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In traditional plumbing in the UK, the space-heating boiler is set up to heat a separate hot water cylinder or water heater for potable hot water. Such water heaters are often fitted with an auxiliary electrical immersion heater for use if the boiler is out of action for a time. Heat from the space-heating boiler is transferred to the water ...
The energy required to heat water is significantly lower than that needed to vaporize it, for example for steam distillation [10] and the energy is easier to recycle using heat exchangers. The energy requirements can be calculated from steam tables. For example, to heat water from 25 °C to steam at 250 °C at 1 atm requires 2869 kJ/kg.
A hot water dispenser which keeps water hot in a tank uses the energy needed to heat the water to the required temperature and wastes the energy needed to keep the water hot permanently in a thermally-insulated tank when not being used. These tank type dispensers often also consists of energy wasting 'keep warm' and 'reboil' functions.
An electric water boiler is a device comprising a water reservoir equipped with a heating element positioned at the bottom. While some models offer the convenience of multiple temperature settings, others are integrated into larger water systems capable of boiling water and dispensing it in various forms: hot, cold, or lukewarm.
A heat exchanger brings the heat from the burner to the water. Its job is to bring heat to the water without having contact with the water, similar to boiling water in a pot. An exhaust stack takes the hot gases and transfers them away from the boiler. Boiler controls are there to make sure the hot water or steam is produced in a safe way. [5]
Superheating can occur when an undisturbed container of water is heated in a microwave oven. At the time the container is removed, the lack of nucleation sites prevents boiling, leaving the surface calm. However, once the water is disturbed, some of it violently flashes to steam, potentially spraying boiling water out of the container. [6]
However, the water bath was known many centuries earlier (Hippocrates and Theophrastus), [3] and the balneum Mariae attributed to Mary the Jewess was used to heat its contents above 100 °C, while the bain-marie that continues to be used today only heats its contents up to a gentle heat of less than 100 °C. [4]
The specific enthalpy of fusion (more commonly known as latent heat) of water is 333.55 kJ/kg at 0 °C: the same amount of energy is required to melt ice as to warm ice from −160 °C up to its melting point or to heat the same amount of water by about 80 °C. Of common substances, only that of ammonia is higher.
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