An investigation into exhaled particle dispersion under stratum ventilation with a pulsating air supply

Stratum ventilation (SV) with a pulsating air supply (PASV) can enhance thermal comfort. However, no studies have focused on the cross-infection prevention performance of PASV. In this study, six experimental cases were conducted to analyse the air distribution characteristics at the breathing zone of PASV, SV and mixing ventilation (MV), further comparing the exposure risks amongst the three air distribution methods. Subsequently, by varying the average supply air velocity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mover> <mml:mi>v</mml:mi> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> ), total cycle duration ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mtext>total</mml:mtext> </mml:msub> </mml:mrow> </mml:math> ) and the supply air velocity difference between duty and idle periods ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>v</mml:mi> </mml:math> ), numerical simulations were conducted on six cases under PASV. This further investigated the effects of supply air parameters on particle dispersion characteristics. The results showed that PASV had the potential to reduce indoor cross-infection risk. The magnitude of indoor cross-infection risk amongst different air distribution methods was as follows, PASV ≈ SV &lt; MV. Reducing the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mtext>total</mml:mtext> </mml:msub> </mml:mrow> </mml:math> of the air supply to 120 s enhanced particle dilution at the breathing zone, thereby mitigating the indoor cross-infection risk by 20%. Higher <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mover> <mml:mi>v</mml:mi> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> (1.8 m/s) and smaller <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>v</mml:mi> </mml:math> (0.3 m/s) enhanced breathing-zone particle dilution, lowering cross-infection risk by 30% and 15%, respectively. The impact of PASV parameters on particle dispersion was ranked as follows: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mover> <mml:mi>v</mml:mi> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> </mml:mrow> <mml:mo>&gt;</mml:mo> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mtext>total</mml:mtext> </mml:msub> </mml:mrow> <mml:mo>&gt;</mml:mo> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>v</mml:mi> </mml:math> .