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The Selection Of Screw Rotor Geometry With Compressor Speed As A Design Variable

Variable frequency drives (VFD) are becoming increasingly popular in screw compressor applications. The popularity is being driven by the demand for higher part load performance. Reducing speed to modulate capacity has proven to be more efficient than traditional methods of mechanical unloading. Compressors that are designed with the intent of applying VFD’s now have speed as a variable at the design point as well. Guidance is required to choose the correct speed and other geometric parameters associated with screw compressors. An analytical study using a one-dimensional (chamber) model has been done to explore the interactions between rotor speed and diameter, length, wrap angle, number of lobes, and discharge port. Correlations of compressor efficiency revealed by the study are explained based on fundamental principles. The correlations will help guide the design engineer in selecting the proper combination of speed and compressor geometry to achieve the best compressor efficiency for an application. The results of the study are then expressed using the non-dimensional parameters of specific speed and diameter. Compressor efficiency is known to be optimized when the value of these parameters fall within a specific range. The optimum values determined in this study are compared to historical values and differences are explained

Scottish exceptionalism? Normative codes of Scottish nationalism in the British and EU crises

Scotland has thus far proved immune to the appeal of right-wing populism present in many European neoliberal democracies. This paper argues that changing tension balances in the crises facing the UK as a union state cannot be reduced to an understanding of the supposedly internal challenge of Scottish sub-state nationalism. Instead sub-state nationalism needs to be situated in the shifting long-term, inter-state power balances of Britain as a union state and a rising and falling world power. Such an approach builds on the promise offered by the historical sociology of Norbert Elias to account for the over-functioning of the normative humanist we-ideals of Scottish civic nationalism in the British and EU crises

Selection of Twin Screw Compressor Economizer Port Location to Optimize Unit Efficiency

Twin screw compressors are widely used in many applications. The performance limits of screw compressors are continuously being pushed to meet increased demand for energy efficiency. Several design adjustments can be made to the compressor to create a more efficient unit, such as the proper design of an economizer. The economizer is a port where refrigerant vapor is (re-)injected. General compressor effects of using an economizer are increase in compressor power, increase in discharge mass flow, and reduction of isentropic efficiency. However, the unit experiences an increase in refrigeration capacity and efficiency. The use of economizers for screw compressors is a developing application. This paper examines the addition of an economizer to a water chiller system with the intent of achieving a unit efficiency improvement. The economizer port size and location impacts the compressor performance. For this study, the port size location is varied to understand how it affects the unit performance. A useful procedure is developed to optimize the unit efficiency using internal compressor and system modeling tools is discussed within this paper. The selected port location will be used to create a new screw compressor design that is anticipated to achieve a 2% to 3% improvement in the unit coefficient of performance

Outcomes and quality of life issues in the pharmacological management of benign prostatic hyperplasia (BPH)

BackgroundBenign prostatic hyperplasia (BPH) is a common disease of the aging male population. BPH treatment includes a variety of pharmacological and surgical interventions. The goal of this paper is to review the natural history of BPH, outcomes of pharmacological management, effects on quality of life (QoL), future pharmacotherapies, and associated patient-focused perspectives.Materials and methodsMedline searches for the keywords benign prostatic hyperplasia, BPH, alpha blockers, 5 alpha-reductase, and quality of life were performed. Relevant literature was reviewed and analyzed.ResultsAlpha blockers, 5 alpha-reductase inhibitors, and phytotherapy are the three categories of pharmaceutical interventions currently available for BPH. Various clinical trials have shown that alpha blockers and 5 alpha-reductase inhibitors are safe, efficacious, and improve QoL in patients with BPH. The evidence for phytotherapeutics is not as convincing. The current armamentarium of pharmaceutical interventions are encompassed in these three classes of medications. New pharmacotherapies based on novel mechanisms are on the horizon.ConclusionThere are a variety of safe and efficacious medical therapies available for the management of BPH and it is important for the practicing physician to have an understanding of these pharmacotherapies and their potential impact on the patient. There is not enough evidence to make a recommendation regarding phytotherapy use. New classes of drugs for BPH will likely find their way into routine use

Campaign for a Moral, Balanced Immigration Overhaul (CAMBIO), Strategic Review

In March 2014, Campaign for an Accountable, Moral, and Balanced Immigration Reform (CAMBIO) commissioned us to conduct an external review of the CAMBIO campaign. This report summarizes findings based on data gathered during an in-person focus group conducted with members of the CAMBIO Steering Committee in May 2014; a review of approximately 20 CAMBIO corporate documents and 36 internal meeting minutes; and 41 semi-structured telephone interviews conducted principally in June and July 2014

A CFD Investigation Of The Suction Process In A Screw Compressor

Computational fluid dynamics (CFD) has been widely applied to screw compressors. CFD has allowed engineers to gain a better understanding of the complex flows that occur inside the screw compressor. In many cases, the details revealed are only possible with CFD compared to 1-D simulations. Both CFD and 1D can reduce development costs and as in this case, guide decisions on the choice of hardware to be tested. This paper presents the flow details of the suction process in a screw compressor and the effects on performance. The cases presented are a twin screw rotor set applied to two different suction port designs. One suction port matches the helix angle of the rotors and closes at the maximum suction volume. The other suction port stays open for 20 degrees of rotation past the maximum suction volume and does not match the rotor helix angle. The paper presents the effects of the geometry difference at various rotor rotational speeds

Embajador Horacio Sevilla. Eros en el arte ecuatoriano

Embajador Horacio Sevilla. Eros en el arte ecuatoriano. Horacio Sevilla Borja / Eros en el Arte Ecuatoriano / Museo Nacional de Arqueología, Antropología e Historia / Exposición / Banco Central de Reserva Ecuador / Tolita / Chorrera / Machalilla / Abstracto elaborado por Viviana Leandro Orejon, en el marco del Programa “Soy Cultura” Voluntariado. Documento que forma parte de la colección documental "Recortes periodísticos del Instituto Nacional de Cultura [LIM-150121-MUS-CCN-001-26-06-1998