thermofluids Flashcards
What is specific volume and specific gravity of a material?
Specific volume is density times gravity. Specific gravity, surprisingly is density of a material/density of water.
Define manometry. When is an inverted U-tube manometer used?
Normally the fluid in the pipe is less dense, but an inverted U-tube manometer is used when the fluid in the piper is denser than the fluid in the manometer.
Slide 10 revision pptx. Manometry is the measurement of pressures using manometers.
What are the equations of total force for inclined submerged surfaces and how do you calculate the centre of pressure for one.
The total force is F = rgAh where h is the centre of the inclined plane in relation to the surface. The centre of pressure is 2nd Moment of Area / 1st Moment of Area. 2nd moment of Area is the ICC + A(y bar) squared. !st moment of Area is A time y bar. Again always in relation to the surface of the water.
How do you calculate Bouyancy force. What is the archimedes principle
B =V rho(fluid)g. A partially immersed object displaces its own weight of fluid.
How to calculate the force on a horizontal surface. And from there, derive to get the centre of pressure. Define Centre of Pressure.
See slide 11 pptx. Centre of pressure is a point on a shape where the total sum of the pressure field acts on a body, causing a force to act through that point.
Find the total force for a vertical wall. and the centre of pressure.
Again the same start of the equation. See slide 23 pptx. ultimately y-dash - 2b/3.
What are the forces acting on a fluid? Why are they important?
Forces include resistance forces such as Inertia Force and viscous force. Then there is the Pressure Force. and Gravity - which is the weight of the fluid. There might sometimes be surface tension as well, although often times they are small and ignored. The relative magnitude of such forces determine the nature and type of the
fluid flow. This is extremely important in fluid mechanics as many possible
forces act together in a complex manner.
What is the reynold’s number?
Often it is possible to characterize flows by looking at the ratio of two of the forces (the most dominant factors). Ratio of forces represented as a dimensionless number. the Reynolds number (Re) is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions. to indicate whether fluid flow past a body or in a duct is steady or turbulent.
What does a low or high reynold’s number indicate?
A low reynold’s number means the viscous forces are high and low inertial forces. This could mean Low velocity. Laminar flow. Re = 0 - 2000.
A high reynold’s number suggests a lower viscous force and a high inertial forces. High velocity, High density and turbulent flow. Re > 2000
How do you calculate the propulsive force? How do you calculate the efficiency ?
-mdot(v-u) where v is the velocity of the fluid behind whatever is being propelled. The efficiency is the Power in moving the boat/power in accelerating fluid. Which again is Force x distance/time / Change in KE of water. That force is simply gained by using the momentum equation.
What are the basic dimensions to do dimensional analysis.
They are length (L), Mass (M), Time (T), and absolute temperature. There are more like light intensity but we don’t need them just yet.
What is the Buckingham pi theory and how do you do it.
The Buckingham pi theory is a method of forming dimensionless groups and NDCE ( Non-dimensional Characteristic Equations). It states that for a system that has m number of independent variables and n basic dimensions, the relationship between the dimensionless groups can be expressed in (m-n) dimensionless groups. Then choose the pro-basic dimensions which must include all the basic dimensions in the system. it should be the samoe number as the common variables.
