TY - JOUR
T1 - The characterization of flow regimes with power spectral density distributions of pressure fluctuations during condensation in smooth and micro-fin tubes
AU - Liebenberg, Leon
AU - Meyer, Josua P.
N1 - Funding Information:
The authors are indebted to Mr. Petur Thors (Wolverine Inc.) and Dr. Axel Kriegsmann (Wieland-Werke AG) who supplied the experimental micro-fin tubes. The research work was performed with a South African National Research Foundation grant, under grant number 2053287.
PY - 2006/11
Y1 - 2006/11
N2 - This paper presents an objective predictor of the prevailing flow regime during refrigerant condensation inside smooth-, micro-fin and herringbone tubes. The power spectral density (PSD) distribution of the fluctuating condensing pressure signal was used to predict the prevailing flow regime, as opposed to the traditional (and subjective) use of visual-only methods, and/or smooth-tube flow regime maps. The prevailing flow regime was observed by using digital cameras and was validated with the use of the conventional smooth-tube flow regime transition criteria, Froude rate criteria, as well as a new flow regime map that was developed for micro-fin tube condensation. Experimental work was conducted for condensing R-22, R-407C, and R-134a at an average saturation temperature of 40 °C with mass fluxes ranging from 300 to 800 kg/m2 s, and with vapour qualities ranging from 0.85-0.95 at condenser inlet to 0.05-0.15 at condenser outlet. Tests were conducted with one smooth-tube condenser and three micro-fin tube condensers (with helix angles of 10°, 18°, and 37°, respectively). It is shown that the micro-fin tubes cause a delay in the transition from annular to intermittent flow by at least 19% (compared to the smooth tube), thus significantly contributing to the enhancement of heat transfer.
AB - This paper presents an objective predictor of the prevailing flow regime during refrigerant condensation inside smooth-, micro-fin and herringbone tubes. The power spectral density (PSD) distribution of the fluctuating condensing pressure signal was used to predict the prevailing flow regime, as opposed to the traditional (and subjective) use of visual-only methods, and/or smooth-tube flow regime maps. The prevailing flow regime was observed by using digital cameras and was validated with the use of the conventional smooth-tube flow regime transition criteria, Froude rate criteria, as well as a new flow regime map that was developed for micro-fin tube condensation. Experimental work was conducted for condensing R-22, R-407C, and R-134a at an average saturation temperature of 40 °C with mass fluxes ranging from 300 to 800 kg/m2 s, and with vapour qualities ranging from 0.85-0.95 at condenser inlet to 0.05-0.15 at condenser outlet. Tests were conducted with one smooth-tube condenser and three micro-fin tube condensers (with helix angles of 10°, 18°, and 37°, respectively). It is shown that the micro-fin tubes cause a delay in the transition from annular to intermittent flow by at least 19% (compared to the smooth tube), thus significantly contributing to the enhancement of heat transfer.
KW - Condensation
KW - Flow regimes
KW - Micro-fins
KW - Power spectral density
KW - Refrigerants
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U2 - 10.1016/j.expthermflusci.2006.03.023
DO - 10.1016/j.expthermflusci.2006.03.023
M3 - Article
AN - SCOPUS:33750612121
SN - 0894-1777
VL - 31
SP - 127
EP - 140
JO - Experimental Thermal and Fluid Science
JF - Experimental Thermal and Fluid Science
IS - 2
ER -