4. For a flat plate, the transition from the free convection boundary layer to the free convection turbulent boundary layer takes place at a Rayleigh number of about Ra = 1E9. A flat plate at 70 C is placed in a colder medium at 27 C. Find the location on the plate where this transition takes if the plate is placed in: a) air, b) Ammonia, c) water. All fluids are at 1 atm. %3D

Radioactive wastes are pack

An airtight freezer is filled with air at 298 K and 1 atm. The thermostat is set so that the air is cooled to a temperature of 255 K. Calculate the ∆S for an isobaric and isochoric process.

Find the steady-state temperature distribution in a (very long) solid cylinder if the boundary temperatures are T(s=0, θ, z)=0 and T(s, θ, z=0)=s*sinθ

Air at 20◦C blows over a hot plate 50 by 75 cm maintained at 250◦C.The convection heat-transfer coefficient is 25 W/m2◦C. Calculate the heat transfer.Assuming that the plate is made of carbon steel (1%) 2 cm thick andthat 300 W is lost from the plate surface by radiation, calculate theinside plate temperature.

2. Calculate the mass of silver initially at 445 °C which would be needed to be dropped into a 435 mL sample of water initially at 23.0 °C in an insulated container to raise the temperature of the water to 33.5 °C. The specific heat capacity of water is 4.184 J K-¹ g¹ and the molar heat capacity of silver is 25.9 J K¹ mol¹¹. 2 Tot 21

..P15 A horizontal cylinder 10 cm in diameter contains helium gas at room temperature and atmospheric pressure. A piston keeps the gas inside a region of the cylinder 20 cm long. (a) If you quickly pull the piston outward a distance of 12 cm, what is the approximate temperature of the helium immediately afterward? What approximations did you make? (b) How much work did you do, including sign? (Note that you need to consider the outside air as well as the inside helium in calculating the amount of work you do.) (c) Immediately after the pull, what force must you exert on the piston to hold it in position (with the helium enclosed in a volume that is 20 + 12 = 32 cm long)? (d) You wait while the helium slowly returns to room temperature, maintaining the piston at its current location. After this wait, what force must you exert to hold the piston in position? (e) Next, you very slowly allow the piston to move back into the cylinder, stopping when the region of helium gas is 25 cm long.…

Problem 3 The air above the surface of a freshwater lake is at temperature TA while the water is at its freezing point T,(T,< T,). After a time t elapsed, ice of thickness y has formed. Ássuming that the heat, which is liberated when the water freezes, flows through the ice by conduction and then into the air by natural convection, prove y T, – T, pl h 2K where h is the convection coefficient per unit area and is assumed constant while ice forms, K is the thermal conductivity of ice, I is the latent heat of fusion of ice, and p is the density of ice (Hint: the temperature of the upper surface is variable. Ássume that the ice has a thickness y and imagine an infinitesimal thickness dy to form in time dt.)