ENCIT2012-235 THE EFFECT OF VALVE LEAKAGE ON COMPRESSOR PERFORMANCE - PDF
Leandro R. Silva, Cesar J. Deschamps, UFSC, Brazil
Abstract: Gas leakage that may occur in the incomplete sealing of compressor valves affects both the volumetric and isentropic efficiencies. This paper describes a numerical study of gas leakage in reed type valves of small reciprocating compressors commonly adopted in household refrigeration. The mathematical modeling approach takes into account important flow phenomena, such as acceleration and compressibility. The computations are carried out for a wide range of pressure differences that occur during a complete compression cycle. Results for the suction and discharge valves are used to analyze the influence of geometric parameters and fluid properties on the leakage process, with and without the deflection of the valves due to pressure load.
Keywords:Compressor; valve; leakage.
Presentation Schedule: Thursday, 11:00-11:20. Session: HVR2. Presenter: Cesar J. Deschamps.
ENCIT2012-013 A STUDY ON CYCLE DESIGNS FOR LIGHT COMMERCIAL CO2 REFRIGERATION SYSTEMS - PDF
Gustavo Portella Montagner, Cláudio Melo, UFSC, Brazil
Abstract: This paper compares three different cycle designs - capillary tube, thermostatic expansion valve and medium-pressure receiver - by experimentally evaluating the system behavior under variable ambient temperature. To this end, a detailed analysis was carried out focused on the effects of both the cycle design and ambient temperature on the system performance. It is shown that the thermostatic valve and the capillary tube designs have contrasting effects on the evaporator superheating and discharge pressure and that their effects on the overall system performance are quite similar. It is also shown that the medium-pressure receiver design is able to simultaneously control the superheating and the discharge pressure, leading to a performance improvement at low ambient temperatures. At high ambient temperatures no significant differences between the studied designs were observed.
Keywords:capillary tube; thermostatic valve; carbon dioxide; cycle design.
Presentation Schedule: Thursday, 11:40-12:00. Session: HVR2. Presenter: Gustavo Portella Montagner.
ENCIT2012-082 REDUCTION OF ENERGY CONSUMPTION IN REFRIGERATION AND AIR CONDITIONING VIA PROGRAMMABLE LOGIC CONTROLLER (PLC) - PDF
Carlos Pinnola, José Viriato Coelho Vargas, UFPR, Brazil
Abstract: This paper intends to implement a program for the PLC (Programmable Logic Control) to be applied in a refrigeration chamber to control the frequency of the inverter compressor motor according to a law potential. The results show that in the vapor compression refrigeration using speed control there is a reduction of energy of approximately 30\% in relation to conventional control turn-off. Experimental parameters relevant will be used in PLC programming for various configurations of refrigerators, compressors and thermal loads using a thermal camera in the laboratory itself UFPR
Keywords:speed; control; compressor; refrigerated kit smart.
Presentation Schedule: Thursday, 12:40-13:00. Session: HVR2. Presenter: Carlos Fernando Pinnola.
ENCIT2012-033 MAPPING THE ENERGY CONSUMPTION OF HOUSEHOLD REFRIGERATORS BY VARYING THE REFRIGERANT CHARGE AND THE EXPANSION RESTRICTION - PDF
Joel Boeng, Cláudio Melo, UFSC, Brazil
Abstract: In this work the thermodynamic behavior of a household refrigerator was experimentally studied by simultaneously varying the refrigerant charge and the expansion restriction. For this purpose a special charging device was designed and constructed. Such a device was comprised of a cylinder suspended by a cell charge and two solenoid valves. In addition, a metering valve was installed in series with a capillary tube whose diameter was a bit larger than that of the original tube. The pair capillary tube-metering valve allowed the growth or reduction of the flow restriction in respect to that provided by the original capillary tube. A specific household refrigerator was subjected to several combinations of refrigerant charge an expansion restriction and tested in a climate-controlled chamber, providing a database of 95 data points. The energy consumption was measured according to a steady-state methodology which substantially reduced the testing time. A minimum energy consumption region comprised of several combinations of refrigerant charge and expansion restriction was clearly identified. It was also observed that an improper combination of capillary tube and expansion restriction may increase the energy consumption by up to 30\%.
Keywords:household refrigerator; expansion device; capillary tube; refrigerant charge; energy consumption.
Presentation Schedule: Thursday, 11:20-11:40. Session: HVR2. Presenter: Claudio Melo.
ENCIT2012-195 ANALYSIS OF HEAT TRANSFER BEHAVIOR OF AN EVAPORATIVE CONDENSER USING DESIGN OF EXPERIMENTS METHODOLOGY - PDF
Rodrigo Ghiorzzi Donni, Paulo Smith Schneider, UFRGS, Brazil
Ivoni Carlos Acunha Jr, IFRS, Brazil
Abstract: This work aims to apply the methodology of design of experiments in an experimental model of an evaporative condenser built in small scale, keeping geometric similarity to real size equipments. The experimental condenser has a bundle of 35 copper tubes and is assembled with 6 rows inside a glass enclosure to allow for water and air flows visualization. The system operates with R22 as working fluid under different water and air mass flow rates. The large numbers of parameters involved in this experiment makes it hard to investigate its relationship and a Artificial Neural Network (ANN) is used to simulate the condenser behavior on a more controlled base, allowing for the statistical assessment by Design of Experiments (DoE) distinguishing the parameters that actually influence the phenomena. The ANN model achieved a satisfactory prediction of the rejected heat rate with a coefficient of determination R$^2$ of 94.7\% and a root mean square error (RMSE) of 0.0259kW. The application of DoE analysis of simulated data resulted in a correlation to predict the overall heat transfer coefficient (R$^2$) of 94.7\%. The higher deviation found between the experimental and the correlation was 13.28\%.
Keywords:evaporative condenser; design of experiments; artificial neural network; heat exchange.
Presentation Schedule: Thursday, 12:00-12:20. Session: HVR2. Presenter: Rodrigo Ghiorzzi Donni.
ENCIT2012-398 COP DEGRADATION DUE TO SUCTION SUPERHEATING IN REFRIGERATION CYCLES OPERATING WITH NON-AZEOTROPIC MIXTURES - PDF
Ricardo Fernando Paes Tiecher, José Alberto dos Reis Parise, PUC-Rio, Brazil
Abstract: The present work is concerned with the development of a thermodynamic model in which condensing and evaporating temperatures, as well as compressor empirical performance, are provided individually as input data. The primary goal is to obtain efficiency parameters for non-azeotropic R-22 replacements (R-410A, R-404A and R-407C) in simple vapor compression refrigeration cycles. The effect of evaporator superheat on cycle performance is studied. Results are presented as the discharge temperature, suction pressure and COP against the degree of superheating. The midpoint approach was adopted to define nominal condensing and evporating temperatures. Given the dependence of the heat transfer coefficient on the local governing conditions on each side of the heat exchangers, and in order to allow fora future extension of this work to UA models, a multi-zone approach was adopted.
Keywords:no-azeotropic; glide; multi-zone; simulation; COP degradation.
Presentation Schedule: Thursday, 12:20-12:40. Session: HVR2. Presenter: Ricardo Fernando Paes Tiecher.