scholarly journals AN ASSESSMENT OF FLOW REGIME MAPS AND A NUMERICAL HEAT TRANSFER CORRELATION FOR THE STRATIFIED/ANNULAR REGIME OF SHEAR-DRIVEN INTERNAL CONDENSING FLOWS

2014 ◽  
Author(s):  
FNU Nikhil Shankar
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Heat Transfer Correlation ◽  
Numerical Heat Transfer ◽  
Condensing Flows ◽  
Annular Regime ◽  
Internal Condensing Flows ◽  
Flow Regime Maps

Condensation Heat Transfer of Soliman Flow Pattern in Mini-Channel

2006 ◽  
Author(s):  
Q. Chen ◽  
R. S. Amano
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flow Pattern ◽  
Flow Regime ◽  
Flow Region ◽  
Condensation Heat Transfer ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Annular Regime ◽  
Fin Tubes

The condensation heat transfer for R134a in the two kinds of in-tube three-dimensional (3-D) micro-fin tubes with different geometries is experimentally investigated. Based on the flow pattern observations, the flow patterns in the Soliman flow regime map are divided into two-flow regimes; one with the vapor-shear-dominant annular regime and the other with the gravitational-force-dominant stratified-wavy regime. In the annular regime, the heat transfer coefficients of the two kinds of in-tube 3-D micro-fin tubes decreases as the vapor quality decreases. The regressed condensation heat transfer correlation from the experimental data of the annular flow region is obtained. The dispersibility of the experimental data is inside the limits of ±25%. In the stratified-wavy regime, the average heat transfer coefficient of the two kinds of in-tube 3-D micro fin tubes increases as the mass flux increases and the number of micro fins in the 3-D micro-fin tube is not the controlling factor for performance of a condensation heat transfer. The regressed condensation heat transfer correlation of the stratified-wavy flow regime is experimentally obtained. The dispersibility of the experimental data is inside the limits of ±22%. Combined with the criteria of flow pattern transitions, the correlations can be used for the design of a condenser with 3-D micro fin tubes.

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.

A New Heat Transfer Correlation and Flow Regime Map for Tube Bundles

1990 ◽  
Vol 112 (1) ◽  
pp. 150-156 ◽  
Author(s):  
Y. A. Hassan ◽  
T. K. Blanchat
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Steam Generator ◽  
Tube Bundle ◽  
Nucleate Boiling ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Tube Bundles ◽  
Regime Map ◽  
Flow Regime Map

A RELAP5/MOD2 computer code model for a once-through steam generator has been developed. The calculated heat transfer in the nucleate boiling flow was underpredicted as shown by a predicted superheat of only 11°C (20°F), whereas plant values range from 22–30°C (40–60°F). Existing heat transfer correlations used in thermal-hydraulic computer codes do not provide accurate predictions of the measurement-derived secondary convective heat transfer coefficients for steam generators because they were developed for flow inside tubes, not tube bundles. The RELAP5/MOD2 flow regime map was modified to account for flow across bundles. This modified flow regime map predicts better transition criteria between bubbly-to-slug and slug-to-annular flow. Consequently, improved saturated conditions for the fluid flow at the entrance to the boiler were obtained. A modified Chen-type heat transfer correlation was developed to predict the boiling heat transfer for steam generator tube bundle geometries. This correlation predicts better superheat.

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.

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