The Effect of Inclination on Natural Convective Heat Transfer from a Slender Cuboid
Abstract
:1. Introduction
2. Numerical Solution Procedures
- (i)
- On the plane of symmetry (SINDLMEFOTS), the normal dimensionless velocity is set to zero, the gradients of the other velocity components and temperature normal to the plane of symmetry are also set to zero.
- (ii)
- On the adiabatic base (NBAFEGCDN), the boundary conditions imposed on all dimensionless velocities set the values of those velocities to zero and the dimensionless temperature normal to the adiabatic surface is set to zero.
- (iii)
- On the other planes of the solution domain, both the dimensionless velocity components in the plane and the dimensionless temperature are set to zero.
- (iv)
- On the slender cuboid surfaces, the dimensionless velocity components are equal to zero and the dimensionless temperature normal to the surfaces is set to minus one for a constant wall heat flux boundary condition, while dimensionless temperature normal to the surfaces is set to zero for the imposed constant wall temperature boundary condition for surfaces.
3. Results and Discussion
- The Ra*, the heat flux Rayleigh number, dependent on the height, h, of the heated slender cuboid, is set as the length scale, and is set as the temperature scale.
- The Ra, Rayleigh number, dependent on the height, h, of the heated slender cuboid, is set as the length scale, and the global difference in temperature TH–TF is set as the temperature scale.
- The dimensionless width of the slender cuboid, W = w/h, i.e., W << h.
- The Prandtl number, Pr.
- The positions of the slender cuboid, φ, in relation to the vertical.
3.1. Validation
3.2. Evaluation of the Width Effect of a Slender Cuboid
3.3. Evaluation of the Inclination Angle of a Slender Cuboid
3.4. Evaluation of the Local Nusselt Number
3.5. Correlating the Numerical Results
4. Conclusions
- The values of the mean Nusselt number for the total heated surface of the cuboid and for the separate heated surfaces decreased with increasing dimensionless width under all considered conditions.
- The values of the mean Nusselt number for the heated surfaces as a whole and for the individual heated surfaces of the slender cuboid change with position, dimensionless width, heat flux Rayleigh number, and Rayleigh number due to edge effects as well as the interaction of the buoyancy-driven natural flow over the surfaces that make up the cuboid.
- The mean Nusselt numbers obtained for the heated surfaces of the slender cuboid are almost independent of position at the lowest value of the heat flux Rayleigh number and Rayleigh number, for all dimensionless widths considered. However, at a high heat flux Rayleigh number and Rayleigh number, the mean Nusselt number behaves differently for higher W values than for lower W values.
- The mean Nusselt number for individual surfaces of the slender cuboid changes in magnitude with the inclination angle, φ, and is different at lower and higher Rayleigh numbers and heat flux Rayleigh numbers. The maximum and minimum magnitude of the mean Nusselt number for individual surfaces of the slender cuboid changes as the angles of inclination change between 0° and 180°. The maximum and minimum magnitude of the mean Nusselt number for individual surfaces of the slender cuboid at different inclination angles change with the values of Rayleigh numbers and heat flux Rayleigh numbers.
- The mean Nusselt number values from the individual heated surfaces of the slender cuboid are less significant and there are small changes in the mean Nusselt number at the lowest values of the Rayleigh number and heat flux Rayleigh number and for higher, W, dimensionless width, greater than 0.15 for all values of inclination angle, φ.
- The obtained mean Nusselt number for slender cuboids for the case of constant temperature boundary conditions with different angles of inclination, a broad range of Rayleigh numbers, and different dimensionless widths can be adequately derived from Equation (17).
- The mean Nusselt number for a slender cuboid under constant heat flux boundary conditions, at different angles of inclination, with a broad range of heat flux Rayleigh numbers, and different dimensionless widths can be adequately derived from Equation (19).
- Natural convective heat transfer from a cuboid cylinder in transition and a turbulent flow region needs to be investigated as future research. Transient natural convective flow over an inclined slender cuboid is a subject of interest for future investigation.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
A, B | Best fit value for constants given in Table 3 which are used in Equation (17) |
g | Gravitational acceleration, m⋅s−2 |
h | Height of heated slender cuboid, m |
k | Thermal conductivity of fluid, W⋅m−1⋅K−1 |
Nu | Numerical mean Nusselt number based on h and |
Nuw | Mean Nusselt number based on w and |
Nuleft | Numerical mean Nusselt number for heated left-side surface of slender cuboid |
Nuright | Numerical mean Nusselt number for heated right-side surface of slender cuboid |
Nufront | Numerical mean Nusselt number for heated front surface of slender cuboid |
n | Value of constant given in Table 3 which is used in Equation (17) |
Nu | Numerical and experimental mean Nusselt number based on h |
Nuemp | Empirical mean Nusselt number for the entire heated surface of the slender cuboid |
Num | Mean Nusselt number based on h and on (Tw–TF) |
NuL | Mean Nusselt number for heated left-side surface of slender cuboid |
NuR | Mean Nusselt number for heated right-side surface of slender cuboid |
NuF | Mean Nusselt number for heated front surface of slender cuboid |
Pr | Prandtl number |
P | Dimensionless pressure |
p | Pressure, Pa |
pF | Pressure in undisturbed fluid, Pa |
Uniform heat flux over heated surfaces of slender cuboid, W⋅m−2 | |
Constant heat flux over heated left-side surface of slender cuboid, W⋅m−2 | |
Constant heat flux over heated right-side surface of slender cuboid, W⋅m−2 | |
Constant heat flux over heated front surface of slender cuboid, W⋅m−2 | |
Ra | Rayleigh number based on h and temperature differences |
Ra* | Heat flux Rayleigh number based on h and |
Heat flux Rayleigh number based on w and | |
T | Temperature, K |
TF | Fluid temperature, K |
TH | Temperature of heated surface of slender cuboid, K |
Average surface temperature of entire heated surfaces of slender cuboid, K | |
Average surface temperature of heated left-side surface of slender cuboid, K | |
Average surface temperature of heated right-side surface of slender cuboid, K | |
Average surface temperature of heated front surface of slender cuboid, K | |
Mean heat flux over entire heated surfaces of slender cuboid, W⋅m−2 | |
Mean heat flux over left-side surface of heated slender cuboid, W⋅m−2 | |
Mean heat flux over right-side surface of heated slender cuboid, W⋅m−2 | |
Mean heat flux over front surface of heated slender cuboid, W⋅m−2 | |
ur | Reference velocity, m⋅s−1 |
UX | Dimensionless velocity component in X direction |
ux | Velocity component in x direction, m⋅s−1 |
UY | Dimensionless velocity component in Y direction |
uy | Velocity component in y direction, m⋅s−1 |
UZ | Dimensionless velocity component in Z direction |
uz | Velocity component in z direction, m⋅s−1 |
W | Dimensionless width of slender cuboid, W= w/h |
w | Width of slender cuboid, m |
X | Dimensionless horizontal coordinate |
x | Horizontal coordinate, m |
Y | Dimensionless horizontal coordinate |
y | Horizontal coordinate, m |
z | Vertical coordinate, m |
Z | Dimensionless vertical coordinate |
Greek symbols | |
α | Thermal diffusivity, m2⋅s−1 |
β | Bulk coefficient, K−1 |
μ | Dynamic viscosity, N⋅s/m2 |
ν | Kinematic viscosity, m2⋅s−1 |
θ | Dimensionless temperature |
φ | Position of slender cuboid relative to the vertical |
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Rayleigh No., Ra | Inclination Angle, φ | No. of Nodes | NuL | NuR | NuF | Num | Rayleigh No., Ra | NuL | NuR | NuF | Num |
---|---|---|---|---|---|---|---|---|---|---|---|
1 × 107 | 0° | 132300 | 31.3 | 31.3 | 31.63 | 30.05 | 1 × 103 | 4.65 | 4.65 | 4.55 | 4.6 |
195600 | 31.4 | 31.4 | 31.73 | 30.2 | 4.66 | 4.66 | 4.55 | 4.61 | |||
321444 | 31.4 | 32.06 | 31.55 | 30.34 | 4.66 | 4.64 | 4.58 | 4.62 | |||
508320 | 31.41 | 31.89 | 31.3 | 30.18 | 4.65 | 4.63 | 4.6 | 4.63 | |||
761760 | 31.31 | 31.65 | 31.27 | 30.07 | 4.66 | 4.64 | 4.59 | 4.63 | |||
1063120 | 31.17 | 31.2 | 31.07 | 29.84 | 4.68 | 4.68 | 4.58 | 4.63 | |||
1194600 | 30.84 | 30.94 | 30.83 | 29.56 | 4.68 | 4.68 | 4.6 | 4.64 | |||
1538550 | 30.84 | 30.84 | 30.84 | 29.3 | 4.68 | 4.68 | 4.6 | 4.64 | |||
90° | 132300 | 10.84 | 30.94 | 30.83 | 29.56 | 3.39 | 5.95 | 5.09 | 5.04 | ||
206974 | 10.84 | 30.84 | 30.84 | 29.3 | 3.4 | 5.95 | 5.09 | 5.04 | |||
336510 | 10.55 | 32.14 | 39.37 | 31.11 | 3.39 | 5.93 | 5.13 | 5.07 | |||
528654 | 10.28 | 32.29 | 38.4 | 30.67 | 3.38 | 5.91 | 5.14 | 5.07 | |||
788478 | 10.32 | 32.28 | 38.25 | 30.63 | 3.4 | 5.93 | 5.13 | 5.07 | |||
1097052 | 10.45 | 31.77 | 37.82 | 30.33 | 3.41 | 5.977 | 5.12 | 5.07 | |||
1233063 | 10.96 | 31.18 | 37.05 | 29.84 | 3.47 | 5.99 | 5.17 | 5.1 | |||
1584308 | 11.06 | 31.02 | 36.91 | 29.75 | 3.43 | 6 | 5.17 | 5.1 | |||
180° | 132300 | 29.27 | 29.26 | 29.91 | 29.86 | 4.26 | 4.26 | 4.24 | 4.51 | ||
195600 | 29.15 | 29.15 | 29.78 | 29.88 | 4.27 | 4.27 | 4.24 | 4.51 | |||
321444 | 28.99 | 29.27 | 29.38 | 29.81 | 4.26 | 4.23 | 4.26 | 4.52 | |||
508320 | 28.91 | 29.25 | 28.99 | 29.66 | 4.25 | 4.22 | 4.27 | 4.52 | |||
761760 | 28.86 | 29.1 | 28.87 | 29.57 | 4.27 | 4.24 | 4.26 | 4.53 | |||
1063120 | 28.87 | 28.87 | 28.47 | 29.43 | 4.28 | 4.28 | 4.25 | 4.53 | |||
1194600 | 28.81 | 28.81 | 28.86 | 29.33 | 4.33 | 4.33 | 4.32 | 4.59 | |||
1538550 | 28.82 | 28.81 | 28.84 | 29.29 | 4.29 | 4.29 | 4.29 | 4.54 |
Constant Wall Temperature (CWT) | Constant Wall Heat Flux (CWF) | Equation Number |
---|---|---|
(10) | ||
(11) | ||
(12) | ||
(13) |
Angle, φ | Value of n | Best Fit Value of A | Best Fit Value of B |
---|---|---|---|
0°, 45°, 90°, 135° and 180° | 0.28 | 0.3 | 0.5 |
0° | 0.25 | 0.47 | 0.5 |
180° | 0.25 | 0.47 | 0.52 |
45° | 0.28 | 0.3 | 0.58 |
90° | 0.28 | 0.3 | 0.6 |
135° | 0.28 | 0.3 | 0.55 |
Angle, φ | Remarks | Best Fit Equation |
---|---|---|
0°, 180° | ||
45° | ||
135° | ||
90° | ||
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Kalendar, A.; Alhendal, Y.; Hussain, S.; Oosthuizen, P. The Effect of Inclination on Natural Convective Heat Transfer from a Slender Cuboid. Processes 2021, 9, 1668. https://0-doi-org.brum.beds.ac.uk/10.3390/pr9091668
Kalendar A, Alhendal Y, Hussain S, Oosthuizen P. The Effect of Inclination on Natural Convective Heat Transfer from a Slender Cuboid. Processes. 2021; 9(9):1668. https://0-doi-org.brum.beds.ac.uk/10.3390/pr9091668
Chicago/Turabian StyleKalendar, Abdulrahim, Yousuf Alhendal, Shafqat Hussain, and Patrick Oosthuizen. 2021. "The Effect of Inclination on Natural Convective Heat Transfer from a Slender Cuboid" Processes 9, no. 9: 1668. https://0-doi-org.brum.beds.ac.uk/10.3390/pr9091668