A general procedure to collect data was developed by systematic investigation of the behavior of the system under different flow and heat transfer conditions. The procedure is outlined below.

All water runs used tap water that was filtered and de-ionized with a Culligan Duo Bed Deionizer system. The polyacrylamide solution was made by mixing 14 fl. oz. of Praestol-2273 into 110 gallons of filtered and de-ionized water. This provides a mixing ratio of 1000 ppm by volume. The solution was allowed to set for one week being stirred every other day to allow all clumps to be dissolved. The solution was also stirred before each run.

Before the first run of a fluid all of the air bubbles were removed from the system. The air valves in the calming section, mixing section, and surge tank are opened. The fluid was allowed to enter the flow loop by gravity feed which removed most of the air. When the surge tank is approximately half full, it’s valve was shut. Once the pressure from the gravity feed had removed as much air as possible, the valves in the flow loop were re-configured for pump flow and the pressure raised to about 20 psi. It was important that, before the pump started, the variable speed control actuator be set to the minimum speed position (i.e. speed control screw handle must be in the counter- clockwise most position). To prevent damage to the pump and the variable speed clutch mechanism, the pump speed should also be reduced to minimum before shutting the system down. Once the pump is running, the remaining air bubbles were removed through the pressure tap lines. To remove air bubbles from the calming section, the inlet valve must be partially closed while the pump is running. For high viscosity fluids the system must be pressurized with air in the surge tank and then the air bubbles in the pressure tap lines can be removed with static pressure. After removal of all the air bubbles the system is ready for operation.

A thermos with a thermocouple mounted through its lid was filled with an ice-water mixture twenty-four hours in advance of any test runs for use as the cold junction thermocouple. The voltmeter was turned on at least thirty minutes before taking measurements to allow sufficient time to warm up. The heating system was set for either both wall or top wall heating by bolting the proper lines to the switching connector. All measurements were made using once-through or gravity-feed flow. A desired flow rate (based on desired Reynolds number) and approximate bulk fluid temperature differences were selected for each trial run. Fluid flow was then started. The flow rate was measured and adjusted by varying the pump speed and the by-pass valve position or the outlet valve position. When the desired flow rate was reached, the power level was set at the value determined by the equation:

m× c_p× D T-P_t-P_b=0 (4.1)

where:

A MathCad program called Powercheck (see Appendix B) written by the author was then used to determine when equilibrium is reached. The measured flow rate, the voltage across the stainless steel walls, the current through the shunts, and the inlet/outlet bulk fluid temperatures are input into the program which calculates the power balance. The power balance is defined by the power lost divided by the power input as shown in equations 4.2 through 4.5.

P_output = m× c_p(T_bulk,out-T_bulk,in) (4.3)

P_loss = P_input - P_output (4.4)

P_ratio = P_loss/P_input (4.5)

Where:

Equilibrium is considered reached when the inlet/outlet bulk fluid temperatures cease to change and the power balance is within ± 5%. The length of time required to reach equilibrium varies with flow rate and heating rate. However, the slower the flow rate the longer the time needed to reach equilibrium. Once equilibrium is reached, readings were taken from all of the thermocouples. This required six to ten minutes, after which the inlet and outlet bulk fluid temperatures were re-measured to verify the system is in equilibrium. When all temperature measurements were complete the flow rate was measured again. The power supply used for heating was then turned off, but the fluid flow continued for several minutes to cool the system down. For flow rates of Re < 1500, the system was easily handled by one person. However for high-speed once-through flows (Re > 50000), the pump would empty one reservoir into the other in fifteen minutes or less. Since the time needed to reach equilibrium was approximately 8-10 minutes at these flow rates, one person often has trouble taking all of the measurements. It was sometimes necessary to switch tanks during this process that changed inlet temperatures slightly. Also for higher gravity flow rates (i.e. Re = 1500 to 10000) the head level in the reservoir tank would change while measurements were being taken. This created up to fifteen percent decreases in the flow rate that would render the results useless. These higher flow rates would be better accomplished with two persons or by upgrading the system to use data acquisition for collection of temperature data.

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