scientists have determined the composition of the lithosphere and asthenosphere but have struggled to discover much about the lower mantle (mesosphere). what are the compositions of the upper two parts of the mantle? why is it difficult for scientists to learn about the mesosphere? How could they try to gather more information about it?

What happens in a global convection cell

As part of an industrial process, air as an ideal gas at 10 bar, 400k expands at steady state through a valve to a pressure of 4 bar. the mass flow rate of air is 0.5 kg/s. the air then passes through a heat exchanger where it is cooled to a temperature of 295k with negligible change in pressure. the valve can be modeled as a throttling process, and kinetic and potential energy effects can be neglected. (a) for a control volume enclosing the valve and heat exchanger and enough of the local surroundings that the heat transfer occurs at the ambient temperature of 295 k, determine the rate of entropy production, in kw/k. (b) if the expansion valve were replaced by an adiabatic turbine operating isentropically, what would be the entropy production? compare the results of parts (a) and (b) and discuss.

What is the average speed of a car that travels 40 mph for 1 hour and 60 mph in another hour?