【Test Your Knowledge】Basic Chemical Engineering Knowledge (256) Question 9
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9. When water flows stably in a circular pipe with a constant inner diameter, and if the mass flow rate of the water remains constant, then as the temperature of the water increases, Re will ( A ). A、Increase B、Decrease C、Unchanged D、Uncertain Why?
I chose D, but I’m not sure, because the density of water is highest at 4 degrees Celsius.
As the water temperature rises, its viscosity decreases. . . The density change is not significant; it increases as calculated by the Re formula
When the mass flow rate is constant, density has no effect on the Reynolds number; only the effect of viscosity needs to be considered.
Generally, as the temperature of a liquid increases, its viscosity decreases while its density remains constant. When the inner diameter of the pipe and the mass flow rate are fixed, the Re value increases as calculated by the Re formula
When the mass flow rate remains constant, the product of flow velocity and density stays unchanged; therefore, as the temperature rises, the viscosity of the liquid decreases and the Reynolds number increases
Since it is a liquid, its viscosity decreases as the temperature rises; meanwhile, the pipe diameter, flow rate (mass flow rate remains constant), and density (change is minimal and can be ignored) stay unchanged, resulting in an increase in the Reynolds number. In the case of a gas, however, the Reynolds number decreases as the temperature rises.
The statements for floors 4 and 6 are correct; the issue has been resolved.