Chaotic and Periodic Natural Convection for Moderate and High Prandtl Numbers in a Porous Layer subject to Vibrations

Vadasz, Johnathan J.; Meyer, Josua P.; Govender, S.

doi:10.1007/s11242-014-0301-z

Cited by 23 publications

(33 citation statements)

References 38 publications

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“…In the current study, it was shown experimentally that the rate of solidification is increased when vibrations were introduced during the solidification process. Since the effects of vibration would only affect the porous section and/or liquid we can assume that the results presented by Vadasz et al [8] in the porous medium might be linked to the results seen in the current study of solidification. It is also clear that vibrations do have an effect on the porous medium section as presented by Vadasz et al [8] for…”

Section: Effect Of Vibration On Solidification Timessupporting

confidence: 63%

“…The third part is to determine the effects the vibrations had on the solidification time. The fourth part is to compare the results presented in the current study with the numerical results presented by Vadasz et al [8].…”

Section: Resultsmentioning

confidence: 85%

“…Figure 8 (a) shows chaotic "bursts" at specific values of the scaled Raleigh number. This behaviour is quite distinct from the case without forced vibrations, when the chaotic solution occupies a wide range of scaled Rayleigh number values, interrupted only by periodic "bursts" in Vadasz et al [8]. This result shows that the vibrations affect the heat transfer in a porous medium, yet what that effect is, is still to be determined.…”

Section: Effect Of Vibration On Solidification Timesmentioning

confidence: 71%

“…The numerical results presented by Vadasz et al [8] considered the vibration effects in a porous medium and were therefore used for comparison purposes. In Figure 8 (a), a chaotic orbit is observed at a scaled Rayleigh number when there is one or more positive Lyapunov exponents, a quasi-periodic orbit is observed when there is one negative Lyapunov exponent and two equal to zero, a periodic orbit is observed when there are two negative Lyapunov exponents and one equal to zero, and a fixed point is observed when all Lyapunov exponents are negative.…”

Section: Effect Of Vibration On Solidification Timesmentioning

confidence: 99%

“…However, very limited experimental work if any was done on the effects of vibration during solidification on the cooling rate independent of any other effects. One such work (although numerical) was by Vadasz et al [8] which studied the porous region under forced vibrations and the results showed that vibration influenced the heat transfer.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Study of Vibration Effects on Heat Transfer during Solidification of Paraffin in a Spherical Shell

Vadasz

Meyer

Govender

et al. 2015

Experimental Heat Transfer

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Two effects that have been observed when metals and metal alloys are vibrated during solidification are a decrease in dendritic spacing, which directly affects density, and faster cooling rates and associated solidification times. Because these two effects happen simultaneously during solidification it is challenging to determine the one effect independently from the other. Most previous studies were on metals and metal alloys. In these studies, the one effect, i.e. the decrease in dendritic spacing, might influence the other, i.e. the faster cooling rates, and vice versa. The direct link between vibration and heat transfer has not yet been studied independently. The purpose of this study was to experimentally investigate the effect of vibration only on heat transfer and thus solidification rate. Experiments were conducted on paraffin wax, because it had a clearly defined macroscopic crystal structure consisting of mostly large straight-chain hydrocarbons. The advantage of the large straight-chain hydrocarbons was that the dendritic spacing was not affected by the cooling rate.Experiments were done with paraffin wax inside hollow plastic spheres of 40 mm 2 diameter with 1 mm wall thickness. The paraffin wax was initially in a liquid state at a uniform temperature of 60°C and then submerged into a thermal bath at a uniform constant temperature of 15°C, which was approximately 20°C below the mean solidification temperature of the wax. Experiments were conducted in approximately 300 samples, with and without vibration at frequencies varying from 10 -300 Hz.The first set of experiments were conducted to determine the solidification times. In the second set of experiments, the mass of wax solidified was determined at discrete time steps, with and without vibration. The results showed that paraffin wax had vibration independent of solid density contrary to other materials, eg. metals and metal alloys. Enhancement of heat transfer resulted in quicker solidification times and possible control over the heat transfer rate. The increase in heat transfer leading to faster solidifcation times was observed to first occur, as frequency increased and then to decrease.

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Section: Effect Of Vibration On Solidification Timessupporting

confidence: 63%

Section: Resultsmentioning

confidence: 85%

Section: Effect Of Vibration On Solidification Timesmentioning

confidence: 71%

Section: Effect Of Vibration On Solidification Timesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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