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Aleonysh [2.5K]
3 years ago
12

3. Write down the total thermal resistance for a double-pipe heat exchanger. Show how to convert from total resistance to an ove

rall heat-transfer coefficient. Explain how flow regime may affect overall heat transfer rate.

Engineering
2 answers:
wlad13 [49]3 years ago
8 0

Answer: please check image for detailed calculation and explanation.

At the boundary between the pipes, there is discontinuity due to different regime; this gap can insulate heat flow causing a fluctuation in heat flow from the inner pipe to the outer pipe.

Nutka1998 [239]3 years ago
8 0

Answer:

\frac{1}{UA} =\frac{1}{A_{0}h_{0}  } +\frac{Rf_{0} }{A_{0} } +\frac{1}{2k\pi L} ln(\frac{di,0}{di,i} )+\frac{Rf_{i} }{A_{i} }

Explanation:

Global heat transfer determines the heat that is transferred from the inner tube to the outer tube. In the double tube heat exchanger, this global heat transfer coefficient is equal to:

\frac{1}{UA} =\frac{1}{A_{0}h_{0}  } +\frac{Rf_{0} }{A_{0} } +\frac{1}{2k\pi L} ln(\frac{di,0}{di,i} )+\frac{Rf_{i} }{A_{i} }

where subscript i refers to the inner surface and subscript 0 refers to the outer surface

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Homes may be heated by pumping hot water through radiators. What mass of water (in g) will provide the same amount of heat when
Nitella [24]

Answer:

a mass of water required is mw= 1273.26 gr = 1.27376 Kg

Explanation:

Assuming that the steam also gives out latent heat, the heat provided should be same for cooling the hot water than cooling the steam and condense it completely:

Q = mw * cw * ΔTw = ms * cs * ΔTw + ms * L

where m = mass , c= specific heat , ΔT=temperature change, L = latent heat of condensation

therefore

mw = ( ms * cs * ΔTw + ms * L )/ (cw * ΔTw )

replacing values

mw = [182g * 2.078 J/g°C*(118°C-100°C) + 118 g * 2260 J/g ] /[4.187 J/g°C * (90.7°C-39.4°C)] = 1273.26 gr = 1.27376 Kg

3 0
3 years ago
The kinetic energy correction factor depends on the (shape — volume - mass) of the cross section Of the pipe and the (velocity —
butalik [34]

Answer:

The kinetic energy correction factor the depends on the shape of the cross section of the pipe and the velocity distribution.

Explanation:

The kinetic energy correction factor take into account that the velocity distribution over the pipe cross section is not uniform.  In that case, neither the pressure nor the temperature are involving and as we can notice, the velocity distribution depends only on the shape of the cross section.

3 0
3 years ago
A power company desires to use groundwater from a hot spring to power a heat engine. If the groundwater is at 95 deg C and the a
prisoha [69]

Answer:

W  = 12.8 KW

Explanation:

given data:

mass flow rate = 0.2 kg/s

Engine recieve heat from ground water at 95 degree ( 368 K)  and reject that heat to atmosphere  at 20 degree (293K)

we know that maximum possible efficiency is given as

\eta = 1- \frac{T_L}{T_H}

\eta = 1 - \frac{ 293}{368}

\eta = 0.2038

rate of heat transfer is given as

Q_H = \dot m C_p \Delta T

Q_H = 0.2 * 4.18 8(95 - 20)

Q_H = 62.7 kW

Maximuim power is given as

W = \eta Q_H

W = 0.2038 * 62.7

W  = 12.8 KW

3 0
3 years ago
A bus travels the 100 miles between A and B at 50 mi/h and then another 100 miles between B and C at 70 mi/h.
stira [4]

Answer:

c. less than 60 mi/h

Explanation:

To calculate the average speed of the bus, we need to calculate the total distance traveled by the bus, as well as the total time of travel of the bus.

Total Distance Traveled = S = 100 mi + 100 mi

S = 200 mi

Now, for total time, we calculate the times for both speeds from A to b and then B to C, separately and add them.

Total Time = t = Time from A to B + Time from B to C

t = (100 mi)/(50 mi/h) + (100 mi)(70 mi/h)

t = 2 h + 1.43 h

t = 3.43 h

Now, the average speed of bus will be given as:

Average Speed = V = S/t

V = 200 mi/3.43 h

<u>V = 58.33 mi/h</u>

It is clear from this answer that the correct option is:

<u>c. less than 60 mi/h</u>

7 0
3 years ago
If a hoist lifts a 4500lb load 30ft in 15s, the power delivered to the load is a) 18.00hp b) 9000hp c) 16.36hp d) None of the ab
12345 [234]

Answer:

Explanation:

load = 4500lb                   lift height= 30 ft

time =15 s

velocity=\frac{30}{15} ft/s

velocity=2 ft/s

power = force\times velocity

power={4500}\times2

power= 9000 lb ft/s

1 hp= 550 lb ft/s

power= \frac{9000}{550} =16.36 hp

5 0
3 years ago
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