Fully-developed Flow Conditions Research Articles

Robust bubble feature extraction in gas-liquid two-phase flow using object detection technique

ABSTRACT Identification of flow regime and feature extraction of bubble characteristics in gas-liquid two-phase flow systems have been significant issues in various engineering disciplines, including nuclear thermal-hydraulics field. In nuclear safety analysis codes, flow regime transition criteria and bubble size-dependent correlations are often utilized to obtain solutions for the governing equations. However, even today, they still rely on flow regime maps and empirical criteria that are based on visual observations and fully-developed flow conditions. In the present study, the AI-based object detection approach was adapted by utilizing convolutional neural networks to extract bubbly flow features. The model network is capable of extracting real-time bubbly flow features in an internal multiphase flow system. From the coordinate information of each individual detected bubbles, features such as void fraction, bubble number density, and average bubble sizes can be acquired instantly. The present approach has the potential to replace the traditional hand-coded image analysis method and open up a path for a fully automated and versatile two-phase flow feature extraction.

Development length in planar channel flows of inelastic non-Newtonian fluids

This work presents a numerical study on the development length (L=L/H) required to reach fully-developed flow conditions at the entrance of a planar channel for inelastic non-Newtonian fluids modeled by the Sisko model. The simulations were carried out for low Reynolds number flows in the range 0 < Re ≤ 100, for a power law index, n, in the range 1/3 ≤ n ≤ 1 and for a dimensionless infinite viscosity, μ¯∞, varying in the range 0≤μ¯∞≤0.1. A new non-linear relationship between L and Re was derived, taking into account the different values of n and μ¯∞. Moreover, new exact solutions are presented for the velocity profile under fully developed flow conditions (for specific values of n).

Periodically Fully-Developed Flow and Heat Transfer Over Flat and Oval Tubes Using a Control Volume Finite-Element Method

A Control Volume Finite-Element Method in conjunction with imposed periodically fully-developed flow conditions was used to perform a two-dimensional, laminar, steady-flow numerical study comparing the performance of a flat tube and an oval tube to that of a round tube in a simulated heat exchanger device for the case of specified heat flux along the tube walls. The Reynolds number range for the study was 50 to 350. Fluids of Prandtl number 0.7 and 7.0 were considered. For the cases studied, the heat transfer enhancement ratio was less than one indicating that the round tube outperformed both the flat tube and the oval tube based on heat transfer considerations alone. However, for all cases studied, the heat transfer performance ratio was greater than one indicating that if both heat transfer performance and required pumping power are considered, both the flat tube and oval tube outperformed the round tube.

The second-law analysis of mixed convection in rectangular ducts

The rate of entropy generation, S˙′G[W/mK], is examined both theoretically and numerically for forced and mixed convection in a rectangular duct heated at the bottom. Under fully-developed flow conditions S˙′G is expressed in terms of relevant non-dimensional hydrodynamic and thermal parameters. Numerically, it is demonstrated that S˙′G is a single, effective parameter to examine both thermal and hydrodynamic fields and their variations.

Developing Flow of Gas-Particle Mixtures in Vertical Ducts

It is well-known that during high-velocity flow of gas-particle mixtures through a vertical duct the particles are distributed nonuniformly over the cross section. We had shown in an earlier paper that such a nonuniform state is sustained under fully-developed flow conditions by the large scale fluctuations accompanying such flows. In the present study, we have carried out a simple analysis of the developing flow problem to demonstrate that the evolution of the nonuniform distribution is indeed driven by turbophoresis.