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3 years ago

The "view factor" Fij depends on surface emissivity and surface geometry. a) True b) False

Engineering

1 answer:

Alex3 years ago

4 0

Answer:

(B) FALSE

Explanation:

view factor $F_{ij}$ depends on the surface emissivity and the surface of geometry view factor is the term used in radiative heat transfer. View factor is depends upon the radiation which leave the surface and strike the surface.View factor is also called shape factor configuration factor it is denoted by $F_{ij}$

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A thick casting with a thermal diffusivity of 5 x 10-6 m2/s is initially at a uniform temperature of 150oC. One surface of the c

fredd [130]

Answer:

$T_o = 141.81 ^0C$

Explanation:

Given that;

Thermal diffusivity $\alpha = 5 \times 10 ^{-6} m^2/s$

Thermal conductivity $k = 20 \ W/m.K$

Heat transfer coefficient h = ( we are to assume the imposed surface temperature ) = 20 W/m².K

Initial temperature = 150 ° C = (150+273) K = 423 K

Then coolant temperature with which the casting is exposed to = 20° C = (20+273)K = 293 K

Time = 40 seconds

Length = 20mm = 0.02 m

The objective is to determine the temperature at the surface at a depth of 20 mm after 40 seconds.

$Bi = \dfrac{hL}{k}$

$Bi = \dfrac{20*0.02}{20}$

Bi == 0.02

$\tau = \dfrac{\alpha t}{L^2}$

$\tau= \dfrac{5*10^{-6 }* 40}{0.020^2}$

$\tau = 0.5$

For a wall at 0.2 Bi

$A_1 = 1.0311$

$\lambda _1 = 0.4328$

Therefore;

$\dfrac{T_o - T_{\infty}}{T_i - T_{\infty}}= A_1 e ^{-( \lambda_1^2 \ \tau)$

$\dfrac{T_o - 293 }{423 - 293}= 1.0311 \times e ^{-( 0.438^2 \times 0.5 )$

$\dfrac{T_o - 293 }{423 - 293}= 1.0311 \times e ^{-( 0.0959 )$

$\dfrac{T_o - 293 }{130}= 1.0311 \times 0.9085$

$\dfrac{T_o - 293 }{130}= 0.937$

$T_o - 293= 0.937 \times 130$

$T_o - 293= 121.81$

$T_o = 121.81+ 293$

$T_o = 414.81 \ K$

$T_o = (414.81 - 273)^0C$

$T_o = 141.81 ^0C$

4 0

4 years ago

QUESTÃO 13. Explique o uso das aspas no trecho "Darei a cada uma de vocês

lesya [120]

Answer: speaks Portuguese

Eu disse a todos a tradução para que possam te ajudar

Explanation: Y’all can help I have no idea

QUESTION 13. Explain the use of quotation marks in the excerpt "I will give each of you

seed. The one who will bring me the most beautiful flower within six months will be chosen but

wife and the future empress of China. ".

QUESTION 14. The palace servant considered the idea of her daughter attending the celeb

organized by the prince of the region, a foolish idea, a madness. This is an OP

Do you agree with this opinion of the character? Justify your answer.

6 0

3 years ago

3 cm of water evaporated from a 200-hectare vertical walled reservoir during 24 hours. Storm water was added to the reservoir at

ycow [4]

Answer:

water released through the bottom of the reservoir in 24 hrs is 1992 ha-cm

Explanation:

Given the data in the question;

A = 200 hectare = 2 × 10⁶ m²

water evaporated Ve = 2 × 10⁶ m² × 3 × 10⁻² = 60000 m³ { in 24 hrs }

Water added by storm in 24hrs Vi = 3 × 24 × 3600 = 259200 m³

now let water released be Vr

ΔV = V_ini - V_final = 0

Vi - Ve - Vr = 0

Vr = Vi - Ve

Vr = 259200 m³ - 60000 m³

Vr = 199200 m³ = 19920000 m² - cm

Vr = 1992 ha-cm

Therefore, water released through the bottom of the reservoir in 24 hrs is 1992 ha-cm

7 0

3 years ago

A particle travels rectilinearly a ceertain distance s. The particle travels half the distance (s/2) at a velocity v1. It travel

lara31 [8.8K]

Answer:

s(2v₁+v₂+v₃)/4

Explanation:

Recall that relationship between speed,distance and time is expressed as

speed=distance/time.

For the first part of the journey travelled at a speed of V₁ and covered a distance of (s/2), the time taken t₁=(s/2)/v₁

for the second part of the journey,let the time taken to complete both half of the second journey be t₂ and t₃ respectively. since it travel each half each distance at equal half time,then

t₂₌t₃

let the distance of the second journey be (s/2), where each time complete (s/4) distance. the time taken is

t₂₌(s/4)/v₂ and t₃=(s/4)/v₃

hence the total time taken is to cover the distance s is

t=t₁+t₂+t₃

t=(v₁s/2)+ (v₂s/4)+(v₃s/4)

t=s(2v₁+v₂+v₃)/4

6 0

3 years ago

Show the ERD with relational notation with crowfoot. Your ERD must show PK, FKs, min and max cardinality, and correct line types

zhenek [66]

Answer

The answer and procedures of the exercise are attached in the following archives.

Step-by-step explanation:

You will find the procedures, formulas or necessary explanations in the archive attached below. If you have any question ask and I will aclare your doubts kindly.

3 0

4 years ago