ARS | Publication request: Flow characteristics of the dynamic "EPA flux chamber"

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: July 16, 2011
Publication Date: August 7, 2011
Citation: Woodbury, B.L., Parker, D.B., Eigenberg, R.A., Spiehs, M.J. 2011. Flow characteristics of the dynamic "EPA flux chamber". In: Proceeding fo the American Society of Agricultural and Biological Engineers (ASABE) Annual International Meeting, August 7-10, 2011, Louisville, Kentucky. Paper No. 1111096.

Interpretive Summary: The mixing properties of a chamber commonly used to estimate gas emissions from feedlot surfaces were evaluated. Understanding the mixing properties of the chamber is important for determining the suitability of these chambers for estimating the amount of gases coming from feedlot pen surfaces. A series of tests were completed that measured the mixing properties of the chamber when the mixing gas flow was varied. Also, an internal mixing fan was used at the different mixing gas flow rates to determine if the internal mixing fan provided any advantages. These tests determined that mixing within the chamber was similar to what would be expected for a chamber with ideal mixing, particularly when the mixing gas flow was high or the internal mixing fan was used. However, when the mixing gas flow was low, the level of mixing was reduced slightly. The lower flow through the chamber did not provide the same level of mixing when compared to the high mixing flow rate or when the internal fan mixing was used. It was concluded from this study that the chamber will be suitable for measuring gas coming from feedlot surfaces when a sufficient rate of mixing gas is used to provide adequate internal mixing of the emitted gases.

Technical Abstract: A dynamic flux chamber, commonly referred as the “EPA chamber”, is one method that has been adapted to investigate spatial gas emission on feedlot surfaces. However, the flow characteristics within the chamber have not been evaluated to determine if it can be effectively used outside of its original design specifications. Understanding the chamber flow characteristics will improve the proper application for determining the spatial distribution of emissions from feedlot surfaces. A series of pulse tracer studies at flow rates of 2.5, 5 and 7.5 L min-1 with and without an internal mixing fan were performed to determine tracer break-through curve (BTC) characteristics. Tracer BTCs indicated ideally mixed conditions in the chamber at the evaluated flow rates. However, deviations in the actual retention times from the calculated retention times were greater at the 2.5 and 5.0 L min-1 flow rate when the mixing fan was not used. It appears the deviation was driven by the “tailing” of the BTCs. The tailing was not a problem when the flow rate was increased to 7.5 L min-1 or when the mixing fan was used. This tailing is not expected to limit the effectiveness of the chamber for evaluating treatment effects on spatial gas emission from feedlot surfaces, but others have shown that low flow rates inhibit the overall emission rate from flux chambers.