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Computational Fluid Mechanics And Heat Transfer

A comprehensive review on jet impingement heat transfer is presented to consider the state-of the art in this field. Among all the single-phase heat transfer arrangements possible, it has the maximum heat transfer rate. A number of arrangements are possible to represent a practical or physical situation, such as, jet impingement on a solid flat surface or surface fitted with different kinds of turbulent promoters, inclined plane surface and cylindrical convex/concave surface, etc. A significant number of papers dealing with experimental and computational studies on different physical and computational aspects of jet impinging flows are reviewed. Several parameters were found to influence the characteristics, such as, flow confinement, nozzle shape, jet to plate spacing and Reynolds number. An extremely small number of studies dealing with application based jet impingement heat transfer configurations (e.g., ribs fitted impingement plate, moving impingement plate, etc) experimentally and numerically have been reported in the literature. Various computational approaches, such as, RANS, LES, DNS and hybrid models, that are used to study the jet impingement heat transfer, with their complexities and boundary conditions, have been reviewed. It was observed that majority of RANS based turbulence models did not predict impinging flows accurately and its complexities except a few. Many authors have reported that LES is capable of predicting the flow field and heat transfer data within the accepted accuracy limits. DNS can be applied to simple geometry with low Reynolds number. Recently some authors have employed hybrid models, such as, PANS, DES, etc., and concluded that these models provide reasonably accurate results and were found to be computationally less expensive than LES and DNS.

Flow and thermal characteristics of jet impingement: comprehensive review

In this study, thermal performance and flow characteristics of a shell and tube heat exchanger equipped with various baffle angles were studied. The heat exchanger was operated with distilled water, and a hybrid nanofluid at three concentrations of 0.04% and 0.10% of GNP-Ag/water within Reynolds numbers ranged between 10,000 and 20,000. The thermophysical properties of nanofluid varied with temperature and nanoparticles’ concentration. The baffle angles were set at 45°, 90°, 135°, and 180°. Results showed that the calculated Nusselt number (Nu) could be improved by adding nanoparticles to the distilled water or increasing the fluid’s Reynolds number. At a low Re number, the Nu corresponding to baffle angle of 135° was very close to that recorded for the angle of 180°. At Re = 20,000, the Nu number was the highest (by 35% compared to the reference case), belonging to a baffle angle of 135°. Additionally, results related to friction factor and pressure drop showed that more locations with fluid blocking were observed by increasing the baffle angle, resulting in increased pressure drop value and friction. Finally, the temperature streamlines counter showed that the best baffle angle could be 135° in which maximum heat removal and the best thermal performance can be observed.

https://www.mdpi.com/2227-7390/9/8/881/pdf

Combination Effect of Baffle Arrangement and Hybrid Nanofluid on Thermal Performance of a Shell and Tube Heat Exchanger Using 3-D Homogeneous Mixture Model

We numerically examine the thermal performance of a round tubular heat exchanger featuring a combination of three passive techniques for heat-transfer enhancement: (i) center-cleared twisted-tape i...

Heat transfer performance of a nanofluid-filled tube with wall corrugations and center-cleared twisted-tape inserts

Experimental research on vibration-enhanced heat transfer of fin-tube vehicle radiator

In this work, a pipe provided with twisted tape inserts is analyzed. This system allows a significant increase of convective heat transfer coefficient by introducing a swirl motion which determines greater heat removal from the solid surface, by improving the fluid mixing. The analysis performed in this paper focuses on the evaluation of the thermal and flow quantities for a pipe of a shell and tube heat exchanger, previously optimized through a design software widely used in the petrochemical industry. The thermo and fluid dynamics analysis were performed by using a commercial CFD software (FluentTM). After performing the necessary computational checks for the acceptance of the results provided by the solver, a pitch parameterization was performed through a finite volume simulation. In this way the behaviour of a highly viscous fluid was studied, whose thermo-physical characteristics are highly variable with temperature. Furthermore, using water as fluid, the behaviour of the pipe provided with inserts was investigated by varying the Reynolds number, through mass flow rate variation. To verify the correctness of the results, they were compared in both cases with correlations in the literature.

/pdf/cfd-analysis-of-a-pipe-equipped-with-twisted-tape-zmq1pn0py5.pdf

CFD Analysis of a Pipe Equipped with Twisted Tape

Parametric CFD Analysis for the Evaluation of Evaporative Cooler Performances

In the article, a three-dimensional numerical solution of two real shell-and-tube heat exchangers, with different types of baffles, segmental, and pseudohelical, is presented, through the use of co...

Computational Fluid Dynamics Analysis of a Heat Exchanger Provided with Helical Baffles

Received: 5 March 2019 Accepted: 8 May 2019 Air cooler heat exchangers are devices widely used in industrial applications to cool a process fluid. Most plants are built in arid areas with high air temperature but limited water resources. Therefore, in the hottest periods, a considerable air-cooler performance decrease occurs. Evaporative cooling by water spray, to cool the inlet air, is increasingly used as an efficient approach to enhance the air-cooler performance. This paper presents the study of the effect of evaporative cooling provided by the use of a water spray system. It has been developed through numerical simulation with Computational Thermo-fluid Dynamics that can be an effective tool for the performance evaluation of such system. CFD simulations easily allow parametric studies for the evaluation of alternative design configurations, especially when the different configurations are all embedded within the same computational domain and grid. In the vast majority of these studies the Lagrangian-Eulerian (LE) approach has been used, with the continuous phase (air in this study) represented in a Eulerian reference frame while the discrete phase (water droplets in this study) in a Lagrangian reference frame. This study, in particular, focuses on the effect of droplet size, nozzle arrangement and air velocity on performance of air-cooler. This knowledge is crucial for designing efficient spray cooling systems. Due to a number of reasons, which include water consumption restriction and the regulation of plant, spray cooling systems are becoming the preferred choice for many power plants because they can be applied in existing plants, and this is an enormous economic saving. In this way, it is possible to enhance the performance in high ambient air temperature without high costs.

/pdf/computational-fluid-dynamics-simulations-to-evaluate-the-44sbn29qpo.pdf

Computational Fluid Dynamics simulations to evaluate the performance improvement for Air-cooler equipped with a water spray system.

Received: 2 October 2019 Accepted: 5 November 2019 This paper aims to give a new analysis approach of the crude oil fouling phenomenon through CFD. Heat exchangers are analyzed in order to evaluate the effects of the presence of turbulators on thermal resistance. In particular, it will be investigated if fouling increases in presence or in absence of mechanical inserts inside tubes for heat exchangers, performing transient 3-D and 2-D simulations, paying attention to some parameters to which fouling is tied. The inserts analyzed are twisted tapes. They are static mixers used to improve thermal performances by enhancement of heat transfer coefficient and generation of a secondary swirl flow. The chemical reactions that generate fouling in the case of crude oil are those of asphaltene and salt. To understand the concentrations of species in each point of the tube, a species transport model is set in the CFD analysis. Then, to describe the chemical reaction fouling phenomena, and appreciate its dependence on time, a multicomponent approach for a binary diffusion coefficient is used. The main aim of the work is to evaluate the influence of twisted tapes on fouling and, therefore, on the resulting thermal resistance, comparing the case in question with a classic heat exchanger without inserts.

/pdf/evaluation-of-crude-oil-fouling-formation-in-a-heat-2rxwdrlork.pdf

A. Galloro

Papers

CFD Analysis of a Pipe Equipped with Twisted Tape

Parametric CFD Analysis for the Evaluation of Evaporative Cooler Performances

Computational Fluid Dynamics Analysis of a Heat Exchanger Provided with Helical Baffles

Computational Fluid Dynamics simulations to evaluate the performance improvement for Air-cooler equipped with a water spray system.

Evaluation of Crude Oil Fouling Formation in a Heat Exchanger with Twisted Tape Inserts