233 Formation Parameters of Zero-Net-Mass-Flux Jet Flow Patterns

2005 ◽  
Vol 2005.2 (0) ◽  
pp. 149-150
Author(s):  
Takashi NAITOH ◽  
Seishi Suzuki
Keyword(s):  
Mass Flux ◽  
Jet Flow ◽  
Flow Patterns ◽  
Zero Net Mass Flux

Flow patterns of zero-net-mass-flux jets and parameters

2004 ◽  
Vol 2004.2 (0) ◽  
pp. 265-266
Author(s):  
Takashi NAITOH ◽  
Chieko YAMAMOTO
Keyword(s):  
Mass Flux ◽  
Flow Patterns ◽  
Zero Net Mass Flux

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Chang Yong Park ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Abstract C O 2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and heat flux from 5kW∕m2 to 15kW∕m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kg∕m2s. However, enhanced convective boiling contribution was observed at 400kg∕m2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

Transient Two-Phase Flow Patterns by Application of a High Voltage Pulse Width Modulated Signal and the Effect on Condensation Heat Transfer

2010 ◽  
Author(s):  
K. Ng ◽  
C. Y. Ching ◽  
J. S. Cotton
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Electric Fields ◽  
High Voltage ◽  
Mass Flux ◽  
Pulse Width ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Pulse Width Modulated

The objectives of this study are (i) to determine the transient phase redistributions of a two-phase flow in a smooth horizontal annular channel by applying high voltage pulses to induce electric fields and (ii) to quantify the resultant changes in the condensation heat transfer. The experiments were performed using refrigerant R-134a flowing in a tube that was cooled on the outside by a counter-current flow of water. The electric fields are established by applying high voltage to a concentric rod electrode inside a grounded tube. The effect of the electrohydrodynamic (EHD) forces on the changes to the initial stratified/stratified wavy flow pattern was visualized using a high speed camera. The EHD effect results in the redistribution of the liquid-vapour phase within the channel and unique flow structures, such as twisted liquid cones and entrained droplets, are observed. These structures only appear during the initial application of EHD and are absent in the steady state flow pattern. Experiments were performed using a 8kV pulse width modulated (PWM) signal with duty cycles ranging from 0–100% to evaluate the heat transfer and pressure drop characteristics of the transient EHD flow patterns. The resultant heat transfer increased with the duty cycle to approximately 2.7-fold at a low mass flux (45–55kg/m2s) and 1.2-fold at a high mass flux (110kg/m2s). The enhancement was higher as the pulse width was increased.

Interactions Between Parallel Minichannels During Flow Boiling of R134A

2014 ◽  
Author(s):  
Dolaana M. Khovalyg ◽  
Predrag S. Hrnjak ◽  
Aleksandr V. Baranenko ◽  
Anthony M. Jacobi
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Visualization ◽  
Mass Flux ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transient Pressure ◽  
Correlation Degree ◽  
Channel Relationship ◽  
The Individual

This work focuses on the study of flow boiling of R134a in 0.54 mm square parallel minichannels, with a particular focus on the transient pressure drop of individual channels and their interaction. The individual pressure drop in each passage was analyzed to establish the inter-channel relationship; additionally, the effect of heat and mass flux and the inlet vapor qualities on the flow patterns of each channel was studied based on flow visualization and pressure drop measurements. The mass flux and heat flux in the experiments were varied up to 800 kg/m2s and 10 kW/m2 respectively. The heat flux was controlled and varied independently in each channel. Results illustrate that interaction between channels exists, and the correlation degree depends on the flow boiling dynamics in each passage. The pressure drop oscillation in each channel affects the flow redistribution between channels. A channel subjected to the least heat flux tends to correlate the most with greater heated channels because of the mass flux fluctuations caused by boiling phenomena in other channels.

Transitory Behavior of Synthetic Jets

2005 ◽  
Author(s):  
Michael Amitay ◽  
Florine Cannelle
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Input Signal ◽  
Mass Flux ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Hot Wire ◽  
Stroke Length ◽  
Zero Net Mass Flux

The transitory behavior of an isolated synthetic (zero net mass flux) jet was investigated experimentally using PIV and hot-wire anemometry. In the present work, the synthetic jet was produced over a broad range of length- and time-scales, where three formation frequencies, f = 300, 917, and 3100Hz, several stroke lengths (between 5 and 50 times the slit width) and Reynolds numbers (between 85 and 408) were tested. The transitory behavior, following the onset of the input signal, in planes along and across the slit was measured. It was found that the time it takes the synthetic jet to become fully developed depends on the stroke length, formation frequency and Reynolds number. In general, the transients consist of four stages associated with the merging of vortices in both cross-stream and spanwise planes that grow in size, which lead to the pinch off of the leading vortex before the jet reaches its steady-state.

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