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Barbosa Jr. J.R.,Federal University of Santa Catarina | Ribeiro G.B.,Embraco Compressors | De Oliveira P.A.,Federal University of Santa Catarina
Heat Transfer Engineering | Year: 2012

We present a critical review of the literature on the fundamentals, design, and application aspects of compact and miniature mechanical vapor compression refrigeration systems. Examples of such systems are those envisaged for electronics and personal cooling. In comparison to other refrigeration technologies (e.g., solid-state), vapor compression enables the attainment of low evaporating temperatures while maintaining a large cooling capacity per unit power input to the system. Over the past decade, there have been a significant number of studies devoted to the miniaturization of system components, with the most critical being the compressor. When compared with competing cooling technologies, such as flow boiling in microchannels, jet impingement, and spray cooling, refrigeration is the only one capable of lowering the junction temperature to values below the ambient temperature. The combination of vapor compression refrigeration with the aforementioned technologies is also possible, necessary, and beneficial, since it increases greatly the potential for reducing the system size. For each main application, this paper sheds some light on the thermodynamic and thermal aspects of the cooling cycle and on recent developments regarding its components (compressor, heat exchangers, and expansion device). Whenever appropriate, issues and challenges associated with the different cycle designs are addressed. An overview of the ongoing efforts in competing technologies is also presented. © 2012 Copyright Taylor and Francis Group, LLC.

Alves M.V.C.,Federal University of Santa Catarina | Barbosa Jr. J.R.,Federal University of Santa Catarina | Prata A.T.,Federal University of Santa Catarina | Ribas Jr. F.A.,Embraco Compressors
International Journal of Refrigeration | Year: 2011

This work presents a mathematical analysis of an oil supply system for reciprocating compressors. The system is based on a single screw pump attached to the bottom end of the vertical rotating shaft immersed in the oil sump. The fluid flow in the pump was modeled with a semi-analytical approach based on the solution for the laminar fully developed oil flow in a screw extruder via the Generalized Integral Transform Technique. The screw pump model is coupled with that for the flow in the shaft region so as to provide an estimate of the oil flow rate and of the so-called 'climbing-time', i.e., the amount of time needed for a fluid particle to travel from the oil sump to the top of the shaft. The calculation method was verified against experimental data and Computational Fluid Dynamics modeling results. © 2010 Elsevier Ltd and IIR. All rights reserved.

Pussoli B.F.,Federal University of Santa Catarina | Barbosa Jr. J.R.,Federal University of Santa Catarina | Da Silva L.W.,Embraco Compressors | Kaviany M.,University of Michigan
International Journal of Heat and Mass Transfer | Year: 2012

The peripheral finned-tube (PFT) is a new geometry for enhanced air-side heat transfer under moisture condensate blockage (evaporators). It consists of individual hexagonal (peripheral) fin arrangements with radial fins whose bases are attached to the tubes and tips are interconnected with the peripheral fins. In this paper, experimentally validated semi-empirical models for the air-side heat transfer and pressure drop are combined with the entropy generation minimization theory to determine the optimal characteristics of PFT heat exchangers. The analysis is based on three independent parameters, i.e.; porosity, equivalent particle diameter and particle-based Reynolds number. The total heat transfer rate is a fixed constraint. The optimal heat exchanger configurations, i.e.; those in which the entropy generation number reaches a minimum, are calculated for constant heat flux and constant tube wall temperature boundary conditions. Performance evaluation criteria of fixed geometry, fixed face area and variable geometry were implemented. In all cases, it was possible to determine a combination of independent parameters that provided a minimum entropy generation rate. © 2012 Elsevier Ltd. All rights reserved.

Pussoli B.F.,Federal University of Santa Catarina | Barbosa J.R.,Federal University of Santa Catarina | Da Silva L.W.,Embraco Compressors | Kaviany M.,University of Michigan
International Journal of Heat and Mass Transfer | Year: 2012

The peripheral-finned tube is a new geometry aimed at avoiding moisture-condensate blockage hindering of the air-side heat transfer, by allowing for robust air flow pathways. It consists of a porous structure formed by periodic, radial-hexagonal fin arrangements of different radial extents mounted with a 30°offset from its neighboring level. Here, the air-side pressure drop and the heat transfer characteristics of five different heat exchanger prototypes with different geometric characteristics, such as the radial fin length, fin distribution, and heat exchanger length, were evaluated experimentally in an open-loop wind-tunnel calorimeter. The results demonstrate the effective performance, i.e., the pressure drop and heat transfer characteristics, of this new heat exchanger. A one-dimensional theoretical model based on the porous media treatment was also developed to predict the thermal-hydraulic behavior of the heat exchanger. The model incorporates the actual fin geometry into the calculation of the air-side porosity. The air-side permeability is calculated according to the Kozeny-Carman model and the particle-diameter based analysis. The model predicts the experimental data within a few percent RMS, depending on the correlations used for the friction coefficient and interstitial Nusselt number. © 2012 Elsevier Ltd. All rights reserved.

Kremer R.,Embraco Compressors | Barbosa Jr. J.R.,Federal University of Santa Catarina | Deschamps C.J.,Federal University of Santa Catarina
HVAC and R Research | Year: 2012

An analysis of the influence of oil atomization in the cylinder of a reciprocating compressor is presented in this paper. During compression, oil atomization enhances heat removal from the refrigerant gas. This cooling effect, which eventually results in a global temperature decrease of the compressor parts, aims primarily at reducing the refrigerant superheating in the suction system and inside the cylinder, which is largely responsible for overall energy losses and a decrease of the volumetric efficiency. A prototype was constructed and tested with R-134a in a hot gas-cycle calorimeter. A significant reduction of the compressor thermal profile has been achieved, with the largest variations of 30.9°C (55.6°F) and 23.6°C (42.5°F) in the discharge chamber and cylinder wall, respectively. A major dependence of the compressor efficiency parameters on the refrigerant solubility in the oil has been observed. A simulation model using an integral control volume formulation for mass and energy conservation in the cylinder and in other compressor components is proposed. Based on this model, the effect of oil atomization on the compressor performance is presented and discussed in terms of oil injection parameters, such as nozzle position, oil temperature and flow rate. © 2012 2012 ASHRAE.

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