Transient free convection within air-filled hemispherical enclosures. Nu-Ra-Fo relationships for isothermal and inclined disk with dome oriented upwards

2015 ◽  
Vol 25 (3) ◽  
pp. 629-638 ◽  
Author(s):  
Abderrahmane Baïri
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Numerical Approach ◽  
Content Type ◽  
Turbulent Natural Convection ◽  
Higher Temperature ◽  
Fourier Type ◽  
Volume Method

Purpose – Nusselt-Rayleigh-Fourier type correlations are proposed to quantify the temporal evolution of convective heat transfer occurring within air-filled hemispherical enclosures whose disk, initially at ambient temperature, is suddenly maintained at a higher temperature. The temperature difference imposed between this hot wall and the isothermal cold dome involves Rayleigh number varying between 104 and 2.55×1012. Depending on the application, the disk can be inclined with respect to the horizontal plane by an angle varying between 0° (horizontal disk) and 90° (vertical disk) in steps of 15°. The paper aims to discuss these issues. Design/methodology/approach – The results are obtained by means of a numerical approach based on the finite volume method. The proposed correlations linked to the steady state Nusselt-Rayleigh internships recently published, concerning the same inclination angle and Rayleigh ranges. Findings – The statistical analysis of a large number of calculations leads to reliable results covering laminar, transitional and turbulent natural convection heat transfer zones. Practical implications – The proposed relationships can be applied in several engineering fields such as nuclear technology, solar energy, security and safety electronics, building, domotics or aeronautics. Originality/value – The new relationships proposed in this paper provide important information on the evolution of convective heat transfer during the transient regime.

Natural convective heat transfer in the air-filled interstice between inclined concentric hemispheres

2017 ◽  
Vol 27 (10) ◽  
pp. 2375-2384 ◽  
Author(s):  
Nacim Alilat
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Design Methodology ◽  
Numerical Approach ◽  
Constant Heat Flux ◽  
Horizontal Position ◽  
Content Type ◽  
Thermal Boundary Conditions ◽  
Volume Method

Purpose The main purpose of this work is to quantify the convective heat transfer occurring between two inclined and concentric hemispheres. Design/methodology/approach The inner one is an electronic assembly generating a constant heat flux during operation. The outer hemisphere is maintained isothermal at cold temperature. The interstitial space is air-filled. The base of the equipment can be inclined with respect to the horizontal plane by an angle ranging from 0° (horizontal position with dome faced upwards) to 180° (horizontal position with dome faced downwards). Findings Nusselt–Rayleigh correlations are proposed for several configurations obtained by varying the generated power and the base inclination. The large resulting Rayleigh number ranging between 2.4 × 105 and 1.7 × 107 allows using these new and original correlations in various engineering fields, such as electronics in the present work. The calculations are realized by means of a 3D numerical approach based on the finite volume method. Originality/value The geometry and the thermal boundary conditions considered in the present survey are suitable for applications in many engineering areas.

A computational analysis on convective heat transfer for impinging slot nanojets onto a moving hot body

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hakan Coşanay ◽  
Hakan F. Oztop ◽  
Fatih Selimefendigil
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Computational Analysis ◽  
Impinging Jets ◽  
Content Type ◽  
Moving Body ◽  
Flow Effects

Purpose The purpose of this study is to perform computational analysis on the steady flow and heat transfer due to a slot nanojet impingement onto a heated moving body. The object is moving at constant speed and nanoparticle is included in the heat transfer fluid. The unsteady flow effects and interactions of multiple impinging jets are also considered. Design/methodology/approach The finite volume method was used as the solver in the numerical simulation. The movement of the hot body in the channel is also considered. Influence of various pertinent parameters such as Reynolds number, jet to target surface spacing and solid nanoparticle volume fraction on the convective heat transfer characteristics are numerically studied in the transient regime. Findings It is found that the flow field and heat transfer becomes very complicated due to the interaction of multiple impinging jets with the movement of the hot body in the channel. Higher heat transfer rates are achieved with higher values of Reynolds number while the inclusion of nanoparticles resulted in a small impact on flow friction. The middle jet was found to play an important role in the heat transfer behavior while jet and moving body temperatures become equal after t = 80. Originality/value Even though some studies exist for the application of jet impingement heat transfer for a moving plate, the configuration with a solid moving hot body on a moving belt under the impacts of unsteady flow effects and interactions of multiple impinging jets have never been considered. The results of the present study will be helpful in the design and optimization of various systems related to convective drying of products, metal processing industry, thermal management in electronic cooling and many other systems.

Numerical Analysis of Convection Heat Transfer for Subsea Xmas Tree Assembly

2012 ◽  
Author(s):  
Kuang Ding ◽  
Hongwu Zhu ◽  
Jinya Zhang ◽  
Xuan Luo ◽  
Junyao Zhu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Loss ◽  
Convective Heat ◽  
Structural Reliability ◽  
Sea Water ◽  
Convective Heat Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Water Velocity ◽  
Convection Heat

This study aims to investigate the convection heat transfer of a horizontal subsea Xmas tree assembly at a high spatial resolution. Such study is important for increasing the structural reliability design and flow assurance level of subsea Xmas tree. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) is adopted to evaluate the forced convective heat transfer of the subsea Xmas tree assembly. The temperature, the convection heat loss and the convective heat transfer coefficient (CHTC) at the surfaces of the subsea Xmas tree assembly are numerically obtained with low-Reynolds number modeling (LRNM). The numerical results show that the outer surface temperatures of the subsea tree are close to that of the ambient cold sea water with the exception of the pipeline. The components along the internal production tubes are typical “hot spots,” which have high CHTHs and cause a great deal of heat loss. Under the designed water depth, the effects of installation orientation and sea water velocity on convective heat transfer are investigated. The overall average CHTCs and the local CHTC distribution of the subsea Xmas tree assembly are depended on the installation orientation. Meanwhile, with the increase of the sea water velocity, the growth rates of the CHTCs for individual components show great difference. Ultimately, for selected installation orientation, the CHTC-sea water velocity correlation is derived by using a power-law CHTC-Uin correlation.

Computational analysis of convective heat transfer properties of turbulent slot jet impingement

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Anuj Kumar Shukla ◽  
Anupam Dewan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
High Efficiency ◽  
Stokes Equations ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Complex Flow ◽  
Content Type

Purpose Convective heat transfer features of a turbulent slot jet impingement are comprehensively studied using two different computational approaches, namely, URANS (unsteady Reynolds-averaged Navier–Stokes equations) and SAS (scale-adaptive simulation). Turbulent slot jet impingement heat transfer is used where a considerable heat transfer enhancement is required, and computationally, it is a quite challenging flow configuration. Design/methodology/approach Customized OpenFOAM 4.1, an open-access computational fluid dynamics (CFD) code, is used for SAS (SST-SAS k-ω) and URANS (standard k-ε and SST k-ω) computations. A low-Re version of the standard k-ε model is used, and other models are formulated for good wall-refined calculations. Three turbulence models are formulated in OpenFOAM 4.1 with second-order accurate discretization schemes. Findings It is observed that the profiles of the streamwise turbulence are under-predicted at all the streamwise locations by SST k-ω and SST SAS k-ω models, but follow similar trends as in the reported results. The standard k-ε model shows improvements in the predictions of the streamwise turbulence and mean streamwise velocity profiles in the zone of outer wall jet. Computed profiles of Nusselt number by SST k-ω and SST-SAS k-ω models are nearly identical and match well with the reported experimental results. However, the standard k-ε model does not provide a reasonable profile or quantification of the local Nusselt number. Originality/value Hybrid turbulence model is suitable for efficient CFD computations for the complex flow problems. This paper deals with a detailed comparison of the SAS model with URANS and LES for the first time in the literature. A thorough assessment of the computations is performed against the results reported using experimental and large eddy simulations techniques followed by a detailed discussion on flow physics. The present results are beneficial for scientists working with hybrid turbulence models and in industries working with high-efficiency cooling/heating system computations.

Development and validation of an incompressible Navier-Stokes solver including convective heat transfer

2015 ◽  
Vol 25 (4) ◽  
pp. 861-886 ◽  
Author(s):  
Konstantinos Stokos ◽  
Socrates Vrahliotis ◽  
Theodora Pappou ◽  
Sokrates Tsangaris
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Laminar Flows ◽  
Navier Stokes ◽  
Content Type ◽  
Strongly Coupled ◽  
Loosely Coupled ◽  
Wide Range ◽  
Coupled Solution

Purpose – The purpose of this paper is to present a numerical method for the simulation of steady and unsteady incompressible laminar flows, including convective heat transfer. Design/methodology/approach – A node centered, finite volume discretization technique is applied on hybrid meshes. The developed solver, is based on the artificial compressibility approach. Findings – A sufficient number of representative test cases have been examined for the validation of this numerical solver. A wide range of the various dimensionless parameters were applied for different working fluids, in order to estimate the general applicability of our solver. The obtained results agree well with those published by other researchers. The strongly coupled solution of the governing equations showed superiority compared to the loosely coupled solution as inviscid effects increase. Practical implications – Convective heat transfer is dominant in a wide variety of practical engineering problems, such as cooling of electronic chips, design of heat exchangers and fire simulation and suspension in tunnels. Originality/value – A comparison between the strongly coupled solution and the loosely coupled solution of the Navier-Stokes and energy equations is presented. A robust upwind scheme based on Roe’s approximate Riemann solver is proposed.

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%.

Enclosure Phenomenon in Varying Forced Flow Convection

2019 ◽  
Author(s):  
Ribhu Bhatia ◽  
Sambit Supriya Dash ◽  
Vinayak Malhotra
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Relative Effectiveness ◽  
Convection Heat Transfer ◽  
Forced Flow ◽  
Forced Convective Heat Transfer

Abstract Systematic experimentation was carried out on forced convection heat transfer apparatus under varying non-linear flow conditions to understand the energy transfer as heat, with the purpose of enhancing performance of numerous engineering applications. Plate orientations, types of enclosures (solid, meshed, perforated), flow velocity variations etc. are taken as governing parameters to effect convective heat transfer phenomenon which is perceived as deviations in value of heat transfer coefficient. RV zonal system is utilized to simplify the fundamental understanding of heat transfer coefficient variation with surface orientation under varying flow field. The objectives of this work are as follows: 1) To establish relative effectiveness of forced convective heat transfer under varying flow field. 2) To investigate the implications of varying shapes and sizes of perforations on confined forced convective heat transfer. To understand the controlling mechanism and role of key controlling parameters.

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

2019 ◽  
Author(s):  
Yantao Li ◽  
Yulong Ji ◽  
Katsuya Fukuda ◽  
Qiusheng Liu ◽  
Hongbin Ma
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Inlet Temperature ◽  
Experiment Data ◽  
Forced Convective Heat Transfer ◽  
Nusselt Numbers ◽  
Mini Channels ◽  
Heat Transfer Correlations

Abstract In this paper, the forced convective heat transfer of FC-72 was experimentally investigated for various of parameters like velocity, inlet temperature, tube size, and exponential period of heat generation rate. Circular tubes with different inner diameters (1, 1.8 and 2.8 mm) and heated lengths (30–50 mm) were used in this study. The experiment data suggest that the single-phase heat transfer coefficient increases with increasing flow velocity as well as decreasing tube diameter and ratio of heated length to inner diameter. The experiment data were nondimensionalized to study the effect of Reynolds number (Red) on forced convection heat transfer. The results indicate that the relation between Nusselt numbers (Nud) and Red for d = 2.8 mm show the same trend as the conventional correlations. However, the Nud for d = 1 and 1. 8 mm depend on Red in a different manner. The conventional heat transfer correlations are not adequate for prediction of forced convective heat transfer in mini channels. The heat transfer correlations for FC-72 in vertical small tubes with diameters of 1, 1.8 and 2.8 mm were developed separately based on the experiment data. The differences between experimental and predicted Nud are within ±15%.

Geometrical Evaluation of a Pair of Elliptical Tubes Subjected to a Flow with Forced Convection Heat Transfer

2019 ◽  
Vol 396 ◽  
pp. 155-163
Author(s):  
Ana Paula Del Aghenese ◽  
Eliander Manke Heinemann ◽  
Gabriel de Avila Barreto ◽  
Filipe Branco Teixeira ◽  
Liércio André Isoldi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Degrees Of Freedom ◽  
Fluid Dynamic ◽  
Convection Heat Transfer ◽  
Numerical Approach ◽  
Angle Of Incidence ◽  
Prandtl Numbers ◽  
Forced Convective Flow ◽  
Volume Method

In the present work it is performed a study on the geometric evaluation of a pair of elliptical tubes subjected to external flow with forced convection by means of numerical approach. The objectives are the maximization of Nusselt number (NuD) and the minimization of drag coefficient (CD). The degrees of freedom for the pair of tubes arrangement are: the ratio between the transverse pitch and characteristic length of tubes (ST/D), where D = (A)1/2, the ratio of the main and secondary axes of the elliptical tube (a/b) and the angle of incidence of the flow on the pair of tubes (α). The simulations were carried out considering two-dimensional forced convective flows, in the laminar regime and incompressible conditions. For all configurations, Reynolds and Prandtl numbers are constant, ReD = 100 and Pr = 0.71. The Finite Volume Method (FVM) is used to solve conservation equations of mass, momentum and energy. The software Gmsh is used for creation of the geometries and generation of the meshes. Results showed that the degrees of freedom affected the fluid dynamic and thermal performance of the forced convective flow. According to the objectives outlined in this study, the best performance for the maximization of heat transfer was obtained when α = 0o, a/b = 1⁄2 and ST/D = 3.5. In the case of the fluid dynamics study, the optimal result for CD minimization occurred when α = 0o, a/b = 2.0 and ST/D = 4.0. Thus, the optimal geometry will depend on the indicator performance where the problem is evaluated.

Heat transfer modeling within the microclimate between 3D human body and clothing: effects of ventilation openings and fire intensity

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Miao Tian ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Temperature Distribution ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Human Body ◽  
Thermal Environment ◽  
Heat Transfer Process ◽  
Fire Intensity ◽  
Content Type

PurposeThe purpose of this study is to determine the effect of ventilation openings and fire intensity on heat transfer and fluid flow within the microclimate between 3D human body and clothing.Design/methodology/approachOn account of interaction effects of fire and ventilation openings on heat transfer process, a 3D transient computational fluid dynamics model considering the real shape of human body and clothing was developed. The model was validated by comparing heat flux history and distribution with experimental results. Heat transfer modes and fluid flow were investigated under three levels of fire intensity for the microclimate with ventilation openings and closures.FindingsTemperature distribution on skin surface with open microclimate was heavily depended on the heat transfer through ventilation openings. Higher temperature for the clothing with confined microclimate was affected by the position and direction of flames injection. The presence of openings contributed to the greater velocity at forearms, shanks and around neck, which enhanced the convective heat transfer within microclimate. Thermal radiation was the dominant heat transfer mode within the microclimate for garment with closures. On the contrary, convective heat transfer within microclimate for clothing with openings cannot be neglected.Practical implicationsThe findings provided fundamental supports for the ease and pattern design of the improved thermal protective systems, so as to realize the optimal thermal insulation of the microclimate on the garment level in the future.Originality/valueThe outcomes broaden the insights of results obtained from the mesoscale models. Different high skin temperature distribution and heat transfer modes caused by thermal environment and clothing structure provide basis for advanced thermal protective clothing design.

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