Numerical modeling of indoor radon concentration distribution within an air-conditioned space

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Numerical modeling of indoor radon concentration distribution within an air-conditioned space

 

Author: Lee, Chi-kin
Title: Numerical modeling of indoor radon concentration distribution within an air-conditioned space
Degree: M.Sc.
Year: 1995
Subject: Radon -- Environmental aspects
Indoor air pollution
Air conditioning
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: v, 123 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1219797
URI: http://theses.lib.polyu.edu.hk/handle/200/2410
Abstract: Radon and its daughters have aroused the public health concern all over the world as they are suspected to be one of the causes of lung cancer. Several major sources of indoor radon in buildings of Hong Kong are principally building materials, soil and rock underlying and outdoor air. As the large population and the small size of city in Hong Kong, most people live and work in high-rise buildings. Thus they are surrounded by a greater amount of building materials and have more chances of radon exposure. In addition, because of its hot and humid weather, air conditioning is not uncommon nowadays in Hong Kong. Under this unique indoor conditions, it will be of general interest to study the level of indoor radon concentration especially in poorly ventilated indoor environments where accumulation will result in high indoor radon concentration. At present, the study of indoor radon concentration within an air-conditioned space is still in preliminary stage. There is no publication on the indoor radon concentration distribution under the effect of different inlet velocity of supply air, initial radon concentration within the space, supply/return air diffusers configuration and the radon source strength of walls/floors. In order to investigate the above issues, a series of research works are required which include the study of three-dimensional, turbulent, temperature dependent, two-phase mass diffusion model together with an extensive experimental works for validation. In this initial investigation, a simplified two-dimensional, laminar, isothermal, one-phase mass diffusion mathematical model was developed, and a numerical modeling technique using finite difference method was adopted to determine the velocity flow fields and the radon concentration within the space. Afterwards, four different types of supply air inlet and outlet diffusers arrangement are used as the configuration of the Trial Test Cases to implement the study. Having determined the necessary constant parameters and setting up the required numerical scheme, results are acquired by using the FORTRAN computer program. The program is capable of determining the flow fields and indoor radon concentration distribution, computing the maximum, minimum and average values of velocities and radon concentration, generating the vector plots and contour plots for visualization as well as producing data files to collect numerical results for analysis purposes. Finally, parametric studies are performed and the results are presented and analyzed. From the results obtained, it is observed that the inlet velocity of supply air is inversely proportional to the average indoor radon. In addition, the radon source strength is found to be directly proportional to the steady state average indoor radon concentration and the initial indoor radon concentration with values of 0.0, 5.0 Bq/m3 and 10.0 Bq/m3 retained in the space has no contribution to the steady state average indoor radon concentration for the four Trial Test Cases. Furthermore, the average indoor radon concentration increases as the model dimension decreases. In general, among the four different Trial Test Cases, the average indoor radon concentration in descending order is : Trial Test Case No. III, Case No. IV, Case No. II and Case No. I Considering the maximum-over-average ratio of the indoor radon concentration, Trial Test Case No. IV seems to produce the lowest ratio, independently of the model dimension. For the indoor radon concentration distribution, the results indicate that the maximum indoor radon concentration can be significantly higher than the average indoor radon concentration in all studied cases. From this dissertation, the radon concentration distribution within the four trial test cases can be obtained and visualized by means of contour plots. Moreover, several elementary relationships were established from the parametric study. For future works, energy equation and two-phase flow can be incorporated into the mathematical model and furniture/occupancy arrangement can be considered in this two-dimensional model so as to make the model more realistic and persuasive.

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