Ask question

Ask question

All categories

Maksim231197 [3]

3 years ago

5

When brazing, the lowest effective brazing temperatures possible should be used to minimize the effects of heat on the base meta

l. MAR O True False

1 answer:

nordsb [41]3 years ago

5 0

Answer:

False

Explanation:

You might be interested in

The speed of ac motors is primarily<br>determined by which two factors?<br>

maw [93]

The two factors used to determine the speed of ac motors are the frequency of the power supply and the number of poles in the motor winding.

Explanation:

The frequency of the power supply and the number of poles of the machine states the synchronous speed.

The poles combined with ac line frequency determines the no-load revolutions per minute of the monitor. So all four-pole motors will run at same speed under no-load conditions, then all six-pole motors will run at the same speed.

The speed of the induction motor depends on stator frequency "s ". By varying the stator voltage and constant supply frequency the speed can be controlled. The two main components of the electric motor are stator and rotor.

3 0

3 years ago

Relationship between civil engineering and geology

natka813 [3]

Answer:

Geological and civil engineers sometimes work together, but have very different responsibilities. While geological engineers study the earth's inner and outer surface to evaluate potential mining and infrastructure construction sites, civil engineers design the infrastructure to be built.

5 0

3 years ago

What should I do I if a patient I’s bleeding th our his penis

Brilliant_brown [7]

Answer:

YOU SHOULD HELP HIM

Explanation:

6 0

3 years ago

Read 2 more answers

A plane surface 25 cm wide has its temperature maintained at 80°C. Atmospheric air at 25°C ows parallel to the surface

Gre4nikov [31]

Answer:

See the detailed answer in attached file.

Explanation :

3 0

3 years ago

A counter-flow double-piped heat exchange is to heat water from 20oC to 80oC at a rate of 1.2 kg/s. The heating is to be accompl

lawyer [7]

Answer:

110 m or 11,000 cm

Explanation:

let mass flow rate for cold and hot fluid = M<em>c</em> and M<em>h</em> respectively
let specific heat for cold and hot fluid = C<em>pc</em> and C<em>ph </em>respectively
let heat capacity rate for cold and hot fluid = C<em>c</em> and C<em>h </em>respectively

M<em>c</em> = 1.2 kg/s and M<em>h = </em>2 kg/s

C<em>pc</em> = 4.18 kj/kg °c and C<em>ph</em> = 4.31 kj/kg °c

<u>Using effectiveness-NUT method</u>

<em>First, we need to determine heat capacity rate for cold and hot fluid, and determine the dimensionless heat capacity rate</em>

C<em>c</em> = M<em>c</em> × C<em>pc</em> = 1.2 kg/s × 4.18 kj/kg °c = 5.016 kW/°c

C<em>h = </em>M<em>h</em> × C<em>ph </em>= 2 kg/s × 4.31 kj/kg °c = 8.62 kW/°c

From the result above cold fluid heat capacity rate is smaller

Dimensionless heat capacity rate, C = minimum capacity/maximum capacity

C= C<em>min</em>/C<em>max</em>

C = 5.016/8.62 = 0.582

.<em>2 Second, we determine the maximum heat transfer rate, Qmax</em>

Q<em>max</em> = C<em>min </em>(Inlet Temp. of hot fluid - Inlet Temp. of cold fluid)

Q<em>max</em> = (5.016 kW/°c)(160 - 20) °c

Q<em>max</em> = (5.016 kW/°c)(140) °c = 702.24 kW

.<em>3 Third, we determine the actual heat transfer rate, Q</em>

Q = C<em>min (</em>outlet Temp. of cold fluid - inlet Temp. of cold fluid)

Q = (5.016 kW/°c)(80 - 20) °c

Q<em>max</em> = (5.016 kW/°c)(60) °c = 303.66 kW

.<em>4 Fourth, we determine Effectiveness of the heat exchanger, </em>ε

ε<em> </em>= Q/Qmax

ε <em>= </em>303.66 kW/702.24 kW

ε = 0.432

.<em>5 Fifth, using appropriate effective relation for double pipe counter flow to determine NTU for the heat exchanger</em>

NTU = $\\ \frac{1}{C-1} ln(\frac{ε-1}{εc -1} )$

NTU = $\frac{1}{0.582-1} ln(\frac{0.432 -1}{0.432 X 0.582 -1} )$

NTU = 0.661

<em>.6 sixth, we determine Heat Exchanger surface area, As</em>

From the question, the overall heat transfer coefficient U = 640 W/m²

As = $\frac{NTU C{min} }{U}$

As = $\frac{0.661 x 5016 W. °c }{640 W/m²}$

As = 5.18 m²

<em>.7 Finally, we determine the length of the heat exchanger, L</em>

L = $\frac{As}{\pi D}$

L = $\frac{5.18 m² }{\pi (0.015 m)}$

L= 109.91 m

L ≅ 110 m = 11,000 cm

3 0

3 years ago