Experimental investigation on the drying characteristics in a solar assisted ejector enhanced heat pump dryer system

A new designed solar assisted ejector enhanced heat pump dryer system (SE-HPD) with closed-loop drying chamber using the R134A refrigerant has been experimentally investigated. In the SE-HPD, a hot water cycle system has been designed to simulate the solar collector. The dynamic drying characteristic of SE-HPD and the conventional heat pump dryer system (CHPD) were compared. Further, various drying characteristic parameters and the ejector performances of the new system under different solar radiation intensities, valve opening (OP) of electronic expansion valves and by-pass return air ratios (BR) were studied. The experimental results revealed that the exergy efficiency and moisture extraction rate (MER) of SE-HPD were always better than those of the CHPD. The exergy efficiency and MER of SE-HPD were improved by 28.7% and 54.3% compared with those of CHPD under the given operating condition. It was found that higher solar radiation intensity could significantly improve the pressure lift ratio of the ejector and contributed to the higher heating performance of SE-HPD. The optimum OP and BR to obtain the maximum MER for SE-HPD were also found to be 50 % and 70 %, respectively. The performance advantages of the proposed system have been verified through this experimental research.