Mathematical model of a vapour absorption refrigeration unit

By means of carefully devised assumptions, a simple linear model is presented for an absorption refrigeration unit employing either water-lithium bromide or ammonia-water refrigerant-absorbent pairs. Absorption systems are an alternative to vapour compression systems by being thermally activated. Such heat energy may come from the sun or even from hot exhaust gases from a particular engineering process. A thorough investigation of the optimal operating temperatures is necessary to ensure effective operation of the system. By means of this simulation, the system response to varying absorber, generator and condenser temperatures was analyzed.peer-reviewe

Complete Clearance of Resistant Granuloma Faciale With Pulsed Dye Laser After Pre-treatment With Mometasone and Tacrolimus

Introduction: Granuloma faciale is an uncommon inflammatory dermatosis which usually affects the face and is often resistant to treatment.Case Report: A 39-year-old English lady with Fitzpatrick skin phototype II presented with typical lesions of granuloma faciale, confirmed on biopsy, on her cheeks and nose. Treatment with ScleroPlus pulsed dye laser (Candela Corporation, Wayland, Mass) produced no visible improvement. The patient re-presented 5 years later with the same lesions, now more prominent. No improvement was noted with topical mometasone, however addition of topical tacrolimus caused significant flattening. Since the erythema and telangiectases persisted, treatment with ScleroPlus pulsed dye laser was re-attempted. Treatments were performed with a wavelength of 595 nm, pulse duration of 1.5 ms and 7 mm spot at a fluence of 8.5 J/cm2 in the first session and 9.5 J/cm2 in the subsequent 2 sessions. This resulted in complete resolution without scarring or pigmentary change. There was no recurrence at follow-up one year later.Conclusion: Our observation supports the use of combination therapy in resistant cases of granuloma faciale. One such combination would be the application of a topical corticosteroid and tacrolimus followed by pulsed dye laser

Auditing thrombolysis service for stroke at Mater Dei Hospital

Thrombolysis for acute ischaemic stroke was introduced locally in October 2010. In 2012, the practice was audited to analyse the prevalence of inclusion and exclusion criteria for thrombolysis. Data about the local incidence of stroke, demographics and outcome was also obtained. All patients admitted to Mater Dei Hospital with a diagnosis of stroke over an 8 month period were recruited. Standard data collection sheets were used to obtain data. 251 patients were admitted with a confirmed stroke over the 8-month period. The time of onset was recorded in only 37.4% of cases. All patients had CT scanning of the brain within 24 hours of presentation, of which 70% were performed within 3 hours. The commonest 5 reasons for which thrombolysis was withheld were: presentation beyond 3 hours of symptom onset (73.7%), age over 80 years (29.9%), hypertension (13.9%), haemorrhagic stroke (13.1%) and minor deficit or rapid improvement (8.4%). Overall, only 4 patients (1.59%) were eligible for thrombolysis in our cohort, all of whom received the treatment. The study identified late presentation to A&E as the commonest exclusion criterion for thrombolysis. This prompted the launch of a stroke awareness ‘Act FAST’ campaign and increasing efforts to educate general practitioners to refer patients with acute stroke immediately. In addition, stroke pathway booklets were reviewed and simplified to increase their use. Since July 2013, the time window has been widened to 4.5 hours in accordance with international guidelines. Ongoing audit of thrombolysis is being carried out.peer-reviewe

Benchmarking local practice in view of introduction of thrombolysis for stroke in Malta

The aim of the study was to benchmark the quality of local stroke care in view of introduction of thrombolysis. Stroke patients admitted to Mater Dei Hospital over 6 weeks in 2008 were recruited. A questionnaire based on the 2006 Royal College of Physicians (RCP) National Sentinel Stroke Audit phase II (Clinical Audit) was used. Results were compared to the 2008 RCP National Sentinel Stroke Audit phase II (Clinical Audit) report. 42 confirmed strokes were admitted. All patients underwent CT scanning within 24 hours. 97% received aspirin within 48 hours. 26.2% spent >50% of their stay in the neurology ward. 81% were discharged alive. At 24 hours from admission, 54.7% were not screened for swallowing. 47.6% were not assessed by an occupational therapist. 81% were assessed by physiotherapy at 72 hours of admission. None of the patients had documented goals set by a multi- disciplinary team. If thrombolysis were available, 16.7% would have been eligible. The commonest contraindications were late presentation (52.4%) and age >80 years (35.7%). Local results compared well to the RCP 2008 results in initiation of aspirin, imaging, and nutrition. However, we noted need for improvement in the assessment of swallowing, mood and cognitive function as well as involvement of a multidisciplinary team. Since then, adherence to international guidelines has improved by the introduction of thrombolysis, a dedicated multidisciplinary service and the use of local guidelines for stroke.peer-reviewe

A parametric building energy simulation case study on the potential and limitations of passive design in the Mediterranean climate of Malta

The present case study sets out to investigate the potential and limitations of passive building design in a typical Mediterranean climate. The Maltese Islands were taken as the case study location. Assuming a fully detached, cuboid-shaped, generic multi-storey office building, one representative storey was modelled by means of the building energy simulation code WUFI®Plus. Thermal comfort was analysed based on the adaptive acceptable operative room temperature concept of EN 15251 for buildings without mechanical cooling systems. Assuming neither artificial heating nor cooling, the free-running operative room temperature was evaluated. By means of a parametric study, the robustness of the concept was analysed and the impact of orientation, window to wall area ratio, glazing, shading, thermal insulation, nighttime ventilation and thermal mass on the achievable level of thermal comfort is shown and discussed. It is concluded that in a well-designed building and by means of decent insulation (present case: Uwall = 0.54 W/(m2 · K)), double glazing, variable external shading devices and passive cooling by nighttime ventilation, a high level of thermal comfort is achievable in this climate using only very minor amounts of energy for artificial heating and cooling or possibly even none at all.peer-reviewe

A Review of Wind Turbine Yaw Aerodynamics

The fundamental physics of HAWT aerodynamics in yaw is reviewed with reference to some of the latest scientific research covering both measurements and numerical modelling. The purpose of this chapter is to enable a concise overview of this important subject in rotor aerodynamics. This will provide the student, researcher or industry professional a quick reference. Detailed references are included for those who need to delve deeper into the subject. The chapter is also restricted to the aerodynamics of single rotors and their wake characteristics. Far wake and wind turbine to turbine effects experienced in wind farms are excluded from this review. Finally, a future outlook is provided in order to inspire further research in yawed aerodynamics

Effects of geometry and tip speed ratio on the HAWT blade's root flow

In this study, the effect of the parameters playing a role in the root flow behavior of HAWT are only partly understood. To better reveal the root flow properties, this study presents the progression of HAWT blade root flow at two different blade geometries and at two different tip speed ratios. The effects of the geometry and the tip speed ratio on the root flow behavior and on the evolution of the root flow features are investigated. This study aims to answer the following questions: (i) What are the effects of the blade geometry and tip speed ratio on the root flow behavior? (ii) How are the blade wake and the root vortex evolution affected by the change of these parameters? The analysis of the velocity fields shows that the radial flow behavior changes with different blade geometries but a remarkable difference in the radial flow behavior is not observed with the change of tip speed ratio. The formation of the wake is different at three test cases because of different loading that the blades are encountered. From the circulation distribution along the blades, while a strong root vortex can be observed in Blade 1, the bound vorticity along Blade 2 builds up gradually when moving outboard, and do not show a trace of a strong root vortex.peer-reviewe

Evaluation of the lifting line vortex model approximation for estimating the local blade flow fields in horizontal-axis wind turbines

Lifting line vortex models have been widely used to predict flow fields around wind turbine rotors. Such models are known to be deficient in modelling flow fields close to the blades due to the assumption that blade vorticity is concentrated on a line and consequently the influences of blade geometry are not well captured. The present study thoroughly assessed the errors arising from this approximation by prescribing the bound circulation as a boundary condition on the flow using a lifting line free-wake vortex approach. The bound circulation prescribed to free- wake vortex model was calculated from two independent sources using (1) experi- mental results from SPIV and (2) data generated from a 3D panel free-wake vortex approach, where the blade geometry is fully modelled. The axial and tangential flow fields around the blades from the lifting line vortex model were then compared with those directly produced by SPIV and the 3D panel model. The comparison was carried out for different radial locations across the blade span. The study revealed the cumulative probability error distributions in lifting line model estima- tions for the local aerofoil flow field under both 3D rotating and 2D non-rotating conditions. It was found that the errors in a 3D rotating environment are consider- ably larger than those for a wing of infinite span in 2D flow. Finally, a method based on the Cassini ovals theory is presented for defining regions around rotating blades for which the lifting line model is unreliable for estimating the flow fields.peer-reviewe

Rotor aerodynamics in sheared inflow : an analysis of out-of-plane bending moments

A sheared wind profile creates an asymmetric wind field and an asymmetric wind turbine wake. Both of these have been described in the past but a study on their implications on the out-of-plane moment on the rotor is still a gap which needs to be addressed. A numerical assessment has been undertaken using a lifting-line free-wake vortex code. Owing to the lack of experimental validation, two other modelling approaches are used to assess the consistency of results - an actuator disc approach and a blade element momentum approach. Results were found to show acceptably good agreement. The line of action of the thrust force is found to be shifted by around 10% upwards above the rotor axis for the extreme shear case of α = 0.55. The wake was found to add to the asymmetry of the wind field by increasing the vertical shift in the line of action by 100% compared to the wind field alone. The results have important implications on the role of the out-of-plane bending moment on the wake kinematics as well as other issues related to fatigue performance of the rotor.peer-reviewe