Use of solar green house for ventilated drying vegetables process with use of Clay CaCl2
Use of solar green house for ventilated drying vegetables process with use of Clay CaCl2
The use of solar energy in drying of tomatoes through improved post harvesting technology may solve some problems of processing products. Most of the solar crop drying systems in market have small loading capacity and cannot operate during the night. By using new technology of integrated solar greenhouse dryer system [SGDS] with Clay-CaCl2 desiccant energy storage system was designed and tested. This model overcome the issues of old technologies and it had high loading capacity, able to dry at night and structural simplicity. In this system enhanced night-time drying capacity by integrated with a low-cost Clay-CaCl2. The dryer was able to dry fresh tomatoes from 93.9% to 8.3% within 27 hours with solar greenhouse drying efficiency of 23% during daytime and desiccant drying efficiency of 19.9% during nighttime. These techniques benefits to tropical areas.
Experimental Setup
The experimental greenhouse solar dryer with solid Clay-CaCl2 desiccant energy storage system was constructed using locally available materials and equipment. For a maximum passage of solar radiation, the system was covered with transparent greenhouse plastic with transmittance value of 80%. The system was specifically designed to dry fresh tomatoes during day time using solar thermal energy and night-time using solid Clay-CaCl₂desiccants. The solar greenhouse dryer system was positioned with its longest side on North-South direction to capture maximum solar radiation. Four 25 W, 12 Volts DC solar photovoltaic powered fans with speed regulator were installed in the system. The extractive fans were mounted on both solar greenhouse chamber and desiccant chamber to extract moist air out and enhance the drying process. One fan was positioned in between greenhouse dryer and desiccant chamber to enable moisture removal during the night time using desiccant energy storage system. All fans were powered by two solar modules Polycrystalline 50-Watt solar panel Victron 50W 12V the make of China to charge battery of capacity 200Ah to be used during night. Ambient temperature, greenhouse dryer air temperature, relative humidity of the inlet and outlet air conditions were recorded, and as well solar radiation.Airflow rate were set at three levels for both drying and desiccant chamber. A 0.19 m3/s, 0.28 m3/s and 0.45 m3/s; and 0.07 m3/s 0.17 m3/s and 0.36 m3/s as independent variables termed as low, medium and high flow rates, for dryer and desiccant chamber respectively. The data was collected for set of three rates at different times to establish the optimum parameters. The best rate selected for this study was 0.28 m3/s and 0.07 m3/s for tomato and desiccant chamber respectively.
The greenhouse shield facilitated the heating of air within the system to create hot air to dry sliced tomatoes. The sliced tomatoes were spread in eight trays in two-layer vis upper and lower layer each carry four trays. The drying process was observed until the product was completely dried under the greenhouse dryer. Lastly under each tray the weight loss of the product was measured and the overall drying performance of the system was estimated. Solar photovoltaic powered fans with battery energy storage air flow mode during day and night time. During the day solar energy enters the greenhouse and is converted into heat and exhaust fans move the moisture. During the night desiccant energy storage adsorbs the moisture from the tomatoes via desiccant air dehumidification process thereby continuing the overall tomato drying process.
Solid CaCl2 – Clay Desiccant Preparation
Solid Clay – CaCl2 desiccants were prepared by mixing clay with CaCl2 as recommended by Thoruwa et al. A total of 32.3 kg solid Clay-CaCl2 desiccants were spread uniformly onto desiccant trays and loaded into the chamber
Recommendation
In order to improve the performance of the solar greenhouse dryer with Clay-CaCl₂desiccant energy storage, air flow needs further evaluation to improve on the desiccant moisture uptake especially during night drying operation.
Reference:
Susan Andrew Mbacho, Thomas Thoruwa, Nickson Kipngetich Lang’at, Elias Ako. Performance of an Integrated Solar-Greenhouse Photovoltaic Ventilated Dryer with Clay-CaCl2 Energy Storage Desiccants for Tomato Drying. American Journal of Energy Engineering. Vol. 9, No. 2, 2021, pp. 19-29. doi: 10.11648/j.ajee.20210902.11
