A Dynamic Programming Approach to Stabilize Forced-Convection Two-Phase Flow Systems With “Pressure-Drop” Oscillations

1970 ◽  
Vol 92 (1) ◽  
pp. 94-100
Author(s):  
C. J. Maday
Keyword(s):  
Dynamic Programming ◽  
Pressure Drop ◽  
Forced Convection ◽  
Two Phase Flow ◽  
Oscillatory Behavior ◽  
Order System ◽  
Programming Approach ◽  
Phase Flow ◽  
Two Phase ◽  
Dynamic Programming Approach

Optimization theory is applied to a forced-convection two-phase flow system with heat addition described by a second-order system of differential equations. The mathematical model describes a physical system in which low-frequency pressure-drop oscillations occur, and these oscillations may either grow or decay with time depending on whether the system is stable. The dynamic programming approach is applied to obtain a suboptimal feedback control system which is very stable and exhibits no oscillatory behavior. A system is synthesized whereby pressure and temperature fluctuations are used to control heat-input fluctuations in order to provide stability.

Two-Phase Boiling Flow in Microchannels: Instabilities Issues and Flow Regime Mapping

2003 ◽  
Author(s):  
Y. Peles
Keyword(s):  
Heat Exchanger ◽  
Pressure Drop ◽  
Flow Regime ◽  
Forced Convection ◽  
Two Phase Flow ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Two Phase ◽  
Micro Scale ◽  
Micro Channels

The design, fabrication, and evaluation of forced convection boiling two-phase flow, micro scale heat exchanger are described. The micro heat exchanger consist of a heater, and 16 mm long multiple parallel triangular micro channels, with hydraulic diameter ranging from 50 μm to 200 μm. The system allowed simultaneously visualizing the flow regime, to measure the resistor temperature distribution, the pressure drop, and input power levels. Experiments were conducted using water with mass flow rate of 1–10 g/min and heat fluxes ranging from 10–60 W/cm2 in order to better understand the flow mechanism associated with micro scale forced convection boiling two-phase flow. The pressure drop, temperature, fluctuation and flow regimes map were obtained. The results are consistent with newly reported studies and show that flow fluctuation at that scale is exaggerated with respect to conventional size channels. A unique flow regime was observed and was named “rapid bubble growth”.

Pressure Drop for Oil-Gas Two-Phase Flow Through Straight Horizontal Pipe

2007 ◽  
Author(s):  
Wenhong Liu ◽  
Liejin Guo ◽  
Ximin Zhang ◽  
Kai Lin ◽  
Long Yang ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Horizontal Pipe ◽  
Flow Through ◽  
Oil Gas

scholarly journals Experimental Investigation and Prediction on Pressure Drop during Flow Boiling in Horizontal Microchannels

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 510
Author(s):  
Yan Huang ◽  
Bifen Shu ◽  
Shengnan Zhou ◽  
Qi Shi
Keyword(s):  
Pressure Drop ◽  
Flow Model ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Separated Flow ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Vapor Quality ◽  
Two Phase ◽  
Gas Flux

In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122, heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. The experimental results show that the Chisholm parameter in the separated flow model relies heavily on the vapor quality, especially in the low vapor quality region (from 0 to 0.1), where the two-phase flow pattern is mainly bubbly and slug flow. Then, the measured pressure drop data are compared with those from six separated flow models. Based on the comparison result, the superficial gas flux is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux . The mean absolute error (MAE ) of the new flow correlation is 16.82%, which is significantly lower than the other correlations. Moreover, the applicability of the new expression has been verified by the experimental data in other literatures.

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2003 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

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