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This paper reports on experiments conducted with a cold flow model utilized for the investigation of the particle residence time distribution and mixing characteristics in a bubbling fluidized bed with continuous solids exchange. The investigated system is of a rectangular cross section (0.4 × 0.2 m) with a bed height of 0.17 m. A measurement device based on an alternating current bridge circuitry coupled with lock-in amplifier technology was built in the scope of quantifying the solids residence time distribution, whereby a pulse-injected ferromagnetic tracer creates the input signal. The implementation of a profound mathematical routine ensures the reproducible calculation of the particles mean residence time and characteristic values describing particle mixing phenomena. Therefore, the E-curve was modeled by mathematical convolution of the exit age distributions available for an ideally mixed continuous stirred tank reactor and a plug flow reactor with axial dispersion. It is shown that the in-bed mixing is highly dependent on the fluidization rate as well as on the solids circulation rate. Albeit the lowest superficial gas velocity equals a fluidization number of 4.7, the formation of dead spaces and short-circuit flows was observed under these conditions. Axial dispersion coefficients in the range of 5 · 10 - 3 to 7 · 10 - 1 m2 s−1 were obtained.

Literature offers several excellent contributions in view of hydrodynamics and heat transfer characteristics of fluidized beds. Our investigations deal with the achievable wall-to-bed heat transfer rates at a tube bundle heat exchanger immersed in a bubbling bed of Geldart Type B particles. We confirm the findings of other authors, who described the lateral distribution of bed voidage as well as horizontal and vertical particle velocity and heat transfer. The heat transfer coefficients in the core of the bed are significantly higher than they are at the walls. An adapted gas distributor with a non-uniform nozzle-grid was used to overcome the disadvantage of unevenly distributed heat transfer. While the heat transfer coefficients close to the wall are 25–50% lower than in the core region when a uniform nozzle-grid is used, the effect can be fully balanced with the modified gas distributor. We conclude that a more even lateral distribution of heat transfer rates is possible while the overall heat exchange rate remains unchanged. Nevertheless, an increased uniformity in lateral particle mixing may indicate an improvement in heat surface load and mass transfer.

Heat transfer between bubbling fluidized beds and immersed heat exchanger surfaces is studied in view of continuously operated temperature swing adsorption processes for post-combustion CO2 capture. A novel heat transfer measurement test device was used to measure wall-to-bed heat transfer coefficients. The present work focuses on the comparison of experimentally obtained and calculated heat transfer coefficients. Heat transfer at horizontal single tubes and tube bundles immersed in fluidized particle beds of glass beads with 140 μm and 200 μm in Sauter mean diameter is investigated. It is shown that the experimental results for single tubes are in mediocre agreement to established mathematical models, such as the ones proposed by Natusch et al. (1975) and Molerus et al. (1995), and that heat transfer is significantly influenced by the tube diameter. The model by Petrie et al. (1968) was considered to take the effect of the tube diameter into account, which lead to promising results. Furthermore, measured heat transfer coefficients at tube bundles of different geometries are compared to predictions using the models by Natusch et al. (1975) and Lechner et al. (2013). Some of the tube bundle reduction factors predicted by the model by Lechner et al. (2013) are larger than one, which stands in contrast to the finding that the highest heat transfer coefficients occur at single tubes. However, both models lead to adequate results when calculating heat transfer coefficients for different tube bundle geometries.

Functionalized solid amine-based temperature swing adsorption (TSA) processes have recently been proposed as a potential way to reduce the energy-penalty of post-combustion carbon capture processes. Thereby, multi-stage fluidized bed contactors with immersed heat exchanger surfaces and counter-current flow of solids and gas phase may solve the heat transfer challenge while maintaining the thermodynamic process requirements. Hence, the present work develops design requirements for TSA stages based on achievable heat transfer rates in bubbling fluidized beds. The considered particles are Geldart Type B. It is shown that the pressure drop of multi-stage fluidized bed TSA units for flue gas CO 2 capture is practically determined by the heat exchange requirement. Scalability, maintainability and durability of different heat exchanger geometries are considered. The net movement and mixing of particles within the bubbling bed stage must be maintained in spite of the immersed heat exchangers concerning possible dead zones in the area of the tube bundles. Comprehensive models are used to predict heat transfer coefficients for tubes immersed in fluidization. A heat transfer measurement test device for optimization of the heat exchanger geometry has been put into operation and heat exchange measurement results are compared to calculated heat transfer coefficients. It is shown that experimentally obtained heat transfer rates for single tubes are in good agreement with modeled values. A model proposed for Geldart A particles is used to estimate heat transfer rates for two particular tube bundles with a tube diameter of 25 mm and horizontal tube spacing of 2.2 and 2.8. It is shown that the calculated results represent heat transfer rates qualitatively and quantitatively for tube bundle heat exchangers immersed in Geldart Type B particle fluidized beds. Although this article has been motivated by heat exchange in TSA, it may be of interest for other applications concerned with heat transfer between bubbling fluidized beds and immersed heat exchanger surfaces.

Nitric oxide inhibits growth of glomerular mesangial cells: Role of the transcription factor Egr-1 Background In previous studies, we found a close link of early growth response gene-1 (Egr-1) expression to mesangial cell (MC) proliferation. Antiproliferative agents inhibited mitogen-induced Egr-1 expression. Here we investigated the effect of S-nitrosoglutathione (GSNO) on the proliferation of MCs, specifically asking how GSNO regulates the transcription factor Egr-1, which we have previously shown to be critical for the induction of MC mitogenesis. Methods The proliferation of MCs was measured by thymidine incorporation and cell counting. Egr-1 mRNA and protein levels were detected by Northern and Western blots. Electrophoretic mobility shift assays (EMSAs) and chloramphenicol acetyltransferase (CAT) assays were performed to test whether GSNO modulates DNA binding and transcriptional activation of Egr-1. Results GSNO strongly inhibited serum-induced MC proliferation (-84% at 1 mmol/L). A mild inhibition of serum-induced Egr-1 mRNA was observed at GSNO concentrations from 50 to 200 μmol/L, whereas mRNA levels increased again at concentrations above 500 μmol/L. This increased mRNA expression, however, was not translated into Egr-1 protein. Instead, Egr-1 protein induction was inhibited (-40%). EMSAs indicated that GSNO inhibited specific binding of Egr-1 to its DNA consensus sequence. Moreover, transcriptional activation by Egr-1 in CAT assays using a reporter plasmid bearing three Egr-1 binding sites was strongly suppressed by GSNO. Conclusions Our data identify GSNO as a potent inhibitor of MC growth with potential beneficial effects in proliferative glomerular diseases. This antimitogenic property is mediated at least in part by inhibitory effects of GSNO on Egr-1 protein levels and by reducing the ability of Egr-1 to activate transcription by impairing its DNA binding activity.

Expression of the transcriptional regulator Egr-1 in experimental glomerulonephritis: Requirement for mesangial cell proliferation. The early growth response gene-1 (Egr-1), a zinc finger transcriptional regulator, was induced in a rat model of mesangioproliferative glomerulonephritis (GN). Northern blot analysis revealed a maximal 14.9-fold increase in glomerular Egr-1 mRNA at day 6 of GN. By immunohistochemistry Egr-1 protein expression was demonstrated to be mainly confined to glomerular mesangial cells (MC). To test whether Egr-1 directly regulates MC proliferation, cultured MCs were stimulated with platelet-derived growth factor (PDGF) after preincubation with different Egr-1 antisense oligonucleotides (ASOs). PDGF-induced Egr-1 mRNA levels were inhibited by up to 75% and protein levels by up to 91%. In addition Egr-1-specific ASOs blocked PDGF-induced rise in 3 H-thymidine uptake by 83% and almost completely abrogated increase in MC number. We conclude that Egr-1 induction is of critical importance for PDGF-induced mitogenic signaling in MCs, and inhibition of Egr-1 in vivo may offer an approach to oppose glomerular MC proliferation in glomerular inflammatory disease.

A method and apparatus for ascertaining internal stresses in a hardened region to be tested for a component made of a predetermined material includes measuring coercive field strength and amplitude of magnetic Barkhausen noise as a function of mechanical stress and hardness in calibration samples of a predetermined material of known hardness and known internal stress. Calibration functions are ascertained from the measured values indicating the dependency of the hardness and the amplitude of the magnetic Barkhausen noise as functions of the hardness and mechanical stress. The coercive field strength and the amplitude of the magnetic Barkhausen noise is measured in a location-dependent manner over the region of the component to be tested. The measured values of the coercive field strength and the amplitude of the magnetic Barkhausen noise are converted in the region to be tested into location-dependent hardness and into location-dependent mechanical stress using the ascertained calibration functions. The location-dependent mechanical stress and the location-dependent hardness in the region to be tested are present independently of one another and are available for further processing.