Leidenfrost Cart

2012 ◽  
Author(s):  
Ali Hashmi ◽  
Benjamin Coder ◽  
Gan Yu ◽  
Yuhao Xu ◽  
Jonathon Spafford ◽  
...  
Keyword(s):  
Gravitational Force ◽  
Consumption Rate ◽  
Flat Surface ◽  
Theoretical Calculations ◽  
Maximum Load ◽  
Vapor Layer ◽  
Leidenfrost Effect ◽  
Hot Surface ◽  
First Time ◽  
Measured Water

Friction is a major inhibitor in almost every mechanical system. Enlightened by the Leidenfrost effect — a droplet can be levitated by a vapor layer on a hot surface — we demonstrate for the first time that a small cart also can be levitated by Leidenfrost vapor provided that the surface temperature is above the Leidenfrost point. The levitated cart can carry certain amount of load and move frictionless on the hot surface. The maximum load that the cart can carry is experimentally tested over a range of surface temperatures. We show that the Leidenfrost levitated cart can not only be propelled by gravitational force on a slanted flat surface, but also can be self-propelled on a ratchet shaped horizontal surface. In the end, we experimentally measured water consumption rate for the Leidenfrost levitated cart, and compared the results to theoretical calculations. If perfected, this frictionless Leidenfrost cart could be used in numerous applications.

Electrostatic Suppression of the Leidenfrost State Using AC Voltages

2017 ◽  
Author(s):  
Onur Ozkan ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Evaporation Rate ◽  
Important Determinant ◽  
Electrostatic Force ◽  
Vapor Layer ◽  
Lower And Upper Bounds ◽  
Dc Voltage ◽  
Leidenfrost Effect ◽  
Hot Surface

The Leidenfrost effect is a well-known phenomenon in boiling, wherein a vapor layer forms between a hot surface and the liquid, thereby degrading heat transfer. Electrowetting (EW) can be used to fundamentally eliminate the Leidenfrost state by electrostatically attracting the liquid towards the surface; the resulting enhanced wetting substantially increases heat transfer. This work presents preliminary results of a study to understand the influence of AC voltages on Leidenfrost state suppression; prior studies have only utilized DC voltages. It is seen that the AC frequency is a very important determinant of the effectiveness of Leidenfrost state suppression. The electrostatic force which attracts the liquid to the surface decreases with increasing AC frequency; this reduces the extent of suppression. This effect is measured and studied by high speed visualization of suppression as well as measurements of the evaporation/boiling rate under AC EW conditions. It is observed that the instabilities (resulting in suppression) at the vapor-liquid interface reduce at higher frequency. The evaporation rate also reduces with AC frequency, as less heat is picked up by the droplet. It is noted that the evaporation rate has lower and upper bounds, which correspond to the evaporation rates without any EW and with DC voltage, respectively. Overall, this work highlights the importance of the AC frequency as a tool to control the extent of suppression and the boiling heat transfer rate.

scholarly journals Insights on forming N,O-coordinated Cu single-atom catalysts for electrochemical reduction CO2 to methane

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yanming Cai ◽  
Jiaju Fu ◽  
Yang Zhou ◽  
Yu-Chung Chang ◽  
Qianhao Min ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Active Sites ◽  
Theoretical Calculations ◽  
High Energy ◽  
Single Atom ◽  
Faradaic Efficiency ◽  
High Energy Barrier ◽  
Catalytic Sites ◽  
Electron Reduction ◽  
First Time

AbstractSingle-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN2O2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO2 to CH4 with current density of 40 mA·cm-2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN2O2 active sites are due to the proper elevated CH4 and H2 energy barrier and fine-tuned electronic structure of Cu active sites.

scholarly journals The SN2 reaction and its relationship with the Walden inversion, the Finkelstein and Menshutkin reactions together with theoretical calculations for the Finkelstein reaction

2021 ◽  
Author(s):  
Ibon Alkorta ◽  
José Elguero
Keyword(s):  
Linear Models ◽  
Theoretical Calculations ◽  
Computational Method ◽  
Basis Set ◽  
Free Energies ◽  
Nitrogen And Phosphorus ◽  
Atom Pairs ◽  
Leaving Groups ◽  
First Time ◽  
Nitrogen Phosphorus

AbstractThis communication gives an overview of the relationships between four reactions that although related were not always perceived as such: SN2, Walden, Finkelstein, and Menshutkin. Binary interactions (SN2 & Walden, SN2 & Menshutkin, SN2 & Finkelstein, Walden & Menshutkin, Walden & Finkelstein, Menshutkin & Finkelstein) were reported. Carbon, silicon, nitrogen, and phosphorus as central atoms and fluorides, chlorides, bromides, and iodides as lateral atoms were considered. Theoretical calculations provide Gibbs free energies that were analyzed with linear models to obtain the halide contributions. The M06-2x DFT computational method and the 6-311++G(d,p) basis set have been used for all atoms except for iodine where the effective core potential def2-TZVP basis set was used. Concerning the central atom pairs, carbon/silicon vs. nitrogen/phosphorus, we reported here for the first time that the effect of valence expansion was known for Si but not for P. Concerning the lateral halogen atoms, some empirical models including the interaction between F and I as entering and leaving groups explain the Gibbs free energies.

Wallach rearrangement of azoxypyridines and azoxypyridine N-oxides — Charge distributions and dramatic reactivity differences

2008 ◽  
Vol 86 (4) ◽  
pp. 298-304 ◽  
Author(s):  
Erwin Buncel ◽  
Sam-Rok Keum ◽  
Srinivasan Rajagopal ◽  
Eric Kiepek ◽  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Positive Charge ◽  
Theoretical Calculations ◽  
Medium Effect ◽  
Mulliken Charge ◽  
Reaction Intermediates ◽  
Charge Distributions ◽  
First Time ◽  
Acid Region

Extension of our studies of the generic Wallach rearrangement (of azoxybenzene to 4-hydroxyazobenzene) to the heteroaromatic series (azoxypyridines and axoxypyridine N-oxides) has revealed some dramatic reactivity differences, particularly for the α and β compounds. We have studied the 3-isomers and the 4-isomers in each series, each with α and β forms, eight compounds in all, in the 100 wt% sulfuric acid region of acidity. In those cases in which a product could be observed, the α and β isomers both give the same one, the corresponding 4′-hydroxyazo compounds. All the compounds react much more slowly than does azoxybenzene itself, presumably because of the extra positive charge present in the substrates, but the β isomers have half-lives of seconds and the α isomers half-lives of hundreds of hours in the 100 wt% H2SO4 acidity region. The α compounds have measurable pKBH+ values, but the β compounds do not, exhibiting only a medium effect in the acidity region in which the α compounds protonate. This means that for the β compounds, the protonated intermediates must be much less stable and the postulated reaction intermediates must be much more stable than for the α compounds. To clarify this, we have obtained Mulliken charge distributions for the various species concerned, calculating the charge carried by each half of the molecule, larger charge separations being taken to indicate lesser stability. As far as we can establish, this is the first time that this technique has been used to indicate the stabilities of carbocationic species.Key words: azoxypyridines, azoxypyridine N-oxides, Wallach rearrangement, excess acidity, basicities, theoretical calculations, charge distributions, reactivities.

Theoretical calculations of electronic Raman effects of the NO and O2 molecules

1970 ◽  
Vol 48 (14) ◽  
pp. 1664-1674 ◽  
Author(s):  
D. W. Lepard
Keyword(s):  
Raman Spectrum ◽  
Raman Spectra ◽  
Theoretical Calculations ◽  
Diatomic Molecules ◽  
Wave Functions ◽  
Rotational Structure ◽  
Intermediate Case ◽  
First Time

This paper presents a method for calculating the relative intensities and Raman shifts of the rotational structure in electronic Raman spectra of diatomic molecules. The method is exact in the sense that the wave functions used for the calculations may belong to any intermediate case of Hund's coupling schemes. Using this method, theoretical calculations of the pure rotational and electronic Raman spectrum of NO, and the pure rotational Raman spectrum of O2, are presented. Although a calculated stick spectrum for NO was previously shown by Fast et al., the details of this calculation are given here for the first time.

scholarly journals Calculated mixing enthalpies of 11 IIB-IVB and IIB-VB binary alloy systems using a subregular model

2010 ◽  
Vol 46 (2) ◽  
pp. 141-151 ◽  
Author(s):  
Z. Bangwei ◽  
S. Xiaolin ◽  
L. Shuzhi ◽  
Y. Xiaojian ◽  
X. Haowen
Keyword(s):  
Binary Alloy ◽  
First Principles ◽  
Theoretical Calculations ◽  
Points Of View ◽  
Group B ◽  
Miedema Theory ◽  
First Time ◽  
Subregular Model ◽  
Mixing Enthalpies ◽  
Alloy Systems

There have been no theoretical calculations of the mixing enthalpies for group B metal alloy systems using the famous Miedema theory or from first principles. Therefore such systematic calculations for the 11 group IIB?IVB and IIB?VB binary alloy systems are performed for the first time using a subregular model. The results show that the agreement between the calculations and experimental data is pretty good and could be accepted from the theoretical or experimental points of view. It can be concluded from the results that the subregular model can be used for calculating the mixing enthalpies of the group B alloy systems, at least for the IIB?IVB and IIB?VB alloy systems.

CONVECTIVE MOTIONS IN NEMATIC LIQUID CRYSTAL HOMEOTROP AND PLANAR CELLS INDUCED BY GAUSSIAN LASER BEAM

2012 ◽  
Vol 15 ◽  
pp. 129-139 ◽  
Author(s):  
A.K. ALEKSANYAN ◽  
A.K. MINASYAN ◽  
R.S. HAKOBYAN
Keyword(s):  
Liquid Crystal ◽  
Laser Beam ◽  
Theoretical Calculations ◽  
Navier Stokes ◽  
Gaussian Laser Beam ◽  
Planar Cells ◽  
Thermal Origin ◽  
Convective Motions ◽  
Laser Beam Heating ◽  
First Time

Laser beam heating the medium induces instability in the liquid crystal (LC) cell. This instability in conjunction with influence of gravitational force results in convective motions in the cell. In this paper theoretical modeling for studying convection induced by Gaussian laser beam in nematic LC homeotrop and planar cells is presented for the first time. Velocity field and LC director distribution are obtained for various light powers and LC cell sizes by solving Navier-Stokes, heat transfer and director equations simultaneously. The modeling allows us to solve the problems of convections induced by Gaussian laser beam due to Rayleigh-Benard and Marangoni mechanisms as well. There is a good qualitative agreement between theoretical calculations and prior experimental results. The possibility of control and stability of convective motions are studied. Instabilities of the Benard cells are of thermal origin because the Prandtl number for the medium under study is considerably larger than unity.

Spectroscopic Investigation of V3+:YAG Crystal

2013 ◽  
Vol 774-776 ◽  
pp. 811-815 ◽  
Author(s):  
Jian Ma
Keyword(s):  
Room Temperature ◽  
Factor Model ◽  
Theoretical Calculations ◽  
Czochralski Method ◽  
Experiment Data ◽  
Crystal Field Theory ◽  
Calculation Results ◽  
First Time ◽  
Pure Argon Atmosphere ◽  
Good Agreement

V3+ions doped YAG crystals were grown using the Czochralski method in a highly pure argon atmosphere. The transmission spectrum of trivalent vanadium in YAG crystal has been measured at room temperature. Eight bands were observed in which two bands centered at 690nm (14493cm-1) and 1490nm (6711cm-1) are reported for the first time. By using the crystal-field theory and introducing the average covalent factor model, we also presented the theoretical calculations of the energy level splitting of tetrahedrally coordinated V3+impurity systems in YAG crystal. These calculation results are in good agreement with the optical experiment data.

The Effect of the Surface Inclination on the Hydrodynamics and Thermodynamics of Leidenfrost Droplets

2014 ◽  
Vol 30 (2) ◽  
pp. 145-151 ◽  
Author(s):  
P. Pournaderi ◽  
A. R. Pishevar
Keyword(s):  
Contact Time ◽  
Heat Removal ◽  
Total Heat ◽  
Vapor Layer ◽  
Accurate Calculation ◽  
Simulation Process ◽  
Mesh Resolution ◽  
Surface Inclination ◽  
Hot Surface ◽  
Maximum Spreading

ABSTRACTIn this research, the effect of the surface inclination on the hydrodynamics and heat transfer of droplets impinging on very hot surfaces is studied. The applied numerical algorithm is based on the accurate calculation of the vaporization rate in the simulation process using a combination of the level set and ghost fluid methods. Also a mesh clustering technique is utilized to create sufficient mesh resolution near the surface in order to take into account the effect of the thin vapor layer between droplet and very hot surface. The results are verified against available experiments. The effect of the surface inclination on the droplet maximum spreading radius, droplet contact time and total heat removal from the surface is considered. Results show that for the studied regime, the maximum spreading radius of the droplet is decreased with an increase in the surface inclination while the droplet contact time on the surface is independent from the surface inclination. For inclinations greater than 45°, the total heat removal is decreased considerably with an increase in the inclination angle. For smaller inclinations, the dependency of the total heat removal on the surface inclination is not strong.

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