Modelling of transient heat transfer in annealing furnaces

This is a study of heat transfer in a lift-off furnace which is employed in the batch annealing of a stack of coils of steel strip. The objective of the project is to investigate the various factors which govern the furnace design and the heat transfer resistances, so as to reduce the time of the annealing cycle, and hence minimize the operating costs. The work involved mathematical modelling of patterns of gas flow and modes of heat transfer. These models are: Heat conduction and its conjectures in the steel coils;Convective heat transfer in the plates separating the coils in the stack and in other parts of the furnace; and Radiative and convective heat transfer in the furnace by using the long furnace model. An important part of the project is the development of numerical methods and computations to solve the transient models. A limited number of temperature measurements was available from experiments on a test coil in an industrial furnace. The mathematical model agreed well with these data. The model has been used to show the following characteristics of annealing furnaces, and to suggest further developments which would lead to significant savings: - The location of the limiting temperature in a coil is nearer to the hollow core than to the outer periphery. - Thermal expansion of the steel tends to open the coils, reduces their thermal conductivity in the radial direction, and hence prolongs the annealing cycle. Increasing the tension in the coils and/or heating from the core would overcome this heat transfer resistance. - The shape and dimensions of the convective channels in the plates have significant effect on heat convection in the stack. An optimal design of a channel is shown to be of a width-to-height ratio equal to 9. - Increasing the cooling rate, by using a fluidized bed instead of the normal shell and tube exchanger, would shorten the cooling time by about 15%, but increase the temperature differential in the stack. - For a specific charge weight, a stack of different-sized coils will have a shorter annealing cycle than one of equally-sized coils, provided that production constraints allow the stacking order to be optimal. - Recycle of hot flue gases to the firing zone of the furnace would produce a. decrease in the thermal efficiency up to 30% but decreases the heating time by about 26%.

Kinetic studies of the metathesis of 1-hexene using Re2O7/γ-Al2O3 and the synthesis and metathesis of oxazolines

The kinetics of the metathesis of 1-hexene using Re2O7/-Al_2O_3 as the catalyst were investigated under a variety of conditions. The experiments were carried out under high vacuum conditions. The product solutions were characterised by gas liquid chromatography and mass spectroscopy. The initial kinetics of the metathesis of 1-hexene showed that the reaction was first order in the weight of the catalyst and second order in the concentration of 1-hexene. A kinetic scheme which correlated the experimental data with the metallocarbene chain mechanism postulated by Herisson and Chauvin and the kinetics of the reaction was explained using a model based on the Langmuir-Hinshelwood theory. The low conversion of 1-hexene to its products is due to termination reactions which most likely occur by the decomposition of the metallocyclobutane intermediate to produce a cyclopropane derivative and an inactive centre. The optimum temperature for the metathesis of 1-hexene over Re_2O_7/-Al2O3 is 45oC and above this temperature, the rate of metathesis decreases rapidly. Co-catalysts alter the active sites for metathesis so that the catalyst is more selective to the metathesis of 1-hexene. However, the regeneration of metathesis activity is much worse for promoted catalysts than for the unpromoted. The synthesis and metathesis of 4,4-dimethyl-2-allowbreak (9-decenyl)-1,3-oxazoline and 4,4-dimethyl-2-allowbreak (3-pentenyl)-1,3-oxazoline was attempted and the products were analysed by thin layer chromatography, infra-red, 13C and 1H nmr and mass spectroscopy. Obtaining the oxazolines in a good yield with high purity was difficult and consequently metathesis of the impure products did not occur.

Preparation and electrical properties of graphene nanosheet/Al2O3 composites

Fully dense graphene nanosheet(GNS)/Al2O3 composites with homogeneously distributed GNSs of thicknesses ranging from 2.5 to 20 nm have been fabricated from ball milled expanded graphite and Al2O3 by spark plasma sintering. The percolation threshold of electrical conductivity of the as-prepared GNS/Al2O3 composites is around 3 vol.%, and this new composite outperforms most of carbon nanotube/Al2O3 composites in electrical conductivity. The temperature dependence of electrical conductivity indicated that the as-prepared composites behaved as a semimetal in a temperature range from 2 to 300 K.

Utilisation of thermal annealing to record multiplexed FBG sensors in multimode microstructured polymer optical fibre

Fibre Bragg gratings have been UV inscribed in multimode microstructured polymer optical fibre in both the 1550nm and 800nm spectral regions. Thermally annealing the fibre at 80°C has been shown to shrink the fibre length and as a result a permanent negative Bragg wavelength shift is observed. The blue shift can be tuned between 0-16nm in the 1550nm spectral region and 0-6nm in the 800nm spectral region, depending on the duration the heat is applied before a saturation level is reached and the fibre stops shrinking in the region of 2 hours. Exploiting this, wavelength division multiplexed sensors have been UV inscribed in both the 1550nm and 800nm regions using a single phase mask for each wavelength region. The 800nm sensor takes advantage of the lower attenuation of poly (methyl methacrylate) of 2dB/m compared to 100dB/m at 1550nm.

Annealing and spectral characteristics of femtosecond laser inscribed long period gratings written into a photonic crystal fibre

A series of LPGs with the same period was inscribed by femtosecond laser into photonic crystal fibre with various powers. All suffered post-fabrication spectral evolution at low temperatures, apparently related to inscription power.

Investigating the molecular structures of solid dispersions by the simulated annealing method

Knowledge of the molecular structures of solid dispersions is vital, yet, despite thousands of reports in this area, it remains unclear. The aim of this research is to investigate the molecular structure of solid dispersions with hot melt preparation method by the simulated annealing method. Simulation results showed linear polymer chains form the random coils under heat and the drug molecules stick on the surface of polymer coils, while drug molecules are dispersed molecularly but irregularly within the amorphous low molecular weight carriers. This research presents more reasonable molecular images of solid dispersions than the existed theory.

Physicochemical properties of Pt-SO4/Al2O3 alkane oxidation catalysts

A series of sulfated alumina catalysts were synthesised by wet impregnation with sulfate-containing solutions. The degree of surface sulfation and corresponding surface acidity could be readily tuned by varying the molarity of impregnating solution. Strong acid treatments (>0.1 M) induced aluminium-sulfate crystallisation with a concomitant decrease in porosity and surface acidity. Platinum-doped sulfated aluminas showed enhanced activity towards methane, ethane and propane combustion. Activity scaled with the degree of accessible surface sulfate and platinum loading, however C-H bond scission appeared rate-limiting over both pure and presulfated aluminas. The magnitude of sulfate-promoted propane oxidation was greatest under heavily oxidising conditions (C3H6∶O2 > 1:20) but independent of Pt loading, confirming that support-mediated alkane activation is the dominant factor in the promotional mechanism.

Effects of annealing, pre-tension and mounting on the hysteresis of polymer strain sensors

When exposed to high levels of strain, polymer optical fibre grating sensors recorded in poly(methyl methacrylate) based fibre often exhibit hysteresis in the response of their Bragg wavelength to strain. We demonstrate that the application of pre-tension and annealing of the polymer fibre can reduce this hysteresis when the fibre is suspended freely between two supports, but much better performance is obtained when the sensor is attached directly to a substrate. In this case, the hysteresis can be lessened by more than a factor of 12. © 2014 IOP Publishing Ltd.

Improving the performance of FBG sensors in a WDM network using a simulated annealing technique

Simulated annealing technique is used to improve the performance of fiber Bragg grating (FBG) sensors in a wavelength-division-multiplexed network. Experiments demonstrated strain detection accuracy of ̃2.5 με when the spectrums of FBGs are fully or partially overlapped.

High-activity, single-site mesoporous Pd/Al2O3 catalysts for selective aerobic oxidation of allylic alcohols

Pd does it alone : Tailored heterogeneous catalysts offer exciting, alternative, clean technologies for regioselective molecular transformations. A mesoporous alumina support stabilizes atomically dispersed PdII surface sites (see picture, C light gray, O red, Pd dark gray, Al purple, H white), thereby dramatically enhancing catalytic performance in the aerobic selective oxidation of alcohols.

Annealing and temperature coefficient study of type IA fibre Bragg gratings inscribed under strain and no strain - Implications to optical fibre component reliability

The annealing properties of Type IA Bragg gratings are investigated and compared with Type I and Type IIA Bragg gratings. The transmission properties (mean and modulated wavelength components) of gratings held at predetermined temperatures are recorded from which decay characteristics are inferred. Our data show critical results concerning the high temperature stability of Type IA gratings, as they undergo a drastic initial decay at 100°C, with a consequent mean index change that is severely reduced at this temperature However, the modulated index change of IA gratings remains stable at lower annealing temperatures of 80°C, and the mean index change decays at a comparable rate to Type I gratings at 80°C. Extending this work to include the thermal decay of Type IA gratings inscribed under strain shows that the application of strain quite dramatically transforms the temperature characteristics of the Type IA grating, modifying the temperature coefficient and annealing curves, with the grating showing a remarkable improvement in high temperature stability, leading to a robust grating that can survive temperatures exceeding 180°C. Under conditions of inscription under strain it is found that the temperature coefficient increases, but is maintained at a value considerably different to the Type I grating. Therefore, the combination of Type I and IA (strained) gratings make it possible to decouple temperature and strain over larger temperature excursions.

Support-mediated alkane activation over Pt-SO4/Al2O3 catalysts

The development of catalytic materials for the efficient combustion of light alkanes is fundamentally important for both automotive pollution control and the control of emissions produced from bio-fuel combustion. The presence of trace gas-phase SO2 is known to promote low temperature propane combustion over conventional Pt/Al2O3 combustion catalysts, however, there have been no systematic efforts to isolate the respective roles of support and metal, and it remains unclear, which plays the dominant role in this unusual phenomenon. Light alkane combustion over Pt/Al2O3 using pre-sulfated alumina supports to tune the physicochemical catalyst properties was presented. Support sulfation significantly enhanced ethane combustion, and improved methane and propane light-off. Catalyst activity increased with Pt loading, while the magnitude of sulfate promotion scales with alkane chain length. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).

Support-mediated alkane activation over Pt-SO4/Al2O3 catalysts

Sulphate-promoted alkane combustion has been investigated over a series of Pt/Al2O3 catalysts using pre-sulphated alumina supports. Catalyst sulphation greatly enhanced ethane combustion over Pt/Al2O3, and also improved methane and propane light-off performance. Catalyst activity increased with Pt loading, however the magnitude of sulphate promotion was independent of Pt loading under oxidising conditions, but scaled with alkane chain length. Propane combustion activity was directly proportional to the surface coverage of aluminium sulphate sites; support-mediated alkane activation is the dominant process in sulphate promotion.

Propene combustion over a model Pt/Al2O3/NiAl{110} catalyst

The genesis of a catalytically active model Pt/Al2O3/NiAl{110} oxidation catalyst is described. An ultrathin, crystalline γ-Al2O3 film was prepared via direct oxidation of a NiAl{110} single-crystal substrate. The room-temperature deposition of Pt clusters over the γ-Al2O3 film was characterised by LEED, AES and CO titration and follows a Stranski–Krastanov growth mode. Surface sulfation was attempted via SO2/O2 adsorption and thermal processing over bare and Pt promoted Al2O3/NiAl{110}. Platinum greatly enhances the saturation SOx coverage over that of bare alumina. Over clean Pt/γ-Al2O3 surfaces some adsorbed propene desorbs molecularly [similar]250 K while the remainder decomposes liberating hydrogen. Coadsorbed oxygen or sulfate promote propene combustion, with adsorbed sulfoxy species the most efficient oxidant. The chemistry of these alumina-supported Pt clusters shows a general evolution from small polycrystalline clusters to larger clusters with properties akin to low-index, Pt single-crystal surfaces.