1. What is the term X in the following equation for overall heat transfer coefficient?
\(\frac{1}{U}= \frac{1}{hAb}+\frac{X}{K}+\frac{1}{hAc}\)
a) Thickness of jacket
b) Thickness of vessel wall
c) Thickness of vessel + jacket
d) Thickness of vessel – jacket
Explanation: We have the conductivity of the vessel wall only and not of the jacket, hence the given X is the thickness of the vessel and not the combined thickness.
2. What is the correct expression for calculating Nusselt number for a Jacketed Vessel?
a) Nu=\(\frac{0.03Re^{3/4}Pr}{1+1.74Re^{-1/8}(Pr-1)}\frac{\theta^{0.14}}{\theta w} \)
b) Nu=\(\frac{0.03Re^{3/4}Pr}{1+Re^{-1/8}(Pr-1)}\frac{\theta^{0.14}}{\theta w} \)
c) Nu=\(\frac{0.03Pr}{1+1.74Re^{-1/8}(Pr-1)}\frac{\theta^{0.14}}{\theta w} \)
d) Nu=\(\frac{0.03Re^{3/4}}{1+1.74Re^{-1/8}(Pr-1)} \)
Explanation: When we are calculating the Reynolds number for the jacket side, we cannot apply Sieder-Tate Equation as the heat is not transferred from all the side; hence the below formula is used.
Nu=\(\frac{0.03Re^{3/4}Pr}{1+1.74Re^{-1/8}(Pr-1)}\frac{\theta^{0.14}}{\theta w} \)
3. What is the equivalent diameter of Jacketed vessel, if the diameter of the jacket is 40mm and that of vessel is 30mm?
a) 8mm
b) 8.16mm
c) 9mm
d) 10mm
Explanation: The equivalent thickness is the difference of the jacket thickness and the vessel thickness multiplied with the constant 0.816. That is De = 0.816(Dj – Dt) = 0.816(40-30) = 8.16mm.
4. What is the expression for Equivalent diameter?
Dj = jacket thickness and
Dt = the vessel thickness
a) 0.816Dj
b) 0.8(Dj – Dt)
c) 0.816(Dj – Dt)
d) 0.8Dt
Explanation: The equivalent thickness is the difference of the jacket thickness and the vessel thickness multiplied with the constant 0.816.
5. What is the correct expression for Reynolds number in service side for jacket type Agitated Vessels?
a) \(Nu=K(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/4}\)
b) \(Nu=K(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/3}\)
c) \(Nu=K(\frac{\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/4}\)
d) \(Nu=K(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/4}\)
Explanation: The expression for the Nusselt number in terms of the vessel length and its density terms is represented as \(Nu=K(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/3}\);here ΔTm is the mean temperature difference between the service and the vessel wall.
6. For conventional unbaffled jacket, what is the term X in the expression for Reynolds number in service side for upward flow, heating and downward flow cooling?
\(Nu=X(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/3}\)
a) 0.15
b) 0.015
c) 0.128
d) 0.28
Explanation: The value of X the proportionality constant is K=0.15 for the formula \(Nu=K(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/3}\) when it is calculated for upward flow, heating and downward flow cooling
7. For conventional unbaffled jacket, what is the term X in the expression for Reynolds number in service side for upward flow, cooling and downward flow heating?
\(Nu=X(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/3}\)
a) 0.15
b) 0.015
c) 0.128
d) 0.28
Explanation: The value of X the proportionality constant is K=0.128 for the formula \(Nu=K(\frac{z^3\rho^2\beta g \Delta Tm}{\mu^2})^{1/3}Pr^{1/3}\) when it is calculated for upward flow, cooling and downward flow heating.
8. A condensing coefficient in a jacket should be ______ compared to the process side.
a) Extremely High
b) Extremely Low
c) Equal
d) Approximate equal
Explanation: The condensing coefficient in the jacket should be really large else there would be unnecessary heat losses on the service side or the jacketside.
9. For a half pipe coil, the equation for Reynolds number is usually the formula_______
a) Sieder Tate
b) Gnielinski correlation
c) Dittus-Boelter equation
d) Sieder
Explanation: As the half pipe coil is completely immersed in the vessel where the fluid is in contact with all the sides, hence we use Sieder-Tate equation.
10. A conventional jacket is usually fitted with baffles.
a) True
b) False
Explanation: There is already an agitator in the vessel to support the forced convection. If we want to add turbulence to the jacket side, we add baffles to that side. Hence baffles are usually added to the jacket side.