SPTV sheds light on flow dynamics of fractal-induced turbulence over a plate-fin array forced convection

A 3D stationary particle tracking velocimetry (SPTV) with a unique recursive corrective algorithm has been successfully established to detect the instantaneous regional fluid flow characteristics. The veracity of SPTV is corroborated by conducting actual displacement measurement validation, which gives a maximum percentage deviation of about 0.8%. This supports the accuracy of the current SPTV system in 3D position detection. More importantly, the SPTV detected velocity fluctuations are highly repeatable. In this study, SPTV is proven to be able to express the nature of chaotic fractal grid-induced regional turbulence, namely: the high turbulence intensity attributed to multilength-scale wake interactions, the Kolmogorov’s −5/3 law decay, vortex shedding, and the Gaussian flow undulations immediately leeward of the grid followed by non-Gaussian behaviour further downstream. Moreover, by comparing the flow fields between control no-grid and fractal grid-generated turbulence of a plate-fin array, SPTV reveals vigorous turbulence intensity, smaller regional integral-length-scale, and energetic vortex shedding at higher frequency for the latter, particularly between fins. Thereupon, it allows the unravelling of detailed thermofluid interplays of plate-fin heat sink heat transfer augmentation. The novelty of SPTV lies in its simplicity, use of low-cost off-the-shelf components, and most remarkably, low computational complexity in detecting fundamental characteristics of turbulent fluid flow.

Heat Transfer Characteristic on Wing Pairs Vortex Generator using 3D Simulation of Computational Fluid Dynamic

Vortex generators are addition surface that can increase heat transfer area and change the fluid flow characteristics of the working fluid to increase heat transfer coefficient. The use of vortex generators produces longitudinal vortices that can increase the heat transfer performance because of the low pressure behind vortex generators. This investigation used delta winglet vortex generator that was combined with rectangular vortex generator to Reynold numbers ranging 6,000 to 10,000. The parameters of Nusselt number, friction factor, velocity vector and temperature distribution will be evaluated.

Experimental and Simulation of Solar Drying Cabinet with PCM and SiO2 Materials

Solar energy is a potential renewable source in Indonesia, especially for the drying process. The process needs a drying cabinet as a support component to store the drying product. A high-quality drying cabinet to store heat for a long time is needed. This research aims to compare the thermal performance of the drying cabinet without PCM (phase change material) and SiO2 materials or DC I (drying cabinet I) with the drying cabinet that uses PCM and SiO2 materials or DC II (drying cabinet II). The research was carried out by experimental and simulation to investigate thermal performance and fluid flow characteristics. The experiment was carried out inside the laboratory to set uniform initial parameters and the simulation using computational fluid dynamics software. The drying cabinet was modeled in 3D. The experiment result showed DC II had a higher air temperature and lowered relative air humidity for two hours than DC I. The simulation result showed air temperature differences and backflow in the air streamline in the DC II.

Influence of fluid flow characteristics and heat transfer in a tube heat exchanger using H-shape inserts with circular ring

The heat transfer and fluid flow characteristics in a tube heat exchanger using H-shape inserts with circular ring (CRWHS) has been done by computationally and experimentally. In this investigation parameters like ratio of the diameters and pitches are considered. The value of diameter and pitch ratios are (DR=0.8, 0.9), (PR=3, 4) respectively. The main section in which investigation was done is 1.5m long and the hydraulic diameter of the tube is 68.1mm. 1000 W/m2 heat flux was provided in the main section. Heat flux was constant throughout the investigation. Air is used as a working medium in which 6000 to 21000 Reynolds number was used for the investigation. The observation revealed that the increment in heat transfer rate is 4.56 times as compare to smooth tube for the circular ring with H-shape inserts. In case of DR=0.8 and PR=3, maximum thermal performance factor was obtain which is 3.24. In GIT the deviation in Nusselt number & friction factor is limited to ±0.4% & ±0.1% respectively. CFD analysis result comparisons with experimental one are presented in which the maximum deviations for thermal performance factor are limited to ±3.6%.

Performance Assessment of Different Turbulence Models for a Dual Jet Flowing Over a Heated Sinusoidal Wavy Surface

An enhancement in heat transfer is the key objective in any thermal system where an efficient cooling is needed. This requirement becomes more important for turbulent flow. A turbulent dual jet is associated with entrainment and mixing processes in several applications. This paper aims at enhancing the heat transfer rate by utilizing the wavy surface of a heated plate. Heat transfer and flow characteristics are studied using five low-Re RANS turbulence models, namely, Yang and Shih k-ε (YS), Launder and Sharma k-ε (LS), realizable k-ε, renormalization group k-ε (RNG) and shear-stress transport k-ω (SST) models. The amplitude of the wavy surface is varied from 0.1 to 0.8 for the number of cycles fixed to 7. The Reynolds number and offset ratio are set to 15000 and 3, respectively. An isothermal wall condition is used at the wavy wall. An experimental validation has been performed. An enhancement of 55.94% in heat transfer is achieved by the RNG k-ε model. Further, it is noticed that the YS model fails to predict the flow separation as the amplitude of the sinusoidal wavy surface increases. However, the SST model reveals that the flow separates when the amplitude increases beyond 0.6. The thermal-hydraulic performance (THP) is found to increase for the RNG model by approximately 13.9% for the maximum amplitude considered. As the profiles of the bottom walls change, various turbulence models predict different fluid flow characteristics.

Effect of magnetic field on fluid flow characteristics and augmentation of heat transfer in a heat exchanger

The study of fluid flow, subjected to an external magnetic field has become an attractive and demanding research area because of its huge applications. In this work, water base magnetic nanofluid dynamics, taking into account the Magnetohydrodynamics (MHD) phenomenon has been explicitly investigated. In this study, governing equations are coupled with Magnetohydrodynamics (MHD) and are solved with the help of a finite volume procedure based on a control volume approach. The numerical outcomes of the simulation are depicted and discussed sequentially in terms of different contour and flow parameters. The impact of Magnetic number arising from Magneto Hydro Dynamics (MHD) ranging from 302 to 377 for a fixed Reynolds number of 100 on the flow characteristics has been presented in detail. The flow parameters like wall shear and pressure of wall are increased with increasing Magnetic number and the number of recirculating bubbles increases with decreasing in Magnetic number. Thus, to generate the maximum number of recirculating bubbles,a lower magnetic number is being recommended. The formation of the recirculating zone increases the retention time of fluid which results in the enhancement of heat transfer for a specific surface of a heat exchanger.