The effect of subcooling and length of hydrophobic-spot periphery on nucleate pool boiling heat transfer from TiO 2 -coated surface with and without PTFE (polyetatafluoroethylene) hydrophobic circle spots at intermediate heat flux has been examined. The experiments are performed with liquid subcooling ranging from 0-20 K and heat transfer block used were TiO 2 -coated copper block with a PTFE hydrophobic circle spot with various diameters with total area of PTFE being constant. Bubble nucleation and behavior were observed by using high-speed camera. The results showed that the heat transfer performance of surfaces with PTFE hydrophobic circle spot is better than superhydrophilic surface in overall condition. Furthermore, the heat transfer performance decreases under subcooled condition for all surfaces. Increase in peripheral length of hydrophobic-spot enhances the heat transfer performance.

The elastic-plastic fracture toughness, JIc, of SM490B carbon steel plate was investigated in air and 0.7 MPa hydrogen gas. JIc tests were conducted in accordance with the JSME standard, JSME S001 (1981). JIc was much smaller in hydrogen at a displacement velocity of V = 2 × 10 -3 mm/s (JIc = 10.0 kJ/m 2 ) than in air at V = 2 × 10 -3 mm/s (JIc = 248.6 kJ/m 2 ). JIc in air does not satisfy the validity requirement. In hydrogen, surprisingly, a further decrease in V did not decrease JIc, but increased it. JIc in hydrogen at V = 2 × 10 -5 mm/s was 60.9 kJ/m 2 . The large and small values of JIc in air and hydrogen corresponded to the fracture morphology. In air at V = 2 × 10 -3 mm/s, a critical stretched zone, SZWc, was formed at the tip of the fatigue pre-crack, followed by dimples. In hydrogen at V = 2 × 10 -3 mm/s, quasi-cleavage instead of SZWc and dimples were formed at the pre-crack tip. In hydrogen at V = 2 × 10 -5 mm/s, SZWc was formed at the precrack tip, followed by dimples again. This elastic-plastic fracture toughness behavior was analyzed assuming HESFCG (hydrogen-enhanced successive fatigue crack growth), which is proposed by the authors to explain the acceleration of fatigue crack growth rate in the presence of hydrogen. The elastic plastic fracture toughness test shown in 0.7 MPa hydrogen gas at V = 2 × 10 -3 mm/s is the same as that shown in a fatigue crack growth test in 0.7 MPa hydrogen gas at a number of cycles of n = 1 and stress ratio of R = 0; and thus JIc in 0.7 MPa hydrogen gas at V = 2 × 10 -3 mm/s is not the real elastic-plastic fracture toughness. We conclude that the real elastic-plastic fracture toughness in 0.7 MPa hydrogen gas can be determined by fracture toughness testing in 0.7 MPa hydrogen gas at V = 2 × 10 -5 mm/s.

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The effects of hydrophobic circle spot size and subcooling on local film boiling phenomenon from the copper surface with single PTFE (Polytetrafluoroethylene) hydrophobic circle spot at low heat flux has been investigated. The experiments were performed using pure water as the working fluid and subcooling ranging from 0 and 10K. The heat transfer surfaces are used polished copper block with single PTFE hydrophobic circle spot of diameters 2, 4 and 6 mm, respectively. A high-speed camera was used to capture bubble dynamics and disclosed the sequence of the process leading to local film boiling. The result shows that local films boiling occurs on the PTFE circle spot at low heat flux and was triggered by the merging of neighboring bubbles. The study also showed that transition time required for change from nucleate boiling regime to local film boiling regime depends on the diameter of the hydrophobic circle spot and the subcooling. A stable local film boiling occurs at the smallest diameter of hydrophobic spot. Subcooling cause the local film boiling occur at negative superheat and oscillation of bubble dome.

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