FORCED-CONVECTION GAS-TO-WALL HEAT TRANSFER IN A PACKED BED FOR HIGH-TEMPERATURE ENERGY STORAGE

Measurements of the gas-to-wall forced-convection heat transfer coefficient in a packed-bed, high-temperature, thermal energy storage system were carried out. The maximum temperature attained was 1,000°C. Effects of media property variations with temperature were incorporated along with detailed uncertainty analysis. Results were correlated in terms of Nusselt number, Prandtl number, and Reynolds number. The operating fluid during energy storage was flue gas and air during recovery, making this more applicable to industrial waste recovery and similar systems. Similar studies used air for both storage and recovery and developed correlations from experiments at either room temperature or slightly above. Few associated results with corresponding uncertainty margins. Due to substantial uncertainties associated with the measurements of this heat transfer coefficient, it is significant to note that no firm conclusions can be reached on the validity or otherwise of existing similar correlations for which the uncertainty margins were not reported.     

High energy ion irradiation-induced ordered macropores in zeolite crystals

The present study demonstrated the possibility to form a secondary system of parallel macropores in zeolite crystals. The secondary pore formation was predetermined by the creation of defect zones in ZSM-5 crystals. A high energy (238)U ion beam was employed to form latent tracks in zeolite crystals, which were further subjected to attack with diluted HF solution and thus developed to uniformally sized macropores. The selective extraction of material from latent tracks was due to the higher etching velocity of highly agitated zones created by heavy ion bombardment. The combination of complementary methods unambiguously demonstrated the formation of hierarchical zeolite material comprising parallel macropores that extended through the entire crystal. The catalytic tests revealed improved activity at retained selectivity in the reaction of m-xylene conversion. The possibility to control the number of macropores per unit of crystal surface and thus the catalytic performance of the material was demonstrated. This model material is expected to bring better understanding to the effect of a secondary pore system in the catalytic performance of hierarchical zeolites obtained by the top-down or bottom-up approach.     

Synthesis of [Sar1, Val5, (4′-Azido-3′,5′-ditritio)Phe8] Angiotensin II,a Photoaffinity Label for the Isolation of Angiotensin II Receptors Communication 1

The synthesis of [Sar¹, Val⁵, (4′-azido-3′,5′-ditritio)Phe⁸] angiotensin II from a iodinated precursor peptide is described. The principal problems of this synthesis and their resolution are discussed: (i) The β-induced autophotolysis of the highly tritiated (73 Ci/mmol) and photosensitive label, and (ii) the absorption problems encountered during the purification of microgramm quantities. Such photoaffinity labels are being used for specific labeling and isolation of peptide hormone receptors.     

Conformational analysis of ochratoxin a by NMR spectroscopy and computational molecular modeling

Two-dimensional NMR spectroscopy has been used for a complete assignment of the proton and carbon-13 spectra of the metabolite from Aspergillus ochraceus, ochratoxin A. In addition, phase-sensitive nuclear Overhauser effect spectrometry experiments and computational molecular modeling (MM2 and MMFF force field programs) have been employed to examine the conformational properties of ochratoxin A in chloroform solutions. Particular attention has been given to intramolecular hydrogen-bonding formation involving the phenolic group on dihydroisocoumarin, which may be responsible for the toxic mechanism of ochratoxin A.