Operation of crossflow ultrafiltration devices with open rectangular or circular channels under laminar flow conditions is well understood and documented. However, many commercial devices are available which operate in flow regimes which cannot be described as laminar. Examples of such devices include those constructed with plastic mesh spacers which define and partially obstruct the path of recirculating flow (spiral wound and cassette configurations) as well as those with wide open channels capable of operation in the turbulent flow regime (tubular and open channel flat plate configurations). The presence of flow spacers has the disadvantage of limiting the use of these devices in processing streams containing suspended solids. Their presence in the flow channel increases resistance to flow of the recirculating fluid and requires increased pumping energy. To their advantage these spacers change the flow dynamics of the recirculating stream and can, by promoting regions of turbulence, enhance process flux. Devices with open channel configurations operated in turbulent flow regimes do not have the same limitations regarding the presence of suspended material in the feed stream. They do, however, require larger pumps and increased pumping energy in order to maintain operation at turbulent flow conditions. Contrasting experiments were performed, using well-defined process streams, on a crossflow device capable of operation with open channels or channels formed by spacers at the same channel heights. Additional experiments were performed at various recirculating fluid solute concentrations and superficial velocities. Performance could then be compared based on flux and energy requirements. Implications from these tests can be drawn concerning module design and optimal operating conditions for ultrafiltration of particulate-free solutions.