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3 years ago

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Consider a flat plate that is 25 mm long, 30 mm wide, and 1 mm thick and a 50 mm long cylinder with the same volume as the plate

. Compare the heat transfer of the plate in parallel air flow to the heat transfer of the cylinder in cross flow under the same conditions. Both the plate and cylinder have a surface temperature of 80°C. The air is at 25°C with a velocity of 3 m/s. Note: Use the Churchill and Bernstein correlation to determine the Nusselt number for the cylinder case.

1 answer:

Blizzard [7]3 years ago

4 0

Answer:

Average heat transfer =42.448w/m^2k

Nud = 13.45978

Explanation:

See attachment for step by step guide

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Air at 2.5 bar, 400 K is extracted from a main jet engine compressor for cabin cooling. The extracted air enters a heat exchange

Shkiper50 [21]

Answer:

a) Power developed by the turbine = 132.89 kW

b) magnitude of the rate of heat transfer from the air to the ambient, in kw = 251.25 kW

Explanation:

b) The process is a constant pressure process (Isobaric process)

The constant pressure specific heat of air, $c_{p} = 1.005 kJ/kg -K$

Specific heat ratio for air, $\gamma = 1.4$

The mass flow rate of air, $\dot{m} = 2.5 kg/s$

P₁ = 2.5 bar, T₁ = 400 K

P₂ = 2.5 bar, T₂ = 300 K

Using the steady flow energy equation:

$Q_{1-2} = \dot{m} c_{p} (T_{2} - T_{1} \\Q_{1-2} = 2.5 * 1.005 * (300 - 400)\\Q_{1-2} = -251.25 kW$

Therefore, the magnitude of the rate of heat transfer from the air to the ambient, in kw, $Q_{1-2} = 251.25 kW$

a) For the isentropic process:

Power developed by the turbine is given by the relation $\dot{W} = \dot{M} c_{p} (T_{2} - T_{3})$

Isentropic efficiency, $\eta_{t} = 80%$

P₂ = 2.5 bar, T₂ = 300 K

P₃ = 1 bar, $T_{3s}$ = ? where $T_{3s}$ is the isentropic temperature at 100% efficiency

The isentropic relation is given by:

$\frac{T_{3s} }{T_{2} } = (\frac{P_{3} }{P_{2} }) ^{\frac{\gamma - 1}{\gamma} } \\\frac{T_{3s} }{300 } = (\frac{1 }{2.5 }) ^{\frac{1.4 - 1}{1.4 }$

$T_{3s} = 230.9 K$

To get the temperature at 80% efficiency, we will use the relation:

$\eta_{t} = \frac{T_{2} - T_{3} }{T_{2} - T_{3s} } \\0.8= \frac{300 - T_{3} }{300 - 230.9 }$

T₃ = 244.72 K

Power developed by the turbine is given by the relation:

$\dot{W} = \dot{M} c_{p} (T_{2} - T_{3})\\ \dot{W} = 2.5 * 1.005* (300-244.72)\\ \dot{W} = 138.89 kW$

4 0

3 years ago

Read 2 more answers

Air is to be heated steadily by an 8-kW electric resistance heater as it flows through an insulated duct. If the air enters at 5

Furkat [3]

To solve this problem it is necessary to apply the concepts related to the heat exchange of a body.

By definition heat exchange in terms of mass flow can be expressed as

$W = \dot{m}c_p \Delta T$

Where

$C_p =$ Specific heat

$\dot{m}$ = Mass flow rate

$\Delta T$ = Change in Temperature

Our values are given as

$C_p = 1.005kJ/kgK \rightarrow$ Specific heat of air

$T_1 = 50\°C$

$\dot{m} = 2kg/s$

$W = 8kW$

From our equation we have that

$W = \dot{m}c_p \Delta T$

$W = \dot{m}c_p (T_2-T_1)$

Rearrange to find $T_2$

$T_2 = \frac{W}{\dot{m}c_p}+T_1$

Replacing

$T_2 = \frac{8}{2*1.005}+(50+273)$

$T_2 = 326.98K \approx 53.98\°C$

Therefore the exit temperature of air is 53.98°C

6 0

3 years ago

Which is the required type of fire extinguisher for standard naval vessels

Bess [88]

Answer:

Mentioned below are the required types of fire extinguishers for standard naval vessels:

Soda Acid Fire Extinguisher
Water Extinguisher
Foam Extinguisher – Chemical and Mechanical
Carbon Dioxide Extinguisher
Dry Powder Extinguisher

Explanation:

A fire extinguisher is a functioning fire insurance gadget used to douse or control little fires, regularly in crisis circumstances. It isn't planned for use on a wild fire, for example, one which has arrived at the roof, jeopardizes the client (i.e., no way out course, smoke, blast danger, and so on.), or in any case requires the mastery of a fire unit. Ordinarily, a fire extinguisher comprises of a hand-held barrel shaped weight vessel containing an operator that can be released to stifle a fire. Fire extinguishers made with non-round and hollow weight vessels likewise exist however are less normal.

A naval vessel is a military boat (or in some cases pontoon, contingent upon arrangement) utilized by a naval force. Naval boats are separated from non military personnel delivers by development and reason. By and large, naval boats are harm versatile and furnished with weapon frameworks, however combat hardware on troop transports is light or non-existent. Naval vessel is planned fundamentally for naval fighting are named warships, rather than help (assistant boats) or shipyard activities.

3 0

3 years ago

A coal-burning power plant generates electrical power at a rate of 650 megawatts (MW), or 6.50 × 108 J/s. The plant has an overa

Vinvika [58]

Answer:

Energy produce in one year =20.49 x 10¹⁶ J/year

Explanation:

Given that

Plant produce 6.50 × 10⁸ J/s of energy.

It produce 6.50 × 10⁸ J in 1 s.

We know that

1 year = 365 days

1 days = 24 hr

1 hr = 3600 s

1 year = 365 x 24 x 3600 s

1 year = 31536000 s

So energy produce in 1 year = 31536000 x 6.50 × 10⁸ J/year

Energy produce in one year = 204984 x 10¹² J/year

Energy produce in one year =20.49 x 10¹⁶ J/year

7 0

4 years ago

Which sentence is correct about the exergy of an empty (pressure around zero Pascal) tank with a volume of V, located in an envi

sineoko [7]

Answer:

The correct option is;

c. the exergy of the tank can be anything between zero to P₀·V

Explanation:

The given parameters are;

The volume of the tank = V

The pressure in the tank = 0 Pascal

The pressure of the surrounding = P₀

The temperature of the surrounding = T₀

Exergy is a measure of the amount of a given energy which a system posses that is extractable to provide useful work. It is possible work that brings about equilibrium. It is the potential the system has to bring about change

The exergy balance equation is given as follows;

$X_2 - X_1 = \int\limits^2_1 {} \, \delta Q \left (1 - \dfrac{T_0}{T} \right ) - [W - P_0 \cdot (V_2 - V_1)]- X_{destroyed}$

Where;

X₂ - X₁ is the difference between the two exergies

Therefore, the exergy of the system with regards to the environment is the work received from the environment which at is equal to done on the system by the surrounding which by equilibrium for an empty tank with 0 pressure is equal to the product of the pressure of the surrounding and the volume of the empty tank or P₀ × V less the work, exergy destroyed, while taking into consideration the change in heat of the system

Therefore, the exergy of the tank can be anything between zero to P₀·V.

6 0

3 years ago