No abstract available

No abstract available

No abstract available

[en] Fuel-element appendages affect the thermalhydraulic performance of a CANDU fuel channel by increasing its pressure drop and enhancing fuel-to-coolant heat transfer. The high cost of characterization of these effects through experiments provides incentive to develop reliable numerical methodologies by which to quantify relevant parametric trends. Recent studies at Chalk River Laboratories indicate that the current capabilities of Computational Fluid Dynamics (CFD) are adequate to assess the fuel-appendage effects under normal operating (single-phase) conditions from simulations alone. This paper describes the experimental work undertaken to provide data for validation of CFD models used in the numerical assessment of appendage effects, and presents preliminary results of a validation study completed with the TASCflow software. Heat transfer and pressure drop in single-phase flow through a vertical pipe obstructed by a cylindrical ring were investigated experimentally in the MR-7A loop at Chalk River Laboratories using Freon-134a as a coolant. The test section was a vertical 8 mm ID directly heated tube, made of Inconel 600. Two ring-shaped flow obstructions were tested; they reduced the flow area by 17.8% and 30%. The presence of the flow obstructions enhanced heat transfer up to 38% and 61%, respectively. These significant changes were observed in the downstream region, over a very short distance behind the obstruction. The tests were carried out within the mass flux range between 1 and 6 Mg/m²s, and the highest relative heat-transfer enhancement occurred at 1 Mg/m²s. The pressure drop increase due to the flow obstructions was characterized by the form loss factor, K, which was found to be 0.18 and 0.45, for the 17.8% and 30% rings, respectively. 6 refs., 1 tab., 10 figs

[en] Horizontal steam generators are typical parts of nuclear power plants with pressure water reactor type VVER. By means of this computer program, a detailed thermal-hydraulic study of the horizontal steam generator PGV-1000 has been carried out and a special attention has been paid to the thermal-hydraulics of the secondary side. A set of important steam generator characteristics has been obtained and analyzed. Some of the interesting results of the analysis are presented in the paper. (author)

[en] We present a model of coupling of shear flow to microscopic degrees of freedom in the lyotropic Smectic A (lamellar phase ). This coupling is then shown to produce macroscopic buckling instability analogous to well known undulation instability appearing in thermotropic smectics under dilatation in the direction perpendicular to the layers. The Iyotropic Lamellar phase is experimentally known to become unstable under shear flow. The instability occurs at shear rate γ ∼ 1sec^-1and the so called 'onions' (multi lamellar vesicles) are formed. We propose that the instability occurs in two stages. At the first stage, the layers are buckled by shear -induced microscopic tension σ ≅ η_eγd where η_e is an effective viscosity of the system (which can be very large :η_e ≅ 1000η_solvent) and d is all inter- layer spacing. As the membrane projected area cannot increase (for example, being sandwiched between defects) it has to buckle in the direction perpendicular to itself.There is a critical tension however due to energy cost of compression of layers in the buckled state and of bending and expansion of individual layers. Then one is able to calculate the buckling amplitude U_o and the wavevector k as a function of γ. Denoting K usual smectic bending modulus and B the compressional one, the result is that the transition occurs at σ ≅ T/D_d, where D is the width of a film. For σ - σ_c >> σ_c we have k ≅ √(8σ/3dB). At the second stage the buckled structure is deformed by shear (by coupling to Macroscopic degrees of freedom) nad eventually broken, resulting in the formation of onions. We speculate that the buckled state will become unstable when the relaxation time of the buckling structure τ_c ≅ η_c/Kk² is shorter than the one needed for shear to deform the structure to a degree that maxima are shifted to the position of neighboring minima. The estimate is γ ≅ Kk²(U₀k)^-1 which gives γ ∼ d^-a with 7/3 < a < 17/7 which is consistent with experimental data a= 2.4 ±: 0.4

[en] Critical heat flux (CHF) data were obtained for upward crossflow of R-114 in a heated staggered rod bundle. Data were obtained over a broad range of mass fluxes (135 to 1,221 kg/m² sec), inlet subcooling (0 to 55 C), and qualities (-0.42 to 0.92). The present work extends the available database to higher quality, inlet subcooling, and mass flux. The test section is 3.43 cm x 15.24 cm (1.35 in. x 6 in.) in cross section with a total length of 55.88 cm (22 inches) from the top of the inlet flow straightener to the perforated plate at the test section exit. The rod bundle has a triangular pitch with a diameter (D) of 0.635 cm (0.25 in), and a pitch to diameter (P/D) ratio of 1.5. The rod bundle has 165 rods with a 15.24 cm (6 in.) heated length arranged in 55 rows of three rods each. Unheated half rods were positioned on the walls of the test section to maintain the regular rod arrangement and prevent flow bypass along the gaps between the window and the first column of heated rods. A single instrumented heater was positioned five rows upstream from the bundle exit to determine CHF. The last three rows of rods in the bundle were unheated to prevent undetected dryout downstream of the CHF position. Temperature excursions due to CHF were sensed using four imbedded thermocouples (TC) in the heater rod. The four TC temperatures were continuously monitored on a strip chart recorder. The rod heat was gradually increased until CHF was detected. Overall, the data are in good agreement with the Jensen and Tang correlation in the range of application of this correlation. The local minima in CHF which occurs near zero quality is slightly lower in the present experiment than for the Jensen and Tang correlation. At high quality, CHF drops off more rapidly than the Jensen-Tang prediction. Data are now available to extend the existing correlations to higher quality, and higher inlet subcooling

[en] This textbook contains the following main topics: Heat conductivity, convection, condensation and evaporation, radiation heat transfer and heat exchangers. It includes the physical foundations for all these aspects and many examples. (WL)

[en] Formula which unifies with ±40% accuracy the experimental data on critical thermal loads under boiling on immersed lattice surfaces is given. The suggested dependence covers the experimental data for water, methyl, butyl and grain alcohol, for acetone and cooling agent

[en] In this paper an 'ad hoc' asymptotic approach is employed in order to study nonlinear wave propagation compatible with the non-diffusive version of the model of bubbly liquids introduced by Drumheller and Bedford [13]. A third order transport equation representing a generalization of the usually considered Kortweg-de Vries-Burgers equation and a simplified version of the evolution equation obtained in a previous paper by Fusco and Oliveri [16] for the full model including the diffusion of the bubbles with respect to the liquid is constructed. The related wave profiles are investigated through numerical integrations. (author)