Vapor mushroom

Gaertner (1965) studied nucleate pool boiling on a horizontal surface in a water pool under atmospheric pressure. He increased the surface heat flux gradually. The vapor structures on the surface progressed from discrete bubbles to vapor columns and vapor mushrooms, and finally to vapor patches (dryout). The observed pictures of vapor mushroom and vapor patch are also sketched in Figure 5.3. 

Katto and Yokoya [102] showed that the volume of the vapor mushrooms increased linearly with time (which is consistent with the hypothesis of the growth being governed in the macrolayer) and obtained the following expression for the hovering period x between vapor mushroom departures ... 

Where v is the volumetric growth rate of the bubble (calculable from the heat flux). The time required for the formation of a new macrolayer with its associated vapor mushroom was very short and the frequency of vapor mushroom departure is therefore f 1/x. 

Macrolayer consumption model. Here it is postulated that the macrolayer formed under the vapor mushrooms in fully developed boiling (see Fig. 15.48) is totally evaporated in the time between the release of the mushroom-shaped bubbles. 

Macrolayer Consumption Model. Although the hydrodynamic instability model agrees well with much of the experimental data, the very extensive photographic studies that have been conducted on boiling (exemplified by those sketched in Fig. 15.48) indicate a quite different pattern of behavior as the critical heat flux is approached. Thus, vapor mushrooms are... 

Hot-Spot Heating. This mechanism has been investigated by Unal et al. [169], The stages envisaged are that, on departure of the vapor mushroom in the fully developed... 

T Ti Stefan-Boltzmann constant (5.669 x 10"8), W/m2K4 t/tc (Fig. 15.24) hovering period of vapor mushrooms, s dimensionless time (Eq. 15.151) interfacial shear stress, N/m2... 

Fallout Radioactive material that falls back to earth after a nuclear explosion. Contains highly radioactive materials from the original weapon, vaporized material from ground zero, and other materials pulled into the mushroom cloud. The amount of fallout and spread of radioactivity depends on weapon yield and meteorological conditions. 

Bubble mergers normal to the heater and along the heater leading to the formation of vapor columns and mushroom type bubbles have been studied. 

Ingestion is the most likely route of exposure however, it has been stated (without good documentation) that poisoning can occur from inhaling monomethylhydrazine vapors that come off in the steam during boiling of the mushrooms. 

Naled is a fast acting, nonsystemic contact and stomach organophosphorus insecticide used to control aphids, mites, mosquitoes, and flies on crops and in greenhouses, mushroom houses, animal and poultry houses, kennels, food processing plants, and aquaria. Naled is also used in outdoor mosquito control. Liquid formulations can be applied to greenhouse heating pipes to kill insects by vapor action. It has been used by veterinarians to kill parasitic worms (other than tapeworms) in dogs. Naled is available in dust, emulsion concentrate, liquid, and ultra-low volume (ULV) formulations. 

Lighting should be provide by a few banks of wide spectrum fluorescent tubes fairly evenly distributed across the ceiling and turned on for 10-12 hours regularly each day. These are great dust catchers, however, and must be wiped clean periodically. The work table should also be painted with a hard smooth, white finish. If the table is metal, a small, clean cutting board must be provided on which to pin down mushroom caps when disecting them. Shelf boards on the wall next to the table may be extended above the table to provide space for storage of work equipment and ready containers. A hood should be constructed around the table to protect it from dust, etc. A fume hood with a flu vent and spark-free exhaust fan should be constructed over the extraction area to remove toxic and combustible methanol vapors. 

Most mushroom growers use steam as the principal means of humidification. The steam is injected into the air system duct on the downstream side of the fan and filter. Household vaporizers are well suited for small growing rooms. They are available in various capacities and can be fined with a duct running to the air system. The vaporizer can also be positioned under the mixing box for steam uptake with the recirculated air. Keep in mind that cold fresh air has much less capacity for moisture absorbtion and therefore does not mix well with large volumes of steam. 

Some species of mushrooms have been recommended as sentinel species of mercury contamination because of their ability to accumulate very high concentrations of mercury from the ambient air. In one study, shiitake mushrooms, Lentinus edodus, exposed to Hg vapor at 172.0 xg Hg/m for up to 7 days had grossly elevated concentrations of mercury in caps and stalks. After 3 days caps had 125.0 mg Hg/kg DW and stalks 10.0 mg Hg/kg DW. After 7 days, these values were 310.0 00.0 mg/kg DW in caps and 20.0-30.0 mg/kg DW in stalks. 

It s my mother s mushroom soup story again (Sec. 1.4). Converting the sensible-heat content of the water into latent heat of evaporation of the water. But for the air to carry away the evolved water vapor, it has to be below its dew-point temperature. 

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