Q1: A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of

ANS:B - 2^0.8

The film heat transfer coefficient (h) is influenced by various factors such as fluid properties, flow conditions, and surface characteristics. When transitioning from a single pass air heater to a two-pass unit while keeping the air flow rate and other conditions constant, the film heat transfer coefficient for air typically increases. This is because in a two-pass unit, the air has a longer residence time within the heat exchanger, allowing for more heat transfer to occur between the air and the heat transfer surface. The increased residence time enhances turbulence and promotes better mixing, which in turn increases the heat transfer coefficient. However, it's difficult to provide an exact ratio without knowing specific details about the design and operating conditions of the heat exchanger. The ratio could vary depending on factors such as the geometry of the heat exchanger, flow patterns, and thermal properties of the materials involved. So, without more information, it's challenging to determine the exact ratio. But generally, you would expect the film heat transfer coefficient to increase when transitioning from a single pass to a two-pass unit.