Everything on MEC203 Flashcards
Gain a good understanding of the basic concepts to enable you to answer the questions.
What is Beta?
It is the volume expansion coefficient. Variation of fluid density with temperature at constant pressure.
What does the Grashof (Gr) number represent?
The natural convection effects in the momentum equation.
What does the Biot number represent?
The ratio of convection at the surface of a body to conduction within the body.
What kind of bodies are most likely to satisfy the condition for lumped system analysis?
Small bodies with large thermal conductivities and low convection coefficients.
What is a thermal boundary layer?
The flow region over the surface in which the temperature difference in the direction normal to the surface is significant.
What does the Nusselt number represent?
The enhancement of heat transfer through a fluid layer as a result of convection relative to conduction across the SAME fluid layer.
True or false, the larger the Nusselt number, the more effective the conduction?
FALSE. The larger the Nusselt number, the more effective the convection.
What is the Fourier number?
The ratio:
The rate at which heat is conducted across a body of length L and volume L^3.
—————————–DIVIDE—————————————–
The rate at which heat is stored in a body of L^3.
What does a large Fourier number suggest?
A large propagation of heat through a body.
What is the Biot number?
The ratio of external convection resistance to internal diffusion resistance.
What is FILM temperature?
Tf=0.5*(Ts+Tinfinity)
What is the Rayleigh number?
A dimensionless parameter that measures the instability of a layer of fluid due to differences in temperature and density at the top and bottom of the flow.
Describe the no-slip condition.
It occurs when a fluid in direct contact with a surface sticks to the surface and there isn’t any slip. It is due to the fluid’s viscosity.
What does the friction coefficient represent in fluid flow over a flat plate?
Represents the resistance to fluid flow over a flat plate.
What is turbulent thermal conductivity (kt)?
It accounts for thermal energy transport by turbulent eddies.
Why nondimensionalise the convection equation?
- Reduction in parameters. You go from six to two (Re and Pr)
- Allows you to group a large number of experiments and compare data
Define isothermal.
No change in temperature.
What is the definition of heat flux (q)?
q=-k(dt/dy)
True or false, for an ideal gas, kinematic viscosity is inversely proportional to pressure?
TRUE
True or false, for an ideal gas, thermal conductivity and Prandtl number are independent of pressure.
TRUE
What is the Prantdl Number?
It is a dimensionless number, representing the ratio of momentum diffusivity to thermal diffusivity.
What is the Nusselt number?
The Nusselt number is the ratio of convective to conductive heat transfer across a boundary.
What is the general formula for Nusselt number to find h?
Nu=(hD/k) where k is thermal conductivity and D is diameter.
What is kinematic viscosity?
Dynamic viscosity PER UNIT DENSITY