Acoustic radiation force on a heated sphere including effects of heat transfer and acoustic streaming

Lee, Chun P.; Wang, Taylor G.

doi:10.1121/1.395936

Cited by 14 publications

(11 citation statements)

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“…Once the systems reach T max , the temperatures decrease as the fuel is consumed. At the end after about 60 ms, the droplet falls out of the trap and drops on the transducer . Since our goal is to study the combustion of the levitated droplet, the temperature fluctuations occurring by the splash ignition are neither shown in Figure nor discussed.…”

Section: Resultsmentioning

confidence: 99%

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Catalytic Effects of Zeolite Socony Mobil-5 (ZSM-5) on the Oxidation of Acoustically Levitated exo-Tetrahydrodicyclopentadiene (JP-10) Droplets

et al. 2021

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Jet propulsion 10 (JP-10) droplets with and without aluminum nanoparticles in conjunction with HZSM-5 zeolite and surfactants were ultrasonically levitated, and their oxidation processes were explored to identify how the oxidation process of JP-10 is catalytically affected by the HZSM-5 zeolites and how the surfactant and Al NPs in the system impacted the key experimental parameters of the ignition such as ignition delay time, burn rate, and the maximum temperatures. Singly levitated droplets were ignited using a carbon dioxide laser under an oxygen−argon atmosphere. Pure JP-10 droplets and JP-10 droplets with silicon dioxide of an identical size distribution as the zeolite HZSM-5 did not ignite in strong contrast to HZSM-5-doped droplets. Acidic sites were found to be critical in the ignition of the JP-10. With the addition of the surfactant, the characteristic features of the JP-10 ignition were improved, so the ignition delay time of the zeolite-JP-10 samples were decreased by 2−3 ms and the burn rates were increased by 1.3 to 1.6 × 10 5 K s −1 . The addition of Al NPs increased the maximum temperatures during the combustion of the systems by 300−400 K. Intermediates and end products of the JP-10 oxidation over HZSM-5 were characterized by UV−vis emission and Fourier-transform infrared transmission spectroscopies, revealing key reactive intermediates (OH, CH, C 2 , O 2 , and HCO) along with the H 2 O molecules in highly excited rovibrational states. Overall, this work revealed that acetic sites in HZSM-5 are critical in the catalytic ignition of JP-10 droplets with the addition of the surfactant and Al NPs, enhancing the oxidation process of JP-10 over HZSM-5 zeolites.

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Section: Resultsmentioning

confidence: 99%

“… a Measurements are accurate to within 2 nm. b Reference . c Reference . d Reference . e Reference . f Reference . g Reference . h Reference . i Reference . …”

Section: Resultsmentioning

confidence: 99%

Catalytic Effects of Zeolite Socony Mobil-5 (ZSM-5) on the Oxidation of Acoustically Levitated exo-Tetrahydrodicyclopentadiene (JP-10) Droplets

et al. 2021

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“…which is rather close to (9.15) and (9.16), especially given ν 0 /D 0 = O(1). (A similar approximation was used in Lee & Wang (1988) to estimate the Nusselt number in the acoustic field). The data computed with variable SPL agree well with the measurements.…”

Section: Comparison Of Theoretical and Experimental Resultsmentioning

confidence: 99%

Evaporation of acoustically levitated droplets

et al. 1999

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The rate of heat and mass transfer at the surface of acoustically levitated pure liquid droplets is predicted theoretically for the case where an acoustic boundary layer appears near the droplet surface resulting in an acoustic streaming. The theory is based on the computation of the acoustic field and squeezed droplet shape by means of the boundary element method developed in Yarin, Pfaffenlehner & Tropea (1998). Given the acoustic field around the levitated droplet, the acoustic streaming near the droplet surface was calculated. This allowed calculation of the Sherwood and Nusselt number distributions over the droplet surface, as well as their average values. Then, the mass balance was used to calculate the evolution of the equivalent droplet radius in time. The theory is applicable to droplets of arbitrary size relative to the sound wavelength λ, including those of the order of λ, when the compressible character of the gas flow is important. Also, the deformation of the droplets by the acoustic field is accounted for, as well as a displacement of the droplet centre from the pressure node. The effect of the internal circulation of liquid in the droplet sustained by the acoustic streaming in the gas is estimated. The distribution of the time-average heat and mass transfer rate over the droplet surface is found to have a maximum at the droplet equator and minima at its poles. The time and surface average of the Sherwood number was shown to be described by the expression Sh = KB/√ω[Dscr ]0, where B = A0e/(ρ0c0) is a scale of the velocity in the sound wave (A0e is the amplitude of the incident sound wave, ρ0 is the unperturbed air density, c0 is the sound velocity in air, ω is the angular frequency in the ultrasonic range, [Dscr ]0 is the mass diffusion coefficient of liquid vapour in air, which should be replaced by the thermal diffusivity of air in the computation of the Nusselt number). The coefficient K depends on the governing parameters (the acoustic field, the liquid properties), as well as on the current equivalent droplet radius a.For small spherical droplets with a[Lt ]λ, K = (45/4π)1/2 = 1.89, if A0e is found from the sound pressure level (SPL) defined using A0e. On the other hand, if A0e is found from the same value of the SPL, but defined using the root-mean-square pressure amplitude (prms = A0e/√2), then Sh = KrmsBrms/ √ω[Dscr ]0, with Brms = √2B and Krms = K/√2 = 1.336. For large droplets squeezed significantly by the acoustic field, K appears always to be greater than 1.89. The evolution of an evaporating droplet in time is predicted and compared with the present experiments and existing data from the literature. The agreement is found to be rather good.We also study and discuss the effect of an additional blowing (a gas jet impinging on a droplet) on the evaporation rate, as well as the enrichment of gas at the outer boundary of the acoustic bondary layer by liquid vapour. We show that, even at relatively high rates of blowing, the droplet evaporation is still governed by the acoustic streaming in the relatively strong acoustic fields we use. This makes it impossible to study forced convective heat and mass transfer under the present conditions using droplets levitated in strong acoustic fields.

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“…In addition, there have some investigations on the thermal effects. 12,13 In relation to microgravity, acoustic levitation is a good way to stabilize a levitated drop. There has been considerable experimental activity in this area, 14,15 together with analytical studies such as that by Lee and Wang.…”

Section: Introductionmentioning

confidence: 99%

Internal circulation in a drop in an acoustic field

Zhao

Sadhal

Trinh³

1999

The Journal of the Acoustical Society of America

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An investigation of the internal flow field for a drop at the antinode of a standing wave has been carried out. The main difference from the solid sphere case is the inclusion of the shear stress and velocity continuity conditions at the liquid-gas interface. To the leading order of calculation, the internal flow field was found to be quite weak. Also, this order being fully time dependent has a zero mean flow. At the next higher order, steady internal flows are predicted and, as in the case of a solid sphere, there is a recirculating layer consisting of closed streamlines near the surface. In the case of a liquid drop, however, the behavior of this recirculating Stokes layer is quite interesting. It is predicted that the layer ceases to have recirculation when [formula: see text], where [symbol: see text] is the liquid viscosity, mu is the exterior gas-phase viscosity, and M is the dimensionless frequency parameter for the gas phase, defined by M = i omega a2 rho/mu, with a being the drop radius. Thorough experimental confirmation of this interesting new development needs to be conducted. Although it seems to agree with many experiments with levitated drops where no recirculating layer has been clearly observed, a new set of experiments for specifically testing this interesting development need to be carried out.

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Acoustic radiation force on a heated sphere including effects of heat transfer and acoustic streaming

Cited by 14 publications

References 0 publications

Catalytic Effects of Zeolite Socony Mobil-5 (ZSM-5) on the Oxidation of Acoustically Levitated exo-Tetrahydrodicyclopentadiene (JP-10) Droplets

Catalytic Effects of Zeolite Socony Mobil-5 (ZSM-5) on the Oxidation of Acoustically Levitated exo-Tetrahydrodicyclopentadiene (JP-10) Droplets

Evaporation of acoustically levitated droplets

Internal circulation in a drop in an acoustic field

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