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- Karimipanah, Taghi, 1953-
(author)
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Turbulent jets in confined spaces : application in mixing ventilation: experimental and numerical studies
- 1996
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Doctoral thesis (other academic/artistic)abstract
- The basis of mixing ventilation is the airflow supply to the room by means of jets initiatedfrom the ventilation diffusers. To avoid the draught problem, the design of mixing ventilationmakes uses the throw term, which is defined as the distance to the supply air terminal inwhich the jet centreline mean velocity is decreased to a given value. Traditionally, the throw ismeasured by the supply air device manufacturer. The throw is applied by designers to estimatethe velocity levels in the occupied zone. A standard for determining the throw is the CENstandard CEN/TC156/WG4 N86 "Draft Standard. Air terminal Devices. AerodynamicsTesting And Rating For Mixed Flow Application".The measurement of the throw is very time consuming even with the free jets and theinfluence of the room (the effect of confinement) is not considered. The objective of thepresent study is to give a basis for modifying the existing design and testing method used topredict the velocities in the occupied zone during the design process. A new method whichmay probably be more easier than the existing methods and at the same time give a betterprecision by including the confinement effect.In this thesis two methodological systems of experiment and numerical simulations have beenused. The numerical predictions are used in comparison with the measurements. Thereasonable agreement of the above mentioned methods is implemented to numerical study ofthe other room configurations which are not experimentally studied. This examining methodallows the possibility of studying a lot of configurations and in this manner generalising of theresults. Although the experimental part was made for both model-scale and full-scale testrooms, a large amount of data was obtained for a new test room whose dimension aresystematically varied. All of studies have been made for the isothermal case and themeasurements of velocities and pressures conducted along the room perimeters. The effect ofshort and deep rooms on the properties of the jet ( velocities, pressure, integral scale, jetmomentum, the rate of spreading of jet and turbulence intensities) have been carried out.Some old and recent investigations have been examined. Specially the concept of correlationsfrom open to closed rooms is criticised. It is also shown that the flow field in a confined roomis affected by many other factors than the Reynolds number. The surface pressure on theperimeters was used to calculate the reaction forces at the corners which causes recirculatingbubbles at corners. A study of the turbulent axisymmetric jet which is the basic element inturbulent shear flows and some restrictions of the traditional measurement techniques at theregion of interest in ventilation applications are discussed. The jet momentum is measured byweighing on a balance. Also a study of jets which collide with a wall , that is impinging jet,the effect of walls and confinement on the jet momentum have experimentally andnumerically been carried out. A new momentum balance model was developed for both thefree jet and confined one. An empirical relation has been found for estimation of the room’srotation centre which is used for validation of CFD results.Finally, it is found that the jets in a ventilated room which are a combination of free jet, walljet and impinging jet differ from the traditional wall jets. The rate of spreading of the jet andthe maximum velocity decay in a ventilated room are also different depending on the roomsize and its confinement.
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- Türk, Maria, et al.
(author)
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Reduction in the levels of phytate during wholemeal bread making : Effect of yeast and wheat phytases
- 1996
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In: Journal of Cereal Science. - : Elsevier BV. - 0733-5210 .- 1095-9963. ; 23:3, s. 257-264
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Journal article (peer-reviewed)abstract
- No difference in wheat phytase activity was observed when different types of acid were used to adjust the pH of wholemeal wheat flour suspensions to pH 5·0, the optimum for wheat phytase. When whole wheat bread was made without additives or after adjustment of the dough pH with acetic acid or lingonberry (traditional ingredients in bread making in Sweden), 64%, 96% and 83%, respectively, of the initial phytate was hydrolysed. A small but significant difference between breads with and without yeast or with deactivated yeast was found, indicating that yeast contributed some phytase activity under the conditions of bread making (pH 5·3-5·8 and 30-37°C). The optimum pH of yeast phytase was found to be 3·5. The isomers of IP5 formed with purified wheat phytase or yeast phytase were studied using sodium phytate as substrate. Wheat phytase formed 1,2,3,4,5-IP5 whereas yeast phytase formed 1,2,4,5,6-IP5. Determination of the isomers of inositol pentaphosphate demonstrated that the reduction in phytate levels in bread compared with wholemeal flour resulted from both wheat and yeast phytase activities. © 1996 Academic Press Limited.
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- Wallengren, Nils-Olof, et al.
(author)
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Preoperative staging of rectal carcinoma using double-contrast MR imaging. Technical aspects and early clinical experiences
- 1996
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In: Acta Radiologica. - 1600-0455. ; 37:5, s. 791-798
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Journal article (peer-reviewed)abstract
- PURPOSE: To improve preoperative staging of rectal carcinoma with MR imaging, using a double-contrast technique. MATERIAL AND METHODS: Imaging was performed in 12 patients before and after i.v. injection of Gd-DTPA and rectal administration of a superparamagnetic contrast medium, mainly containing magnetite. The diagnostic information was evaluated and compared with findings at surgery and histopathological analysis. RESULTS: The superparamagnetic contrast medium enema caused a distension of the rectum and intraluminal signal void, whereas Gd-DTPA enhanced the mucosa in T1-weighted images. This allowed an evaluation of the normal rectal wall and separation of the mucosa, tunica muscularis and perirectal space in all cases, which was not possible in T1- or T2-weighted precontrast images. The rectal carcinoma could be delineated and tumor invasion to the rectal wall determined in all cases. The findings in postcontrast MR corresponded with the findings at histopathological examination in 11 of 12 patients. The histopathological examination in one patient revealed metastases (< 1 cm) in regional lymph nodes, too small to be identified in pre- or postcontrast MR images. CONCLUSION: Double-contrast-enhanced MR imaging allows evaluation of the normal rectal wall and preoperative staging of rectal carcinoma.
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