Show that the flow is irrotational.

Water flows steadily from a large open reservoir through a short length of pipe and a nozzle with cross-sectional area A=0 864 in 2 . A well-insulated 10 kW heater surrounds the pipe. Find the temperature rise of the water. Consider the flow field given by ? =ax 2 -ay 2 , where a=3 s – 1 . Show that the flow is irrotational. Determine the velocity potential for this flow.