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3 years ago

What must happen to the temperature of a material for thermal expansion to occur.

1 answer:

8 0

In most cases the temperature must increase for thermal expansion to occur. Most substances expand as temperature increases because the atoms or molecules vibrate faster as temperature increases and experience greater separation.

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Steam enters the condenser of a steam power plant at 20kPa and a quality of 95% with a mass flow rate of 20,000kg/h. It is to be

avanturin [10]

Answer:

The mass rate of the cooling water required is: $1'072988.5\frac{kg}{h}$

Explanation:

First, write the energy balance for the condensator: The energy that enters to the equipment is the same that goes out from it; consider that there is no heat transfer to the surroundings and kinetic and potential energy changes are despreciable.

${m_{w}}*{h_{w}}^{in}+m_s{h_{s}}^{in}=m_w{h_{w}}^{out}+m_s{h_{s}}^{out}$

Where w refers to the cooling water and s to the steam flow. Reorganizing,

$m_w({h_{w}}^{out}-{h_{w}}^{in})=m_s({h_{s}}^{in}-{h_{s}}^{out})\\m_w=\frac{m_s({h_{s}}^{in}-{h_{s}}^{out})}{({h_{w}}^{out}-{h_{w}}^{in})}$

Write the difference of enthalpy for water as Cp (Tout-Tin):

$m_w=\frac{m_s({h_{s}}^{in}-{h_{s}}^{out})}{C_{pw}({T_{w}}^{out}-{T_{w}}^{in})}$

This equation will let us to calculate the mass rate required. Now, let's get the enthalpy and Cp data. The enthalpies can be read from the steam tables (I attach the tables I used). According to that, ${h_{s}}^{out}=251.40\frac{kJ}{kg}$ and ${h_{s}}^{in}$ can be calculated as:

${h_{s}}^{in}={h_{f}}+x{h_{fg}}=251.40+0.95*2358.3=2491.8\frac{kJ}{kg}$ .

The Cp of water at 25ºC (which is the expected average temperature for water) is: 4.176 $\frac{kJ}{kgK}$ . If the average temperature is actually different, it won't mean a considerable mistake. Also we know that ${T_{w}}^{out}-{T_{w}}^{in}\leq 10$ , so let's work with the limit case, which is ${T_{w}}^{out}-{T_{w}}^{in}=10$ to calculate the minimum cooling water mass rate required (A higher one will give a lower temperature difference as a result). Finally, replace data:

$m_w=\frac{20000\frac{kg}{h}(2491.8-251.40)\frac{kJ}{kg} }{4.176\frac{kJ}{kgK} (10C)}=1'072988.5\frac{kg}{h}$

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5 0

3 years ago

You are a member of an alpine rescue team and must get a box of supplies, with mass 3.00 kg , up an incline of constant slope an

Sever21 [200]

Answer:

v = 8.45 m/s

Explanation:

given,

mass = 3 kg

angle = 30.0°

vertical distance = 3.3 m

μ = 0.06

according to conservation of energy

KE(loss) = PE(gain) + Work done (against\ friction)..............(1)

frictional Force

$F_f = \mu N$

$F_f = \mu m g cos \theta$

work against friction

W = F d

$W = \mu m g cos \theta \times h l sin\theta$

$W = \dfrac{\mu m g \times h}{tan\theta}$

Potential energy

PE = mgh

$\dfrac{1}{2}mv^2= \dfrac{\mu mgh}{tan \theta}+ mgh$

$\dfrac{1}{2}v^2= \dfrac{0.06 \times 9.81 \times 3.3}{tan 30^0}+ 9.8\times 3.3$

v = 8.45 m/s

the minimum speed is equal to 8.45 m/s

6 0

3 years ago

If the air is only holding one-third as much moisture as it can possibly hold

dolphi86 [110]

Answer:

humoidity

Explanation:

6 0

3 years ago

What is the definition of ecosystem?

dimaraw [331]

Answer:

A place where organic and non organic materials interact to make a living space

7 0

3 years ago

Which labels best complete the diagram?

nlexa [21]

Answer: D

Explanation: Look at the figure, we can conclude that the correct answer is

X: Low potential energy

Y: High potential energy

Z: Flow of electrons

Because electrons flow where there is difference in potential energy. And electrons move from a region of high potential energy to a region of low potential energy.

Since the arrow is pointing to X, that means

Z is the flow of electrons, X is of low potential energy and Y is of high potential energy.

6 0

3 years ago