Extensional flow of blood analog solutions in microfluidic devices

In this study, we show the importance of extensional rheology, in addition to the shear rheology, in the choice of blood analog solutions intended to be used in vitro for mimicking the microcirculatory system. For this purpose, we compare the flow of a Newtonian fluid and two well-established viscoelastic blood analog polymer solutions through microfluidic channels containing both hyperbolic and abrupt contractions∕expansions. The hyperbolic shape was selected in order to impose a nearly constant strain rate at the centerline of the microchannels and achieve a quasihomogeneous and strong extensional flow often found in features of the human microcirculatory system such as stenoses. The two blood analog fluids used are aqueous solutions of a polyacrylamide (125 ppm w∕w) and of a xanthan gum (500 ppm w∕w), which were characterized rheologically in steady-shear flow using a rotational rheometer and in extension using a capillary breakup extensional rheometer (CaBER). Both blood analogs exhibit a shear-thinning behavior similar to that of whole human blood, but their relaxation times, obtained from CaBER experiments, are substantially different (by one order of magnitude). Visualizations of the flow patterns using streak photography, measurements of the velocity field using microparticle image velocimetry, and pressure-drop measurements were carried out experimentally for a wide range of flow rates. The experimental results were also compared with the numerical simulations of the flow of a Newtonian fluid and a generalized Newtonian fluid with shear-thinning behavior. Our results show that the flow patterns of the two blood analog solutions are considerably different, despite their similar shear rheology. Furthermore, we demonstrate that the elastic properties of the fluid have a major impact on the flow characteristics, with the polyacrylamide solution exhibiting a much stronger elastic character. As such, these properties must be taken into account in the choice or development of analog fluids that are adequate to replicate blood behavior at the microscale.     

A system for rapid production of photographic records

In the land-based radar direction of aircraft it was found necessary to transfer to a large plotting screen a 10X magnification of the PPI cathode-ray tube face. An instrument was developed to do this photographically, with the projected image lagging only 15 seconds behind the latest information. A single 360-degree sweep on the PPI tube is reduced to a $\text{1}\text{2}$-inch diameter image on Eastman Type 5302 Fine Grain Release Positive Film. The resultant image is rapid-processed by the application of hot solutions in a special processing cup which restricts the liquids to a small circular area on the film.The spent solutions are quickly removed by a vacuum line and the near dry image is indexed into the projection system where an air pressure gate completes the drying, cools the film, and holds it flat during projection.The projected image, at a magnification of over 300X, has sufficient quality to resolve all the pertinent detail of the tube face.The method is felt to have some general application.     

连州发电厂#2机组汽轮机测速装置改造

广东省连州发电厂#1、2机组使用的是上海汽轮机厂生产的125MW汽轮机,由于汽轮机转速测速齿轮盘晃动将转速探头磨损,差点造成汽机超速保护误动或汽机超速失控而转速保护拒动失效造成"飞车"等险情。将转速测速齿轮盘进行改造后避免了探头的磨损,提高了机组运行安全性。