Flow regime heated transfer

Note that the tube contains a liquid before the bubbly flow regime and a vapor after the mist-flow regime. Heat transfer in those two cases can be determined using the appropriate relations for single-phase convection heat transfer. Many correlations are proposed for the determination of heat transfer... 

FIGURE 15.89 Flow regimes, heat transfer regimes, and wall and fluid temperatures in forced convective boiling (from Collier and Thome [3], by permission of Oxford University Press). 

In Chap. 5 the available data related to flow and heat transfer of a gas-liquid mixture in single and parallel channels of different size and shape are presented. These data concern flow regimes, void fraction, pressure drop and heat transfer. The effects of different parameters on flow patterns and hydrodynamic and thermal characteristics of gas-liquid flow are discussed. 

For conventional size pipes the flow regimes depend on orientation. Two-phase air-water flow and heat transfer in a 25 mm internal diameter horizontal pipe were investigated experimentally by Zimmerman et al. (2006). Figure 5.38 shows the flow... 

The present model takes into account how capillary, friction and gravity forces affect the flow development. The parameters which influence the flow mechanism are evaluated. In the frame of the quasi-one-dimensional model the theoretical description of the phenomena is based on the assumption of uniform parameter distribution over the cross-section of the liquid and vapor flows. With this approximation, the mass, thermal and momentum equations for the average parameters are used. These equations allow one to determine the velocity, pressure and temperature distributions along the capillary axis, the shape of the interface surface for various geometrical and regime parameters, as well as the influence of physical properties of the liquid and vapor, micro-channel size, initial temperature of the cooling liquid, wall heat flux and gravity on the flow and heat transfer characteristics. 

The mean heat-transfer coefficient will depend on the number of tubes crossed. Figure 12.31 is based on data for ten rows of tubes. For turbulent flow the correction factor Fn is close to 1.0. In laminar flow the heat-transfer coefficient may decrease with increasing rows of tubes crossed, due to the build up of the temperature boundary layer. The factors given below can be used for the various flow regimes the factors for turbulent flow are based on those given by Bell (1963). 

Lahey, R. T., Jr., and F. A. Schraub, 1969, Mixing, Flow Regimes and Void Fraction for Two-Phase Flow in Rod Bundles, in Two-Phase Flow and Heat Transfer in Rod Bundles, ASME, New York. (5) Lahey, R. T., Jr., B. S. Shiralkar, and D. W. Radeliffe, 1971, Mass Flux and Enthalpy Distribution in a Rod-Bundle for Single and Two-Phase Flow Conditions, Trans. ASME, J. Heat Transfer, 93 197-209. (5)... 

Therefore, there is still a need for further research for a fundamental understanding of fluid flow and heat transfer phenomena in microchaimels in order to explore and control the phenomena in a length scale regime in which we have very little experience. 

Bayazitoglu, Y., and Kakac, S., (2005) Flow Regimes in MicroChannel Single-Phase Gaseous Fluid Flow, Microscale Heat Transfer-Fundamentals and Applications, S. Kakae (ed.), Kluwer Academie Publishers, Dordrecht (This publication). 

As far as convective heat transfer is concerned, liquid and gaseous flows musf be considered separately. Liquid flow has been investigated experimentally, whereas analytical, numerical and molecular simulation techniques have been applied to understand the characteristics of gaseous flow and heat transfer. While the Navier-Stokes equations can still be applied, due to the small size of microchannels, some deviations from the conventionally sized applications have been observed. Flow regime boundaries are significantly different, as well as flow and heat transfer characteristics. 

The present lecture summarizes some of tiie most recent joint research results from tiie cooperation between the Federal University of Rio de Janeiro, Brasil, and tiie University of Miami, USA, on tiie fransient analysis of both fluid flow and heat transfer within microchannels. This collaborative link is a natural extension of a long term cooperation between the two groups, in the context of fimdamental work on transient forced convection, aimed at tiie development of hybrid numerical-analytical techniques and tiie experimental validation of proposed models md methodologies [1- 9]. The motivation of this new phase of tiie cooperation was thus to extend the previously developed hybrid tools to handle both transient flow and transient convection problems in microchannels within the slip flow regime. 

Kuznetsov, V.V., Shamirzaev, A.S., Ershov I.N., (2004), Flow Boiling Heat Transfer and Regimes of Upward How in Minichannels, 3 Int. Symposium on Two-Phase Flow Modeling and Experimentation, 22-25 September, Pisa, Italy, ven 03. 

MULTIPLE FLOW REGIME HEAT AND MASS TRANSFER MODEL... 

Willet, S.D. and D.S. Chapman, 1989. Temperatures, fluid flow and heat transfer mechanisms in the Uinta Basin. In Beck, A.E., Garven, G. and L. Stegena (eds.), 1989. Hydrogeological regimes and their subsurface thermal effects. Geophysical Monograph 47/ lUGG Volume 2, pp. 29-33... 

Y. Bayazitoglu and S. Kakac, Flow regimes in microchaimel single-phase gaseous flow, Microscale Heat Transfer - Fundamentals and Applications in Biological Systems and MEMS, edited by S. Kakac, L. Vasihev, Y. Bayazitoglu, and Y. Yener (Kluwer Academic Publishers, The Netherlands 2005). 

Cooling channels of the type depicted in Fig. 4.206 and c will first be discussed. For channels that are very long relative to the spacing of the vertical surfaces, the flow and heat transfer become fully developed (i.e., velocity and temperature profiles become invariant with distance along the channel) and are described by simple equations. For short channels or widely spaced vertical surfaces, a boundary layer regime is observed in which the boundary layers on the vertical walls remain well separated. In the latter case the heat transfer relation is similar... 

A. Blumenkrantz, A. Yarden, and J. Taborek, Performance Prediction and Evaluation of Phelps Dodge Spirally Grooved Tubes, Inside Tube Flow Pressure Drop and Heat Transfer in Turbulent Regime, Heat Transfer Research, Inc., Rep. 2439-300-4, HTRI, Pasadena, CA, 1969. 

Figure 15.89 shows an expanded view of the regimes of flow and heat transfer in a single tube (which might correspond roughly to tube N in Fig. 15.88). Also shown in Fig. 15.89 is the...

Fig. 3. Schematic diagram of the various modes of two-phase flow and heat transfer regimes at a...

The large surface-to-volume ratio in microchannels tends to enhance several factors that were neglected in macroscale flow and heat transfer, such as surface frictiOTi, compressibility, surface roughness, viscous, channel surface geometry, surface electrostatic charges, axial wall heat conduction, and measurement errors. Velocity slip flow has been widely studied accurately to model the characteristics of gas flow in the Knudsen layer for aU flow regimes. A review of the slip velocity can be fotmd in Zhang et al. [4]. 

Regimes of flow and heat transfer in a tube with vertical upflow forced convective boiling subjected to axially uniform heat. (Data from Jones, O.C., Jr., Nuclear Reactor Safety Heat Transfer, Hemisphere Publishing Corp., New York, 1981.)... 

In the Couette flow inside a cone-and-plate viscometer the circumferential velocity at any given radial position is approximately a linear function of the vertical coordinate. Therefore the shear rate corresponding to this component is almost constant. The heat generation term in Equation (5.25) is hence nearly constant. Furthermore, in uniform Couette regime the convection term is also zero and all of the heat transfer is due to conduction. For very large conductivity coefficients the heat conduction will be very fast and the temperature profile will... 

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