Q1: If h₁ = inner film co-efficient and /h₂ = outer film co-efficient, then the overall heat transfer co-efficient is

ANS:B - always between h₁ and h₂

The overall heat transfer coefficient (U) in a heat exchanger is determined by the combined thermal resistances of both the inner and outer film coefficients, as well as the thermal conductivity of the material separating the fluids (metal resistance). The formula for calculating the overall heat transfer coefficient in terms of the individual film coefficients (ℎ1h1​ and ℎ2h2​) and the metal resistance (Rm​) is: =11ℎ1++1ℎ2U=h1​1​+Rm​+h2​1​1​ From this formula, we can see that the overall heat transfer coefficient is influenced by all three factors: ℎ1h1​, ℎ2h2​, and Rm​. Given this formula, we cannot make a blanket statement about the relationship between the overall heat transfer coefficient and the individual film coefficients ℎ1h1​ and ℎ2h2​. It depends on the specific values of ℎ1h1​, ℎ2h2​, and Rm​. Therefore, the statement "dependent on metal resistance" is most accurate, as the overall heat transfer coefficient depends on both the film coefficients and the metal resistance.