Computational fluid dynamics and experimental analysis of the heat transfer in a room with a roof solar chimney

2021 ◽  
pp. 1-26
Author(s):  
Adolfo Vazquez ◽  
Jose MA Navarro ◽  
Jesus Hinojosa ◽  
Dr. Jesús Xamán
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Heat Flux ◽  
Computational Fluid Dynamics ◽  
Experimental Analysis ◽  
Vertical Wall ◽  
Temperature Fields ◽  
Heated Wall ◽  
Transfer Coefficients ◽  
Solar Chimney

Abstract This study reports a numerical-experimental analysis of heat transfer and airflow in a scaled room with a heated wall coupled with a double-channel vertical roof solar chimney. For the experimental part, a parametric study was performed in the thermal system, considering different values of heat flux supplied to a vertical wall of the scaled room (75 and 150 W/m2) and the absorber surface of the solar chimney (151 and 667 W/m2). Experimental temperature profiles were obtained at six different depths and heights, and experimental heat transfer coefficients were computed for both heated surfaces. The renormalization group k-e turbulence model was evaluated against experimental data using computational fluid dynamics software. With the validated model, the effect of the heated wall and solar chimney on temperature fields, flow patterns, and heat transfer convective coefficients are presented and discussed. The cases with heat flux on the heated wall of the scaled room produce the biggest air changes per hour (ACH), being 30.1, 31.2, and 23.4 ACH for cases 1 to 3 respectively, while cases with no heated wall produce fewer ACH (11.72 and 12.28 for case 4 and 5). The comparison between cases with and without heat flux on one vertical wall but the same solar chimney heat flux shows that the ACH increases between 154 % and 156% respectively.

A CFD (Computational Fluid Dynamics) Based Thermal Performance of Solar Air Heater With Rib-Roughened Channels

2016 ◽  
Author(s):  
Mumtaz Hussain Qureshi ◽  
M. Shakaib
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Heat Flux ◽  
Computational Fluid Dynamics ◽  
Research Work ◽  
Solar Air Heater ◽  
Transfer Coefficients ◽  
Turbulent Fluid Flow ◽  
Transfer Rates ◽  
Air Heater

Computational Fluid Dynamics (CFD) study is conducted to determine turbulent fluid flow and temperature profiles in rectangular ribbed channels of solar air heater. The results show significant effect of Reynolds number and ribs height and pitch on turbulence and heat transfer rates. When heat flux is defined at the bottom wall, the temperature values increase rapidly near the ribs due to stagnant zones. The heat transfer coefficients are lower at these locations. When heat flux is specified at the top wall, the variation in heat transfer coefficient is relatively smooth. From the research work, the channel containing ribs of 3mm and pitch 40mm are determined suitable due to higher heat transfer rates.

Computational Fluid Dynamics Analysis of the Transient Cooling of the Boiling Surface at Bubble Departure

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Giovanni Giustini ◽  
S. P. Walker ◽  
Yohei Sato ◽  
Bojan Niceno
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Heat Flux ◽  
Computational Fluid Dynamics ◽  
Mechanistic Modeling ◽  
Heated Wall ◽  
Cfd Modeling ◽  
Scale Modeling ◽  
Flux Partitioning ◽  
Computational Fluid Dynamics Analysis

Component-scale computational fluid dynamics (CFD) modeling of boiling via heat flux partitioning relies upon empirical and semimechanistic representations of the modes of heat transfer believed to be important. One such mode, “quenching,” refers to the bringing of cool water to the vicinity of the heated wall to refill the volume occupied by a departing vapor bubble. This is modeled in classical heat flux partitioning approaches using a semimechanistic treatment based on idealized transient heat conduction into liquid from a perfectly conducting substrate. In this paper, we apply a modern interface tracking CFD approach to simulate steam bubble growth and departure, in an attempt to assess mechanistically (within the limitations of the CFD model) the single-phase heat transfer associated with bubble departure. This is in the spirit of one of the main motivations for such mechanistic modeling, the development of insight, and the provision of quantification, to improve the necessarily more empirical component scale modeling. The computations indicate that the long-standing “quench” model used in essentially all heat flux partitioning treatments embodies a significant overestimate of this part of the heat transfer, by a factor of perhaps ∼30. It is of course the case that the collection of individual models in heat flux partitioning treatments has been refined and tuned in aggregate, and it is not particularly surprising that an individual submodel is not numerically correct. In practice, there is much cancelation between inaccuracies in the various submodels, which in aggregate perform surprisingly well. We suggest ways in which this more soundly based quantification of “quenching heat transfer” might be taken into account in component scale modeling.

scholarly journals Experimental Heat Transfer Investigation of Stationary and Orthogonally Rotating Asymmetric and Symmetric Heated Smooth and Turbulated Channels

1992 ◽  
Author(s):  
H. A. El-Husayni ◽  
M. E. Taslim ◽  
D. M. Kercher
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rotation Number ◽  
Symmetric Case ◽  
Wall Heat Flux ◽  
Heated Wall ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Smooth Channel

An experimental investigation was conducted to determine the effects of variations in wall thermal boundary conditions on local heat transfer coefficients in stationary and orthogonally rotating smooth wall and two opposite-wall turbulated square channels. Results were obtained for three distributions of uniform wall heat flux: asymmetric, applied to the primary wall only; symmetric, applied to two opposite walls only; and fully-symmetric, applied to all four channel walls. Measured stationary and rotating smooth channel average heat transfer coefficients at channel location L/Dh = 9.53 were not significantly sensitive to wall heat flux distributions. Trailing side heat transfer generally increased with Rotation number whereas the leading wall results showed a decreasing trend at low Rotation numbers to a minimum and then an increasing trend with further increase in Rotation number. The stationary turbulated wall heat transfer coefficients did not vary markedly with the variations in wall heat flux distributions. Rotating leading wall heat transfer decreased with Rotation number and showed little sensitivity to heat flux distributions except for the fully-symmetric heated wall case at the highest Reynolds number tested. Trailing wall heat transfer coefficients were sensitive to the thermal wall distributions generally at all Reynolds numbers tested and particularly with increasing Rotation number. While the asymmetric case showed a slight deficit in trailing wall heat transfer coefficients due to rotation, the symmetric case indicated little change whereas the fully-symmetric case exhibited an enhancement.

Benchmarking Computational Fluid Dynamics for Application to PWR Fuel

2002 ◽  
Author(s):  
L. D. Smith ◽  
M. E. Conner ◽  
B. Liu ◽  
B. Dzodzo ◽  
D. V. Paramonov ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Temperature Fields ◽  
Cfd Modeling ◽  
Spacer Grid ◽  
Cfd Models ◽  
Computational Mesh ◽  
Transfer Testing ◽  
Visualization Techniques

The present study demonstrates a process used to develop confidence in Computational Fluid Dynamics (CFD) as a tool to investigate flow and temperature distributions in a PWR fuel bundle. The velocity and temperature fields produced by a mixing spacer grid of a PWR fuel assembly are quite complex. Before using CFD to evaluate these flow fields, a rigorous benchmarking effort should be performed to ensure that reasonable results are obtained. Westinghouse has developed a method to quantitatively benchmark CFD tools against data at conditions representative of the PWR. Several measurements in a 5×5 rod bundle were performed. Lateral flowfield testing employed visualization techniques and Particle Image Velocimetry (PIV). Heat transfer testing involved measurements of the single-phase heat transfer coefficient downstream of the spacer grid. These test results were used to compare with CFD predictions. Among the parameters optimized in the CFD models based on this comparison with data include computational mesh, turbulence model, and boundary conditions. As an outcome of this effort, a methodology was developed for CFD modeling that provides confidence in the numerical results.

scholarly journals Heat dissipation from a stationary brake disc, Part 2: CFD modelling and experimental validations

2017 ◽  
Vol 232 (10) ◽  
pp. 1898-1924 ◽  
Author(s):  
Marko Tirovic ◽  
Kevin Stevens
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Dissipation ◽  
Axial Flow ◽  
Flow Visualisation ◽  
Brake Disc ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Static Conditions

Following from the analytical modelling presented in Part 1, this paper details a comprehensive computational fluid dynamics modelling of the three-dimensional flow field around, and heat dissipation from, a stationary brake disc. Four commonly used turbulence models were compared and the shear stress turbulence model was found to be most suitable for these studies. Inferior cooling of the anti-coning disc type is well known but the core cause in static conditions was only now established. The air flow exiting the lower vane channels at the inner rotor diameter changes direction and flows axially over the hat region. This axial flow acts as a blocker to the higher vane inlets, drastically reducing convective cooling from the upper half of the disc. The complexity of disc stationary cooling is further caused by the change of flow patterns during disc cooling. The above axial flow effects slowly vanish as the disc temperatures reduce. Consequently, convective heat transfer coefficients are affected by both, the change in the flow pattern and decrease in air velocities due to reduced air buoyancy as the disc cools down. As in Part 1, the special thermal rig was used to validate the computational fluid dynamics results quantitatively and qualitatively. The former used numerous thermocouples positioned strategically around the brake disc, with the latter introducing the concept of laser generated light plane combined with a smoke generator to enable flow visualisation. Predicted average heat transfer coefficients using computational fluid dynamics correlate well with the experimental values, and even two-dimensional analytical values (as presented in Part 1) reasonably closely follow the trends. The results present an important step in establishing cooling characteristics related to the electric parking brake application in commercial vehicles, with future publications detailing heat transfer from the entire brake assembly.

Turbulent Heat Transfer Characteristics of Supercritical Carbon Dioxide for a Vertically Upward Flow in a Pipe Using Computational Fluid Dynamics and Artificial Neural Network

2021 ◽  
Author(s):  
Rajendra Prasad K S ◽  
Krishna V ◽  
Sachin Bharadwaj ◽  
Babu Rao Ponangi
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbulence Model ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Ansys Fluent ◽  
Artificial Neural ◽  
Turbulent Models

Abstract Modelling of turbulence heat transfer for supercritical fluids using Computational Fluid Dynamics (CFD) software is always challenging due to the drastic property variations near critical point. Use of Artificial Neural Networks (ANN) along with numerical methods have shown promising results in predicting heat transfer coefficients of heat exchangers. In this study, accuracy of four different turbulent models available in the commercial CFD software - Ansys Fluent is investigated against the available experimental results. The k-e Re Normalization Group (RNG) model with enhanced wall treatment is found to be the best-suited turbulence model. Further, K-e RNG Turbulence Model is used in CFD for parametric analysis to generate the data for ANN studies. A total of 1,34,698 data samples were generated and fed into the ANN program to develop an equation that can predict the heat transfer coefficient. It was found that, for the considered range of values the absolute average relative deviation is 3.49%.

scholarly journals Effect of Inlet and Outlet Locations on Transverse Mixed Convection Inside a Vented Enclosure

1970 ◽  
Vol 36 ◽  
pp. 27-37 ◽  
Author(s):  
Sumon Saha ◽  
Md. Tofiqul Islam ◽  
Mohammad Ali ◽  
Md. Arif Hassan Mamun ◽  
M Quamrul Islam
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Reynolds Number ◽  
Finite Element ◽  
Mixed Convection ◽  
Vertical Wall ◽  
Flow Fields ◽  
Temperature Fields ◽  
Heated Wall ◽  
Element Method

Transverse mixed convection is studied numerically in a vented enclosure with constant heat flux from uniformly heated bottom wall. An external airflow enters the enclosure through an opening in one vertical wall and exits from another opening in the opposite wall. The two-dimensional mathematical model includes the system of four partial differential equations of continuity, linear momentum and energy, solved by the finite element method. Flow fields are investigated by numerical simulations for air flowing with a Reynolds number in the range 50 ≤ Re ≤ 1000, for Richardson numbers: 0 ≤ Ri ≤ 10. Four different locations of inlet and outlets are introduced to analyze the effect of heat transfer in terms of velocity and temperature fields within the enclosure. The computational results show that the location of inlet and outlets alters significantly the temperature distribution in the flow fields and the heat transfer across the heated wall of the cavities. Empirical correlation is developed for relations using Nusselt number, Reynolds number and Richardson number, based on the enclosure height.   Keywords: Mixed convection, finite element method, vented enclosure, Richardson number.Journal of Mechanical Engineering Vol.36 Dec. 2006 pp.27-37DOI = 10.3329/jme.v36i0.808

scholarly journals HEAT TRANSFER FOR FILN BOILING OF A LIQUID ON A VERTICAL HEATED WALL IN A POROUS MEDIUM

2021 ◽  
Vol 43 (1) ◽  
pp. 20-29
Author(s):  
A.A. Avramenko ◽  
M.M. Kovetskaya ◽  
E.A. Kondratieva ◽  
T.V. Sorokina
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Medium ◽  
Fluid Flow ◽  
Wall Temperature ◽  
Heated Wall ◽  
Film Boiling ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients

The paper presents results of the modelling of heat transfer at film boiling of a liquid in a porous medium on a vertical heated wall. Such processes are observed at cooling of high-temperature surfaces of heat pipes, microstructural radiators etc. Heating conditions at the wall were the constant wall temperature or heat flux. An analytical solution was obtained for the problem of fluid flow and heat transfer using the porous medium model in the Darcy-Brinkman. It was shown that heat transfer at film boiling in a porous medium was less intensive than in the absence of a porous medium (free fluid flow) and further decreased with the decreasing permeability of the porous medium. A sharp decrease in heat transfer was observed for the Darcy numbers lower than five. The analytical predictions of heat transfer coefficients qualitatively agreed with the data [14] though demonstrated lower values of heat transfer coefficients for the conditions of the constant wall temperature and constant wall heat flux.

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