Q2. Answer the questions below regarding the heat transfer. Here the following symbols are used. Thermal conductivity , boundary film thickness 6, characteristic length d, mass density p, specific heat at constant pressure Cp, velocity u, and viscosity . 2-1) Express the heat transfer coefficient h between the fluid and solid wall using the symbols above. Also show the SI unit for h. 2-2) Heat transfer by convection is enhanced by the flow, and the degree of enhancement is expressed by a dimensionless number. Show its name and symbol and express it using the symbols above. 2-3) The dimensionless number in 2-2 can be expressed using two other dimensionless numbers. Show their names and symbols and explain their physical meaning (ratio of properties A and B, for example). 2-4) Thermal diffusivity a is a physical property showing the easiness of temperature change of an object. Express a using the symbols above. Also show the SI unit for a. 2-5) Consider the heat transfer in a solid sphere of a diameter of 2R. It has a uniform temperature of 20 C initially, and put in boiling water at 1 atm and 100 C instantly. Describe the time constant for its temperature change using the symbols above.