scholarly journals ELEMENTARY ASSESSMENTS AND SIMULATIONS BASED PROPOSALS FOR NEW HEAT TRANSFER CORRELATIONS AND FLOW REGIME MAPS FOR ANNULAR/STRATIFIED REGIME OF SHEAR DRIVEN INTERNAL CONDENSING FLOWS

2015 ◽  
Author(s):  
Siddharth Ravikumar
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Condensing Flows ◽  
Heat Transfer Correlations ◽  
Internal Condensing Flows ◽  
Stratified Regime ◽  
Flow Regime Maps

On the Application of Macro-Pipe Two-Phase Heat Transfer Correlations and Flow Regime Maps to Mini-Channels

2006 ◽  
Author(s):  
Avram Bar-Cohen ◽  
Ilai Sher ◽  
Emil Rahim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Regime ◽  
Annular Flow ◽  
Negative Slope ◽  
Two Phase ◽  
Heat Transfer Correlations ◽  
Two Phase Heat Transfer ◽  
Flow Regime Maps

The present study is aimed at evaluating the ability of conventional “macro-pipe” correlations and regime transitions to predict the two-phase thermofluid characteristics of mini-channel cold plates. Use is made of the Taitel-Dukler flow regime maps, seven classical heat transfer coefficient correlations and two dryout predictions. The vast majority of the mini-channel two-phase heat-transfer data, taken from the literature, is predicted to fall in the annular regime, in agreement with the reported observations. A characteristic heat transfer coefficient locus has been identified, with a positive slope following the transition from Intermittent to Annular flow and a negative slope following the onset of partial dryout at higher qualities. While the classical two-phase heat transfer correlations are generally capable of providing good agreement with the low-quality annular flow data the quality at which partial dryout occurs and the ensuing heat transfer rates are not predictable by the available macro-pipe correlations.

Internal Condensing Flows Inside a Vertical Pipe: Experimental/Computational Investigations of Effects of Constrained and Natural Exit Conditions

2005 ◽  
Author(s):  
A. Narain ◽  
A. Siemionko ◽  
J. H. Kurita ◽  
T. W. Ng ◽  
N. Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Power Plants ◽  
Computational Simulation ◽  
Vertical Tube ◽  
Film Condensation ◽  
Flow Loop ◽  
Transfer Rates ◽  
Application Systems ◽  
Condensing Flows ◽  
Internal Condensing Flows

The flow and heat transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. For steady/quasi-steady internal condensing flows (that involve compressible vapor at low Mach Numbers), the vapor’s ability to change its density — and hence interfacial mass transfer rates and associated locations of the interface — allows the flow to have a rather significant dependence on exit conditions. Both experimental and direct computational simulation results presented here show that this is indeed the case for flows of pure vapor experiencing film condensation on the inside walls of a vertical tube. In applications, the totality of boundary conditions are determined not only by the condenser; but also by the flow-loop (or the system) — of which the condenser is only a part. Therefore, the results outlined here should contribute towards a better understanding of the behavior (particularly the extent to which vapor compressibility effects affect the flow regimes of operation — i.e. annular, plug/churn, etc.) and response (transients due to start-up, system instabilities, etc.) of condensers in application systems (e.g. Rankine Cycle power plants, Capillary Pumped Loops, Looped Heat Pipes, etc.). In this connection, an experimental example of a relevant system instability is presented here. In summary, the experimental results presented here, and computational results presented elsewhere, reinforce the fact that there exist multiple steady solutions (with different heat transfer rates) for different exit conditions and that there also exists a “natural” steady solution for straight vertical condensers (circular and rectangular cross-sections).

Experimental Study on the Flow Regime Identification in the Case of Co-Current Condensation of R134a in a Vertical Smooth Tube

2010 ◽  
Author(s):  
Ahmet Selim Dalkilic ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Flow Rate ◽  
Annular Flow ◽  
Cooling Water ◽  
Test Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Regime Identification ◽  
Flow Regime Maps

The present study investigates an intensive comparison of flow regime maps for the verification of annular condensation flow of R134a checked by sight glasses at the inlet and outlet sections of a vertical smooth copper tube having inner diameter of 8.1 mm and a length of 500 mm. R134a and water are used as working fluids in the tube side and annular side of a double tube heat exchanger, respectively. The experimental apparatus are designed to capable of changing the different operating parameters such as mass flow rate, condensation temperature of refrigerant, cooling water temperature and mass flow rate of cooling water etc. and investigate their effect on heat transfer coefficients and pressure drops. Condensation experiments are performed at the mass flux of 456 kg m−2s−1, the saturation temperature is around 40°C, heat fluxes and average qualities are between 16.16–50.89 kW m−2 and 0.81–0.93 respectively. Considering Chen et al.’s annular flow theory on the heat transfer coefficients that are independent from tube orientation as long as annular flow exists along the tube length, experimental data belong to annular flow inside the test tube are plotted on the various flow regime maps and used in the flow regime identification correlations proposed for two-phase flow in horizontal and vertical tubes separately. In spite of their different operating conditions, Barnea et al., Hewitt and Robertson, Baker, Thome, Kattan et al., Chen et al.’s flow regime maps and Taitel and Dukler’s, Dobson’s, Akbar et al.’s, Breber et al.’s, Cavallini et al.’s, Soliman’s flow pattern correlations from literature are found to be predictive for the annular flow conditions in the test tube.

Effects of Gravity and Surface Tension and Interfacial-Waves and Heat-Transfer Rates in Internal Condensing Flows

2003 ◽  
Author(s):  
Q. Liang ◽  
X. Wang ◽  
A. S. Barve ◽  
A. Narain
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Numerical Solutions ◽  
Film Condensation ◽  
Vapor Flow ◽  
Transfer Rates ◽  
Condensing Flows ◽  
Steady Solutions ◽  
Internal Condensing Flows ◽  
Good Agreement

The paper presents accurate numerical solutions of the full 2D governing equations for steady and unsteady laminar/laminar internal condensing flows. The chosen geometry allows for film condensation on the bottom wall of a tilted (from vertical to horizontal) channel. It is found that it is important to know whether the exit conditions are constrained or unconstrained because incompressible vapor flows occur only for exit conditions that are unconstrained. For the incompressible vapor flow situations, a method for computationally obtaining the stable steady/quasi-steady solutions is given here and the resulting solutions are shown to be in good agreement with some relevant experimental data for horizontal channels. These solutions are shown to be sensitive to the frequency-content and strength of ever-present minuscule transverse vibrations of the condensing surface. The effects of noise-sensitivity, gravity (terrestrial to zero-gravity), and surface tension on the attainability of stable steady/quasi-steady solutions, structure of superposed waves, and heat-transfer rates are discussed. It is shown that significant enhancement in wave-energy and heat-transfer rates are possible by designing the condensing surface noise to be in resonance with the intrinsic waves.

Development of a Flow Regime Map for a Horizontal Pipe With the Multi-Classification Support Vector Machines

2008 ◽  
Author(s):  
L. M. Tam ◽  
A. J. Ghajar ◽  
H. K. Tam ◽  
S. C. Tam
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mixed Convection ◽  
Flow Regime ◽  
Single Phase ◽  
Flow Regimes ◽  
Support Vector ◽  
Flow Maps ◽  
Vector Machines ◽  
Flow Regime Maps

For horizontal circular pipes under uniform wall heat flux boundary condition and three different inlet configurations (re-entrant, square-edged, bell-mouth), Ghajar and Tam (1995) developed flow regime maps for the determination of the boundary between single-phase forced and mixed convection using experimental data of Ghajar and Tam (1994). Based on the ratio of the local peripheral heat transfer coefficient at the top and the bottom, the heat transfer data was classified as either forced or mixed convection among the different flow regimes. The forced-mixed convection boundary was then obtained by empirical correlations. From the flow maps, heat transfer correlations for different flow regimes were recommended. Recently Trafalis et al. (2005) used the Multiclass Support Vector Machines (SVM) method to classify vertical and horizontal two-phase flow regimes in 4 pipes with good accuracy. In this study, the SVM method was applied to the single-phase experimental data of Ghajar and Tam (1994) and new flow regime maps were developed. Five flow regimes (forced turbulent, forced transition, mixed transition, forced laminar, mixed laminar) were identified in the flow maps using Reynolds and Rayleigh numbers as the identifying parameters. The flow regimes on the boundaries of the new maps were represented by the SVM decision functions. The results show that the new flow regime maps for the three types of inlets can classify the forced and mixed convection experimental data in different flow regimes with good accuracy.

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