Question

Refer to Q7, Q8 and Q9, and determine Power Number from the appropriate correlation, and calculate the uncorrected Power required. (Gc = 32.2).

(a) 5.3 Hp

(b) 6.3 Hp

(c) 5.6 Hp

(d) 6.6 Hp

The question was posed to me in an interview for internship.

Enquiry is from Power Requirements for Mixing topic in chapter Fluid Flow and Mixing of Bioprocess Engineering

Answer 1

Right answer is (a) 5.3 Hp

For explanation: The correlations calculate the delivered Power to the fluid. This must be corrected back to the agitator motor and account for efficiency losses in the motor, gearbox, and bearings.

PDelivered = (NP ρB * N^3 * DA^5) / GC

PDelivered = 6 * 64 * 1^3 * 3^5 / 32.2

PDelivered = 2,898 ft-lb/sec

or using 550 ft-lb/sec per Hp,

PDelivered = 5.3 Hp.