Question

Water flowing in a broad pipe enters in to a narrow pipe. How does its Reynold's number change? (Pipe is horizontal)

Answer 1

Explanation:

since the water is entering into a small diameter pipe from a larger diameter pipe, so the diameter is decreasing across the flow at the same time the velocity is increasing, because of decreasing cross section. so the overall effect will be increase in the Reynolds number, because the increase in velocity is much more than the decrease in diameter of pipe.