Study On The Influences Of Air Flow Pattern On Contaminant Distribution In Laboratory

As an important place for scientific research work, the laboratory usually has many questions, such as the high energy consumption and the dangerous working environment with serious air pollution. The contradiction between high energy consumption caused by exhaust equipment and strong local exhaust ventilation has been the focus of laboratory ventilation design. How to exchange the indoor air effectively, to ensure the contaminant control ability of local exhaust equipment, and to achieve the safe and energy-saving effect is a major task for laboratory ventilation design.Based on the laboratory air distribution pattern in this paper, the numerical analysis model of laboratory room under different air distribution patterns was established with FLUENT software, and the reliability of the numerical analysis model was verified with experimental data. The influence of the fume hood face velocity, the contaminant type, and the other factors on the contaminant concentration around fume hood and worker, the indoor air velocity field, and the indoor temperature field was investigated by numerical simulation analysis. The simulating results showed that both the air supply velocity and the horizontal distance between the air supply inlet and the window of fume hood can affect the airflow distribution within the fume hood. Through the simulating analysis of higher density contaminant sf6(about 5 times of air density) and lower density contaminant NO2 and NH3(about 1.6 times and 0.5 times of air density respectively), it was found that the better air distribution modes on laboratory contaminant removal are the air distribution mode of displacement ventilation with up-return and down-supply and the air distribution mode of mixing ventilation with up-supply and down-return.Different face velocities of fume hood were simulated and analyzed in allusion to the conception that some laboratory staff think that the larger the face velocity is, the less is the possibility of contaminant escaping from the fume hood. The simulating results showed that when the face velocity is larger than 0.3m/s, the average contaminant concentration of the fume hood operating window decreases obviously. When the face velocity increases from 0.5m/s to 0.7m/s, the performance of fume hood has no significant improvement although the contaminant concentration decreases a little. In consideration that the energy consumption of the fan increases quickly with larger face velocity which is not conducive to energy saving and note that the 0.5m/s face velocity can control the contaminant concentration within the safety limit of protecting laboratory personnel's security, there is no need to use greater face velocity which results in unnecessary waste of energy.The laboratory energy consumption was also analyzed for different air distribution modes in this paper. The research results showed that under the condition of same laboratory supply air volume, the required cooling capacity for displacement ventilation is less than the one for mixing ventilation because of its higher supply air temperature, but its reheating energy consumption is higher than mixing ventilation. In order to decrease the reheating energy consumption, heat recovery device such as heat pipe can be employed in displacement ventilation system. Note that the ventilation efficiency of the displacement ventilation system is higher than the mixing ventilation system and the displacement ventilation system can extend the time of using outdoor air for free cooling during the transition season in which the energy consumption of mechanical cooling can be reduced, the displacement ventilation system has more potential for energy-saving than the mixing ventilation system when it is applied in laboratory in a place where the transition season is long and the outer door air is relatively dry.