Mechanical Engineering Answers

The heat transfer from a 2 m diameter sphere to a 25 °C air stream over a time interval of one
hour is 3000 kJ. Estimate the surface temperature of the sphere if the heat transfer coefficient is
10 W/m2 K

Determine the moving boundary work done by the atmosphere (14.7 psia) as a cube of ice
2.00 inches on a side melts into a pool of liquid water. At 32.0 °F, the density of ice is
3
57.2 lbm ft
and that of liquid water is
3
62.4 lbm ft .

Determine the heat transfer rate, in
Btu/h,
required to cool a 200. kW electric generator that is
driven by a 300. hp diesel engine. Note: The generator will run cool if it has a zero net energy
transport rate.

A piston-cylinder arrangement contains 0.05 m
3
of air at 70 C and 500 kPa. Heat is added in
the amount of 75 kJ and work is done by a paddle-wheel until the temperature reaches 500 
C. If the pressure is held constant (hint) how much paddle-wheel work must be added to the
air? Assume constant specific heats.

The pressure in an isochoric automobile tire increases from 40.0 psia at 80.0 °F to 50.0 psia
on a trip during hot weather. Assume the air behaves as an ideal gas. a) What was the air
temperature inside the tire at the end of the trip. b) How much heat was absorbed per unit
mass of air in the tire during the trip?

Exactly 1.73 kg of water vapor is contained in a piston–cylinder assembly at a pressure of
1.00 MPa and temperature 600. °C. The vapor is isothermally compressed to 80.0 MPa.
Determine the sum of the work and heat energy transports in this process.

A 1000. kg battery-powered adiabatic electric vehicle has a fully charged battery containing
30.0 MJ of stored energy. If it requires 20.0 kW of power to keep it moving at a constant
velocity on a horizontal road, determine how long the vehicle will operate before its battery
is fully discharged.

0.5kg of air is compressed reversibly and adiabatically from 80kpa, 60°c to 0.4Mpa and is then expanded at constant pressure to the original volume. Calculate the heat transfer and work transfer for the whole path.
Take R = 0.247kj/kg.k, Cp = 1.005kj/kg.k, Cv = 0.718kj/kg.k

A cylinder has a volume of 0.4 m3
holds 2.0 kg of a mixture of liquid water and water vapor. The
mixture is in equilibrium at a pressure of 0.6 MPa.
Calculate:
a. Mass of liquid
b. Mass of Vapor

A domestic freezer has an internal capacity of 1m * 10.5m * 0.5m. The temperature inside is maintained at -5°c in ambient temperature of up to 35°c. Calculate the maximum rate of heat transfer to the freezer if the wall and door consists of:
5mm plastic. K = 1W/mK
15mm insulation K = 0.05W/mK
2mm steel. K = 40W/mK
and the convective heat transfer coefficient is 8W/m²K on both sides of the freezer