Boiling

Boiling water in a sealed cooking pot

Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. The higher the pressure the higher the boiling point. There are two main types of boiling; nucleate boiling where small bubbles of vapour form at discrete points, and critical heat flux boiling where the boiling surface is heated above a certain critical temperature and a film of vapor forms on the surface. Transition boiling is an intermediate, unstable form of boiling with elements of both types. The boiling point of water is 100 °C or 212 °F, but is lower with the decreased atmospheric pressure found at higher altitudes.

Boiling water is used as a method of making it potable by killing microbes that may be present. The sensitivity of different micro-organisms to heat varies, but if water is held at 70 °C (158 °F) for ten minutes, many organisms are killed, but some are more resistant to heat and require one minute at the boiling point of water. Clostridium spores can survive this treatment, but as the infection caused by this microbe is not water-borne, this is not a problem.

Boiling is also used in cooking. Foods suitable for boiling include vegetables, starchy foods such as rice, noodles and potatoes, eggs, meats, sauces, stocks and soups. As a cooking method it is simple and suitable for large scale cookery. Tough meats or poultry can be given a long, slow cooking and a nutritious stock is produced. Disadvantages include loss of water-soluble vitamins and minerals. Commercially prepared foodstuffs are sometimes packed in polythene sachets and sold as "boil-in-the-bag" products.

Types

Nucleate

Nucleate boiling of water over a kitchen stove burner

Nucleate boiling is characterized by the growth of bubbles or pops on a heated surface, which rise from discrete points on a surface, whose temperature is only slightly above the liquid’s. In general, the number of nucleation sites are increased by an increasing surface temperature.

An irregular surface of the boiling vessel (i.e., increased surface roughness) or additives to the fluid (i.e., surfactants and/or nanoparticles [1]) can create additional nucleation sites, [2] while an exceptionally smooth surface, such as plastic, lends itself to superheating. Under these conditions, a heated liquid may show boiling delay and the temperature may go somewhat above the boiling point without boiling.

Critical heat flux

As the boiling surface is heated above a critical temperature, a film of vapor forms on the surface. Since this vapor film is much less capable of carrying heat away from the surface, the temperature rises very rapidly beyond this point into the transition boiling regime. The point at which this occurs is dependent on the characteristics of boiling fluid and the heating surface in question. [1]

Transition

Transition boiling may be defined as the unstable boiling, which occurs at surface temperatures between the maximum attainable in nucleate and the minimum attainable in film boiling.

The formation of bubbles in a heated liquid is a complex physical process which often involves cavitation and acoustic effects, such as the broad-spectrum hiss one hears in a kettle not yet heated to the point where bubbles boil to the surface.

Film

If a surface heating the liquid is significantly hotter than the liquid then film boiling will occur, where a thin layer of vapor, which has low thermal conductivity, insulates the surface. This condition of a vapor film insulating the surface from the liquid characterizes film boiling.

In distillation, boiling is used in separating mixtures. This is possible because the vapor rising from a boiling fluid generally has a ratio of components different from that in the liquid.

Other Languages
العربية: غليان
armãneashti: Hearbiri
azərbaycanca: Qaynama
Bân-lâm-gú: Hùi-thêng
беларуская: Кіпенне
беларуская (тарашкевіца)‎: Кіпеньне
български: Кипене
català: Ebullició
čeština: Var
chiShona: Fanza
Cymraeg: Berwi
dansk: Kogning
Deutsch: Sieden
eesti: Keemine
Ελληνικά: Βρασμός
español: Ebullición
Esperanto: Bolado
euskara: Irakite
فارسی: جوشیدن
français: Ébullition
Gàidhlig: Bruich
한국어: 끓음
Հայերեն: Եռում
हिन्दी: क्वथन
hrvatski: Vrenje (fizika)
Bahasa Indonesia: Mendidih
íslenska: Suða
italiano: Ebollizione
עברית: הרתחה
Latina: Ebullitio
latviešu: Viršana
lietuvių: Virimas
македонски: Вриење
മലയാളം: തിളയ്ക്കൽ
Bahasa Melayu: Pendidihan
မြန်မာဘာသာ: ကျိုခြင်း
日本語: 沸騰
norsk bokmål: Koking
norsk nynorsk: Koking
occitan: Ebullicion
português: Ebulição
română: Fierbere
Runa Simi: T'impuy
русский: Кипение
Scots: Bylin
sicilianu: Vugghiuta
Simple English: Boiling
slovenčina: Var (fyzika)
slovenščina: Vrenje
srpskohrvatski / српскохрватски: Vrenje (fizika)
svenska: Kokning
татарча/tatarça: Кайнау
Türkçe: Haşlama
українська: Кипіння
Tiếng Việt: Sự sôi
粵語: 沸騰
中文: 沸腾