Comparative Study on Heat Transfer Enhancement of Low Volume Concentration of Al2O3–Water and Carbon Nanotube–Water Nanofluids in Laminar Regime Using Helical Screw Tape Inserts

2013 ◽  
Vol 4 (4) ◽  
Author(s):  
Sandesh S. Chougule ◽  
S. K. Sahu
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Volume Concentration ◽  
Constant Heat Flux ◽  
Transfer Enhancement ◽  
Straight Pipe ◽  
Maximum Enhancement ◽  
Flux Boundary Condition ◽  
Twist Ratio ◽  
Heat Flux Boundary Condition

An experimental study has been carried out to evaluate the heat transfer and friction factor characteristics of helical screw inserts in Al2O3–water and carbon nanotubes (CNT)–water nanofluids through a straight pipe in laminar flow regime with constant heat flux boundary condition. Tests have been performed by using 0.15% volume concentration Al2O3–water and CNT–water nanofluid with helical tape inserts of twist ratio (TR) = 1.5, 2.5, and 3. The helical screw tape inserts with CNT–water nanofluid exhibits higher thermal performance compared to Al2O3–water nanofluid. The maximum enhancement in heat transfer was obtained for CNT–water nanofluid with helical tape inserts of TR = 1.5. The increase in pressure drop of Al2O3–water nanofluid with helical screw tape inserts is found to be higher compared to CNT–water nanofluid with helical screw tape inserts at lower value of TR. For both the nanofluids (CNT–water and Al2O3–water), the thermal performance factor was found to be greater than unity for all TRs.

On Effects of Temperature Boundary Conditions on Heat Transfer in Turbulent Low-Prandtl-Number Flows

2020 ◽  
Author(s):  
Ivan Otic
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Large Eddy ◽  
Heat Flux Boundary Condition ◽  
Effects Of Temperature

Abstract One important issue in understanding and modeling of turbulent heat transfer is the behavior of fluctuating temperature close to the wall. Common engineering computational approach assumes constant heat flux boundary condition on heated walls. In the present paper constant heat flux boundary condition was assumed and effects of temperature fluctuations are investigated using large eddy simulations (LES) approach. A series of large eddy simulations for two geometries is performed: First, forced convection in channels and second, forced convection over a backward facing step. LES simulation data is statistically analyzed and compared with results of direct numerical simulations (DNS) from the literature which apply three cases of heat flux boundary conditions: 1. ideal heat flux boundary condition, 2. non-ideal heat flux boundary condition, 3. conjugate heat transfer boundary condition. For low Prandtl number flows LES results show that, despite very good agreement for velocities and mean temperature, predictions of temperature fluctuations may have strong deficiencies if simplified boundary conditions are applied.

scholarly journals CFD-Entropy generation analysis of refrigerant-based nanofluids flow in a tube

2020 ◽  
Vol 307 ◽  
pp. 01038
Author(s):  
Mohammed Zohud ◽  
Ahmed Ouadha ◽  
Redouane Benzeguir
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Entropy Generation ◽  
Constant Heat Flux ◽  
Flux Boundary Condition ◽  
Flow Heat ◽  
Heat Flux Boundary Condition ◽  
The Heat Transfer Coefficient

The present paper aims to numerically investigate the flow, heat transfer and entropy generation of some hydrocarbon based nanorefrigerants flowing in a circular tube subject to constant heat flux boundary condition. Numerical tests have been performed for 4 types of nanoparticles, namely Al2O3, CuO, SiO2, and ZnO with a diameter equal to 30 nm and a volume concentration of φ = 5%. These nanoparticles are dispersed in some hydrocarbon-based refrigerants, namely tetrafluoroethane (R134a), propane (R290), butane (R600), isobutane (R600a) and propylene (R1270). Computations have been performed for Reynolds number ranging from 600 to 2200. The numerical results in terms of the average heat transfer coefficient of pure refrigerants have been compared to values obtained using correlations from the literature. The results show that the increase of the Reynolds number increases the heat transfer coefficient and decreases the total entropy generation.

scholarly journals Effect of Conical Strip Inserts and ZrO2/DI-Water Nanofluid on Heat Transfer Augmentation: An Experimental Study

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4554
Author(s):  
Mohamed Iqbal Shajahan ◽  
Jee Joe Michael ◽  
M. Arulprakasajothi ◽  
Sivan Suresh ◽  
Emad Abouel Nasr ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Test Section ◽  
Volume Concentration ◽  
Swirl Flow ◽  
Performance Ratio ◽  
Transfer Rates ◽  
Heat Transfer Augmentation ◽  
Twist Ratio ◽  
Constant Wall Heat Flux

There is a significant enhancement of the heat transfer rate with the usage of nanofluid. This article describes a study of the combination of using nanofluid with inserts, which has proved itself in attaining higher benefits in a heat exchanger, such as the radiator in automobiles, industries, etc. Nanofluids are emerging as alternative fluids for heat transfer applications due to enhanced thermal properties. In this paper, the thermal hydraulic performance of ZrO2, awater-based nanofluid with various volume concentrations of 0.1%, 0.25%, and 0.5%, and staggered conical strip inserts with three different twist ratios of 2.5, 3.5, and 4.5 in forward and backward flow patterns were experimentally tested under a fully developed laminar flow regime of 0–50 lphthrough a horizontal test pipe section with a length of 1 m with a constant wall heat flux of 280 W as the input boundary condition. The temperatures at equidistant position and across the test section were measured using K-type thermocouples. The pressure drop across the test section was measured using a U-tube manometer. The observed results showed that the use of staggered conical strip inserts improved the heat transfer rates up to that of 130.5%, 102.7%, and 64.52% in the forward arrangement, and similarly 145.03%, 116.57%, and 80.92% in the backward arrangement with the twist ratios of 2.5, 3.5, and 4.5 at the 0.5% volume concentration of ZrO2 nanofluid. It was also seen that the improvement in heat transfer was comparatively lower for the other two volume concentrations considered in this study. The twist ratio generates more swirl flow, disrupting the thermal hydraulic boundary layer. Nanofluids with a higher volume concentration lead to higher heat transfer due to higher effective thermal conductivity of the prepared nanofluid. The thermal performance factor (TPF) with conical strip inserts at all volume concentrations of nanofluids was perceived as greater than 1. A sizable thermal performance ratio of 1.62 was obtained for the backward-arranged conical strip insert with 2.5 as the twist ratio and a volume concentration of 0.5% ZrO2/deionized water nanofluid. Correlations were developed for the Nusselt number and friction factor based on the obtained experimental data with the help of regression analysis.

Turning Guide Vane Effect on Internal Cooling of Two-Passage Channel With Parallel Ribs

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Mandana S. Saravani ◽  
Ryoichi S. Amano ◽  
Nicholas J. DiPasquale ◽  
Joseph Wayne Halmo
Keyword(s):  
Heat Transfer ◽  
Guide Vane ◽  
Constant Heat Flux ◽  
Operating Conditions ◽  
Internal Cooling ◽  
Flux Boundary Condition ◽  
Flow And Heat Transfer ◽  
Computational Fluid Dynamics Simulations ◽  
Heat Flux Boundary Condition ◽  
Dynamics Simulations

Abstract The present work investigates the effects of various guide vane designs on the heat transfer enhancement of rotating U-duct configuration with parallel 45-deg ribs. The ribs were installed on the bottom wall of the channel, which has a constant heat flux boundary condition. The channel has a square cross section with a 5.08 cm hydraulic diameter. The first and second passes are 514 mm and 460 mm, respectively. The range of Reynolds number for turbulent flow is up to 35,000. The channel rotates at various speeds up to 600 rpm, which brings the maximum rotation number of 0.75. Several computational fluid dynamics simulations are carried out for this study to understand the effect of guide vanes on flow and heat transfer in serpentine channels under various operating conditions.

Pool boiling heat transfer enhancement by using perforated twisted tape fins

2021 ◽  
pp. 1-10
Author(s):  
Parimesh Joshi ◽  
Anil Kumar Patil ◽  
Manoj Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Twisted Tape ◽  
Transfer Enhancement ◽  
Maximum Enhancement ◽  
Twist Ratio ◽  
Plain Surface ◽  
Considerable Enhancement

Abstract The application of twisted tape fins showed a considerable enhancement in pool boiling heat flux. The present study experimentally investigates the effect of solid and perforated twisted tape fins on pool boiling of water by varying the twist ratio (y) and perforation index (PI) from 3 - 4.3 and 5 - 10, respectively. An arrangement of five twisted tape fins with twist ratio of 3 showed 18.6% enhancement as compared to the plain surface whereas an arrangement of five perforated twisted tape fins having perforation index (PI) of 7 and twist ratio of 3 showed a maximum enhancement of 28.7%.

Melting Around a Horizontal Heated Cylinder: Part I—Perturbation and Numerical Solutions for Constant Heat Flux Boundary Condition

1984 ◽  
Vol 106 (2) ◽  
pp. 376-384 ◽  
Author(s):  
J. Prusa ◽  
L. S. Yao
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Perturbation Method ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Heated Cylinder ◽  
Heat Flux Boundary Condition ◽  
Rayleigh Numbers

The melting of a solid about a heated cylinder presents an irregularly shaped, moving boundary problem. A transformation is used to immobilize this boundary—replacing the problem of variable geometry by one of constant geometry. A constant heat flux boundary condition is used along the cylinder surface. Using perturbation and numerical methods, several solutions for this transient problem are generated for Stefan, Rayleigh, and Prandtl numbers of Stq = 0.374, Ra = 5000, and Pr = 54. Stq is the ratio of heat transfer rate to the thermal energy needed to melt the solid. Ra • B3 is the measure of the magnitude of the natural convection effect, where B is a dimensionless measure of the size of the melt region called the gap function. Ra itself can be thought of as a dimensionless heat flux, since it does not take the size of the melt region into account. The dimensionless groups Stq and Ra (based upon the surface heat flux) are used to determine two parameter expansions of the dependent variables for the regular perturbation method. The first three terms of the series solutions are determined. They provide accurate solutions for short times after the start of melting, for small values of Stefan and Rayleigh numbers. The accuracy of the perturbation method is verified using a numerical method, which is not limited to short initial time intervals or to small values of Stefan and Rayleigh numbers. Detailed predictions of the melt volume, shape, temperature field, global and local heat transfer rates are given for representative cases. Comparisons with earlier experimental results are made.

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