through the solar collector at a mass flow rate of 4·81 m3 s−1. The average mid-day thermal efficiency was around 16·5% and the peaks out of this average are due to the inertia effect that keeps the collector temperature almost constant for some minutes when the radiation falls. A linear correlation between the temperature difference from ambient (T−Ta) and the radiation I, as well as inlet and outlet air temperature and RH were obtained. Cauliflower was blanched for 3 min in boiling water and dipped in sodium chloride, potassium metabisulphite and sodium benzoate for 15 min in 1·0% preservative concentration level before drying cauliflower in solar dryer. The treatments were found to be significantly different (probability P