Characterization of R134a two-phase flow regimes in horizontal and vertical smooth tubes with capacitive sensors. (May 2021)

• Record Type: Journal Article
• Authors: Qian, Hongliang; Hrnjak, Pega
• Is Part Of: International journal of refrigeration. Volume 125(2021)
• Page Start: 90
• Page End: 103
• Publication Date: 2021-05
• Subjects: Capacitive sensor -- Two-phase flow -- Flow regime -- Void fraction -- Horizontal and vertical flow; Capteur capacitif -- Écoulement diphasique -- Régime d'écoulement -- Fraction de vide -- Écoulement vertical et horizontal; Refrigeration and refrigerating machinery -- Periodicals; 621.56
• DOI: 10.1016/j.ijrefrig.2021.01.015
• Languages: English
• ISSNs: 0140-7007

Abstract

Highlights: R134a two-phase flow regimes in horizontal and vertical tube are detected by capacitive sensors. All major flow regimes that appear within the tested mass flux range are characterized statistically. Sensors with three different axial lengths are built and evaluated. Sensors with shorter axial lengths have the same capability to characterize flow regimes. Abstract: This paper presents the identification of slug/stratified-wavy, stratified-wavy and annular regimes for horizontal flow (in the range of mass fluxes 40 – 150 kg m −2 s −1 ), and slug, churn, and annular flow regimes for vertical upward flow (in the range 65 – 115 kg m −2 s −1 ) for R134a flow through 7 mm ID tube. Flow regimes are characterized based on time plot of normalized capacitive signals, kernel density estimation (KDE), power spectral density (PSD), and visualization results from a high-speed camera. Sensors with different axial lengths (D, 2D/3, and D/2) are also tested to study the adequacy of shorter sensors for the characterization of flow regimes. Results show that all three sensors have a similar capability of characterizing flow regimes, justifying the use of the shorter sensors in many applications with limited space.