Análise teórico-experimental do coeficiente de perfomance (COP) de um sistema de refrigeração por jato-compressão

The use of waste heat of energy conversion equipment to produce a cooling effect, consists currently in a very interesting way of efficiency improvement of energy systems. The present research has as intention the theoretical and experimental study of a new intermittent refrigeration system ejector cycle characteristics, with use of waste heat. Initially, was doing a bibliographical survey about the vapor ejector refrigeration system technology. In the following stage was doing a simulation of the corresponding thermodynamic cycle, with preliminarily intention to evaluate the performance of the system for different refrigerants fluids. On the basis of the results of the simulation were selected the refrigerant fluid and developed an experimental group of benches of the refrigeration system considered, where pressure and temperature sensory had been inserted in strategical points of the refrigeration archetype and connected to a computerized data acquisition system for measure the refrigerant fluid properties in the thermodynamic cycle. The test results obtained show good agreement with the literature

Análise da eficácia de um refrigerador doméstico com condensador modificado: revestimento com meio poroso dissipativo

The development of home refrigerators generally are compact and economic reasons for using simplified configuration. The thermodynamic coefficient of performance ( COP ) is limited mainly in the condenser design for reasons of size and arrangement ( layout ) of the project ( design ) and climatic characteristics of the region where it will operate. It is noteworthy that this latter limitation is very significant when it comes to a country of continental size like Brazil with diverse climatic conditions. The COP of the cycle depends crucially on the ability of heat dissipated in the condenser. So in hot climates like the northeast, north, and west-central dispel ability is highly attenuated compared to the south and southeast regions with tropical or subtropical climates when compared with other regions. The dissipation in compact capacitors for applications in domestic refrigeration has been the focus of several studies, that due to its impact on reducing costs and power consumption, and better use of the space occupied by the components of refrigeration systems. This space should be kept to a minimum to allow an increase in the useful storage volume of refrigerator without changing the external dimensions of the product. Due to its low cost manufacturing, wire on tube condensers continue to be the most advantageous option for domestic refrigeration. Traditionally, these heat exchangers are designed to operate under natural convection. Not always, the benefits of greater compactness of capacitors for forced outweigh the burden of pumping air through the external heat exchanger. In this work we propose an improvement in convective condenser changing it to a transfer mechanism combined in series with conductive pipes and wire to a moist convective porous medium and the porous medium to the environment. The porous media used in the coating was composed of a gypsum plaster impregnated fiber about a mesh of natural cellulosic molded tubular wire mesh about the original structure of the condenser , and then dried and calcined to greater adherence and increased porosity. The proposed configuration was installed in domestic refrigeration system ( trough ) and tested under the same conditions of the original configuration . Was also evaluated in the dry condition and humidified drip water under natural and forced with an electro - fan ( fan coil ) convection. Assays were performed for the same 134- refrigerant charge e under the same thermal cooling load. The performance was evaluated in various configurations, showing an improvement of about 72 % compared with the original configuration proposed in humidification and natural convection.

Análise tribo-termodinâmica da aplicação de nanopartículas de Al2O3 como aditivo lubrificante em compressor hermético de refrigeração

The thermodynamic performance of a refrigeration system can be improved by reducing the compression work by a particular technique for a specific heat removal rate. This study examines the effect of small concentrations of Al2O3 (50 nm) nanoparticles dispersion in the mineral oil based lubricant on the: viscosity, thermal conductivity, and lubrication characteristics as well as the overall performance (based on the Second Law of Thermodynamics) of the refrigerating system using R134a or R600a as refrigerants. The study looked at the influences of variables: i) refrigerant charge (100, 110, 120 and 130 g), ii) rotational speed of the condenser blower (800 and 1100 RPM) and iii) nanoparticle concentration (0.1 and 0.5 g/l) on the system performance based on the Taguchi method in a matrix of L8 trials with the criterion "small irreversibility is better”. They were carried pulldown and cycling tests according to NBR 12866 and NBR 12869, respectively, to evaluate the operational parameters: on-time ratio, cycles per hour, suction and discharge pressures, oil sump temperature, evaporation and condensation temperatures, energy consumption at the set-point, total energy consumption and compressor power. In order to evaluate the nanolubricant characteristics, accelerated tests were performed in a HFRR bench. In each 60 minutes test with nanolubricants at a certain concentration (0, 0.1 and 0.5 g/l), with three replications, the sphere (diameter 6.00 ± 0.05 mm, Ra 0.05 ± 0.005 um, AISI 52100 steel, E = 210 GPa, HRC 62 ± 4) sliding on a flat plate (cast iron FC200, Ra <0.5 ± 0.005 um) in a reciprocating motion with amplitude of 1 mm, frequency 20 Hz and a normal load of 1,96 N. The friction coefficient signals were recorded by sensors coupled to the HFRR system. There was a trend commented bit in the literature: a nanolubricant viscosity reduction at the low nanoparticles concentrations. It was found the dominant trend in the literature: increased thermal conductivity with increasing nanoparticles mass fraction in the base fluid. Another fact observed is the significant thermal conductivity growth of nanolubricant with increasing temperature. The condenser fan rotational speed is the most influential parameter (46.192%) in the refrigerator performance, followed by R600a charge (38.606%). The Al2O3 nanoparticles concentration in the lubricant plays a minor influence on system performance, with 12.44%. The results of power consumption indicates that the nanoparticles addition in the lubricant (0.1 g/L), together with R600a, the refrigerator consumption is reduced of 22% with respect to R134a and POE lubricant. Only the Al2O3 nanoparticles addition in the lubricant results in a consumption reduction of about 5%.

Análise tribo-termodinâmica da aplicação de nanopartículas de Al2O3 como aditivo lubrificante em compressor hermético de refrigeração

The thermodynamic performance of a refrigeration system can be improved by reducing the compression work by a particular technique for a specific heat removal rate. This study examines the effect of small concentrations of Al2O3 (50 nm) nanoparticles dispersion in the mineral oil based lubricant on the: viscosity, thermal conductivity, and lubrication characteristics as well as the overall performance (based on the Second Law of Thermodynamics) of the refrigerating system using R134a or R600a as refrigerants. The study looked at the influences of variables: i) refrigerant charge (100, 110, 120 and 130 g), ii) rotational speed of the condenser blower (800 and 1100 RPM) and iii) nanoparticle concentration (0.1 and 0.5 g/l) on the system performance based on the Taguchi method in a matrix of L8 trials with the criterion "small irreversibility is better”. They were carried pulldown and cycling tests according to NBR 12866 and NBR 12869, respectively, to evaluate the operational parameters: on-time ratio, cycles per hour, suction and discharge pressures, oil sump temperature, evaporation and condensation temperatures, energy consumption at the set-point, total energy consumption and compressor power. In order to evaluate the nanolubricant characteristics, accelerated tests were performed in a HFRR bench. In each 60 minutes test with nanolubricants at a certain concentration (0, 0.1 and 0.5 g/l), with three replications, the sphere (diameter 6.00 ± 0.05 mm, Ra 0.05 ± 0.005 um, AISI 52100 steel, E = 210 GPa, HRC 62 ± 4) sliding on a flat plate (cast iron FC200, Ra <0.5 ± 0.005 um) in a reciprocating motion with amplitude of 1 mm, frequency 20 Hz and a normal load of 1,96 N. The friction coefficient signals were recorded by sensors coupled to the HFRR system. There was a trend commented bit in the literature: a nanolubricant viscosity reduction at the low nanoparticles concentrations. It was found the dominant trend in the literature: increased thermal conductivity with increasing nanoparticles mass fraction in the base fluid. Another fact observed is the significant thermal conductivity growth of nanolubricant with increasing temperature. The condenser fan rotational speed is the most influential parameter (46.192%) in the refrigerator performance, followed by R600a charge (38.606%). The Al2O3 nanoparticles concentration in the lubricant plays a minor influence on system performance, with 12.44%. The results of power consumption indicates that the nanoparticles addition in the lubricant (0.1 g/L), together with R600a, the refrigerator consumption is reduced of 22% with respect to R134a and POE lubricant. Only the Al2O3 nanoparticles addition in the lubricant results in a consumption reduction of about 5%.