Refrigerator COP with thermal storage

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A sustainable alternative for cooling the machining processes using a refrigerant fluid in recirculation inside the toolholder

This article presents a cooling system for cutting tool in turning based in a toolholder with cooling fluid flowing inside its body being that this fluid must necessarily be able to phase change due to heat generated from machining processes. In this way, the fluid evaporates just under the cutting tool allowing a heat transfer more efficient than if were used a fluid without phase change once the latent heat of evaporation is beneficial for removal heat. Following, the cooling fluid evaporated passes through a condenser located out of the toolholder where it is condensated and returns to the toolholder again and a new cycle is started. In this study, the R-123, a hydrochlorofluorocarbon (HCFC) fluid, was selected for the turning of a Cr-Ni-Nb-Mn-N austenitic steel of hard machinability. The machining tests were carried out under three different machining conditions: dry machining, external cutting fluid (conventional method), and with the toolholder proposed. As result, the developed system allows a surface roughness up to 10% better than dry machining and a tool life close to the conventional method, but 32% superior to dry machining; moreover, there are environmental and economics advantages once the cooling fluid is maintained in a loop circuit.

Effectiveness-ntu computation with a mathematical model for cross-flow heat exchangers

Due to the wide range of design possibilities, simple manufactured, low maintenance and low cost, cross-flow heat exchangers are extensively used in the petroleum, petrochemical, air conditioning, food storage, and others industries. In this paper a mathematical model for cross-flow heat exchangers with complex flow arrangements for determining epsilon -NTU relations is presented. The model is based on the tube element approach, according to which the heat exchanger outlet temperatures are obtained by discretizing the coil along the tube fluid path. In each cross section of the element, tube-side fluid temperature is assumed to be constant because the heat capacity rate ratio C*=Cmin/Cmax tends toward zero in the element. Thus temperature is controlled by effectiveness of a local element corresponding to an evaporator or a condenser-type element. The model is validated through comparison with theoretical algebraic relations for single-pass cross-flow arrangements with one or more rows. Very small relative errors are obtained showing the accuracy of the present model. epsilon -NTU curves for several complex circuit arrangements are presented. The model developed represents a useful research tool for theoretical and experimental studies on heat exchangers performance.

Experimental analysis of heat recoveries with heat pipes operating in low inclination angle

Heat recovery devices are important in the optimization of thermal systems, since they can be used to reduce thermal losses to the environment. The use of heat pipes in these types of equipment can provide heat recoveries of higher efficiency, since both fluid flows are external and there are less contamination risks between the hot and cold fluids. The objective of this work is to study a heat recovery unit constructed with heat pipes and mainly, to analyze the influence of the inclination of the heat pipes on the performance of the equipment. For this analysis, a heat recovery unit was constructed which possesses 48 finned heat pipes in triangular geometry, the evaporator and condenser being of the same length. This unit was tested in an air-air system simulating a heat recovery process in which heat was supplied to the hot fluid by electrical resistances. The results have shown that there exists an inclination at which the system has a better performance, but for higher inclinations there is no significant increase of the efficiency of the system. This paper also presents the influence of inclination of heat pipes on effectiveness and NTU parameters which are important in heat exchanger design.

Coeficiente de operación de un sistema formado por un refrigerador doméstico acoplado a un acumulador de agua caliente para la recuperación de energía

An experimental apparatus containing a domestic refrigerator coupled to a vertical hot water storage tank was used for energy recovery. The original condenser of the refrigerator was maintained, but modified with a concentric tubes heat exchanger with countercurrent water and refrigerating gas flows. The coefficient of performance for the heat pump is calculated by the ratio of energy in the heat storage and the electric power consumed by the domestic refrigerator compressor. The results show that the increasing of hydrostatic pressure in the storage tank increases the water flow rate and the coefficient of performance. The proposed device also reduces the heat dissipation to the surroundings. This is more important in small confinements found in low-cost houses.

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.

Simulação do escoamento bifásico da mistura óleo-refrigerante através da folga radial de compressores rotativos de pistão rolante

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise numérica de condensadores do tipo arame-sobre-tubo usados em refrigeradores domésticos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Levantamento de coeficientes de desempenho de armazenador térmico associado a refrigerador doméstico modificado

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação do efeito da umidade relativa do ar no coeficiente de performance de um sistema de ar condicionado

Os fatores que influenciam no consumo de energia de um sistema de ar condicionado de pequeno porte, que merecem destaque são a eficiência do compressor através do modelo empregado, a forma que a vazão do refrigerante é condicionada, o modelo do ventilador empregado, o rendimento do evaporador, o condensador e as condições climáticas. Dentro da questão climática, uma questão bastante interessante é que a umidade relativa do ar, quando se trata do efeito que ela causa, principalmente no rendimento do condensador a ar, em geral não é considerada nos projetos. Este trabalho tem como objetivo avaliar a influência da umidade relativa do ar no coeficiente de performance do sistema (COP), procurando quantificar sua influência nas respectivas faixas em que elas acontecem. Nos resultados encontrados foi possível identificar que existe uma influência bastante significativa, principalmente quando comparam-se condições de alta umidade com de baixa umidade destacando que somente a partir da 65% de umidade relativa é que encontra-se alterações significativas no COP do sistema

A method for retrieving endodontic or atypical non-endodontic separated instruments from the root canal: a report of two cases

Aim: This clinical report presents a new method for retrieving separated instruments from the root canal with minimally invasive procedures. Background: The presence of separated instrument in root canal may interfere in the endodontic treatment prognosis. There are several recommended methods to retrieve separated instruments, but some are difficult in clinically practice. Case report: This study describes two cases of separated instrument removal from the root canal using a stainless-steel prepared needle associated with a K-file. Case 1 presented a fractured gutta-percha condenser within the mandibular second premolar, it was separated during incorrect intracanal medication calcium hydroxide placement. Case 2 had a fractured sewing needle within the upper central incisor that the patient used to remove food debris from the root canal. After cervical preparation, the fractured instruments were fitted inside a prepared needle and then an endodontic instrument (#25 K-file) was adapted with clockwise turning motion between the needle inner wall and the fragment. Conclusion: The endodontic or atypical nonendodontic separated instrument may be easily pull on of the root canal using a single and low cost device. Clinical significance: The methods for retrieving separated instruments from root canal are difficult and destructive procedures. The present case describes a simple method to solve this problem.

Ability of different methods to fill retrograde cavities with MTA.

The Mineral Trioxide Aggregate (MTA) has excellent biological property. However, its consistency makes it difficult to be inserted into retrograde cavities. Objective:To evaluate the ability of different methods to fill retrograde cavities with MTA. Material and methods: Root canals of thirty single-rooted resin teeth were prepared and filled. After the cut of 3 mm short of apical third, retrograde cavities with 3 mm deep were prepared using an ultrasound device and retrotips (CVD, São José dos Campos, SP, Brazil). The retrograde preparation was evaluate by using an operative microscope (D.F. Vasconcellos, São Paulo, SP, Brazil). The teeth were randomly divided into three groups (n = 10), according to the method: 1) condenser (Trinity, São Paulo, SP, Brazil); 2) MTA applicator (Angelus, Londrina, Brazil) + condenser; 3) condenser associated with ultrasound (CVD, São José dos Campos, SP, Brazil). After the filling of retrograde cavities with white MTA (Angelus, Londrina, Brazil), teeth were radiographed using a digital system (Kodak RVG 6000, Rochester, NY, USA). The images were analyzed by UTHSCSA Image Tool 3.0 software. The percentage of filling was calculated by the proportion between the total area of retrograde cavity and the filled area. The radiographic density mean of each third of retrograde cavity filled with MTA was measured by using the histogram tool of the software. The results were submitted to ANOVA and Tukey tests, with 5% of significance. Results: There was no difference in percentage of filling among the groups (p > 0.05) (approximately 85%). By comparing the thirds, the condenser and MTA applicator groups showed higher density for apical and middle third than cervical third (p < 0.05). The ultrasound group presented similar density among the thirds. Conclusion: The filling ability was similar for the studied methods. Ultrasound promoted better distribution of MTA in retrograde cavity, but did not increase the density of material.

Levantamento de coeficientes de desempenho de refrigeradores domésticos associados a armazenador térmico

Pós-graduação em Engenharia Mecânica - FEB