Computational Fluid Dynamics (CFD) Study on the Influence of Airflow Patterns

on Carbon Dioxide Distribution and Emission Rate in a Scaled Livestock

Building

Li Rong1), Peter V. Nielsen1), GuoHong Tong2) Guoqiang Zhang3), Peter Ravn3)

1)Department of Civil Engineering, Aalborg University

2) Shenyang Agricultural University , China

3) Department of Agricultural Engineering, Research Centre Bygholm, University of Aarhus

24/06/2008

Outline

• Introduction• Validation of CFD model• Results• Conclusion

Introduction

• Concentration distribution inside the livestock building relating to:

ventilation system

heat condition

manure condition

etc.• Objective of this paper is to investigate the influence of the

ventilation system on concentration distribution

Validation of CFD model

(a) Model in experiment 2.2m*0.62m*2.41m

(b)45 degree deflector setting model

(c) 90 degree deflector setting model

1 － inlet, 2 － outlet, 3 － deflector, 4 － slatted floor, ‘ ’﹡ － measurement points

Figure 1 models in experiment and simulations

Boundary condition• Isothermal case

• Inlet: velocity in 0.2196m/s, turbulence intensity in 5% and automatic turbulence length scale, CO2 concentration in 900mg/m3

• Outlet: average pressure in 0Pa

• Floor: CO2 concentration in 2000mg/m3

• Other walls: with no CO2 emission

Turbulence model

k model

Vector and CO2 concentration distribution

(a) Vector and CO2 distribution in 45 degree setting model

(b) Vector and CO2 distribution in 90 degree setting model

Figure 2 vector and CO2 concentration distribution at Z=0.31m

Definition of non-dimensional CO2 concentration

* 0

0r

c cc

c c

*c

c

0c

rc

Non-dimensional CO2 concentration

CO2 concentration inside the building

Inlet CO2 concentration

Outlet CO2 concentration

Definition of non-dimensional CO2 concentration

(a) 45 degree deflector setting model (b) 90 degree deflector setting model

Figure 4 comparison of non-dimensional CO2 concentration between measurements and simulations at y=0.51m, z=0.31m

• Influence of airflow rate on non-dimensional CO2 concentration

• Influence of airflow rate on emission rate• Influence of an extra outlet setting below the slatted floor

on emission rate

Results

Influence of airflow rate on non-dimensional CO2 concentration distribution and emission rate

Boundary conditions

• Airflow rate including 100, 150, 200m3/h• Isothermal cases• Floor: with CO2 concentration in 2000mg/m3• Other walls: with no CO2 emission • Deflector: 45 degree, 90 degree

(a) 45 degree

(b) 90 degreeFigure 5 non-dimensional CO2 distribution along the line with y=0.51m, z=0.31m

Figure 6 influence of airflow rate on emission rate

Influence of setting an extra outlet below the slatted floor on emission rate

(a) Left model, outlet 2 located at y=0.13m on the left

(b) Right model, outlet 2 located at y=0.13m on the right

(c) Top left model, outlet 2 located at y=0.235m on the left

(d) Top right model, outlet 2 located at y=0.235m on the right side

Figure 7 models in simulation with an extra outlet

1 － inlet, 2 － outlet 1, 3 － deflector, 4 － the slatted floor, 5 － manure surface, 6 －outlet 2

Boundary conditions• Isothermal case

• Inlet: velocity in 0.2196m/s, turbulence intensity in 5% and automatic turbulence length scale, CO2 concentration in 900mg/m3

• Outlet 1: average pressure in 0Pa

• Outlet 2: 10%, 15%, 20%, 30% of ventilation rate

• Floor: CO2 concentration in 2000mg/m3

• Other walls: with no CO2 emission

Turbulence modelk model

(a) Total emission rate from outlet 1 and outlet 2

(b) Emission rate from outlet 1

Figure 8 Influence of setting an extra outlet below the slatted floor on emission rate in 45 degree deflector setting models

(a) Total emission rate from outlet 1 and outlet 2

(b) Emission rate from outlet 1

Figure 9 Influence of setting an extra outlet below the slatted floor on emission rate in 90 degree deflector setting models

Conclusion

• K-e model is an appropriate model to predict concentration distribution in this case

• Airflow patterns have an important effect on concentration distribution and the emission rate increases with increasing the airflow rate as expected

• Setting an extra outlet below the slatted floor can decrease the emission rate if the contaminants can be cleaned completely from this outlet and the emission rate will decrease when the percent of the ventilation rate from the outlet below the slatted floor increases in these cases

Thank you very much!