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.

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.

scholarly journals Turbulent Natural Convection from a Vertical Plane Surface

1968 ◽  
Vol 90 (1) ◽  
pp. 1-6 ◽  
Author(s):  
R. Cheesewright
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Natural Convection ◽  
Vertical Plane ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Boundary Layer ◽  
Transfer Coefficients ◽  
Turbulent Natural Convection ◽  
Heat Transfer Coefficients

The paper reports the results of an experimental investigation which was intended to clarify the present uncertain position with regard to the distributions of mean temperature and mean velocity in a turbulent natural-convection boundary layer. Data reported for the turbulent boundary layer for Grashof numbers between 1010 and 1011 include local heat transfer coefficients as well as temperatures and velocities. Local heat transfer coefficients and temperature distributions are also reported for the laminar and transitional boundary-layer regions. Results are compared with other experimental data and with theoretical predictions.

Natural Convection Heat Transfer From a Staggered Vertical Plate Array

1993 ◽  
Vol 115 (4) ◽  
pp. 938-945 ◽  
Author(s):  
G. Tanda
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Vertical Plate ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental study was performed to evaluate the natural convection heat transfer characteristics of an array of four staggered vertical plates. The thermal input at each plate was the same or differed from plate to plate depending on various heating modes. The effects of the interplate spacing and the plate-to-ambient temperature difference were investigated. The experiments were performed in air. Convective interactions among the plates were identified by examining the per-plate heat transfer coefficients and the local heat transfer coefficients along the vertical sides of plates. Local heat transfer results were obtained by means of the schlieren quantitative technique. Comparison of local heat transfer coefficients along the plate assembly with those of a continuous vertical plate (having the same height) showed enhancements up to a factor of two. Comparison of average heat transfer results with those for a parallel plate channel having the same exchanger size showed only little reductions in heat transfer rate, despite a 28 percent reduction in heat transfer area, with enhancements, in terms of specific heat flux, up to 30 percent.

scholarly journals Heat Transfer Performance Potential with a High-Temperature Phase Change Dispersion

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4899
Author(s):  
Ludger Fischer ◽  
Ernesto Mura ◽  
Poppy O’Neill ◽  
Silvan von Arx ◽  
Jörg Worlitschek ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Local Heat Transfer ◽  
High Temperature Phase ◽  
Operating Conditions ◽  
Phase Changes ◽  
Temperature Phase ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers

Phase change dispersions are useful for isothermal cooling applications. As a result of the phase changes that occur in PCDs, they are expected to have greater storage capacities than those of single-phase heat transfer fluids. However, for appropriate heat exchanger dimensions and geometries for use in phase change dispersions, knowledge about the convective heat transfer coefficients of phase change dispersions is necessary. A test unit for measuring the local heat transfer coefficients and Nusselt numbers of PCDs was created. The boundary condition of constant heat flux was chosen for testing, and the experimental heat transfer coefficients and Nusselt numbers for the investigated phase change dispersion were established. Different experimental parameters, such as the electrical wall heat input, Reynolds number, and mass flow rate, were varied during testing, and the results were compared to those of water tests. It was found that, due to the tendency of low-temperature increases in phase change dispersions, the driving temperature difference is greater than that of water. In addition, larger heat storage capacities were obtained for phase change dispersions than for water. Through this experimentation, it was acknowledged that future investigation into the optimised operating conditions must be performed.

The Multi-Phase Flow Test Facility “EMMA” to Investigate Local Heat Transfer Coefficients and Liquid Water Films at Wet Steam Conditions

2020 ◽  
Author(s):  
Florian Felix Lapp ◽  
Simon Hecker ◽  
Sebastian Schuster ◽  
Dieter Brillert
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measurement Methods ◽  
Wet Steam ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Phase Change Phenomena ◽  
Multi Phase

Abstract Conventional power plants are obliged to compensate for the fluctuations in power generation, due to the rising amount of renewable energies, to ensure grid stability. Consequently, steam turbines are more frequently facing load variation and startup/shut-down cycles leading to an increase of thermal stress induced by phase change phenomena. The review of existing test facilities providing measurement data of heat transfer coefficients influenced by multiphase phenomena, such as surface wettability and dry-out, revealed the necessity for a new measurement application. This paper presents the design of the Experimental Multi-phase Measurement Application “EMMA” to generate the required conditions in combination with an academic turbine housing geometry. The performed investigations are focused on the local distribution of heat transfer coefficients (HTC) and the surface wettability affected by phase change phenomena. Two main film formation mechanisms can be observed, depending on the thermal gradient between the fluid and the wall. These are a) saturated/superheated steam in contact with a sub-cooled wall leading to film-wise/drop-wise condensation and b) primary condensed wet steam droplets depositing on a superheated wall, leading to evaporation. Both, the liquid film and the local heat transfer are measured simultaneously. An overview of applicable thickness measurement methods for transparent liquid films is given and the applied optical measurement system is further described. Moreover the HTC measurement methods are presented considering the occurring case of phase change.

Heat Transfer of Melting Nonadecane Spheres in Natural Convection of Water

2005 ◽  
Author(s):  
Yuta Tanaka ◽  
Makoto Hishida ◽  
Gaku Tanaka
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Shape Transformation ◽  
Heat Transfer Coefficients ◽  
Lower Hemisphere ◽  
Transfer Study ◽  
Good Agreement

This paper deals with experimental and analytical heat transfer study of nonadecane spheres melting in natural convection of water. Experimental local and average heat transfer coefficients were obtained by analyzing photo images of the shape transformation of the nonadecane spheres. The relevant dimensionless parameters were varied in the ranges of 1.8×107 ≤ Grn·Prn ≤ 1.8×108 and 0.04 ≤ CnΔT/Ln ≤ 0.16. We found that (1) the melting nonadecane sphere was covered with thin nonadecane liquid film flowing upwards along the sphere to make a liquid cap on the top. The cap regularly repeated formation and splitting off, (2) on the lower hemisphere the experimental local heat transfer coefficients were slightly higher than the analytical ones and on the upper hemisphere the experimental local heat transfer coefficients were slightly lower than the analytical ones, and (3) the experimental average Nusselt number was correlated by Nu = 0.151 (Grn·Prn)0.257(CnΔT/Ln)0.117 that was in good agreement with the theoretical one.

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