An Investigation of Refrigerant Void Fraction in Horizontal, Microfin Tubes

Abstract

A series of evaporation and condensation experiments have been performed on horizontal microfin tubes with refrigerants R134a and R410A. Mass flux varied from 75 kg/m 2 -s to 700 kglm 2 -s and average test section quality varied from 5 percent to 80 percent. Zero degree (axial grooving) and 18 degree helix micro fin tube configurations have been examined in both condensation and evaporation. Four tubes were examined (7.3mm and 8.9mm diameters with axial and 18 degree helix angle microfins). Evaporation and adiabatic conditions in microfin tubes generally show similar void fraction trends found in smooth tubes. Condensation void fraction results tend to show a reduction in void fraction relative to smooth tube results, possibly indicating liquid filling of groove regions.

The Impact of Modeling Complexity and Two-Phase Flow Parameters on the Accuracy of System Modeling for Unitary Air Conditioners

“…Void fraction model selection is important and mainly affects the discharge pressure and the compressor power consumption. Baroczy (1965) separated empirical tabular vertical upflow Yashar et al (2001) separated empirical explicit horizontal Taitel and Barnea (1990) slug semi-empirical explicit Tandon et al (1985) annular semi-empirical explicit Taitel and Barnea (1990) Figure 3: Cooling capacity comparisons for the 7½-ton split system using the Baroczy void fraction correlation. …”

Condensation in Minichannels and Microchannels

“…Like the flow regime studies discussed above, most existing void fraction investigations have focused on larger tubes with adiabatic airÀwater flows. The validity of extrapolating these findings to two-phase refrigerant flows has not been established, and has been questioned by researchers including Yashar et al (2001) and Winkler et al (2012b). Winkler et al (2012b) presented a comprehensive review of experimental and modeling techniques to obtain void fractions, with a focus on condensation in small channels.…”

“…Yashar et al (2001) acknowledged the higher vapor phase densities in condensing flows compared to airÀwater or evaporating flows, and pointed out that this leads to lower vapor velocities, more stratified flows, and a dependence of the void fraction on mass flux. Many of these models assume annular flow regardless of the flow conditions.…”

A first-principles simulation model for the start-up and cycling transients of household refrigerators

“…The void fraction models proposed by Baroczy (1965) and Yashar et al (2001) were used to estimate the refrigerant masses in the condensing and evaporating regions, respectively.…”