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.

Dynamic and Controlled Tuning of the Boiling Curve During Quenching

2016 ◽  
Author(s):  
Arjang Shahriari ◽  
Mark Hermes ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
Cooling Rate ◽  
Electric Fields ◽  
Vapor Layer ◽  
Steam Generation ◽  
Transfer Enhancement ◽  
Heat Transfer Mode ◽  
Electrical Control ◽  
Transfer Mode ◽  
Quenching Media

Boiling influences many industrial processes like quenching, desalination and steam generation. Boiling heat transfer at high temperatures is limited by the formation of a vapor layer between the solid and fluid. Low thermal conductivity of this vapor layer inhibits heat transfer. Electrowetting (EW) fields can breakdown this vapor layer to promote wetting, and this concept works for many quenching media including water and organic solvents. This work studies the suppression of this vapor layer and measures the resulting heat transfer enhancement during quenching of metals. We image the fluid-surface interactions and boiling patterns in the presence of an electrical voltage. EW fields replace film boiling with periodic wetting-rewetting cycles and thus fundamentally change the heat transfer mode. The increased wettability substantially reduces the cool down time. The cooling rate can by increased by as much as 3X. The results show that electric fields can dynamically tune the classical quenching curve. This study opens up new avenues to control the metallurgy of metals via electrical control of the cooling 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.

Film Boiling Heat Transfer Enhancement via Electrostatic Leidenfrost State Suppression

2015 ◽  
Author(s):  
Arjang Shahriari ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Dissipation ◽  
Nuclear Reactor ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Vapor Layer ◽  
Steam Generation ◽  
Boiling Regime ◽  
Enhanced Boiling

Boiling heat transfer has enormous impact on the effectiveness of various industrial processes like steam generation, desalination, and nuclear reactor operations. Heat transfer in the film boiling regime is significantly reduced as compared to the nucleate boiling regime due to the existence of a vapor layer at the solid-liquid interface (Leidenfrost effect). This vapor layer degrades heat transfer by up to two orders of magnitude and causes dryout, which can result in severe temperature excursions. This work maps out the heat transfer benefits of electrostatic suppression of the Leidenfrost state. Electrical suppression of the Leidenfrost state is observed for a variety of liquids, including organic solvents, water and electrically conducting salt solutions. Successful Leidenfrost state suppression is observed with moderate voltages even at ultrahigh temperatures exceeding 550 °C. Elimination of the vapor layer increases heat dissipation capacity of film boiling by more than one order of magnitude; up to 45X enhancement was measured in this work. This work also introduces the concept of tunable film boiling heat transfer. Overall, electrically-enhanced boiling can enable a new class of technologies for active control and enhancement of boiling heat transfer, with various applications in energy systems.

A review on effects of magnetic fields and electric fields on boiling heat transfer and CHF

2019 ◽  
Vol 151 ◽  
pp. 11-25 ◽  
Author(s):  
Sajjad Ahangar Zonouzi ◽  
Habib Aminfar ◽  
Mousa Mohammadpourfard
Keyword(s):  
Heat Transfer ◽  
Magnetic Fields ◽  
Electric Fields ◽  
Boiling Heat Transfer

scholarly journals ELETRIC FIELD ENHANCEMENT AND DETERIORATION OF BOILING HEAT TRANSFER AND CRITICAL HEAT FLUX IN DIELECTRIC FLUIDS

2001 ◽  
Vol 1 (1) ◽  
pp. 32
Author(s):  
P. M. Carrica ◽  
V. Masson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Electric Fields ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Two Phase ◽  
Boiling Regime ◽  
Dielectric Fluids

We present the results of an experimental study of the effects of externally imposed electric fields on boiling heat transfer and critical heat flux (CHF) in dielectric fluids. The study comprises the analysis of geometries that, under the effects of electric fields, cause the bubbles either to be pushed toward the heater or away from it. A local phase detection probe was used to measure the void fraction and the interfacial impact rate near the heater. It was found that the critical heat flux can be either augmented or reduced with the application of an electric field, depending on the direction of . In addition, the heat transfer can be slightly enhanced or degraded depending on the heat flux. The study of the two-phase flow in nucleate boiling, only for the case of favorable dielectrophoretic forces, reveals that the application of an electric field reduces the bubble detection time and increases the detachment frequency. It also shows that the two-phase flow characteristics of the second film boiling regime resemble more a nucleate boiling regime than a film boiling regime.

scholarly journals ELETRIC FIELD ENHANCEMENT AND DETERIORATION OF BOILING HEAT TRANSFER AND CRITICAL HEAT FLUX IN DIELECTRIC FLUIDS

2002 ◽  
Vol 1 (1) ◽  
Author(s):  
P. M. Carrica ◽  
V. Masson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Electric Fields ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Two Phase ◽  
Boiling Regime ◽  
Dielectric Fluids

We present the results of an experimental study of the effects of externally imposed electric fields on boiling heat transfer and critical heat flux (CHF) in dielectric fluids. The study comprises the analysis of geometries that, under the effects of electric fields, cause the bubbles either to be pushed toward the heater or away from it. A local phase detection probe was used to measure the void fraction and the interfacial impact rate near the heater. It was found that the critical heat flux can be either augmented or reduced with the application of an electric field, depending on the direction of . In addition, the heat transfer can be slightly enhanced or degraded depending on the heat flux. The study of the two-phase flow in nucleate boiling, only for the case of favorable dielectrophoretic forces, reveals that the application of an electric field reduces the bubble detection time and increases the detachment frequency. It also shows that the two-phase flow characteristics of the second film boiling regime resemble more a nucleate boiling regime than a film boiling regime.

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.

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