Shell & Tube Heat Exchanger sizing
Shell & Tube experiment
This experiment was designed for students to learn the importance of fouling factors as well as develop an approach for sizing pilot plant operations to full scale while accounting for economics.
We were given control of a pilot-sized experiment with 2 shell and tube heat exchanger2 from Standard Xchange and asked to determine the fouling factor for each. Then, assuming the fouling factor is constant between scalar models, we determined which larger model should be used for full scale operations.
Figure 1 below illustrates the set up used to find the fouling factors for the two baffle spacing options. We filled the water storage tank to ¾ full and adjusted the water flowrate with a pneumatic globe valve before the exchanger. The water pumped through the exchanger tubes was recycled back to the tank. Of the two baffle spacing options, one had 1.5” spacings and the other had 4” spacings. Both were model 3014 to assure a controlled comparison. Various steam pressures flowed through the shell side of the exchangers.
We collected data over 8 hours and regulated steam pressure and water flowrates with electronic software. We kept flowrates between 10-40 gpm and steam pressure between 10-40 psig. To test the exchangers under different circumstances, we set one flowrate or pressure and varied the other across its threshold by increments of 10. We collected inlet and outlet temperatures for both steam and water streams. From this data we calculated fouling factors for both baffle spacing options.
Without knowing the actual surface temperature, we had to solve for the inner and outer convection coefficients two ways and solve the resulting system of equations. For each data point collected, we calculated a fouling factor in the wide and ordinary spaced baffle exchangers and averaged the results. We did not see any indication for a trend, confirming fouling consistency across models. With this knowledge, sizing the heat exchanger for full scale operations was a simple function of the projected plant's duty requirement.