Latent Heat-of-Fusion Energy Storage: Experiments on Heat Transfer from Cylinders During Melting

1979 ◽  
Vol 101 (3) ◽  
pp. 453-458 ◽  
Author(s):  
A. G. Bathelt ◽  
R. Viskanta ◽  
W. Leidenfrost
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Fusion Energy ◽  
Conclusive Evidence ◽  
Heat Of Fusion ◽  
Heat Sources ◽  
Transfer Coefficients ◽  
Melting Front ◽  
Analysis And Design ◽  
Heat Transfer Coefficients

Melting from an array of three staggered, electrically heated cylinders imbedded in a paraffin (n-octadecane) has been studied. The shape of the melting front has been determined photographically, and the local heat transfer coefficients were measured using a shadowgraph technique. The experiments provide conclusive evidence of the important role played by natural convection on the timewise variation of the melt shape, the surface temperature and the instantaneous local as well as circumferentially averaged heat transfer coefficients around the imbedded heat sources. After a common solid-liquid interface is formed around the cylinders, natural convection circulation around each cylinder interacts strongly with the other two cylinders. The arrangement of heat sources affects significantly the melt shape but the circumferentially averaged instantaneous heat transfer coefficients differ only by about 10 percent for the two arrangements studied. The experimental findings indicate that natural convection effects are important and should be considered in analysis and design of systems involving phase change.

An experimental investigation of natural convection in the melted region around a heated horizontal cylinder

1979 ◽  
Vol 90 (2) ◽  
pp. 227-239 ◽  
Author(s):  
A. G. Bathelt ◽  
R. Viskanta ◽  
W. Leidenfrost
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Phase Change ◽  
Local Heat Transfer ◽  
Horizontal Cylinder ◽  
Conclusive Evidence ◽  
Transfer Coefficients ◽  
Quantitative Evidence ◽  
Analysis And Design ◽  
Heat Transfer Coefficients

Melting from an electrically heated horizontal cylinder embedded in a paraffin (n-octadecane, fusion temperature 301·3 °K) has been studied experimentally. The shape of the solid-liquid interface has been determined photographically, and the local heat transfer coefficients have been measured using a shadowgraph technique. The experiments provide conclusive evidence of the important role played by natural convection in melting a solid due to an embedded cylindrical heat source. The four distinct pieces of quantitative evidence which contribute to this conclusion are the melt shape, surface temperature, local and average heat transfer coefficients and their variation with time.The experimental findings prove the importance of natural convection in phase change problems involving melting and indicate that continued practice of neglecting the effects in the analysis of such problems does not appear reasonable. Natural convection should be considered in analysis and design of systems involving phase change.

Experimental Analysis of the Pool Boiling Phenomenon of Sugarcane Juice

2015 ◽  
Vol 789-790 ◽  
pp. 489-495 ◽  
Author(s):  
Daniel Marcelo ◽  
Paul Villar Yacila ◽  
Raúl La Madrid Olivares
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Experimental Analysis ◽  
Electrical Power ◽  
Power Input ◽  
Sugarcane Juice ◽  
Middle Level ◽  
Transfer Coefficients ◽  
Combustion Gases ◽  
Heat Transfer Coefficients

In Peru, jaggery making process has low energy efficiency and it is due to low heat transfer coefficients for natural convection linked to the sugar cane movement generated by the heat exchange between the sugarcane juice and the combustion gases. This low heat transfer coefficients are caused by improper heat exchangers designs. In this work, is performed an experimental analysis that consist in supplie heat to a pot containing sugarcane juice using a hot plate of constant electrical power. This study consist in identify boiling regimes and estimate the heat transfer coefficients linked to natural convection boiling, measuring: (i) the temperature at the bottom of the pot (ii) the temperature at the bottom level of sugarcane juice (iii) the temperature at middle level of sugarcane juice (iv) the temperature at free surface of sugarcane juice (v) rate of water evaporated. The method of linear regression and the correlation of Rohsenow were used for obtaining the values of the heat transfer coefficients ranging from 4088.6 W/m2°C to 12592.8 W/m2°C with power input ranging from 700W to 1300W.

Experimental Investigation of Natural Convection Heat Transfer in Volumetrically Heated Spherical Segments

1996 ◽  
Vol 118 (1) ◽  
pp. 31-37 ◽  
Author(s):  
F. J. Asfia ◽  
B. Frantz ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Reactor Vessel ◽  
Core Material ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
External Cooling

External cooling of a light water reactor vessel by flooding of the concrete cavity with subcooled water is one of several management strategies currently being considered for accidents in which significant relocation of core material is predicted to occur. At present, uncertainty exists with respect to natural convection heat transfer coefficients between the pool of molten core material and the reactor vessel wall. In the present work, experiments were conducted to examine natural convection heat transfer in internally heated partially filled spherical pools with external cooling. In the experiments, Freon-113 was contained in a Pyrex bell jar, which was cooled externally with subcooled water. The pool was heated using a 750 W magnetron taken from a conventional microwave. The pool had a nearly adiabatic free surface. The vessel wall temperature was not uniform and varied from the stagnation point to the free surface. A series of chromel–alumel thermocouples was used to measure temperatures in both steady-state and transient conditions. Each thermocouple was placed in a specific vertical and radial location in order to determine the temperature distribution throughout the pool and along the inner and outer walls of the vessel. In the experiments, pool depth and radius were varied parametrically. Both local and averages heat transfer coefficients based on pool maximum temperature were obtained. Rayleigh numbers based on pool height were varied from 2 × 1010 to 1.1 × 1014. Correlations for the local heat transfer coefficient dependence on pool angle and for the dependence of average Nusselt number on Rayleigh number and pool depth have been developed.

Laminar Natural Convection in Isosceles Triangular Enclosures Heated From Below and Symmetrically Cooled From Above

2000 ◽  
Vol 122 (3) ◽  
pp. 485-491 ◽  
Author(s):  
G. A. Holtzman ◽  
R. W. Hill ◽  
K. S. Ball
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Pitchfork Bifurcation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Triangular Enclosure ◽  
Laminar Natural Convection ◽  
Flow Symmetry

A numerical study of natural convection in an isosceles triangular enclosure with a heated horizontal base and cooled upper walls is presented. Nearly every previous study conducted on this subject to date has assumed that the geometric plane of symmetry is also a plane of symmetry for the flow. This problem is re-examined over aspect ratios ranging from 0.2 to 1.0 and Grashof numbers from 103 to 105. It is found that a pitchfork bifurcation occurs at a critical Grashof number for each of the aspect ratios considered, above which the symmetric solutions are unstable to finite perturbations and asymmetric solutions are instead obtained. Results are presented detailing the occurrence of the pitchfork bifurcation in each of the aspect ratios considered, and the resulting flow patterns are described. A flow visualization study is used to validate the numerical observations. Computed local and mean heat transfer coefficients are also presented and compared with results obtained when flow symmetry is assumed. Differences in local values of the Nusselt number between asymmetric and symmetric solutions are found to be more than 500 percent due to the shifting of the buoyancy-driven cells. [S0022-1481(00)02503-2]

scholarly journals Effect of Heat Source Placement on Natural Convection from Cylindrical Surfaces

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4334
Author(s):  
Andrej Kapjor ◽  
Peter Durcansky ◽  
Martin Vantuch
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Theoretical Models ◽  
Heat Transfer Process ◽  
Heat Output ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Thermal Fields ◽  
Horizontal Cylinders

Placement of heat source can play a significant role in final heat output, or heat source effectivity. Because of this, there is a need to analyze thermal fields of the heat exchange system by natural convection, where the description by criterion equations is desired, as the net heat output from tubes can be quantified. Based on known theoretical models, numerical methods were adapted to calculate the heat output with natural air flow around tubes, where mathematical models were used to describe the heat transfer more precisely. After validation of heat transfer coefficients, the effect of wall and heat source placement was studied, and the Coanda effect was also observed. The heat source placement also has an effect at the boundary layer, which can change and therefore affect the overall heat transfer process. The optimal wall-to-cylinder distance for an array of horizontal cylinders near a wall was also expressed as a function of the Rayleigh number and number of cylinders in the array.

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.

Radiative and convective heat transfer coefficients of the human body in natural convection

2008 ◽  
Vol 43 (12) ◽  
pp. 2142-2153 ◽  
Author(s):  
Yoshihito Kurazumi ◽  
Tadahiro Tsuchikawa ◽  
Jin Ishii ◽  
Kenta Fukagawa ◽  
Yoshiaki Yamato ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Human Body ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients
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