1 (4 pts.) If I initially have a gas at a pressure of 12 atm, and a volume of 23 L, and a...

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1	(4 pts.) If I initially have a gas at a pressure of 12 atm, and a volume of 23 L, and a temperature of 200K, and I then raise the pressure to 14 atm and increase the temperature to 300K, what is the new volume of the gas?  2	(10 pts.) A 5-cm-diameter spherical ball whose surface is maintained at a temperature of 70°C is suspended in the middle of a room at 20°C. If the convection heat transfer coefficient is 15 W/m2 °C and the emissivity of the surface is 0.8. Determine the total rate of heat transfer from the ball. Repeat for surface emissivities of 0.1 and 1 and discuss the results.  3	(9 pts.) In solar-heated buildings, energy is often stored as sensible heat in rocks, concrete, or water during the day for use at night. To minimize the storage space, it is desirable to use a material that can store a large amount of heat while experiencing a small temperature change. A large amount of heat can be stored essentially at constant temperature during a phase change process, and thus materials that change phase at about room temperature such as glaubers salt (sodium sulfate decahydrate), which has a melting point of 32°C and a heat of fusion of 329 kJ/L, are very suitable for this purpose. Determine how much heat can be stored in a 5-m3 storage space using (a) glaubers salt undergoing a phase change, (b) granite rocks with a heat capacity of 2.32 kJ/kg °C and a temperature change of 20°C, and (c) water with a heat capacity of 4.00 kJ/kg °C and a temperature change of 20°C.  4	(10 pts.) A 3.27-m3 tank contains 100 kg of nitrogen at 175 K. The pressure in the tank was determined in HW1 using the ideal-gas equation, the van der Waals equation, and the Beattie-Bridgeman equation. The tabulated value is 1505 kPa. Determine the pressure using the a) Redlich-Kwong, and b) Redlich-Kwong-Soave Equation and discuss any differences or improvements, or if no differences or improvements are observed, discuss why not. For the RKS Eq. use the following: 				        	 XXXXXXXXXXa=?1+?(1-vT_r )?^2 ?= XXXXXXXXXX? XXXXXXXXXX?^2 ?= XXXXXXXXXX	(4 pts.) Is there any way to increase the efficiency of a Carnot heat engine other than by increasing TH or decreasing TL?

Robert · Accepted Answer

Thermodynamics/ME 340                                    HOMEWORK 2 
1. (4 pts.) If I initially have a gas at a pressure of 12 atm, and a volume of 23 L, and a temperature 
of 200K, and I then raise the pressure to 14 atm and increase the temperature to 300K, what is 
the new volume of the gas?
 

2. (10 pts.) A 5-cm-diameter spherical ball whose surface is maintained at a 
temperature of 70°C is suspended in the middle of a room at 20°C. If the 
convection heat transfer coefficient is 15 W/m2 °C and the emissivity of the 
surface is 0.8. Determine the total rate of heat transfer from the ball. Repeat for 
surface emissivities of 0.1 and 1 and discuss the results.
 

3. (9 pts.) In solar-heated buildings, energy is often stored as sensible heat in rocks, 
concrete, or water during the day for use at night. To minimize the storage space, 
it is desirable to use a material that can store a large amount of heat while 
experiencing a small temperature change. A large amount of heat can be stored 
essentially at constant temperature during a phase change process, and thus 
materials that change phase at about room temperature such as glaubers salt 
(sodium sulfate decahydrate), which has a melting point of 32°C and a heat of 
fusion of 329 kJ/L, are very suitable for this purpose. Determine how much heat 
can be stored in a 5-m3 storage space using (a) glaubers salt undergoing a 
phase change, (b) granite rocks with a heat capacity of 2.32 kJ/kg °C and a 
temperature change of 20°C, and (c) water with a heat capacity of 4.

1 (4 pts.) If I initially have a gas at a pressure of 12 atm, and a volume of 23 L, and a temperature of 200K, and I then raise the pressure to 14 atm and increase the temperature to 300K, what is the...

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