Cooling of a Finned Cylinder by a Jet Flow of Air

2005 ◽  
Vol 127 (12) ◽  
pp. 1416-1421 ◽  
Author(s):  
F. Gori ◽  
M. Borgia ◽  
A. Doro Altan ◽  
M. Mascia ◽  
I. Petracci
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Jet Flow ◽  
Steel Tube ◽  
Finned Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Smooth Cylinder ◽  
Convective Heat Transfer Coefficients

A submerged slot jet of air is used to cool an externally finned cylinder, heated by electric current. The cylinder ensemble is made of a stainless steel finned tube and a Teflon bar core inside. Five thermocouples, pressed inside the steel tube by the Teflon bar, measure the wall temperature to determine local and mean convective heat transfer coefficients. The local Nusselt number has the maximum on the impinging point and the minimum on the rear point. The variation of local and mean Nusselt numbers with the distance from the slot exit is investigated. Empirical expressions are proposed to correlate the experimental data. The cooling of a finned cylinder with a jet flow realizes a higher heat transfer as compared to a smooth cylinder.

Cooling of a Finned Cylinder by a Jet Flow of Air

2003 ◽  
Author(s):  
F. Gori ◽  
M. Borgia ◽  
A. Doro Altan
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Wall Temperature ◽  
Experimental Tests ◽  
Jet Flow ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Electric System ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Experimental tests have been carried out to evaluate the heat transfer characteristics on an externally finned cylinder impinged by a jet flow of air. The cylinder is internally heated with an electric system. Thermocouples located inside the cylinder allow to evaluate the wall temperature distribution, in order to calculate the local and average convective heat transfer coefficients.

Study on Forced Convective Heat Transfer of FC-72 in Vertical Small Tubes

2020 ◽  
Vol 12 (6) ◽  
Author(s):  
Yantao Li ◽  
Yulong Ji ◽  
Katsuya Fukuda ◽  
Qiusheng Liu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Bulk Liquid ◽  
Transfer Coefficients ◽  
Forced Convective Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Abstract This paper presents an experimental investigation of the forced convective heat transfer of FC-72 in vertical tubes at various velocities, inlet temperatures, and tube sizes. Exponentially escalating heat inputs were supplied to the small tubes with inner diameters of 1, 1.8, and 2.8 mm and effective heated lengths between 30.1 and 50.2 mm. The exponential periods of heat input range from 6.4 to 15.5 s. The experimental data suggest that the convective heat transfer coefficients increase with an increase in flow velocity and µ/µw (refers to the viscosity evaluated at the bulk liquid temperature over the liquid viscosity estimated at the tube inner surface temperature). When tube diameter and the ratio of effective heated length to inner diameter decrease, the convective heat transfer coefficients increase as well. The experimental data were nondimensionalized to explore the effect of Reynolds number (Re) on forced convection heat transfer coefficient. It was found that the Nusselt numbers (Nu) are influenced by the Re for d = 2.8 mm in the same pattern as the conventional correlations. However, the dependences of Nu on Re for d = 1 and 1.8 mm show different trends. It means that the conventional heat transfer correlations are inadequate to predict the forced convective heat transfer in minichannels. The experimental data for tubes with diameters of 1, 1.8, and 2.8 mm were well correlated separately. And, the data agree with the proposed correlations within ±15%.

The Correlation of Heat Transfer Coefficients for the Laminar Natural Convection in a Circular Finned-Tube Heat Exchanger

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Hie Chan Kang ◽  
Se-Myong Chang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Finned Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Laminar Natural Convection

This study proposes an empirical correlation for laminar natural convection applicable to external circular finned-tube heat exchangers with wide range of configuration parameters. The transient temperature response of the heat exchangers was used to obtain the heat transfer coefficient, and the experimental data with their characteristic lengths are discussed. The data lie in the range from 1 to 1000 for Rayleigh numbers based on the fin spacing: the ratio of fin height to tube diameter ranges from 0.1 to 0.9, and the ratio of fin pitch to height ranges from 0.13 to 2.6. Sixteen sets of finned-tube electroplated with nickel–chrome were tested. The convective heat transfer coefficients on the heat exchangers were measured by elimination of the thermal radiation effect from the heat exchanger surfaces. The Nusselt number was correlated with a newly suggested composite curve formula, which converges to the quarter power of the Rayleigh number for a single cylinder case. The proposed characteristic length for the Rayleigh number is the fin pitch while that for the Nusselt number is mean flow length, defined as half the perimeter of the mean radial position inside the flow region bounded by the tube surface and two adjacent fins. The flow is regarded as laminar, which covers heat exchangers from a single horizontal cylinder to infinite parallel disks. Consequently, the result of curve fitting for the experimental data shows the reasonable physical interpretation as well as the good quantitative agreement with the correction factors.

scholarly journals Numerical Investigation On The Impingement Of A Circular Jet Of Nanofluids On A Circular Flat Plate

2021 ◽  
Author(s):  
Dhimitri Kucuqi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Convective Heat Transfer ◽  
Experimental Model ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

A numerical study was conducted to investigate and validate experimental convective heat transfer coefficient data associated with an Al2O3-H2O nanofluid through the use of an impingement jet on a flat, circular disk. It was observed that, in conjunction with experimental data, nanofluids provided increased local convective heat transfer coefficients in comparison to the base fluid. Nanofluid concentrations outlined in the experimental model, from 0.0198 to 0.0757 wt%, were investigated in a numerical model and resulting convective heat transfer coefficients were compared. In contrast to the experimental model, the maximum heat transfer enhancement occurred at the nanofluid concentration of 0.0757 wt%. In addition, several other models were tested with various Reynolds numbers and jet height-to-jet diameter ratios for further investigation along with discussion of sources of error. Overall, in comparison to experimental data, the lowest percentage errors achieved for the Reynolds numbers of 4245.7 and 8282 were 17.9% and 34.9%, respectively.

Analytical and Experimental Analysis of a High Temperature Mercury Thermosyphon

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
André Felippe Vieira da Cunha ◽  
Marcia B. H. Mantelli
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
High Temperature ◽  
Temperature Distribution ◽  
Tube Wall ◽  
Finned Tube ◽  
Liquid Pool ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Noncondensable Gases

High temperature thermosyphons are devices designed to operate at temperatures above 400°C. They can be applied in many industrial applications, including heat recovery from high temperature air fluxes. After a short literature review, which shows a deficiency of models for liquid metal thermosyphons, an analytical model, developed to predict the temperature distribution and the overall thermal resistance, is shown. In this model, the thermosyphon is divided into seven regions: three regions for the condensed liquid, including the condenser, adiabatic region, and evaporator; one region for vapor; one for the liquid pool; one for the noncondensable gases; and another for the tube wall. The condensation phenomenon is modeled according to the Nusselt theory for condensation in vertical walls. Numerical methods are used to solve the resulting equations and to determine the temperature distribution in the tube wall. Ideal gas law is applied for the noncondensable gases inside the thermosyphon, while the evaporator and condenser heat transfer coefficients are obtained from literature correlations. Experimental tests are conducted for thermosyphon with mercury as working fluid, designed and constructed in the laboratory. The results for two thermosyphons with different geometry configurations are tested: one made of a finned tube in the condenser region and another of a smooth tube. The finned tube presents lower wall temperature levels when compared with the smooth tube. The experimental data are compared with the proposed model for two different liquid pool heat transfer coefficients. It is observed that the comparison between the experimental data and theoretical temperature profiles is good for the condenser region. For the evaporator, where two distinct regions are observed (liquid film and pool), the comparison is not so good, independent of the heat transfer coefficient used. In a general sense, the model has proved to be a useful tool for the design of liquid metal thermosyphons.

The Rules of Single-Phase Forced Convection in Microchannels

2012 ◽  
Author(s):  
Gian Luca Morini
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Gas Flows ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Liquid Flows ◽  
The University ◽  
Convective Heat Transfer Coefficients

This paper deals with the experimental analysis of forced micro-convection features of liquid and gas flows through microchannels. An overview of the main effects that tends to play an important role on the determination of the Nusselt numbers in microchannels is presented. Some experimental data obtained at the Microfluidics Lab of the University of Bologna together with the main results appeared recently in the open literature are used in order to highlight the characteristics of the convective heat transfer through microchannels with inner diameter from 0.75 mm down to and 0.15 mm. It is shown that the behavior of gas and liquid flows through microchannels in terms of convective heat transfer coefficients can be strongly affected by scaling and micro-effects as by practical issues linked to the geometry of the test rig, fittings, position of the sensors and so on. It is demonstrated that the comparison with the conventional correlations for the prediction of the convective heat transfer coefficients gives good results only if one has verified beforehand that the main scaling and micro-effects are negligible.

Analysis of a Load-Side Heat Exchanger for a Solar Domestic Hot Water Heating System

1998 ◽  
Vol 120 (4) ◽  
pp. 270-274 ◽  
Author(s):  
T. R. Smith ◽  
P. J. Burns ◽  
D. C. Hittle
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Heating System ◽  
Hot Water ◽  
Transfer Coefficients ◽  
Adequate Model ◽  
Domestic Hot Water ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Testing is done of an unpressurized drainback system with a load-side heat exchanger. Analytical calculations for the heat exchanger effectiveness and three models for convective heat transfer coefficients from correlations are compared against the experimental data. TRNSYS simulations were performed using the average effectiveness of 0.78 (the calculated effectiveness varies from 0.68 to 0.95); the results compare favorably with experimental results, indicating that a constant effectiveness is an adequate model for the system.

scholarly journals Numerical Investigation On The Impingement Of A Circular Jet Of Nanofluids On A Circular Flat Plate

2021 ◽  
Author(s):  
Dhimitri Kucuqi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Convective Heat Transfer ◽  
Experimental Model ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

A numerical study was conducted to investigate and validate experimental convective heat transfer coefficient data associated with an Al2O3-H2O nanofluid through the use of an impingement jet on a flat, circular disk. It was observed that, in conjunction with experimental data, nanofluids provided increased local convective heat transfer coefficients in comparison to the base fluid. Nanofluid concentrations outlined in the experimental model, from 0.0198 to 0.0757 wt%, were investigated in a numerical model and resulting convective heat transfer coefficients were compared. In contrast to the experimental model, the maximum heat transfer enhancement occurred at the nanofluid concentration of 0.0757 wt%. In addition, several other models were tested with various Reynolds numbers and jet height-to-jet diameter ratios for further investigation along with discussion of sources of error. Overall, in comparison to experimental data, the lowest percentage errors achieved for the Reynolds numbers of 4245.7 and 8282 were 17.9% and 34.9%, respectively.

Heat Transfer Measurements and Numerical Simulations in the Cooling of a Circular Cylinder by a Slot Jet of Air

2003 ◽  
Author(s):  
F. Gori ◽  
I. Petracci
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Numerical Simulations ◽  
Convective Heat Transfer ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Commercial Code ◽  
Convective Heat Transfer Coefficients

The present paper reports heat transfer measurements on a circular cylinder, electrically heated, and cooled by a slot jet of air. The diameter of the cylinder is equal to the slot height. Temperature measurements in five positions along the circumference of the circular cylinder, allow the evaluation of the convective heat transfer coefficients or Nusselt numbers at several Reynolds numbers. The Nusselt numbers are compared with the corresponding results in uniform flow around a circular cylinder. The experiments have been performed at several distances from the slot jet exit and different Reynolds numbers. Numerical simulations have been carried out with a commercial code.

Convective Heat Transfer Coefficients of Multifaceted Longitudinal and Transversal Bricks of Lattice Setting in Tunnel Kilns

2018 ◽  
Vol 10 (5) ◽  
Author(s):  
Hosny Z. Abou-Ziyan ◽  
Issa F. Almesri ◽  
Mosab A. Alrahmani ◽  
Jaber H. Almutairi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Sensitivity Analysis ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Specific Energy Consumption ◽  
Uniform Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

This paper reports the local multifaceted and area-averaged convective heat transfer coefficients (CHTCs) of longitudinal and transverse bricks arranged in lattice brick setting in tunnel kilns, using a three-dimensional (3D) computational fluid dynamics (CFD) model. A mesh sensitivity analysis was performed and the model was validated against reported experimental data in tunnel kilns. Three turbulence models were tested: the standard k–ε, re-normalization group (RNG) k–ε, and k–ω. The k–ω model provided the closest results to the experimental data. The CHTCs from the front, back, left, and right faces of the longitudinal and transverse bricks were calculated under various conditions. Area-averaged CHTCs for bricks were determined from the multifaceted CHTCs. Effects of rows, layers, and walls on faces and area-averaged CHTCs were investigated. A sensitivity analysis was performed to explore the effect of flow channels on the CHTCs. The numerical results showed that the CHTCs are enhanced by 17% for the longitudinal bricks and 27% for the transverse bricks when a uniform flow is reached in the tunnel kilns. Also, similar area-averaged CHTCs for the longitudinal and transverse bricks were obtained as a result of the uniform flow. Therefore, the specific energy consumption, quality, and quantity of brick production could be enhanced.

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