Complete Condensation of Forced Convection Two-Phase Flow in a Miniature Tube

1999 ◽  
Vol 121 (4) ◽  
pp. 904-915 ◽  
Author(s):  
E. Begg ◽  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Two Phase Flow ◽  
Film Condensation ◽  
Vapor Flow ◽  
Pressure Jump ◽  
Phase Flow ◽  
Two Phase ◽  
Vapor Interface ◽  
Complete Condensation ◽  
Annular Film ◽  
Liquid Vapor

A physical and mathematical model of annular film condensation in a miniature tube has been developed. In the model the liquid flow has been coupled with the vapor flow along the liquid-vapor interface through the interfacial temperature, heat flux, shear stress, and pressure jump conditions due to surface tension effects. The model predicts the shape of the liquid-vapor interface along the condenser and the length of the two-phase flow region. The numerical results show that complete condensation of the incoming vapor is possible at comparatively low heat loads. Observations from a flow visualization experiment of water vapor condensing in a horizontal glass tube confirm the existence and qualitative features of annular film condensation leading to the complete condensation phenomenon in small diameter (d < 3.5 mm) circular tubes.

Control of Adiabatic Liquid/Vapor Flow Utilizing EHD Conduction Pumping Mechanism

2004 ◽  
Author(s):  
Yinshan Feng ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Mass Flux ◽  
Two Phase Flow ◽  
Finite Thickness ◽  
Flow Distribution ◽  
Vapor Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Phase Liquid ◽  
Liquid Vapor

Unlike the electrohydrodynamic (EHD) induction and iondrag pumping, the conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes which are based on the process of dissociation of the neutral electrolytic species and recombination of the generated ions. The conduction term here represents a mechanism for electric current flow in which charged carriers are produced not by injection from electrodes, but by dissociation of molecules within the fluid. This paper presents the control of adiabatic two-phase (liquid/vapor) flow distribution with EHD conduction pumping mechanism at two mass flux levels, Gtotal = 50 kg/m2s and Gtotal = 100 kg/m2s. The effects of the vapor quality, ranging from 0 to 26%, on the EHD conduction pumping have also been experimentally investigated. The measured pressure data show that the EHD conduction pumping can significantly decrease the pressure drop of the two-phase flow. It is also found that the performances of the EHD conduction pump are related to the mass flux and quality of two-phase flow.

Numerical Simulation for Two-Phase Flows in Fuel Cell Minichannels

2011 ◽  
Vol 8 (4) ◽  
Author(s):  
Jean-Baptiste Dupont ◽  
Dominique Legendre ◽  
Anna Maria Morgante
Keyword(s):  
Fuel Cell ◽  
Numerical Simulations ◽  
Two Phase Flow ◽  
Numerical Code ◽  
Experimental Investigations ◽  
Pressure Jump ◽  
Phase Flow ◽  
Two Phase Flows ◽  
Two Phase ◽  
Flow Configurations

This work presents direct numerical simulations of two-phase flows in fuel cell minichannels. Different two-phase flow configurations can be observed in such minichannels, which depend on gas-flow rate, liquid holdup, and wettability of each wall. These flows are known to have a significant impact on the fuel cell’s performance. The different two-phase flow configurations must be studied specially concerning the prediction of the transition among them. In the fuel cell minichannels, experimental investigations are difficult to perform because of the small size of the device and the difficult control of the wettability properties of the walls. In such systems, numerical approach can provide useful information with a perfect control of the flow characteristics, particularly for the wettability aspect. The numerical code used in this study is the JADIM code developed at IMFT, which is based on a “volume of fluid” method for interface capturing without any interface reconstruction. The numerical description of the surface tension is one of the crucial points in studying such systems where capillary effects control the phase distribution. The static and the dynamics of the triple line between the liquid, the gas, and the wall is also an essential physical mechanism to consider. The numerical implementation of this model is validated in simple situations where analytical solutions are available for the shape and the pressure jump at the interface. In this paper we present the characteristics of the JADIM code and its potential for the studies of the fuel cell internal flows. Numerical simulations on the two-phase flows on walls, in corners, and inside channels are shown.

Coupled Liquid and Vapor Flow in Miniature Passages With Micro Grooves

1999 ◽  
Vol 121 (3) ◽  
pp. 729-733 ◽  
Author(s):  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Liquid Flow ◽  
Shear Stresses ◽  
Vapor Flow ◽  
Two Phase ◽  
Interface Shear ◽  
Element Analysis ◽  
Vapor Interface ◽  
Vapor Channel ◽  
Frictional Interaction ◽  
Liquid Vapor

Friction factor coefficients for liquid flow in a rectangular micro-groove coupled with the vapor flow in a vapor channel of a miniature two-phase device were calculated using finite element analysis. The results show that the effect of the vapor-liquid frictional interaction on the liquid flow decreases with curvature of the liquid-vapor interface. Shear stresses at the liquid-vapor interface are significantly nonuniform, decreasing towards the center of the liquid-vapor meniscus.

Two-Phase Flow Phenomena for Boiling in Two Parallel Microchannels

2004 ◽  
Author(s):  
H. Y. Li ◽  
P. C. Lee ◽  
F. G. Tseng ◽  
Chin Pan
Keyword(s):  
Heat Transfer ◽  
Slug Flow ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Nucleate Boiling ◽  
Vapor Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Silicon Bulk ◽  
Flow Phenomena

Boiling heat transfer and corresponding two-phase flow phenomena are of significant interest for the design of a compact evaporator. The present work investigates experimentally, using a high-speed digital CCD camera, the two-phase flow phenomena for boiling in a silicon-based, two parallel trapezoid microchannels, which were prepared by the combination of silicon bulk micro machining and Pyrex-silicon wafer bonding. Onset of nucleate boiling, bubbly flow, slug flow, and partial dry out slug flow are typically observed along the flow direction. The appearance of the partial dryout slug flow may degrade the nucleate boiling heat transfer in the microchannel. At a low flow rate, reversed vapor flow is observed. In such a flow pattern, liquid droplets are formed intermittently on the inner wall of top Pyrex glass due to vapor condensation. Moreover, the reversed vapor flow usually accompanies with large magnitude two-phase flow oscillations.

Heat Transfer for Annular Flow in Microchannel Bends: A Free Energy Minimization Model for Square Channels

2007 ◽  
Author(s):  
Sara Beaini ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Free Energy ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Centrifugal Acceleration ◽  
Two Phase ◽  
The Mean ◽  
Flow Morphology ◽  
Liquid Vapor

For annular liquid-vapor two-phase flow in straight microchannels, effects of gravity are generally small compared to viscous and/or inertia forces. In serpentine evaporator or condenser passages with semicircular return bends, the bend radius may be so small that large centrifugal body forces are generated as the fluid flows through the bend region of the passage. This paper summarizes a model analysis based on the premise that flow morphology in the bend is dictated by radial acceleration forces and the thermodynamic Second Law requirement that the established two-phase flow morphology minimizes the free energy at the local temperature and pressure. An analytical model is derived relating the dependence of the free energy on vapor core geometry, and the geometry that minimizes free energy is determined numerically. This provides a prediction of the mean thickness of the liquid surrounding the vapor core, and the mean heat transfer coefficient for annular flow vaporization or condensation, as a function of flow parameters and physical properties. When this relation is cast in dimensionless form, the effect of centrifugal acceleration is quantified in terms of a Weber number (We) that represents the ratio of centrifugal body force to surface tension force. The analysis indicates that centrifugal acceleration acts to displace the vapor towards the inside of the curved passage and distort the liquid-vapor interface. Displacement occurs at any level of acceleration. Significant distortion is found to occur only for We &gt; 1. The effects of these morphology changes on heat transfer are analyzed and the implications of these predictions for designing microchannel evaporators and condensers are explored.

Analysis of Two-Phase Flow in Cryogenic Damper Seals—Part I: Theoretical Model

1998 ◽  
Vol 120 (2) ◽  
pp. 221-227 ◽  
Author(s):  
Grigory L. Arauz ◽  
Luis San Andre´s
Keyword(s):  
Two Phase Flow ◽  
Flow Region ◽  
Forced Response ◽  
Dynamic Force ◽  
Phase Flow ◽  
Two Phase ◽  
Fluid Damper ◽  
Theoretical Predictions ◽  
Saturated Mixture ◽  
Liquid Vapor

Cryogenic fluid damper seals operating close to the liquid-vapor region (near the critical point or slightly sub-cooled) are likely to develop a two-phase flow region which affects the seal performance and reliability. An all-liquid, liquid-vapor, and all-vapor, i.e., a “continuous vaporization” bulk flow model is presented for prediction of the seal dynamic forced response. Continuity, momentum, and energy (enthalpy) transport equations govern the two-phase flow of a homogeneous saturated mixture in thermodynamic equilibrium. Static and dynamic force performance characteristics for the seal are obtained from a perturbation analysis of the governing equations. Theoretical predictions and comparisons to experimental measurements in a liquid and gaseous nitrogen seal are presented in Part II. The effects of two-phase flow regimes on the dynamic force coefficients and stability of an oxygen damper seal are also discussed.

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