Energy and exergy analysis in solar drying of pistachio with air recycling system

ABSTRACT

A solar drier with and without air recycling (Methods I and II) along with a sun drying system (Method III) were used to reduce the moisture content of pistachio from 40 to ∼5% (wet basis) at similar weight conditions. Although the ΔT’s of ambient air in Methods I and II reached, respectively, to 18 and 14°C, it did not increase more than 2°C in Method III. The drying air of Method I obtained ∼55% more enthalpy from its solar collectors and transferred ∼35% more heating energy to the product than the one in Method II. Consequently it’s thermal and pickup efficiencies became, respectively, 40 and 80% more than Method II. Although the highest exergy efficiencies of Methods I and II were equal to each other (∼95%), the maximum exergy loss of Method I was higher than Method II due to its higher air temperature and pressure loss (because of continuous air circulation). Although its energy utilization ratio and drying rate were, respectively, 30% more than Method II and 20% higher than Method III, its drying time was 20 and 30% less than the ones in Methods II and III. Overall, the pistachio dried with Method I used much less energy than those dried with other methods and had a higher quality than those dried with commercial driers due to drying temperature <50°C.

KEYWORDS:

• Air recycling mode
• energy utilization ratio
• enthalpy
• solar drying of pistachio
• temperature rise in ambient air