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3 years ago

Need help with these 3 questions pls help

Engineering

1 answer:

Burka [1]3 years ago

8 0

Answer:

Explanation:

First one is passion i think

second one is true im not sure

Third one is Time managaemant

Hope this helps!

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Clothing made of several thin layers of fabric with trapped air in between, often called ski clothing, is commonly used in cold

Pavlova-9 [17]

Answer:

Q=127.66W

L=9.2mm

Explanation:

Heat transfer consists of the propagation of energy in the form of heat in different ways, these can be convection if it is through a fluid, radiation through electromagnetic waves and conduction through solid solids.

To solve any problem related to heat transfer, the general equation is used

Q = delta / R

Where

Q = heat

Delta = the temperature difference

R = is the thermal resistance by conduction, convection and radiation

to solve this problem we propose the previous equation

Q = delta / R

later we find R

$R=[tex]r=\frac{6L1}{AK1} +\frac{5L2}{AK2}+\frac{1}{Ah}$

$R=\frac{6(0.0001)}{(1.25)(0.026)} +\frac{5(0.012)}{(1.25)(0.026)}+\frac{1}{(25)(1.25)} =0.235 K/w$

Q=(25-(-5))/0.235=127.66W

part b

we use the same ecuation with Q=127.66

Q = delta / R

Δ $R=\frac{L}{KA} +\frac{1}{hA} \\R=\frac{L}{(0.035)(1.25)} +\frac{1}{(25)(1.25)}\\ R=22.85L+0.032\\Q=(T1-T2)/R\\\\127.66=(25-(-5))/(22.85L+0.032)\\solving for L\\L=9.2mm$

6 0

3 years ago

If i build thing a and thing a builds thing b did i build thing b

postnew [5]

Answer:

Explanation:

If you build thing "a" and thing "a" builds thing "b" you <u>indirectly</u> build thing "b".

3 0

3 years ago

Read 2 more answers

Asperities are microscopic peaks and valleys on

Rudiy27

Answer:

On a surface.

Explanation:

Asperities are microscopic peaks and valleys on a surface. This simply means that, when asperities contacts, surfaces also make contact. Asperities are the roughness or unevenness of a surface coming in contact during wear or friction.

8 0

3 years ago

Read 2 more answers

Air modeled as an ideal gas enters a turbine operating at steady state at 1040 K, 278 kPa and exits at 120 kPa. The mass flow ra

gladu [14]

Answer:

a) $T_{2}=837.2K$

b) $e=91.3$ %

Explanation:

A) First, let's write the energy balance:

$W=m*(h_{2}-h_{1})\\W=m*Cp*(T_{2}-T_{1})$ (The enthalpy of an ideal gas is just function of the temperature, not the pressure).

The Cp of air is: 1.004 $\frac{kJ}{kgK}$ And its specific R constant is 0.287 $\frac{kJ}{kgK}$ .

The only unknown from the energy balance is $T_{2}$ , so it is possible to calculate it. The power must be negative because the work is done by the fluid, so the energy is going out from it.

$T_{2}=T_{1}+\frac{W}{mCp}=1040K-\frac{1120kW}{5.5\frac{kg}{s}*1.004\frac{kJ}{kgk}} \\T_{2}=837.2K$

B) The isentropic efficiency (e) is defined as:

$e=\frac{h_{2}-h_{1}}{h_{2s}-h_{1}}$

Where ${h_{2s}$ is the isentropic enthalpy at the exit of the turbine for the isentropic process. The only missing in the last equation is that variable, because $h_{2}-h_{1}$ can be obtained from the energy balance $\frac{W}{m}=h_{2}-h_{1}$

$h_{2}-h_{1}=\frac{-1120kW}{5.5\frac{kg}{s}}=-203.64\frac{kJ}{kg}$

An entropy change for an ideal gas with constant Cp is given by:

$s_{2}-s_{1}=Cpln(\frac{T_{2}}{T_{1}})-Rln(\frac{P_{2}}{P_{1}})$

You can review its deduction on van Wylen 6 Edition, section 8.10.

For the isentropic process the equation is:

$0=Cpln(\frac{T_{2}}{T_{1}})-Rln(\frac{P_{2}}{P_{1}})\\Rln(\frac{P_{2}}{P_{1}})=Cpln(\frac{T_{2}}{T_{1}})$

Applying logarithm properties:

$ln((\frac{P_{2}}{P_{1}})^{R} )=ln((\frac{T_{2}}{T_{1}})^{Cp} )\\(\frac{P_{2}}{P_{1}})^{R}=(\frac{T_{2}}{T_{1}})^{Cp}\\(\frac{P_{2}}{P_{1}})^{R/Cp}=(\frac{T_{2}}{T_{1}})\\T_{2}=T_{1}(\frac{P_{2}}{P_{1}})^{R/Cp}$