Biomedical Engineering: Bridging Medicine and Technology 1st Edition by Veronique Tran,Mark Saltzman

Exercise 7

A proportional control scheme for heating a water stream is illustrated in Box 6.3. Use the information in that box to answer the following questions.
a. Assume that the input stream is following into the process at 10 L/min at a temperature of 20◦C, and that you want to heat the liquid to body temperature (37◦C). What is the steady-state heat input to this process?
b. Assume that, at some time t = 0, the temperature of the input stream suddenly changes to 25◦C. If the heat input to the unit is not changed, what will the temperature of the output stream be once a new steady- state is reached? How long do you think it will take to reach this new steady-state temperature?
c. Describe a strategy for controlling the output stream temperature at a desired temperature of 37◦C with the possibility that the input stream temperature will be a function of time. Draw a block control diagram for your process. How will you implement it? Draw a diagram (by plotting temperature versus time) for what you would expect to observe if the sudden temperature rise described in (b) were to occur, with your new process in place.