- Paddy is an important food crop in the world, especially in Thailand. Before being processed, freshly-harvested paddy needs to be dried in order to avoid quality deterioration by microorganisms and respiration. Impinging stream dryer is one of the energy efficient dryer (ISD) for removing surface moisture of particulate materials including freshly-harvested paddy. However, energy efficiency of ISD can still be improved. One of the possible methods that can be used to reduce the net energy supply to the ISD is the reuse of exhaust air leaving a drying system. In this study, an impinging stream dryer with exhaust air recycle system was therefore developed. In addition, a system combining the principles of impinging stream drying and pneumatic drying (ISD-PD) for paddy was developed to enhance the energy efficiency of the drying process. Drying experiments were divided into two parts: namely, ISD system alone and ISD-PD system. The overall performance (in terms of volumetric water evaporation rate, volumetric heat transfer coefficient and specific energy consumption) of the drying system at various conditions was investigated. The quality of dried paddy was evaluated in terms of head rice yield and whiteness. In the case of ISD system alone, the effect of exhaust air recycle on the overall performance of the drying system and quality of dried paddy was also assessed. It was found from the experiments that, in the case of ISD system alone, the moisture content of paddy was reduced from its original value by 3.3 to 6.0% (d.b.) within a very short period of time (less than 2.1 s). The maximum value of the volumetric water evaporation rate was found to be about 144 kgwater/m3 h, while the maximum value of the volumetric heat transfer coefficient was about 6871 W/m3 K. The lowest total specific energy consumption of the process was 4.4 MJ/kgwater when using inlet air temperature of 100 oC, particle flow rate of 120 kgdry solid/h and air recycle ratio of 40%. With the use of exhaust air recycle, the energy consumption of the drying ง process could be reduced by around 20%. The head rice yield significantly decreased only with an increase in the inlet air temperature. The effects of inlet air temperature, paddy feed flow rate and air recycle ratio on whiteness was not significant, however. In the case of ISD-PD system, the moisture content of paddy was reduced from its original value by 6.6 to 9.7% (d.b.) within a very short period of time (2.4 to 2.6 s). The mean residence time of the paddy was increased by 33 to 41% via the use of the ISD-PD system, leading to moisture reduction rates 55 to 166% higher than those for the pneumatic dryer (PD) alone. The lowest total specific energy consumption of 2.6 MJ/kgwater was noted at the inlet air temperature of 70 oC and paddy feed flow rate of 62 kgdrysolid/h. The head rice yield decreased with an increase in the inlet air temperature and paddy feed flow rate. On the other hand, the effects of inlet air temperature and paddy feed flow rate on whiteness was not significant.