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umka21 [38]
3 years ago
13

Just about everyone at one time or another has been burned by hot water or steam. This problem compares the heat input to your s

kin from steam as opposed to hot water at the same temperature.
Assume that water and steam, initially at 100?C, are cooled down to skin temperature, 34?C, when they come in contact with your skin. Assume that the steam condenses extremely fast. We will further assume a constant specific heat capacity c=4190J/(kg?K) for both liquid water and steam.

How much heat H1 is transferred to the skin by 25.0 g of steam onto the skin? The latent heat of vaporization for steam is L=2.256
Physics
1 answer:
tatyana61 [14]3 years ago
4 0

Answer:

Q_T=63313.5\ J

Explanation:

Given:

  • temperature of skin, T_s=34^{\circ}C
  • initial temperature of steam vapour, T_v=100^{\circ}C
  • latent heat of steam, L=2256\ J.g^{-1}
  • mass of steam, m=25\ g
  • specific heat of water, c=4190\ J.kg^{-1}.K^{-1}=4.19\ J.g^{-1}.K^{-1}
  • final temperature, T_f=34^{\circ}C

<em>Assuming that no heat is lost in the surrounding.</em>

<u>We know:</u>

Q=m.c.\Delta T

<u>Now the total heat given by the steam to form water at the given conditions:</u>

Q_T=Q_{Lv}+Q_w ..............................(1)

where:

Q_{Lv}= latent heat given out by vapour to form water of 100°C

Q_w= heat given by water of 100°C to come at 34°C.

putting respective values in eq. (1)

Q_T=m(L+c.\Delta T)

Q_T=25(2256+4.19\times 66)

Q_T=63313.5\ J

is the heat transferred to the skin.

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An automobile tire having a temperature of
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Answer:

Psm = 30.66 [Psig]

Explanation:

To solve this problem we will use the ideal gas equation, recall that the ideal gas state equation is always worked with absolute values.

P * v = R * T

where:

P = pressure [Pa]

v = specific volume [m^3/kg]

R = gas constant for air = 0.287 [kJ/kg*K]

T = temperature [K]

<u>For the initial state</u>

<u />

P1 = 24 [Psi] + 14.7 = 165.47[kPa] + 101.325 = 266.8 [kPa] (absolute pressure)

T1 = -2.6 [°C] = - 2.6 + 273 = 270.4 [K] (absolute Temperature)

Therefore we can calculate the specific volume:

v1 = R*T1 / P1

v1 = (0.287 * 270.4) / 266.8

v1 = 0.29 [m^3/kg]

As there are no leaks, the mass and volume are conserved, so the volume in the initial state is equal to the volume in the final state.

V2 = 0.29 [m^3/kg], with this volume and the new temperature, we can calculate the new pressure.

T2 = 43 + 273 = 316 [K]

P2 = R*T2 / V2

P2 = (0.287 * 316) / 0.29

P2 = 312.73 [kPa]

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Psm = 30.66 [Psig]

3 0
3 years ago
4.1 A steel spur pinion has a pitch of 5 teeth/in, 20 full-depth teeth, and a 20° pressure angle. The pinion runs at a speed of
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Answer:

15.07 ksi

Explanation:

Given that:

Pitch (P) = 5 teeth/in

Pressure angle (\Phi) = 20°

Pinion speed (n_p ) = 2000 rev/min

Power (H) = 30 hp

Teeth on gear (N_G) = 50

Teeth on pinion (N_p) = 20

Face width (F) = 1 in

Let us first determine the diameter (d) of the pinion.

Diameter (d) = \frac{N}{P}

=\frac{20}{5}

= 4 in

From the values of Lewis Form Factor Y for (n_p ) = 20 ; at 20°

Y = 0.321

To find the velocity (V); we use the formula:

V = \frac{\pi d n_p}{12}

V = \frac{\pi *4*2000}{12}

V = 2094.40 ft/min

For cut or milled profile; the velocity factor (K_v) can be determined as follows:

K_v = \frac{2000+V}{2000}

K_v = \frac{2000+2094.40}{2000}

= 2.0472

However, there is need to get the value of the tangential load(W^t), in order to achieve that, we have the following expression

W^t=\frac{T}{\frac{d}{2} }

W^t = \frac{63025*H}{\frac{n_pd}{2}}

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W^t = 472.69 lbf

Finally, the bending stress is calculated via the formula:

\sigma = \frac{K_vW^tp}{FY}

\sigma = \frac{2.0472*472.69*5}{1*0.321}

\sigma = 15073.07 psi

\sigma = 15.07 ksi

∴ The estimate of the bending stress = 15.07 ksi

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。☆✼★ ━━━━━━━━━━━━━━  ☾

The correct option would be A. solar.

We also use solar energy to produce electricity.

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。☆✼★ ━━━━━━━━━━━━━━  ☾

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