Differential heat and mass transfer rate influences on the activation efficiency of laminar flow condensation particle counters

Jikku M. Thomas, Xiaoshuang Chen, Anne Maißer, Chris Hogan

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Laminar flow condensation particle counters (CPCs) are uniquely sensitive detectors for aerosol particles in the nanometer size range (i.e. below 10 nm in size they can have single particle sensitivity). Their operation hinges upon the creation of supersaturation of a working fluid; particles exposed to supersaturated vapor grow by condensation to optically detectable sizes. The degree of supersaturation is fully controlled via differential rates of heat transfer and working fluid vapor mass transfer. Because of the Kelvin relationship governed vapor pressure of small particles, in all CPCs there is a critical size/cut-size (diameter), and particles smaller than this size do not grow and are not detected efficiently. While efforts have been made to control the CPC activation efficiency (i.e. the fraction of particles detected as a function of size), prior studies have not examined how differential heat and mass transfer in CPCs are governed by changes in gas composition. Here, we measure and model CPC activation efficiencies (with 1-butanol as the working fluid) in mixtures of gases of disparate thermophysical properties, namely helium and molecular nitrogen. Our experiments show that the activation efficiency of smaller particles (i.e. below 8 nm in the tested CPC) can be increased by adding a modest amount of helium to the aerosol (mole fractions near 0.20). This is expected based upon the increased Lewis number brought about by Helium addition, and supported by predictions of CPC activation efficiency based upon thermophysical property variable models of coupled heat, mass, and momentum transfer within the CPC condenser region. Interestingly, we find that when operating with a constant precision orifice diameter (choked flow), the activation efficiency for a given sub-10 nm particle diameter first increases with increasing Helium mole fraction and then decreases as the Helium mole fraction increases beyond 0.67. In comparison, experiments with constant mass transfer Peclet number (Pem = 77) show an increase in CPC activation efficiency up to a helium mole fraction of 0.67, but then the activation efficiency decreases more modestly beyond this helium mole fraction. We attribute these contrasting results to the increased flowrate through the instrument under constant orifice diameter conditions, which affects the performance of the CPC saturator. Finally, through modeling we show that the ability to enhance the activation efficiency of a CPC via a modest amount of helium addition is general, and can be applied with other heavy working fluids. The results presented in this study elucidate the importance of gas composition and Lewis number controlled differential heat and mass transfer rates on the performance of condensation based nanoparticle detectors.

Original languageEnglish (US)
Pages (from-to)740-750
Number of pages11
JournalInternational Journal of Heat and Mass Transfer
Volume127
DOIs
StatePublished - Dec 1 2018

Fingerprint

Radiation counters
radiation counters
laminar flow
Laminar flow
mass transfer
Condensation
Mass transfer
condensation
Helium
Chemical activation
heat transfer
activation
Heat transfer
helium
working fluids
Lewis numbers
Fluids
Gases
Supersaturation
gas composition

Keywords

  • Condensation particle counters
  • Gas mixture transport
  • Lewis number
  • Peclet number

Cite this

Differential heat and mass transfer rate influences on the activation efficiency of laminar flow condensation particle counters. / Thomas, Jikku M.; Chen, Xiaoshuang; Maißer, Anne; Hogan, Chris.

In: International Journal of Heat and Mass Transfer, Vol. 127, 01.12.2018, p. 740-750.

Research output: Contribution to journalArticle

@article{dfd4e3cd84794718867766f63e97c9a4,
title = "Differential heat and mass transfer rate influences on the activation efficiency of laminar flow condensation particle counters",
abstract = "Laminar flow condensation particle counters (CPCs) are uniquely sensitive detectors for aerosol particles in the nanometer size range (i.e. below 10 nm in size they can have single particle sensitivity). Their operation hinges upon the creation of supersaturation of a working fluid; particles exposed to supersaturated vapor grow by condensation to optically detectable sizes. The degree of supersaturation is fully controlled via differential rates of heat transfer and working fluid vapor mass transfer. Because of the Kelvin relationship governed vapor pressure of small particles, in all CPCs there is a critical size/cut-size (diameter), and particles smaller than this size do not grow and are not detected efficiently. While efforts have been made to control the CPC activation efficiency (i.e. the fraction of particles detected as a function of size), prior studies have not examined how differential heat and mass transfer in CPCs are governed by changes in gas composition. Here, we measure and model CPC activation efficiencies (with 1-butanol as the working fluid) in mixtures of gases of disparate thermophysical properties, namely helium and molecular nitrogen. Our experiments show that the activation efficiency of smaller particles (i.e. below 8 nm in the tested CPC) can be increased by adding a modest amount of helium to the aerosol (mole fractions near 0.20). This is expected based upon the increased Lewis number brought about by Helium addition, and supported by predictions of CPC activation efficiency based upon thermophysical property variable models of coupled heat, mass, and momentum transfer within the CPC condenser region. Interestingly, we find that when operating with a constant precision orifice diameter (choked flow), the activation efficiency for a given sub-10 nm particle diameter first increases with increasing Helium mole fraction and then decreases as the Helium mole fraction increases beyond 0.67. In comparison, experiments with constant mass transfer Peclet number (Pem = 77) show an increase in CPC activation efficiency up to a helium mole fraction of 0.67, but then the activation efficiency decreases more modestly beyond this helium mole fraction. We attribute these contrasting results to the increased flowrate through the instrument under constant orifice diameter conditions, which affects the performance of the CPC saturator. Finally, through modeling we show that the ability to enhance the activation efficiency of a CPC via a modest amount of helium addition is general, and can be applied with other heavy working fluids. The results presented in this study elucidate the importance of gas composition and Lewis number controlled differential heat and mass transfer rates on the performance of condensation based nanoparticle detectors.",
keywords = "Condensation particle counters, Gas mixture transport, Lewis number, Peclet number",
author = "Thomas, {Jikku M.} and Xiaoshuang Chen and Anne Mai{\ss}er and Chris Hogan",
year = "2018",
month = "12",
day = "1",
doi = "10.1016/j.ijheatmasstransfer.2018.07.002",
language = "English (US)",
volume = "127",
pages = "740--750",
journal = "International Journal of Heat and Mass Transfer",
issn = "0017-9310",
publisher = "Elsevier Limited",

}

TY - JOUR

T1 - Differential heat and mass transfer rate influences on the activation efficiency of laminar flow condensation particle counters

AU - Thomas, Jikku M.

AU - Chen, Xiaoshuang

AU - Maißer, Anne

AU - Hogan, Chris

PY - 2018/12/1

Y1 - 2018/12/1

N2 - Laminar flow condensation particle counters (CPCs) are uniquely sensitive detectors for aerosol particles in the nanometer size range (i.e. below 10 nm in size they can have single particle sensitivity). Their operation hinges upon the creation of supersaturation of a working fluid; particles exposed to supersaturated vapor grow by condensation to optically detectable sizes. The degree of supersaturation is fully controlled via differential rates of heat transfer and working fluid vapor mass transfer. Because of the Kelvin relationship governed vapor pressure of small particles, in all CPCs there is a critical size/cut-size (diameter), and particles smaller than this size do not grow and are not detected efficiently. While efforts have been made to control the CPC activation efficiency (i.e. the fraction of particles detected as a function of size), prior studies have not examined how differential heat and mass transfer in CPCs are governed by changes in gas composition. Here, we measure and model CPC activation efficiencies (with 1-butanol as the working fluid) in mixtures of gases of disparate thermophysical properties, namely helium and molecular nitrogen. Our experiments show that the activation efficiency of smaller particles (i.e. below 8 nm in the tested CPC) can be increased by adding a modest amount of helium to the aerosol (mole fractions near 0.20). This is expected based upon the increased Lewis number brought about by Helium addition, and supported by predictions of CPC activation efficiency based upon thermophysical property variable models of coupled heat, mass, and momentum transfer within the CPC condenser region. Interestingly, we find that when operating with a constant precision orifice diameter (choked flow), the activation efficiency for a given sub-10 nm particle diameter first increases with increasing Helium mole fraction and then decreases as the Helium mole fraction increases beyond 0.67. In comparison, experiments with constant mass transfer Peclet number (Pem = 77) show an increase in CPC activation efficiency up to a helium mole fraction of 0.67, but then the activation efficiency decreases more modestly beyond this helium mole fraction. We attribute these contrasting results to the increased flowrate through the instrument under constant orifice diameter conditions, which affects the performance of the CPC saturator. Finally, through modeling we show that the ability to enhance the activation efficiency of a CPC via a modest amount of helium addition is general, and can be applied with other heavy working fluids. The results presented in this study elucidate the importance of gas composition and Lewis number controlled differential heat and mass transfer rates on the performance of condensation based nanoparticle detectors.

AB - Laminar flow condensation particle counters (CPCs) are uniquely sensitive detectors for aerosol particles in the nanometer size range (i.e. below 10 nm in size they can have single particle sensitivity). Their operation hinges upon the creation of supersaturation of a working fluid; particles exposed to supersaturated vapor grow by condensation to optically detectable sizes. The degree of supersaturation is fully controlled via differential rates of heat transfer and working fluid vapor mass transfer. Because of the Kelvin relationship governed vapor pressure of small particles, in all CPCs there is a critical size/cut-size (diameter), and particles smaller than this size do not grow and are not detected efficiently. While efforts have been made to control the CPC activation efficiency (i.e. the fraction of particles detected as a function of size), prior studies have not examined how differential heat and mass transfer in CPCs are governed by changes in gas composition. Here, we measure and model CPC activation efficiencies (with 1-butanol as the working fluid) in mixtures of gases of disparate thermophysical properties, namely helium and molecular nitrogen. Our experiments show that the activation efficiency of smaller particles (i.e. below 8 nm in the tested CPC) can be increased by adding a modest amount of helium to the aerosol (mole fractions near 0.20). This is expected based upon the increased Lewis number brought about by Helium addition, and supported by predictions of CPC activation efficiency based upon thermophysical property variable models of coupled heat, mass, and momentum transfer within the CPC condenser region. Interestingly, we find that when operating with a constant precision orifice diameter (choked flow), the activation efficiency for a given sub-10 nm particle diameter first increases with increasing Helium mole fraction and then decreases as the Helium mole fraction increases beyond 0.67. In comparison, experiments with constant mass transfer Peclet number (Pem = 77) show an increase in CPC activation efficiency up to a helium mole fraction of 0.67, but then the activation efficiency decreases more modestly beyond this helium mole fraction. We attribute these contrasting results to the increased flowrate through the instrument under constant orifice diameter conditions, which affects the performance of the CPC saturator. Finally, through modeling we show that the ability to enhance the activation efficiency of a CPC via a modest amount of helium addition is general, and can be applied with other heavy working fluids. The results presented in this study elucidate the importance of gas composition and Lewis number controlled differential heat and mass transfer rates on the performance of condensation based nanoparticle detectors.

KW - Condensation particle counters

KW - Gas mixture transport

KW - Lewis number

KW - Peclet number

UR - http://www.scopus.com/inward/record.url?scp=85049787787&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85049787787&partnerID=8YFLogxK

U2 - 10.1016/j.ijheatmasstransfer.2018.07.002

DO - 10.1016/j.ijheatmasstransfer.2018.07.002

M3 - Article

AN - SCOPUS:85049787787

VL - 127

SP - 740

EP - 750

JO - International Journal of Heat and Mass Transfer

JF - International Journal of Heat and Mass Transfer

SN - 0017-9310

ER -