Periodically fully developed convective heat transfer characteristics in a two-dimensional wavy channel are investigated numerically with a constant wall temperature. The calculations are performed with Pr=0.7, Re=20-...
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Periodically fully developed convective heat transfer characteristics in a two-dimensional wavy channel are investigated numerically with a constant wall temperature. The calculations are performed with Pr=0.7, Re=20-500 on non-orthogonal non-staggered grids generated by an elliptic equation system. A semi-implicit method for pressure linked equations revised (SIMPLER) algorithm in curvilinear body-fitted coordinates is employed. Effects of Reynolds number and geometric parameters, such as aspect ratio φ and shape ratio γ, on heat transfer and friction factor are studied. It shows that no recirculation region occurs through the whole channel at low Reynolds numbers, small aspect ratio or small shape ratio. With the increase of Reynolds number, aspect ratio or shape ratio, heat transfer is enhanced due to flow recirculation. Corresponding friction factor increases simultaneously.
In this paper, we provide a method which can be used to measure the viscosity coefficient of the liquid under high-pressure condition and low-boil substances using inclined tube, and measurement system was designed an...
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In this paper, we provide a method which can be used to measure the viscosity coefficient of the liquid under high-pressure condition and low-boil substances using inclined tube, and measurement system was designed and constructed. The kinematic viscosity coefficients of pure water which is the standard substance to calibrate viscosity measurement system were measured to verify the accuracy and reliability of the experimental system. The measurement results show that the absolute average of relative deviations is 0.65%. Then the kinematic viscosity coefficients of the saturated liquid of the low-boil substance, R134a were also measured to detect the measurement system.
A direct numerical simulation of a fully developed turbulent flow and heat transfer in a square duct is studied based on high resolution finite difference scheme. The flow and temperature fields are obtained at a turb...
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A direct numerical simulation of a fully developed turbulent flow and heat transfer in a square duct is studied based on high resolution finite difference scheme. The flow and temperature fields are obtained at a turbulent Reynolds number of 400 based on the mean friction velocity and the hydraulic diameter, and the Prandtl number (Pr) of 0.71. Two kinds of point-stencil method are used for the spatial derivatives of the pressure Poisson equation, i.e. the second-order and fourth-order central difference, respectively. The results show that satisfactory solutions can be obtained in the present DNS simulation with coarse grids compared with the method of second-order central difference. And the solutions from the two kinds of point-stencil method for pressure Poisson equation are consistent with the second-order central difference being more economical in saving computation time.
In bubbly two‐phase flow, the gas phase and liquid phase have different flow fields. The mathematical expression for the motion of a small bubble at low Re number has been already established, the liquid velocity alo...
In bubbly two‐phase flow, the gas phase and liquid phase have different flow fields. The mathematical expression for the motion of a small bubble at low Re number has been already established, the liquid velocity along the trajectory of the bubble is calculated inversely by using the motion equation. Whole field liquid flow structure has also estimated using a spatial and/or temporal interpolation method. This paper proposes an algorithm for estimating the liquid phase flow field based on measurement data on bubble data on bubble motion. The applicability of the algorithm is examined with Taylor‐Green vortex flow as an analytical test case. Meanwhile, The result, based on the theory, has been applied to reconstruct liquid phase velocity field by using the data of bubble velocity in an aeration tank.
Presents a set of data for flow and heat transfer of finned-tube bundle under the condition of high air flow velocity. Air flow and heat transfer over a 4 × 4 （ columns × rows） finned-tube heat exchanger w...
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Presents a set of data for flow and heat transfer of finned-tube bundle under the condition of high air flow velocity. Air flow and heat transfer over a 4 × 4 （ columns × rows） finned-tube heat exchanger with rectangular fins was investigated experimentally in a wind tunnel with constant wall temperatures condition. The air flow velocity based on the minimum flow cross-section area over flow channel ranged from 13.8 to 50. 2 m/s, the heal transfer rate ranged from 21.8 to47. 1 kW, and the air temperatures increase ranged from 10. 9 to 19. 8 ℃. The present results were compared with results calculated from correlations proposed by CSPE. For air flow velocity less than 25 m/s, these two results of heat transfer agreed well with each other, whereas for larger velocity, our test data disagreed with the CSPE correlations. For the friction factor, present data are much higher than the predicted results in the whole range. Finally, correlations for friction factors and heat transfer coefficients are DrODosed based on the experimental results.
This work used artificial neural network(ANN)to predict the heat transfer rates of shell-and-tube heatexchangers with segmental baffles or continuous helical baffles,based on limited experimental *** BackPropagation (...
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This work used artificial neural network(ANN)to predict the heat transfer rates of shell-and-tube heatexchangers with segmental baffles or continuous helical baffles,based on limited experimental *** BackPropagation (BP) algorithm was used in training the *** network configurations were *** deviation between the predicted results and experimental data was less than 2%.Comparison withcorrelation for prediction shows ANN *** is recommended that ANN can be easily used to predict theperformances of thermal systems in engineering applications,especially to model heat exchangers for heattransfer analysis.
Aeration plays an important role in the treatment of activated sludge. The aeration performance is deeply affected by the movement law of bubble liquid flow in aeration tank. In order to discuss the influence of gas‐...
Aeration plays an important role in the treatment of activated sludge. The aeration performance is deeply affected by the movement law of bubble liquid flow in aeration tank. In order to discuss the influence of gas‐phase, liquid‐phase motions in an aeration tank on the sewage disposal, three kinds of boundaries and initial conditions were applied in the experiment to study the law of two‐phase flow. A developed two‐equation turbulence model was employed in this paper. Results obtained by experiment are compared with those from the mathematical model. It is found that the results of measurement and simulation agree with each other.
This article presents a theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor. Through numerically solving the one-dimensional steady-state single...
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This article presents a theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor. Through numerically solving the one-dimensional steady-state single-phase conservative equations for the primary circuit and the steady-state two-phase drift-flux conservative equations for the secondary side of the steam generator, the natural circulation characteristics were studied. On the basis of the pre- liminary calculation analysis, it was found that natural circulation mass flow rate was proportional to the exponential function of the power and that the value of the exponent is related to the operating conditions of the secondary side of the steam generator. The higher the outlet pressure of the secondary side of the steam generator, the higher the pri- mary natural circulation mass flow rate. The larger height difference between the core center and the steam generator center is favorable for the heat removal capacity of the natural circulation.
Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model ...
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Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model the dynamics. The purpose of this study is to present a numerical model for the analysis of flow-induced instabilities in forced-convection steam generator. The model is based on the assumption of homogeneous two-phase flow and ther- modynamic equilibrium of the phases. The thermal capacity of the heater wall has been included in the analysis. The model is used to analyze the flow instabilities in the steam generator and to study the effects of system pressure, mass flux, inlet temperature and inlet/outlet restriction, gap size, the ratio of do / di, and the ratio of qi / qo on the system be- havior.
Prediction of critical heat flux (CHF) in annular flow is important for the safety of once - through steam generator and the reactor core under accident conditions. The dryout in annular flow occurs at the point where...
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Prediction of critical heat flux (CHF) in annular flow is important for the safety of once - through steam generator and the reactor core under accident conditions. The dryout in annular flow occurs at the point where the film is depleted due to entrainment, deposition, and evaporation. The film thickness, film mass flow rate along axial distribution, and CHF are calculated in vertical upward round tube on the basis of a separated flow model of annular flow. The theoretical CHF values are higher than those derived from experimental data, with error being within 30%.
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