Joaquim Rigola

Detailed Experimental Validation of the Thermal and Fluid Dynamic Behavior of Hermetic Reciprocating Compressors

A detailed experimental analysis of the thermal and fluid dynamic behavior of hermetic reciprocating compressors is presented. A hermetic compressor for household appliances has been experimentally tested. The fluid and solid thermal map evolution has been logged in several strategic points. The absolute instantaneous pressure has been determined in three specific zones: suction muffler, compression chamber, and cylinder head. The pV diagram inside the compressor chamber has also been experimentally obtained for the different working conditions studied without any previous hypothesis to determine the absolute pressure level. A complete description of the experimental equipment and its instrumentation is included. This experimental approach has allowed validating a mathematical model developed for the numerical simulation of the thermal and fluid dynamic behavior of hermetic reciprocating compressors. Good agreement between the detailed numerical results and the experimental data has been obtained, allowing a better understanding of the thermal and fluid dynamic behavior of these compressors.

Modeling and Numerical Simulation of the Thermal and Fluid Dynamic Behavior of Hermetic Reciprocating Compressors—Part 2: Experimental Investigation

An experimental validation of a mathematical model developed for the numerical simulation of the thermal and fluid dynamic behavior of hermetic reciprocating compressors is presented. Details of the physical model and a critical analysis of the quality of the numerical solutions are presented in a companion paper (Part 1). Different compressor geometries have been tested considering a wide range of working conditions and refrigerant fluids. A complete description of the experimental equipment and its instrumentation is included here. Good agreement between numerical and experimental data has been obtained, generating a better understanding of the thermal and fluid dynamic behavior of these compressors.

Modeling and Numerical Simulation of the Thermal and Fluid Dynamic Behavior of Hermetic Reciprocating Compressors—Part 1: Theoretical Basis

A detailed numerical simulation of the thermal and fluid dynamic behavior of reciprocating compressors, commonly used in household refrigerators and freezers, has been developed. The model is based on the integration of the transient fluid conservation equations (continuity, momentum, and energy) in the whole compressor domain (compression chamber, valves, manifolds, mufflers, shell, piston, connecting tubes, parallel paths, etc.) using instantaneous local mean values for different variables. Effective flow areas are evaluated considering a multidimensional model based on modal analysis of fluid interaction in the valve. In order to evaluate the instantaneous compression chamber volume, force balances in the crankshaft connecting rod mechanical system are simultaneously solved at each time-step. The thermal analysis of the solid elements is based on global energy balances at each macro-volume considered (shell, muffler, tubes, cylinder head, crankcase, motor, etc.). The resulting governing equations (fluid flow, valve dynamics, conductive heat transfer in solids, etc.) are discretized by means of a fully implicit control volume formulation. The complete set of algebraic equations is coupled using the segregated pressure-based algorithm Semi-Implicit Method for Pressure-Linked Equations (SIMPLEC) extended to compressible flow. A detailed numerical analysis is presented with the aim of verifying the quality of the numerical solution. A comparison between numerical simulation results and experimental data is presented in the companion paper (Part 2).

Fixed-Grid Modeling of Solid-Liquid Phase Change in Unstructured Meshes Using Explicit Time Schemes

Fixed-grid enthalpy models have been used extensively for solid-liquid phase-change computational fluid dynamics (CFD) simulations with implicit time schemes. In this work, this technique is implemented for explicit time schemes and collocated unstructured domain discretization, due to the interest in coupling phase-change formulations with turbulence models for liquid motion. Issues regarding the form of the energy equation, the treatment of the pressure equation, as well as the momentum source term coefficient introduced by the enthalpy-porosity method are described in detail. Numerical implementation is tested with different study cases, showing good agreement with other experimental and numerical results.

A novel Sigma–Delta ADC application oriented to test hermetic reciprocating compressors

A novel data acquisition approach to test hermetic reciprocating compressors is presented. A non-uniformly sampled application of a ΣΔ analogue-to-digital converter was used to investigate the compressor pV diagram, together with accurate spectral analysis of pressure readings. Several previous approaches are presented and compared with the one proposed here. Different statistical comparisons have been carried out with the main objective of demonstrating the good performance of the proposal.

A level-set method for thermal motion of bubbles and droplets

A conservative level-set model for direct simulation of two-phase flows with thermocapillary effects at dynamically deformable interface is presented. The Navier-Stokes equations coupled with the energy conservation equation are solved by means of a finite-volume/level-set method. Some numerical examples including thermocapillary motion of single and multiple fluid particles are computed by means of the present method. The results are compared with analytical solutions and numerical results from the literature as validations of the proposed model.

DNS of the wall effect on the motion of bubble swarms

Abstract This paper presents a numerical study of the gravity-driven motion of single bubbles and bubble swarms through a vertical channel, using High-Performance Computing (HPC) and Direct Numerical Simulation (DNS) of the Navier-Stokes equations. A systematic study of the wall effect on the motion of single deformable bubbles is carried out for confinement ratios CR = {2,4,6} in both circular and square channels, for a broad range of flow conditions. Then, the rising motion of a swarm of deformable bubbles in a vertical channel is researched, for void fractions α = {8.3%, 10.4%, 12.5%} and CR = {4, 6}. These simulations are carried out in the framework of a novel multiple marker interface capturing approach, where a conservative level-set function is used to represent each bubble. This method avoids the numerical and potentially unphysical coalescence of the bubbles, allowing for the collision of the fluid particles as well as long time simulations of bubbly flows. Present simulations are performed in a periodic vertical domain discretized by 2 × 106 control volumes (CVs) up to 16.6 × 106 CVs, distributed in 128 up to 2048 processors. The collective and individual behavior of the bubbles are analyzed in detail.

Feasibility of CO2 Compressors for Light Commercial Appliances

Commercial refrigerating systems are mostly based on hydrochlorofluorocarbon (HCFC) fluids. The Kyoto Protocol requirements encouraged the promotion of policies for sustainable development and reduction of global warming potential, including the regulation of HCFCs. In that sense, R-744 is the only natural refrigerant replacement known to be nontoxic, nonflammable, and not harmful to the environment. The aim of this work is to aid in the development of new reciprocating compressors for light commercial applications that use CO2 as the fluid refrigerant. First, a numerical analysis and experimental validation were developed and carried out, not only for laboratory compressor prototypes, but also for the whole transcritical CO2 cycle. The numerical comparative results present a reasonably good agreement and successfully allow the use of these numerical tools to improve the successive designs. Consequently, several compressor pre-industrial prototypes have been designed, validated, and improved. The experimental results against standard compressors show the possibilities that CO2 compressors offer in terms of efficiency and COP. Finally, an appliance test is presented to check the performance of the overall system and confirm the preliminary results obtained in the calorimeter tests. The appliance platform results prove the feasibility of these light commercial applications using R-744 as the fluid refrigerant.

Transient and dynamic numerical simulation of the fluid flow through valves based on large eddy simulation models

The present paper attempts the dynamic simulation of the fluid flow through valve reed using the in-house implemented CFD and moving mesh coupled code TermoFluids. The CFD solver is based on a parallel, second-order, conservative and unstructured finite volume discretization. Large eddy simulation is performed to solve the turbulent flow, using the subgrid scale WALE model. The moving mesh technique uses RBF interpolation. As a preliminary approach, a simplified geometry of an axial hole plus a radial diffuser with a piston based inlet condition is considered. The valve dynamics is modelled by a specific law according modal analysis of valve reed.

A parallel object oriented code framework for numerical simulation of reciprocating compressors – introduction of solid parts modeling

A partitioned coupled approach is employed to modeling a reciprocating compressor in a modular way. The approach allows the implementation of an object oriented parallel code framework for simulation of multiphysics systems in general and hermetic reciprocating compressors in particular.