Question

A complex medium needs to be heated from 15°C to 37°C prior to use in mammalian cell culture. You are responsible for deciding the type of heat exchanger to adopt to achieve this heating. You are considering using a doublepipe heat exchanger with either co-current or counter-current flow. The medium flows through the inner tube and hot water enters the outer annulus at 80°C. You are given the following data:

Cell culture medium: Mass flowrate = 2 kg s-1 Specific heat capacity = 3.5 kJ kg-1K-1 Water: Mass flowrate = 2.5 kg s-1

Specific heat capacity = 4.2 kJ kg-1K-1)

Assuming an overall heat transfer coefficient of 2000 W m2 K- 1 , calculate the required heat transfer areas for the following configurations:

i) Co-current flow

ii) Counter-current flow

Based on your calculations, which heat exchanger configuration would you opt for?

b) You find an old double-pipe heat exchanger in your pilot plant with a heat transfer area of 1.5 m2

Deposits on the inner tube surface have 2 resulted in a fouling factor of 5000 W m- K 1 . You realise that to achieve the same desired heating of the cell culture medium with this old heat exchanger, you will need to reduce the mass flowrate of the cell culture medium. Given processing time constraints, you cannot use a mass flowrate below 1.25 kg s-1. You can operate this heat exchanger in co-current or counter-current mode.

For each heat exchanger configuration calculate

i) the expected reduction in heat transfer rate.

ii) the necessary mass flowrate of the cell culture medium.

Which heat exchanger configuration (co-current or counter-current flow) will be able to meet the design requirement and constraints?

Answer 1