Wärme- und strömungstechnische Untersuchungen an fluchtendenRohrbündel-Wärmeaustauschern aus pyramidenförmig aufgerauhten Rohren

Integral values of heat transfer and pressure drop are reported. They have been gained from 5 tube banks in cross flow of different tube pitches and roughnesses. The experiments were conducted at Reynolds numbers 5 $\cdot$ 10$^{3}$ < Re < 10$^{6}$ with air and helium as experimental fluid on the outside of the tubes. Increasing artificially the roughness of the tubes a gain in heat transfer was achieved up to 50% compared to a tube arrangement of technically smooth tubes without increasing the flow resistance. Besides this the fraction of each tube row of the integral heat transfer coefficient of the bundle was measured. In comparison to an arrangement of smooth tubes the heat transfer of the first tube row was increased in relation to the following ones. Furthermore the artificial roughness of the tubes effected an equalisation of the velocity profiles behind the heat exchanger

Abschlussbericht über die Untersuchungen an einem schraubenförmig gewendelten Wärmetauscher für den Dampferzeuger des THTR

Im Hochdruck-Gaskanal des Instituts für Reaktorbauelemente der KFA Jülich (Abb. 60) wurde als Modell der innere und verkürzte Teil eines gewendelten Wärmetauschers hinsichtlich seines strömungstechnischen und thermodynamischen Verhaltens untersucht. Auf 8 verschiedenen Durchmessern waren insgesamt 23 gewendelte Rohre in Form mehrgängiger Gewinde angeordnet {Abb. 61 und 62). Die Untersuchungen erstreckten sich über einen Reynoldsbereich vonRe = 6 000 .•. 740 000. Als Versuchsmedium diente Luft bei Drucken von 1 bis 40 ata. Im folgenden seien noch die wichtigsten Daten des Wärmetauschers angeführt. Gewisse Abmessungen hatten sich bei der Fertigung gegenüber den Konstruktionsmaßen etwas geändert. [...

Wirkung supramolekularer Polymerstrukturen auf die Mineralisation aus waessriger Loesung Schlussbericht

In the framework of the cooperative research project, the effects of the microstructure of polymeric deposition agents on the deposition and mineralising of ZnO and CaCO3 particles from aqueous solutions has been studied by G.Wegner, J.Norwig and F.Groehn (Max-Planck-Institute for polymer research, Mainz); M.Ballauff (Polymer-Institute of the University of Karlsruhe); F.Aldinger and R.Hoffmann (Institute for non-metallic inorganic materials, Stuttgart), and J.Rieger (BASF AG, Ludwigshafen). PEO, PMMA, PEO-b-PMMA, PMMA-g-PEO, ammonium salt of polyacrylic acid and acrylic acid-co-maleic acid random copolymers were evaluated, The crystallization, crystalline structure, and nanostructure of the deposited ZnO and CaCO3 particles and their suitability as green ceramic powder and their sintering behavior were investigated.Available from TIB Hannover: F03B1085 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Influence of Phosphonium Alkyl Substituents on the Rheological and Thermal Properties of Phosphonium-PAA-Based Supramolecular Polymeric Assemblies

A noncovalent synthetic strategy to supramolecular polymeric assemblies, including network structures, is described by the complexation of various phosphonium monocations and dications with the multianion, poly(acrylic acid). The alkyl chains surrounding the phosphonium cation were systematically varied from butyl, hexyl, to octyl in order to probe the effect of sterics and ion pairing on the resulting macroscopic properties of the assemblies. The supramolecular assemblies were characterized by TGA, DSC, oscillatory rheometry, steady-state flow rheometry, and SAXS. The rheological and thermal properties, as well as the flow activation energies, are highly dependent on the alkyl chain length. All of the supramolecular assemblies have glass transition temperatures lower than room temperature and range from 8 °C to below −40 °C. Di-ButC10PAA has the shortest alkyl chain length and affords the highest glass transition temperature. Correspondingly, it shows the largest viscosity and storage and loss moduli. For example, its viscosity is 3 orders of magnitude greater than di-OctC10PAA. In creep-recovery experiments, di-ButC10PAA shows the highest percent of strain recovery after the stress is removed, followed by di-HexC10PAA and di-OctC10PAA. The rheological and thermal properties of monoIL-PAA assemblies show similar alkyl chain length dependence, but the magnitude is significantly less because of the lack of cross-linking. A reversibility test of the supramolecular networks demonstrates that the ionic network material can fully reassemble within a short time period after disruption of the network due to heat or shear without sacrificing the mechanical properties