Master of Science By Research

Permanent URI for this collectionhttp://192.248.9.226/handle/123/11526

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Browsing Master of Science By Research by Subject "COMPUTATIONAL FLUID DYNAMICS"

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    Numerical evaluation of energy labeling test setups of ceiling fans
    (2019) Casseer DR; Ranasinghe RACP
    Ceiling fans are widely used as a means of providing thermal comfort to occupants in an indoor environment all around the world and it contributes to a significant portion of annual energy consumption throughout the world. A number of standards for efficiency analysis of ceiling fans are employed by many countries, with the intention of making ceiling fans more efficient. In these test standards, different test setups have been utilised. Work performed on analysis of the effect of these setups on performance evaluation of ceiling fans is currently unavailable. Further, there is a scarcity of research work performed on analysis of flow characteristics around a rotating ceiling fan. Understanding the proper flow around a rotating ceiling fan can lead to designing more efficient fan blades, which can lead to significant energy savings. Therefore, this study is split into two sections. In section one, a systematic investigation of the different test standards available for performance analysis of ceiling fans is performed, namely standards considered are ANSI/AMCA 230 standard, IEC 60879: 1986 standard, SLS 1600:2011 standard and Energy Star v1.2 standard for performance testing of ceiling fans. In section two, a flow physics analysis around a ceiling fan is carried out. For these, a CFD model was developed and it was validated using experimental results. The analysis of test standards was carried out by using a RANS method whereas the analysis of flow physics was carried out by using LES method. The numerical results obtained shows that the test cylinder present in some of the standards mentioned above, does not have a significant impact on the measured performance of the tested ceiling fan (variation is less than 2%), therefore having a test cylinder at an extra cost have no benefit on the measured results of ceiling fan testing. On the other hand, maintaining test cylinders for every fan size would impart a significant cost on the testing process and having a cylinder which is not correctly aligned can lead to inaccurate readings. From the flow results of the LES simulations, creation of two major vorticial structures is seen arising from the tip and the root of the blade. As these vorticial structures move further downward, more vortices were formed due to the action of these and the number of vortices keep growing with flow time, resulting the flow to become turbulent with the flow time. Furthermore, it was seen that the flow transition from laminar to turbulent occurred at the mid chord section, starting from the deflected section of the blade
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    Numerical modeling of the flow field for indoor thermal comfort of a building under stack effect
    (2015-11-27) Nimarshana, PHV; Attalage, RA; Perera, KKCK
    In recent years natural ventilation is widely recognised as excellent contributing towards in design low energy buildings. The main challenge in natural ventilation is identified as lack of knowledge in providing acceptable thermal comfort in an occupied space to meet the internal requirements against the prevailing climatic conditions variations. Numerical investigations of the indoor thermal comfort condition in a simple office space governed by the solar chimney stack effect have been undertaken using CFD techniques. A mathematical model was developed based on the relevant analytical framework governing the phenomena to simulate the velocity flow field and temperature distribution on the designated plane within the indoor space. Boussinesq approximation was incorporated to numerical scheme with realistic boundary conditions for flow simulation. The model was enriched by incorporating a sufficient fluid volume to represent environment surrounding the space and thereby eliminating the entry effect to the flow. Hexahedral cells were used in a non-uniform grid distribution to minimise numerical diffusion. A fine mesh is used near the walls to enhance the resolution and accuracy resolving the problems under the turbulent flow conditions. Grid independence analysis was carried out to ensure the accuracy of the numerical results. Under-relaxation factors 0.3, 1, 2, 0.8, 0.8, 1, 0.9 for pressure, density, momentum, turbulence kinetic energy, turbulence dissipation rate, turbulent viscosity, energy respectively were used. The model outputs were compared with the available experimental measurements taken under the same condition to calibrate the numerical scheme. A parametric study was carried out using the calibrated model to assess the distribution of thermal comfort index against the changes in geometrical and solar radiation parameters. The values of activity, metabolic rate for seated activity and clothing insulation were selected as 0, 60 W/m2 and 0.5 Clo respectively for thermal performance analysis. The effect of each input parameter was investigated in terms of mean value and standard deviation corresponding to the flow velocity and the PPDNV value. It can be concluded that the present model is capable of predicting the indoor thermal performance of a building under stack effect.