Instruct: Given a question, retrieve relevant documents that answer the question.
Query: What's the temperature water boils at?
The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100°C (212°F) at sea level, but at 93.4°C (200.1°F) at 1,905 metres (6,250ft) [3] altitude. For a given pressure, different liquids will boil at different temperatures.
Water cooling also has a boiling point temperature of around 100 degrees C at atmospheric pressure. Engines operating at higher temperatures may require a pressurized recycle loop to prevent overheating. Modern automotive cooling systems often operate at to raise the boiling-point of the recycling water coolant and reduce evaporative losses.
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. 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.
When a mixture of two practically immiscible liquids is heated while being agitated to expose the surface of each liquid to the vapor phase, each constituent independently exerts its own vapor pressure as a function of temperature as if the other constituent were not present. Consequently, the vapor pressure of the whole system increases. Boiling begins when the sum of the vapour pressures of the two immiscible liquids just exceeds the atmospheric pressure (approximately 101 kPa at sea level). In this way, many organic compounds insoluble in water can be purified at a temperature well below the point at which decomposition occurs. For example, the boiling point of bromobenzene is 156 °C and the boiling point of water is 100 °C, but a mixture of the two boils at 95 °C. Thus, bromobenzene can be easily distilled at a temperature 61 °C below its normal boiling point.
The boiling point of water is typically considered to be 100 °C or 212 °F. Pressure and a change in the composition of the liquid may alter the boiling point of the liquid. For this reason, high elevation cooking generally takes longer since boiling point is a function of atmospheric pressure. In Denver, Colorado, USA, which is at an elevation of about one mile, water boils at approximately 95 °C or 203 °F. Depending on the type of food and the elevation, the boiling water may not be hot enough to cook the food properly. Similarly, increasing the pressure as in a pressure cooker raises the temperature of the contents above the open air boiling point.
There are two methods of coddling eggs. The first is to cook the egg in its shell, by immersing it in near-boiling water. This can be done either in a pan where the water is kept below boiling point, or by pouring boiling water over the egg and letting it stand for 2 to 5 minutes, based on starting temperature of the eggs, number of eggs cooked at once and amount of boiling water used.
While boiling, it is useful to recover some of the energy used to boil the wort. On its way out of the brewery, the steam created during the boil is passed over a coil through which unheated water flows. By adjusting the rate of flow, the output temperature of the water can be controlled. This is also often done using a plate heat exchanger. The water is then stored for later use in the next mash, in equipment cleaning, or wherever necessary. Another common method of energy recovery takes place during the wort cooling. When cold water is used to cool the wort in a heat exchanger, the water is significantly warmed. In an efficient brewery, cold water is passed through the heat exchanger at a rate set to maximize the water's temperature upon exiting. This now-hot water is then stored in a hot water tank.
The nominal temperature of the cooling water at the inlet of the reactor is about and the outlet temperature , at pressure in the drum separator of . The pressure and the inlet temperature determine the height at which the boiling begins in the reactor; if the coolant temperature is not sufficiently below its boiling point at the system pressure, the boiling starts at the very bottom part of the reactor instead of its higher parts. With few absorbers in the reactor core, such as during the Chernobyl accident, the positive void coefficient of the reactor makes the reactor very sensitive to the feedwater temperature. Bubbles of boiling water lead to increased power, which in turn increases the formation of bubbles. After 1986 absorbers were introduced in the fuel assembly, permanently assuring a negative void coefficient at the cost of higher enrichment requirements of the uranium fuel.
The heat needed to boil water is thus equivalent to a 540 °C rise in temperature, or about 7 times that needed to raise the temperature of the water from ambient to boiling.
The bowl is filled with rice and water. During cooking, the rice/water mixture is heated at full power. The water reaches a temperature of 100 °C (212 °F); it cannot get hotter than its boiling point (all the energy goes into vapourizing the water). At the end of cooking there will be no free water left; most will have been absorbed by the rice, and some boiled off. As heating continues, the temperature can now rise above boiling point; this makes the thermostat trip. Some cookers switch to low-power "warming" mode, keeping the rice at a safe temperature of approximately 65 °C (150 °F); simpler models switch off.
Superheated water is liquid water under pressure at temperatures between the usual boiling point, and the critical temperature, . It is also known as "subcritical water" or "pressurized hot water." Superheated water is stable because of overpressure that raises the boiling point, or by heating it in a sealed vessel with a headspace, where the liquid water is in equilibrium with vapour at the saturated vapor pressure. This is distinct from the use of the term superheating to refer to water at atmospheric pressure above its normal boiling point, which has not boiled due to a lack of nucleation sites (sometimes experienced by heating liquids in a microwave).
The technology is based on the phenomenon that as the vapour pressure on a liquid reduces, its boiling point reduces. The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid is equal to the external pressure. When the pressure above a liquid is reduced, the vapour pressure needed to induce boiling is also reduced, and the boiling point of the liquid decreases. By reducing pressure we can even boil off water at lower temperatures. This rapid evaporation of moisture from the surface and within the products due to the low surrounding pressure, absorbs the necessary latent heat for phase change from the product itself. This latent heat required for evaporation is obtained mostly from the sensible heat of the product and as a consequence of this evaporation the temperature of the product falls and the product can be cooled down to its desired storage temperature.
Pressure in the primary circuit is maintained by a pressurizer, a separate vessel that is connected to the primary circuit and partially filled with water which is heated to the saturation temperature (boiling point) for the desired pressure by submerged electrical heaters. To achieve a pressure of , the pressurizer temperature is maintained at 345 °C (653 °F), which gives a subcooling margin (the difference between the pressurizer temperature and the highest temperature in the reactor core) of 30 °C (54 °F). As 345 °C is the boiling point of water at 155 bar, the liquid water is at the edge of a phase change. Thermal transients in the reactor coolant system result in large swings in pressurizer liquid/steam volume, and total pressurizer volume is designed around absorbing these transients without uncovering the heaters or emptying the pressurizer. Pressure transients in the primary coolant system manifest as temperature transients in the pressurizer and are controlled through the use of automatic heaters and water spray, which raise and lower pressurizer temperature, respectively.
In an ordinary, non-pressurized cooking vessel, the boiling point of water is at standard pressure; the temperature of food is limited by the boiling point of water because excess heat causes boiling water to vaporize into steam. In a sealed pressure cooker, the boiling point of water increases as the pressure rises, resulting in superheated water. At a pressure of 1 bar or approximately above the existing atmospheric pressure, water in a pressure cooker will reach a temperature of . The boiling temperature of water (and water-based liquids) is determined by the ambient atmospheric pressure. Pressure cookers always require liquid in order to cook food under pressure. Inside a pressure cooker, once the water (liquid) is boiling and the steam is trapped, the pressure from the steam increases and pushes on the liquid, which increases its boiling temperature. The heat applied to the liquid by the heat source continues to create more steam pressure, and increases the temperature of the liquid. Both the liquid and steam are at the same temperature. Once the selected pressure level is reached, the pressure regulator on the lid releases any excess steam, and the heat can be lowered to maintain the pressure and save energy, since the pressure will increase no further.
A well-known example of a positive azeotrope is 95.63% ethanol and 4.37% water (by mass) boils at 78.2 °C.
Ethanol boils at 78.4 °C, water boils at 100 °C, but the azeotrope boils at 78.2 °C, which is lower than either of its constituents. Indeed, 78.2 °C is the minimum temperature at which any ethanol/water solution can boil at atmospheric pressure. In general, a positive azeotrope boils at a lower temperature than any other ratio of its constituents. Positive azeotropes are also called "minimum boiling mixtures" or "pressure maximum" azeotropes.
Nucleate boiling is a type of boiling that takes place when the surface temperature is hotter than the saturated fluid temperature by a certain amount but where the heat flux is below the critical heat flux. For water, as shown in the graph below, nucleate boiling occurs when the surface temperature is higher than the saturation temperature (T) by between to . The critical heat flux is the peak on the curve between nucleate boiling and transition boiling. The heat transfer from surface to liquid is greater than that in film boiling.
In general, a negative azeotrope boils at a higher temperature than any other ratio of its constituents. Negative azeotropes are also called "maximum boiling mixtures" or "pressure minimum" azeotropes. An example of a negative azeotrope is hydrochloric acid at a concentration of 20.2% and 79.8% water (by mass). Hydrogen chloride boils at −84 °C and water at 100 °C, but the azeotrope boils at 110 °C, which is higher than either of its constituents. The maximum temperature at which any hydrochloric acid solution can boil is 110 °C. Other examples:
Any form of cooking will destroy some nutrients in food, but the key variables are how much water is used in the cooking, how long the food is cooked, and at what temperature.[44] Nutrients are primarily lost by leaching into cooking water, which tends to make microwave cooking healthier, given the shorter cooking times it requires.[45] Like other heating methods, microwaving converts vitamin B12 from an active to inactive form; the amount of conversion depends on the temperature reached, as well as the cooking time. Boiled food reaches a maximum of 100°C (212°F) (the boiling point of water), whereas microwaved food can get locally hotter than this, leading to faster breakdown of vitamin B12. The higher rate of loss is partially offset by the shorter cooking times required.[46]
Water must be purified of harmful living organisms and chemicals. Some commercial filters can remove most organisms and some harmful chemicals, but they are not 100% effective. Distillation filters, purifies, and removes some harmful chemicals. Chemicals with a lower or about equal boiling point of water are not eliminated by distilling. Iodine or chlorine dioxide solutions or tablets can be used to purify water. It can be boil water in a fire-resistant pot or water bottle. Water can be boiled in some flammable materials like bark because the water absorbs the heat. Pasteurization takes place at temperatures lower than boiling point, but knowing the temperature of the water and calculating the duration of treatment can be difficult. This technique is useful when only non-durable containers are available. Sunlight can be used with a clear container. Filters made from heat-treated diatomaceous earth can also be used.
Originally stemming from ocean thermal energy conversion research, low-temperature thermal desalination (LTTD) takes advantage of water boiling at low pressure, even at ambient temperature. The system uses pumps to create a low-pressure, low-temperature environment in which water boils at a temperature gradient of between two volumes of water. Cool ocean water is supplied from depths of up to . This water is pumped through coils to condense the water vapor. The resulting condensate is purified water. LTTD may take advantage of the temperature gradient available at power plants, where large quantities of warm wastewater are discharged from the plant, reducing the energy input needed to create a temperature gradient.
Open pan evaporation methods have been streamlined since colonial days, but remain basically unchanged. Sap must first be collected and boiled down to obtain pure syrup without chemical agents or preservatives. Maple syrup is made by boiling between 20 and 50 volumes of sap (depending on its concentration) over an open fire until 1 volume of syrup is obtained, usually at a temperature over the boiling point of water. As the boiling point of water varies with changes in air pressure the correct value for pure water is determined at the place where the syrup is being produced, each time evaporation is begun and periodically throughout the day. Syrup can be boiled entirely over one heat source or can be drawn off into smaller batches and boiled at a more controlled temperature.
Like all liquids, water boils when its vapor pressure reaches its surrounding pressure. In nature, the atmospheric pressure is lower at higher elevations and water boils at a lower temperature. The boiling temperature of water for atmospheric pressures can be approximated by the Antoine equation:
In boiling water cooled reactors (BWR) and partly in pressure water cooled reactors (PWR and PHWR) the heat transfer is made with a vapor phase in the cooling medium, which is why this type of heat transfer is called heat transfer in a biphasic system. This allows obtaining much higher transfer coefficients than the one-phase heat transfer described in the Dittus-Boelter equation.
Increasing the flow of heat, reducing the agent flow and lowering the pressure can lead to increased temperature of the cooled surface. If the temperature of the fluid in the channel section that we consider is lower than the boiling temperature under local pressure conditions, the vaporization is limited to the immediate vicinity of the surface and in this case the boiling is called submerged boiling. There is no proportionality between the heat flow and the difference between the surface temperature and the coolant temperature that allows the definition of a heat transfer coefficient similar to the one-phase case. In this situation we can use the equation of Jens and Lottes, which establishes a connection between the difference formula_47 between the surface temperature and the boiling temperature of the cooling agent under local pressure conditions formula_48 below the thermal flux formula_20:      
When the plant is operating in steady state, feed water at the cold inlet temperature flows, or is pumped, through the heat exchangers in the stages and warms up. When it reaches the brine heater it already has nearly the maximum temperature. In the heater, an amount of additional heat is added. After the heater, the water flows through valves back into the stages that have ever lower pressure and temperature. As it flows back through the stages the water is now called brine, to distinguish it from the inlet water. In each stage, as the brine enters, its temperature is above the boiling point at the pressure of the stage, and a small fraction of the brine water boils ("flashes") to steam thereby reducing the temperature until an equilibrium is reached. The resulting steam is a little hotter than the feed water in the heat exchanger. The steam cools and condenses against the heat exchanger tubes, thereby heating the feed water as described earlier.
The total evaporation in all the stages is up to approximately 15% of the water flowing through the system, depending on the range of temperatures used. With increasing temperature there are growing difficulties of scale formation and corrosion. 120 °C appears to be a maximum, although scale avoidance may require temperatures below 70 °C.
The Leidenfrost effect is a physical phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer keeping that liquid from boiling rapidly. Because of this 'repulsive force', a droplet hovers over the surface rather than making physical contact with it. This is most commonly seen when cooking: one sprinkles drops of water in a pan to gauge its temperature: if the pan's temperature is at or above the Leidenfrost point, the water skitters across the pan and takes longer to evaporate than in a pan with a temperature below the Leidenfrost point but still above boiling. It is named after Johann Gottlob Leidenfrost, who discussed it in "A Tract About Some Qualities of Common Water" in 1751.