PERFORMANCE AND FLOW CHARACTERISTICS OF NOZZLES FOR INITIALLY SUBCOOLED HOT WATER (INFLUENCE OF TURBULENCE AND DECOMPRESSION RATE)

The purpose of this study was to improve the performance characteristics of a convergent-divergent nozzle for flashing expansion of initially subcooled hot water. The slip between the vapor and liquid along the divergent passage and the maximum nonequilibrium pressure drop at the nozzle throat(this is related to the thermal nonequilibrium) cause a decline in the nozzle efficiency. To decrease the maximum pressure drop,a nozzle with thin wires just upstream of the throat and a nozzle with a smaller convergent angle were manufactured and tested. Initially subcooled hot water at an inlet pressure of 0.47MPa and inlet temperatures of 409.9 to 421.8K (inlet subcoolings of 0.9-12.9K) were used with the nozzle back pressures ranging from 5 to 101.3kPa. The following results were attained:(1)the maximum nonequilibrium pressure drop at the throat decreased and the thrust coefficient increased by 10％; (2)the thrust coefficient was found to be independent of the inlet subcooling and exit stream-expansion ratio; (3)a correlation between the ratio of the exit pressure to the inlet pressure and the appropriate exit stream-expansion ratio was obtained empirically;and (4)the critical flow rate was found to be lower than that for an ordinary convergent-divergent nozzle

Magnetoresistance in Heavily Underdoped YBa_2Cu_3O_{6+x}: Antiferromagnetic Correlations and Normal-State Transport

We report on a contrasting behavior of the in-plane and out-of-plane magnetoresistance (MR) in heavily underdoped antiferromagnetic (AF) YBa_2Cu_3O_{6+x} (x<0.37). The out-of-plane MR (I//c) is positive over most of the temperature range and shows a sharp increase, by about two orders of magnitude, upon cooling through the Neel temperature T_N. A contribution associated with the AF correlations is found to dominate the out-of-plane MR behavior for H//c from far above T_N, pointing to the key role of spin fluctuations in the out-of-plane transport. In contrast, the transverse in-plane MR (I//a(b);H//c) appears to be small and smooth through T_N, implying that the development of the AF order has little effect on the in-plane resistivity.Comment: 4 pages, 5 figures, accepted for publication in Phys.Rev.Let

EVALUATION OF EXHAUST GAS FROM BIO-DIESEL FUEL ENGINE

Joint Research on Environmental Science and Technology for the Eart

Normal-state resistivity anisotropy in underdoped RBa_2Cu_3O_{6+x} crystals

We have revealed new features in the out-of-plane resistivity rho_c of heavily underdoped RBa_2Cu_3O_{6+x} (R=Tm,Lu) single crystals, which give evidence for two distinct mechanisms contributing the c-axis transport. We have observed a crossover towards "metal-like" (d rho_c/d T > 0) behavior at the temperature T_m which quickly increases with decreasing doping. The "metal-like" conductivity contribution dominates at T < T_m and provides a saturation of the resistivity anisotropy, rho_c / rho_{ab}. The antiferromagnetic ordering is found to block this "metal-like" part of the c-axis conductivity and complete decoupling of CuO_2 planes, which may be the reason of superconductivity disappearance.Comment: RevTex, 4 pages including 4 eps figures. To be published in Phys.Rev.Let

SONOLYTICAL PRODUCTION OF BIO-DIESEL FUEL FROM NON-EDIBLE VEGETABLE OIL

Joint Research on Environmental Science and Technology for the Eart

Coherence, incoherence and scaling along the c axis of YBa_2Cu_3O_{6+x}

The optical properties of single crystals of YBa_2Cu_3O_{6+x} have been examined along the c axis above and below the critical temperature (T_c) for a wide range of oxygen dopings. The temperature dependence of the optically-determined value of the dc conductivity (\sigma_{dc}) in the normal state suggests a crossover from incoherent (hopping-type) transport at lower oxygen dopings (x \lesssim 0.9) to more coherent anisotropic three-dimensional behavior in the overdoped (x \approx 0.99) material at temperatures close to T_c. The assumption that superconductivity occurs along the c axis through the Josephson effect yields a scaling relation between the strength of the superconducting condensate (\rho_{s,c}, a measure of the number of superconducting carriers), the critical temperature, and the normal-state c-axis value for \sigma_{dc} just above T_c; \rho_{s,c} \propto \sigma_{dc} T_c. This scaling relation is observed along the c axis for all oxygen dopings, as well as several other cuprate materials. However, the agreement with the Josephson coupling model does not necessarily imply incoherent transport, suggesting that these materials may indeed be tending towards coherent behavior at the higher oxygen dopings.Comment: Six pages with four figures and one tabl