6. Liquid/petroleum fuel storage tanks are built underground (as in case of petrol pumps), when the storage capacity is less than __________ kilolitres.
10. Tube side pressure drop in a 1-2 heat exchanger (for turbulent flow of fluids through the tubes) is about __________ times, that in a 1-1 heat exchanger having the same size & number of tubes and operated at the same liquid flow rate.