Question

A hot air balloon, initially an expandable sphere 10 meters in
radius, contains 100 kg of helium at a temperature of 25 degrees
Centigrade. 1000 KJoules of heat are transferred to the gas.
(Helium c_{p}=5.19 kJ/(kg-K), c_{v}=3.12
kJ/(kg-K)(Volume of a sphere = 4/3*Pi*r^{3})

- What is the final pressure in the balloon if the process takes place at constant volume?
- What is the final volume in the balloon if the process takes place at constant pressure?

Answer #1

A 0.2 m3 piston-cylinder initially contains 400 K air. A heavy
frictionless piston maintains a pressure of 500 kPa abs. Then, a
weakness in the cylinder wall blows out and creates a hole. Air
escapes through the hole until the piston drops far enough to cover
the hole. At that point, the volume is half the initial volume.
During this process, 75 kJ of heat is transferred to the 100 kPa,
300 K surroundings. Using Cp = 1.005 kJ/kg-K and...

A sample of gas is contained in an expandable balloon. 10 KJ of
heat is transferred to the gas which causes the balloon to expand
at constant pressure. If the internal energy of the gas does not
change during this process, calculate the work done and the change
in volume ( in L) of the balloon. ( the pressure of the
surroundings is 1030 mBar). ( 1 J= 1 Pa m^3 )

In a cylinder/piston arrangement, air is compressed in a
reversible polytropic process to a final state of 800 kPa, 500 K.
Initially air is at 110 kPa and 25oC. During the
compression process heat transfer takes place with the ambient
maintained at 25oC. Assume air as an ideal gas (R =0.287
kJ/kg) and has constant specific heats of Cp = 1.004
kJ/kgK and Cv = 0.717 kJ/kgK. If the mass of air in the
cylinder is 0.1286 kg, determine
a)...

A hot air balloon has a mass of 250 kg and carries two
passengers whose average weight is 84 Kg. The balloon, which has a
diameter of 12 m, rises through atmospheric air which is at 20oC.
Find the total buoyant force on the balloon. Atmospheric pressure
is 100 kPa with gas constant = 8.13 kJ/kmol.K and molar mass of the
air is 28.97 g/mol

Suppose a helium balloon is a perfect sphere, with volume = 2.44
x 10-2 m3. Suppose at room temperature
(20o C) its internal pressure is 1.06 x 105
Pa. Remember also that K = 273 + C.
(a) How many moles of gas are present?
(b) Now suppose that the temperature is raised to 40o
C while holding the volume constant. What variable changes? What is
its new value?
(c) Now suppose the balloon is allowed to expand from the...

Determine the final specific volume (m3/kg) for a gas undergoing
a process from state 1 (T1 = 324 K, v1 = 0.2353 m3/kg) to a
temperature of T2 = 883 K if s2 - s1 = 0.961 kJ/kg-K. Assume
constant specific heats as given below (DO NOT USE the ideal gas
tables).
Cp = 1.135 kJ/kg-K
Cv = 0.759 kJ/kg-K
Note: Give your answer to four decimal places.
Correct Answer:
[Correct] 0.4006 ± 1%
Please show your methodology.

H3.3 A frictionless piston-cylinder device contains 2 kg of H2O
initially at T1 = 300◦C and p1 = 5 bar. The device is cooled at
constant pressure until the volume is ∀2 = 0.5 m3 . Assume a
quasiequillibrium process which occurs slowly with no acceleration
as the piston moves. Kinetic and potential energy effects are
negligible. Determine: a. work [kJ] during process (indicate
magnitude and direction) b. heat transfer [kJ] during process
(indicate magnitude and direction)

A weather balloon contains 222 L of He gas at 20. °C and 760.
mmHg. What is the volume of the balloon when it ascends to an
altitude where the temperature is -40. °C and 540. mmHg?
1
What volume does 12.5 g of Ar gas at a pressure of 1.05 atm and
a temperature of 322 K occupy? Would the volume be different if the
sample were 12.5 g of He gas under the same conditions?
How many moles...

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