Flow Visualization and Flow Pattern Identification With Power Spectral Density Distributions of Pressure Traces During Refrigerant Condensation in Smooth and Microfin Tubes
Author:
Liebenberg Leon1, Thome John R.2, Meyer Josua P.1
Affiliation:
1. Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria, 0002, South Africa 2. Laboratory of Heat and Mass Transfer, Faculty of Engineering Science, Swiss Federal Institute of Technology-Lausanne (EPFL), Lausanne 1015, Switzerland
Abstract
This paper presents a flow pattern identifier of the prevailing flow regime during refrigerant condensation inside smooth- and microfin tubes. The power spectral density distribution of the fluctuating condensing pressure signal was used to identify 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, as well as a new flow regime map for microfin-tube condensation. Experimental work was conducted for condensing refrigerants R-22, R-407C, and R-134a at an average saturation temperature of 40°C with mass fluxes ranging from 300–800 kg/m2 s, and with vapor qualities ranging from 0.05–0.15 at condenser outlet to 0.85–0.95 at condenser inlet. Tests were conducted with one smooth-tube condenser and three microfin-tube condensers (with helix angles of 10°, 18°, and 37° respectively). The power spectral density distributions of the condensing pressure signals distinguish the annular and intermittent (slug and plug) flows. A very low resonant frequency (<40 Hz) and low power spectral density amplitude of the pressure oscillation denoted stratified and wavy flows. As the annular flow regime was approached, the oscillations became larger and their frequencies increased (typically 40–120 Hz). Intermittent flow showed the most distinct character of all flow regimes. Its trace consisted of large amplitude pressure pulses occurring at fairly constant frequencies (approximately 50, 60, 80, 100, and 120 Hz). As the transition from intermittent to annular flow began, the pressure fluctuations became less regular and the amplitude dropped sharply.
Publisher
ASME International
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics,General Materials Science
Reference22 articles.
1. Liebenberg, L., Bergles, A. E., and Meyer, J. P., 2000, “A Review of Refrigerant Condensation in Horizontal MicroFin Tubes,” 40, Proc. ASME Advanced Energy Systems Division, pp. 155–168. 2. Kattan, N., Thome, J. R., and Favrat, D., 1998a, “Flow Boiling in Horizontal Tubes. Part 1: Development of a Diabatic Two-Phase Flow Pattern Map,” ASME J. Heat Transfer, 120(1), pp. 140–147. 3. Kattan, N., Thome, J. R., and Favrat, D., 1998b, “Flow Boiling in Horizontal Tubes. Part 3: Development of a New Heat Transfer Model Based on Flow Patterns,” ASME J. Heat Transfer, 120(1), pp. 156–165. 4. Kattan, N., Thome, J. R., and Favrat, D., 1995a, “Measurement and Prediction of Two-Phase Flow Patterns for New Refrigerants Inside Horizontal Tubes,” ASHRAE Trans., 101(2), 95-17. 5. Kattan, N., Thome, J. R., and Favrat, D., 1995b, “Boiling of R-134a and R-123 in a Microfin Tube,” Proc. 19th Int. Congress of Refrigeration, The Hague, Vol. IVa, pp. 337–344.
Cited by
41 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|