| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
An experimental study has been made of heat transfer characteristics and homogeneous nucleation with an impinging water jet. The experimental condition is varied from jet velocity of 3 to 15 m/s, liquid temperature of 20 to 95 ℃, jet diameter of 2 and 3 mm, and initial block temperature of 250 to 600 ℃. Three different materials of copper, brass and carbon steel are employed as tested block.
When the block temperature higher than Leidenfrost temperature is cooled by liquid, condition whether an occurrence of wetting high temperature surface appears or not, strongly depends on whether in the case that the surface temperature is kept higher than the thermodynamic limit of liquid superheat the cooling capacity is enough or not. For the case of cooling the surface higher than the thermodynamic limit of liquid superheat and enough cooling capacity of liquid, the wet and dry conditions are alternatively repeated at very short time during which the surface temperature gradually goes down. When
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the surface temperature becomes lower than the thermodynamic limit of liquid superheat, a stable wetting is confirmed on a limited area of the surface, namely near the center of impinging jet zone, but the wetted area never expand over the heated surface. This condition is lasting until the surface temperature reaches a surface temperature. We define this lasting time as a resident time, t^*, and then can determine the surface temperature, Tw^*, at the resident time. The resident time and the surface temperature can be predicted by the following equations,
(1)
(2)
After the resident time, the wetted area starts expanding to cover the entire surface. We can clarify how the surface temperature and surface heat flux change with moving the wetted area. For example, we can point out the position at which the maximum heat flux, q_<max>, appears within the wetted zone and can estimate the maximum heat flux by the following equation ;
(3)
where p, c and λ are density, heat capacity and thermal conductivity, respectively and q_c is critical heat flux under the steady cooling with impinging jet. Less
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