Analytical investigation of laminar flow through expanding or contracting gaps with porous walls

AbstractLaminar, isothermal, incompressible and viscous flow in a rectangular domain bounded by two moving porous walls, which enable the fluid to enter or exit during successive expansions or contractions is investigated analytically using optimal homotopy asymptotic method (OHAM). OHAM is a powerful method for solving nonlinear problems without depending to the small parameter. The concept of this method is briefly introduced, and it׳s application for this problem is studied. Then, the results are compared with numerical results and the validity of these methods is shown. After this verification, we analyze the effects of some physical applicable parameters to show the efficiency of OHAM for this type of problems. Graphical results are presented to investigate the influence of the non-dimensional wall dilation rate (α) and permeation Reynolds number (Re) on the velocity, normal pressure distribution and wall shear stress. The present problem for slowly expanding or contracting walls with weak permeability is a simple model for the transport of biological fluids through contracting or expanding vessels

Incorporation of Labelled Amino Acid into Ova during Ovarian Development in the Silkworm, Bombyx mori L.

© 2019 Elsevier B.V. Helical turbulator has been adopted in this article, to enhance the convective flow within a pipe. Homogeneousmodel was carried out for nanomaterial modeling. The Reynolds number (Re) and width of turbulator (b) vary from 5000 to 15000 and 5 to 15mm, respectively. Copper oxide nanoparticles were considered as an additive in to pure carrier fluid to gain better thermal behavior. Furthermore, exergy loss distributions for different cases have been reported. Outputs indicate that disturbance of the boundary layer enhances with rise of b. Mixing of core nanofluid flow and boundary layer enhances with augment of width of turbulator

Second law analysis for nanofluid turbulent flow inside a circular duct in presence of twisted tape turbulators

Finite volume method is employed to simulate water based nanofluid turbulent flow and entropy generation in a heat exchanger. In order to augment heat transfer rate, twisted tape turbulators insert inside the pipe. Second law analysis are presented for various values of height ratio (BR) and pitch ratio (PR) and Reynolds number (Re). Related formulas for entropy generation and Bejan number are provided. Results indicate that secondary flow increases with increasing number of revolution. Bejan number and total entropy generation augment with augment of pitch ratio. But they decreases with augment of Reynolds number and height ratio

Simulation of melting paraffin with graphene nanoparticles within a solar thermal energy storage system

Abstract In this paper, applying new structure and loading Graphene nanoparticles have been considered as promising techniques for enhancing thermal storage systems. The layers within the paraffin zone were made from aluminum and the melting temperature of paraffin is 319.55 K. The paraffin zone located in the middle section of the triplex tube and uniform hot temperatures (335 K) for both walls of annulus have been applied. Three geometries for the container were applied with changing the angle of fins (α = 7.5°, 15° and 30°). The uniform concentration of additives was assumed involving a homogeneous model for predicting properties. Results indicate that loading Graphene nanoparticles causes time of melting to decrease about 4.98% when α = 7.5° and the impact of ϕ improves about 5.2% with reduce of angle from 30° to 7.5°. In addition, as angle declines, the period of melting decreases around 76.47% which is associated with augmentation of driving force (conduction) in geometry with lower α

Simulation of nanomaterial flow within an absorber duct of LFR solar system under the influence of complex turbulator

In this work, for decreasing the irreversibility of system and augmenting the thermal performance, hybrid nanomaterial was utilized as testing fluid inside the pipe of concentrating solar unit with presence of complex disturber device. The base fluid for this domestic usage is water and concentration of each nanoparticle is 0.01, thus, assumption of homogeneous fluid is correct. After finding the best position and angles of minors as primary concentrator, Monte-Carlo method has been incorporated to measure the outer wall's boundary condition. Then, FVM was hired for 3D modeling of hybrid nanofluid flow with incorporation of k-ε technique. As hybrid nanoparticles have been dispersed into water, the pressure drop and frictional irreversibility (Sgen,f) augment around 7.98% and 5.02% while heating irreversibility (Sgen,h) declines around 4.01% when BR= 0.24, PR= 0.15, Q= 15. Increase of PR leads to greater mixing and Sgen,f augments around 74.3% due to augment of swirl flow but Sgen,h decreases about 47.41%. Considering higher Q can augment the radial velocity and stronger resistance with wall leads to increase of Sgen,f about 357.21% whereas Sgen,h reduces about 81.56%

CuO-water nanofluid flow and heat transfer in a heat exchanger tube with twisted tape turbulator

In this article, water based nanofluid pressure drop and heat transfer augmentation due to using twisted tape insert was investigated. Behaviors of CuO-H2O are predicted according to single phase model. Entropy generation due to fluid friction and heat transfer are presented as contours. Roles of Reynolds number, pitch and height ratios are reported by means of Finite volume method. Formulas for Darcy factor and Nusselt number have been offered. Results demonstrate that better mixing of nanofluid occurs for lower values of pitch ratio. Secondary flow becomes stronger with rise of inlet velocity. Height of turbulator has reverse relationship with thermal boundary layer thickness

Time-dependent heat transfer simulation for NEPCM solidification inside a channel

The aim of current investigation is to model NEPCM behavior in an air heat exchanger storage unit by means of FVM. Unsteady governing equations are obtained including single-phase model for NEPCM. Thermal properties of paraffin are enhanced with dispersing CuO nanoparticles. The geometry was symmetric, and so there is no need to simulate the whole domain. Converting liquid to solid makes the air flow warmer and helps the ventilation of building. Wavy wall was employed to accelerate the discharging rate. Outputs reveal that dispersing nanoparticles leads to propagation of solid front. Discharging rate enhances with augmenting amplitude of inner wall

Nanofluid turbulent convective flow in a circular duct with helical turbulators considering CuO nanoparticles

Nanofluid heat transfer augmentation in a heat exchanger equipped with helical twisted tape turbulator is simulated numerically via Finite volume method. Impacts of width ratio, Reynolds number and pitch ratio on nanofluid hydrothermal behavior were illustrated. Related formulas for Nusselt number and Darcy factor are provided according to obtained results. Outputs show that thermal boundary layer thickness decreases with augment of width ratio due to stronger secondary flow. Better nanofluid mixing can be obtained for lower values of pitch ratio