Papers by Evandro Luiz Lange Pereira
Proceedings of the 23<sup>rd</sup> IIR International Congress of Refrigeration: Prague, Czech Republic, August 21-26, 2011. Overarching theme: Refrigeration for Sustainable Development., Aug 21, 2011
The efficiency of reciprocating compressors adopted for household refrigeration is quite affected... more The efficiency of reciprocating compressors adopted for household refrigeration is quite affected by gas superheating in the suction system. This paper reports a numerical analysis of turbulent flow through the suction muffler of a small reciprocating compressor with especial attention to the heat transfer process. The integration of the flow conservation equations (continuity, momentum and energy) is carried out via the finite volume method. A hermetic reciprocating compressor was instrumented with several sensors to measure heat flux at the muffler wall, as well as temperature and velocity transients undergone by the fluid flow in the suction chamber. Overall, the numerical results are seen to be in reasonable agreement with the measurements, allowing the description of complex phenomena due to pressure pulsation and heat transfer in the muffler.
Reed valve dynamics has a major role on the performance and reliability of compressors and has be... more Reed valve dynamics has a major role on the performance and reliability of compressors and has been the subject of many studies over the years. In terms of mathematical modeling, most of these studies describe valve dynamics through a mass-spring-damper system in which a damping coefficient has to be empirically adjusted. This is a consequence of little knowledge about the effect of different parameters on valve damping. For instance, in spite of great effort to understand viscous effects on the pressure distribution acting on the valve surface, very few works have addressed such effects on valve damping, especially for valve geometries found in compressors. The present study aims to experimentally quantify valve damping under controlled conditions considering the effects of clamping geometry, clamping force, gasket thickness and the presence of fluid around the valve. Finally, experimental data of damping coefficients are used to predict valve dynamics and compressor efficiency. We found that the damping coefficients of typical valves adopted in small reciprocating compressors have negligible effect on compressor efficiency and valve bending stress, but can change by up to 17% the valve impact velocity against the seat.
Elsevier eBooks, 2013
The volumetric and isentropic efficiencies of scroll compressors are affected by the heat transfe... more The volumetric and isentropic efficiencies of scroll compressors are affected by the heat transfer that takes place inside the pockets during suction and compression processes. The present paper details a numerical model developed to predict the conduction heat transfer and temperature distribution of scroll wraps. The model was developed via the finite volume method and coupled to a thermodynamic model of the compression cycle. The results showed that the discharge temperature predicted with the solution of heat conduction through the scroll wraps was slightly lower than that obtained when a linear temperature profile was prescribed. It was also found that the heat transfer taking place in the metallic contact between the scrolls wraps acts to produce a linear temperature variation along their length.
Convective heat transfer in the compression chambers of scroll compressors affects important quan... more Convective heat transfer in the compression chambers of scroll compressors affects important quantities associated with the compression cycle, such as the volumetric efficiency and the discharge gas temperature. In spite of its relevance, heat transfer in scroll compressors has not been sufficiently studied mainly due to difficulties associated with its geometry. This paper presents a numerical model developed to predict the convective heat transfer in the compression chambers of scroll compressors, by applying the finite volume method to solve the conservation equations for mass, momentum and energy. An equation of state for real gas was also considered to complete the system of equations and relate pressure, temperature and density along the compression cycle. Due to the singular geometry of scroll compressors, an algorithm was developed to adapt the computational mesh throughout the simulation. The near wall region plays an important role on heat transfer and hence a low Reynolds turbulence model was adopted in the solution procedure. Results for convective heat transfer coefficient are compared with values returned by correlations commonly adopted in the literature.
Simulations of small reciprocating refrigeration compressors have been carried out by using one-,... more Simulations of small reciprocating refrigeration compressors have been carried out by using one-, two-and threedimensional formulations. In all approaches, the valve dynamics was described through a one-degree of freedom model, whereas a finite volume methodology was employed to discretize the governing flow equations. The valve dynamics and the time dependent flow field were coupled and solved simultaneously. Experimental data are used for an assessment of the accuracy of each model. The three-dimensional formulation allowed the inclusion of actual suction and discharge geometries in the simulation and served as the baseline to verify whether simpler and computationally less expensive models can satisfactorily predict the compressor performance. Results included in the analysis are p-V and T-V diagrams, valve displacement and pressure pulsation in the valve suction chamber.
Reed valve dynamics has a major role on the performance and reliability of compressors and has be... more Reed valve dynamics has a major role on the performance and reliability of compressors and has been the subject of many studies over the years. In terms of mathematical modeling, most of these studies describe valve dynamics through a mass-spring-damper system in which a damping coefficient has to be empirically adjusted. This is a consequence of little knowledge about the effect of different parameters on valve damping. For instance, in spite of great effort to understand viscous effects on the pressure distribution acting on the valve surface, very few works have addressed such effects on valve damping, especially for valve geometries found in compressors. The present study aims to experimentally quantify valve damping under controlled conditions considering the effects of clamping geometry, clamping force, gasket thickness and the presence of fluid around the valve. Finally, experimental data of damping coefficients are used to predict valve dynamics and compressor efficiency. We...
Suction and discharge systems have an important role in the efficiency of reciprocating machines.... more Suction and discharge systems have an important role in the efficiency of reciprocating machines. Several authors have dedicated attention to this subject, proposing different simulation methodologies to solve the pulsating flow that prevails in such systems. In this work, two numerical approaches are applied to predict the unsteady gas flow through the suction muffler of a reciprocating refrigeration compressor: a linear acoustic method and a finite volume model. The acoustic model considers mufflers as Helmholtz resonators and requires empirical loss coefficients to bring about pressure oscillation damping. In the finite volume methodology, the governing equations are integrated over control volumes placed along the solution domain, resulting in a system of algebraic equations that is then solved. Both models are implemented into a computaional code written to simulate the dynamic behavior of refrigeration compressors. Numerical results for pressure pulsation in the suction chambe...
Data in Brief, 2020
The data presented herein are related to the simulations and correlations reported in the article... more The data presented herein are related to the simulations and correlations reported in the article entitled "Numerical analysis and correlations for radial and tangential leakage of gas in scroll compressors" . The numerical simulations were carried out using the ANSYS FLUENT 12.1.4 CFD code, which is based on the finite volume method. Details of the numerical modeling setup and data collection are provided to allow reproducibility. The datasets include predicted values of radial and tangential leakage carried out using ANSYS FLUENT 12.1.4 CFD code for different gases, operating conditions and geometries expressed as dimensionless parameters. The scripts in Cþþ for the correlations of radial and tangential leakages developed based on the numerical predictions are also provided together with experimental and numerical data used to validate the correlations.
International Journal of Refrigeration-revue Internationale Du Froid, Oct 1, 2017
Heat transfer in the suction and compression chambers of scroll compressors has not been sufficie... more Heat transfer in the suction and compression chambers of scroll compressors has not been sufficiently studied and typical correlations available in the literature are based on simplified flow conditions. This paper presents the results of a model developed to predict fluid flow and heat transfer inside the suction and compression chambers of scroll compressors. Due to the particular geometry of scroll compressors, an algorithm was developed to automatically adapt the computational mesh for each orbiting angle. Convective heat transfer is strongly affected by the flow in the nearwall region and for this reason a low Reynolds number turbulence model was adopted in the simulations. The study covered a wide range of operating conditions and geometric parameters, allowing the proposal of a new heat transfer correlation for scroll compressors that is compared with other correlations available in the literature.
Simulations of small reciprocating refrigeration compressors have been carried out by using one-,... more Simulations of small reciprocating refrigeration compressors have been carried out by using one-, two-and threedimensional formulations. In all approaches, the valve dynamics was described through a one-degree of freedom model, whereas a finite volume methodology was employed to discretize the governing flow equations. The valve dynamics and the time dependent flow field were coupled and solved simultaneously. Experimental data are used for an assessment of the accuracy of each model. The three-dimensional formulation allowed the inclusion of actual suction and discharge geometries in the simulation and served as the baseline to verify whether simpler and computationally less expensive models can satisfactorily predict the compressor performance. Results included in the analysis are p-V and TV diagrams, valve displacement and pressure pulsation in the valve suction chamber.
Procceedings of the 16th Brazilian Congress of Thermal Sciences and Engineering
Gas leakage through the clearance between piston and cylinder is a major source of thermodynamic ... more Gas leakage through the clearance between piston and cylinder is a major source of thermodynamic inefficiency in reciprocating compressors, therefore, any simulation model should accurately predict its effect on the overall performance. Factors like misalignment between piston and cylinder and components geometric errors are not taken into account in the simpler numerical models usually adopted to estimate the gas leakage. This paper aims to analyze the impact of such simplifications using a three-dimensional computational fluid dynamics (CFD) model, including transient effects resulting from the piston movement as well as actual geometric errors characteristic of the usual manufacturing processes adopted for the household compressor industry. The results are compared to numerical predictions of simpler models and its benefits are emphasized.
Fluid flow through acoustic mufflers is a complex phenomenon that has been investigated for many ... more Fluid flow through acoustic mufflers is a complex phenomenon that has been investigated for many years due to its importance in compressor efficiency. A one dimensional computational fluid dynamics model based on the finite volume methodology is developed to solve this flow, considering compressibility and thermal effects. Head losses of a suction muffler are evaluated with the model taking into account the pulsating flow condition in a dynamic simulation of the whole compressor. The results are compared with those given by an analytical acoustic model and with experimental data so as to assess the model capability. The acoustic model uses an equation to estimate the friction losses but requires empirical loss coefficients that vary according to the compressor working conditions. On the other hand, the computational fluid dynamics model estimates directly the friction losses from its transport equations and therefore requires no such adjustments. Another benefit provided by the fluid dynamics model is the evaluation of gas temperature throughout the muffler, which is considered to be constant in the acoustic model.
This paper presents a numerical analysis of the unsteady in-cylinder heat transfer for a simplifi... more This paper presents a numerical analysis of the unsteady in-cylinder heat transfer for a simplified model of a small reciprocating compressor under actual operating conditions, with an assessment of the influence of suction and discharge processes. A two-dimensional finite volume model is used to numerically solve the associated turbulent flow field, whereas the dynamics of valves is described by a one-degree of freedom model. Numerical results are provided for the instantaneous heat transfer at different wall surfaces inside the cylinder. Additionally, predictions for heat transfer are compared with estimates of correlations available in the literature. It is found that heat transfer is strongly affected by suction and discharge processes and this aspect is not well represented by current correlations.
The gas superheating that takes place throughout the suction system and inside the cylinder of re... more The gas superheating that takes place throughout the suction system and inside the cylinder of reciprocating compressors adversely affects their overall efficiency. Simulation models adopted in the design of reciprocating compressors are generally based on lumped formulation and rely on empirical correlations for different physical phenomena, including the gas-to-wall heat transfer in the cylinder. The present paper reports a numerical study of heat transfer inside the cylinder of a simplified geometry of reciprocating compressor, considering the effect of fluid flow through the valves. Predictions for the instantaneous heat transfer at the walls are obtained for actual operating conditions and compared with estimates given by correlations commonly adopted for reciprocating compressors. It is shown that the increase of heat transfer during the suction and discharge processes is not properly accounted for by such correlations. Based on the predictions, a new correlation for the in-cylinder heat transfer is put forward and tested in different operating conditions.
Convective heat transfer in the compression chambers of scroll compressors affects important quan... more Convective heat transfer in the compression chambers of scroll compressors affects important quantities associated with the compression cycle, such as the volumetric efficiency and the discharge gas temperature. In spite of its relevance, heat transfer in scroll compressors has not been sufficiently studied mainly due to difficulties associated with its geometry. This paper presents a numerical model developed to predict the convective heat transfer in the compression chambers of scroll compressors, by applying the finite volume method to solve the conservation equations for mass, momentum and energy. An equation of state for real gas was also considered to complete the system of equations and relate pressure, temperature and density along the compression cycle. Due to the singular geometry of scroll compressors, an algorithm was developed to adapt the computational mesh throughout the simulation. The near wall region plays an important role on heat transfer and hence a low Reynolds turbulence model was adopted in the solution procedure. Results for convective heat transfer coefficient are compared with values returned by correlations commonly adopted in the literature.
A lumped parameter thermal model has been developed to predict the temperature distribution of sc... more A lumped parameter thermal model has been developed to predict the temperature distribution of scroll compressors with especial attention to gas superheating in the suction process. Thermal resistances between the components were based on global heat transfer coefficients, whereas conduction heat transfer through the scroll wraps was solved via a one dimensional finite volume method. The thermal model was coupled to a thermodynamic model of the compression cycle and then applied to simulate the compressor performance at different conditions of speed and pressure ratio. The model was able to correctly predict the compressor temperature distribution for operating conditions within the range of those adopted for its calibration. The results showed a strong coupling between the compressor thermal profile and the temperatures of the motor and lubricating oil. The model demonstrated that heat conduction through the scroll wraps reduces slightly the discharge temperature.
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Papers by Evandro Luiz Lange Pereira