Question

Air is flowing steadily through a horizontal, constant diameter pipe. The pipe wall is heated uniformly so that the temperature of the air increases as the air flows through the pipe. You may assume that the air temperature is constant across the cross-section at any length down the pipe. If the air pressure remains constant (pressure drop is small enough to ignore), what can you say about the average velocity of air in the pipe?

Group of answer choices:

(a)velocity will increase because increased temperature indicates the air molecules are moving faster and have higher kinetic energy

(b)velocity will increase in the flow direction because density decreases as air temperature increases

(c)velocity will decrease because hot pipe walls will increase friction inflowing air

(d)velocity remains constant because the pipe is rigid so air can’t expand or change density

(e)velocity remains constant since flow is steady