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  • 1
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Industrial & engineering chemistry research 32 (1993), S. 1304-1314 
    ISSN: 1520-5045
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Colloid & polymer science 264 (1986), S. 362-367 
    ISSN: 1435-1536
    Schlagwort(e): Methanol [67-56-1] ; high temperature adsorption ; silica-alumina ; multilayers ; adsorption heat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract The methanol adsorption capacity of an amorphous silica-alumina was measured using an equilibrium technique. The experimental temperature range was of 140 to 260°C and the pure methanol pressure range was 0.1 to 1.2 MPa. A multilayer adsorption was found, also for temperatures above the critical temperature of the adsorbate. Based on the Jovanovic adsorption model, the mean residence times of the adsorbed molecules were calculated. Surprisingly, the heat of adsorption was found to be independent of the temperature in the multilayer adsorption range.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    European journal of nutrition 36 (1997), S. 306-309 
    ISSN: 1436-6215
    Schlagwort(e): Respiration chamber ; substrate oxidation ; respiratory quotient ; high-fat diet ; Respirationskammer ; Substratoxidation ; respiratorischer Quotient ; Hochfettdiät
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Untersuchungen haben gezeigt, daß die Anpassung der Fettoxidation an die Fettaufnahme, wenn Änderungen im Nahrungsfettgehalts vorgenommen werden, nicht abrupt geschieht. In dieser Untersuchung wurde der Zeitverlauf der Anpassung der Oxidationraten bei Vergrößerung des Nahrungsfettgehalts im Energiegleichgewicht gemessen. Zwölf gesunde, nicht übergewichtige männliche und weibliche Probanden (Alter: 26±2, BMI: 21,4±0,5, gewohnheitsmäßige Fettaufnahme: 29±1% Energie) erhielten über 6 Tage eine Niedrigfettdiät (Tag 1–6). Anschließend folgte eine 7tägige Hochfettdiät (Tag 7–13). Während der Tage 5–9 und 13 befanden sich die Probanden in einer Respirationskammer. Nach Einstellung der Energieaufnahme auf den 24h-Energiebedarf am Tag 5, waren die Probanden im Energiegleichgewicht (−0,15 ±0,23 kJ/d) während der Tage 6–9 und 13. Die Fettbilanz war am Tag 6 ausgeglichen, wurde aber positiv nach Umstellung auf Hochfettdiät (1,06 ±0,15, 0,75±0,15; 0,55±0,14 MJ/d für die Tage 7, 8 und 9 (p〈0.05) und erreichte nach 7 Tagen ein neues Gleichgewicht (Tag 13). Schlußfolgernd kann gesagt werden, daß im Falle des Energiegleichgewichts, schlanke Personen in der Lage sind, die Fettoxidation innerhalb von 7 Tagen an die Fettaufnahme anzupassen, wenn der Nahrungsfettgehalt erhöht wird.
    Notizen: Summary Intervention studies have shown that the adaptation of fat oxidation to fat intake, when changing the dietary fat content, is not abrupt. This study was conducted to measure the time course of adaptation of oxidation rates to increases in the fat content of the diet, when feeding subjects at energy balance. Twelve healthy, non-obese males and females (age: 26±2, BMI: 21.4±0.5, habitual fat intake: 29±1% energy) consumed a low-fat diet for 6 days (day 1–6) followed by a high-fat diet for 7 days (day 7–13). Days 5–9 and day 13 were spent in a respiration chamber. After adjusting energy intake to 24h energy expenditure on day 5, subjects were in energy balance (range −0.15 to +0.23 kJ/day) on days 6–9 and day 13. Fat balance was zero on day 6 but became positive after changing to the high-fat diet (1.06±0.15, 0.75±0.15, and 0.55±0.14 MJ/day for days 7, 8, and 9 respectively, p.〈0.05), reaching a new balance on day 13, 7 days afterwards. Thus, in case of energy balance, lean subjects are capable of adjusting fat oxidation to fat intake within 7 days, when dietary fat content is increased.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    European journal of nutrition 36 (1997), S. 303-305 
    ISSN: 1436-6215
    Schlagwort(e): Energy metabolism ; diet ; fat composition ; fatty acids ; thermogenesis ; obesity ; indirect calorimetry ; Energieumsatz ; Diät ; Fettzusammensetzung ; Fettsäuren ; Thermogenese ; Adipositas ; indirekte Kalorimetrie
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Untersuchungen an Tieren und am Menschen zeigen, daß polyungesättigate Fettsäuren (P) schneller als gesättigte Fettsäuren (S) oxidiert werden. Es gibt Hinweise dafür, daß Diäten mit einem hohen P/S-Verhältnis einen relativ hohen Ruheenergieumsatz (RMR) und eine hohe diät-induzierte Thermogenese (DIT) verursachen. Untersuchungen beim Menschen sind jedoch begrenzt. Die Effekte der Nahrungsfettsäuren-Zusammensetzung auf den Energieumsatz wurden bei 6 männlichen Personen (Alter 25–48 Jahre) untersucht. In einer randomisierten Crossover-Studie wurden 2 Diäten über eine Zeitperiode von 14 Tagen mit einer anschließenden washout-Periode verabreicht. Das P/S-Verhältnis betrug bei diesen Diäten 0,19 und 1,67. RMR wurde am 14. Tag früh im Nüchternzustand mittels indirekter Kalorimetrie (ventilierte Haube) bestimmt. Daran schloß sich nach Aufnahme einer standardisierten Mahlzeit mit einem Energiegehalt von 3,3 MJ (gleiche Fettsäuren-Zusammensetzung wie während der Diätperiode) eine 4h-Messung der DIT an. Die Mahlzeit enthielt 46, 37 und 17 Energie% an Fett, Kohlenhydrate und Protein. RMR war nach der Periode mit hohem P/S-Verhältnis signifikant höher als nach der Periode mit niedrigem P/S-Verhältnis. Die mittlere Differenz betrug 0,17±0,14 (SD) kJ/min bzw. 3,6±2,7 % von RMR. DIT war bei allen untersuchten Personen während eines Frühstücks mit einem hohen P/S-Verhältnis höher. Die mittlere Differenz betrug 0,29±0,16 (SD) kJ/min bzw. 3,6±2,7 % von DIT. Die Untersuchung zeigt, daß eine prolongierte Aufnahme einer Diät mit einem hohen P/S-Verhältnis zu relativ hohem RMR und DIT führt. Diese Ergebnisse weisen auf die Bedeutung des Nahrungsfettprofils bei der Behandlung der Fettsucht hin.
    Notizen: Summary Animal and human studies show that polyunsaturated fatty acids (P) are oxidized more rapidly than saturated fatty acids (S). There are indications that diets high in P/S ratio result in a relatively high resting metabolic rate (RMR) and high diet induced thermogenesis (DIT). However, studies with human subjects are limited. The effect of dietary fatty acid composition on energy metabolism was studied in 6 male subjects, age 25–48 y. Two diets were supplied, each over a period of 14 days, in a randomized crossover design with a washout period of 14 days. P/S ratios of the diets were 0.19 and 1.67. On day 14, RMR was determined in the morning in fasting state by means of indirect calorimetry (ventilated hood), followed by a 4 hour measurement of the DIT after consumption of a standardized meal of 3.3 MJ with the same fatty acid composition as during the dietary period. The meal contained 46, 37, and 17 % energy as fat, carbohydrate, and protein, respectively. RMR after the period with the high P/S diet was significantly higher than after the period of the low P/S diet. The average difference (±SD) was 0.17 ± 0.14 kJ/min or 3.6±2.7 % of RMR. The DIT was also higher in all subjects during a breakfast with a high P/S ratio. The average difference was 0.29 ± 0.16 kJ/min, which is 22.1±12.6 % of DIT. The study showed that a prolonged food intake of a diet with a high P/S ratio results in a relatively high RMR and DIT. These results indicate the importance of dietary lipid profile in the treatment of obesity.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 703-715 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Influence of the tube and particle diameter and shape, as well as their ratio, on the radial heat transport in packed beds has been studied. Heat transport experiments were performed with four different packings in three wall-cooled tubes, which differed in inner diameter only. Experimental values for the effective radial heat conductivity and wall heat-transfer coefficient for the pseudo-homogeneous two-dimensional model and the overall heat-transfer coefficient for the one-dimensional model are presented. Values were obtained for glass spheres, alumina cylinders, and alumina Raschig rings. The effective radial heat conductivity and wall heat-transfer coefficient can both be correlated as a linear function of the gas flow rate. The Bodenstein number for heat at fully developed turbulent flow is influenced strongly by the shape of the packing: 10.9 for glass spheres, 7.6 for alumina cylinders, and 4.2 for alumina Raschig rings. For the same packing, no significant influence is found of the tube diameter on the effective radial heat conductivity or on the wall heat-transfer coefficient. The overall heat-transfer coefficient can be described very well by the so-called “lump equation,” which gives the relations among the overall heat-transfer coefficient, effective radial heat conductivity, and wall heat-transfer coefficient. The “lump factor,” as used in the lump equation, has a best-fit experimental value of 7.4.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2029-2039 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An analysis and applications of the wave model for longitudinal dispersion are pre-sented. Asymptotic forms of the wave model are considered and analytical solutions of typical linear stationary and nonstationary problems of chemical reactor engineering interest are obtained and compared to those for the Fickian dispersion model. The wave model leads to efficient analytical solutions for linear problems, which in principle differ from the solutions of the Fickian dispersion model; only for slowly varying concentration fields do the soluctions of both models approach each other. Spatial and time moments of the concentration distribution are obtained for pulse-dispersion problems; the first three spatial moments of the mean, variance, and skewness have exact, large-time asymptotic forms in the case of Taylor dispersion. Old experiments that could not be explained with the standard dispersion model are reconsidered and explained: the change with time of the variance of a concentration pulse when the flow direction is reversed and the difference in values of the apparent axial dispersion coefficient and the backmixing coefficient in a rotating disk contactor. The experimental determination of model parameters is discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1849-1862 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Data on design and operation of trickle beds at elevated pressures are scarce. In this study the influence of the gas density on the liquid holdup, the pressure drop, and the transition between trickle and pulse flow has been investigated in a tricklebed reactor operating up to 7.5 MPa and with nitrogen or helium as the gas phase. Gas-liquid interfacial areas have been determined up to 5.0 MPa by means of CO2 absorption from CO2/N2 gas mixtures into amine solutions.A comparison of the results from nitrogen as the gas phase to those of helium shows that at equal gas densities the hydrodynamic states are the same. The gas-liquid interfacial area increases when operating at higher gas densities. When the determined dimensionless interfacial areas agl/as are all within the range 0.25-0.8, the trickle-bed reactor is suggested to operate in the trickle-flow regime. The gas density has a strong influence on the liquid holdup. Due to the higher pressure gradients at elevated gas densities, the liquid holdup decreases noticeably. Besides, the boundary between the trickle-flow and pulse-flow regime shifts toward higher liquid throughputs: the region for trickle-flow operationg becomes larger. For the liquid holdup and the pressure gradient in the trickle-flow regime, correlations derived based on dimensionless numbers can be applied to high-prssure trickle beds.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 862-869 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A novel perfectly mixed laboratory reactor for determining kinetics of heterogeneously catalyzed gas-phase reactions has been developed. Perfect mixing is achieved by circulating the gas in the reactor using an axial flow impeller in a well streamlined enclosure. Pellets are fixed in a rectangular opening in the blades of the impeller. They rotate with the impeller, thus realizing high particle velocities in the reactor. Interparticle mass transfer was studied experimentally by vaporization of naphthalene pellets. The mass-transfer coefficient in the novel reactor was found to depend on the velocity of a particle in the reactor. Mass-transfer coefficients in an internal recycle reactor at equal impeller tip speeds are 4-6 times lower than those in the novel reactor, and conditions can be chosen easily where at higher rotational speeds the mass- and heat-transfer rates are 8-10 times higher than in classical recycle reactors. The recycle flow rate in a recycle reactor was found to depend strongly on the resistance to flow caused by the catalyst bed itself. The novel reactor was tested under reacting conditions using the hydrogenation of ethene.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 1871-1880 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The dynamic behaviour of an adiabatic tubular plant reactor during the startup is demonstrated, together with the impact of a feed-pump failure of one of the reactants. A dynamic model of the reactor system is presented, and the system response is calculated as a function of experimentally-determined, time-dependent, manipulated variables. The values of model parameters are estimated by using the SimuSolv (1991) computer program. The data set collected during the reactor start-up is used for the parameter estimation procedure. An excellent agreement is obtained between the experimental and the calculated system response. Many continuously-operated commercial reactors require a complete conversion of one of the main reactants at the reactor exit. It is shown that for an industrial tubular reactor a much higher initial reactor temperature is required during the startup, compared to the reactor inlet temperature during normal steady-state operation, to ensure a complete reactant conversion. Much more research is necessary to determine whether this is a generally valid rule.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2013-2028 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A new 1-D model for longitudinal dispersion is proposed as an alternative to the Fickian-type dispersed plug-flow model. Accounting for significant features of longitudinal mixing gives rise to a quasilinear hyperbolic system of two first-order equations for the average concentration. The model equations are obtained based on minor extensions of the heuristic equilibrium analysis of Taylor. A qualitative, more general derivation of the equations is given on the basis of the simple generalization of Fick's law, taking into account the finite velocity of fluid elements. For linear problems the mean concentration and the dispersion flux obey a hyperbolic equation of the second order. The proposed hyperbolic model contains three parameters that depend only on the flow conditinos, the physical properties of the fluid, and the gemetry of the system. It effectively resolves the well-known problem of boundary conditions that, for unidirectional flow, are formulated now only at the reactor inlet. The new model eliminates the conceptual shortcomings inherent to the Fickian dispersed plug-flow model: it predicts a finite velocity of signal propagation and does not involve backmixing in the case of unidirectional flow.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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