The gravitational force between two objects is 100 N.
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Saturated ethylene glycol at 1 atm is heated by a chromium-plated surface which is circular in shape and has a diameter of 200-mm and is maintained at 480 K.
At 470 K the properties of the saturated liquid are mu = 0.38 * 10-3 N. s/m^2, Cp = 3280 J/kg. K and Pr = 8.7. The saturated vapour density is p= 1.66 kg/m^3. Take the liquid to surface constants to be Cnb = 0.010 and m=4.1.
Estimate the heating power requirement and the rate of evaporation
What fraction is the power requirement of the maximum power associated with the critical heat flux
Answer:
The heating power requirement = 559.2 W
The rate of evaporation =
The fraction of the power requirement of operating heat flux to the maximum power associated with the critical heat flux is = 0.026
Explanation:
From the thermodynamics tables; we deduced the value for enthalpy at the pressure 1 atm and = 470 K for the saturated ethylene glycol.
Value for enthalpy of formation = 812 kJ/kg
Density of saturated ethylene glycol = 1111 kg/m³
Surface tension
The heat flux can be calculated by using the formula:
= 308.56 × 576.6 × 0.1
= 1.78 × 10⁴ W/m²
Now; to find the heating power requirement; we have:
=
Thus, the heating power requirement = 559.2 W
The rate of evaporation is given as:
=
=
Thus, the rate of evaporation =
To determine to what fraction in the power requirement of the maximum power is associated with the critical total flux ; we needed to first calculate the critical heat flux.
So, the calculation for the critical heat is given as:
=
= 200840.08 × 3.37
= 6.77 × 10⁵ W/m²
Finally, the fraction of the power requirement of operating heat flux to the maximum power associated with the critical heat flux is as follows:
=
=
= 0.026
Thus, the fraction of the power requirement of operating heat flux to the maximum power associated with the critical heat flux is = 0.026