Question

Water flows through a tube of length L with a mean inlet temperature (Ti). The tube is held at a uniform surface temperature (Ts) greater than (Ti). Assuming fully developed, laminar flow, the heat flow _______ when the mass flow rate is doubled. Assume that the mean temperature of the water at the outlet is equal to Ts.

A. increases
B. stays the same
C. impossible to tell from the information provided
D. decreases

Answer 1

When the mass flow rate is doubled in a tube with a constant surface temperature higher than the inlet temperature, the heat flow increases due to the proportional relationship between the mass flow rate and heat transfer rate.

Step-by-step explanation:

The question deals with how heat flow through a tube changes when the mass flow rate is doubled. When the mass flow rate is doubled, we would typically expect the heat transfer rate to increase as well. This is because, in a fully developed laminar flow regime with constant surface temperature, the heat transfer rate is proportional to the mass flow rate and the temperature difference between the inlet and the surface temperature. Since the surface temperature is greater than the inlet temperature and remains constant and the mass flow rate is doubled while all other conditions remain the same, the heat flow would increase as it is able to carry away more energy due to the higher mass flow rate. Therefore, the correct answer is A. increases.