Simultaneous Boiling Visualization and Heat Transfer Measurement of Two Adjacent Water Impinging Jets

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Jungho Lee ◽  
Sang Gun Lee
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
High Speed ◽  
Nucleate Boiling ◽  
Impinging Jets ◽  
High Speed Imaging ◽  
Transfer Measurement ◽  
Rapid Temperature ◽  
Wall Jet Flow ◽  
Heat Transfer Measurement

The effect of jet-to-jet distance of two adjacent jets on boiling heat transfer was investigated by a simultaneous boiling visualization and heat transfer measurement. The hydrodynamics of two adjacent jets were visualized by the high-speed imaging and the 4K camera on unheated surface. The surface temperature of the hot steel plate was estimated by formulating 2-D inverse heat conduction, which was measured through the flat-plate heat flux gauge. The jet Reynolds number was fixed at Re = 17,000 and the jet-to-jet distance of two adjacent jets was set to the three different jet-to-jet distances (p/d = 10, 20 and 30). The wall jet flow interference between two adjacent impinging jets forms a vertical fountain at its boundary. The more scattered water droplets are observed from the fountain due to the higher intensity at the p/d = 10. The flow interaction becomes to reduce its momentum as increasing the p/d. The boiling visualization shows which boiling mode starts to occur and turns to be disappeared from film boiling to nucleate boiling on the hot surface. The measured surface temperature has a good agreement with the corresponding boiling visualization. The closer jet distance (lower p/d) shows the rapid temperature gradient along the interaction, which provides much higher cooling rate in a multiple jet nozzle when designing an intensive quenching device.

Nucleate Boiling From Micro-Machined Surfaces

2003 ◽  
Author(s):  
Adrian M. Holland ◽  
Colin P. Garner
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Imaging System ◽  
Laser System ◽  
Ccd Camera ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Frame Rate ◽  
High Speed Imaging ◽  
Machined Surfaces

This paper discusses the production and use of laser-machined surfaces that provide enhanced nucleate boiling and heat transfer characteristics. The surface features of heated plates are known to have a significant effect on nucleate boiling heat transfer and bubble growth dynamics. Nucleate boiling starts from discrete bubbles that form on surface imperfections, such as cavities or scratches. The gas or vapours trapped in these imperfections serve as nuclei for the bubbles. After inception, the bubbles grow to a certain size and depart from the surface. In this work, special heated surfaces were manufactured by laser machining cavities into polished aluminium plates. This was accomplished with a Nd:YAG laser system, which allowed drilling of cavities of a known diameter. The size range of cavities was 20 to 250 micrometers. The resulting nucleate pool boiling was analysed using a novel high-speed imaging system comprising an infrared laser and high resolution CCD camera. This system was operated up to a 2 kHz frame rate and digital image processing allowed bubbles to be analysed statistically in terms of departure diameter, departure frequency, growth rate, shape and velocity. Data was obtained for heat fluxes up to 60 kW.m−2. Bubble measurements were obtained working with water at atmospheric pressure. The surface cavity diameters were selected to control the temperature at which vapour bubbles started to grow on the surface. The selected size and spacing of the cavities was also explored to provide optimal heat transfer.

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).]

Boiling Visualization of Two Adjacent Impinging Jets on Hot Steel Plate

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Jungho Lee ◽  
Sangho Sohn ◽  
Sang Gun Lee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Flat Plate ◽  
Boiling Heat Transfer ◽  
Steel Plate ◽  
Nucleate Boiling ◽  
Impinging Jets ◽  
High Heat Flux ◽  
Plate Heat

The simultaneous measurement between the boiling visualization and the boiling heat transfer characteristics by two adjacent impinging jets on hot steel plate was made by the experimental technique that has a function of high-temperature flat-plate heat flux gauge. The 22 K-type thermocouples were installed at 1 mm below the surface of flat-plate heat flux gauge. The 2-D inverse heat conduction was formulated to solve the surface temperature and heat flux. The boiling visualization was synchronized with a 4K video camera which was meaningful to understand complex boiling heat transfer phenomena. The heat flux gauge was uniformly heated up to 900°C by induction heating. The successive boiling images show where the nucleate boiling starts to occur on hot surface and the film boiling turns to be collapsed. The measured surface temperature and heat flux distribution agrees well with the corresponding boiling visualization: While heat transfer at the stagnation point shows a maximum heat flux, the interaction between two adjacent impinging jets exhibits a relative high heat flux and a steep temperature gradient until the end of boiling heat transfer at which single-phase convection occurs near 200°C.

scholarly journals Operating temperatures of oil-lubricated medium-speed gears: Numerical models and experimental results

2003 ◽  
Vol 217 (2) ◽  
pp. 87-106 ◽  
Author(s):  
H Long ◽  
A A Lord ◽  
D T Gethin ◽  
B J Roylance
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Rotational Speed ◽  
High Speed ◽  
Applied Load ◽  
Frictional Heat ◽  
Transfer Coefficients ◽  
Gear Teeth ◽  
Heat Transfer Coefficients

This paper investigates the effects of gear geometry, rotational speed and applied load, as well as lubrication conditions on surface temperature of high-speed gear teeth. The analytical approach and procedure for estimating frictional heat flux and heat transfer coefficients of gear teeth in high-speed operational conditions was developed and accounts for the effect of oil mist as a cooling medium. Numerical simulations of tooth temperature based on finite element analysis were established to investigate temperature distributions and variations over a range of applied load and rotational speed, which compared well with experimental measurements. A sensitivity analysis of surface temperature to gear configuration, frictional heat flux, heat transfer coefficients, and oil and ambient temperatures was conducted and the major parameters influencing surface temperature were evaluated.

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