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RideAnS [48]
3 years ago
15

An automotive fuel cell consumes fuel at a rate of 28m3/h and delivers 80kW of power to the wheels. If the hydrogen fuel has a h

eating value of 141,790 kJ/kg and a density of 0.0899 kg/m3, determine the efficiency of this fuel cell.
Engineering
1 answer:
EastWind [94]3 years ago
3 0

Answer:

The efficiency of this fuel cell is 80.69 percent.

Explanation:

From Physics we define the efficiency of the automotive fuel cell (\eta), dimensionless, as:

\eta = \frac{\dot W_{out}}{\dot W_{in}} (Eq. 1)

Where:

\dot W_{in} - Maximum power possible from hydrogen flow, measured in kilowatts.

\dot W_{out} - Output power of the automotive fuel cell, measured in kilowatts.

The maximum power possible from hydrogen flow is:

\dot W_{in} = \dot V\cdot \rho \cdot L_{c} (Eq. 2)

Where:

\dot V - Volume flow rate, measured in cubic meters per second.

\rho - Density of hydrogen, measured in kilograms per cubic meter.

L_{c} - Heating value of hydrogen, measured in kilojoules per kilogram.

If we know that \dot V = \frac{28}{3600}\,\frac{m^{3}}{s}, \rho = 0.0899\,\frac{kg}{m^{3}}, L_{c} = 141790\,\frac{kJ}{kg} and \dot W_{out} = 80\,kW, then the efficiency of this fuel cell is:

(Eq. 1)

\dot W_{in} = \left(\frac{28}{3600}\,\frac{m^{3}}{s}\right)\cdot \left(0.0899\,\frac{kg}{m^{3}} \right)\cdot \left(141790\,\frac{kJ}{kg} \right)

\dot W_{in} = 99.143\,kW

(Eq. 2)

\eta = \frac{80\,kW}{99.143\,kW}

\eta = 0.807

The efficiency of this fuel cell is 80.69 percent.

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Answer:

0.304 L of Freon is needed

Explanation:

Q = mCT

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C is specific heat of Freon = 74 J/mol.K = 74 J/mol.K × 1 mol/120 g = 0.617 J/g.K

T is temperature in the area of Mars = 189 K

m = Q/CT = 49587.82/(0.617×189) = 452.23 g = 452.24/1000 = 0.45223 kg

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Volume of Freon = mass/density = 0.45223/1490 = 0.000304 m^3 = 0.000304×1000 = 0.304 L

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A fatigue test was conducted in which the mean stress was 46.2 MPa and the stress amplitude was 219 MPa.
sleet_krkn [62]

Answer:

a)σ₁ = 265.2 MPa

b)σ₂ = -172.8 MPa

c)Stress\ ratio =-0.65

d)Range = 438 MPa

Explanation:

Given that

Mean stress ,σm= 46.2 MPa

Stress amplitude ,σa= 219 MPa

Lets take

Maximum stress level = σ₁

Minimum stress level =σ₂

The mean stress given as

\sigma_m=\dfrac{\sigma_1+\sigma_2}{2}

2\sigma_m={\sigma_1+\sigma_2}

2 x 46.2 =  σ₁ +  σ₂

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The amplitude stress given as

\sigma_a=\dfrac{\sigma_1-\sigma_2}{2}

2\sigma_a={\sigma_1-\sigma_2}

2 x 219 =  σ₁ -  σ₂

 σ₁ -  σ₂ = 438 MPa    --------2

By adding the above equation

2  σ₁ = 530.4

σ₁ = 265.2 MPa

-σ₂ = 438 -265.2 MPa

σ₂ = -172.8 MPa

Stress ratio

Stress\ ratio =\dfrac{\sigma_{min}}{\sigma_{max}}

Stress\ ratio =\dfrac{-172.8}{265.2}

Stress\ ratio =-0.65

Range = 265.2 MPa - ( -172.8 MPa)

Range = 438 MPa

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Explanation:

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