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ch4aika [34]
3 years ago
11

A thick oak wall (rho = 545 kg/m3 , Cp = 2385 J/kgK, and k = 0.17 W/mK) initially at 25°C is suddenly exposed to combustion prod

ucts at 800°C. Determine the time of exposure necessary for the surface to reach the ignition temperature of 400°C, assuming the convection heat transfer coefficient between the wall and the products to be 20 W/m2 K. At that time, what is the temperature 1 cm below the surface? (Note: use an appropriate equation for the semi-infinite wall case; compare equations 18.20 and 18.21 in the text).

Engineering
1 answer:
Nimfa-mama [501]3 years ago
8 0

Answer:

Explanation:

The detailed calculation and appropriate equation with substitution is as shown in the attached file.

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A simple ideal Rankine cycle with water as the working fluid operates between the pressure limits of 4 MPa in the boiler and 20
viktelen [127]

Answer:

a) 69,630KW

b) 203 KW

Explanation:

The data obtained from Tables A-4, A-5 and A-6 is as follows:

h_{1} = h_{f,@20KPa} = 251.42 KJ/kg\\v_{1} = v_{f,@20KPa} = 0.001017 KJ/kgK\\\\w_{p,in} = v_{1} * (P_{2} - P_{1})\\w_{p,in} = (0.001017)*(4000-20)\\\\w_{p,in} = 4.05 KJ/kg\\\\h_{2} = h_{1} - w_{p,in} \\h_{2} = 251.42 + 4.05\\\\h_{2}  =  255.47KJ/kg\\\\P_{3} = 4000KPa\\T_{3} = 700 C\\s_{3} = 7.6214 KJ/kgK\\\\h_{3} = 3906.3 KJ/kg\\\\P_{4} = 20 KPa\\s_{3} = s_{4} = 7.6214KJ/kgK\\s_{f} = 0.8320 KJ/kgK\\s_{fg} = 7.0752 KJ/kgK\\\\

x_{4} = \frac{s_{4} - s_{f} }{s_{fg} }  \\\\x_{4} = \frac{7.6214-0.8320}{7.0752} = 0.9596\\\\h_{f} = 251.42KJ/kg \\h_{fg} = 2357.5KJ/kg \\\\h_{4} = h_{f} + x_{4}*h_{fg} = 251.42 + 0.9596*2357.5 = 2513.7KJ/kg\\\\

The power produced and consumed by turbine and pump respectively are:

W_{T,out} = flow(m) *(h_{3} - h_{4}) \\W_{T,out} = 50 *(3906.3-2513.7)\\\\W_{T,out} = 69,630 KW\\\\W_{p,in} = flow(m) *w_{p,in} = 50*4.05 = 203 KW

7 0
3 years ago
2 Air enters the compressor of a cold air-standard Brayton cycle at 100 kPa, 300 K, with a mass flow rate of 6 kg/s. The compres
lutik1710 [3]
You can see and download from the link

https://tlgur.com/d/GYYVL5lG

Please don't forget to put heart ♥️
5 0
3 years ago
Given a two-dimensional steady inviscid air flow field with no body forces described by the velocity field given below. Assuming
kolbaska11 [484]

Answer:

the pressure gradient in the x direction = -15.48Pa/m

Explanation:

  • The concept of partial differentiation was used in the determination of the expression for u and v.
  • each is partially differentiated with respect to x and the appropriate substitution was done to get the value of the pressure gradient as shown in the attached file.

4 0
3 years ago
A DC generator turns at 2000 rpm and has an output of 200 V. The armature constant is 0.5 V-min/Wb, and the field constant of th
WITCHER [35]

Answer:

b. 10A

Explanation:

Using the formula, E= k × r×I

200= 0.5 ×2000×0.02×I

200=20×I

Dividing with 20

I = 200/20= 10A

4 0
3 years ago
Read 2 more answers
‏What is the potential energy in joules of a 12 kg ( mass ) at 25 m above a datum plane ?
Virty [35]

Answer:

E = 2940 J

Explanation:

It is given that,

Mass, m = 12 kg

Position at which the object is placed, h = 25 m

We need to find the potential energy of the mass. It is given by the formula as follows :

E = mgh

g is acceleration due to gravity

E=12\times 9.8\times 25\\\\E=2940\ J

So, the potential energy of the mass is 2940 J.

3 0
3 years ago
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