The study of the buoyancy–driven displacement ventilation flows has been conducted earlier through both mathematical modelling and experiments. There can be some assumptions made in the studies for thermal analysis such as: adiabatic boundaries, neglecting radiation heat transfer between wall surfaces, and neglecting the absorptivity of the air on simulating the thermal distribution within the ventilated spaces. This study considers heat conduction at boundaries, heat radiation between wall surfaces and radiative absorptivity of the air when modelling buoyancy-driven displacement ventilation flows. The simulations were carrying out using computational fluid dynamic (CFD) programme Star-CCM+. This study investigates the influence of the absorptivity of the air on thermal distribution within an enclosure ventilated by buoyancy-driven displacement ventilation flows. Two cases of buoyancy-driven displacement ventilation experiments conducted early by Sandbach (2009) and Li et al. (1993b) were modelled. To consider the absorptivity of the air, the local weather data were retrieved and were used for calculating the absorption coefficient of the air under different weather conditions. The participating media radiation model was employed to compute the radiation heat absorbed by the air. In addition, the performances of the turbulence models on modelling buoyancy-driven displacement ventilation flows were investigated to ensure the predicted results were accurate and satisfactory. The simulation results presented in this study have shown to agree well with the experimental data in two different experiment cases. In the case of the experiments conducted by Sandbach and Lane-Serff (2011b), the predicted results match well with the measurements when considering absorptivity of the air. The errors between the simulation results and the measurements were less than 10% in most cases. The results also suggest that the absorption coefficient has an influence on ventilation flow rate and consequently has an effect on the strength of the stratification. This indicates that the absorption coefficient should be determined according to the conditions rather than be given an one-and-for-all value. The simulation results have also shown to agree well with the measurements given in the literature presented by Li et al. (1993b). The effect of the absorptivity was shown to be more significant in the case of high supply airflow temperature or high supply heat load. Hence, radiative absorptivity of the air should be taken into account in order to accurately model the thermal distribution in the ventilated enclosure.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:697767 |
| Date | January 2016 |
| Creators | Chang, Chun-Chuan |
| Contributors | Apsley, David ; Lane-Serff, Gregory |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/computational-modelling-of-buoyancydriven-displacement-ventilation-flows(b733bf3b-6900-47f5-86a1-d0a7b2198f3c).html |
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