Heat Transfer and Pressure Drop of Periodically Fully Developed Swirling Laminar Flows in Twisted Tubes With Elliptical Cross Sections

2009 ◽  
Author(s):  
Fady Bishara ◽  
Milind A. Jog ◽  
Raj M. Manglik
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Cross Section ◽  
Cross Sections ◽  
Laminar Flows ◽  
Elliptical Cross ◽  
Twist Ratio ◽  
Twisted Tubes

Periodically fully-developed swirling laminar flows in twisted tubes with elliptical cross sections are computationally simulated. The tubes are helically twisted and their geometry is described by the 180° twist ratios y of 3.0, 4.5 and 6.0, and ellipse cross-section aspect ratio of 0.7. Constant-property flow of water (nominal Pr = 3.0) with a Reynolds number range of 10 to 1200 is considered. The analysis quantifies the improvement in the Nusselt number as well as the increase in friction factor in order to map the effective heat transfer enhancement due to the twisted-tube-geometry-induced swirl flows. To this effect, the numerical results are compared with the baseline cases having a twist ratio of y = infinity, or straight elliptical cross-section tubes for which well established correlations are available. Numerical results show that the friction factor and the Nusselt number are a strong function of the twist ratio and the Reynolds number. The increase in fRe and Nu is higher as the twist becomes tighter (lower values of y). For Reynolds numbers below about 100, the heat transfer results do not deviate significantly from the straight-tube values, but at higher values of Re, significant enhancement in heat transfer is evident for all twist ratios considered here. The friction factor and Nusselt number results provided in this paper will help practicing engineers in integrating twisted elliptical tubes in various heat transfer applications.

Efficiency assessment of using graphene nanoplatelets-silver/water nanofluids in microchannel heat sinks with different cross-sections for electronics cooling

2019 ◽  
Vol 30 (1) ◽  
pp. 347-372 ◽  
Author(s):  
Marjan Goodarzi ◽  
Iskander Tlili ◽  
Zhe Tian ◽  
Mohammad Reza Safaei
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Cross Sections ◽  
Graphene Nanoplatelets ◽  
Heat Sinks ◽  
Pumping Power ◽  
Content Type

Purpose This study aims to model the nanofluid flow in microchannel heat sinks having the same length and hydraulic diameter but different cross-sections (circular, trapezoidal and square). Design/methodology/approach The nanofluid is graphene nanoplatelets-silver/water, and the heat transfer in laminar flow was investigated. The range of coolant Reynolds number in this investigation was 200 ≤ Re ≤ 1000, and the concentrations of nano-sheets were from 0 to 0.1 vol. %. Findings Results show that higher temperature leads to smaller Nusselt number, pressure drop and pumping power, and increasing solid nano-sheet volume fraction results in an expected increase in heat transfer. However, the influence of temperature on the friction factor is insignificant. In addition, by increasing the Reynolds number, the values of pressure drop, pumping power and Nusselt number augments, but friction factor diminishes. Research limitations/implications Data extracted from a recent experimental work were used to obtain thermo-physical properties of nanofluids. Originality/value The effects of temperature, microchannel cross-section shape, the volume concentration of nanoparticles and Reynolds number on thermal and hydraulics behavior of the nanofluid were investigated. Results are presented in terms of velocity, Nusselt number, pressure drop, friction loss and pumping power in various conditions. Validation of the model against previous papers showed satisfactory agreement.

scholarly journals The Effect of Nanofluid Volume Concentration on Heat Transfer and Friction Factor inside a Horizontal Tube

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Adnan M. Hussein ◽  
K. V. Sharma ◽  
R. A. Bakar ◽  
K. Kadirgama
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Thermal Properties ◽  
Friction Factor ◽  
Volume Concentration ◽  
Convection Heat Transfer ◽  
Horizontal Tube ◽  
Maximum Deviation ◽  
Flat Tube

The additives of solid nanoparticles to liquids are significant enhancement of heat transfer and hydrodynamic flow. In this study, the thermal properties of three types of nanoparticles (Al2O3, TiO2, and SiO2) dispersed in water as a base fluid were measured experimentally. Forced convection heat transfer turbulent flow inside heated flat tube was numerically simulated. The heat flux around flat tube is 5000 W/m2and Reynolds number is in the range of5×103to50×103. CFD model by finite volume method used commercial software to find hydrodynamic and heat transfer coefficient. Simulation study concluded that the thermal properties measured and Reynolds number as input and friction factor and Nusselt number as output parameters. Data measured showed that thermal conductivity and viscosity increase with increasing the volume concentration of nanofluids with maximum deviation 19% and 6%, respectively. Simulation results concluded that the friction factor and Nusselt number increase with increasing the volume concentration. On the other hand, the flat tube enhances heat transfer and decreases pressure drop by 6% and −4%, respectively, as compared with circular tube. Comparison of numerical analysis with experimental data available showed good agreement with deviation not more than 2%.

A Comparative Study of Performance of Low Reynolds Number Turbulence Models for Various Heat Transfer Enhancement Simulations

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ankit Tiwari ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Fluid Dynamic ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Transfer Enhancement ◽  
Low Reynolds

The goal of this study is to evaluate the computational fluid dynamic (CFD) predictions of friction factor and Nusselt number from six different low Reynolds number k–ε (LRKE) models namely Chang–Hsieh–Chen (CHC), Launder–Sharma (LS), Abid, Lam–Bremhorst (LB), Yang–Shih (YS), and Abe–Kondoh–Nagano (AKN) for various heat transfer enhancement applications. Standard and realizable k–ε (RKE) models with enhanced wall treatment (EWT) were also studied. CFD predictions of Nusselt number, Stanton number, and friction factor were compared with experimental data from literature. Various parameters such as effect of type of mesh element and grid resolution were also studied. It is recommended that a model, which predicts reasonably accurate values for both friction factor and Nusselt number, should be chosen over disparate models, which may predict either of these quantities more accurately. This is based on the performance evaluation criterion developed by Webb and Kim (2006, Principles of Enhanced Heat Transfer, 2nd ed., Taylor and Francis Group, pp. 1–72) for heat transfer enhancement. It was found that all LRKE models failed to predict friction factor and Nusselt number accurately (within 30%) for transverse rectangular ribs, whereas standard and RKE with EWT predicted friction factor and Nusselt number within 25%. Conversely, for transverse grooves, AKN, AKN/CHC, and LS (with modified constants) models accurately predicted (within 30%) both friction factor and Nusselt number for rectangular, circular, and trapezoidal grooves, respectively. In these cases, standard and RKE predictions were inaccurate and inconsistent. For longitudinal fins, Standard/RKE model, AKN, LS and Abid LRKE models gave the friction factor and Nusselt number predictions within 25%, with the AKN model being the most accurate.

scholarly journals Experimental Study on Liquid Flow and Heat Transfer in Rough Microchannels

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Xuan Zhang ◽  
Taocheng Zhao ◽  
Suchen Wu ◽  
Feng Yao
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Cross Section ◽  
Liquid Flow ◽  
Flow And Heat Transfer ◽  
Section Shape ◽  
Poiseuille Number

Although roughness is negligible for laminar flow through tubes in classic fluid mechanics, the surface roughness may play an important role in microscale fluid flow due to the large ratio of surface area to volume. To further verify the influence of rough surfaces on microscale liquid flow and heat transfer, a performance test system of heat transfer and liquid flow was designed and built, and a series of experimental examinations are conducted, in which the microchannel material is stainless steel and the working medium is methanol. The results indicate that the surface roughness plays a significant role in the process of laminar flow and heat transfer in microchannels. In microchannels with roughness characteristics, the Poiseuille number of liquid laminar flow relies not only on the cross section shape of the rough microchannels but also on the Reynolds number of liquid flow. The Poiseuille number of liquid laminar flow in rough microchannels increases with increasing Reynolds number. In addition, the Nusselt number of liquid laminar heat transfer is related not only to the cross section shape of a rough microchannel but also to the Reynolds number of liquid flow, and the Nusselt number increases with increasing Reynolds number.

Analytical Solution for Newtonian Laminar Flow Through the Concave and Convex Ducts

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
M. Firouzi ◽  
S. H. Hashemabadi
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Friction Factor ◽  
Cross Section ◽  
Cross Sections ◽  
Fully Developed Flow ◽  
Pipe Flows ◽  
Dimensionless Velocity ◽  
Flow Through ◽  
Fanning Friction Factor

In this paper, the motion equation for steady state, laminar, fully developed flow of Newtonian fluid through the concave and convex ducts has been solved both numerically and analytically. These cross sections can be formed due to the sedimentation of heavy components such as sand, wax, debris, and corrosion products in pipe flows. The influence of duct cross section on dimensionless velocity profile, dimensionless pressure drop, and friction factor has been reported. Finally based on the analytical solutions three new correlations have been proposed for the product of Reynolds number and Fanning friction factor (Cf Re) for these geometries.

Heat Transfer and Pressure Drop Correlation for Helicoidal Pipes of Rectangular Cross Section

2009 ◽  
Author(s):  
Christopher Katinas ◽  
Ahmad Fakheri
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Friction Factor ◽  
Cross Section ◽  
Numerical Solutions ◽  
Rectangular Cross Section ◽  
Dean Number ◽  
Curvature Effects ◽  
The Impact

In this study, flow and heat transfer for laminar flow in curved channels of rectangular cross section is examined. The focus of the numerical solutions is on rectangular cross sections with an aspect ratio less than one, since little information is available for heat transfer in curved rectangular pipes whose width is greater than height. The study examines the impact of the aspect ratio and Dean number on both friction factor and Nusselt number. The results show that although both friction factor and Nusselt number increase as a result of curvature effects, the heat transfer enhancements significantly outweigh the friction factor penalty. Numerical solutions in this study consider the more realistic case of hydrodynamically developed and thermally developing flow.

scholarly journals CFD Analysis on the Heat Transfer and Fluid Flow of Solar Air Heater having Transverse Triangular Block at the Bottom of Air Duct

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1099
Author(s):  
Hwi-Ung Choi ◽  
Kwang-Hwan Choi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Design Parameters ◽  
Solar Air Heater ◽  
Air Heater ◽  
Geometric Conditions ◽  
Computational Fluid Dynamics Analysis ◽  
Triangular Block

In this study, a two-dimensional CFD (computational fluid dynamics) analysis was performed to investigate the heat-transfer and fluid-friction characteristics in a solar air heater having a transverse triangular block at the bottom of the air duct. The Reynolds number, block height (e), pitch (P), and length (l) were chosen as design parameters. The results are validated by comparing the Nusselt number predicted by simulation with available experimental results. Renormalization-group (RNG) k - ε model with enhanced wall-treatment was selected as the most appropriate turbulence model. From the results, it was found that the presence of a transverse triangular block produces a higher Nusselt number than that of smooth air duct. The enhancement in Nusselt number varied from 1.19 to 3.37, according to the geometric conditions investigated. However, the use of transverse triangular block also results in significantly higher friction losses. The thermohydraulic performance (THPP) was also estimated and has a maximum value of 1.001 for height (e) of 20 mm, length (l) of 120 mm, and pitch (P) of 150 mm, at Reynolds number of 8000. Furthermore, in the present study, correlations of the Nusselt number and friction factor were developed as a function of geometrical conditions of the transverse triangular block and Reynolds number, which can be used to predict the value of Nusselt number and friction factor with the absolute percentage deviations of 3.29% and 7.92%, respectively.

Two-phase modeling of nanofluid forced convection in different arrangements of elliptical tube banks

2019 ◽  
Vol 30 (4) ◽  
pp. 1937-1966 ◽  
Author(s):  
Seyed Mohammad Mousavi ◽  
Omid Ali Akbari ◽  
Ghanbarali Sheikhzadeh ◽  
Ali Marzban ◽  
Davood Toghraie ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Section ◽  
Dimensional Space ◽  
Two Dimensional ◽  
Two Phase ◽  
Elliptical Cross ◽  
Cooling Fluid ◽  
Content Type ◽  
Tube Banks

Purpose The purpose of this study is two phase modeling of Water/Cu nanofluid forced convection in different arrangements of elliptical tube banks in a two-dimensional space. Design/methodology/approach The arrangements of tube banks have been regarded as equal spacing triangle (ES), equilateral triangle (ET) and the rotated square (RS). The obtained results indicate that, among the investigated arrangements, the RS arrangement has the maximum value of heat transfer with cooling fluid. Also, the changes of Nusselt number and the local friction factor are under the influence of three main factors including volume fraction of slid nanoparticles, the changes of fluid velocity parameters on the curved surface of tube and flow separation after crossing from a specified angle of fluid rotation. Findings In Reynolds number of 250 and in all arrangements of the tube banks, the behavior of Nusselt number is almost the same and the separation of flow happens in almost 155-165 degrees from fluid rotation on surface. In RS arrangement, due to the strength of vortexes after fluid separation, better mixture is created and because of this reason, after the separation zone, the level of local Nusselt number graph enhances significantly. Originality/value In this research, the laminar and two-phase flow of Water/Cu nanofluid in tube banks with elliptical cross section has been numerically investigated in a two-dimensional space with different longitudinal arrangements. In this study, the effects of using nanofluid, different arrangements of tube banks and the elliptical cross section on heat transfer and cooling fluid flow among the tube banks of heat exchanger have been numerically simulated by using finite volume method.

scholarly journals Effect of Pin Diameter Degressive Gradient on Heat Transfer in a Microreactor with Non-Uniform Pin-Fin Array under Low Reynolds Number Conditions

Energies ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2702
Author(s):  
Miao Qian ◽  
Jie Li ◽  
Zhong Xiang ◽  
Chao Yan ◽  
Xudong Hu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Low Reynolds Number ◽  
Hydrodynamic Characteristics ◽  
Pin Fin ◽  
Low Reynolds ◽  
Pin Fin Array

To improve the efficiency of hydrogen-producing microreactors with non-uniform pin-fin array, the influence of the pin diameter degressive gradient of the non-uniform pin-fin array (NPFA) on heat transfer and pressure drop characteristics is analyzed in this study via numerical simulation under low Reynolds number conditions. Because correlations in prior studies cannot be used to predict the Nusselt number and pressure drop in the NPFA, new heat transfer and friction factor correlations are developed in this paper to account for the effect of the pin diameter degressive gradient, providing a method for the optimized design of the pin diameter degressive gradient for a microreactor with NPFA. The results show that the Nusselt number and friction factor under a low Reynolds number are quite sensitive to the pin diameter degressive gradient. Based on the new correlations, the exponents of the pin diameter degressive gradient for the friction factor and Nusselt number were 6.9 and 2.1, respectively, indicating the significant influence of the pin diameter degressive gradient on the thermal and hydrodynamic characteristics in the NPFA structure.

A Numerical Simulation of Heat Transfer Enhancement Using Al2O3 Nanofluid

2020 ◽  
Vol 10 (5) ◽  
pp. 610-621
Author(s):  
Taliv Hussain ◽  
Mohammad T. Javed
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Volume Concentration ◽  
Numerical Study ◽  
Pure Water ◽  
Maximum Deviation ◽  
Nanoparticle Concentration ◽  
Maximum Increase

Introduction: A numerical study is performed in which the friction factor and forced convection heat transfer is studied for Al2O3 nanoparticle dispersed in water as a base fluid. Methods: Four concentrations of nanofluids in the range of 0-2.5 vol% have been simulated. The Reynolds Number is varied in the range of 100-500 by varying inlet velocity. Cross flow of air is assumed over the pipe with air velocity of 2.2 m/s. Results: The results depict that the friction factor decreases with an increase in flow rate and increases with increase in volume concentration. The maximum deviation for friction factor obtained by simulation from that obtained using Darcy’s relation is about 21.5% for water. Nusselt number increases with increase in Reynolds Number and nanofluid volume concentration with a maximum of 7653.68 W/m2 at a nanoparticle concentration of 2.5% and Reynolds Number of 500. Heat transfer rate enhancement of upto 13.6% is obtained as compared to pure water. The maximum increase in Nusselt Number is about 13.07% for a nanoparticle concentration of 2.5%. Conclusion: The simulation results are compared with established relations obtained by other researchers and there is a good agreement in terms of trends obtained. The deviations from established relations are also depicted.

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