Ven Te Chow Hydrosystems Laboratory

Facilities: Odell-Kovasnay Recirculation flume

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The Odell-Kovasnay recirculation flume was built by Engineering Laboratory Design in Lake City Minnesota and it measures 3.18 m long, 1.3 m high, and 1.34 m wide with a capacity of approximately 615 liters. The entire flume, except for the test section and parts of the pump section, is insulated using a composite lamination of fiberglass-reinforced plastic and polyvinyl chloride (PVC) foam core material. The straight Plexiglas test section is 2 m long, 15 cm wide, and 60 cm deep. Opposite the test section is the pump section, which is divided by two diffusers to keep the cross section constant and allow space for the disk pump. The two straight sections are joined on the ends by two semicircular annuli of mean radius 45 cm. The entire tank is covered by a four- part Plexiglas lid with a slit in the test section and high density brush seal allowing probes and other instrumentation to be inserted while minimizing heat losses from the tank. The tank is supported by a welded steel frame and the inlet/outlet of the tank is located on the bottom of the tank in the pump section. Rails are integrated into the cover of the test section and atop these rails rolls an aluminum cart to which the instrumentation can be mounted. This cart can roll along the frame and reach nearly the full length of the test section.

The fluid in the facility is driven by means of a disk pump. The pump is similar to that used by Odell and Kovasnay (1971) and others (e.g. Narimousa et al. 1986, Strang and Fernando 2001a,b). The mechanism behind the disk pump is relatively simple: two counter-rotating stacks of disks with alternating small diameter and large diameter impart momentum to the fluid by dragging the fluid in the boundary layers of the spaces between the disks (Figure 4.3b). This pump mechanism produces a uniform velocity profile with minimal disturbance to the flow (Stephenson and Fernando 1991, Strang and Fernando 2001a). The disk stacks can be arranged in virtually any configuration to generate numerous flow profiles including uniform flow over the whole depth to flows only on the upper or lower layers in a stratified flow. The disk stacks are driven by a single 1/2-hp, 3-phase induction motor on a mount between the test section and the pump section. The motor is connected to the inside disk stack shaft with a belt system. The inside disk stack then drives the outer disk stack with gears atop the disk stacks. The disks are 260 mm in diameter and 4.7 mm thick, and the spacer disks are 90 mm in diameter and available in two thicknesses (5.6 mm and 1.524 mm). The disks are stacked in an alternating sequence (one 260-mm disk, then one of each spacer disks) on two 316 alloy stainless steel shafts that are connected to the drive assembly. The rotation rate of the disks, and thus the flowrate, can be precisely controlled to generate a range of flow velocities. A thin (5mm) Plexiglas plate is placed just below the bottom disk and extends into the diffuser sections to prevent fluid from below the disk stacks from being pumped toward the rotating disks. The splitter plate was found to significantly decrease turbulence near the pump in previous experiments (Stephenson and Fernando 1991). The thermal isolation of the test fluid from the motor driving the pump means that the tank could be run for a long time with no significant change in the test fluid temperature (Garcia et al. 2005).

Two 475-liter (125 gallon) storage tanks from Design Tanks Inc. are used to hold and mix the water used in the facility for stratified flow conditions. The tanks are constructed out of centrifugally cast isophthalic polyester with a dish bottom and structural skirt that lifts the tank bottom off the floor for piping access. The tanks are insulated with two inch thick polyurethane insulation coated with Hypalon overcoat. Hinged lids with mixer cutouts are bolted to the top of the tanks using type 304 stainless steel hold down lugs. The tanks are fitted with 1-inch NPT male fittings at the apex of the convex tank floor. The tanks stand vertically and have an approximate height of 190 cm (75 inches) and an inside diameter of 61 cm (24 inches). The tanks are fitted with Neptune model JD-2.0 dual, direct drive (1/3 hp, 110 VAC/1 phase/60Hz TEFC) mixing motors with 1/2" stainless steel shafts (62 inches long) and dual 4", 3 blade impellers. Since the motors rotate at 1725 RPM, the mixers were mounted off vertical and off axis to avoid draw down caused by tank scale vortices.

Recirculating flume.

Salt and heat stratified flow with only the upper warm, fresh layer driven by the disk pump.

Disk pump.