Particle deposition from turbulent flow: Review of published research and its applicability to ventilation ducts in commercial buildings

Abstract

This report reviews published experimental and theoretical investigations of particle deposition from turbulent flows and considers the applicability of this body of work to the specific case of particle deposition from flows in the ducts of heating, ventilating and air conditioning (HVAC) systems. Particle deposition can detrimentally affect the performance of HVAC systems and it influences the exposure of building occupants to a variety of air pollutants.The first section of this report describes the types of HVAC systems under consideration and discusses the components, materials and operating parameters commonly found in these systems. The second section reviews published experimental investigations of particle deposition rates from turbulent flows and considers the ramifications of the experimental evidence with respect to HVAC ducts. The third section considers the structure of turbulent airflows in ventilation ducts with a particular emphasis on turbulence investigations that have been used as a basis for particle deposition models.The final section reviews published literature on predicting particle deposition rates from turbulent flows.A large quantity of experimental data regarding particle deposition from turbulent flows has been collected using a range of techniques of varying quality. Nearly all of these data have been collected from straight tubes or ducts with a fully developed turbulent flow profile and the data are widely scattered. Most of the data of acceptable quality have been collected from tubes or ducts with hydraulic diameters much smaller than ducts in typical HVAC systems. Particle deposition from turbulent flow with a developing flow profile has not been systematically investigated and only two investigations of particle deposition from turbulent flow through bends have been published. Developing turbulent flow profiles and bends are common in HVAC ducts.Owing to the large number of investigations into particle deposition from turbulent flow, much is known; however, the direct applicability to the case of particles in HVAC ducts is limited. Particle size, turbulence intensity and the roughness and orientation (horizontal or vertical) of the deposition surface are the parameters that control particle deposition rates and all of these factors are likely to be pertinent in HVAC ducts. Particle diameters of concern in HVAC ducts range from about 0.003 to 30 µm and deposition rates are known to vary strongly in this range. Friction velocities in HVAC ducts are iii likely to be in the range 0.1-1 m/s and variations of turbulence intensities in this range are likely to influence deposition rates. Both microscale surface roughness (from less than 1 micron up to hundreds of microns) and macroscale roughness (about 1 mm and larger) have been demonstrated to enhance particle deposition relative to the case of a smooth surface. Microscale roughness intrinsic to the duct material, or due to corrosion or previous deposition of particles, and macroscale roughness from thermal insulation, joi...

Parameterization of aerosol dry deposition velocities onto smooth and rough surfaces

“…Experimental data for the deposition velocity (Davies, 1966;Fan & Ahmadi, 1993;Johansen, 1991;Liu & Agarwal, 1974;Sippola & Nazaroff, 2002;Wood, 1981a) are limited, mainly, to measurements in small-diameter pipes, paths of physical facilities or ventilation ducts. As a rule, these measurements are taken only for a small roughness parameter, in the range of hundreds of micrometers.…”

“…distance to the surface (wall) y + dimensionless distance to the surface (wall) y + = yu * / z 0 surface roughness parameter , u d pollutant dry deposition velocity air molecular path air dynamic viscosity air kinematic (molecular) viscosity = / t air turbulent viscosity air density p particle density p characteristic time of particle relaxation (deceleration) p = u s /g L Lagrangian timescale of turbulence + dimensionless relaxation time + = p u * 2 / Numerous papers (Davies, 1966;Fan & Ahmadi, 1993;Johansen, 1991;Kharchenko, 1997;Liu & Agarwal, 1974;Nho-Kim, Michou, and Peuch, 2004;Sehmel, 1973Sehmel, , 1980Sehmel & Hodgson, 1978;Sippola & Nazaroff, 2002;Slinn, 1978Slinn, , 1982Valentine and Smith, 2005;Wood, 1981aWood, , 1981bZaichik and Alipchenkov, 2007) describe semiempirical relations for the velocities of deposition onto vertical and horizontal walls. These were determined mainly from experimental data on turbulent deposition in ducts and channels.…”

Preventing Indoor Bioaerosol Contamination in Food Processing Environments and HVAC Systems: Assessment of Particle Deposition for Hygienic Design Purposes

“…Markedly, one of the relevant conclusions was the significance of the 2-7 μm particle size for airborne contamination of ventilation ducts with non-fully developed regime [54]. Previous studies have reported comparable observations with these particle sizes but for nonindustrial HVAC systems [47,[56][57][58].…”

“…Sippola and Nazaroff [56,57] substantially reviewed these data and pointed out widely scattered results. Thus, Sippola and Nazaroff [65,66] conducted new experiments with steel and internally insulated rectangular ducts at air speeds typically found in ventilation ducts, 2-9 m s À1 .…”

Transport efficiency and deposition velocity of fluidized spores in ventilation ducts

“…A comprehensive literature review (Sippola, 2002) revealed that considerable experimental data regarding particle deposition from turbulent flows has been collected using a range of techniques of varying quality (Sippola and Nazaroff, 2002). According to the authors, models can capture broad trends seen in experiments, but modeled results can deviate markedly from observations.…”