During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the in...During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.展开更多
Liquid ternary Fe47.5Cu47.5Sn5 alloy displayed dual solidification mechanisms when it was undercooled by up to 329 K （0.19TL）. Below a critical undercooling of about 196 K, it solidified just like a normal peritecti...Liquid ternary Fe47.5Cu47.5Sn5 alloy displayed dual solidification mechanisms when it was undercooled by up to 329 K （0.19TL）. Below a critical undercooling of about 196 K, it solidified just like a normal peritectic alloy, even though metastable phase separation occurred to a microscopic extent. Once bulk undercooling exceeds 196 K, macroscopic segregation played a domi- nant role in solidification. In both cases, the solidification process was always characterized by two successive peritectic trans- formations： firstly primary yFe dendrites reacted with liquid phase to form （Cu） phase, and subsequently the （Cu） phase reacted with residual liquid phase to yield β-Cu5.6Sn intermetallic compound. The primary yFe dendrites achieved a maximum growth velocity of 400 mm/s and experienced a growth kinetics transition as a result of macrosegregation. Since the （Cu） phase was both the product phase of the first peritectic transformation and also the reactant phase for the second peritectic transformation, it appeared as two layers in solidification microstructures due to the microsegregation of Sn solute. The boundary continuity between the macroscopically separated Fe-rich and Cu-ricb zones was enhanced with the increase of undercooling.展开更多
文摘During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51101123 and 50971105)the Fundamental Research Fund of Northwestern Polytechnical University (GrantNo. JC201050)
文摘Liquid ternary Fe47.5Cu47.5Sn5 alloy displayed dual solidification mechanisms when it was undercooled by up to 329 K （0.19TL）. Below a critical undercooling of about 196 K, it solidified just like a normal peritectic alloy, even though metastable phase separation occurred to a microscopic extent. Once bulk undercooling exceeds 196 K, macroscopic segregation played a domi- nant role in solidification. In both cases, the solidification process was always characterized by two successive peritectic trans- formations： firstly primary yFe dendrites reacted with liquid phase to form （Cu） phase, and subsequently the （Cu） phase reacted with residual liquid phase to yield β-Cu5.6Sn intermetallic compound. The primary yFe dendrites achieved a maximum growth velocity of 400 mm/s and experienced a growth kinetics transition as a result of macrosegregation. Since the （Cu） phase was both the product phase of the first peritectic transformation and also the reactant phase for the second peritectic transformation, it appeared as two layers in solidification microstructures due to the microsegregation of Sn solute. The boundary continuity between the macroscopically separated Fe-rich and Cu-ricb zones was enhanced with the increase of undercooling.
