Heat Transfer by Natural Convection between Vertically Eccentric Spheres

1973 ◽  
Vol 95 (1) ◽  
pp. 47-52 ◽  
Author(s):  
N. Weber ◽  
R. E. Powe ◽  
E. H. Bishop ◽  
J. A. Scanlan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convective Motion ◽  
Outer Sphere ◽  
Correlation Equation ◽  
Mapping Technique ◽  
Transfer Rates ◽  
Concentric Spheres ◽  
Wide Range ◽  
Inner Sphere

Natural convection to a cooled sphere from an enclosed, vertically eccentric, heated sphere is described in this paper. Water and two silicone oils were utilized in conjunction with four different combinations of sphere sizes and six eccentricities for each of these combinations. Both heat-transfer rates and temperature profiles are presented. The effect of a negative eccentricity (inner sphere below center of outer sphere) on the temperature distribution was an enhancement of the convective motion, while a positive eccentricity tended to stabilize the flow field and promote conduction rather than convection. As for concentric spheres, a multicellular flow pattern was postulated to explain the thermal field observed for the largest inner sphere utilized. In all cases the heat-transfer rates were increased by moving the inner sphere to an eccentric position, and the utilization of a conformal-mapping technique to transform the eccentric spheres to concentric spheres enabled the application of existing empirical correlations for concentric spheres to the eccentric-sphere data. It is significant to note that this technique yields a single correlation equation, in terms of only keff/k and a modified Rayleigh number, which is valid for an extremely wide range of diameter ratios, eccentricities, Rayleigh numbers, and Prandtl numbers.

Forced Convection in Concentric-Sphere Heat Exchangers

1968 ◽  
Vol 90 (1) ◽  
pp. 125-129 ◽  
Author(s):  
H. A. Rundell ◽  
E. G. Ward ◽  
J. E. Cox
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Empirical Relation ◽  
Outer Sphere ◽  
Coolant Fluid ◽  
Transfer Rates ◽  
Concentric Spheres ◽  
Temperature Heat ◽  
Inner Sphere ◽  
Visualization Techniques

The first experimental investigation of forced convection of a fluid through the annulus formed by two concentric spheres was performed. The fluid enters and leaves the annulus through diametrically opposed openings in the outer sphere. The inner sphere serves as a constant-temperature heat source. Four sphere-size combinations were tested. The flow patterns in the annulus were established by flow visualization techniques; characteristic photographic results are presented. Energy considerations include heat transfer rates, inner-sphere surface temperatures, and temperature traverses of the coolant fluid. An empirical relation correlates the heat transfer data.

Natural Convection Heat Transfer From a Cylinder With High Conductivity Permeable Fins

2003 ◽  
Vol 125 (2) ◽  
pp. 282-288 ◽  
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
High Heat ◽  
Horizontal Cylinder ◽  
High Conductivity ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Wide Range

The problem of laminar natural convection from a horizontal cylinder with multiple equally spaced high conductivity permeable fins on its outer surface was investigated numerically. The effect of several combinations of number of fins and fin height on the average Nusselt number was studied over a wide range of Rayleigh number. Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Rayleigh number, number of fins, and fin height. This ratio was as high as 8.4 at Rayleigh number of 106, non-dimensional fin height of 2.0, and with 11 equally spaced fins. The use of permeable fins is very advantageous when high heat transfer rates are needed such as in today’s high power density electronic components.

Heat Transfer by Natural Convection of Helium Between Horizontal Isothermal Concentric Cylinders at Cryogenic Temperature

1988 ◽  
Vol 110 (1) ◽  
pp. 109-115 ◽  
Author(s):  
E. H. Bishop
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Transfer Rate ◽  
Correlation Equation ◽  
Diameter Ratio ◽  
Temperature Profiles ◽  
Cryogenic Temperatures ◽  
Transfer Rates ◽  
Concentric Cylinders

An experimental study was performed of the heat transfer by natural convection of helium between horizontal isothermal concentric cylinders at cryogenic temperatures. Time-averaged temperature profiles at various locations in the annulus and overall heat transfer rates were measured as the Rayleigh number was varied from 6 × 106 to 2 × 109 and the expansion number from 0.20 to 1.0 for a constant Prandtl number of 0.688 and diameter ratio of 3.36. It was found that the heat transfer rate depends on the magnitude of the expansion number as well as on the magnitude of the Rayleigh number. With gas properties evaluated at a volume-weighted reference temperature, a correlation equation is presented that correlates the heat transfer data with maximum deviations of −8.2 and +8.5 percent. The results of this study are compared with previously published studies of other investigators.

Convection in a spherical capacitor

2002 ◽  
Vol 450 ◽  
pp. 297-316 ◽  
Author(s):  
KAMEL AMARA ◽  
JOHN HEGSETH
Keyword(s):  
Heat Transfer ◽  
Constant Temperature ◽  
Large Scale ◽  
Experimental System ◽  
Outer Sphere ◽  
Parameter Range ◽  
Polarization Force ◽  
Voltage Difference ◽  
Concentric Spheres ◽  
Inner Sphere

Real-time holographic interferometry and shadowgraph visualization are used to study convection in the fluid between two concentric spheres when two distinct buoyancy forces are applied to the fluid. The heated inner sphere has a constant temperature that is greater than the constant temperature of the outer sphere by ΔT. In addition to the usual gravitational buoyancy from temperature induced density differences, another radial buoyancy is imposed by applying an a.c. voltage difference, ΔV between the inner and outer spheres. The resulting electric field gradient in this spherical capacitor produces a central polarization force. The temperature dependence of the dielectric constant results in the second buoyancy force that is especially large near the inner sphere. The normal buoyancy is always present and, within the parameter range explored in our experiment, always results in a large-scale cell that is axisymmetric about the vertical. We have found that this flow becomes unstable to toroidal or spiral rolls that form near the inner sphere and travel vertically upward when ΔT and ΔV are suffciently high. These rolls start near the centre sphere's equator and travel upward toward its top. The onset of this instability depends on both the temperature difference at onset ΔTc and the voltage difference at onset ΔVc and these two quantities appear to be related, within the parameter range accessible to our experimental system, by a power law ΔVc ∝ ΔT1/3c. Measurements of the heat transfer show that these travelling rolls increase the heat transfer at onset. Far above onset, the heat transfer may actually decrease with increasing ΔT. The travelling roll's frequency increases with increasing ΔT near onset and with increasing ΔV far above onset. These results have been interpreted in terms of a flow structure that includes a thermal boundary-layer-like behaviour. This layer has a radial width that increases from the bottom pole to an unstable ‘latitude’ near the equator where the rolls appear.

scholarly journals Experimental analysis and ANN prediction on performances of finned oval-tube heat exchanger under different air inlet angles with limited experimental data

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 968-980
Author(s):  
Xueping Du ◽  
Zhijie Chen ◽  
Qi Meng ◽  
Yang Song
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Correlation Equation ◽  
Tube Heat Exchanger ◽  
Flow Friction ◽  
Air Inlet ◽  
Comparison Results ◽  
Wide Range ◽  
Oval Tube

Abstract A high accuracy of experimental correlations on the heat transfer and flow friction is always expected to calculate the unknown cases according to the limited experimental data from a heat exchanger experiment. However, certain errors will occur during the data processing by the traditional methods to obtain the experimental correlations for the heat transfer and friction. A dimensionless experimental correlation equation including angles is proposed to make the correlation have a wide range of applicability. Then, the artificial neural networks (ANNs) are used to predict the heat transfer and flow friction performances of a finned oval-tube heat exchanger under four different air inlet angles with limited experimental data. The comparison results of ANN prediction with experimental correlations show that the errors from the ANN prediction are smaller than those from the classical correlations. The data of the four air inlet angles fitted separately have higher precisions than those fitted together. It is demonstrated that the ANN approach is more useful than experimental correlations to predict the heat transfer and flow resistance characteristics for unknown cases of heat exchangers. The results can provide theoretical support for the application of the ANN used in the finned oval-tube heat exchanger performance prediction.

Three-Dimensional Natural Convection From Vertical Heated Plates With Adjoining Cool Surfaces

1992 ◽  
Vol 114 (1) ◽  
pp. 115-120 ◽  
Author(s):  
B. W. Webb ◽  
T. L. Bergman
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Control Volume ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Infrared Thermal Imaging ◽  
Transfer Rates ◽  
Thermal Boundary Conditions

Natural convection in an enclosure with a uniform heat flux on two vertical surfaces and constant temperature at the adjoining walls has been investigated both experimentally and theoretically. The thermal boundary conditions and enclosure geometry render the buoyancy-induced flow and heat transfer inherently three dimensional. The experimental measurements include temperature distributions of the isoflux walls obtained using an infrared thermal imaging technique, while the three-dimensional equations governing conservation of mass, momentum, and energy were solved using a control volume-based finite difference scheme. Measurements and predictions are in good agreement and the model predictions reveal strongly three-dimensional flow in the enclosure, as well as high local heat transfer rates at the edges of the isoflux wall. Predicted average heat transfer rates were correlated over a range of the relevant dimensionless parameters.

Design of a Plane-Type Bidirectional Thermal Diode

1988 ◽  
Vol 110 (4) ◽  
pp. 299-305 ◽  
Author(s):  
K. Chen
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Transfer Rate ◽  
Reverse Bias ◽  
Energy Utilization ◽  
Heat Transfer Analysis ◽  
Transfer Rates ◽  
One Dimensional ◽  
Plane Type ◽  
Solar Energy Utilization

The design of a plane-type, bidirectional thermal diode is presented. This diode is composed of two vertical plates and several fluid-filled loops with their horizontal segments soldered to the vertical plates. This invention is simple in construction and low in cost. The direction of heat transfer in the invented thermal diode can be easily reversed. These features of the present invention make it very attractive to solar energy utilization. Natural convection analysis for thermosyphon operations was adopted for heat transfer calculations of the fluid-filled loops. A one-dimensional heat transfer analysis was employed to estimate the heat transfer rate and ratio of heat transfer rates of the diode under forward and reverse bias.

Heat Transfer Associated With Air-Water Spray Cooling of Forgings From High Temperatures

2001 ◽  
Author(s):  
J. Ward ◽  
M. de Oliveira ◽  
D. R. Garwood ◽  
R. A. Wallis
Keyword(s):  
Heat Transfer ◽  
Water Flow ◽  
Gas Turbines ◽  
Spray Cooling ◽  
Solution Temperature ◽  
Air Cooling ◽  
Water Spray ◽  
Transfer Rates ◽  
Wide Range ◽  
Water Spray Cooling

Abstract The desired mechanical properties of the nickel-based or titanium forgings used in gas turbines for aircraft and power generation applications can be controlled by varying the rate of cooling from the so-called solution temperature during an initial heat treatment process. The use of dilute air-water spray cooling of these forgings is a technique which can provide heat transfer rates lying between those associated with conventional oil quenching or convective air-cooling. Air assisted atomisation can result in fine sprays over a wide range of water flow rates and it has a further advantage in that the air “sweeps” the surface and hence helps to prevent the build up of deleterious vapour films at high surface temperatures. The paper presents experimental data for the heat transfer rates associated with the use of these sprays to cool surfaces from temperatures of approximately 800°C. Many forgings contain surface recesses, which can lead to build up or “pooling” of the water so that the effect of variations in surface geometry is also reported. Periodic interruption of the water flow is a technique which can be employed to provide additional control of the heat transfer rate, particularly at temperatures below 500°C so that data is also presented for pulsed sprays.

Heat transfer from a circular cylinder by acoustic streaming

1967 ◽  
Vol 30 (2) ◽  
pp. 337-355 ◽  
Author(s):  
Peter D. Richardson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Convection ◽  
Circular Cylinder ◽  
Prandtl Number ◽  
Acoustic Streaming ◽  
Mean Flow ◽  
Wide Range ◽  
Transverse Oscillations ◽  
Streaming Flow

An analysis is described for convection from a circular cylinder subjected to transverse oscillations relative to the fluid in which it is immersed. The analysis is based upon use of the acoustic streaming flow field. It is assumed that the frequency involved is sufficiently small that the acoustic wavelength in the fluid is much larger than the cylinder diameter, and that there is no externally imposed mean flow across or along the cylinder. Solutions are presented which are appropriate for a wide range of Prandtl number, and the cases of small and of large streaming Reynolds number are distinguished. The analysis compares favourably with experiments when the influence of natural convection is small.

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