On the Use of a Parallel Object-Oriented Code for Solving the Heat Transfer in Hermetic Reciprocating Compressors

The heat transport phenomenon in a hermetic reciprocating compressor is addressed in this work. This is far from straightforward. It involves several transient physical phenomena interacting to each other. The heat is exchanged between the refrigerant fluid and the solid parts of the compressor (suction muffler, cylinder head, crankcase, etc.). At the same time, the solid parts exchange heat to each other by means of conduction and radiation. Moreover, the phenomenon happens in non-symmetrical complex geometries and the solid parts are made of different materials. This is interesting from both the software engineering and the compressor design viewpoint. A parallel object-oriented software platform for the resolution of multiphysics problems is employed. This platform allows the use of partitioned strategies so that the compressor heat transport problem -a global problem- can be divided into several smaller parts -local problems-. This makes possible the use of multilevel modeling strategies for thermal systems analysis. Furthermore, in order to couple the several sub-problems in an integrated simulation, the platform provides data transfer tools -for matching and non-matching meshes- to exchange sub-domain state information. In particular, the work provides detailed information on the heat distribution and the temperature of the components of a test compressor. By means of comparative studies the thermal properties of some of its components are analyzed. This highlights the importance of choosing proper materials. For example, different suction muffler materials are tested to investigate their influence on the volumetric efficiency. Since the whole compressor is simulated, the consequences of altering specific component properties are also appreciated on the other components. In sum, the work presents illustrative numerical results of the three-dimensional heat transfer in a compressor that show the potential use of computer simulation to support design of components to attain feasibility and energy efficiency

Combined heat and moisture transfer in buildings systems

Temperature and humidity are the two main parameters indicating the comfort level of the building occupants. Although the effect of temperature is taken into account in thermal simulation of buildings, the moisture transfer through the rooms and porous building walls is sometimes neglected. The level of humidity can give different sensations of thermal comfort. It is necessary to take into account both heat and moisture transport in and around buildings to predict the hygrothermal behavior of rooms and building walls so as to calculate the energy demands correctly. In this work some benchmark exercises are worked out to see the performance of the heat and moisture transfer model implemented for rooms and porous walls. Finally, numerical results are compared with the measured data for a room exposed to varying outdoor conditions

Analysis of IAQ Based on Modeling of Building Envelope Coupled with CFD&HT Room Airflow

Buildings represent a major part of the world energy requirement. The simulation of combined heat, air and moisture (HAM) and pollutant transfer in this context is important to predict the indoor air quality (IAQ), along with the thermal comfort inside the buildings. Moreover, it is important to have appropriate levels of indoor humidity along with the room temperature as movement of water vapor through the building envelope causes a lot of harm to the building structure and reduces the quality of its thermal insulation leading to higher energy demand. The knowledge of the peak loads, temperatures, humidity levels can help to optimize the design of new buildings or existing buildings that need to refurbished and therefore results in energy efficient buildings. In this work a modular object-oriented building simulation tool (NEST) Damle (2011) with CFD&HT code Termofluids Lehmkuhl (2007), capable of coupling different levels of simulation models, allowing the simulation of heat, air, moisture and pollutant distribution (multizone model, envelope model, room analysis and HVAC system), is presented. The modular approach gives flexibility of choosing a model for each element and to have different levels of modeling for different elements in the system. Special attention has been focused on: the large eddy simulation turbulence models used for the room air dynamics and pollutants distribution transport and high performance parallel software. Parallelization of the building simulation is necessary if some critical processes/zones need to be modeled with more detail for reducing computational time. The main focus of this article is to couple the HAM and pollutants models for the building envelope with CFD&HT models with heat, moisture and pollutant transfer models for room airflow. An analysis of the effect of different materials on the IAQ of the buildings will performed. REFERENCES Damle, O. Lehmkuhl, G. Colomer, “Modular simulation of buildings with an object-oriented tool”, IIR International Conference of Refrigeration, Praga ,2011 O. Lehmkuhl, R. Borrell, C.D.Pérez-Segarra, M. Soria, A. Oliva, A new parallel unstructured CFD code for the simulation of turbulent industrial problems on low cost PC cluster, Parallel Computational Fluid Dynamics, Ankara, Turkey, 2007

Fluid-Structure Interaction of a Reed Type Valve

This paper aims at studying numerically the flow of a fluid through reed type valves, which are generally used in some reciprocating compressors and engines. The analysis and design of these valves serve not only to improve the performance of filling or discharging, but also to ensure system reliability. The valve opening-closing process involves fluid dynamics and deformation of a flat plate structure, both physics being completely coupled. To overcome this and other kind of fluid-structure interaction (FSI) problems, an in-house CFD-CSD (Computational Fluid Dynamics-Computational Structural Dynamics) coupled solver has been implemented within TermoFluids code. The CFD solver consists of a three dimensional explicit finite volume fractional step algorithm formulated in a second order, conservative and collocated unstructured grid arrangement. Since this case involves a turbulent flow, the wall adapting local eddy viscosity (WALE) model is employed. In order to save considerable effort in time and cost, the normal mode summation method is used to solve the deformation of the elastic valve. The geometric interaction between both dynamically moving media is managed with a fluid deformable mesh with moving boundaries, which belong to the solid valve. The static bodies, such as the walls, are embedded into the fluid mesh thanks to the immerse boundary method. The ‘CFD - Moving Mesh’ coupling is built by means of the space conservation law. From the point of view CFD-CSD coupling, a partitioned algorithm is used. For each time step, fluid and solid are solved consecutively until fluid pressure on the interface and displacements of the structure converge. In fact, only the Poisson equation for the fluid pressure ought to be coupled with the structure solver. Thus, grid updates and predicted fluid velocity calculation are solved only once at the beginning of the time step. First of all, the simulation platform is validated reproducing a benchmark FSI case from the literature that concerns a transient flat plate deflection analogous to the reed valve\u27s. Then, a sensitivity analysis is carried out in order to compare the transient operation of a generic reed valve under variations in its thickness

Numerical Analysis of Suction Mufflers

The aim of this paper is to present a group of numerical experiments of the fluid flow through different suction mufflers geometries to analyse pressure and velocity behaviour in addition with acoustic pressure effect. The numerical results are oriented to compare how suction muffler geometry affects mas flow rate and compressor efficiency performance on one side and pressure pulsations, transmission losses and compressor noise on the other side (1). The CFD&HT results have been obtained by means of TermoFluids code, a new unstructured and parallel object-oriented CFD&HT code for accurate and reliable solving of industrial flows (2). In all studied cases a multi-dimensional explicit finite volume fractional-step based algorithm has been used with symmetry preserving discretization scheme. When turbulence modelling is needed, an extension of the Yoshizawa non-equilibrium fixed-parameter subgrid-scale (3) model to non-structured meshes is used. The pressure equation is solved by means of parallel Fourier Schur decomposition solver, which is an efficient direct solver for loosely coupled PC clusters (4). Different CFD analysis of compressor suction mufflers has been developed (5) mainly based on k-e RANS models. The present paper is oriented on Large Eddy Simulation (LES) models. On the other hand, boundary conditions are coupled with a modular, unstructured and object oriented tool of the numerical simulation of hermetic reciprocating compressors (6)(7). (1) W. Soedel, Mechanics, simulation and design of compressor valves, gas passages and pulsation mufflers, Purdue University, 1992. (2) O. Lehmkuhl, R. Borrell, C.D.Pérez-Segarra, M. Soria, A. Oliva, A new parallel unstructured CFD code for the simulation of turbulent industrial problems on low cost PC cluster, Parallel Computational Fluid Dynamics, Ankara, Turkey, 2007. (3) W. Rodi, DNS and LES of some engineering flows, Fluid Dynamic Research, vol. 38, pp. 145-173, 2006 (4) R. Borrell, O. Lehmkuhl, M. Soria, A. Oliva; Direct Schur method for the solution of Poisson equation with unstructured meshes; Parallel CFD Congress, Antalya, Turkey, 2007 (5) (4)K. Sar?o?lu, A. Özdemir, A. Kaya, E. O?uz, An experimental and numerical analysis of refrigerant flow inside the suction muffler ofhermetic reciprocating compressor, International Compressor Engineering Conference at Purdue, 2012. (6) R. Damle, J. Rigola, C.D. Pérez-Segarra, J. Castro, A. Oliva, “Object oriented simulation of reciprocating compressors: Numerical verification and experimental comparison”, International Journal of Refrigeration, 34 (2011) 1989-1998. (7) J. López, O. Lehmkuhl, J. Rigola, C.D. Pérez-Segarra, “ Use of Low-Mach modelo n a CFD&HT solver for the elements of an object oriented program to numerically simulate hermetic reciprocating compressors”, International Compressor Engineering Conference at Purdue, 2012

Parallel Object-Oriented Algorithms for Building Performance Simulation. Application to an existing dwelling.

In the present work an existing dwelling, situated in the Netherlands, has been modeled by means of a parallel object-oriented simulation tool, called NEST-Buildings. The model is based on a pre-defined collection of elements (e.g., walls, rooms, openings, outdoors, occupants, ventilation tubes and boxes, solar radiation distributors, HVAC equipment, etc.) that are connected to each other conforming a dynamic thermal system. New configurations can be easily handled by adding or removing elements. Moreover, the building elements can be modeled at distinct levels of accuracy ranging from lumped volumes mixed with one-dimensional to detailed CFD&HT models. This approach makes possible the assessment of general-type buildings (residential, services, old, modern, etc.) using the appropriate modeling level at each component. The work is one more step in the improvement of this computer simulation tool. So far, the full simulation of the overall building model is based on block-Jacobi and Gauss-Seidel algorithms. With the current implementation, the computational time for performing practical simulations may become an important impediment as the size of the building increases. For instance, the computational expenses of a family house are far larger than those in a single apartment since the number of rooms, walls, events and so on is bigger. The last advances in this research line, including the use of optimum time stepping, proper mesh sizes, convergence criteria, loop control strategies and the use of other non-linear solvers based on the Newton method, are presented and discussed through comparative analysis of the simulated dwelling. The advances in this direction will help first to better understand the behavior of the already available algorithms and later to speed up the simulations. The second is important in the attainment of optimal designs of dwellings or other type of buildings.