CFD Simulation of Helical Shell and Tube Heat Exchanger Using Optimization Techniques

The objective of this study is to simulate the performance of helical tube shell and tube heat exchanger with several optimization techniques using computational fluid dynamics CFD. To check the performance of a designed model of heat exchanger various techniques are available. In this study, the various possible model of the heat exchanger to enhance the performance of the device have been designed. Firstly, the straight tube is replaced by helical tube in the heat exchanger and used 10, 12, 14 number of helical baffles with 50% baffle cut. Total ten models have been developed. These models are model-I 4-turns without baffle, model-II 4-turns with 10 number baffles, model-III 5-turns without baffle, model-IV 5-turns with 12 number baffles, model-V 6-turns without baffle, model-VI 6-turns with 10 number baffles 0.083m baffle space, model-VII 6-turns with 12 number 0.083m baffle space, model-VIII 6-turns with 14 number baffles 0.064m baffle space, model-IX 7-turns without baffle, model-X 7-turns with 14 number baffles, different number of baffles and baffle space with 50% baffle cut and used CUO nanofluid model-XI 6-turns with 14 number baffle CUO fluid 0.083m baffle space CFD analysis simulation done on ANSYS FLUENT 18. The simulated result shows that the model XI is approximately 40% more optimized as compared to model-I and approximately 24% than model-VIII. It also found that the high heat transfer obtains with increased number of baffles.

Effect of external sound superimposed on the self-excited oscillation in loop-tube thermoacoustic system

The influence of application of external sound to loop-tube type thermoacoustic system on the energy conversion efficiency is experimentally examined. The investigation is carried out by paying attention on the effect of loudspeaker (SP) set as external sound source. As a result, it is found that the setting of SP affects the sound field in the system and the amount of energy generation increases or decreases. The increasing or decreasing effect differs depending on the setting position of SP. Furthermore, it is confirmed that, provided SP is set near the node of particle velocity, the sound energy can be increased by more than the input power to SP, without changing the sound field in the tube. From these results it can be confirmed that, similar to straight-tube type thermoacoustic system, the energy conversion efficiency can be enhanced by setting SP at suitable position even in loop-tube type without end surfaces.

The Bent-Tube Nozzle Optimization of Force-Spinning With the Gray Wolf Algorithm

Force-spinning is a popular way to fabricate various fine fibers such as polymer and metal nanofibers, which are being widely employed in medical and industrial manufacture. The spinneret is the key of the device for spinning fibers, and the physical performance and morphology of the spun nanofibers are largely determined by its structure parameters. In this article, the effect of spinneret parameters on the outlet velocity is explored and the spinneret parameters are also optimized to obtain the maximum outlet velocity. The mathematical model of the solution flow in four areas is established at first, and the relationship between outlet velocity and structure parameters is acquired. This model can directly reflect the flow velocity of the solution in each area. Then, the optimal parameters of outlet diameter, bending angle, and curvature radius are obtained combined with the gray wolf algorithm (GWA). It is found that a curved-tube nozzle with a bending angle of 9.1°, nozzle diameter of 0.6 mm, and curvature radius of 10 mm can obtain the maximum outlet velocity and better velocity distribution. Subsequently, the simulation is utilized to analyze and compare the velocity situation of different parameters. Finally, the fiber of 5 wt% PEO solution is manufactured by a straight-tube nozzle and optimized bent-tube nozzle in the laboratory, and the morphology and diameter distribution were observed using a scanning electron microscope (SEM). The results showed that the outlet velocity was dramatically improved after the bent-tube parameters were optimized by GWA, and nanofibers of better surface quality could be obtained using optimized bent-tube nozzles.

Sensitivity Analysis of Influencing Factors of Supercritical Methane Flow and Heat Transfer in a U-Tube

Due to the existence of a Dean vortex in a U-tube, the flow and heat transfer process of supercritical methane is complex, and its thermophysical property are greatly influenced by different factors. Based on computational fluid dynamics theory, the numerical simulation of the turbulent flow and heat transfer characteristics of supercritical methane in a U-tube with an inner diameter of 10 mm and a radius of curvature of 27 mm carried out by using the finite volume method. On the basis of verifying the reliability of the model, the influences of inlet mass flux (G), heat flux on the tube wall boundary (q), pressure on the outlet (P), and gravity acceleration factors (g) on heat transfer characteristics were analyzed. The calculation results show that the sensitivity of the effects of G, q, P, and g on the heat transfer coefficient is, from large to small, in the order of P, G, g, and q. Compared with a horizontal straight tube, a U-tube can significantly improve heat transfer in the elbow part, but the presence of the elbow reduces heat transfer in the subsequent straight pipe section. The research in this paper has significance as a reference for the construction of the LNG gasification process.

A Study of RANS Turbulence Models in Fully Turbulent Jets: A Perspective for CFD-DEM Simulations

This paper presents an analysis of linear viscous stress Favre averaged turbulence models for computational fluid dynamics (CFD) of fully turbulent round jets with a long straight tube geometry in the near field. Although similar work has been performed in the past with very relevant solutions, considerations were not given for the issues and limitations involved with coupling between an Eulerian and Lagrangian phase, such as in fully two-way coupled CFD-DEM. These issues include limitations on solution domain, mesh cell size, wall modelling, and momentum coupling between the two phases in relation to the particles size. Therefore, within these considerations, solutions are provided to the Navier–Stokes equations with various turbulence models using a three-dimensional wedge long straight tube geometry for fully developed turbulence flow. Simulations are performed with a Reynolds number of 13,000 and 51,000 using two different tube diameters. It is found that a modified k-ε turbulence model achieved the most agreeable results for both the velocity and turbulent flow fields between these two flow regimes, while a modified k-ω SST/BSL also provided suitable results.

A Comparison Study of Several Ultrasonic Endoscopy Technology for Tubes’ Inspection

Ultrasonic technology has developed rapidly in decades. However, few ultrasonic technologies have been proposed for tubes’ internal inspection. In this paper, 6 types of ultrasonic endoscopic transducers are brought to detect volumetric and planar flaws in tubes. Steam generator tube is application target. Beam simulations are implemented and compared using an open source acoustic simulation toolbox to illustrate beneficial effects of the different transducers. The results show the proposed endoscopic array transducers can form focused ultrasonic beams in tube wall, which do helps when detecting complex defects, such as crevice with uncertain direction. A prototype circular array transducer with 64 elements is fabricated to demonstrate the design. A straight tube (Φ19 × 3mm) made of carbon-steel with 8 longitudinal grooves and 8 ring grooves of no more than 0.5mm width on both inner and outer tube wall are applied in endoscopy experiments. The results demonstrate the detection sensitivity of the circular array transducer reaches 0.2mm in both circumferential direction and axial direction. The combination of the above proposed transducers and advanced imaging algorithms such as total focusing method may build an integrated array ultrasonic endoscopic inspection scheme for the internal inspection of tubes.

Numerical Studies on Modal Analysis of Curved Tube and Coil Tube in Coil-Wound Heat Exchanger

Coil-wound heat exchanger, which has a large-scale turbulence in the shell side and a great heat transfer coefficient, has been widely used in chemical industry, such as liquefied natural gas (LNG) and crude pyrolysis of ethylbenzene. To investigate the general vibration characteristics, a complete wound tube can be divided into the curved tube and the coil tube for easy research because of its constraint condition. A finite element analysis is used to obtain the natural frequencies and corresponding mode shapes of the curved tubes and the coil tubes with various parameters. For the curved tube, the deformation of middle position of the tube is larger than that of the clamped ends. The maximum deformation occurs at the transition from the bending tube to the straight tube. With the increase of R1 and the decrease of R2, H1, H and θ, the natural frequencies of curved tube increase which is more likely to avoid the fluid-elastic instability, in which R1 is circumferential radius of the straight part of curved tube, R2 is coil radius, H1 is axial straight tube length, H is axial height of curved tube and θ is deflection angle. And for the coil tube, all the deformation for mode shape occurs in the axial direction, and there is no obvious deformation in the radial direction. With the increase of support number and the decrease of R2, the basic frequency of the coil tube increases. It provides a certain reference for the support layout of coil-wound heat exchanger.

3D printed ascending aortic simulators with physiological fidelity for surgical simulation

IntroductionThree-dimensional (3D) printed multimaterial ascending aortic simulators were created to evaluate the ability of polyjet technology to replicate the distensibility of human aortic tissue when perfused at physiological pressures.MethodsSimulators were developed by computer-aided design and 3D printed with a Connex3 Objet500 printer. Two geometries were compared (straight tube and idealised aortic aneurysm) with two different material variants (TangoPlus pure elastic and TangoPlus with VeroWhite embedded fibres). Under physiological pressure, β Stiffness Index was calculated comparing stiffness between our simulators and human ascending aortas. The simulators’ material properties were verified by tensile testing to measure the stiffness and energy loss of the printed geometries and composition.ResultsThe simulators’ geometry had no effect on measured β Stiffness Index (p>0.05); however, β Stiffness Index increased significantly in both geometries with the addition of embedded fibres (p<0.001). The simulators with rigid embedded fibres were significantly stiffer than average patient values (41.8±17.0, p<0.001); however, exhibited values that overlapped with the top quartile range of human tissue data suggesting embedding fibres can help replicate pathological human aortic tissue. Biaxial tensile testing showed that fiber-embedded models had significantly higher stiffness and energy loss as compared with models with only elastic material for both tubular and aneurysmal geometries (stiffness: p<0.001; energy loss: p<0.001). The geometry of the aortic simulator did not statistically affect the tensile tested stiffness or energy loss (stiffness: p=0.221; energy loss: p=0.713).ConclusionWe developed dynamic ultrasound-compatible aortic simulators capable of reproducing distensibility of real aortas under physiological pressures. Using 3D printed composites, we are able to tune the stiffness of our simulators which allows us to better represent the stiffness variation seen in human tissue. These models are a step towards achieving better simulator fidelity and have the potential to be effective tools for surgical training.

A Study of RANS Turbulence Models in Fully Turbulent Jets: A Perspective for CFD-DEM Simulations

This paper presents an analysis of linear viscous stress Favre-Averaged turbulence models for computational fluid dynamics (CFD) of fully turbulent round jets with a long straight tube geometry in the near field. Although similar work has been performed in the past with very relevant solutions, considerations were not given for the issues and limitations involved with coupling between an Eulerian and Lagrangian phase, such as in fully two-way coupled CFD-DEM. These issues include limitations on solution domain, mesh cell size, wall modelling, and momentum coupling between the two phases in relation to the particles size. Therefore, within these considerations, solutions are provided to the Navier-Stokes equations with various turbulence models using a three-dimensional wedge long straight tube geometry for fully developed turbulence flow. Simulations are performed with a Reynolds number of 15000 and 50000 using two different tube diameters. It is found that a modified k−ε turbulence model achieved the most agreeable results for both the velocity and turbulent flow fields between these two flow regimes, while a modified k−ω SST/BSL also provided suitable results.