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3 years ago

List one advantage and one disadvantage of the use of the commutator?

Engineering

1 answer:

Mariulka [41]3 years ago

3 0

Answer and Explanation:

Commutator are used in DC machine commutator is mainly used for the reversing the direction of the current .It is connected to the armature of the DC generator or motor

ADVANTAGE OF COMMUTATOR The main advantage of the commutator in DC motor is to keep keep the direction of the toque always in the same direction by changing the current direction

DISADVANTAGE OF COMMUTATOR : The main disadvantage is due to the friction between the commutator and brushes there is a friction loss.

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Define ways in which you would go about networking to explore opportunities in your career field and obtain more information for

kkurt [141]

Answer:

mmmmmm

Explanation:

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3 years ago

The Aluminum Electrical Conductor Handbook lists a dc resistance of 0.01558 ohm per 1000 ft at 208C and a 60-Hz resistance of 0.

Bogdan [553]

Answer:

a) 0.01558 Ω per 1000 feet

b) 0.0923 Ω per mile

c) 3.57%

Explanation:

a) Calculate and verify the DC resistance

Dc resistance = R = р $\frac{l}{A}$

for aluminum at 20°C

р = 17 Ωcmil/ft

hence R = 17 * 1000 / ( 113000 ) = 0.01527 Ω per 1000 feet

there when there is an increase in resistance of 2% spiraling

R = 1.02 * 0.01527 = 0.01558 Ω per 1000 feet

b) Calculate the DC resistance at 50°C

R2 = R1 ( $\frac{T+t2}{T+ t1}$ )

where ; R1 = 0.01558 , T = 228 , t2 = 50, t1 = 20 ( input values into equation above )

hence R2 = ( 0.01746 / 0.189 ) Ω per mile = 0.0923 Ω per mile

c ) Determine the percentage increase due to skin effect

AC resistance = 0.0956 ohm per mile

Hence; Increase in skin effect

= ( 0.0956 -0.0923 ) / 0.0923

= 0.0357 ≈ 3.57%

4 0

3 years ago

2 Consider airflow over a plate surface maintained at a temperature of 220°C. The temperature profile of the airflow is given as

lutik1710 [3]

Answer:

Heat flux on the plate surface is 1.45 x 10⁴ W/m², Heat transfer coefficient is 72.6 W/m². K

Explanation:

The temperature profile of the airflow is given as

T(y) = T∞ – (T∞ - Ts)exp[(-V/α fluid)y]

Calculate the mean film temperature of air

T(f) = T(s) + T∞/2, where T(s) is the surface temperature of the plate and T∞ is the temperature of free stream

Substitute Ts = 220 C and T∞ = 20 C

T(f) = 220 +20/2 = 120 C

Obtain the properties of air from Table A- 15 (Properties of air at 1 atm pressure) in the text book of from the internet at T(f) = 120 C, which would give us the quantities of thermal diffusivity (α fluid) and the thermal conductivity (k) of air

α fluid = 3.565 x 10⁻⁵ m²/s

k = 0.03235 W/m.k

Calculate the temperature gradient for the given profile

T(y) = T∞ – (T∞ - Ts)exp({-V/α fluid}y)

Where, T∞ is the ambient temperate, V is the free stream velocity of air and y is the temperature displacement thickness

Differentiate the expression with respect to y

dT/dY = - (T∞ - Ts){-V/α fluid}e[(-V/α fluid) x 0]

dT/dy = -(T∞ - Ts){-V/α fluid}

Substitute T∞ = 20 C, Ts = 220 C, V = 0.08 m/s and α = 3.565 x 10⁻⁵ m²/s

dT/dy = - (20 - 220)(-0.08/3.565 x 10⁻⁵)

dT/dy = -448807.8541

Calculate the heat flux on the plate surface

Q = -kdT/dy

K = 0.03235 W/m.k, dT/dy = -448807.8541

Q = -(0.03235)(-448807.8541)

Q = 1.45 x 10⁴ W/m²

Therefore, the heat flux on the plate surface is 1.45 x 10⁴ W/m²

Calculate the heat transfer coefficient

Q = h(Ts - T∞), where h is the transfer coefficient

1.45 x 10⁴ = h(220 - 20)

H = 72.6 W/m2.k

Therefore, the heat transfer coefficient is 72.6 W/m². K

6 0

3 years ago

Please help me with this. Picture

qwelly [4]

Answer:

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6и876&*b n™Ο65656&^cxCv876и876&*b n™‰‰ay^547.'":87765^&* kIKUYtb

Explanation:

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3 years ago

What kind of value should an employee possess when employees are expected to be responsible and fair?

jasenka [17]

Answer:

E self-confidence

Explanation:

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3 years ago