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SCORPION-xisa [38]

4 years ago

7

A composite wall is to be used to insulate a freezer chamber at -350C. Two insulating materials are to be used with conductiviti

es of 0.04 W/mK and 0.1 W/mK. If the outside surface temperature of the inner layer (0.04 W/mK) should not go below zero and if the exposed surface temperature should not go below (the expected wet bulb temperature) 220C determine the insulation thicknesses. The heat gain is to be limited to 10 W/m^2. Also estimate the value of convection coefficient at such a situation. Outside is at 250C.

1 answer:

choli [55]4 years ago

7 0

Answer:

thickness1=1.4m

thickness2=2.2m

convection coefficient=0.33W/m^2K

Explanation:

you must use this equation to calculate the thickness:

L=K(T2-T1)/Q

L=thickness

T=temperature

Q=heat

L1=0.04*(0--350)/10=1.4m

L2=0.1(220-0)/10=2.2m

Then use this equation to calculate the convective coefficient

H=Q/(T2-T1)

H=10/(250-220)=0.33W/m^2K

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77julia77 [94]

Answer:

Explanation:

The image attached to the question is shown in the first diagram below.

From the diagram given ; we can deduce a free body diagram which will aid us in solving the question.

IF we take a look at the second diagram attached below ; we will have a clear understanding of what the free body diagram of the system looks like :

From the diagram; we can determine the length of BC by using pyhtagoras theorem;

SO;

$L_{BC}^2 = L_{AB}^2 + L_{AC}^2$

$L_{BC}^2 = (3.5+2.5)^2+ 4^2$

$L_{BC}= \sqrt{(6)^2+ 4^2}$

$L_{BC}= \sqrt{36+ 16}$

$L_{BC}= \sqrt{52}$

$L_{BC}= 7.2111 \ m$

The cross -sectional of the cable is calculated by the formula :

$A = \dfrac{\pi}{4}d^2$

where d = 4mm

$A = \dfrac{\pi}{4}(4 \ mm * \dfrac{1 \ m}{1000 \ mm})^2$

A = 1.26 × 10⁻⁵ m²

However, looking at the maximum deflection in length $\delta$ ; we can calculate for the force $F_{BC$ by using the formula:

$\delta = \dfrac{F_{BC}L_{BC}}{AE}$

$F_{BC} = \dfrac{ AE \ \delta}{L_{BC}}$

where ;

E = modulus elasticity

$L_{BC}$ = length of the cable

Replacing 1.26 × 10⁻⁵ m² for A; 200 × 10⁹ Pa for E ; 7.2111 m for $L_{BC}$ and 0.006 m for $\delta$ ; we have:

$F_{BC} = \dfrac{1.26*10^{-5}*200*10^9*0.006}{7.2111}$

$F_{BC} = 2096.76 \ N \\ \\ F_{BC} = 2.09676 \ kN$ ---- (1)

Similarly; we can determine the force $F_{BC}$ using the allowable maximum stress; we have the following relation,

$\sigma = \dfrac{F_{BC}}{A}$

${F_{BC}}= {A}*\sigma$

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$\sigma =$ maximum allowable stress

Replacing 190 × 10⁶ Pa for $\sigma$ ; we have :

${F_{BC}}= 1.26*10^{-5} * 190*10^{6} \\ \\ {F_{BC}}=2394 \ N \\ \\ {F_{BC}}= 2.394 \ kN$ ------ (2)

Comparing (1) and (2)

The magnitude of the force $F_{BC} = 2.09676 \ kN$ since the elongation of the cable should not exceed 6mm

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$\sum M_A = 0$

$3.5 P - (6) ( \dfrac{4}{7.2111}F_{BC}) = 0$

$3.5 P - 3.328 F_{BC} = 0$

$3.5 P = 3.328 F_{BC}$

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3 years ago

Please help me please

VashaNatasha [74]

Answer: C

Explanation:

5 0

3 years ago

A 100-horsepower, three-phase squirrel-cage induction motor is connected to a 240-volt line. A dual-element time-delay fuse is t

antoniya [11.8K]

Based on the National Electrical Code (NEC), a 450-Ampere fuse should be used to protect this polyphase (three-phase) squirrel cage inductor motor.

<u>Given the following data:</u>

Power rating = 100-horsepower.

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<h3>How to determine the correct fuse rating?</h3>

According to Table 430.52 of the National Electrical Code (NEC), a dual-element time delay fuse should be calculated at 175% (1.75) of the full-load current rating for an alternating current (AC) polyphase (three-phase) squirrel cage inductor motor.

In this scenario, the squirrel cage inductor motor didn't list a NEMA design code on its nameplate. Thus, we'll assume that the inductor motor is design B and its fuse rating is given by:

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In conclusion, the nearest standard fuse size which is above the computed value listed in Section 240.6 of the National Electrical Code (NEC) is 450 amperes.

Read more on National Electrical Code here: brainly.com/question/10619436

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2 years ago

Consider a system whose temperature is 18°C. Express this temperature in R, K, and °F.

zvonat [6]

Answer:

In Rankine 524.07°R

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Explanation:

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We have to convert 18°C

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3 years ago

Which of the following is true about silicosis?

user100 [1]

Answer:

D. The damage it causes is irreversible

Explanation:

Silicosis is a long term lung disease caused by crystalline silica dust inhalation. There is no cure, and once the damage is done it cannot be reversed.

------------------

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2 years ago