Subcooled boiling regime map for water at low saturation temperature and subatmospheric pressure

2020 ◽  
Vol 118 ◽  
pp. 110150 ◽  
Author(s):  
K. Wojtasik ◽  
R. Rullière ◽  
Z. Krolicki ◽  
B. Zajaczkowski ◽  
J. Bonjour
Keyword(s):  
Saturation Temperature ◽  
Subcooled Boiling ◽  
Subatmospheric Pressure ◽  
Boiling Regime ◽  
Regime Map

Evaporation and Nucleate Boiling of an Individual Droplet on Surfaces

2005 ◽  
Author(s):  
X. D. Wang ◽  
G. Lu ◽  
X. F. Peng ◽  
B. X. Wang
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Bubble Dynamics ◽  
Imaging System ◽  
Dynamical Behavior ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Dynamical Process ◽  
Boiling Regime ◽  
Film Evaporation

A visual study was conducted to investigate the evaporation and nucleate boiling of a water droplet on heated copper, aluminum, or stainless surfaces with temperature ranging from 50°C to 112°C. Using a high-speed video imaging system, the dynamical process of the evaporation of a droplet was recoded to measure the transient variation of its diameter, height, and contact angle. When the contact temperature was lower than the saturation temperature, the evaporation was in film evaporation regime, and the evaporation could be divided into two stages. When the surface temperature was higher than the saturation temperature, the nucleate boiling was observed. The dynamical behavior of nucleation, bubble dynamics droplet were detail observed and discussed. The linear relationships of the average heat flux vs. temperature of the heated surfaces were found to hold for both the film evaporation regime and nucleate boiling regime. The different slopes indicated their heat transfer mechanism was distinct, the heat flux decreased in the nucleate boiling regime more rapidly than in the film evaporation due to the strong interaction between the bubbles.

CFD Modeling of Single Bubble Collapse in Subcooled Boiling

2013 ◽  
Author(s):  
Eyitayo J. Owoeye ◽  
DuWayne Schubring
Keyword(s):  
Open Source Software ◽  
Saturation Temperature ◽  
Cfd Modeling ◽  
Bubble Collapse ◽  
Rise Velocity ◽  
Subcooled Boiling ◽  
Fluid System ◽  
Bubble Rise Velocity ◽  
Pressure Steam ◽  
Parameter Ranges

The open-source software OpenFOAM has been employed to better understand the transport, deformation, and collapse of single, isolated bubbles in subcooled boiling. High pressure steam-water was selected as the fluid system of interest due to its relevance to the power generation industry. Ranges of bubble size, subcooling, pressure/saturation temperature, and mesh refinement have been employed. Both quantitative (bubble rise velocity and collapse times) and qualitative (bubble shape) results are discussed across the parameter ranges studied.

Modeling of Film Boiling and Film Vaporization on Engine Piston Tops

2012 ◽  
Author(s):  
Timothy H. Lee ◽  
Dimitrios C. Kyritsis ◽  
Chia-fon F. Lee
Keyword(s):  
Heat Flux ◽  
Liquid Fuel ◽  
Combustion Process ◽  
Infinite Plate ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Spark Ignition Engine ◽  
Film Boiling ◽  
Engine Fuel ◽  
Boiling Regime

Engine-out HC emissions resulting from liquid fuel, which escapes from the combustion process, provides the motivation to better understand the film vaporization in a combustion chamber. Previous work theorized that the removal of liquid fuel from the combustion cycle was a result of the increase in film vaporization time due to the Leidenfrost phenomenon. Currently, KIVA 3V predicts a continuous decrease in vaporization time for piston top films. The objective of this work is to improve the KIVA 3V film vaporization model through the inclusion of established boiling correlations, and thus, the Leidenfrost phenomenon. Experimental results have been reviewed from which expressions encompassing high acceleration effects for the nucleate boiling regime and the film boiling regime were investigated, implemented, and validated. Validation was conducted using published experimental data sets for boiling heat flux. As a result of the implementation, a noticeable increase in heat flux occurred due to high accelerations for films in saturated film boiling in both nucleate and film boiling. Computational simulations were conducted using a semi-infinite plate and a direct-injection spark-ignition engine. The semi-infinite plate provided a controlled environment which could separate the effects of pressure and acceleration on film boiling heat flux, film vaporization rates, and film vaporization times. The effect of decreased film vaporization rates, during the Leidenfrost phenomenon, was observed to decrease with increasing acceleration. Finally, the engine computations were used to provide the first film boiling and film vaporization rates for engine fuel films at temperatures above saturation temperature. As a result of this work, a film vaporization model capable of improved prediction of vaporization rates of piston top films in saturated boiling conditions has been created.

NUMERICAL ANALYSIS OF CAVITATION SUSCEPTIBILITY FOR STEAM GENERATOR INTEGRAL PREHEATER TUBES

2014 ◽  
Vol 3 (01) ◽  
pp. 37-46 ◽  
Author(s):  
S. Laroche ◽  
L. Sun ◽  
J. Pietralik
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Steam Generator ◽  
Cavitation Erosion ◽  
Saturation Temperature ◽  
Fluid Temperature ◽  
Baffle Plate ◽  
Subcooled Boiling ◽  
Local Flow ◽  
Flow And Heat Transfer

A new tube degradation mechanism was observed in a recirculating steam generator (SG) with an integral preheater tube at the clearance gap between the tube and the preheater baffle. The general pattern of the damage and material composition in the degraded region suggested that the degradation was cavitation erosion. Cavitation erosion occurs when vapour bubbles exist or form in the flowing liquid and then these bubbles collapse violently in the vicinity of a solid wall. The bubbles collapse when they contact water that is sufficiently subcooled, i.e., below the saturation temperature. In the clearance gap between the tube and the preheater baffle, secondary fluid flow exists due to the pressure difference across the baffle plate. Meanwhile, heat transfer occurs from the primary-side fluid to the secondary-side fluid within this clearance gap, driven by the primary-to-secondary temperature difference. Factors such as the tube position in the baffle hole and fouling may influence the local flow and heat transfer conditions and can cause subcooled boiling that results in cavitation. This paper presents a numerical analysis of flow and heat transfer phenomena to determine the factors contributing to cavitation erosion of tubes in the preheater of a recirculating SG. The analysis used the THIRST code for a 3-dimensional thermalhydraulic simulation of steam generator and the ANSYS Fluent® code for detailed calculations of flow and heat transfer in the clearance gaps. A detailed temperature distribution in the gap was obtained using this analysis to determine the regions where subcooled boiling could occur by comparing the local fluid temperature with its saturation temperature. The susceptibility to cavitation was found to increase with increased inclination (i.e., tilt) and eccentricity (i.e., off-centre) of the tube in the baffle plate gap, and increased fouling on baffle plate surfaces. This methodology could be applied to analyze the cavitation susceptibility for other preheater types with this “tube to baffle plate” gap, as these preheaters might have conditions where boiling followed by the rapid condensation of the steam bubbles are present.

Numerical Simulation of Dynamics and Heat Transfer Associated With a Single Bubble in Subcooled Boiling and in the Presence of Noncondensables

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Jinfeng Wu ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Thermocapillary Convection ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Saturation Temperature ◽  
Subcooled Boiling ◽  
Bubble Liquid ◽  
Subcooled Liquid ◽  
Noncondensable Gases ◽  
Induced Flow

During phase change at the bubble-liquid interface, under subcooled boiling conditions, noncondensable gases dissolved in the liquid will be injected into the bubble along with vapor. Due to heat transfer into subcooled liquid, vapor will condense in the upper regions of the bubble while noncondensables will continue to accumulate. Subsequently, thermocapillary convection caused by nonuniform saturation temperature at the interface may occur. The aim of this work is to investigate the effects of noncondensables on heat transfer and bubble dynamics. The numerical results show that the effects of noncondensables on 5°C subcooled boiling of water are minor in terms of the equilibrium bubble diameter and overall Nusselt number. However, induced flow pattern around the bubble is altered, especially under reduced gravity conditions.

A Comparative Study of Subcooled Flow Boiling in Uniform, Diverging Cross-Section and Segmented Finned Microchannels

2014 ◽  
Author(s):  
Yogesh K. Prajapati ◽  
Manabendra Pathak ◽  
Mohd. Kaleem Khan
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Electronics Cooling ◽  
Subcooled Boiling ◽  
Heat Transfer Characteristics ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Uniform Cross Section

In this work an experimental investigation has been performed to assess the heat transfer characteristics during subcooled flow boiling in diverging and segmented finned microchannels relevant to applications in electronics cooling systems. Experiments have been also performed in uniform cross-section microchannels to compare their performances with other two types of channels configurations. Arrays of microchannel consisting of 12 numbers of channels with rectangular cross-section have been fabricated on individual copper block for these three different geometrical configurations. Deionized water has been used as the working fluid in the experiment. Experiments have been performed mostly in subcooled boiling regions relevant to cooling of electronic components where bulk fluid was below the saturation temperature and the surface temperature was around the saturation temperature of the coolant. The heat transfer characteristics of all three configurations have been compared in terms of heat transfer coefficient and thermal instability during highly subcooled and developed subcooled flow boiling. Although diverging channel performs significantly better in saturated and superheated regions of boiling with high heat flux as observed in literature, in present work its performance has been found slightly better in subcooled boiling regions compared to uniform cross-section channel. Segmented finned channels have shown the best performance both in sensible heating and subcooled region and thus demonstrate high potential for electronics cooling applications.

Heater Size and Gravity Based Pool Boiling Regime Map: Transition Criteria Between Buoyancy and Surface Tension Dominated Boiling

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Rishi Raj ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Pool Boiling ◽  
Threshold Value ◽  
Gravity Level ◽  
Capillary Length ◽  
Boiling Regime ◽  
Transition Criteria ◽  
Regime Map ◽  
Transition Criterion

A pool boiling regime map demarcating the boundary between the surface tension and buoyancy dominated boiling regimes is developed based on heater size and gravity. For large heaters and/or high gravity conditions, boiling is dominated by buoyancy, and the ebullition cycle dominates the contribution to heat transfer. As the gravity level and/or heater size is decreased, surface tension forces become increasingly dominant, and a decrease in heat transfer is observed. The ratio of the heater size Lh (length of a side for a square heater) to the capillary length Lc is found to be a suitable parameter to define the transition criterion between these regimes. Based on the data obtained using FC-72 and pentane, the threshold value of Lh/Lc above which pool boiling is buoyancy dominated was found to be about 2.1. This transition criterion was found to be the same for gravity levels between ∼0g–1.7g and liquid subcoolings between 6.6°C and 26.6°C.

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