Chimneys, draft

Chimney draft is based upon the difference of specific gravity of cold air and heated air. The column of warm air in the chimney exerts a pressure per square foot at the base of hdi, where h is the height in feet and di is the density of hot gases in pounds per cubic foot. The pressure of the outside air for the same height is hd2f where d2 is the density of cold air in pounds per cubic foot. The motive force is therefore the difference of these two, or h(d2 — di), in pounds per square foot. For ordinary calculations,... 

In a tall furnace, it is impossible to have the same pressure at all levels because the furnace acts as a chimney, with its internal pressures increasing with elevation within the furnace. Depending on the magnitude of (a) pressure created by a forced draft fan or blower or (b) suction created by an induced draft fan, eductor, or natural chimney draft, the furnace may have any of the following situations ... 

Gases are diseharged into the ambient atmosphere by means of staeks (referred to as chimneys by some in industry) of several t> pes. Stub or short stacks are usually fabrieated of steel and e.xtend a minimum distanee up from the diseharge of an indueed draft fan. These are eonstrueted of steel plate, either unlined or refraetory-lined, or entirely of refraetory and struetural briek. Tall... 

Unvented kerosene and gas space heaters leaking chimneys and furnaces back-drafting from furnaces, gas water heaters, woodstoves, and fireplaces automobile exhaust from attached garages environmental tobacco smoke. Humans are normally the main indoor source of carbon dioxide. Unvented or imperfectly vented combustion appliances can also increase indoor COj concentrations. 

Kerosene lamps have a flat cloth wick. Flame height is determined by the height of the wick, which is controlled by a ratchet knob. A glass chimney ensures both safety and a stable, draft-free flame. 

Gas-Fired water heaters are also made more efficient by a variety of designs that increase the recov-ei y efficiency. These can be better flue baffles multiple, smaller-diameter flues submerged combustion chambers and improved combustion chamber geometry. All of these methods increase the heat transfer from the flame and flue gases to the water in the tank. Because natural draft systems rely on the buoyancy of combustion products, there is a limit to the recovery efficiency. If too much heat is removed from the flue gases, the water heater won t vent properly. Another problem, if the flue gases are too cool, is that the water vapor in the combustion products will condense in the venting system. This will lead to corrosion in the chimney and possible safety problems. 

Forced draft ducts Induced-draft flues and breeching Chimneys and stacks Water lines (max.)... 

This tower depends upon natural draft action the same as a chimney to draw cool air in at the bottom and expel it out the top as warm moist air (Figure 9-101). The action of the tower depends upon the atmospheric temperature therefore, on a hot day the action of the tower may be less than on a cool day. These towers are relatively large, and require power for pumping the water to a point in the tower which is usually lower than for an atmospheric tower. There are no fan costs. Units have been built 310 ft high, base diameter 210 ft and a throat of 120 ft, wdening to 134 ft in diameter at the top [30]. 

Originally, the height of the chimney was designed to produce a draft sufficient to produce induced-draft air for combustion. With modern boiler plant, forced-draft and/or induced-draft fans are used. This allows for the greater degree of control of the air to be designed into the combustion appliance. The chimney is therefore only required to disperse the gases. 

These positively shut off the draft that naturally occurs due to chimney buoyancy when the burner is in its off cycle, thereby reducing standby losses. Burners... 

Mechanical draft developed by a fan located between the boiler and the chimney. 

Chimney-assisted natural draft towers are of hyperboloidal shapes because they have greater strength for a given thickness a tower 250 ft high has concrete walls 5-6 in. thick. The enlarged cross section at the top aids in dispersion of. exit humid air into the atmosphere. 

Leonardo utilized his conception by devising a lamp chimney to regulate the draft, but seems not to have discussed the problem further. 

Fan power consumption is the major operating cost and can be counterbalanced in part by greater investment in natural draft construction. In the majority of process applications, fen-operated towers are preferred. Very large installations such as those in power plants employ chimney assisted natural draft installations. A limited use of atmospheric towers is made in areas where power costs are especially high. 

In an atmospheric spray tower the air movement - is dependent on atmospheric conditions and the aspirating effect of the spray nozzles. Natural-draft cooling tower operation depends on a chimney or stack to induce air movement. Mechanical-draft cboling towers utilize fans to move ambient air through the tower. Deck-filled towers contain tiers of splash bars or decks to assist in the breakup of water drops to increase the total water surface and subsequently the evaporation rate. Spray-filled towers depend only on spray nozzles for water breakup. Coil shed towers are comprised of a combination structure of a cooling tower installed on top of a substructure that contains atmospheric section coils. Hyperbolic natural-draft cooling towers are typically large-capacity systems. 

All that exists for these facilities67 are a few documents and contradictory, partly unbelievable eyewitness statements.68 According to Pressac, the two western, heated, unidentified rooms, as well as their anterooms, served as gas chambers . There is no evidence for any ventilation facility for these rooms prior to May 1944. For this reason Pressac suggests that up to that date ventilation was achieved by means of natural draft. In crematorium IV, but not in crematorium V, a ventilation facility is said to have been installed in May 1944, when the extermination of the Hungarian Jews allegedly began 69 Pressac shows a blueprint for this, but fails to cite a source for it. According to his blueprint, the ventilation shaft would have opened into an additional chimney of crematorium IV. How-... 

The two openings visible in the ceiling of the room today measure approximately 60 cm x 60 cm (the eastern opening),54 and 40 cm x 40 cm (the western opening).55 Both led to a wooden shaft in which a small chimney made of planks had been built. This shaft was closed by means of a lid, also made of wood, on the roof of the hut. Measured from the ceiling of the room, the chimney is approximately 1.15 m in height. Its present condition (except with regards to the size and selection of raw materials), corresponds to the draft of the cost estimate dated November 18, 1942 so that the actual structure, as built, was modified later. This is shown by the fact that, inside the room, the... 

Chimney-assisted natural draft towers also do not have fans, as shown in Figure 9.17(b). Most have tall chimneys, a fill that occupies a small percentage of the tower and no fan. They depend on a stack or chimney to induce the airflow through the tower. The hyperboloidal shape has greater strength for a given wall thickness. 

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