Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : turbulent flow


Numerical and Experimental Investigation of Heat Transfer Enhancement by Hybrid Nanofluid and Twisted Tape

noor F. A. Hamza; Sattar Aljabair

Engineering and Technology Journal, 2023, Volume 41, Issue 1, Pages 69-85
DOI: 10.30684/etj.2022.131909.1069

This paper presents an experimental and numerical study to investigate the heat transfer enhancement in a horizontal circular tube using hybrid nanofluid (CuO, Al₂O₃/ distilled water) and fitted with twisted tape (typical twisted tape, with twist ratios (TR=9.2). Under fully developed turbulent flow and uniform heat flux conditions, the studied hybrid nanofluid concentrations are (=0.6, 1.22, and 1.8% by volume). The experimental test rig includes all the required instruments to study the heat transfer enhancement. All the tests were carried out with a Reynolds number range of 3560-8320 and uniform heat flux (13217.5 W/m². The twisted tape, manufactured from polylactic acid (PLA) by 3-dimensional printer technology, was inserted inside the tube. In this numerical study, the finite volume method (CFD) procedure was employed to pattern the forced convection turbulent flow through the tube. For hybrid nanofluid with twisted, the maximum enhancement in the maximum thermal performance factor was 2.18 for φ = 1.8%, while for a tube (water with twisted) under the same conditions, it was (2.04). A high Nusselt number was obtained with a concentration of 1.8% and an enhancement in the heat transfer of about 6.70%) than water.

Experimental Investigation of Combined Effect of Particle Size and Stability of Al2O3-H2O Nanofluid on Heat Transfer Augmentation Through Horizontal Pipe

Abdulhassan A. Karamallah; Hayder H. Abed

Engineering and Technology Journal, 2020, Volume 38, Issue 4A, Pages 561-573
DOI: 10.30684/etj.v38i4A.177

The stability of nanofluid plays a rule in heat transfer growth for different engineering systems. The stability and particle size of Al2O3-H2O nanofluid effects on heat transfer are studied experimentally. Two particle sizes (20 and 50 nm) with (0.1, 0.5 and 1%) concentrations were prepared and tested under constant heat flux (1404 W) with fully developed turbulent flow through a horizontal pipe. The results show an increase in Nusselt number by 20.7% and 17.6% with 1 vol.% concentration for 20 and 50 nm, respectively compared to distilled water. Examined nanofluid showed improvement in Nu number by (30.3 and 23.5) % at 1 vol.% concentration compared to water. Obtained results show minor decrease in the pressure drop and friction factor with nanofluid after stability treatment. Different correlations between Nu number and friction factor relating to studied parameters were observed

Drag Reduction Study of Xathan Gum with Polydiallyldimethylammonium Chloride (PDDAC) Solutions in Turbulent Flow

Zainab Yousif

Engineering and Technology Journal, 2018, Volume 36, Issue 8A, Pages 891-899
DOI: 10.30684/etj.336.8A.8

The transportation of liquids through pipelines is attributed with high-energy consumption due to the turbulent nature of their transportation. Low concentrations of polymeric additives were proven effective flow enhancing agent when injected into these pipelines due to its viscoelastic property capable of suppressing the turbulent structures; however, the mechanical degradation of polymers is a disadvantage, which can be controlled efficiently by using complex in a surfactant- polymer interface. In this presented work, turbulent drag reduction (DR) efficacy of anionic Xathan gum and nonionic surfactant (PDDAC) regarding the surfactant -polymer interface was studied using a rotating disk apparatus (RDA) technique and pipeline. The effect of surfactant addition, critical concentration of XG, and the dependence of drag reduction on the turbulent strength from the rotation speed were also studied. The critical behavior of the interface was found at XG (700 ppm) and (1000-ppm) concentrations, respectively. The drag reduction (~70%) was observed at critical concentration behavior, which is largely reliant on the alkyl chain in the surfactant molecule. The result of the a rotating disk apparatus (RDA) gave about 51% drag reduction with the Xanthan gum alone while in the pipe, about 58% drag reduction percent (DR%) was obtained. (PDDAC) alone yielded about 32% and 36% drag reduction in the rotating disk apparatus (RDA) and pipe respectively. However, combining the Xanthan gum polymer and Polydiallyldimethylammonium chloride (PDDAC) surfactant gave 62% drag reduction. Thus, it could be inferred that the combination of these duo has greater impact than the individual materials. It could thus be concluded that the complex formed by these materials is another form of drag reducing agents.

The Effect of variation Longitudinal Ribs Height in Spanwise Direction on Flow and Heat Transfer Characteristics in a Rectangular Duct

Ekhlas M. Fayyadh; Moayed R. Hasan; Sahira H. Ibrahim

Engineering and Technology Journal, 2016, Volume 34, Issue 2, Pages 368-385

The present work has investigated numerically and experimentally the effect of a streamwise riblet on the flow and heat transfer characteristics for fully developed turbulent flow in a rectangular duct heated with constant heat flux for Reynolds number based on hydraulic diameter range of (1.5×〖10〗^4-6×〖10〗^4).
Numerical simulations have been done by solving thegoverning equations (Continuity, Reynolds.
Averaging Navier-stokes and Energy) in turbulent regime with appropriate turbulence model Shear-Stress Transport (k-ω) in three dimensions by using the FLUENT version (12.1.2).
The variation of peak to peak height of riblet in spanwise direction ratio with 〖(h〗_s⁄h_L =0.5)was simulated. The flow structure and heat transfer characteristics (the velocity contours, vorticity contours, secondary flow contours, temperature contours, the distribution of local wall shear stress and heat transfer coefficient in spanwise direction at ribs)were presented as results. Also the effects of ribs on the flow and heat transfer characteristic at duct were presented, as the percentage of average skin friction, Stanton number and the heat transfer efficiency relative to a smooth surface. Experiments were conducted for rectangular duct of aspect ratio =10.
Experimental results indicated an increase in the thickness of hydraulic and thermal sub-layer and shifted up the velocity profile, reducing the skin friction coefficient and Stanton number by about (6 %) and (23%) respectively. The experimental results gave a good agreement with the numerical simulation and previous works.

Exploring Turbulent Effects on Spray Evaporation Modeling

Noor M. Jasim

Engineering and Technology Journal, 2011, Volume 29, Issue 15, Pages 3097-3107

In this work, numerical investigations are conducted for diesel spray under evaporating conditions. The Eulerian-Eulerian framework of evaporating turbulent spray is presented in terms of the methodology of spray moments of drop size distribution. Turbulence effects on mass and heat transfer in evaporation test case are presented. The simulated results showed that the turbulence intensity decreases with the development of spray under hydrodynamic changes. The simulation shows good agreement with the experimental results illustrated by comparison of spray tip penetration elevations.