Continuing
with the phenomenological description of what happens in a liquid inside a pot to which it is heated gradually. Fluid was left in a state of convection and continued since then.
Suppose that the liquid is heated as it is about to be found within it a boil.
sudden warming
If the heating be conducted in a manner so abrupt that the macroscopic currents could be developed or were not significant, evaporation and expansion of water at the bottom of the pot would resemble the detonation of an explosive power and variable, where the boundary expansion transmits a momentum that can be as vigorous as expel the water outside the container.
SLOW WARMING
If global warming has occurred sufficiently slowly, macroscopically there will be a fully developed convective flow, with standpipes and down rings around these columns. With the liquid near the base of laterally moving towards the base of the columns rising from the pressure difference noted in the previous text and the top liquid moving laterally to the ring dip, creating a form of flow torus. Through the outer surface of the liquid, the flow of molecules with enough energy to leave the liquid will be significantly increased so that the resulting steam can be appreciated at a glance. For boiling is likely to occur in the liquid, the focus will be to establish a thermal gradient large enough to compensate for losses due to cooling due to the escape of more energetic molecules in addition to other losses that may exist.
iron atoms with momentum hit bottom water, in short, all of these impacts increases the kinetic energy of water, which move along the bottom fence to climb the column was anger gradually warming. There will come a time when the temperatures involved will create an area near the base evaporated.
The image above corresponds to the above, but suffers from a gap, ignores the existence of a surface tension in different areas that are created during evaporation of the liquid inside. It is necessary to incorporate.
BUBBLE
When a flow of heat from the bottom stirred enough water, it creates an advancing front in which there a gaseous phase. Sometimes, when heated Alghero bubbles that remain attached to the surface, and do not seem to vary their size, these bubbles are in a steady state.
At steady state there is an equilibrium in which several phenomena:
- vapor molecules due to thermal agitation continuously penetrate into the surrounding water.
- Water molecules diffuse through the surface and will form part of the gas
- A heat leak from the bubble to the liquid
- A heat input of the steam iron.
- There is a surface tension of both steam and iron, which tends to eliminate surface border, the same way that there is an inflated balloon to vary air pressure.
- vapor exerts a pressure against the surface that prevents collapse.
- The weight of the water column
At steady state, the inflows and outflows of heat and water are canceled, and the bubble acquires a curved shape corresponding to its minimum energy for that volume. We have a drop of steam.
To get an idea, a water molecule is about 0.3 nm, this means that if the water molecule had the size pea-5 mm, a water bubble of 5 mm would measure 83 kilometers.
BUBBLE COLLAPSE
may notice that some bubbles grow to a certain size and then collapse, this can happen if environmental conditions vary, for example by the surrounding water cooler because the randomness of turbulent flow, the bubble may be especially sensitive to these changes at an early stage of development. Although it is possible that there are stable boundary conditions, where the bubble can not exceed a size without imploding.
SEPARATION BUBBLE
Among the dome bubble and the background of iron, there is a ring that is the union between two interfaces. The low-density bubble lead to an upward force that at a certain volume is proportional to the volume. A This upward force is opposed by the surface tension in the ring, which is proportional to its circumference. When the volume is small, the bubble may remain attached to the bottom. If the circumference of the ring grows N, N ^ 3 volume increases with the increase in volume therefore comes a time when the thrust is enough to start the union. Using the ring fence closer to the center, until it collapses in the middle and the bubble does not keep the bottom border of iron. Continuing his ascension to the outside.
LEAVING THE BUBBLE LIGHTS
When looking at the boiling point of water, there are areas where you have to build the generation and emission of bubbles, as if these points were privileges. In this may influence several factors:
The first bubbles tend to form at the end of the trail convective by the fund, it is the area where the water has spent more time near the bottom. The base of the convective columns, to be the hottest areas are more likely to generate bubbles.
Since the fluid is warmer in the convective zone, iron also it is therefore the temperature gradient is smaller and cooled to a lesser degree. So is the area where heat can flow more quickly to steam inside a bubble to grow.
A bubble is created outside the convective column, create a new convective pillar in his ascension, a process of creating chains of bubbles on the site. So if to release the heat transferred to the liquid is necessary to create these bubbles No bubbles tend to be clustered in the same column lift.
When the collapse occurs and the ring segregation of the bubble may have been a small bubble attached to the bottom, as when a drop is secreted from a faucet produces smaller drops behind them. This small bubble would be the seed of a bubble that grew favored by environmental conditions, even detach again and replay the cycle.
incorporating these ideas to the previously proposed scheme, would be:
With what this is finalized the track, which has also been developed to across the other 2 chapters; 1 and 2 .
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