Cláudio Melo - melo@nrva.ufsc.br
Jackson B. Marcinichen - jackson@nrva.ufsc.br
Luis A. T. Vieira - torquato@nrva.ufsc.br
Universidade Federal de Santa Catarina, Departamento de Engenharia Mecânica
Caixa Postal 476 - 88.040-900 - Florianópolis - SC

In the Brazilian market most of the refrigerators are assembled with plate-type evaporators. This type of evaporator is constructed of two flat sheets of aluminum so embossed and welded together as to provide a path for refrigerant flow between the two sheets. The air circulation over the evaporator occurs by natural convection. In despite of its.strong influence on the refrigerator performance, this component is frequently sized by empirical correlations relating the evaporator area and the refrigerator internal volume. In doing so the evaporator geometry is not taken into account. This work presents an experimental research plan that has been used in the investigation of plate-type evaporators to establish the inter-dependencies of channel pattern, channel internal diameter, refrigerant pressure drop and the evaporator overall heat transfer coefficient.

Keywords: Household refrigerator, Plate-type evaporator, Heat flux meter
 
 

José L. Gasche*- gasche@dem.feis.unesp.br
Departamento de Engenharia Mecânica
Universidade Estadual Paulista -UNESP
15385-000 Ilha Solteira, SP - Brasil

Rogério T. S. Ferreira - rogério@emc.ufsc.br
Álvaro T. Prata - prata@nrva.ufsc.br
Departamento de Engenharia Mecânica
Universidade Federal de Santa Catarina
88040-900 Florianópolis, SC - Brasil

Gas leakage through the radial clearance is an important cause of volumetric efficiency loss in rolling piston compressors. A good understanding of its mechanism is essential in any attempt to increase the volumetric efficiency of the compressor. In this work the gas leakage is considered to be caused by a mixture composed by oil and refrigerant dissolved in it. The mixture flow is modeled as a stationary homogeneous two-phase flow using complete momentum equations written in bicylindrical coordinate system. The finite volume methodology is used to solve the resultant equations system. The results obtained are compared to those obtained by Gasche et al. (2000), who used a simplified two-phase homogeneous model and they show that the discrepancy in the calculation of refrigerant mass flow rate resulting from both models can reach 30% for flows in lower temperatures through greater clearances.

Keywords: Two-phase flow, Homogeneous, Oil-refrigerant mixture, Radial Clearance
 
 

Marcos Rogério Barbazelli
André Luiz Seixlack - andre@dem.feis.unesp.br
Universidade Estadual Paulista, Câmpus de Ilha Solteira, Departamento de Engenharia Mecânica, 15385-000, Ilha Solteira, SP, Brasil

This work presents an analysis of thermal non-equilibrium influence between the liquid and vapor phases, comparing the calculated results by the two numerical models to simulate refrigerant flow through capillary tube suction line heat exchangers. The well-know two-fluid model is employed for the two-phase flow region. Two versions of this model are considered in this work. In the first, namely Model 1, the hydrodynamic and the thermodynamic non-equilibrium between the liquid and vapor phases are taken into account, whereas for the second, namely Model 2, only the hydrodynamic non-equilibrium between the phases is considered. The refrigerant mass rate is predicted by the model as a function of the heat exchanger geometry and operating conditions. Comparisons with experimental date for HFC134a are performed and discussed. The experimental data were either taken from the literature or supplied by the Center for Refrigeration, Ventilation and Air Conditioning Research, "NRVA". Comparisons are also made with a homogeneous model.

Keywords. Capillary tube, heat exchanger, refrigeration.
 
 

Francisco F. S. Matos - fred@nrva.ufsc.br
Alvaro T. Prata - prata@nrva.ufsc.br
César J. Deschamps - deschamps@nrva.ufsc.br
Departamento de Engenharia Mecânica, Universidade Federal de Santa Catarina
88040-900, Florianópolis, SC, Brasil.

In present work a numerical methodology is developed to predict the dynamic behavior of compressor automatic valves. A one degree of freedom model is adopted for the valve motion and a finite volume method is employed to numerically solve the flow through the valve including the reed and piston move. A moving coordinate system that expand and contract according to the piston and the reed instantaneous positions is used. Results for the force acting on the reed were obtained for a prescribed movement of the piston and allowed an analysis of the adequacy of using pressure as boundary condition for the valve entrance.

Keywords: Prescribed pressure, Valve dynamic, Moving grids.
 
 

Osvaldo J. Venturini - osvaldo@iem.efei.br
Manuel da S. Valente de Almeida - manuelvalente@uol.com.br
Eli Silva - eli_silva@uol.com.br
Escola Federal de Engenharia de Itajubá - EFEI
Av BPS, 1303 CEP 37500-000 Itajubá - MG Brasil

The aim of this work is to present a computational model for simulation of a thermal storage air conditioning system, through which is possible to optimize the ice-on-coil storage tank. The storage process is optimized by minimizing the amount of energy consumption of the refrigeration system, in function of the load profile. The required simulation data, for each component of the system, can be obtained directly from manufacturer catalogues.

Keywords: Thermal storage, Optimization and Direct Expansion.
 
 

George Stanescu - stanescu@demec.ufpr.br
Federal University of Parana, Mechanical Engineering Department
81531-990 - Curitiba, PR - BRAZIL

The Peltier effect or thermoelectric cooling is a solid-state method of heat transfer generated at the junction between two semiconductors made of different materials. The difference between the conventional refrigeration and thermoelectric cooling is that a thermoelectric cooling system refrigerates without use of mechanical devices. Heat absorbed at the cold junction is pumped to the hot junction at a rate proportional to electric current passing through the circuit. The aim of this paper is an attempt to answer the question of shape optimization for maximum refrigeration of a convectively cooled thermoelement with variable circular cross-sectional area. The two-point boundary-value initial problem of temperature distribution in the thermoelement is converted to an equivalent two initial-value problem and then numerically integrated. An iterative routine using the Newton's method is employed to calculate a better approximation for the temperature  distribution. Solutions to these equations show the effects of various concave and convex geometrical shapes and convective cooling conditions on the overall performances of a Peltier-effect cooling device.

Keywords: Thermoelectric cooling, Peltier effect, Thermoelement shape optimization
 
 

Cláudio Melo - melo@nrva.ufsc.br
Universidade Federal de Santa Catarina, Departamento de Engenharia Mecânica
Caixa Postal 476 - 88.040-900 - Florianópolis - SC

Jony M. Zangari - jzangari@hussmann.com.br
Hussann Fast Frio do Brasil Ltda
Avenida Esperanto 443 - cep 88067-050 - Londrina - Pr

This work reports the results of an experimental study on concentric capillary tube-suction line heat exchangers commonly used as expansion devices in household refrigerators and freezers. Heat exchanger performance (mass flow rate and temperature at the outlet of the suction line) with the hydrocarbon R-134a was experimentally evaluated for a  range of heat exchanger assemblies (internal diameter and length of the capillary tube, length and relative position of the heat exchanger) and operating conditions (condensing pressure and subcooling). The tests were planned and performed following a statistical based methodology. Based on the resulting database a set of explicit equations to predict the refrigerant mass flow rate and the suction line outlet temperature was developed. The equations were compared with a large set of experimental data and a reasonable agreement was achieved. It is therefore anticipated that the equations will become a powerful tool for designers modeling refrigeration systems.

Keywords: Household refrigerator, Capillary tube, Heat exchanger, Expansion device