172 Experimental study on optimum CADR filter thickness of air purifiers

People spend most of their time indoors. Additionally, concentrations of certain pollutants are sometimes higher indoors than outdoors. Therefore, there is a need to ensure good indoor air quality, and air purifiers can provide valuable assistance. We constructed a system to compare the filtration efficiency of different air purifier filter media brands when stacked in multiple layers. In addition, the filtration efficiency was obtained by using a Scanning Mobility Particle Sizer to measure the aerosol number concentrations and size distributions upstream and downstream of the air purifier, and the Clean Air Delivery Rate (CADR) was calculated by multiplying the filtration efficiency and the flow rate. In particular, we show that the tested filter media thickness significantly affects the CADR. When the thickness of the filter material reaches a specific value, the filtration efficiency benefit brought by the increase of the filter material thickness is not enough to make up for the loss caused by the reduction of the air volume, and the CADR value begins to decrease as the thickness of the filter material increases. We find that the ideal filter thickness at 2.7 watts is approximately 12 mm for the blower and filter materials examined in this study. When using the MPPS as an indicator, the capture efficiency of the optimally thick filter material ranges from 7% to 35%. In the follow-up, we further explore the influence of the combination of filter materials and blowers with different characteristics and the particulate matter load on designing the optimal CADR value.