|Hjelmfelt Jr, Allen|
Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Proceedings
Publication Acceptance Date: 8/3/1998
Publication Date: N/A
Technical Abstract: A series of laboratory tests were conducted comparing head loss for a range of flow rates through rock media using a vertical column (0.2 m diameter x 2 m long pipe) and horizontal flumes (7.62 m x 0.46 m x 0.31 m). Rock media included creek rock (average diameter 2.00 cm and 1.81 cm for the vertical column and horizontal flumes, respectively) and pea gravel (0.64 cm and 0.62 cm average diameter for the vertical column and horizontal flumes, respectively), with and without the addition of organic solids (e.g., ground sawdust). Results indicated that when sufficient sawdust was added to the pea gravel reducing drainable porosity from 39.5% to below 33.4%, headloss was dominated by the organic solids. When drainable porosity was reduced to 23.9%, the normalized headloss gradient through the column increased by nearly two orders of magnitude. For the flume tests, headloss increased by approximately thirty-five times for both creek rock and pea gravel with the addition of 7.6 g L**1 of sawdust compared with headloss in the clean bed. Ergun's equation, modified to account for sphericity of the media, fit the measured data for clean rockbeds for all flow rates tested from laminar through the turbulent region. However, when sawdust became the dominating factor controlling flow, Ergun's equation underestimated head loss. By fitting the appropriate hydraulic conductivity to the measured data, Darcy's law fit the laminar region well but did not fit the transition nor turbulent regions.