Experimental analysis of mixing ventilation efficiency using a vortex diffuser: Comparison to a lobed multicone diffuser

Abstract

In a recent work, an innovative multi-cone diffuser integrating lobed inserts as vortices promoters was proposed, and was compared to its counterpart without lobed inserts. The former offers better mixing of the jet with the ambient air, and significantly improves thermal comfort. In this study, the innovative diffuser is compared to a vortex diffuser under the same experimental conditions. The vortex diffuser is described in the scientific and technical A c c e p t e d M a n u s c r i p t literature as the best diffuser in terms of mixing efficiency due to the swirling effect, being thereby a reference for the innovative lobed diffuser. The results demonstrate that the vortex diffuser does not produce the expected swirling effect. The rotation of the jet is prevented by the immediate attachment of the flow to the ceiling due to the Coanda effect. The jet behaves as a radial ceiling-attached flow having a poor mixing performance. It is believed that such a diffuser would be efficient when mounted on a long duct far away from the ceiling. Hence, it will be better suited for high ceilings, such as in industrial or commercial spaces. In this case, the proposed lobed diffuser becomes an appropriate and efficient mixing ventilation solution for rooms having low ceiling heights. KEYWORDS Mixing ventilation, lobed diffuser, vortex diffuser, cold jet, PIV measurements, thermal comfort PRACTICAL IMPLICATIONS Flow pattern and thermal comfort are analyzed in a room under mixing ventilation. Vortex (VD) and multi-cone lobed (LD) diffusers are compared in a cooling mode. The jet rotation vanishes near the VD exit due to the Coanda effect. It results in poor mixing performance for VD compare to LD. LD is best in terms of thermal comfort, pressure loss and noise generation.

A review of different ventilation modes on thermal comfort, air quality and virus spread control

“…While in the case of cooling, the pollutant removal rate was not well as MV often leaded to dead corners where clean air could not reach. The solution of increasing air flow rate would cause new problems, such as loud noise and high energy consumption [ 21 ]. In addition, MV had a higher risk of airborne infectious diseases, especially in the era of COVID-19.…”

The Applicability of Coanda Effect Hysteresis for Designing Unsteady Ventilation Systems

“…Mixing ventilation, which is most widely used in modern buildings, relies on the dilution method to optimize thermal comfort, improve energy efficiency and enhance the movement of fresh air [73]. These considerations are particularly important in the cooling mode, where thermal discomfort, the presence of dead pockets in the occupied zone and noise are frequently reported [74]. Mechanical ventilation can also generate drafts.…”

“…This type of draft affects the entire body, but causes discomfort mainly at head and neck level [75]. The geometry and location of the supply nozzle are critical for achieving optimal air velocity, direction of flow and the proportions in which fresh air is mixed with stale air [74]. Various supply nozzles for mechanical ventilation systems have been described in the literature [76,77].…”

Merkezi Klima Santrallerindeki Plakalı Difüzörlerin Akış Alanına ve Basınç Düşümüne Etkisinin Sayısal İncelenmesi

“…They stated that the duct length was reduced by approximately 68 % in the combined system compared to the conventional ventilation system. Meslem et al [25] compared the innovative diffuser and the vortex diffuser with the same operating conditions in their study using the particle imaging velocity measurement (PIV) method. They revealed that the Coanda Effect and the jet effect disappear rapidly near the diffuser outlet in the vortex diffuser.…”

“…Meslem ve ark. [25], parçacık görüntüleme ile hız ölçümü (PIV) yöntemini kullandıkları çalışmalarında, aynı çalışma koşullarına sahip yenilikçi difüzör ile girdap difüzörü karşılaştırmışlar ve girdap difüzörde koanda etkisinin ve jet etkisinin difüzör çıkışının yakınında hızlıca yok olduğunu ortaya koymuşlardır. Çetin ve ark.…”