A bubble is a globule of a gas substance in a liquid. In the opposite case, a globule of a liquid in a gas, is called a drop. [1] Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.
A bubble is a globule of a gas substance in a liquid. In the opposite case, a globule of a liquid in a gas, is called a drop. [1] Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.
Bubbles are seen in many places in everyday life, for example:
Bubbles form and coalesce into globular shapes because those shapes are at a lower energy state. For the physics and chemistry behind it, see nucleation.
Bubbles are visible because they have a different refractive index (RI) than the surrounding substance. For example, the RI of air is approximately 1.0003 and the RI of water is approximately 1.333. Snell's Law describes how electromagnetic waves change direction at the interface between two mediums with different RI; thus bubbles can be identified from the accompanying refraction and internal reflection even though both the immersed and immersing mediums are transparent.
The above explanation only holds for bubbles of one medium submerged in another medium (e.g. bubbles of gas in a soft drink); the volume of a membrane bubble (e.g. soap bubble) will not distort light very much, and one can only see a membrane bubble due to thin-film diffraction and reflection.
Nucleation can be intentionally induced, for example, to create a bubblegram in a solid.
In medical ultrasound imaging, small encapsulated bubbles called contrast agent are used to enhance the contrast.
In thermal inkjet printing, vapor bubbles are used as actuators. They are occasionally used in other microfluidics applications as actuators. [2]
The violent collapse of bubbles (cavitation) near solid surfaces and the resulting impinging jet constitute the mechanism used in ultrasonic cleaning. The same effect, but on a larger scale, is used in focused energy weapons such as the bazooka and the torpedo. Pistol shrimp also uses a collapsing cavitation bubble as a weapon. The same effect is used to treat kidney stones in a lithotripter. Marine mammals such as dolphins and whales use bubbles for entertainment or as hunting tools. Aerators cause the dissolution of gas in the liquid by injecting bubbles.
Bubbles are used by chemical and metallurgic engineer in processes such as distillation, absorption, flotation and spray drying. The complex processes involved often require consideration for mass and heat transfer and are modeled using fluid dynamics. [3]
The star-nosed mole and the American water shrew can smell underwater by rapidly breathing through their nostrils and creating a bubble. [4]
Research on the origin of life on Earth suggests that bubbles may have played an integral role in confining and concentrating precursor molecules for life, a function currently performed by cell membranes. [5]
Bubble lasers use bubbles as the optical resonator. They can be used as highly sensitive pressure sensors. [6]
When bubbles are disturbed (for example when a gas bubble is injected underwater), the wall oscillates. Although it is often visually masked by much larger deformations in shape, a component of the oscillation changes the bubble volume (i.e. it is pulsation) which, in the absence of an externally-imposed sound field, occurs at the bubble's natural frequency. The pulsation is the most important component of the oscillation, acoustically, because by changing the gas volume, it changes its pressure, and leads to the emission of sound at the bubble's natural frequency. For air bubbles in water, large bubbles (negligible surface tension and thermal conductivity) undergo adiabatic pulsations, which means that no heat is transferred either from the liquid to the gas or vice versa. The natural frequency of such bubbles is determined by the equation: [7] [8]
where:
For air bubbles in water, smaller bubbles undergo isothermal pulsations. The corresponding equation for small bubbles of surface tension σ (and negligible liquid viscosity) is [8]
Excited bubbles trapped underwater are the major source of liquid sounds, such as inside our knuckles during knuckle cracking, [9] and when a rain droplet impacts a surface of water. [10] [11]
Injury by bubble formation and growth in body tissues is the mechanism of decompression sickness, which occurs when supersaturated dissolved inert gases leave the solution as bubbles during decompression. The damage can be due to mechanical deformation of tissues due to bubble growth in situ, or by blocking blood vessels where the bubble has lodged.
Arterial gas embolism can occur when a gas bubble is introduced to the circulatory system and lodges in a blood vessel that is too small for it to pass through under the available pressure difference. This can occur as a result of decompression after hyperbaric exposure, a lung overexpansion injury, during intravenous fluid administration, or during surgery.
Foods containing bubbles includes bread, cakes, cereals and chocolate, and drinks including beer, champagne, mineral water and soft drinks, as well as more experimental applications in foams as made by chefs. [12]
Density is a substance's mass per unit of volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume: where ρ is the density, m is the mass, and V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more specifically called specific weight.
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure.
Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density of a substance to the density of a given reference material. Specific gravity for solids and liquids is nearly always measured with respect to water at its densest ; for gases, the reference is air at room temperature. The term "relative density" is preferred in SI, whereas the term "specific gravity" is gradually being abandoned.
A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the end of a tube or other surface boundary, producing a hanging drop called a pendant drop. Drops may also be formed by the condensation of a vapor or by atomization of a larger mass of solid. Water vapor will condense into droplets depending on the temperature. The temperature at which droplets form is called the dew point.
In thermodynamics and fluid mechanics, the compressibility is a measure of the instantaneous relative volume change of a fluid or solid as a response to a pressure change. In its simple form, the compressibility may be expressed as
Foams are two-phase material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. The foam "may contain more or less liquid [or solid] according to circumstances", although in the case of gas-liquid foams, the gas occupies most of the volume. The word derives from the medieval German and otherwise obsolete veim, in reference to the "frothy head forming in the glass once the beer has been freshly poured".
An antibubble is a droplet of liquid surrounded by a thin film of gas, as opposed to a gas bubble, which is a sphere of gas surrounded by a liquid. Antibubbles are formed when liquid drops or flows turbulently into the same or another liquid. They can either skim across the surface of a liquid such as water, in which case they are also called water globules, or they can be completely submerged into the liquid to which they are directed.
In thermodynamics, nucleation is the first step in the formation of either a new thermodynamic phase or structure via self-assembly or self-organization within a substance or mixture. Nucleation is typically defined to be the process that determines how long an observer has to wait before the new phase or self-organized structure appears. For example, if a volume of water is cooled significantly below 0 °C, it will tend to freeze into ice, but volumes of water cooled only a few degrees below 0 °C often stay completely free of ice for long periods (supercooling). At these conditions, nucleation of ice is either slow or does not occur at all. However, at lower temperatures nucleation is fast, and ice crystals appear after little or no delay.
Ostwald ripening is a phenomenon observed in solid solutions and liquid sols that involves the change of an inhomogeneous structure over time, in that small crystals or sol particles first dissolve and then redeposit onto larger crystals or sol particles.
The Kelvin equation describes the change in vapour pressure due to a curved liquid–vapor interface, such as the surface of a droplet. The vapor pressure at a convex curved surface is higher than that at a flat surface. The Kelvin equation is dependent upon thermodynamic principles and does not allude to special properties of materials. It is also used for determination of pore size distribution of a porous medium using adsorption porosimetry. The equation is named in honor of William Thomson, also known as Lord Kelvin.
A soda geyser is a physical reaction between a carbonated beverage, usually Diet Coke, and Mentos mints that causes the beverage to be expelled from its container. The candies catalyze the release of gas from the beverage, which creates an eruption that pushes most of the liquid up and out of the bottle. Lee Marek and "Marek's Kid Scientists" were the first to publicly demonstrate the experiment on the Late Show with David Letterman in 1999. Steve Spangler's televised demonstration of the eruption in 2005 became popular on YouTube, launching a chain of several other Diet Coke and Mentos experiment viral videos. Experiments carried out at altitudes ranging from below sea level in Death Valley to the summit of Pikes Peak have demonstrated that the reaction works better at higher elevations.
Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances.
The hot chocolate effect is a phenomenon of wave mechanics in which the pitch heard from tapping a cup of hot liquid rises after the addition of a soluble powder. The effect is thought to happen because upon initial stirring, entrained gas bubbles reduce the speed of sound in the liquid, lowering the frequency. As the bubbles clear, sound travels faster in the liquid and the frequency increases.
The capillary length or capillary constant is a length scaling factor that relates gravity and surface tension. It is a fundamental physical property that governs the behavior of menisci, and is found when body forces (gravity) and surface forces are in equilibrium.
The Minnaert resonance is a phenomenon associated with a gas bubble pulsating at its natural frequency in a liquid, neglecting the effects of surface tension and viscous attenuation. It is the frequency of the sound made by a drop of water from a tap falling in water underneath, trapping a bubble of air as it falls. The natural frequency of the entrapped air bubble in the water is given by
Sonoluminescence is a phenomenon that occurs when a small gas bubble is acoustically suspended and periodically driven in a liquid solution at ultrasonic frequencies, resulting in bubble collapse, cavitation, and light emission. The thermal energy that is released from the bubble collapse is so great that it can cause weak light emission. The mechanism of the light emission remains uncertain, but some of the current theories, which are categorized under either thermal or electrical processes, are Bremsstrahlung radiation, argon rectification hypothesis, and hot spot. Some researchers are beginning to favor thermal process explanations as temperature differences have consistently been observed with different methods of spectral analysis. In order to understand the light emission mechanism, it is important to know what is happening in the bubble's interior and at the bubble's surface.
Slip ratio in gas–liquid (two-phase) flow, is defined as the ratio of the velocity of the gas phase to the velocity of the liquid phase.
In fluid mechanics, the Rayleigh–Plesset equation or Besant–Rayleigh–Plesset equation is a nonlinear ordinary differential equation which governs the dynamics of a spherical bubble in an infinite body of incompressible fluid. Its general form is usually written as
Classical nucleation theory (CNT) is the most common theoretical model used to quantitatively study the kinetics of nucleation.
The physiology of decompression is the aspect of physiology which is affected by exposure to large changes in ambient pressure. It involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs, or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again.
