A Study of Critical Heat Flux of Butanol Aqueous Solution

2009 ◽  
Author(s):  
Shotaro Nishiguchi ◽  
Masahiro Shoji
Keyword(s):  
Heat Transfer ◽  
Aqueous Solution ◽  
Surface Tension ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Phase Point ◽  
Liquid Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Some alcohol aqueous solution such as butanol shows nonlinear surface tension dependence. Namely, contrary to ordinary liquid or solution, surface tension increases with temperature at the range of high liquid temperature. At the triple-phase point on a heated surface, the thermo-capillary force acts for the liquid to wet the heated surface, so the solutions are sometimes called as “self-rewetting liquid”. Self-rewetting liquids may prohibit the dry-out of a heated surface so that the heat transfer performance would be enhanced. For this reason, applications of self-rewetting liquids to heat transfer devices such as heat pipes are actively studied in recent years. However, the heat transfer characteristics of boiling of self-rewetting liquids are not fully understood. In the present research, a boiling experiment of butanol aqueous solution was performed on a heated wire in order to make clear the fundamental heat transfer characteristics, especially Critical Heat Flux (CHF), by changing solution concentration density and liquid temperature in a wide range. Bubbling aspects were observed by high-speed video camera with the rate of 1000 frames per second. It is found from the experiment that CHF is generally enhanced when compared to the case of pure water. CHF increases with concentration density at any temperatures. CHF generally increases with subcooling but at low subcooling region, it once decreases and then increases after taking a minimum. It is also found that peculiar boiling takes place where many tiny bubbles generate and bubbles are unlikely to coalesce. At high subcoolings, the mode of boiling similar to the so-called MEB (Micro-bubble Emission Boiling) was observed. These results of the present experiment indicate a possible application of butanol aqueous solution to high-performance-cooling-devices utilizing micro-channels because generating bubbles are small enough so that the pressure loss of the coolant may be small and the heat transfer rate is sufficiently high even at the saturated condition.

Critical Heat Flux of Butanol Aqueous Solution

2008 ◽  
Author(s):  
Shotaro Nishiguchi ◽  
Naoki Ono ◽  
Masahiro Shoji
Keyword(s):  
Heat Transfer ◽  
Aqueous Solution ◽  
Surface Tension ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Pure Water ◽  
Liquid Temperature ◽  
Heat Transfer Characteristics ◽  
Heated Wire

Aqueous solutions of some alcohols such as butanol show peculiar temperature dependence of surface tension. Contrary to ordinary liquids or solutions, the surface tension increases with temperature at the range of high liquid temperature. So at the triple-phase point on a heated surface, the thermo-capillary force acts for the liquid to wet the heated surface, so the solutions are sometimes called as “self-wetting liquids”. Self-wetting liquids may prohibit the dry-out of a heated surface so that the heat transfer performance would be enhanced. For this reason, applications of self-wetting liquids to heat transfer devices such as heat pipes are actively studied in recent years. However, the heat transfer characteristics of boiling of self-wetting liquids are not fully understood. In the present research, a boiling experiment of butanol aqueous solution was performed on a heated fine wire in order to make clear the fundamental heat transfer characteristics. A heated wire configuration is easy to observe the phenomena and easy to address the fundamental issues of boiling. In the present experiment, nucleate boiling heat transfer were investigated with special attention to critical heat flux (CHF), by changing solution concentration and temperature. Bubbling aspects were observed by high-speed video camera. It is found from the experiment that CHF is generally enhanced 20 to 50% when compared to the case of pure water. It is also found that at a certain concentration and at a certain liquid temperature, peculiar boiling takes place where very small bubbles are emitted from the heated wire and CHF enhancement becomes very large from 2 to 3 times higher than CHF of pure water. The temperature when the peculiar boiling takes place is close to boiling temperature of the solution. These results suggest the possibility of application of aqueous solution to high-performance cooling devices utilizing micro-scaled channels because generating bubbles are small enough so that the pressure loss of the flow passage is small and heat transfer rate is very large.

Fluid Motion and Heat Transfer of Boiling With Impinging Flow in a Mini-Tube With Nonlinear Thermocapillary Solutions

2010 ◽  
Author(s):  
Naoki Ono ◽  
Atsushi Hamaoka ◽  
Yuta Otsubo
Keyword(s):  
Heat Transfer ◽  
Aqueous Solution ◽  
Surface Tension ◽  
Heat Flux ◽  
Liquid Layer ◽  
Heated Surface ◽  
Pure Water ◽  
Heated Area ◽  
Impinging Flow ◽  
Butanol Solution

Boiling heat transfer with impinging flow can be an effective way for cooling a small heated area such as CPUs and laser emitting devices. In the phenomena the movement of liquid layer on the heated surface strongly affects the detachment of boiling bubbles and the heat flux. In this study, nonlinear thermocapillary solutions such as button aqueous solutions were applied to this type of boiling with impinging flow aiming to promote heat transfer. These solutions have special characteristics that the surface tension increases as the temperature is raised over some temperature. It is expected that this tendency about the surface tension will promote the wetting of the heated surface and the detachment of boiling bubbles. In the experiment, T-shaped mini tubes were built with quartz tubes and used for flow boiling. The inner diameter of the tube was 2 mm and the outer diameter was 4 mm. The liquid flow impinged at the junction point where small area was heated by using a conducting thin film coated at the outer surface of the tube. The test fluids were butanol aqueous solution and pure water. The flow rate of the liquid was the order of 1 ml/min, the concentration of the butanol aqueous solution was 7.15 wt %. The liquid motion was observed by CCD video camera system. It was found from the experiment that the motion of the liquid layer of the butanol solution at the impinging area was very different from that of pure water. The layer of the butanol solution tended to extend to the hotter part of the heated area. In another experiment for precisely fixing the imposed heat flux value, T-shaped mini channel with small copper surface installed for heating the fluid was prepared. The cross section of the channel was rectangular shape of 3 mm × 3 mm, and the entire channel was made of insulating polymer material. It was found that the heat transfer of the boiling with impinging flow in using butanol solution was more promoted than that in using pure water.

Effects of Size of Simulated Microelectronic Chips on Boiling and Critical Heat Flux

1988 ◽  
Vol 110 (3) ◽  
pp. 728-734 ◽  
Author(s):  
K.-A. Park ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Thin Foil ◽  
Circuit Board ◽  
Boiling Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Saturated Boiling ◽  
Bottom Heater

Microelectronic chips were simulated with thin foil heaters supplied with d-c power and arranged in two vertical configurations: flush mounted on a circuit board substrate or protruding from the substrate about 1 mm. Heat transfer characteristics (midpoint) were obtained with varying height (1 mm to 80 mm) and width (2.5 mm to 70 mm) in R-113. Two types of incipient boiling temperature overshoot were observed with saturated boiling. The inception of boiling depended greatly on the location of the active boiling sites on the heater. For arrays, the inception of boiling for the top heater took place at lower superheat than for the bottom heater. Heater size had no effect on established boiling, in contrast to results reported previously in the literature. The critical heat flux for wide heaters increased with decreasing heater height, as expected. The critical heat flux also increased with decreasing width. Correlations are presented that describe these effects.

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