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2 years ago

12

As a means of preventing ice formation on the wings of a small, private aircraft, it is proposed that electric resistance heatin

g elements be installed within the wings. To determine representative power requirements, consider nominal flight conditions for which the plane moves at 100 m/s in air that is at a temperature of -23 degree C. If the characteristic length of the airfoil is L = 2 m and wind tunnel measurements indicate an average friction coefficient of of C_f = 0.0025 for the nominal conditions, what is the average heat flux needed to maintain a surface temperature of T_s = 5 degree C?

1 answer:

DIA [1.3K]2 years ago

7 0

Answer:

Average heat flux=3729.82 W/ $m^{2}$

Explanation:

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3 years ago

Check Your Understanding: True Stress and Stress A cylindrical specimen of a metal alloy 47.7 mm long and 9.72 mm in diameter is

VARVARA [1.3K]

Answer:

The answer is "583.042533 MPa".

Explanation:

Solve the following for the real state strain 1:

$\varepsilon_{T}=\In \frac{I_{il}}{I_{01}}$

Solve the following for the real stress and pressure for the stable. $\sigma_{r1}=K(\varepsilon_{r1})^{n}$

$K=\frac{\sigma_{r1}}{[\In \frac{I_{il}}{I_{01}}]^n}$

Solve the following for the true state stress and stress2.

$\sigma_{r2}=K(\varepsilon_{r2})^n$

$=\frac{\sigma_{r1}}{[\In \frac{I_{il}}{I_{01}}]^n} \times [\In \frac{I_{i2}}{I_{02}}]^n\\\\=\frac{399 \ MPa}{[In \frac{54.4}{47.7}]^{0.2}} \times [In \frac{57.8}{47.7}]^{0.2}\\\\ =\frac{399 \ MPa}{[ In (1.14046122)]^{0.2}} \times [In (1.21174004)]^{0.2}\\\\ =\frac{399 \ MPa}{[ In (1.02663509)]} \times [In 1.03915873]\\\\=\frac{399 \ MPa}{0.0114161042} \times 0.0166818905\\\\= 399 \ MPa \times 1.46125948\\\\=583.042533\ \ MPa$

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3 years ago

A magician claims that he/she has invented a novel, super-fantastic heat engine. This engine operates between two reservoirs of

Marysya12 [62]

Answer:

A) Not possible, B) Posible, C) Possible, D) Not possible.

Explanation:

The maximum theoretical efficiency for any thermal engine is defined by Carnot's cycle, whose energy efficiency ( $\eta$ ), no unit, is expressed below:

$\eta = 1-\frac{T_{L}}{T_{H}}$ (1)

Where:

$T_{L}$ - Cold reservoir temperature, in Kelvin.

$T_{H}$ - Hot reservoir temperature, in Kelvin.

If we know that $T_{L} = 250\,K$ and $T_{H} = 750\,K$ , then the maximum theoretical efficiency for the thermal engine is:

$\eta = 1-\frac{T_{L}}{T_{H}}$

$\eta = 0.667$

For real thermal engines, the following inequation is observed:

$0 \le \eta_{r} \le \eta$ (2)

Where $\eta_{r}$ is the efficiency of the real heat engine, no unit.

There are two possible criteria to determine if a given heat engine is real:

Efficiency

$\eta_{r} = 1 - \frac{Q_{L}}{Q_{H}}$ (3)

Where:

$Q_{L}$ - Heat rejected to the cold reservoir, in kilojoules.

$Q_{H}$ - Heat received from the hot reservoir, in kilojoules.

Power output

$W = Q_{H}-Q_{L}$ (4)

Where $W$ is the power output, in kilojoules.

Now we proceed to verify each case:

A) $Q_{H} = 900\,kJ$ , $Q_{L} = 600\,kJ$ , $W_{m} = 400\,kJ$

$\eta_{r} = 0.333$

$0 \le \eta_{r} \le \eta$

$W = 300\,kJ$

$W \ne W_{m}$

This engine is not possible.

B) $Q_{H} = 900\,kJ$ , $Q_{L} = 500\,kJ$ , $W_{m} = 400\,kJ$

$\eta_{r} = 0.444$

$0 \le \eta_{r} \le \eta$

$W = 400\,kJ$

$W = W_{m}$

The engine is possible.

C) $Q_{H} = 900\,kJ$ , $Q_{L} = 300\,kJ$ , $W_{m} = 600\,kJ$

$\eta_{r} = 0.667$

$0 \le \eta_{r} \le \eta$

$W = 600\,kJ$

$W = W_{m}$

The engine is possible.

D) $Q_{H} = 900\,kJ$ , $Q_{L} = 100\,kJ$ , $W_{m} = 800\,kJ$

$\eta_{r} = 0.889$

$\eta_{r} > \eta$

$W = 800\,kJ$

$W = W_{m}$

The engine is possible.

7 0

2 years ago