Experimental study on turbulent natural convection heat transfer in water with sub-millimeter-bubble injection

Kitagawa, Atsuhide; Kitada, Kenji; Hagiwara, Yoshimichi

doi:10.1007/s00348-010-0838-8

Cited by 23 publications

(6 citation statements)

References 15 publications

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“…Figure (5) shows that thermal boundary layer thickness is inversely proportional to the hydrogen injection rate. The results show that maximum percentage decrease of thermal boundary layer of (40%).…”

Section: Resultsmentioning

confidence: 99%

Experimental study of Hydrogen Bubbles Injection Effect on Thermal Boundary Layer for Laminar Water Flow in Vertical Cylinder

Ezzat¹

2016

IJCA

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Temperature measurements are performed to clarify the effects of sub-millimeter bubble injection on the thermal boundary layer thickness in water flowing in upward direction along a cylindrical shape 0.7m length and 0.065m diameter test section. The test section is subjected to constant heat flux of (24,000w/m 2 ).In particular the research focuses on the relationship between the bubble injection rate and their effect on decreasing thermal boundary layer thickness. This effect led to enhance the heat transfer rate and decrease test section wall temperature. Three pairs of bubble injection electrodes are used in the experiments fixed at equally spaced distances of 0.2m between each pair of them. The experiments based on Reynolds number of (6780) which simulates low water velocity for better distinguishing the enhancements governed the experimental results. Water temperature at seven radial positions from test section center to the wall are measured along the test section in addition to the measurement of water bulk and wall temperatures at these points. K-type 100 lm thermocouples with ±0.12 o C accuracy are used for temperature measurements. The results showed thermal boundary layer thickness is inversely proportional to the hydrogen injection rate and that local heat transfer coefficient is proportional to the later with different proportionality rates. The results showed maximum percentage decrease of thermal boundary layer of (40%) and maximum percentage increase in heat transfer rate of (15.7%). Accordingly the boiling safety factor based on maximum wall temperature showed maximum increase of (9%). These results covered the adopted values of heat flux, Reynolds number and hydrogen bubble injection rate.

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Section: Resultsmentioning

confidence: 99%

Experimental study of Hydrogen Bubbles Injection Effect on Thermal Boundary Layer for Laminar Water Flow in Vertical Cylinder

Ezzat¹

2016

IJCA

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“…Thus the interface location as well as the velocities of the droplets and tracer particles could be obtained. Recently, Kitagawa et al [41] applied this technique to a turbulent natural-convection boundary layer with bubbles. Figure 6a displays the profiles of the liquid mean velocities in the upward direction along a heated wall and the wall-normal direction.…”

Section: Recent Developments In Experimental Methodsmentioning

confidence: 98%

Effects of Bubbles, Droplets or Particles on Heat Transfer in Turbulent Channel Flows

Hagiwara

2010

Flow Turbulence Combust

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Adding small immiscible substances of low volume to turbulent channel water flow modifies turbulence and turbulent heat transfer. We examine the effects on the modifications of the ratios of the physical properties of substances to the physical properties of the carrier fluid, the particle Reynolds number, the Stokes number and the Weber number. We discuss the applicability and importance of the local, instantaneous values of these non-dimensional numbers. In particular, the maxima and minima for the time change in the Stokes number are found to correspond to the minima and maxima respectively for the time change of the wallnormal distance of a heavy, solid particle in turbulent flow in a vertical channel. We also investigate the effectiveness of the recent developments of particle-tracking velocimetry and particle-resolved direct numerical simulation, in increasing the understanding of changes in turbulence.

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“…Gul and Akpinar [6] studied on heat transfer and exergy loss in oscillating circular pipes. Kitagawa et al [7] performed experiments on turbulent natural convection heat transfer in water with sub-millimeter bubble injection. Maximum heat transfer coefficient ratio of 1.9 was obtained in that study.…”

Section: Introductionmentioning

confidence: 99%

Experiments on air bubbles injection into a vertical shell and coiled tube heat exchanger; exergy and NTU analysis

Dizaji

Jafarmadar

Abbasalizadeh

2015

Energy Conversion and Management

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Experimental study on turbulent natural convection heat transfer in water with sub-millimeter-bubble injection

Cited by 23 publications

References 15 publications

Experimental study of Hydrogen Bubbles Injection Effect on Thermal Boundary Layer for Laminar Water Flow in Vertical Cylinder

Experimental study of Hydrogen Bubbles Injection Effect on Thermal Boundary Layer for Laminar Water Flow in Vertical Cylinder

Effects of Bubbles, Droplets or Particles on Heat Transfer in Turbulent Channel Flows

Experiments on air bubbles injection into a vertical shell and coiled tube heat exchanger; exergy and NTU analysis

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