Meteorology The effect of wind, weather, and temperature conditions on the behavior of particle plumes Wind, and its Interaction with Particle Plumes Variation of wind speed with elevation Variation of wind speed during the day Estimating wind speed - The Beaufort scale The undesirable effect of wind on plumes near buildings Variation of wind speed with elevation Variation of wind speed during the day Wind speed increases with altitude. The velocity is called a boundary layer. Solar radiation affects wind conditions. Wind generally varies between night and day. No-slip boundary condition at the ground. Estimating wind speed - The Beaufort scale Observe at 20 ft Approximate speed at ( 6.1 m) above ground 20 ft (6.1 m) above the ground Wind force number (Beaufort number) Description mph km/h knots m/s Observation/Specification 0 Calm < 1 < 1 < 1 < 0.5 Smoke rises vertically 1 Light Air 1-3 1-5 1-3 0.5-1.7 Smoke drifts slowly; wind vanes and flags stay still 2 Slight Breeze 4-7 6-11 4-6 1.8-3.5 Wind felt on face; leaves rustle; flags stir; wind vanes move 3 Gentle Breeze 8-12 12-19 7-10 3.6-5.7 Leaves and small twigs in constant motion; flags are unfurled and flap Dust and loose paper blow around; small branches 4 Moderate Breeze 13-18 20-29 11-16 5.8-8.4 move; flags flap 5 Fresh Breeze 19-24 30-39 17-21 8.5-11.1 Small trees with leaves begin to sway; flags ripple Large branches sway; flags beat; air whistles around 6 Strong Breeze 25-31 40-50 22-27 11.2-14.2 telephone and power wires 7 Moderate Gale 32-38 51-61 28-33 Whole trees sway; flags extended; it can be hard to 14.3-17.3 walk into the wind 8 Fresh Gale 39-46 62-74 34-40 17.4-20.9 Twigs break off trees; walking is hindered 9 Strong Gale 47-54 75-85 41-47 Branches break off trees; slight damage to buildings 21.0-24.5 (shingles blow off roofs) The effect of wind on plumes near buildings Smoke from plume can get sucked into ventilation inlets. Downwash behind building can fumigate the ground. 10 Whole Gale 55-63 89-101 48-55 24.6-28.5 Trees broken or uprooted; buildings definitely damaged 11 Storm 64-73 102-118 56-63 Widespread damage to buildings; trees blow across the 28.6-33.0 ground Extreme destruction; trees and power lines knocked 12 Hurricane 74+ 119+ 64+ 33.1+ down Adapted from Meteorology Education and Training website, http://www.meted.ucar.edu/ 1
Example - fumigation in building wake How to avoid this kind of problem? Taller stack source of smoke is higher up, hopefully out of the way (but more expensive and not always possible). Location of stack may be able to locate it so that interaction with wind and building is less severe (also not always possible; wind is not always in the same direction). Hotter stack sends smoke up higher and out of the way (but more expensive since wasting more energy). Temperature Buoyancy of plumes Lapse rate Atmospheric stability Diurnal temperature variations Buoyancy of plumes A hot plume will rise rapidly, out of the way. (That's good!) A hot plume wastes a lot of energy. (That's bad!) detached steam plume Buoyancy of plumes (continued) A cool plume does not waste a lot of energy. (That's good!) A cool plume does not rise well, and may even fall - downwash. (That's bad!) Example of insufficient buoyancy, downwash 2
Buoyancy of plumes (continued) Hot plumes rise rapidly, but waste energy. Cool plumes save energy, but do not rise well. Bottom line - Must compromise between energy savings and plume buoyancy. Taller stacks help. Example of tall stack: discharge away from problems Tall stack, up and out of the way short stack, smoke can stay near ground Lapse rate The negative of the temperature gradient with elevation is called the lapse rate, lapse rate = - dt/dz = - (change in T)/(change in z) The standard (normal or average) lapse rate is about 6.5 o C per kilometer, i.e., T drops by about 6.5 o C for every 1 km of elevation. In English units, T drops by about 19 o F for every 1 mile of elevation. Dry lapse rate The dry lapse rate corresponds to a neutrally stable atmosphere. In other words, mixing is neither promoted nor inhibited. dry lapse rate = 9.8 o C/km dry lapse rate = 28 o F/mile Atmospheric stability Stability of the atmosphere is determined by comparing actual lapse rate to dry lapse rate. If the actual lapse rate is greater than the dry lapse rate, the atmosphere is unstable - mixing is enhanced (super). If the actual lapse rate is equal to the dry lapse rate, the atmosphere is neutrally stable - mixing is neither inhibited nor enhanced (). If the actual lapse rate is less than the dry lapse rate, the atmosphere is stable - mixing is inhibited (sub). super lapse rate (un Dry lapse rate stable, 9.8 o C/km) Normal (standard) lapse rate (6.5 o C/km) Sub lapse rate ( Temperature inversion (extremely 3
Example of a temperature inversion Example of a temperature inversion Cool, foggy morning Fog trapped in a thin layer near the ground Smoke trapped by the inversion. Typically seen on cold winter mornings. Example of a temperature inversion Cool, foggy morning Fog trapped in a thin layer near the ground Example of a temperature inversion Cold morning with gentle wind Smoke trapped in a thin layer near the ground Diurnal temperature variations (change in temperature throughout a 24-hour period ) Super conditions (very unstable - looping plume): noon mid morning sunrise midnight early evening late afternoon looping plume (strongly un 4
Nearly conditions stable - coning plume): Ground-based temperature inversion and short stack (very stable - fanning plume): coning plume fanning plume (strongly Fanning plume Ground-based temperature inversion and tall stack (stable below, unstable above - lofting plume): lofting plume (stable below, unstable above) Elevated temperature inversion and short stack (unstable below, stable above, - fumigating plume): Ground-based and elevated temperature inversions (stable below, stable above, - trapping plume): fumigating plume (unstable below, stable above) trapping plume (stable below, stable above, unstable in the middle) 5
Examples take a quiz! Photographs of plumes in various atmospheric stability conditions looping plume Name that plume: Lofting? Trapping? Looping? Coning? Fumigating? Fanning? looping particle plume elevated temperature inversion restricts upward mixing steam plume coning or fanning particle plume fumigating particle plume fanning or coning particle plume from tall stack fumigating particle plume from short stack apparently an elevated temperature inversion between the two plumes 6