This experiment consists of a shell and tube and a plate and frame heat exchanger that may be operated separately. Pneumatic control valves control the steam and water flow rates, and flowmeters record and indicate the flow of steam and water into each heat exchanger. Thermocouples measure the inlet and outlet temperature of the water and steam in each exchanger. Temperature measurements from the thermocouples and the water flow rates are displayed on a separate display panel for each heat exchanger.
OPTO 22 is a type of data acquisition and control software that will be used to automate the process. OPTO 22 is introduced in the Gravity-Drained tank experiment in ChE 361. The programs required for this experiment are already set up and will be described later.
The flowmeters, thermocouples, pressure sensors, and actuators are wired into OPTO 22. Using the appropriate program, the heat exchangers are controlled by designating flow rates or setting the desired final temperature. Two and four pass bundles with a choice of copper or stainless steel may be changed depending on the conditions of the experiment, and the number of plates on the plate and frame heat exchanger may also be changed.
Safety
Since steam is used in this experiment, safety is especially important. If the pressure exceeds 45 psi on the water side of the shell and tube, the soldered pipe joints may fail. If the steam pressure exceeds 37 psi on the plate and frame, the plate gaskets will fail.
Specific Outcomes
The student will be provided with a unique design problem. After this lab, the student will hopefully have the following skills:
1. Ability to specify a heat exchanger or heat exchanger system to obtain design conditions, including computer based simulations such as ASPEN.
2. Experience with both a shell & tube and plate & frame heat exchanger-principles of operation, limitations, and approximate heat transfer coefficients.
3. Experience with a PC-based data acquisition and control software such as OPTO 22.
Procedure
Safety
1) Always wear safety glasses.
2) Familiarize with the P&ID in Figures 1 and 2.
Figure 1. P&ID of MAPS Plate and Frame Heat Exchanger
Figure 2. P&ID of MAPS Shell and Tube Heat Exchanger
3) The condensate drains (valves 9 and 16) must be open at all times.
4) Have the manual bypass valves only slightly open (valves 5,6,12 and 13) so that OPTO 22 is controlling the flow rates.
5) Be sure the outlet temperature of the water does not exceed 85 degrees Celsius. If this occurs at any time, shut down the steam line and let the system cool down.
Starting Up
1) The steam lines leaving each heat exchanger have steam traps that must be cleaned before each use. Use a pipe wrench to unscrew the large bolt on the trap and make sure that the screen is clean. Some water may drain from the trap when it is opened.
2) Configure the heat exchangers with the desired bundle or number of plates. (See Appendices A & B)
3) Ensure the drain valves are open on the water and condensate lines (valves 8,9,15, and 16).
4) Open the inlet water valve to the exchanger you are using first so that the system does not heat up right away from the steam (valve 3 for the S&T, 10 for the P&F).
5) After the system is ready to run (water must be flowing in the heat exchanger), turn on the steam:
1. Ensure the main steam header is open (notify TA/Instructor if not).
2. Open the appropriate steam valve to the heat exchanger (4 or 11)
6) Start-up OPTO 22:
a. Turn on the OPTO 22
b. Open PAC Control Basic 9.0
c. Go File -> Shell&Tube or Plate&Frame, depending on heat exchanger being used
d. Go I/O Units -> MAPS_S_T -> PIDs -> Select Temperature_Control (for controlling the Steam valve) or Flow_Control (for controlling the Water valve)
e. Once selected, click the Debug button. Then click Stop Strategy and then Run Strategy.
f. To change between control valves, click Stop Strategy, then either Temperature_Control or Flow_Control, and then Run Strategy.
g. Open PAC Display Runtime Basic 9.0 from the desktop.
h. Ensure that program you are using is the heat exchanger being used. If not, go File -> Open Project -> ‘Up One Level’ button to the ‘MAPS HEX’ folder -> Open the correct heat exchanger folder -> Open Shell_Tube_HEX or Plate_Frame_HEX PAC Display Project
i. On the opening screen, in the ‘Choose Your Control Mode’ dropdown, select the mode that your chose previously in the PAC Control Basic program.
j. Click the graph in the bottom right to control the valve.
k. To change between valves being controlled, exit out of PAC Display Runtime Basic 9.0 and reopen it, choosing the desired control program as shown in step h (NOTE: change the PAC Control Basic program as shown in step e before doing this).
8) To change between heat exchangers, follow this procedure:
a. Close the steam input valve coming from the main line to the previously used exchanger.
b. Fully open the water input valve to the previously used exchanger for at least 5 minutes to cool down the exchanger, and then close the water input valve.
c. Close the condensate valve coming from the previous exchanger (the valve after the steam trap).
d. Follow the start-up procedure to start steam and water flow to the other exchanger.
Procedure
1) Find tuning parameters that give sufficient control of the system for each valve and exchanger.
2) Test the tuning parameters at various temperatures and observe the outlet temperatures of the steam and water.
3) Collect data by clicking On in the Data Log box.
4) To obtain data:
a. For the Plate and Frame, open the Student Data folder -> Plate and Frame.
b. Copy and Paste the flow DATA_LOG and/or temp DATA_LOG onto jump drive or email it to yourself.
c. For the Shell and Tube, open the Student Data folder -> Shell and Tube.
d. Copy and Paste the flow DATALOG and/or temp DATA LOG onto jump drive or email it to yourself.
e. When done with the experiment, open the Temp DATA LOG directly in the folder and delete the data (not the headings) and save.
Shutdown
1) Shut down the OPTO 22 software:
a. Close out of PAC Display Runtime Basic 9.0.
b. In PAC Control Basic, click Stop Strategy and close out.
c. Turn off OPTO 22 device
3) To shut down the exchanger, follow Steps 8a-b in the Starting up procedure.
4) Have TA/Instructor close off steam header.
Reporting
1.
APPENDIX A - CHANGING A BUNDLE
To change the bundle in the shell and tube, follow these steps:
1) Use the bundle support cart to hold the bundles. Never place them anywhere other than the crates or cart.
2) Open the drain on the water line and let the water completely drain out of the heat exchanger.
3) Remove the inlet and outlet lines to the heat exchanger.
4) Remove the head of the shell with the two 7/8 inch wrenches and pull the bundle out, being sure to drain the bundle.
5) Obtain the proper gaskets that are needed for the new bundle:
a. A steam gasket
b. A two or four pass gasket
6) Place the steam gasket on the back side of the new bundle and the water gasket on the front side. The holes should match up.
7) Slide the new bundle into the shell and replace the head, using the tightening pattern shown in Figure 3. Do not tighten the bolts as far as you can the first time around the pattern. It will take a couple of time around the crisscross pattern to correctly tighten the bolts.
Figure 3. Diagram of Shell and Tube
8) Reconnect the tubing to the bundle from the inlet and outlet water stream, checking to make sure there are no leaks.
APPENDIX B - CHANGING THE NUMBER OF PLATES
To change the number of plates on the plate and frame follow these steps:
1) Open the water drain and allow the heat exchanger to drain completely.
2) Use the two 30mm wrenches to remove the nuts.
3) Slide the blue end plate back as far as necessary to get the plates out. It helps to move each side a bit at a time.
4) To get the plates out, lean the top of the plate back and then pull it to the side and remove it. Do this very carefully because the sides of the plates are sharp. The first and last metal plates need to stay on the heat exchanger.
5) When replacing plates be sure to alternate the way that the gaskets are arranged. See the binder for a schematic showing why this is necessary and how the fluid flows in the heat exchanger.
6) Once the correct number of plates is installed, hold the plates vertical while another person slides the blue end plate snugly against the plates.
7) Replace the nuts and tighten them. The best way to tighten them is to start with a corner and the opposite corner bolt. Then, go to the other corners and repeat. Then tighten the 2 middle bolts at the same time. Continue these patterns of tightening until all bolts are tight, again checking for leaks.
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