The use of flow control devices to improve the flow pattern and throughput of sieve trays

Compared to packings trays are more cost effective column internals because they create a large interfacial area for mass transfer by the interaction of the vapour on the liquid. The tray supports a mass of froth or spray which on most trays (including the most widely used sieve trays) is not in any way controlled. The two important results of the gas/liquid interaction are the tray efficiency and the tray throughput or capacity. After many years of practical experience, both may be predicted by empirical correlations, despite the lack of understanding. It is known that the tray efficiency is in part determined by the liquid flow pattern and the throughput by the liquid froth height which in turn depends on the liquid hold-up and vapour velocity. This thesis describes experimental work on sieve trays in an air-water simulator, 2.44 m in diameter. The liquid flow pattern, for flow rates similar to those used in commercial scale distillation, was observed experimentally by direct observation; by water-cooling, to simulate mass transfer; use of potassium permanganate dye to observe areas of longer residence time; and by height of clear liquid measurements across the tray and in the downcomer using manometers. This work presents experiments designed to evaluate flow control devices proposed to improve the gas liquid interaction and hence improve the tray efficiency and throughput. These are (a) the use of intermediate weirs to redirect liquid to the sides of the tray so as to remove slow moving/stagnant liquid and (b) the use of vapour-directing slots designed to use the vapour to cause liquid to be directed towards the outlet weir thus reducing the liquid hold-up at a given rate i.e. increased throughput. This method also has the advantage of removing slow moving/stagnant liquid. In the experiments using intermediate weirs, which were placed in the centre of the tray. it was found that in general the effect of an intermediate weir depends on the depth of liquid downstream of the weir. If the weir is deeper than the downstream depth it will cause the upstream liquid to be deeper than the downstream liquid. If the weir is not as deep as deep as the downstream depth it may have little or no effect on the upstream depth. An intermediate weir placed at an angle to the direction of flow of liquid increases the liquid towards the sides of the tray without causing an increase in liquid hold-up/ froth height. The maximum proportion of liquid caused to flow sideways by the weir is between 5% and 10%. Experimental work using vapour-directing slots on a rectangular sieve tray has shown that the horizontal momentum that is imparted to the liquid is dependent upon the size of the slot. If too much momentum is transferred to the liquid it causes hydraulic jumps to occur at the mouth of the slot coupled with liquid being entrained, The use of slots also helps to eliminate the hydraulic gradient across sieve trays and provides a more uniform froth height on the tray. By comparing the results obtained of the tray and point efficiencies, it is shown that a slotted tray reduces both values by approximately 10%. This reduction is due to the fact that with a slotted tray the liquid has a reduced residence time Ion the tray coupled also with the fact that large size bubbles are passing through the slots. The effectiveness of using vapour-directing slots on a full circular tray was investigated by using dye to completely colour the biphase. The removal of the dye by clear liquid entering the tray was monitored using an overhead camera. Results obtained show that the slots are successful in their aim of reducing slow moving liquid from the sides of the tray, The net effect of this is an increase in tray efficiency. Measurements of slot vapour-velocity found it to be approximately equal to the hole velocity.

Recognition times of different views of 56 depth-rotated objects: a note concerning Verfaillie and Boutsen (1995)

The present study examines the effect of the goodness of view on the minimal exposure time required to recognize depth-rotated objects. In a previous study, Verfaillie and Boutsen (1995) derived scales of goodness of view, using a new corpus of images of depth-rotated objects. In the present experiment, a subset of this corpus (five views of 56 objects) is used to determine the recognition exposure time for each view, by increasing exposure time across successive presentations until the object is recognized. The results indicate that, for two thirds of the objects, good views are recognized more frequently and have lower recognition exposure times than bad views.

What is the prevalence of diabetic macular oedema involving the centre of the macula in patients undergoing digital diabetic retinopathy screening

Free Paper Sessions Design. Retrospective analysis. Purpose. To assess the prevalence of center-involving diabetic macular oedema (CIDMO) and risk factors. Methods. Retrospective review of patients who were screen positive for maculopathy (M1) during 2010 in East and North Birmingham. The CIDMO was diagnosed by qualitative identification of definite foveal oedema on optical coherence tomography (OCT). Results. Out of a total of 15,234 patients screened, 1194 (7.8%) were screen positive for M1 (64% bilateral). A total of 137 (11.5% of M1s) were diagnosed with macular oedema after clinical assessment. The OCT results were available for 123/137; 69 (56.1%) of these had CI-DMO (30 bilateral) which is 0.5% of total screens and 5.8% of those screen positive for M1. In those with CIDMO 60.9% were male and 63.8% Caucasian; 90% had type 2 diabetes and mean diabetes duration was 20 years (SD 9.7, range 2-48). Mean HbA1c was 8.34%±1.69, with 25% having an HbA1c =9%. Furthermore, 62% were on insulin, 67% were on antihypertensive therapy, and 64% were on a cholesterol-lowering drug. A total of 37.7% had an eGFR between 30% and 60% and 5.8% had eGFR <30. The only significant difference between the CIDMO and non-CIDMO group was mean age (67.83±12.26 vs 59.69±15.82; p=0.002). A total of 65.2% of those with CIDMO also had proliferative or preproliferative retinopathy in the worst eye and 68.1% had subsequently been treated with macular laser at the time of data review. Conclusions. The results show that the prevalence of CIDMO in our diabetic population was 0.5%. A significant proportion of macula oedema patients were found to have type 2 diabetes with long disease duration, suboptimal glycemic and hypertensive control, and low eGFR. The data support that medical and diabetic review of CIDMO patients is warranted particularly in the substantial number with poor glycemic control and if intravitreal therapies are indicated.

Networks of learning : how motorsport companies collaborate and share knowledge:evidence from the UK and Italian motorsport industries

The motorsport industry is a high value-added and highly innovative business sector. The UK’s leading racing car manufacturers are world class centres of research, development and engineering. However, individual firms in the sector do not have the range and depth of capabilities to compete independently in motorsport’s dynamic and competitive environment. Industry attention has therefore progressively focused on how networks of collaborating firms can work together to develop new products, improve business processes and reduce costs. This report presents findings from a three year Cardiff Business School study which examined the ways in which firms collaborate as part of wider networks. The research involved gathering data from over 120 firms in the UK and Italian motorsport sectors.

What drives the prediction of early reading? An analysis of stimulus and response-type

Purpose: Phonological accounts of reading implicate three aspects of phonological awareness tasks that underlie the relationship with reading; a) the language-based nature of the stimuli (words or nonwords), b) the verbal nature of the response, and c) the complexity of the stimuli (words can be segmented into units of speech). Yet, it is uncertain which task characteristics are most important as they are typically confounded. By systematically varying response-type and stimulus complexity across speech and non-speech stimuli, the current study seeks to isolate the characteristics of phonological awareness tasks that drive the prediction of early reading. Method: Four sets of tasks were created; tone stimuli (simple non-speech) requiring a non-verbal response, phonemes (simple speech) requiring a non-verbal response, phonemes requiring a verbal response, and nonwords (complex speech) requiring a verbal response. Tasks were administered to 570 2nd grade children along with standardized tests of reading and non-verbal IQ. Results: Three structural equation models comparing matched sets of tasks were built. Each model consisted of two 'task' factors with a direct link to a reading factor. The following factors predicted unique variance in reading: a) simple speech and non-speech stimuli, b) simple speech requiring a verbal response but not simple speech requiring a non-verbal-response, and c) complex and simple speech stimuli. Conclusions: Results suggest that the prediction of reading by phonological tasks is driven by the verbal nature of the response and not the complexity or 'speechness' of the stimuli. Findings highlight the importance of phonological output processes to early reading.