Modeling grooved rolls with moving 2D porous media

Rolls are widely used in paper machines to heat, press and support paper webs and fabrics in order to facilitate rapid drying and transport of the paper web through the machine. In modern high speed paper machines, however, the interaction of boundary layer flows on the rolls, fabrics and the paper web often results in an undesirable pressure development at nip regions, ultimately causing an uncontrolled motion of the paper web. This runnability issue can be mitigated by using a so-called suction roll construction, which forces the required pressure profile over the paper web. Its operational costs are high, however. One result of the study is that the topology and the material of the roll surfaces, in particular the introduction of grooves on the smooth roll surfaces, can have a tremendous impact on the overall runnability potential of the paper web.The complexity of solving the governing Navier-Stokes equations and the sheer variability of paper machine constructions makes a comprehensive analytical study of the roll-grooving effect difficult. To the authors' knowledge, analytical solutions for nip pressures only exist for two-dimensional geometries and for smooth roll's. Moreover, numerical 3D simulations of grooved rolls in large paper machine sections are not feasible with today's computational or modeling resources.In this article, we propose a computational 2D model for a grooved roll. The model reproduces three-dimensional wall friction effects and minor losses in 2D by treating a grooved roll surface as a moving porous medium. The nip pressures are calculated and compared for:a grooved roll interacting with a rigid impermeable horizontal wall at a tangent point (symmetric 3D)a grooved roll interacting with a rigid impermeable horizontal wall at a tangent point where the groove geometry is described in 2D with moving porous media.The roll models describe the roll as infinitely wide, thus capturing friction effects between the roll and the surrounding air. The simulations are conducted with the RANS-method of computational fluid dynamics (CFD) on a commercial solver.The results show that the proposed computational 2D model for a grooved roll yields similar pressure profiles at nip regions as the more computationally expensive full-scale 3D models. The significance of this observation is that the 2D model now facilitates the study of grooved rolls in large sections of paper machines

2D FSI model for paper webs and fabrics moving close to each other in complex geometries

In the present article we develop a two-dimensional computational fluid-structure interaction (FSI) model for small transverse deflections of a moving paper web, supported on one side by a fabric, both moving in an arbitrary geometry containing boundaries and nips (e.g. as in the drying section of a paper machine). In our FSI model, the transverse deflections of the paper web and those of the fabric are individually assumed to satisfy an equation of motion for axially moving membranes

Development of Realistic Simulation Techniques to Predict Cure-Induced Microcracking

Abstract: Three-dimensiona

Transient 2D paper web drying model based on CFD

In the present article, a model combining the benefits of the small scale and large scale approaches towards modeling paper drying in a paper machine dryer section environment is described. The model is transient and two-dimensional, taking into account the MD and the thickness directions but neglecting the phenomena in the CD direction.The combined model consists of two parts:1. A large scale CFD model of the surroundings of the paper web solving the RANS equations2. A specific-purpose small scale model for heat and moisture transport phenomena inside the paper web.The model is aimed at predicting the drying process in a paper production environment. The present model can be combined with a separate paper web deflection model in order to simulate the drying process and the paper web runnability simultaneously

Allergic conditions and risk of hematological malignancies in adults: a cohort study

BACKGROUND: Two contradictory hypotheses have been proposed to explain the relationship between allergic conditions and malignancies, the immune surveillance hypothesis and the antigenic stimulation hypothesis. The former advocates that allergic conditions may be protective against development of cancer, whereas the latter proposes an increased risk. This relationship has been studied in several case-control studies, but only in a few cohort studies. METHODS: The association between allergic conditions and risk of developing leukemia, Hodgkin's disease, non-Hodgkin's lymphoma and myeloma was investigated in a cohort of 16,539 Swedish twins born 1886–1925. Prospectively collected, self-reported information about allergic conditions such as asthma, hay fever or eczema was obtained through questionnaires administered in 1967. The cohort was followed 1969–99 and cancer incidence was ascertained from the Swedish Cancer Registry. RESULTS: Hives and asthma tended to increase the risk of leukemia (relative risk [RR] = 2.1, 95% Confidence Interval [CI] 1.0–4.5 and RR = 1.6, 95% CI 0.8–3.5, respectively). There was also an indication of an increased risk of non-Hodgkin's lymphoma associated with eczema during childhood (RR = 2.3, 95% CI 1.0–5.3). CONCLUSION: In contrast to most previous studies, our results do not indicate a protective effect of allergic conditions on the risk of developing hematological malignancies. Rather, they suggest that allergic conditions might increase the risk of some hematological malignancies