Validation of a Charge-Sensitive Vapor-Injected Compression Cycle Model with Economization

In recent years, research on economized vapor injected (EVI) compression systems showed potential improvements to both cooling capacity and coefficient of performance (COP). In addition, the operating range of compressors can be extended by reducing the discharge temperature. However, the optimum operation of such systems is directly related to the amount of refrigerant charge, which often is not optimized. Therefore, an accurate charge estimation methodology is required to further improve the operation of EVI compression systems. In this paper, a detailed cycle model has been developed for the economized vapor injected (EVI) compression system. The model aims to predict the performance of EVI systems by imposing the amount of required refrigerant charge as an input. In the cycle model, the EVI compressor was mapped based on the correlation of Tello-Oquendo et al. (2017), whereas evaporator, condenser and economizer heat exchanger models were constructed based on the available ACHP models (Bell, 2010). With respect to charge inventory, the 2-point regression model from Shen et al. (2009) was used to account for inaccurate estimation of refrigerant volumes, ambiguity in slip flow model, solubility of refrigerant in the lubricating oil, among others. The cycle model has been validated with experimental performance data taken with a 5-ton Environmental Control Unit (ECU) that utilizes EVI technology. The developed cycle model showed very good agreement with the data with a MAE in COP of less than 4%. Furthermore, the estimated charge inventory has been compared to the one-point regression model. Results showed that the former method allowed to predict the charge inventory with an MAE of less than 0.5%

Development and Validation of a Mechanistic Vapor-Compression Cycle Model

Detailed models are crucial tools for engineers in designing and optimizing systems. In particular, mechanistic modeling of vapor compression systems for accurate performance predictions at both full- and part-load conditions have been improved significantly in the past decades. Yet, fully deterministic models present still challenges in estimating charge inventory in order to optimize the performance. In this work, a generalized framework for simulating vapor compression cycles (VCC) has been develvoped with emphasis on a charge-sensitive model. In order to illustrate the capabilities of the tool, a direct–expansion (DX) cycle has been considered. In the cycle model, the compressor was mapped by employing the ANSI/AHRI 540 10-coefficient correlation, the evaporator and the condenser were constructed based on the ACHP models (Bell, 2010). Furthermore, a TXV model was implemented based on Li and Braun (2008) formulation. With respect to the charge inventory estimation, the two-point regression model proposed by Shen et al. (2009) was used to account for inaccurate estimation of refrigerant volumes, ambiguous flow patterns for two-phase flow, and amount of refrigerant dissolved in the oil. The solution scheme required manufacturer input data for each component as well as the amount of refrigerant charge. Hence, the degree of superheating at the evaporator outlet, the subcooling at the condenser outlet and the perfromance parameters of the VCC system can be predicted. The model was validated with available experimental and numerical data available in literature. The simulation results demonstrated that the proposed model is more accurate and more generic than other methods presented in the literature

CFD Simulations of Single- and Twin-Screw Machines with OpenFOAM

Over the last decade, Computational Fluid Dynamics (CFD) has been increasingly applied for the design and analysis of positive displacement machines employed in vapor compression and power generation applications. Particularly, single-screw and twin-screw machines have received attention from the researchers, leading to the development and application of increasingly efficient techniques for their numerical simulation. Modeling the operation of such machines including the dynamics of the compression (or expansion) process and the deforming working chambers is particularly challenging. The relative motion of the rotors and the variation of the gaps during machine operation are a few of the major numerical challenges towards the implementation of reliable CFD models. Moreover, evaluating the thermophysical properties of real gases represents an additional challenge to be addressed. Special care must be given to defining equation of states or generating tables and computing the thermodynamic properties. Among several CFD suite available, the open-source OpenFOAM tool OpenFOAM, is regarded as a reliable and accurate software for carrying out CFD analyses. In this paper, the dynamic meshing techniques available within the software as well as new libraries implemented for expanding the functionalities of the software are presented. The simulation of both a single-screw and a twin-screw machine is described and results are discussed. Specifically, for the single-screw expander case, the geometry will be released as open-access for the entire community. Besides, the real gas modeling possibilities implemented in the software will be described and the CoolProp thermophysical library integration will be presented

NTERDEPENDÊNCIA e Colaboração em Contextos Escolares Inclusivos

Esta pesquisa teve como objetivo principal analisar as inter-relações do professor de ensino comum e do professor especialista em Educação Especial em um contexto escolar de escolarização de estudantes em situação de deficiência intelectual, considerando a política educacional implementada no município de São Mateus/ESBRA. Sendo, nessas inter-relações, as interdependências e colaboração, foco de nossas análises. Tomamos como referência os pressupostos da Sociologia Figuracional, elaborada no conjunto das obras de Norbert Elias, considerando os conceitos e noções do processo civilizador, figurações e interdependências. No que se refere a políticas e práticas desenvolvidas na Educação Especial, numa perspectiva inclusiva, buscamos conhecer as produções da legislação e dos serviços ofertados pelo município. O nosso caminho metodológico perpassou pela pesquisa de natureza qualitativa, e nos baseamos na pesquisa-ação colaborativocrítico. Como instrumento de coleta de dados, utilizamos a observação, questionários semiestruturados e a construção de práticas colaborativas no contexto de uma escola que conta com a matrícula e presença de estudantes em situação de deficiência intelectual. Os principais apontamentos nos permitem reiterar que a implementação de práticas de colaboração entre os professores de ensino comum e o professor especialista, tendem repercutir positivamente na consecução de práticas pedagógicas e contribuir no processo de constituição de saberes docentes mais qualificados às demandas da escolarização de estudantes com deficiência intelectual. No estudo realizado, contudo, tanto a professora do ensino comum, quanto à professora especialista encontram-se numa dinâmica em que as ações ocorrem muito mais no âmbito individual, marcado por restritas iniciativas de constituir um movimento de (re) criação de oportunidades para construção de elos e práticas em benefício da escola como inclusiva. Constatamos que, salta aos olhos, a ausência de uma organização escolar que permita aos profissionais acima citados, e demais profissionais da escola, momentos que possam discutir para que possivelmente seja construído um espaço que conjugue a coletividade. Sendo o fator tempo justificado para tais ausências como um condicionante para a desqualificação da educação escolar. Reconhecemos ser esse um processo lento e complexo, tanto na figuração da escola, quanto no âmbito municipal, pois exigirá um movimento de permissão, em que cada indivíduo entre no jogo, permitindo assim mudar de posição, refazer caminhos, ora recuar, ora avançar, mas envolver-se com o jogo

Full 3D numerical analysis of a twin screw compressor by employing open-source software

The push for having more reliable and efficient positive displacement machines (both compressors and expanders) for vapor compression and power generation (e.g., ORCs) applications has moved researchers to an always more spread employment of computational fluid dynamics (CFD). In particular, twin screw compressors, because of their high efficiency compared to other compressor types, have received interest over the last years. The numerical analysis of such machines is challenging: the deforming working chambers are very difficult to be correctly replicated. The relative motion of the rotors and the variation of the gaps during machine operation are few of the major difficulties in implementing reliable CFD models. A custom mesh generation algorithm is therefore often required for sumulating the machine operation. In this work, SCORG-V5.2.2 was used to generate the meshes of the deforming domain around rotating parts of the machines. The open-source software OpenFOAM-v1606+ is then employed to compute the flow field associated with the operation of the twin screw. The coupling of the two tools has been carried out in this work, applying the methodology to a twin screw machine

Doses e épocas de aplicação da adubação nitrogenada em quatro ciclos agrícolas de grãos sob sistema plantio direto na Amazônia.

O sistema de plantio direto vem sendo praticado há 40 anos no Brasil e a maior parte da área plantada encontra-se voltada para produção de grãos. Nesse sistema, o nitrogênio é um dos nutrientes que exige maior cuidado nas ações de manejo, em virtude da multiplicidade de reações químicas e biológicas que envolvem sua dinâmica. O objetivo do trabalho foi avaliar o efeito de doses e épocas de aplicação da adubação nitrogenada sobre a produção de milho e soja, durante quatro anos de cultivo. O experimento foi conduzido em área da Embrapa Amazônia Oriental (PA), em um Latossolo Amarelo distrófico. O delineamento experimental foi em blocos casualizados, em parcelas subdivididas. Os tratamentos foram três formas de aplicação e cinco níveis de N (0, 30, 90, 90, 120 kg ha-1). Utilizou-se a sucessão milho/milho/soja/milho por quatro ciclos agrícolas. No primeiro ano de implantação do sistema plantio direto a aplicação de dose crescente de N aumentou a produção de grãos e espigas de milho. No segundo ano de cultivo a produção de grãos de milho e a altura de plantas não sofreram influência da aplicação de dose de N, devido à maior imobilização do nutriente no solo. A produção de grãos de milho e a altura de plantas, no quarto ano agrícola, apresentam comportamento linear crescente, em função de aplicação de doses de N

Broad activation of the ubiquitin-proteasome system by Parkin is critical for mitophagy

Parkin, an E3 ubiquitin ligase implicated in Parkinson's disease, promotes degradation of dysfunctional mitochondria by autophagy. Using proteomic and cellular approaches, we show that upon translocation to mitochondria, Parkin activates the ubiquitin–proteasome system (UPS) for widespread degradation of outer membrane proteins. This is evidenced by an increase in K48-linked polyubiquitin on mitochondria, recruitment of the 26S proteasome and rapid degradation of multiple outer membrane proteins. The degradation of proteins by the UPS occurs independently of the autophagy pathway, and inhibition of the 26S proteasome completely abrogates Parkin-mediated mitophagy in HeLa, SH-SY5Y and mouse cells. Although the mitofusins Mfn1 and Mfn2 are rapid degradation targets of Parkin, we find that degradation of additional targets is essential for mitophagy. These results indicate that remodeling of the mitochondrial outer membrane proteome is important for mitophagy, and reveal a causal link between the UPS and autophagy, the major pathways for degradation of intracellular substrates

Machine Learning Applied to Positive Displacement Compressors and Expanders Performance Mapping

Positive displacement compressors are critical components in today’s vapor compression refrigeration, air conditioning, and heat pumping applications and can also be applied as expanders in power generation systems, such as organic Rankine cycles (ORC). The simulation of such systems is essential to predict and optimize the performance behavior at full- and part-load conditions. To this end, comprehensive system models are built by including different sub-models corresponding to each cycle component (e.g., heat exchangers, compressor, linesets). In general, the higher the complexity of each sub-models utilized to capture the physics, the higher the computational time required to solve a simulation run. In this work, deep learning is utilized to obtain high-accuracy performance predictions of positive displacement machines. A fixed-speed two-phase injected and vapor injected scroll compressor for air-conditioning applications and an oil-free scroll expander for low-grade waste heat recovery by means of an ORC are considered as test cases. In particular, Artificial Neural Network (ANN)-based models have been developed for each of the machines and trained using experimental data collected at the Ray W. Herrick Laboratories. The results of the training and testing of the models are presented as well as a discussion of the reliability of such models for extrapolating performance. In addition, the ANN models are compared with conventional empirical and semi-empirical modeling approaches. The models have been implemented in the Python programming language by using the open-source Keras package