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CFD as a tool for analysis of complex geometry: Perspectives on time efficient simulations of interior household appliance components
Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Throughout recent years, computer based programs has been applied to solve and analyze industrial problems. One of these developed programs is the Computational Fluid Dynamics (CFD) program. The purpose of implementing CFD analysis is to solve complex flow behavior which is not possible with ordinary calculus. The extensive application of CFD in the industry is a result of improved commercial CFD codes  in terms of more advance partial differential equations (PDE) describing various physical phenomena, CAD and mesh-grid generating tools and improved graphical user interfaces (GUI). Today, CFD usage has extended to fields such as aerodynamic, chemical process engineering, biomedical engineering and drying technology.

As there is an on-going expansion of CFD usages in the industry, certain issues need to be addressed as they are frequently encountered. The general demand for simulation of larger control volumes and more advanced flow processes result in extensive requirement of computer resources. Numerous complex flow topics today require computer cluster networks which are not accessible for every company. The second issue is the implementation of commercial CFD codes in minor industrial companies is utilized as a black box based on the knowledge on fluid mechanic theory. A vital part of the simulation process is the evaluation of data through visual analysis of flow patterns, analysis on the sensitivity of the mesh grid, investigation of quantitative parameters such as pressure loss, velocity, turbulence intensity etc. Moreover, increased partnerships between industry and the academic world involving various CFD based design processes generally yields to a verbal communication interface which is a crucial step in the process given the fact of the level of dependency between both sides. The aim of this thesis is to present methods of CFD analysis based on these issues.

In paper I, a heuristically determined design process of the geometry near the front trap door of an internal duct system was achieved by implementing the CFD code COMSOL MultiPhysics as a communication tool. The design process was established by two counterparts in the project in which CFD calculations and geometry modifications were conducted separately. Two design criteria presenting the pressure drop in duct and the outflow uniformity was used to assess geometry modifications conducted by a CAD-engineer. The geometry modifications were based on visual results of the flow patterns. The geometry modifications confirmed an improvement in the geometry as the pressure drop was reduced with 23% and the uniformity was increased with 3%.

In paper II, volume-averaged equations were implemented in a tube-fin heat exchanger in order to simulate airflow. Focus was on achieving a correct volume flow rate and pressure drop (V-p) correlation. The volume averaged model (VAM) is regarded as a porous medium in which the arrangement of fins and tube bundles are replaced with volume-averaged equations. Hence, the computational time was reduced significantly for the VAM model. Moreover, experimental results of the (V-p) correlation showed good agreement with the VAM model.

Place, publisher, year, edition, pages
Karlstad: Karlstad University , 2011. , p. 50
Series
Karlstad University Studies, ISSN 1403-8099 ; 2010:40
Keyword [en]
CFD, Tumble dryer, Fluid mechanics, Design process, Heat exchanger, Comsol MultiPhysics, Volume averaged method
National Category
Fluid Mechanics and Acoustics
Research subject
Environmental and Energy Systems
Identifiers
URN: urn:nbn:se:kau:diva-6687ISBN: 978-91-7063-331-7 (print)OAI: oai:DiVA.org:kau-6687DiVA, id: diva2:376523
Presentation
2011-02-04, 9C203, 13:15 (Swedish)
Opponent
Supervisors
Available from: 2011-02-02 Created: 2010-12-10 Last updated: 2011-11-02Bibliographically approved
List of papers
1. Geometry development of the internal duct system of a heat pump tumble dryer based on fluid mechanic parameters from a CFD software
Open this publication in new window or tab >>Geometry development of the internal duct system of a heat pump tumble dryer based on fluid mechanic parameters from a CFD software
2011 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 5, p. 1596-1605Article in journal (Refereed) Published
Abstract [en]

One aspect of reducing the energy consumption of a household tumble dryer is to reduce the pressure drop of the circulating air in the internal duct system. It is, however, costly and time consuming to design several prototypes for airflow measurements. In this paper, several fluid mechanic parameters in a partial model of the internal duct system of a tumble dryer have been studied in the CFD software Comsol MultiPhysics. The purpose was to establish a numerically based design process, where the design is conducted based on visual analysis of air velocity and vorticity, and two design criteria. The geometry design was conducted by a CAD-engineer, which was the counterpart of this project. In order to enable a successful design process, it was essential to establish a strong relation between fluid parameters and design criteria in order to share knowledge effectively with the CAD engineer. Two geometry modifications, based on a standard model, were conducted on the duct. Based on the design criteria, the pressure drop and the non-uniformity coefficient of the outlet airflow, the second modification (Modification 2) represents an improvement as the pressure drop is reduced by 23% and the uniformity at the outflow section is increased by 3%.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
CFD, Tumble dryer, Fluid mechanics, Design process, Geometry design
National Category
Fluid Mechanics and Acoustics
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-6673 (URN)10.1016/j.apenergy.2010.10.047 (DOI)000288360500015 ()
Available from: 2010-12-09 Created: 2010-12-09 Last updated: 2017-12-11Bibliographically approved
2. A volume averaged method applied to fluid flow in a tube-fin heat exchanger
Open this publication in new window or tab >>A volume averaged method applied to fluid flow in a tube-fin heat exchanger
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Numerical-based design of geometrical structures is common when studying systems involving heat exchangers, which are a central component in several fields such as industrial-, vehicle- and household systems. The geometrical structure of heat exchangers is generally comprised by narrow placed fins and tube bundles. Creating a mesh grid for a geometrically compact heat exchanger results in a dense structure which regularly is not feasible for personal computer usage. Hence, a Volume Averaged Model (VAM) was created based on a Representative Elementary Volume (REV) of tube-fin heat exchanger in an internal duct system of a heat pump tumble dryer.  A correlation of the volume flow rate and the force balance was established in the REV model with a finite element method simulation in COMSOL. The volume flow rate and force balance correlation was subsequently used to create a volume averaged expression of the momentum transport equations. These equations were implemented in the VAM model which represents the entire heat exchanger except the interior arrangements of fins and tube bundles. Hence, the computation time was reduced due to the absence of a dense mesh grid. Experimental results of the heat exchanger showed good agreement with the VAM model in terms of pressure drop and volume flow rate.

Keyword
CFD, Heat exchanger, Tumble dryer, Comsol MultiPhysics, Volume average method
National Category
Fluid Mechanics and Acoustics
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-6686 (URN)
Available from: 2010-12-10 Created: 2010-12-10 Last updated: 2011-11-02Bibliographically approved

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