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2 years ago

If it is safe to do so you should shut off your engine if it’s going to be idling for longer than?

Engineering

1 answer:

Lesechka [4]2 years ago

8 0

Answer: turn your ignition off it you are waiting more than 10 seconds

Explanation: idling for just 10 seconds waste more gas than restarting the engine and idling increases overall engine by causing the car to operate longer

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A car engine operates with a thermal efficiency of 20%. Assume the air-conditioner has a coefficient of performance of β = 2 wor

disa [49]

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5 0

3 years ago

Air is pumped from a vacuum chamber until the pressure drops to 3 torr. If the air temperature at the end of the pumping process

malfutka [58]

Answer:

The final pressure is 3.16 torr

Solution:

As per the question:

The reduced pressure after drop in it, P' = 3 torr = $3\times 0.133\ kPa$

At the end of pumping, temperature of air, $T = 5^{\circ}C = 278 K$

After the rise in the air temperature, $T' = 20^{\circ}C = 293 K$

Now, we know the ideal gas eqn:

PV = mRT

$P = \frac{m}{V}RT$

$P = \rho_{a}RT$ (1)

where

P = Pressure

V = Volume

$\rho_{a} = air\ density$

R = Rydberg's constant

T = Temperature

Using eqn (1):

$P = \rho_{a}RT$

$\rho_{a} = \frac{P}{RT}$

$\rho_{a} = \frac{3 times 0.133\times 10^{3}}{0.287\times 278} = 0.005 kg/m^{3}$

Now, at constant volume the final pressure, P' is given by:

$\frac{P}{T} = \frac{P'}{T'}$

$P' = \frac{P}{T}\times T'$

$P' = \frac{3}{278}\times 293 = 3.16 torr$

7 0

4 years ago

A hot plate with a temperature of 60 C, 50 triangular profile needle wings of length (54 mm), diameter 10 mm (k = 204W / mK) wil

frez [133]

Complete question is;

A hot plate with a temperature of 60 °C will be cooled by adding 50 triangular profile needle blades (k = 204 W/m.K) with a length of 54 mm and diameter 10 mm. According to the ambient temperature 20 °C and the heat transfer coefficient on the surface 20 W/m².K. Calculate,

a-) Wing efficiency

b-) Total heat transfer rate (W) from the wings,

c-) Calculate the effectiveness of a wing.

Answer:

A) Efficiency = 96.05 %

B) Total heat transfer rate = 166.68 W/m

C) Wing Effectiveness = 10.42

Explanation:

Please find attached explanation for all the answers given.

3 0

3 years ago

Refrigerant 134a vapor in a piston-cylinder assembly undergoes a process at constant pressure from an initial state at 8 bar and

jonny [76]

Answer:

- Work done is 2.39 kJ

- heat transfer is 20.23 kJ/kg

Explanation:

Given the data in the question;

First we obtain for specific volumes and specific enthalpy from "Table Properties Refrigerant 134a;

Specific Volume v₁ = 0.02547 m³/kg

Specific enthalpy u₁ = 243.78 kJ/kg

Specific Volume V₂ = 0.02846 m³/kg

Specific enthalpy u₂ = 261.62 kJ/kg

p = 8 bar = 800 kPa

Any changes in kinetic and potential energy are negligible.

So we determine the work done by using the equation at constant pressure

]Work done W = p( v₂ - v₁ )

we substitute

W = 800 kPa( 0.02846 m³/kg - 0.02547 m³/kg )

W = 800 kPa( 0.00299 m³/kg )

W = 2.39 kJ

Therefore, Work done is 2.39 kJ

Heat transfer;

using equation at constant pressure

Heat transfer Q = W + ( u₂ - u₁ )

so we substitute

Q = 2.392 kJ + ( 261.62 kJ/kg - 243.78 kJ/kg )

Q = 2.392 kJ + 17.84 kJ/kg )

Q = 20.23 kJ/kg

Therefore, heat transfer is 20.23 kJ/kg

3 0

3 years ago

If welding is being done in the vertical position, the torch should have a travel angle of?

siniylev [52]

Answer:

Between 35°– 45°

Explanation:

In the vertical position, Point the flame in the direction of travel. Keep the flame tip at the correct height above the base metal. An angle of 35°–45° should be maintained between the torch tip and the base metal. This angle may be varied up or down to heat or cool the weld pool if it is too narrow or too wide

4 0

2 years ago