scholarly journals Final fate of a Leidenfrost droplet: Explosion or takeoff

2019 ◽  
Vol 5 (5) ◽  
pp. eaav8081 ◽  
Author(s):  
Sijia Lyu ◽  
Varghese Mathai ◽  
Yujie Wang ◽  
Benjamin Sobac ◽  
Pierre Colinet ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Evaporation Rate ◽  
Liquid Droplet ◽  
Scaling Law ◽  
Vapor Layer ◽  
Air Interface ◽  
Leidenfrost Effect

When a liquid droplet is placed on a very hot solid, it levitates on its own vapor layer, a phenomenon called the Leidenfrost effect. Although the mechanisms governing the droplet’s levitation have been explored, not much is known about the fate of the Leidenfrost droplet. Here we report on the final stages of evaporation of Leidenfrost droplets. While initially small droplets tend to take off, unexpectedly, the initially large ones explode with a crack sound. We interpret these in the context of unavoidable droplet contaminants, which accumulate at the droplet-air interface, resulting in reduced evaporation rate, and contact with the substrate. We validate this hypothesis by introducing controlled amounts of microparticles and reveal a universal 1/3-scaling law for the dimensionless explosion radius versus contaminant fraction. Our findings open up new opportunities for controlling the duration and rate of Leidenfrost heat transfer and propulsion by tuning the droplet’s size and contamination.

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.

Electrical Suppression of Film Boiling During Quenching

2016 ◽  
Author(s):  
Arjang Shahriari ◽  
Mark Hermes ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
Electric Fields ◽  
Boiling Heat Transfer ◽  
Cooling Curve ◽  
Vapor Layer ◽  
Steam Generation ◽  
Voltage Dependent ◽  
Order Of Magnitude ◽  
Leidenfrost Effect ◽  
Solid Liquid Interface

Boiling heat transfer impacts the performance of various industrial processes like quenching, desalination and steam generation. At high temperatures, boiling heat transfer is limited by the formation of a vapor layer at the solid-liquid interface (Leidenfrost effect), where the low thermal conductivity of the vapor layer inhibits heat transfer. Interfacial electrowetting (EW) fields can disrupt this vapor layer to promote liquid-surface wetting. This concept works for a variety of quenching media including water and organic solvents. We experimentally analyze EW-induced disruption of the vapor layer, and measure the resulting enhanced cooling during quenching. Imaging is employed to visualize the fluid-surface interactions and understand boiling patterns in the presence of an electrical voltage. It is seen that EW fundamentally changes the boiling pattern, wherein, a stable vapor layer is replaced by intermittent wetting of the surface. This switch in the heat transfer mode substantially reduces the cool down time. An order of magnitude increase in the cooling rate is observed. An analytical model is developed to extract instantaneous voltage dependent heat transfer rates from the cooling curve. The results show that electric fields can alter and tune the traditional cooling curve. Overall, this study presents a new concept to control the mechanical properties and metallurgy, by electrical control of the quench rate.

Modeling the Influence of Marangoni Flows on the Leidenfrost State on Solid and Liquid Substrates

2018 ◽  
Author(s):  
Arjang Shahriari ◽  
Palash V. Acharya ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
Layer Thickness ◽  
Nucleate Boiling ◽  
Vapor Layer ◽  
Boiling Regime ◽  
First Order ◽  
Leidenfrost Effect ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Marangoni Flows

Boiling heat transfer affects various processes related to energy, water and manufacturing. In the film boiling regime, heat transfer is substantially lower than in the nucleate boiling regime, due to the formation of a vapor layer at the solid-liquid interface (Leidenfrost effect). In this work, we present analytical modeling of the Leidenfrost state of droplets on solid and liquid substrates. A key aspect of this study is the focus on surface tension gradients on the surface of a liquid (Leidenfrost droplet or liquid substrate), which actuate thermo-capillary driven Marangoni flows. It is noted that this work develops a first-order simplified model, which assumes a uniform vapor layer thickness. The presence of Marangoni flows has non-trivial implications on the resulting thickness of the Leidenfrost vapor layer. Our analysis shows that the pumping effect generated in the vapor layer due to Marangoni flows can significantly reduce the Leidenfrost vapor layer thickness.

Study on heat transfer characteristics of liquid droplet radiator: With VS without inter-droplets coupling

2021 ◽  
Vol 156 ◽  
pp. 108199
Author(s):  
Di Huang ◽  
Kewei Ning ◽  
Fulong Zhao ◽  
Jian Deng ◽  
Xiaoyu Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Liquid Droplet ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Parametric investigation of radiation heat transfer and evaporation characteristics of a liquid droplet radiator

2020 ◽  
Vol 106 ◽  
pp. 106214 ◽  
Author(s):  
Hao Qin ◽  
Chenglong Wang ◽  
Dalin Zhang ◽  
Wenxi Tian ◽  
G.H. Su ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Liquid Droplet ◽  
Radiation Heat Transfer ◽  
Radiation Heat ◽  
Parametric Investigation

scholarly journals Evaporation of water: evaporation rate and collective effects

2016 ◽  
Vol 798 ◽  
pp. 774-786 ◽  
Author(s):  
Odile Carrier ◽  
Noushine Shahidzadeh-Bonn ◽  
Rojman Zargar ◽  
Mounir Aytouna ◽  
Mehdi Habibi ◽  
...  
Keyword(s):  
Evaporation Rate ◽  
Scaling Law ◽  
Solid Substrate ◽  
Collective Effects ◽  
Water Evaporation ◽  
Length Scale ◽  
Onset Of Convection ◽  
Cooperative Effects ◽  
Evaporative Flux ◽  
Drop Size Distributions

We study the evaporation rate from single drops as well as collections of drops on a solid substrate, both experimentally and theoretically. For a single isolated drop of water, in general the evaporative flux is limited by diffusion of water through the air, leading to an evaporation rate that is proportional to the linear dimension of the drop. Here, we test the limitations of this scaling law for several small drops and for very large drops. We find that both for simple arrangements of drops, as well as for complex drop size distributions found in sprays, cooperative effects between drops are significant. For large drops, we find that the onset of convection introduces a length scale of approximately 20 mm in radius, below which linear scaling is found. Above this length scale, the evaporation rate is proportional to the surface area.

Natural Convection in Evaporating Minute Drops

1982 ◽  
Vol 104 (4) ◽  
pp. 656-662 ◽  
Author(s):  
Nengli Zhang ◽  
Wen-Jei Yang
Keyword(s):  
Room Temperature ◽  
Evaporation Rate ◽  
Flow Structures ◽  
Interfacial Flow ◽  
Flat Plates ◽  
Liquid Drops ◽  
Ripple Formation ◽  
Air Interface ◽  
Flow Map ◽  
Interface Type

Interfacial flow structures in small liquid drops evaporating on flat plates are cinematographically investigated using the methods of direct photography and laser shadowgraphy. Various liquids of relatively low boiling point were evaporated on glass and copper plates at room temperature. The laser shadowgraph records the flow patterns simultaneously at both the liquid-air interface and the liquid-solid interface, from which the evaporation rate is determined. It reveals the existence of three distinct flow structures at the liquid air interface: stable, substable, and unstable. An interfacial flow map is constructed. The direct photography is employed to study the morphology during the entire process of the unstable-interface type evaporation. The mechanism of ripple formation which enhances the evaporation rate is found to be caused by hydrophilicity of the liquid.

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