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EFFECT OF ENVIRONMENTAL DEFLECTOR ON AIR EXCHANGE IN SLURRY PIT AND CONCENTRATION DISTRIBUTION IN A TWO-DIMENSIONAL VENTILATION CHAMBER
Abstract
Variations of air exchanges in slurry pit with four angles of an environmental deflector, namely 0° (parallel to the side wall or without deflector), 30°, 45° and 90°, were investigated using a tracer gas method. The investigations were performed in a two-dimensional ventilation chamber in the Air physics Lab, University of Aarhus. Ventilation rates used in the experiments were 100 and 200 m 3 /h. The experiment results showed that using the deflectors of 30°, 45° and 90° the airflow patterns were obviously changed in the room space near the slatted floor and in the head space of the pit compared with the setup without deflector. It was also found that of all the deflector angle performances with respect to air- exchange ratio and concentration distribution, the deflector position of 45° in two airflow rates cases behaved better with the lowest pit ventilation and the highest concentration in the head
... Placing an environmental deflector inside the room and curtains inside the slurry pit may change the airflow pattern and reduce airflow between the slurry pit and the room. Tong et al. (2008) investigated influence of four deflector angles on air exchange rate using a two-dimensional (2D) chamber. However, the important parameters like air velocity and turbulence intensity were not measured. ...
... A 2D ventilation chamber with inside dimensions 2.18 m  0.62 m  2.41 m (L  W  H ) was made as a sub-section of a pig house which corresponds to 4.36 m  4.96 m  2.41 m (L  W  H ) full scale room, Fig. 1. The chamber was the same as used in the investigation by Tong et al. (2008). The front face was made of 2 panes of laminated glass 220 cm long and 240 cm high and 0.6 cm thick, and the back and side plywood surfaces were painted in dark colours in order to facilitate visualization of airflow patterns with illuminated smoke (Fig. 2). ...
... In order to describe the air exchange rates in the slurry channel under different experimental conditions, the ratio between air exchange rate in the pit and room ventilation rate was applied to evaluate the effects of the deflector (Tong et al., 2008). The smaller the value of the air exchange ratio, the more effective the position of deflector is for contaminant control. ...
The main source of ammonia and odour from most livestock buildings is the slurry pit. The ammonia emission rate is affected by the air exchange rate in the slurry pit. Reduction of air exchange between slurry pit and room air may reduce the emissions. The hypothesis that using an environmental deflector in the room and curtains in the slurry pit may affect air exchange rate between the slurry pit and the room air was validated. In the experiment, three position angles for the deflector and three arrangements of curtains were investigated in a two-dimensional ventilation chamber under isothermal conditions at two ventilation airflow rates. The airflow pattern, air velocity and turbulence intensity inside the chamber were also recorded. The results showed that the airflow patterns, air velocities and turbulence intensities in the room space near the slatted floor and in the headspace of the pit were influenced by changing deflector angles and curtain numbers. It was found that the lowest pit ventilation and the highest concentration in the headspace of the pit could be achieved by using a deflector's position angle of 45° at both of two airflow rates. On the other hand, it was also found that more curtain numbers under the slatted floor and lower room ventilation rate caused lowest pit air exchange rate and the highest concentration in the headspace of pit.
... With slatted floors; the inlet air velocity increased and the resulting increased ventilation rate caused a higher air velocity close to the floor. This increased the air exchange rate in the pit room and the air velocity above the manure surface (Tong et al., 2008). ...
To inform the modelling ammonia of emissions from manure surfaces and provide basic knowledge of the characteristics of airflow at the emission surface, laboratory experiments were performed using a scale model of a growing/finishing pig house with water in the pit and a clean slatted floor with various opening areas: 100%, 33.3% and 16.7%. At 100% opening area the headspace formed an integral part of the room airspace and this configuration was used as the reference treatment. The pig house model had two sidewall inlets and exhaust in the middle of the ceiling. The effects of room ventilation rate, slatted floor opening and headspace height in slurry pit on air velocity, turbulence intensity (Ti) and airflow pattern at manure surface were investigated.The mean air velocity at manure surface increased as ventilation rate increased with a constant inlet opening. Increasing the opening ratio of the slatted floor increased the air exchange rate in the slurry pit, resulting in a higher air velocity above manure surface. For 33.3% and 16.7% floor slat openings, the mean air velocity at the manure surface decreased as headspace height increased and this resulted in an increased mean Ti above the manure surface for 50 mm and 82 mm headspace heights, respectively. However, no significant differences were found in the mean Ti between four ventilation rates for 26 mm headspace height. Tests using smoke visualisation showed that the supply air travelled longer distances parallel to the manure surface at lower headspace heights than at higher heights before returning to the room space. Ammonia emission results from previous experiments can be explained by using the results of measurements of air velocity and Ti.A statistical model was developed to calculate the mean air velocity as a function of ventilation rate, opening ratio of the slatted floor and headspace height in the slurry pit (coefficient of determination R2 = 0.97). The mean air velocity was more sensitive to the ventilation rate than to the slatted floor opening ratio and the headspace height in the pit. Moreover, the mean air velocity was much more sensitive to variations in the ventilation rate at higher ventilation rates than at lower ventilation rates. However, the mean air velocity was much more sensitive at lower floor slat opening ratios and headspace heights than at higher ones.
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