For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h₂/k_y.C_z is around

ANS:C - 1

The expression ℎ2𝑘⋅𝐶𝑧kh2​​⋅Cz​ represents the dimensionless parameter in the Nusselt number correlation for free convection heat transfer past a wet bulb thermometer. Here, ℎ2h2​ is the convective heat transfer coefficient, 𝑘k is the thermal conductivity, and 𝐶𝑧Cz​ is a characteristic length. For flow past a wet bulb thermometer in an air-water vapor system, the Nusselt number correlation for free convection can be approximated as: 𝑁𝑢≈0.53(𝐺𝑟⋅𝑃𝑟1+0.56(𝑃𝑟2/3−1))1/4Nu≈0.53(1+0.56(Pr2/3−1)Gr⋅Pr​)1/4 Where:

• 𝐺𝑟Gr is the Grashof number
• 𝑃𝑟Pr is the Prandtl number

The Grashof number in natural convection is given by 𝐺𝑟=𝑔⋅(𝜌2−𝜌02)⋅𝐿3𝜇2Gr=μ2g⋅(ρ2−ρ02​)⋅L3​, where 𝑔g is the acceleration due to gravity, 𝜌ρ is the density, 𝜌0ρ0​ is the density at a reference temperature, 𝐿L is a characteristic length, and 𝜇μ is the dynamic viscosity. 𝐶𝑧Cz​ is typically taken as the diameter of the wet bulb thermometer in these calculations. So, ℎ2𝑘⋅𝐶𝑧kh2​​⋅Cz​ would depend on the values of the Grashof and Prandtl numbers, and it's not a fixed value. However, based on typical correlations and calculations, a value around 0.240.24 is often observed. Therefore, the approximate value of ℎ2𝑘⋅𝐶𝑧kh2​​⋅Cz​ is around 0.240.24.