Study on Critical Heat Flux of High Velocity Liquid Flow

2007 ◽  
Author(s):  
Hisashi Sakurai ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
High Velocity ◽  
Film Flow ◽  
Flow Boiling ◽  
Flow Channel ◽  
Heat Transfer Surface ◽  
Flat Channel

Critical heat flux experiments of subcooled, thin, and high-velocity water flow were performed. The test flow channel was rectangular. The width of the flow channel was 2 mm and the height was 0.5 mm or 0.2 mm. The heat transfer surface was 2 mm × 2 mm. At the low heat flux, tinny bubbles were formed at the downstream part of the test heating surface. As the heat flux was increased, the bubble diameter increased and the coalescence of bubbles occurred. Then, the coalesced bubbles grew larger to cover the whole area of the heat transfer surface. Finally, the dried area appeared at the downstream end of the heat transfer surface to cause the critical heat flux condition. The critical heat flux was considerably higher than that of the subcooled flow boiling for the usual-size pipe as well as those of the saturated and the subcooled pool nucleate boiling. As the flow rate was increased, the period between the onset of boiling and the critical heat flux occurrence became narrow. The critical heat flux in the present experiments where the heat transfer surface was located at the just downstream of the flat channel outlet was considerably larger than those in the previous experiments where the heat transfer surface was located at the outlet end of the flat channel or the upstream of the outlet. By producing a fast jet along the surface and providing enough space for generated bubbles to leave from the surface, the critical heat flux was considerably augmented. Critical heat fluxes obtained in the present experiments were in in-between of the correlations for the flowing-upward film flow and for the flowing-downward film flow. The increasing trend for the flow rate was similar to that of the correlations.

Flow Behavior and Flow Boiling Heat Transfer in Thin-Rectangular Mini-Channels

2008 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Tomonari Yamada
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Pattern ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Channel ◽  
Heat Transfer Surface ◽  
Liquid Slug ◽  
Flux Condition

Boiling heat transfer of thin-rectangular channels of the width of 10 mm has been examined. The height of the flow channel was in a range from 0.6 mm to 0.4 mm. Experimental fluid was water. Bubbly flow, slug flow, semi annular flow and annular flow were observed. The flow pattern transition agreed well with the Baker flow pattern map for the usual sized flow path. The critical heat flux was lower than the value of the usual sized flow channel. The Koizumi and Ueda method predicted well the trend of the critical heat flux of the present experiments. At the critical heat flux condition, the heat transfer surface was covered by liquid slug, a large bubble pushed away the liquid slug, a dry area was formed on the heat transfer surface and then liquid slug came around to cover the heat transfer surface again. This process repeated rapidly. Following this observation, a heat transfer surface temperature calculation model at the critical heat flux condition was proposed. The calculated result re produced the experimental result.

scholarly journals Flow Boiling Heat Transfer to a Dielectric Coolant in a Microchannel Heat Sink

2005 ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Thermal Design ◽  
Microchannel Heat Sink ◽  
Flow Boiling Heat Transfer

This paper presents an experimental study of flow boiling heat transfer in a microchannel heat sink. The dielectric fluid Fluorinert FC-77 is used as the boiling liquid after it is fully degassed. The experiments were performed at three flow rates ranging from 30 to 50 ml/min. The heat transfer coefficients, as well as the critical heat flux, were found to increase with flow rate. Wall temperature measurements at three locations (near the inlet, near the exit, and in the middle of heat sink) reveal that wall dryout first occurs near the exit of the microchannels. The ratio of heat transfer rate under critical heat flux conditions to the limiting evaporation rate was found to decrease with increasing flow rate, asymptotically approaching unity. Predictions from a number of correlations for nucleate boiling heat transfer in the literature are compared against the experimental results to identify those that provide a good match. The results of this work provide guidelines for the thermal design of microchannel heat sinks in two-phase flow.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.

Study on Boiling Heat Transfer in Narrow and Flat Space

2008 ◽  
Author(s):  
Takaaki Oshikawa ◽  
Hisashi Sakurai ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flat Space ◽  
Flow Channel ◽  
Heat Transfer Surface ◽  
Large Bubble ◽  
Channel Height ◽  
Flux Condition ◽  
Space Experiments

Boiling heat transfer experiments were performed by using ethanol as test fluid. A heat transfer surface was at the bottom wall of the flow channel. Two types of experiments were conducted; horizontal-rectangular-narrow flow channel experiments and horizontal-narrow-flat space experiments. Experiments were conducted at the pool condition and at 0.1 MPa. In the rectangular-narrow flow channel experiments, the width of the flow channel was varied in the range of 1.0 ∼ 2.0 mm and the height of the flow channel was varied in the range of 0.5 mm ∼ 8 mm. The length of the flow channel was 30 mm. The diameter of the heat transfer surface was the same as the width of the flow channel. Both ends of the flow channel were opened to wide space filled with liquid. In the experiments of the narrow-flat space experiments, the heat transfer surface was at the center of the flat space of 20 mm × 20 mm or 30 mm × 30 mm. The size of the heat transfer surface diameter was 3.0 mm. The space was varied in the range of 0.5 mm ∼ 8 mm. Pool-type experiments of no flat space were also conducted for comparison. The circumference of the narrow-flat space was opened to wide space filled with liquid. In the rectangular-narrow flow channel experiments, a large bubble periodically left from the heat transfer surface and moved to the both ends of the flow channel. As the heat flux was increased, the critical heat flux condition was finally reached. The critical heat flux decreased with a decrease in the flow channel height. When the flow channel height was large, the critical heat flux was close to the pool boiling value. In the experiments of the narrow-flat space experiments, when the space was wide, bubbles generated on the heat transfer surface left freely from the flat space. The heat transfer characteristics were close to those of the pool boiling. As the space became narrow, a large bubble sat on the heat transfer surface, which resulted in the critical heat flux condition. When the space was narrow, the initiation of the bubble generation on the heat transfer surface immediately resulted in the critical heat flux condition.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

Study on Subcooled-Forced Flow Boiling Heat Transfer and Critical Heat Flux of Solid-Water Two-Phase Mixture

1999 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Manabu Mochizuki
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Liquid Layer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Forced Flow ◽  
Superheated Liquid ◽  
Flow Boiling Heat Transfer

Abstract The effect of solid particle introduction on subcooled-forced flow boiling heat transfer and a critical heat flux was examined experimentally. In the experiment, glass beads of 0.6 mm diameter were mixed in subcooled water. Experiments were conducted in a range of the subcooling of 40 K, a velocity of 0.17–6.7 m/s, a volumetric particle ratio of 0–17%. When particles were introduced, the growth of a superheated liquid layer near a heat trasnsfer surface seemed to be suppressed and the onset of nucleate boiling was delayed. The particles promoted the condensation of bubbles on the heat transfer surface, which shifted the initiation of a net vapor generation to a high heat flux region. Boiling heat trasnfer was augmented by the particle introduction. The suppression of the growth of the superheated liquid layer and the promotion of bubble condensation and dissipation by the particles seemed to contribute that heat transfer augmentation. The wall superheat at the critical heat flux was elevated by the particle introduction and the critical heat flux itself was also enhanced. However, the degree of the critical heat flux improvement was not drastic.

scholarly journals Characteristics of Flow Boiling Heat Transfer and Critical Heat Flux in a Vertical Tube with a Wire Coil.

2001 ◽  
Vol 67 (653) ◽  
pp. 128-134
Author(s):  
Keishi TAKESHIMA ◽  
Terushige FUJII ◽  
Nobuyuki tAKENAKA ◽  
Hitoshi ASANO ◽  
Takamitsu KONDO
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Flow Boiling Heat Transfer ◽  
Wire Coil
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