I´ve found a webpage where the following problem is solved in detail, together with the substitution of numerical values into the pertinent formulas: A plate is of cross-section thickness L = 0.1 m and has an initial temp of To = 250°C. It is suddenly immersed into an oil bath of temperature Ta = 50°C. The material properties are: thermal conductivity k = 204W/m°C heat transfer coefficient h = 80W/m^2°C density rho = 2707 kg/m^3 specific heat Cp = 896 J/kg°C . It is required to determine the time taken for the slab to cool to a temperature of 200°C. The formula used to solve the problem is of the form (T(t)-Ta)/(To-Ta) = e^-(mt) where m is a function of h, rho, Cp and L. The solution is then worked out for the conditions stated above. I had no problem in understanding the steps to solve the problem. But now, suppose the same problem, but instead of submerging the plate into an oil bath at Ta = 50°C, leave the plate to cool into ambient air at Ta = 20°C. My specific question is this: Which coefficients and constants should I change to take care of the air instead of the oil and which are their numeric values? Your help will be greatly appreciated. Thank you.