Influence of environmental conditions on drying efficiency and heat pump performance in closed and open loop drying of paddy

Abstract

The concern of cumulative demand of parboiled paddy dryings signposts the requirement of more optimized and mechanized processing. The study was conducted to fulfill the requirements of an efficient heat pump (HP) dryer unit for paddy drying in subtropical monsoon climate region of China, by utilizing the different hot air circulation methods and environmental conditions in the winter season. Therefore, a newly designed HP drying test bench enhanced with a series of heat pumps was employed for parboiled paddy drying of different varieties and sample loads. The drying efficiency and performance of HP was assessed in terms of specific moisture evaporation rate (SMER), moisture evaporation rate (MER), and coefficient of performance (COP) in closed and open-loop cycles. The closed and open-loop cycles hot air dryings were employed with the temperature and velocity ranges of 50–60˚C and 2–3 m/s, respectively. Furthermore, SMER and MER for both varieties and COP in closed and open loops were optimized using response surface methodology (RSM). The findings of the study revealed the dependency of SMER and MER on the temperature and velocity, as minimum SMER and MER were witnessed at 47.93˚C and 2.5 m/s, while COP in closed loop (2.211) was higher than that of the open cycle (1.409) due to the entrance of a significant amount of ambient air into the designed system during each cycle. Moreover, the intended parameters were optimized by exploiting RSM and were as follows: 60˚C (drying temperature), 2.76 m/s (air velocity), 0.321 (SMER1), 1.318 (SMER2), 0.208 (OSMER1), 0.865 kg/kWh (OSMER2), 0.202 (MER1), 0.796 (MER2), 0.180 (OMER1), 0.689 kg/h (OMER2), 2.211 (COP-closed), and 1.409 (COP-open). We further perceived that the temperature has more effect on the drying efficiency compared to air velocity as performance indicators were found to be increased by lofting the temperature profiles. The confidence of interval was observed significant (5%) as we equated the optimized values with experimental values, that particularly offerings our study a valuable to achieve a high quality of parboiled paddy.

Keywords:

• Coefficient of performance
• drying
• heat pump
• optimization
• specific moisture evaporation

Additional information

Funding

The authors appreciate the support and financial assistance under Jiangsu Agricultural Science and Technology Innovation Fund CX-(17)1003, provided by the College of Engineering, Nanjing Agricultural University, China.