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11.
H. W. Jackson 《Journal of Low Temperature Physics》2007,146(3-4):329-392
Quantized vortices in liquid 4 He are treated quantum mechanically with realistic many-body model wave functions in variational calculations for energy
and core structure at T = 0 K. A rectilinear vortex and both small and large vortex rings are studied. Calculated results indicate that rotons are
not just small-quantized vortex rings. We compare our results for quantized vortices with experimental data and with theoretical
results calculated by others. Correlated basis functions and standard statistical mechanics are used in treating thermohydrodynamic
properties of flowing liquid 4 He. The Helmholtz potential is evaluated for a model of the flowing liquid that includes phonons and interacting rotons.
Characteristics of this potential are discussed. The physical nature of negative superfluid density is explained. Superfluid
density, entropy, and specific heat for liquid He-II are evaluated using our theory and the results are compared with experimental
data. Very good agreement is found, except in a small temperature range near the λ transition. We indicate that results obtained
here can be used in extending the theory to include thermally excited vortices and to investigate the possible role of vortices
in accounting for the λ transition in liquid 4 He.
相似文献
12.
通过刚性模型风洞测压试验,对4种不同圆角率(即圆角半径与模型短边迎风宽度之比分别为0、5%、10%和20%)的矩形截面高层建筑表面风荷载特性进行研究。对比了不同圆角率下建筑表面的风压分布与相关特性:圆角处理使得建筑迎风面边缘倒圆角处出现较大平均风压、极值风吸力和脉动风压;在侧风面上,平均与脉动风压梯度变化范围随圆角率的增大而逐渐减小,且横向相关性明显增强。分析了建筑顺风向与横风向的整体风力,圆角处理通过促进再附着从而减小尾流宽度,可降低高层建筑的顺风向阻力和倾覆弯矩,降幅随着圆角半径的增大而提升,同时,横风向升力和倾覆弯矩也将有所下降。 相似文献
13.
《分离科学与技术》2012,47(12):2479-2495
Abstract A helical flow module with an inner rod mounted membrane was designed and built to reduce gel layer deposit and membrane fouling during microfiltration. Controlled centrifugal instabilities resulting from flow in a helically grooved channel, as well as the leakage flow between adjacent grooves, generated secondary vortex flows. The permeation fluxes for helical modules with Dean vortex flow were compared with flat crossflow modules at different operating pressures, concentrations, and feed flow rates. The permeation flux of the helical module for a feed solution containing 0.3 wt% kaolin solution at 1.2 bar was 57% higher than that of the flat module. Moreover, in addition to secondary vortex flow, compressed air was introduced to the membrane module. The increase in flux for the helical module with air injection was significant: the flux enhancements at 1.3 bar, 2 L‐solution/min and 1.3 L‐air/min for 0.1 wt% solutions of kaolin and bentonite were 47 and 73%, respectively. 相似文献
14.
Patrick M. LaheyDonald A. Drew 《Chemical engineering science》2002,57(24):5161-5173
Perturbation methods are used to study the bifurcation of Couette flow to Taylor vortices in the presence of a small amount of suction flow through the inner cylinder. Taylor vortex flow is described as a small amplitude expansion of the velocity and pressure near the critical Gortler parameter. The suction flow modifies the critical G?rtler number, stabilizing the original Couette flow. 相似文献
15.
16.
The temperature dependence of the critical current density at high temperatures and in weak applied magnetic field for YBa2Cu3O7–y
ceramic samples with a pronounced granular character is analyzed. The experimental results can be explained in terms of thermally activated motion of the intergrain Josephson vortices at grain boundaries, which may be an indication that the actual limiting factor for the critical current density in ceramic samples results from a weak pinning force density for the intergrain vortices rather than from the weak-link quenching. 相似文献
17.
Mohammad Mirhosseini Brandon Rodenburg Mehul Malik Robert W. Boyd 《Journal of Modern Optics》2014,61(1):43-48
AbstractFree-space communication allows one to use spatial mode encoding, which is susceptible to the effects of diffraction and turbulence. Here, we discuss the optimum communication modes of a system while taking such effects into account. We construct a free-space communication system that encodes information onto the plane-wave (PW) modes of light. We study the performance of this system in the presence of atmospheric turbulence, and compare it with previous results for a system employing orbital-angular-momentum (OAM) encoding. We are able to show that the PW basis is the preferred basis set for communication through atmospheric turbulence for a system with a large Fresnel number product. This study has important implications for high-dimensional quantum key distribution systems. 相似文献
18.
应用流场协同理论的多纵向涡强化换热管 总被引:4,自引:0,他引:4
应用流场协同理论研发了两种多纵向涡强化换热管———不连续双斜向内肋管和交叉缩放椭圆管,分析了其强化换热的物理机制。数值模拟和实验结果表明,当Re=500-2300 时,与考虑进口段效应的圆形截面管(L D=300)相比,不连续双斜向内肋管的换热增强250%~650%,阻力增加120% 300%;交叉缩放椭圆管Nu 可提高200%~500%,沿程阻力增加100%~350%;当Re=2300~5×104 时,与圆管相比,不连续双斜向内肋管换热可增强110%~240%,阻力增加120%~240%;交叉缩放椭圆管换热可增强35%~170%,阻力增加130%~160%。两种新型强化换热管具有优良的换热性能,可广泛应用于电力、石化、建筑供热等行业。图7参10 相似文献
19.
Effect of fluid thermal properties on the heat transfer characteristics in a double-pipe helical heat exchanger 总被引:2,自引:0,他引:2
Timothy J. Rennie Vijaya G.S. Raghavan 《International Journal of Thermal Sciences》2006,45(12):1158-1165
Heat transfer characteristics of a double-pipe helical heat exchanger were numerically studied to determine the effect of fluid thermal properties on the heat transfer. Two studies were performed; the first with three different Prandtl numbers (7.0, 12.8, and 70.3) and the second with thermally dependent thermal conductivities. Thermal conductivities of the fluid were based on a linear relationship with the fluid temperature. Six different fluid dependencies were modeled. Both parallel flow and counterflow configurations were used for the second study.Results from the first study showed that the inner Nusselt number was dependent on the Prandtl number, with a greater dependency at lower Dean numbers; this was attributed to changing hydrodynamic and thermal entry lengths. Nusselt number correlations based on the Prandtl number and a modified Dean number are presented for the heat transfer in the annulus. Results from the second part of the study showed that the Nusselt number correlated better using a modified Dean number. The counterflow configuration had higher heat transfer rates than the parallel flow, but the ratio of these differences was not different when comparing thermally dependent properties and thermally independent properties. 相似文献
20.
页岩含油率是页岩油资源评价的基本参数,但其测定方法尚无统一认识,制约了页岩油资源潜力的评估准确率。选取松辽盆地页岩油井的密闭取心页岩样品,依次开展二维核磁共振(T1—T2 NMR)、有机溶剂蒸馏萃取(Dean Stark)、热解气相色谱(PY-GC)和岩石热解(Rock-Eval)4种页岩含油率测定实验。对比分析表明,T1—T2 NMR法与Dean Stark法的页岩含油率测试结果相近,均高于PY-GC法,Rock-Eval法测试结果最低。样品处理方式对页岩含油率的测试结果具有重要影响,块状样品的测试含油率明显高于粉碎样品。综合分析认为,T1—T2 NMR法测试页岩含油率结果的可靠性高,具有时间短、样品无损、样品非均质性影响小等特点,是分析页岩含油率的最优手段,具有良好的推广应用前景。建立了不同热演化成熟度页岩的含油率恢复系数、轻烃恢复系数及校正图版,对于湖相I型有机质页岩发育区开展页岩含油率分析具有重要参考价值。 相似文献