Original papersAssessment of porous media instead of slatted floor for modelling the airflow and ammonia emission in the pit headspace
Introduction
The ammonia emission from dairy cow houses has raised wide concern because of its potential risk in environmental pollution and animal health. In the Netherlands, ammonia emission from the cattle was about 53 kt in 2009, of which 34% originated from dairy cow houses and manure storage facilities (Van Bruggen et al., 2011). Hence, effective control of the ammonia emission from dairy cow houses is very important. Slatted floors above a pit are widely used for slurry management. For such a typical dairy cow house, 60–70% of the ammonia is emitted from the slatted floor surface (Monteny et al., 1998, Braam et al., 1997). Therefore, much effort has been devoted to study the ammonia emission behaviour in the space above the slatted floor, both experimentally and numerically (Norton et al., 2009, Norton et al., 2010, Wu et al., 2012a, Rong et al., 2015, Seo et al., 2012, Snoek et al., 2014). The remaining ammonia emission from the dairy cow house, 30–40% of the total, originates from the slurry pit. The emission rate from the slurry pit is besides slurry characteristics (Monteny et al., 1998), influenced by the air velocity and air flow pattern above the slatted floor (Bjerg et al., 2013), the details of the openings of the slatted floor (Ye et al., 2008), the air velocity and air flow pattern in the headspace of the slurry pit (Wu et al., 2013b). However, the available information is too limited to understand the effects and to develop measures for reduction of pit emission.
So far, only few studies focused on the airflow and mass transfer inside the slurry pit, all of which were carried out on lab-scale (Wu et al., 2013b, Wu et al., 2012b, Zong and Zhang, 2014). Airflow and mass transfer measurements inside a slurry pit are difficult due to the harsh conditions and limitations of devices to capture the very low air velocity and its distribution in space as well as distribution of ammonia concentration in space. Alternatively, numerical modelling based on computational fluid dynamics (CFD) is able to realize this objective, but the large number of slats and slots of a concrete floor pose a challenge; it is hard to directly involve all the slats and slots in a full-scale dairy house model due to the massive time-consumption for building the computational domain. To deal with this problem, porous media was used in some studies to represent the slatted floor for modelling the airflow and mass transfer inside the slurry pit (Wu et al., 2013b, Zong and Zhang, 2014, Sun et al., 2004). A comparison between a porous media model (PMM), a slatted floor model (SFM) and experimental results of a 1:8 scale wind tunnel model of the slurry pit showed that the PMM has potential to represent the SFM for assessing the airflow in the pit headspace (Wu et al., 2013b, Zong and Zhang, 2014). However, a number of aspects in the applied PMM need further attention: (1) the single-slot sub-model for calculating the static pressure drop over the slatted floor and resistance coefficients was not validated, neither numerically nor experimentally; (2) the resistance coefficients for airflow parallel to the slats were assumed to be the same as the assessed coefficients for airflow perpendicular to the slats; (3) the turbulence transportation inside the porous media was not discussed; and (4) the experimental data resulted from a scale model. Each of these assumptions may enlarge the difference between the PMM and the real life circumstance. The goal of our study is to improve the quality of simulation results by the PMM, and assess the effect of easily controllable external factors: (1) the air velocity parallel to slats above the floor (as affected by wind), (2) the pit headspace height (as affected by the amount of slurry in the pit), and (3) the height of sidewalls above the floor, adjacent to the slatted floor, and perpendicular to slats (referring to the sidewalls of the building) on the airflow features inside and ammonia emission from the pit.
The current applied PMM was improved as follows: Firstly, the CFD sub-models for calculating the static pressure drop over the slatted floor were carefully designed to guarantee the estimation accuracy of the resistance coefficients. Secondly, the resistance coefficients parallel and perpendicular to the slats were calculated separately for correct processing of decomposed velocity vectors. And thirdly, the effect of the turbulence model (T or L) in the porous media on the modelling results were taken into account. Section 2 describes the modelling methods and materials. In Section 3 the new PMM was used to determine the effect of the controllable external factors, mean air velocity (Section 3.1), pit headspace height (Section 3.2), and sidewall height (Section 3.3) on the airflow features and the ammonia emission rate.
Section snippets
Modelling methods and materials
This section describes the modelling methods and the data used for model validation. Intermediate result in support of modelling decisions and validation is discussed in this section as well.
Flow field and ammonia emission at different mean flow velocities
Fig. 6 shows the flow path lines and contours of the velocity magnitude, turbulent kinetic energy, and ammonia mass concentration in the headspace at the mean air velocity of 0.8 m s−1, headspace of 0.09 m, and no sidewalls, modelled by the SFM, PMM-T and PMM-L. The corresponding velocity components, turbulent kinetic energy and ammonia mass concentration profiles at three characteristic lines are plotted and shown in Fig. 7. As can be seen from Fig. 6a, a big vortex was formed in the headspace at
Conclusions
In this study on a wind tunnel model of a slurry pit, the feasibility of using porous media instead of slatted floor to model the airflow and ammonia emission in the pit headspace was evaluated under different external conditions. Based on the results and the corresponding discussion, the following was concluded,
- (1)
The sub-model for calculating the resistance coefficients of porous media must be carefully built up. If the single-slot sub-model is employed, the area ratio of the slot opening to the
References (29)
- et al.
Analysis of airflow through experimental rural buildings: sensibility to turbulence models
Biosyst. Eng.
(2007) - et al.
Modelling of ammonia emissions from naturally ventilated livestock buildings. Part 1: Ammonia release modelling
Biosyst. Eng.
(2013) - et al.
Ammonia emission from a double-sloped solid floor in a cubic house for dairy cows
J. Agric. Eng. Res.
(1997) - et al.
Large-Eddy simulations of cavitation in a square surface cavity
Appl. Math. Model.
(2014) - et al.
Parameterization of the pollutant transport and dispersion in urban street canyons
Atmos. Environ.
(1994) - et al.
Assessing the ventilation effectiveness of naturally ventilated livestock buildings under wind dominated conditions using computational fluid dynamics
Biosyst. Eng.
(2009) - et al.
A computational fluid dynamics study of air mixing in a naturally ventilated livestock building with different porous eave opening conditions
Biosyst. Eng.
(2010) - et al.
The effect of wind speed and direction and surrounding maize on hybrid ventilation in a dairy cow building in Denmark
Energy Build.
(2015) - et al.
Effects of airflow and liquid temperature on ammonia mass transfer above an emission surface: experimental study on emission rate
Bioresour. Technol.
(2009) - et al.
Modelling of internal environmental conditions in a full-scale commercial pig house containing animals
Biosyst. Eng.
(2012)
Sensitivity analysis of mechanistic models for estimating ammonia emission from dairy cow urine puddles
Biosyst. Eng.
Control of vorticity of flow over a cavity with the aid of large eddy simulation
Procedia Eng.
Evaluation of methods for determining air exchange rate in a naturally ventilated dairy cattle building with large openings using computational fluid dynamics (CFD)
Atmos. Environ.
An assessment of a partial pit ventilation system to reduce emission under slatted floor – Part 2: Feasibility of CFD prediction using RANS turbulence models
Comput. Electron. Agric.
Cited by (9)
Applicability evaluation of innovative simplified methods of slatted floor in pig houses – A CFD study
2024, Computers and Electronics in AgricultureAn anisotropic prediction model of the resistance coefficient in porous media model for simulating wind flow through building arrays
2023, Building and EnvironmentCitation Excerpt :Fig. 4(a) depicts the computational domain of the PDM. The pressure drop ΔP is defined as the difference of the pressure between the upstream plane (i.e., x = 0 m) and the downstream plane (i.e., x = 450 m) [18,49]. The domain width in the lateral direction (y) is equal to the width of the lot, i.e., 15B (450 m).
Airflow characteristics of attachment ventilation in a nursery pig house under heating mode
2022, Biosystems EngineeringCFD modelling of an animal occupied zone using an anisotropic porous medium model with velocity depended resistance parameters
2021, Computers and Electronics in AgricultureCitation Excerpt :For example fishing nets in the fishing industry (Patursson et al., 2010), soil in geothermal application (Zhou et al., 2019), plants and trees in agriculture (Tiwary and Morvan, 2006), or packed bed for reactors (Ahmadi and Sefidvash, 2018). In livestock buildings, Yin et al. (2016), Rong et al. (2010), for example, used porous media as replacement of slatted floors to investigate air flow and ammonia emission. In this work, however, the porous media was considered as isotropic in the three main directions and the heat transfer was not considered.
Effects of the slatted floor layout on flow pattern in a manure pit and ammonia emission from pit-A CFD study
2020, Computers and Electronics in AgricultureCitation Excerpt :Airflows in the pit were nearly parallel to the manure surface and formed a large vortex occupying the whole pit headspace. Wu et al. (2013) and Yin et al. (2016) studied airflows in the pit with floor slots parallel to the flow direction and indicated that there was a large vortex either in the downwind side (free stream velocity of 1.41 m s−1 (Wu et al., 2013)) or the upwind side (free stream velocity of 0.8 m s−1 (Yin et al., 2016)). Apparently, different orientations of slatted floor to the free stream direction and different free stream airspeeds generate different airflows inside the pit.
CFD simulation of airflows and ammonia emissions in a pig compartment with underfloor air distribution system: Model validation at different ventilation rates
2020, Computers and Electronics in Agriculture