Rate of withdrawal of salt rate of additions of salt to the mixer Rate of additions=(10000)0.4)+(20000)(0.7) 1 8000 lb/hr of salt Water Rate of withdrawal of water rate of additions of water to the mixer Rate of additions=(10000(0.6)+(20000(03) 12000lb/hr Thus the stream leaving the mixer has a flow rate of 18000 lb/hr of salt and 12000 lb/hr of water, for a total of 30000 lb/hr. This is exactly the total flow rate of the mixer output we get by adding up the total flow rates to the mixer. Also, the composition of salt of the stream leaving the mixer (100(1800030000)=60wt% Dynamic Process Consider the surge tank shown in Figure I-1 ater flows into the tank with a flow rate Fin lb/hr. It flows out at a rate fout lb/hr. The flow rates in and out can be adjusted by means of the valves in the inlet and outlet piping. The tank has the form of an upright cylinder that has a cross section area of s ft The liquid level in the tank is z ft We know from experience that if the flow rates in and out are not exactly equal, the level in the tank will change with time If the inlet flow rate exceeds the outlet flow rate. then the level will rise and vice versa. Now, the purpose of a surge tank is to absorb changes in the inlet flow rate while maintaining a relatively constant outlet flow rate CThe reservoirs that supply water to a town or city are surge tanks where the inlet flow is the run -off from rainstorms and the outlet flow Figure 1. Surge Tank is the daily consumption by the town or city. )Thus, a question that designers of surge tanks must ask is, given an estimate of the variations of inlet and outlet flow rates as functions of time, how-10- F in F out z Rate of withdrawal of salt = rate of additions of salt to the mixer Rate of additions = (10000)(0.4) + (20000)(0.7) = 18000 lb/hr of salt Water Rate of withdrawal of water = rate of additions of water to the mixer Rate of additions = (10000)(0.6) + (20000)(0.3) = 12000 lb/hr Thus the stream leaving the mixer has a flow rate of 18000 lb/hr of salt and 12000 lb/hr of water, for a total of 30000 lb/hr. This is exactly the total flow rate of the mixer output we get by adding up the total flow rates to the mixer. Also, the composition of salt of the stream leaving the mixer = (100)(18000)/(30000) = 60 wt %. c. Dynamic Process Consider the surge tank shown in Figure I-1. Water flows into the tank with a flow rate Fin lb/hr. It flows out at a rate Fout lb/hr. The flow rates in and out can be adjusted by means of the valves in the inlet and outlet piping. The tank has the form of an upright cylinder that has a cross section area of S ft2 . The liquid level in the tank is z ft. We know from experience that if the flow rates in and out are not exactly equal, the level in the tank will change with time. If the inlet flow rate exceeds the outlet flow rate, then the level will rise and vice versa. Now, the purpose of a surge tank is to absorb changes in the inlet flow rate while maintaining a relatively constant outlet flow rate. (The reservoirs that supply water to a town or city are surge tanks where the inlet flow is the run-off from rainstorms and the outlet flow Figure I- 1. Surge Tank is the daily consumption by the town or city.) Thus, a question that designers of surge tanks must ask is, given an estimate of the variations of inlet and outlet flow rates as functions of time, how