Film Rupture And Partial Wetting Over Flat Surfaces

Various technical applications require conditions which prevent thin liquid films from breaking into a series of rivulets, leaving the solid surface partly uncovered and lowering the extension of the liquid free interface. What is needed is both a criterion for the stability of the film to identify the minimum flow rate able to ensure the complete wetting of the surface and, after the film rupture, a method to estimate the wet (active) part of the same surface. At low Reynolds and high Weber numbers, the assumptions of a film with uniform thickness and complete wetting of the transfer surface cannot be considered, even approximately, rigorous, hence, leading to unacceptable inaccuracy of simulation results of the transfer performance in that operative region. Accordingly, the inadequacy of previous theoretical models of devices that use falling films as transfer mediums can be ascribed to a major issue, namely the assumption of complete wetting. As they provide a simple variational method to solve complex, multi-variable problems and directly reach a rational explanation of physical phenomena, extremum principles have led to critical results in the theoretical and technical fields. Hamilton’s principle (or principle of least action), Gauss’ principle of least constraint, as well as Oasager’s extremum principle or Prigogine’s principle of minimum entropy production remain central in modern physics and engineering. In this context and with regard to the previously stated technical aim, the principle of minimising the energy of a given stream-wise section of the film is applied in order to model and investigate the film stability. Specifically, a criterion for defining the film stability is established for a rivulet cross-section shape suitable for predicting the transient evolution of the wetting ability under an imposed fluid distribution width. The evolution from uniform film to the stable rivulet configuration is estimated considering the energy of the system under a Lagrangian approach. The Lagrange equation is written with reference to a single generalized wetting coordinate and its time derivative, under the effect of Rayleigh\u27s dissipation function and a generalized force associated to a scalar potential defined as the energy excess with respect to the local energy minimum. This methodology is extended to include the hysteresis behaviour of the contact angle (considering advancing and receding contact angles) and wettability hysteresis when increasing or decreasing mass flow rates are delivered. Finally, a first qualitative and quantitative validation of the results is presented with reference to the visual data captured on a dedicated experimental test section

Influence of the Fluid Distribution Width on the Wettability of Rivulet Flow over Vertical Flat Surfaces

The performance of heat transfer in the processes of evaporation, absorption, distillation and even condensation is affected from the wetting behavior of the liquid film flow on the surface. The complete wetting of the surface is usually required while breaking of thin liquid film is to be avoided. Various experimental settings have been designed by several researchers to investigate the main parameters influencing the stability of the film. However, in order to generalize and properly scale the results, the appropriate dimension of the test section and its influences on the wetting behavior are still unresolved questions that need to be addressed. Three different fluid distribution widths, including 200, 100 and 33 mm, when the geometry of distribution hole, the distance between holes and vertical flat surface are fixed, are carried out. Pure water at ambient temperature is used as working fluid. The measurement is focused on the wettability hysteresis and the shape transition from film to rivulet when the water flow rate are increased or decreased for wetting and dewetting experiments. Visual data captured on the test section under various fluid distribution widths are collected and analyzed using image binarization method to quantify the wetted area. The relation between the wetted area with respect to film Reynolds number and Weber number respectively are presented. The results show that the fluid distribution width can influence the wetting ability. The amount of wetted area, which is used to identify the wetting ability, is quite stable for decreasing flow rates, thus delineating the hysteresis characteristics of the wetting behavior of this solid-liquid pair. In general, a longer distributor width seems to be associated to a lower wetting ability and a lower wetting hysteresis. However, the same observation could not be applied to the results extracted with a 33mm width

Search for Third Generation Vector Leptoquarks in p anti-p Collisions at sqrt(s) = 1.96 TeV

We describe a search for a third generation vector leptoquark (VLQ3) that decays to a b quark and tau lepton using the CDF II detector and 322 pb^(-1) of integrated luminosity from the Fermilab Tevatron. Vector leptoquarks have been proposed in many extensions of the standard model (SM). Observing a number of events in agreement with SM expectations, assuming Yang-Mills (minimal) couplings, we obtain the most stringent upper limit on the VLQ3 pair production cross section of 344 fb (493 fb) and lower limit on the VLQ3 mass of 317 GeV/c^2 (251 GeV/c^2) at 95% C.L.Comment: 7 pages, 2 figures, submitted to PR

Proceedings of Abstracts, School of Physics, Engineering and Computer Science Research Conference 2022

© 2022 The Author(s). This is an open-access work distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For further details please see https://creativecommons.org/licenses/by/4.0/. Plenary by Prof. Timothy Foat, ‘Indoor dispersion at Dstl and its recent application to COVID-19 transmission’ is © Crown copyright (2022), Dstl. This material is licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: [email protected] present proceedings record the abstracts submitted and accepted for presentation at SPECS 2022, the second edition of the School of Physics, Engineering and Computer Science Research Conference that took place online, the 12th April 2022

流下液膜式冷媒吸収プロセスの熱流体力学的挙動に関する研究

早大学位記番号:新7132早稲田大

Thermodynamic Analysis of Irreversible Heat-transformers

Absorption heat transformers extend the possibilities for efficient and environment-friendly energy conversion processes. Based on a general thermodynamic model of three-thermal cycles with finite thermal capacity of the heat sources, this paper is intent upon analyzing and optimizing the performance of absorption heat transformers, by including the influence of irreversibility in the analytical expression of the system efficiency. Dimensionless parameters for an overall optimization are defined and a first screening is performed to clarify their influence. Dependence on the main factors is highlighted to suggest how to change them in order to enhance the whole system performance. Under this point of view, the analysis evaluates coefficient of performance (COP) improvements and can be used to perform existing plant diagnostics, besides predicting the system performance. The use of this criterion is exemplified for specific heat transformers data from literature. This approach identifies the limitations imposed to the physical processes by accounting for the inevitable dissipation due to their constrained duration and intensity, and constitutes a general thermodynamic criterion for the optimization of three-thermal irreversible systems