A. Badarudin

INVESTIGATION OF HEAT TRANSFER ENHANCEMENT IN A FORWARD-FACING CONTRACTING CHANNEL USING FMWCNT NANOFLUIDS

The turbulent forced convection heat transfer of water/functionalized multi-walled carbon nanotube (FMWCNT) nanofluids over a forward-facing step was studied in this work. Turbulence was modeled using the shear stress transport K-ω model. Simulations were performed for Reynolds numbers ranging from 10,000 to 40,000, heat fluxes from 1,000 to 10,000 W/m2, and nanoparticle volume fractions of 0.00% to 0.25%. The two-dimensional governing equations were discretized with the finite volume method. The effects of nanoparticle concentration, shear force, heat flux, contraction, and turbulence on the hydraulics and thermal behavior of nanofluid flow were studied. The model predictions were found to be in good agreement with previous experimental and numerical studies. The results indicate that the Reynolds number and FMWCNT volume fraction considerably affect the heat transfer coefficient; a rise in local heat transfer coefficient was noted when both Reynolds number and FMWCNT volume fraction were increased for all cases. Moreover, the contraction of the channel passage leads to the formation of two recirculation regions with augmented local heat transfer coefficient value.

Numerical Study of Turbulent Heat Transfer in Annular Pipe with Sudden Contraction

Turbulent heat transfer to air flow in annular pipe with sudden contraction numerically studied in this paper. The k-ε model with finite volume method used to solve continuity, moment and energy equations. The boundary condition represented by uniform and constant heat flux on inner pipe with range of Reynolds number varied from 7500 to 30,000 and contraction ratio (CR) varied from 1.2 to 2. The numerical result shows increase in local heat transfer coefficient with increase of contraction ratio (CR) and Reynolds number. The maximum of heat transfer coefficient observed at contraction ratio of 2 and Reynolds number of 30,000 in compared with other cases. Also pressure drop coefficient noticed rises with increase contraction ratio due to increase of recirculation flow before and after the step height. In contour of velocity stream line can be seen that increase of recirculation region with increase contraction ratio (CR).

Investigation on the Use of Graphene Oxide as Novel Surfactant for Stabilizing Carbon Based Materials

The present work reported on the use of graphene oxide (GO) as effective dispersant to isolate different carbon allotropes. The nature of its chemical structure which consists of hydrophobic and hydrophilic components enables GO to behave as surfactant, paving routes for dissolution of graphitic materials and achieving surfactant free all-carbon solutions. Two additional carboneous materials under the family of fullerene (carbon nanofiber—CNF) and graphite (graphene nanoplatelets—GnP) were introduced within the present study to form a new GO based hybrid complexes on top of the commonly investigated carbon nanotube (CNT) based GO hybrid. Investigation on GO stability with respect to particle size and zeta potential measurements showed that the strength of its dispersibility was highly dependent on its morphological size and less affected by the pH. Rheological study revealed that GO shear–strain relationship is highly sensitive to the particle size. The GO viscosity experienced dramatic changes from Newtonian toward shear thinning behaviors as the particle size increases. Thermal conductivity measurement highlighted as high as 8% increase in magnitude with the addition of CNT, CNF, and GnP carbon constituents, indicating that the enhancement may be attributed to the much efficient thermal transport along the conducting path of pristine carbon allotropes. GRAPHICAL ABSTRACT

Simulation of Heat Transfer to Turbulent Nanofluid Flow in an Annular Passage

The heat transfer in annular heat exchanger with titanium oxide of 1.0 volume % concentration as the medium of heat exchanger is considered in this study. The heat transfer simulation of the flow is performed by using Computational Fluid Dynamics package, Ansys Fluent. The heat transfer coefficients of water to titanium oxide nanofluid flowing in a horizontal counter-flow heat exchanger under turbulent flow conditions are investigated. The results show that the convective heat transfer coefficient of the nanofluid is slightly higher than that of the base fluid by several percents. The heat transfer coefficient increases with the increase of the mass flow rate of hot water and also the nanofluid.

A CFD study of turbulent heat transfer and fluid flow through the channel with semicircle rib

In the present paper turbulent heat transfer and fluid flow through the channel with semicircle ribs numerically studied. The SST k-ω turbulence Model with finite volume method was employed in simulation. The adopted boundary condition considered step heights of ribs varied from 2.5mm to 10mm with pitch ratio different from 2.5 to 40 and flow Reynolds number between 10000 to 25000 at constant surface temperature. The computational results showed recirculation region after each ribs which effect on performance of heat transfer rate. Increase of Reynolds number and number of ribs leads to increase in heat transfer coefficient. Step height and pitch ratio of ribs increase local heat transfer coefficient along the channel. This simulation has been done by ANSYS 14 FLUENT.

Numerical Simulation of Heat Transfer to TiO2-Water Nanofluid Flow in a Double-Tube Counter Flow Heat Exchanger

Recently, the means of improvement of heat transfer has been rapidly studied. One of the methods that enhance the heat transfer is by changing the heat exchanging fluids. The poor heat transfer coefficient of common fluids compared to the most solids becomes the primary obstacle to design high compactness and effectiveness of heat exchanger. The primary objective of this chapter is to conduct the study of the heat transfer between the water and nanofluid. Both of the fluids were flowed in the horizontal counter flow heat exchanger under the turbulent flow condition. The flow velocity of the fluids varied with Re between 4,000 and 18,000. Literature review states that the heat transfer coefficient of nanofluid is higher than the water by about 6–11 %. Heat transfer to the nanofluid and water is investigated using a computer fluid dynamics software. Ten percent heat transfer augmentation is observed utilizing nanofluid as heat exchanging fluid compared to water. The results also showed the enhancement of the Reynolds number increases the heat transfer to the nanofluid studied in this investigation.