Detailed Procedure for Co-Current Operation

HEAT EXCHANGER Detailed Procedure for Co-current Operation. For the first day of experimentation, familiarity of the heat exchanger was essential. Knowledge of each valve’s function was needed in order to use the equipment properly. After tracing each of the flow paths (steam, process water, and cooling water), the following procedure for conducting open-loop experiments was followed.

Open-loop Experiments. 1. With the computer on, open the LABVIEW program HXNET. 2. Mark each of a series of boxes in the checklist. While the checklist is nonfunctional, the boxes must be checked to start the program. 3. Select the button for running open-loop experiments. The LABVIEW window will open. Notice that each of the thermocouples has check boxes beside them and that a plot of temperature versus time is shown. T7 and T10 correspond to the process water’s inlet and outlet temperature, respectively. Select T7 and T10 and change the process water’s flow to 5.5mV. This opens the pneumatic valve to allow flow. 4. Open valves labeled C1, C5, C7, C10, C11, and the one located directly behind the main electrical outlet to allow the process and cooling water to flow co- currently. Notice the process water exiting into the floor’s drain reservoir. 5. In LABVIEW, set the cooling water flow to 5.5mV. At this point cooling water should start exiting into the 55-gallon barrel. 6. To heat the process water, close the steam vent and open the steam’s feed valve located near the laboratory ceiling using the attached chain and pulley system. The steam vent is located at lower right of C10. 7. Set the steam flow to 7mV. Condensate should eventually accumulate in the sight glass. Throughout all lab work, the level of the condensate should be maintained at half the sight-glass’s capacity using the valve located at lower-left of C10. 8. Once at steady state (this can be observed by stabilization of the process water’s temperature), open-loop experiments can be performed. For this lab,  Turn the data-smoothing feature on and take data every second. Care must be taken in naming the data files as any attempt to write over an existing file results in program failure.  With the process water at 5.5mV, change the cooling water from 5.5, to 7.5, and then back down to 5.5mV.  With the process water at 7.5mV, change the cooling water from 5.5, to 7.5, and then back down to 5.5mV.  Note that for every step change in cooling water flow rate, a significant amount of time should pass to allow the system to reach steady state. 9. After completing the open-loop experiments, set the steam and cooling water flows to 0.OmV, close the steam’s main feed valve located near the laboratory ceiling, and open the steam vent. Continued process water flow quickens the system’s cooling, as it must be cool before leaving the laboratory. 10. Once the process water’s inlet temperature is near room temperature (observed by the temperature versus time plot), set its flow to 0.0mV and close the process/cooling water flow valve located directly behind the main electrical outlet. 11. Close the HXNET program.

E-1 After calculating PID controller settings, closed-loop experiments can be performed where the set-point temperature can be specified and the controller controls the cooling water valve to achieve the set point.

Closed-loop Experiments. 1. Repeat steps 1 through 7 for open-loop experiments. However, in step 3, select the button for closed-loop experiments. 2. Enter the controller parameter values. 3. Select T10, for the process water’s outlet temperature, as the response variable. 4. Select the cooling water’s flow as the controlling variable. This action closes the loop and the process is being controlled. The cooling water’s pneumatic valve should open and close to attempt to bring the process water to the set point. Tuning of the controller settings may be needed to attain good performance. 5. The performance of the controller is tested by changing the set points over ranges limited by the equipment (cooling water flow rate could only range from 5.5 to 8.0mV), and the water’s temperature. Additionally, disturbances can be introduced by  changing the process water’s flow rate to 7.5mV while keeping the controller settings used for 5.5mV  changing the process water’s flow rate to 5.5mV while keeping the controller settings used for 7.5mV 6. Repeat steps 9 through 11 from the open-loop experiment procedure.