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zysi [14]
3 years ago
14

A student lives in an apartment with a floor area of 60 m2 and ceiling height of 1.8 m. The apartment has a fresh (outdoor) air

exchange rate of 0.5/hr. The stove in the apartment heats by natural gas. The student cooks a meal using two gas burners that each emit carbon monoxide (CO) at a rate of 100 mg/hr. The outdoor CO concentration can be assumed to be negligible (0 ppm). The initial (time = 0) indoor CO concentration can be assumed to be 0 ppm (except for problem 4). Carbon monoxide can be considered as an inert gas, i.e., it does not stick to or react with any surfaces or other gases in air.
1. Assume that the student cooks for a long enough period of time to achieve a steady-state CO concentration in the apartment. What is that concentration in ppb?
2. Assume that the student cooks for only 45 minutes and turns off both burners at that time. What is the CO concentration in ppb at the end of 45 minutes?
3. Repeat problem 2 for air exchange rates that vary from 0.1 to 1/hr and plot the concentration at 45 minutes (in ppb) versus air exchange rate.
4. Assume that for the conditions of problem 2, the student waits 25 minutes after turning the burners off and then starts cooking again with two burners on. How long will it take to reach a concentration that is 95% of steady-state under this condition?
Note that you can actually address this question with an eloquent mathematical derivation (preferred) or simply by crunching the concentration profile in a spreadsheet.
What is the concentration at 95% of steady-state?
Compare your result with the time that would be required to reach 95% of steady-state had the initial indoor CO concentration been 0 ppm.
Engineering
1 answer:
USPshnik [31]3 years ago
5 0

Answer:

4

Explanation:

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An energy system can be approximated to simply show the interactions with its environment including cold air in and warm air out
Elenna [48]

Answer: The energy system related to your question is missing attached below is the energy system.

answer:

a) Work done = Net heat transfer

  Q1 - Q2 + Q + W = 0

b)  rate of work input ( W ) = 6.88 kW

Explanation:

Assuming CPair = 1.005 KJ/Kg/K

<u>Write the First law balance around the system and rate of work input to the system</u>

First law balance ( thermodynamics ) :

Work done = Net heat transfer

Q1 - Q2 + Q + W = 0 ---- ( 1 )

rate of work input into the system

W = Q2 - Q1 - Q -------- ( 2 )

where : Q2 = mCp T  = 1.65 * 1.005 * 293 = 485.86 Kw

             Q2 = mCp T = 1.65 * 1.005 * 308 = 510.74 Kw

              Q = 18 Kw

Insert values into equation 2 above

W = 6.88 Kw

5 0
3 years ago
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Y_Kistochka [10]

Answer:

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8 0
2 years ago
11–17 A long, thin-walled double-pipe heat exchanger with tube and shell diameters of 1.0 cm and 2.5 cm, respectively, is used t
lana [24]

Answer:

the overall heat transfer coefficient of this heat exchanger is 1855.8923 W/m²°C

Explanation:

Given:

d₁ = diameter of the tube = 1 cm = 0.01 m

d₂ = diameter of the shell = 2.5 cm = 0.025 m

Refrigerant-134a

20°C is the temperature of water

h₁ = convection heat transfer coefficient = 4100 W/m² K

Water flows at a rate of 0.3 kg/s

Question: Determine the overall heat transfer coefficient of this heat exchanger, Q = ?

First at all, you need to get the properties of water at 20°C in tables:

k = 0.598 W/m°C

v = 1.004x10⁻⁶m²/s

Pr = 7.01

ρ = 998 kg/m³

Now, you need to calculate the velocity of the water that flows through the shell:

v_{w} =\frac{m}{\rho \pi (\frac{d_{2}^{2}-d_{1}^{2}  }{4} )} =\frac{0.3}{998*\pi (\frac{0.025^{2}-0.01^{2}  }{4}) } =0.729m/s

It is necessary to get the Reynold's number:

Re=\frac{v_{w}(d_{2}-d_{1}) }{v} =\frac{0.729*(0.025-0.01)}{1.004x10^{-6} } =10891.4343

Like the Reynold's number is greater than 10000, the regime is turbulent. Now, the Nusselt's number:

Nu=0.023Re^{0.8} Pr^{0.4} =0.023*(10891.4343)^{0.8} *(7.01)^{0.4} =85.0517

The overall heat transfer coefficient:

Q=\frac{1}{\frac{1}{h_{1} }+\frac{1}{h_{2} }  }

Here

h_{2} =\frac{kNu}{d_{2}-d_{1}} =\frac{0.598*85.0517}{0.025-0.01} =3390.7278W/m^{2}C

Substituting values:

Q=\frac{1}{\frac{1}{4100}+\frac{1}{3390.7278}  } =1855.8923W/m^{2} C

5 0
3 years ago
2x²-6x+10/x-2 x=2<br><br><br>plsssss<br><br><br><br>​
aleksandr82 [10.1K]

Answer:

hope it helps you..

5 0
2 years ago
A water reservoir contains 108 metric tons of water at an average elevation of 84 m. The maximum amount of electric energy that
zavuch27 [327]

Answer:

24.72 kwh

Explanation:

Electric energy=potential energy=mgz where m is mass, g is acceleration due to gravity and z is the elevation.

Substituting the given values while taking g as 9.81 and dividing by 3600 to convert to per hour we obtain

PE=(108*9.81*84)/3600=24.72 kWh

8 0
4 years ago
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