Water In Circular Tube Research Articles

Consistency considerations on a large databank and wide range heat transfer prediction for supercritical water in circular tubes

The heat transfer coefficient (HTC) of supercritical water (SCW) shows abnormal behavior when compared with conventional fluids. This behavior is caused by steady variations of thermal–physical properties of SCW around the pseudo-critical point. A large database of heat transfer of SCW flowing in tube and rod bundles was proposed by the Karlsruhe Institute of Technology (Zhao et al., 2017). This databank contains 28,364 high quality experimental data points (nodes) for heat transfer of supercritical water flowing in tubes, covering a wide domain of flow parameters.Additional consistency checks were made in this work on the experimental data using our own developed procedure. This procedure was able to provide hints on the intrinsic reliability of the data and also error levels for almost all experimental nodes.The derived information on error levels made a high-performance methodology of data assimilation and model calibration (Cacuci and Ionescu-Bujor, 2010) subsequently accessible to this domain of experimental data. The BESTEST module (Badea et al., 2011) based on the methodology of data assimilation and model calibration (Cacuci and Ionescu-Bujor, 2010) was used in an iterative manner to optimize a new proposed correlation able to describe with good accuracy a large domain of the databank.

Numerical models to predict steady and unsteady thermal-hydraulic behaviour of supercritical water flow in circular tubes

The present paper is aimed at the development of numerical models to predict steady and unsteady thermal-hydraulic behaviour of supercritical water flow at various operating conditions. A simple one-dimensional numerical thermal-hydraulic model based on a finite-difference scheme has been developed. A detailed CFD analysis based on two turbulence models, Reynolds Stress Model and k–ω SST model, has also been presented in this paper. Seven experimental cases of steady state and vertically up flowing supercritical water in circular tubes operated at various working regimes, such as normal and deteriorated heat transfer regions, are used to validate the numerical models. Comparisons for steady state flow show good agreement between the numerical and experimental results for all normal heat transfer cases and most of the deteriorated heat transfer cases. Next, the numerical models are used for transient simulations. Three case studies are undertaken with a purpose to quantify the time dependent responses from both the 1-D model and CFD model. The comparisons carried out for both the normal and deteriorated heat transfer conditions show a good agreement between the two numerical models.

Subcooled flow boiling heat transfer of water in circular tubes with twisted-tape inserts under high heat fluxes

This paper presents the heat transfer of subcooled water in swirl flow under high heat fluxes with respect to the heat removal technologies for the divertors in the International Thermonuclear Experimental Reactor (ITER). The experiments were conducted in a vertical circular tube that was heated uniformly with a large AC power supply. A twisted tape with a twist ratio of 2 or 4 was inserted into the circular tube to induce the swirl flow. The test parameters were as follows: heat flux q=5–19.5MW/m2; system pressure P=3, 4.2, 5MPa; mass flux G=6000, 8000, 10,000kg/(m2s); and inlet bulk temperature Tb,i=50–200°C. The heat transfer coefficients and boiling curves are obtained from single-phase forced convection to fully developed nucleate boiling. The influences of mass flux, heat flux, system pressure, thermodynamic quality, and inlet subcooling on heat transfer are discussed in detail. Special attention is paid to the effect of the twisted tape on subcooled heat transfer. More importantly, a wide set of heat transfer correlations are evaluated on the basis of our experimental data, and relevant recommendations for engineering applications are made according to their prediction accuracies.

Heat Transfer Enhancement for Laminar Flow in Circular Tubes with Twisted-Tape Inserts

This paper presents the results of a comprehensive study of heat transfer and pressure drop for the laminar flow of water in circular tubes with twisted-tape inserts. Three different twist ratios and tape thicknesses were considered. Experiments were performed for two different tube diameters with Reynolds numbers ranging from 500 to 2200 under constant-wall-temperature boundary condition. The fully developed Nusselt number and friction factor were found to be influenced by the twist ratio and the tape thickness-to-diameter ratio. The Nusselt number increases with a decreasing twist ratio, increasing tape thickness, and increasing Reynolds number; whereas the friction factor increases with an increasing twist ratio and tape thickness. Correlations for the Nusselt number and friction factor are developed for a tube with inserted-tape inserts. The present correlations consider the effects of the tape thickness-to-diameter ratio and the twist ratio on the Nusselt number and friction factor. The thermal-hydraulic performance ratio decreases with an increasing Reynolds number and twist ratio, whereas the tape thickness has a slight effect on the thermal performance ratio.

Experimental studies on heat transfer to supercritical water in circular tubes at high heat fluxes

Experimental studies on heat transfer to supercritical water flowing upward in circular tubes are carried out at the SWAMUP test facility. Totally more than 10,000 test data were obtained in tubes of two different inner diameters, i.e. 10.0mm and 7.6mm with the following test conditions: pressure from 23.0MPa to 26.0MPa, mass flux from 450kg/m2s to 1500kg/m2s, heat flux from 190kW/m2 to 1400kW/m2 and bulk temperature from 240°C to 460°C. Each test point is accompanied with systematic error analysis. It is found that for 90% of the test data the uncertainty of measured Nusselt number is less than 10%. Based on the test data obtained, the effect of various parameters on heat transfer is investigated, such pressure, mass flux, heat flux and tube diameter. In addition, the importance of several dimensionless numbers and the accuracy of five widely applied heat transfer correlations are assessed. It is concluded that the acceleration number πA and the buoyancy parameter πB show unique effect on heat transfer coefficient. Among the five selected heat transfer correlations, the correlation of Cheng et al. and Jackson show the best agreement with the present test data.

Heat transfer to supercritical water in circular tubes with circumferentially non-uniform heating

Heat transfer was numerically investigated for flow of supercritical water in a vertical circular tube which was heated on one side. The Shear-Stress Transport k-ω (SST) model was employed and preliminarily validated against experimental results under both circumferentially uniform and non-uniform heating. Numerical studies were performed for a pressure of 24.82 MPa, mass velocity of 404 kg/(m2s) and heat flux between 158 and 370 kW/m2. Within the range studied, empirical Nusselt correlations for uniform heating can adequately predict the circumferentially maximum wall temperature of a one-side heated tube. The circumferential difference of inner wall temperature was large (>60 K at high heat flux) due to poor mixing of fluid between the hot and cold side. At low heat flux, maximum wall temperature barely differed from that under uniform heating. While at high heat flux, maximum wall temperature dropped significantly compared with the uniformly heated case. With further heat input, buoyancy-induced local deterioration of heat transfer occurred, though not as severe as uniformly heated cases. Detailed axial velocity and turbulence show that turbulent quantities in the region, which is similar to the law of the wall region for isothermal flow, play an important role in heat transfer. Local deterioration did not happen when turbulent diffusion of this region was intense. Results also indicate that in a one-side heated tube, buoyancy effect is much stronger in upward flow than in downward flow.

Heat Transfer Enhancement Using Nanofluids in a Circular Tube Fitted with Inserts

A numerical investigation is performed to study the effects of different geometrical parameters and nanofluids on the thermal and flow fields through circular tubes fitted with inserts with Reynolds number ranging from 500 to 1750 and heat flux of 1000 W/m(2). The two dimensional continuity, Navier Stokes and energy equations are solved by using the finite volume method. The optimization through twisted tape with eleven types of tube having 20 mm inner diameter was studied by changing the dimensions of twisted tape such as the width ratio (W/D) in the range of 0.2-0.8 and the twist ratio (H/D) in the range of 2.5-4 for water as a working fluid to reach the optimal geometry with maximum performance evaluation criterion (PEC). The effects of using different types of nanoparticles such as Al2O3, CuO, SiO2, and ZnO, different nanoparticles volume fractions in the range of 1% to 4% and different nanoparticles diameters in the range of 25 nm to 80 nm in water base fluid were examined. The effects of different Reynolds numbers and the dispersion of nanoparticle in different types of base fluid such as ethylene glycol, engine oil and water in circular tube were also analyzed. Simulation results show that the Nusselt number increased as the width ratio and Reynolds number increased and twist ratio decreased. The highest Nusselt number was obtained with W/D = 0.8, while the efficient flow (max. PEC) was achieved with W/D = 0.7 for H/D = 2.5. The Nusselt number through the circular tubes with insert was enhanced with the increase of the particle volume fraction and with the decrease of nanoparticles diameter.

Heat transfer deterioration to supercritical water in circular tube and annular channel

In order to ensure the safety of operation in Supercritical Water-Cooled nuclear Reactor (SCWR), heat transfer deterioration (HTD) must be avoided. In this paper, HTD was numerically studied in circular tube and annular channel using eight low-Reynolds-number models to provide detailed information on flow and turbulence structure. All models considered are able to predict HTD phenomena, while SST model performs better than other models quantitatively. Numerical results indicate that acceleration effect is significantly important for HTD at high mass flux while buoyancy effect at low mass flux. The increase of tube diameter leads to the aggravation of HTD phenomena, which is more obvious at low mass flux. At high mass flux, HTD phenomenon in circular tube is severer than that in inner-wall-heated annular channel. However, with both walls heated in annular channel, HTD phenomenon is similar to that in circular tube.

Numerical study on convective heat transfer for water-based alumina nanofluids

The present work is an experimental study of steady state convective heat transfer of de-ionized water with a (0.04% by volume) volume fraction of Al2O3 nanoparticles dispersed to form a nanofluid that flows through an aluminium tube.Laminar fully developed flow heat transfer coefficient of Al2O3 nanoparticles are dispersed in water in circular tube is discussed in this paper. In order to validate the heat transfer coefficient of nanofluid in circular tube commercially available CFD software FLUENT 6.3.26 is used. The thermo-physical properties of the Al2O3nanofluid are estimated by using the equations available in literature. Thermo-physical properties of the nanofluid are considered for heat transfer coefficient by assuming nanofluid is a single-phase fluid. Constant Wall Heat Flux (CWHF) boundary condition is incorporated for heat transfer analysis. The flow and temperature fields are assumed fully developed (x/D>10). The analysis is conducted in the volume concentration from 0.4%.A maximum of 2.25 times heat transfer enhancement is obtained by using nanofluid as working medium.

Numerical investigation of heat transfer in upward flows of supercritical water in circular tubes and tight fuel rod bundles

Heat transfer in upward flows of supercritical water in circular tubes and in tight fuel rod bundles is numerically investigated by using the commercial CFD code STAR-CD 3.24. The objective is to have more understandings about the phenomena happening in supercritical water and for designs of supercritical water cooled reactors. Some turbulence models are selected to carry out numerical simulations and the results are compared with experimental data and other correlations to find suitable models to predict heat transfer in supercritical water. The comparisons are not only in the low bulk temperature region, but also in the high bulk temperature region. The two-layer model (Hassid and Poreh) gives a better prediction to the heat transfer than other models, and the standard k– ɛ high Re model with the standard wall function also shows an acceptable predicting capability. Three-dimensional simulations are carried out in sub-channels of tight square lattice and triangular lattice fuel rod bundles at supercritical pressure. Results show that there is a strong non-uniformity of the circumferential distribution of the cladding surface temperature, in the square lattice bundle with a small pitch-to-diameter ratio ( P/ D). However, it does not occur in the triangular lattice bundle with a small P/ D. It is found that this phenomenon is caused by the large non-uniformity of the flow area in the cross-section of sub-channels. Some improved designs are numerically studied and proved to be effective to avoid the large circumferential temperature gradient at the cladding surface.