TERMODINMICA 1 (SEM0233)

TERMODINÂMICA 1 (SEM0233)
1ero semetre 2009
Prof. Oscar M.H. Rodríguez.
Monitor: Luis Enrique Ortiz Vidal
LISTA N°3
Exercício 1:
Air is contained in a vertical piston–cylinder assembly by a piston of mass 50 kg and having a face area
of 0.01 m2. The mass of the air is 5 g, and initially the air occupies a volume of 5 liters. The atmosphere
exerts a pressure of 100 kPa on the top of the piston. The volume of the air slowly decreases to 0.002
m3 as the specific internal energy of the air decreases by 260 kJ/kg. Neglecting friction between the
piston and the cylinder wall, determine the heat transfer to the air, in kJ.
Exercício 2:
A group of twenty executives attend a board meeting in a room which measures 20 ft by 20 ft and has a
10 ft ceiling. Assume that each person occupies 2.5 ft3 and gives out about 375 Btu of heat per hour.
Calculate the air temperature rise occurring within 15 min of the start of the conference if the room is
completely sealed and insulated. Take c for air as 0.1715 Btu/lbm°F.
Exercício 3:
Se calienta un cuarto de 4 m x 5 m x 7 m mediante el radiador de un sistema de calefacción de vapor. El
radiador de vapor transfiere calor a una tasa de 10000 kJ/h, y se utiliza un ventilador de 100 W para
distribuir el aire caliente en el cuarto. Se calcula que la tasa de pérdida de calor del cuarto será cercana
a 5000 kJ/h. Si la temperatura inicial del aire del cuarto es 10 °C, determine cuánto tiempo se requerirá
para que la temperatura del aire aumente a 20 °C. Suponga calores específicos constantes a
temperatura ambiente.
Exercício 4:
A well-insulated rigid tank contains 5 kg of a saturated liquid–vapor mixture of water at l00 kPa. Initially,
three-quarters of the mass is in the liquid phase. An electric resistor placed in the tank is connected to a
110-V source, and a current of 8 A flows through the resistor when the switch is turned on. Determine
how long it will take to vaporize all the liquid in the tank. Also, show the process on a T-v diagram with
respect to saturation lines.