ANS:B - 2

If all the conditions and dimensions are the same, the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is 2. Here's why: In a single pass heat exchanger, the fluid flows through the tubes once. In a double pass heat exchanger, the fluid flows through the tubes twice, effectively doubling the distance it travels. However, the flow rate of the fluid remains the same in both cases since all conditions and dimensions are identical. Since the fluid in the double pass heat exchanger travels twice the distance in the same amount of time, its velocity must be twice that of the single pass heat exchanger to cover the additional distance. Therefore, the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is 2.