Buoyancy and Property Variation Effects in Turbulent Mixed Convection of Water in Vertical Tubes

1996 ◽  
Vol 118 (2) ◽  
pp. 381-387 ◽  
Author(s):  
Y. Parlatan ◽  
N. E. Todreas ◽  
M. J. Driscoll
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Temperature Dependent Viscosity ◽  
Experimental Conditions ◽  
Property Variation ◽  
Dependent Viscosity ◽  
The Heat Transfer Coefficient

Friction factor and heat transfer coefficient behavior are investigated experimentally under mixed convection conditions in aiding and opposing transition and turbulent flow of water (4000 < Re < 9000 and Bo < 1.3). With increasing buoyancy influence, the friction factor increases by as much as 25 percent in aiding flow, while it decreases by as much as 25 percent in opposing flow (GrΔT < 7·106). The effects of temperature-dependent viscosity variations are also included in the analysis (0.5 < μw/μb < 1.0). When they are taken into account, the increase in the friction factor due to buoyancy forces alone in upward flow becomes larger. The friction factor behavior is compared with previous studies in the literature. Our experimental data agree well with some of the previous experiments described in the literature. The heat transfer coefficient was also measured under the same experimental conditions; the heat transfer coefficient monotonically increases in opposing flow by as much as 40 percent, and first decreases by 50 percent and then recovers in aiding flow with increasing buoyancy influence.

scholarly journals Cooling of High Heat Flux Flat Surface with Nanofluid Assisted Convective Loop: Experimental Assessment

2017 ◽  
Vol 64 (4) ◽  
pp. 519-531 ◽  
Author(s):  
Amir Arya ◽  
Saeed Shahmiry ◽  
Vahid Nikkhah ◽  
Mohamad Mohsen Sarafraz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
High Heat ◽  
High Heat Flux ◽  
Overall Heat Transfer Coefficient ◽  
Cooling Loop ◽  
The Heat Transfer Coefficient

Abstract Experimental investigation was conducted on the thermal performance and pressure drop of a convective cooling loop working with ZnO aqueous nanofluids. The loop was used to cool a flat heater connected to an AC autotransformer. Influence of different operating parameters, such as fluid flow rate and mass concentration of nanofluid on surface temperature of heater, pressure drop, friction factor and overall heat transfer coefficient was investigated and briefly discussed. Results of this study showed that, despite a penalty for pressure drop, ZnO/water nanofluid was a promising coolant for cooling the micro-electronic devices and chipsets. It was also found that there is an optimum for concentration of nanofluid so that the heat transfer coefficient is maximum, which was wt. % = 0.3 for ZnO/water used in this research. In addition, presence of nanoparticles enhanced the friction factor and pressure drop as well; however, it is not very significant in comparison with those of registered for the base fluid.

Prediction of Heat Transfer and Friction for the Louver Fin Geometry

1992 ◽  
Vol 114 (4) ◽  
pp. 893-900 ◽  
Author(s):  
A. Sahnoun ◽  
R. L. Webb
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Maximum Error ◽  
Transfer Coefficients ◽  
Mean Error ◽  
The Heat Transfer Coefficient

This paper is concerned with prediction of the air-side heat transfer coefficient of the louver fin geometry used in automotive radiators. An analytical model was developed to predict the heat transfer coefficient and friction factor of the louver fin geometry. The model is based on boundary layer and channel flow equations, and accounts for the “flow efficiency” in the array, as previously reported by Webb and Trauger. The model has no empirical constants. The model allows independent specifications of all of the geometric parameters of the louver fin. This includes the number of louvers over the flow depth, the louver width and length, and the louver angle. The model was validated by predicting the heat transfer coefficient and friction factor of 32 louver arrays tested by Davenport, which spanned hydraulic diameter based Reynolds numbers of 300–2800. At the highest Reynolds number, all of the heat transfer coefficients were predicted within a maximum error of −14 / + 25 percent, and a mean error of ± 8 percent. The high Reynolds number friction factors were predicted with a maximum error −22 /+ 26 percent, with a mean error of ± 8 percent. The error ratios were slightly higher at the lowest Reynolds numbers.

Convective heat transfer and fluid flow characteristics in fin and oval-tube heat exchanger

2021 ◽  
Vol 15 (2) ◽  
pp. 7936-7947
Author(s):  
Yamina Abdoune ◽  
Sahel Djamel ◽  
Benzeguir Redouane ◽  
Alem Karima
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Tube Heat Exchanger ◽  
Baseline Case ◽  
Oval Tube ◽  
The Heat Transfer Coefficient

The forced convective heat transfer behavior of a turbulent air flow, steady and Newtonian over a fin and oval-tube heat exchanger has been examined numerically. Where, the effect of the tube tilt angle (α) on the heat transfer coefficient and the friction factor was tested. The inclination angle of the oval-tubes going from 0° (Baseline case) to 90° with a step of 10°. The fluid flows and heat transfer characteristics are presented for Reynolds numbers ranging from 3.000 to 12.000. All investigations are carried out with the help of the CFD ANSYS Fluent. Heat transfer coefficient results in the term of the Nusselt number are validated with the available experimental data and a maximum deviation of 9 % is observed. Reasonable agreement is found. The obtained results show that the tube's inclination angle of 20° is the best design which significantly removes the hot spots behind the tubes, thus giving an increase in the heat transfer coefficient of 13 % compared to the baseline case. In addition, useful correlations are developed to predict Nusselt number and friction factor in the fin and oval-tube heat exchanger.

The Effect of Surface Roughness on the Convection Heat-Transfer Coefficient for Fully Developed Turbulent Flow in Ducts With Uniform Heat Flux

1959 ◽  
Vol 81 (2) ◽  
pp. 168-173 ◽  
Author(s):  
R. T. Lancet
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Convection Heat Transfer ◽  
Uniform Heat Flux ◽  
Friction Factors ◽  
Fully Developed Turbulent Flow ◽  
The Heat Transfer Coefficient ◽  
Effect Of Surface

Experimental data are presented for the heat-transfer coefficient and friction factor in a smooth and a rough duct with a hydraulic diameter of approximately 0.035 in. The flow was fully developed and turbulent, and the heat addition was uniform over the length of the tube. The rough tube indicated appreciable increases in heat-transfer coefficient and friction factor. The smooth-tube friction factors corresponded to rough-tube values, indicating the difficulty involved in obtaining smooth surfaces for very small ducts.

scholarly journals Evaporation Heat Transfer and Pressure Drop of Low-Global Warming Potential Refrigerant HFO-1234yf in 6.95-mm Horizontal Smooth Tube

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6325
Author(s):  
Chang-Hyo Son ◽  
Nam-Wook Kim ◽  
Jung-In Yoon ◽  
Sung-Hoon Seol ◽  
Joon-Hyuk Lee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
Experimental Conditions ◽  
Evaporation Heat ◽  
R 134A ◽  
The Heat Transfer Coefficient

This study investigated the evaporative heat transfer coefficient and pressure drop characteristics of R-1234yf in a horizontal tube with an inner diameter of 6.95 mm under various experimental conditions. The heat transfer coefficient increased with an increase in quality but showed a sharp decrease in the high-quality area. In addition, the heat transfer coefficient increased as the mass flux, heat flux, and saturation temperature increased. Although R-1234yf and R-134a presented similar heat transfer coefficients, that of R-134a was higher. The pressure drop increased with an increase in the quality and mass flux but decreased with an increase in the saturation temperature. The pressure drop of R-134a was larger than that of R-1234yf. In light of the flow pattern diagram by Taitel and Dukler, most of the experiments were included in the annular flow region, and some regions showed intermittent and stratified corrugated flow regions. Kandlikar’s heat transfer coefficient correlation provided the best prediction for the experimental database, with approximately 84% of the predicted data within ±30%. Moreno Quibén and Thome’s equation for pressure drop predicted approximately 88.71% of the data within ±30%.

Heat Transfer and Pressure Drop Correlations for Double-Pass Solar Collector With and Without Porous Media

2002 ◽  
Author(s):  
K. Sopian ◽  
Adam M. Elradi ◽  
Shahrir Abdullah ◽  
K. V. Wong
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Operating Conditions ◽  
Transient Heat Transfer ◽  
Double Pass ◽  
The Heat Transfer Coefficient

Correlations of transient heat transfer and pressure drop have been developed for air flowing through the porous media, which packed a double-pass solar air heater. Various porous media are arranged in different porosities to increase heat transfer, area density and the total heat transfer rate. Transient heat transfer experiments indicate that both the heat transfer coefficient and the friction factor are strong functions of porosity. The heat transfer coefficient and the friction factor are also strong functions of the geometrical parameters of the porous media. A test collector was developed and tested indoors by varying the design features and operating conditions using a halogen-lamp simulator as a radiation source. This type of collector can be used for drying and heat applications such as solar industrial processes, space heating and solar drying of agricultural products.

Flow Boiling in Transparent Heated Microtube

2008 ◽  
Author(s):  
Osamu Kawanami ◽  
Shih-Che Huang ◽  
Kazunari Kawakami ◽  
Itsuro Honda ◽  
Yousuke Kawashima ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Flow Boiling ◽  
Flow Behavior ◽  
High Heat Flux ◽  
Experimental Conditions ◽  
The Heat Transfer Coefficient

In the present study, a detailed investigation of flow boiling in a transparent heated microtube was performed. The transparent heated tube was made by electroless gold plating method. The enclosed gas-liquid interface could be clearly recognized through the tube wall, and the inner wall temperature measurement and direct heating of the film were simultaneously conducted by using the tube. The experimental conditions were: tube diameter 1 mm, mass velocity 100 kg/m2s, inlet liquid sub-cooling 20 K and heat flux up to 384 kW/m2 in the open system. Flow fluctuation was minimized by employing a twin plunger pump. Among our experimental results, we observed a high-frequency fluctuation of the inner wall temperature and a sharp peak for the heat transfer coefficient with high heat flux conditions, which have not been reported in previous experiments. This abrupt increase in the heat transfer coefficient coincided with a slight rapid axial growth of an elongated bubble found in the observation of the flow behavior. Hence, in low heat flux conditions, the fluctuations of temperature and heat transfer coefficient are strongly suppressed except for the instances when there is no bubble in the tube.

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