![]() A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion.ġ1 Fluid motion can cause shearing stressesįigure 1.2 (p.A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. It describes the internal friction of a moving fluid. When the tank is filled with air at a gage pressure of 50 psi, determine the density of the air and the weight of air in the tank.Ĩ Example 3 Determine the density, specific gravity and mass of the air in a room whose dimensions are 4 m x 5 m x 6 m at 100 kPa and 25 Cĩ Viscosity Viscosity is a measure of a fluid's resistance to flow. R LV5 Ts are expressed in Kelvin or Rankine Lisa Vink, ħ Example 2 A compressed air tank has a volume of 0.84 ft 3. R is different for each gas and is determined from R=Ru/M where Ru is the universal gas constant, Ru=8.314 kJ/kmol.K=1.986 Btu/lbmol. Gases are highly compressible, gas density changes with pressure and temperature as, where p is the absolute pressure, ρ the density, T is absolute temperature, and R is gas constant Pressure units: lb/ft2 (psf) lb/in2 (psi) N/m2 (Pa) Standard sea-level atmospheric pressure – 14.7 psi kPa Gage pressure + atmospheric pressure = absolute pressureĥ Ts are expressed in Kelvin or Rankine Lisa Vink,.10) Density of water as a function of temperature.Ĥ Ideal/Perfect Gas Law /Equation of State Determine its density and specific weight at this temperature in both BG and SI units,ģ Figure 1.1 (p. Specific Gravity = density of the fluid/density of waterĢ Example 1 The specific gravity of mercury at 80 0C isġ3.4.Specific weight= weight/volume (lb/ft3 N/m3). ![]() Specific volume (volume per unit mass),.Thanks Again to and all for your help! I'm better now as a result.1 Density, ρ= mass/unitvolume –Slugs/ft3 kg/m3 So now my calculation looks like this, where I have added the extra steps just to make it clear I'm playing fair with my units: ![]() (It also helps that it looks like these calculations were performed in Mathcad.) This was for a huge system in a fast river, so the values are quite high, but they handled specific weight and density correctly: ![]() Reading both of your posts made me question everything, so then I dug deeper into previous calculations done for our machines, and found this calculation, done by a structural engineering consultant. This was for a larger machine in a slightly faster flow, but I thought my values had to be in this ball park. You are exactly correct, in that I was looking at a hand calc example from my predecessor, and I was taking it as gospel, when in fact he was confusing specific weight and density. I hope this Thank You very much for your input, and sorry for the delay - I'm just super busy, trying to get this report completed for a project submittal. Yes - I wish the US would just drop this terrible unit system once and for all! The correct drag force should be about 30 lbf. Recall the numeric value of 1 pound of mass weighs (has a force of) 1 pound and is only valid in earth's gravity. The mass density of water is 62.4 pounds mass/ft^2. If you simply change the gamma unit tag in example #2 from "lbf" to "lb", you will get the correct result. Update - the equation you used for the drag force requires a mass density, not weight density.the Mathcad Prime result supports this. I've used this approach many times with great success. Rumor has it Prime 7 will have some controls.maybe a simple drop-down like we have in v15. You will need to standardize on a "density" unit and account for gravity, or not, in your equation.Īlternatively, if you use Mathcad 15, you could create a drop-down unit choice and use an "If" statement to set the equation up to handle the units based on user selection. As you know, a "slug" is a different unit from a "lbf", so you can't use the same equation for both and expect consistent units for a result.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |