Lecture 4: Thermal Analysis Flashcards
What is the aim of reactor cooling?
To remove heat generated by the fuel. and keep the reactor at a safe temperature.
How is heat transferred?
Convection
What is the greatest constraint on how much electricity can be generated?
The amount of heat that can be safely extracted.
How do spacer fuel rod supports aid heat extraction?
Cause flow turbulence for the coolant to improve heat transfer performance by convection.
What is the general strategy for thermal analysis?
Use knowledge of pipe flow.
Convert to flow in an anti-pipe via use of hydraulic/equivalent diameter.
Name five dimensionless numbers:
Reynolds Number
Stanton Number
Nusselt Number
Fanning Friction Factor
Prandtl Number
Define Reynolds Number:
Ratio between momentum and viscous forces
Define Stanton Number:
Relative importance of heat convection through a boundary layer and convection with the flow
Define Nusselt Number:
Relative importance of surface convection and conduction
Define Fanning Friction Factor:
Ratio of wall shear stress and dynamic pressure
Define Prandtl Number:
Ratio of momentum diffusivity and thermal diffusivity
What are the three flow types?
Laminar
Turbulent
Transition
Which dimensionless number can indicate flow type?
Reynolds number
Which flow type is more effective at extracting energy?
Turbulent
Which dimensionless numbers can be used to find the heat transfer coefficient (h)?
Nusselt Number
Stanton Number
What is the purpose of the hydraulic diameter?
To approximate behaviour in non-circular passages from measurement s in circular ones.
What is the importance of preventing boiling?
Must ensure water does not convert to steam as it is an extremely poor coolant.
True or false: Nucleate boiling is poor at heat transfer?
False
Which flow type is fastest?
Turbulent
What Reynolds number is the transition phase of flow?
10^3 to 10^4
What is the Darcy-Weisbach Friction Factor for laminar flow?
= 64/Re
What is the Darcy-Weisbach Friction Factor for turbulent flow?
= 0.184Re^-0.2
What type of convection is used for heat extraction?
Forced
How is the hydraulic diameter calculated?
= 4 (flow area) / wetted perimeter
