Experimental research on the influence of the air humidity conditions in an air conditioning system

The factors that have influence on the energy consumption of a small air conditioning system that are worth mentioning are the efficiencies of the compressor, evaporator and condenser, the form that the refrigerant flow is controlled, the fan model used, and climatic conditions. Within the climate issue, an interesting factor is that the relative humidity when it comes to the effect that it causes, especially in the performance of the air condenser, which generally is not considered in the projects. This study aims to evaluate the influence of humidity on the coefficient of system performance (COP), seeking to quantify their influence when it happens. The tests were performed on a testing bench, mounted at the Laboratory for Energy Efficiency (LAMOTRIZ) UNESP-Campus Guaratinguetá. In the study, the wet bulb temperature was ranged, keeping the rotation of the scroll compressor with application of a frequency inverter in its best performance. The test bench is provided with a supervisory system of data collection that is also able to control all functions of the bench. In the results, there was a significant influence, particularly when comparing high humidity conditions with low humidity, noting that only over 65% relative humidity is that significant changes are observed in the COP of the system. © 2013 Elsevier Inc.

Caracterização da tecnologia de frio comercial e profissional

Hoje em dia a preocupação ambiental e a economia são fatores de sustentabilidade que são tidos em conta em países desenvolvidos, especialmente no seio da União Europeia. Reduzir os consumos de energia é, portanto, um ponto-chave para a redução das emissões de gases com efeito de estufa e aumentar a dependência das energias renováveis. Consequentemente surge então a necessidade de aumentar a eficiência dos equipamentos, em particular no presente caso, equipamentos de refrigeração. Para isso foi adotado pela Comissão Europeia uma rotulagem nos produtos consumidores de energia, em particular na refrigeração, os frigoríficos e congeladores domésticos permitindo informar o consumidor para os equipamentos mais eficientes. Mais recentemente, frigoríficos comerciais e profissionais também terão obrigatoriedade de incluir um rótulo energético na parte externa dos mesmos. Nesses rótulos estão incluídas várias informações técnicas do aparelho representadas de uma forma compreensível e lúdica aos olhos do consumidor mais leigo, entre as quais as classes de eficiência energética. As classes de eficiência energética caracterizam-se pela componente tecnológica dos frigoríficos. Perceber quais os componentes e materiais em particular que promovem uma melhor eficiência, quantificar a sua influência e avaliar os seus custos de integração torna-se assim essencial para toda a cadeia envolvida na produção destes equipamentos. Os fluídos frigorigénios e compressores aparentam ser os que mais exercem influência na eficiência de frigoríficos de baixa potência. Tubos capilares com trocador de calor são uma escolha mais eficiente comparado com o tubo capilar padrão que é utilizado nestes frigoríficos. Por forma a obter informação adicional e relevante do ponto de vista da análise energética realizaram-se simulações para determinação do consumo elétrico anual com recurso ao software Pack Calculation Pro. Entre os fluídos frigorigénios R-134a, R-22 e R-410a, os compressores scroll apresentaram consumos mais reduzidos (no máximo de 16%) do que os compressores alternativos. No caso do amoníaco (R-717) os compressores alternativos consumiram em média 14% menos do que os compressores parafuso. O recurso a velocidade variável em compressores permite reduzir o consumo na ordem dos 25%. Válvulas de expansão eletrónicas trazem reduções no consumo de 1,5% quando comparadas com válvulas de expansão termostáticas em compressores de velocidade variável. O propano (R-290) é um gás que mostra ter um melhor desempenho do que o R-134a e R404a em vários compressores, consumindo 16% menos do que o R-404a. Em função da temperatura exterior, o R-290 também apresentou um bom desempenho consumindo em climas quentes (Belém, Brasil) 24% menos do que o R-404a.

Assessing 1D Loss Models for the Off-Design Performance Prediction of Automotive Turbocharger Compressors

Single-Zone modelling is used to assess three 1D impeller loss model collections. An automotive turbocharger centrifugal compressor is used for evaluation. The individual 1D losses are presented relative to each other at three tip speeds to provide a visual description of each author’s perception of the relative importance of each loss. The losses are compared with their resulting prediction of pressure ratio and efficiency, which is further compared with test data; upon comparison, a combination of the 1D loss collections is identified as providing the best performance prediction. 3D CFD simulations have also been carried out for the same geometry using a single passage model. A method of extracting 1D losses from CFD is described and utilised to draw further comparisons with the 1D losses. A 1D scroll volute model has been added to the single passage CFD results; good agreement with the test data is achieved. Short-comings in the existing 1D loss models are identified as a result of the comparisons with 3D CFD losses. Further comparisons are drawn between the predicted 1D data, 3D CFD simulation results, and the test data using a nondimensional method to highlight where the current errors exist in the 1D prediction.

Elderly Middle Eastern Man Observing a Torah Scroll

Digital image

Elderly Middle Eastern Man Observing a Torah Scroll

Digital image

Scroll-Wave Dynamics in Human Cardiac Tissue: Lessons from a Mathematical Model with Inhomogeneities and Fiber Architecture

Cardiac arrhythmias, such as ventricular tachycardia (VT) and ventricular fibrillation (VF), are among the leading causes of death in the industrialized world. These are associated with the formation of spiral and scroll waves of electrical activation in cardiac tissue; single spiral and scroll waves are believed to be associated with VT whereas their turbulent analogs are associated with VF. Thus, the study of these waves is an important biophysical problem. We present a systematic study of the combined effects of muscle-fiber rotation and inhomogeneities on scroll-wave dynamics in the TNNP (ten Tusscher Noble Noble Panfilov) model for human cardiac tissue. In particular, we use the three-dimensional TNNP model with fiber rotation and consider both conduction and ionic inhomogeneities. We find that, in addition to displaying a sensitive dependence on the positions, sizes, and types of inhomogeneities, scroll-wave dynamics also depends delicately upon the degree of fiber rotation. We find that the tendency of scroll waves to anchor to cylindrical conduction inhomogeneities increases with the radius of the inhomogeneity. Furthermore, the filament of the scroll wave can exhibit drift or meandering, transmural bending, twisting, and break-up. If the scroll-wave filament exhibits weak meandering, then there is a fine balance between the anchoring of this wave at the inhomogeneity and a disruption of wave-pinning by fiber rotation. If this filament displays strong meandering, then again the anchoring is suppressed by fiber rotation; also, the scroll wave can be eliminated from most of the layers only to be regenerated by a seed wave. Ionic inhomogeneities can also lead to an anchoring of the scroll wave; scroll waves can now enter the region inside an ionic inhomogeneity and can display a coexistence of spatiotemporal chaos and quasi-periodic behavior in different parts of the simulation domain. We discuss the experimental implications of our study.

MOMENT ANALYSIS OF A SCROLL EXPANDER USED IN AN ORGANIC RANKINE CYCLE

Recent studies on small-scale power generation with the organic Rankine cycle suggest superior performance of positive displacement type of expanders compared to turbines. Scroll expanders in particular achieve high isentropic efficiencies due to lower leakage and frictional losses. Performance of scroll machines may be enhanced by the use of non-circular involute curves in place of the circular involutes resulting non-uniform wall thickness. In this paper, a detailed moment analysis is performed for such an expander having volumetric expansion ratio of 5 using thermodynamic models proposed earlier by one of the present authors. The working fluid considered in the power cycle is R-245fa with scroll inlet temperature of 125 degrees C for a gross power output of similar to 3.5 kW. The model developed in this paper is verified with an air scroll compressor available in the literature and then applied to an expander Prediction of small variation of moment with scroll motion recommends use of scroll expander without a flywheel over other positive displacement type of expanders, e.g. reciprocating, where a flywheel is an essential component.