Wetting Front Tracking During Metal Quenching Using Array of Jets

2010 ◽  
Author(s):  
Khalid H. M. Abdalrahman ◽  
Umair Alam ◽  
Eckehard Specht
Keyword(s):  
Heat Flux ◽  
Nucleate Boiling ◽  
Temperature Data ◽  
Film Boiling ◽  
Wetting Front ◽  
Inverse Algorithm ◽  
Maximum Heat ◽  
Water Jets ◽  
Maximum Heat Flux ◽  
Hot Surface

Metal quenching is a commonly used heat treatment technique, e.g. Direct Chill aluminum casting, quenching of steel for obtaining desired micro-structures. Film boiling, transition boiling, nucleate boiling and forced convection are the mechanisms of heat transfer during quenching. When the coolant strikes the hot metal surface during quenching, the surface can be divided into two distinct zones which are dry and wet zones. Heat transfer in dry zone is dominated by film boiling and the wet zone is influenced by transition boiling, nucleate boiling and forced convection. Wetting front is the boundary zone which separates the dry and wet regions. Wetting front is a thin region of coolant in which the transition and nucleate boiling occurs. Within a wetting front, the heat flux leaving from the hot surface reaches it global maximum. The speed of the wetting front indicates the quench ability of the hot surface for the corresponding flow conditions and the coolant. Wetting front tracking is more important for the prediction of surface temperature during quenching. This research works presents the combined numerical and experimental aspects of the heat flux estimation during the quenching process. At any instant, the position of the wetting front is simply assumed as the location of maximum heat flux. This assumption implicitly treats the wetting front as a line instead of area. The location of wetting front and its velocity at every instant are determined by using the experimental temperature data and the inverse algorithm. Experimental setup and temperature measurement technique are explained in detail. The developed inverse algorithm predicts the quenched side temperature and heat flux from the measured side temperature. A two-dimensional Inverse Heat Conduction Problem (IHCP) is solved through the non iterative Finite Element Method (FEM). The considered quenching technique for the study, based on the method of coolant supplied which is array of water jets. One kind of coolant used in this study is tap water. Aluminum 2024, Inconel, and Nickel are the three different materials considered for the analysis. A rectangular plate made of Nickel with dimension 140 × 70 × 2 mm, using the same dimensions of the Inconel. As in the case of the use of Aluminum, the thickness is the only change to 3 mm, the plate quenched by array of water jets with velocities 0.9 m/s, 1.2 m/s, 1.5 m/s and 1.8 m/s. The measured temperature data are further processed through the inverse finite element technique for the estimation of heat flux leaving from the quenched surface. The position of maximum heat flux changes with time which indicates the movement of wetting front. In this work, four different coolant velocities are employed, and the change in coolant velocity strongly affects the heat flux and wetting front movement.

Heat Flux Estimation in Direct Chill Casting Using Experimental and Inverse Finite Element Method

2008 ◽  
Author(s):  
Ashok Kumar Nallathambi ◽  
Umair Alam ◽  
Eckehard Specht
Keyword(s):  
Finite Element Method ◽  
Heat Flux ◽  
Finite Element ◽  
Ferrous Metal ◽  
Nucleate Boiling ◽  
Direct Chill ◽  
Wetting Front ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Element Method

In Direct Chill (DC) non-ferrous metal casting, water is used as a cooling medium to extract the heat from the solidified outer layer of the ingot which supports the inner molten metal. Insufficient or excessive water supply changes the heat flux which is favorable for the growth of micro-cracks. This work presents the combined experimental and numerical technique to estimate the heat flux in the DC nickel casting. Experimental techniques are explained for the measurement of temperature. A two-dimensional Inverse Heat Conduction Problem (IHCP) is solved through the non-iterative Finite Element Method (FEM) using the experimental temperature data. Wetting front which separates the film boiling and nucleate boiling zone, changes the order of the heat flux. Maximum heat flux position and its propagation velocity are plotted as a function of time. It is demonstrated that increase in water velocity decreases the maximum heat flux and delays the wetting front movement.

Boiling Heat Transfer Characteristics of Rotary Hollow Cylinders with In-Line and Staggered Multiple Arrays of Water Jets

2021 ◽  
Author(s):  
Mohammad Jahedi ◽  
Bahram Moshfegh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Maximum Heat ◽  
Water Jets ◽  
Maximum Heat Flux ◽  
Inner Surface ◽  
Hollow Cylinders

Abstract Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (ΔTsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area-averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

Influence of Jet Velocities and Material Properties in Quenching of Metal with Array of Jets

2015 ◽  
Vol 1090 ◽  
pp. 63-68
Author(s):  
Peng Zhao ◽  
Sabariman ◽  
Eckehard Specht ◽  
Xin Nan Song
Keyword(s):  
Heat Flux ◽  
Material Properties ◽  
Research Work ◽  
Wetting Front ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Quenching Process ◽  
Leidenfrost Temperature ◽  
Jet Velocities ◽  
Over Time

In this research work, the influence of jet velocities and different kind of metals during the quenching process with the use of array of jets was tested. Three different jet velocities i.e. 0.9m/s, 1.2m/s, and 1.8m/s were applied for the quenching of copper K12. Experiments with different kind of metals are using AA6082, Nickel, and Copper K12 samples. The influence of jet velocities and material properties was characterized by figuring out the trend of propagation of Leidenfrost Point (LFP) and maximum Heat Flux (maxHF) point over time. In addition, Leidenfrost Temperature (LFT), maxHF values with the corresponding DNB temperature as well as the width of wetting front over position were also presented. The results show that the jet velocities and the material properties significantly influence the boiling characteristics in a metal quenching process with array of jets.

Boiling Heat Transfer Characteristics of Staggered-array Water Impinging Jets on Hot Steel Plate

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Sang Gun Lee ◽  
Jin Sub Kim ◽  
Dong Hwan Shin ◽  
Jungho Lee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Boiling Heat Transfer ◽  
Steel Plate ◽  
Nucleate Boiling ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Maximum Heat ◽  
Maximum Heat Flux

The effect of staggered-array water impinging jets on boiling heat transfer was investigated by a simultaneous measurement between boiling visualization and heat transfer characteristics. The boiling phenomena of staggered-array impinging jets on hot steel plate were visualized by 4K UHD video camera. The surface temperature and heat flux on hot steel plate was determined by solving 2-D inverse heat conduction problem, which was measured by the flat-plate heat flux gauge. The experiment was made at jet Reynolds number of Re = 5,000 and the jet-to-jet distance of staggered-array jets of S/Dn = 10. Complex flow interaction of staggered-array impinging jets exhibited hexagonal flow pattern like as honey-comb. The calculated surface heat transfer profiles show a good agreement with the corresponding boiling visualization. The peak of heat flux accords with the location which nucleate boiling is occurred at. In early stage, the positions of maximum heat flux locate at the stagnation point of each jet as the relatively low surface temperature is shown at their positions. At the elapsed time of 10 s, the flat shape of heat flux profile is formed in the hexagonal area where the interacting flow uniformly cools down the wetted surface. After that, the wetted area continuously enlarges with time and the maximum heat flux is observed at its peripheral. These results point out that the flow interaction of staggered-array jets effectively cools down the closer area around jets and also show an expansion of nucleate boiling and suppression of film boiling during water jet cooling on hot steel plate. [This work was supported by the KETEP grant funded by the Ministry of Trade, Industry & Energy, Korea (Grant No. 20142010102910).]

Experimental Investigation of Influence of Dissolved Salts and Surfactant on Heat Transfer in Atomized Spray Quenching of Metal

2010 ◽  
Author(s):  
Umair Alam ◽  
Khalid Abd alrahman ◽  
Eckehard Specht
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Measurement ◽  
Pure Water ◽  
The Other ◽  
Film Boiling ◽  
Wetting Front ◽  
Maximum Heat ◽  
Boiling Regime ◽  
Front Position

Spray quenching is widely used in industrial applications. In atomized spray quenching (ASQ), water and air are supplied to the nozzle at a certain flow rate and pressure to produce a full cone spray consisting of discrete droplets. Impingement density of spray i.e. coolant mass flow per unit area per second is considered to be the most influential parameter for heat transfer. Impingement density varies with radius and so as the heat flux. Water quality is altered by adding five different salts i.e. NaCl, Na2SO4, NaHCO3, Na2CO3, and MgSO4 in de-ionized water with various concentrations. On the other hand, a surfactant Ethoxylated ester, which is commonly added in cooling water in cast houses of metals, is added to pure water in different concentrations i.e 50, 100, 200 and 500ppm. A circular disc made of Nickel of thickness 2mm is heated to 600°C and sprayed on one side by atomized spray and the temperature distribution with respect to time is measured using Infrared camera on the other side of the disc. By this IR thermography, transient temperature measurement can be done within the window of 320×80 pixels with a minimum pixel real distance of 1mm on the sheet surface. Frequency of measurement is 150Hz. Since the temperature measurement and cooling sides are opposite at 2mm thickness apart, inverse heat conduction problem is solved by applying finite element method for calculating temperature and heat flux on the quenched side of metal sheet with respect to space and time. It has been observed that increasing the concentration of salts increase the leidenfrost point and shortens the film boiling regime. While addition of surfactants decrease the leidenfrost point and prolong the film boiling regime. Maximum heat flux position is considered as the wetting front position. There is an abrupt variation of heat flux at wetting front position due to the change of boiling phenomenon. Wetting front velocity has been compared for salt solutions, surfactant and de-ionized or pure water.

Characteristics of Wetting Temperature and Maximum Heat Flux During Spray Cooling of Hot Surface

2010 ◽  
Author(s):  
Yuichi Mitsutake ◽  
Masanori Monde
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
Initial Temperature ◽  
Thermal Inertia ◽  
Spray Cooling ◽  
Inverse Heat Conduction ◽  
Quenching Temperature ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Hot Surface

An experimental investigation has been done to elucidate the effects of mass flux G, degree of subcooling ΔTsub and initial solid temperature Tb0 on transient spray cooling of a downward facing φ89 mm hot block surface. The spray impact diameter was adjusted to φ110mm and φ36mm which simulate uniform and non-uniform spray cooling of the surface. The block made of copper, brass and carbon steel at an initial temperature of 200–500 °C was cooled with subcooled water and ethanol spray. The subcooling was from 10 to 80 K and the mass flux was from 1 to 72 kg/m2s. Surface temperature and surface heat flux were evaluated with an axisymmetric 2D inverse heat conduction analysis. A transient transition regime was characterized with a wetting temperature and a quenching temperature. The wetting and quenching temperatures were correlated fairly with GΔTsub. Effects of G, ΔTsub, Tb0 and a thermal inertia of the solid (ρcλ)s on a maximum heat flux are evaluated.

Void Fraction Measurements During Saturated Pool Boiling of Water on Partially Wetted Vertical Surfaces

1989 ◽  
Vol 111 (3) ◽  
pp. 731-738 ◽  
Author(s):  
S. P. Liaw ◽  
V. K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Void Fraction ◽  
Vertical Wall ◽  
Nucleate Boiling ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Static Contact ◽  
Layer Increase ◽  
Gamma Densitometer

Void fraction profiles adjacent to a vertical wall 6.3 cm wide and 10.3 cm high were measured during nucleate boiling. The experiments were conducted in saturated water at 1 atm pressure. In the experiments, the wettability of the surface was varied by controlling the degree of oxidation of the surface. Static contact angle was used as an indicator of the surface wettability. The void fraction was measured with a gamma densitometer. The experimental results show that the maximum void fraction occurs about 1–1.5 mm away from the heater surface. The wall void fraction, the maximum void fraction, and the thickness of the void layer increase with wall heat flux. It is found that for a given heat flux, the wall void fraction increases as the surface becomes less wettable, whereas the maximum heat flux decreases with increase in contact angle.

Enhancement of Mixing in a Micro TAS by Micro-Bubble Emission Boiling

2007 ◽  
Author(s):  
H. Kato ◽  
T. Kimura ◽  
K. Yamazaki ◽  
M. Yamaguchi
Keyword(s):  
Heat Flux ◽  
Nucleate Boiling ◽  
Mixing Efficiency ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Heat ◽  
Two Fluids ◽  
Maximum Heat Flux ◽  
Mixing Chamber ◽  
Micro Bubble

The mixing of two fluids is important in enhancing chemical reactions in a micro TAS. Some devices or methods are needed to enhance the mixing, because the Reynolds number is very low, on the order of 1. In the present research, we studied the possibility of using micro-bubble emission boiling. A heater made of a platinum wire of 30 micrometer was installed in a Y-shaped micro-channel whose cross sectional area was 2 mm × 0.5 mm. The heater was directly powered by electric current up to 1.5 A. The maximum heat flux was 7.47 MW/m2, which was well above the burnout heat flux. The subcool was 80 degrees and the velocity of fluid (colored water) was changed from 0.5 to 2.0 mm/s. When micro-bubble emission boiling occurred, the mixing was improved drastically. The mixing efficiency reached above 90% at v = 2.0 mm/s and q = 7.47MW/m2. In contrast, the mixing efficiency was poor in the case of normal nucleate boiling. The effect of the mixing chamber was also examined.

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