Experimental study of the ejector structural parameters on the dynamic operating characteristics of heat pump dryer system
A new designed solar assisted ejector enhanced heat pump dryer system (SE-HPD) with closed-loop drying chamber has been experimentally investigated. In the SE-HPD, a hot water cycle system has been designed to simulate the solar collector. This study experimentally investigated the effects of ejector structural parameters on the dynamic operational characteristics of SE-HPD. The effects of nozzle throat diameter, mixing chamber throat diameter, and nozzle exit position (NXP) on dehumidification performance, heating efficiency, and ejector performance were analyzed. Experimental results demonstrated that the system performed best when the nozzle throat diameter was 2.21 mm (adjusting the nozzle needle displacement to 1.8 mm), achieving a moisture extraction rate (MER) of 1.65 kg?h-1, a specific moisture extraction rate (SMER) of 1.76 kg?(kWh)-1, and the highest heating COP of 3.62. However, small nozzle throat diameters (5 mm) caused primary flow jet impingement on the mixing chamber wall, reducing the entrainment ratio to 0.31. Importantly, the study revealed the synergistic matching relationship between mixing chamber throat diameter and nozzle throat diameter: larger mixing chamber required an increased optimal nozzle diameter, with a critical area ratio (AR) optimum value. These findings provide essential experimental insights for dynamically optimizing ejector configurations in heat pump drying system.