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Where hot-water space heating boilers are installed, domestic hot water cylinders are usually heated indirectly by primary water from the boiler, or by an electric immersion heater (often as backup to the boiler). In the UK these vessels are called indirect cylinders and direct cylinders, respectively. Additionally, if these cylinders form part ...
Boilers have a turndown ratio which is the ratio of the maximum power output to the minimum power output for which combustion can be maintained. If the control system determines that the demand falls below the minimum power output, then the boiler will cycle off until the water temperature has fallen, and then will reignite and heat the water.
The only railway use of water-tube boilers in any numbers was the Brotan boiler, invented by Johann Brotan in Austria in 1902, and found in rare examples throughout Europe, although Hungary was a keen user and had around 1,000 of them. Like the Baldwin, it combined a water-tube firebox with a fire-tube barrel.
A flash boiler differs from the type of mono-tube steam generator in which the tube is permanently filled with water. In a flash boiler, the tube is kept so hot that the water feed is quickly flashed into steam and superheated. Flash boilers had some use in automobiles in the 19th century and this use continued into the early 20th century.
The boiler heats water to a temperature controlled by a thermostat. The water then flows (either by natural circulation or by a pump) to radiators in the rooms which are to be heated. Water also flows through a coil in the hot water tank to heat a separate mass of water for bathing, etc.
Many of water's anomalous properties are due to very strong hydrogen bonding. Over the superheated temperature range the hydrogen bonds break, changing the properties more than usually expected by increasing temperature alone. Water becomes less polar and behaves more like an organic solvent such as methanol or ethanol.
Solar heat is clean and renewable. This is the most modern system. Increasingly, solar powered water heaters are being used. Their solar thermal collectors are installed outside dwellings, typically on the roof or walls or nearby, and the potable hot water storage tank is typically a pre-existing or new conventional water heater, or a water heater specifically designed for solar thermal.
For water, as shown in the graph below, nucleate boiling occurs when the surface temperature is higher than the saturation temperature (T S) by between 10 and 30 °C (18 and 54 °F). The critical heat flux is the peak on the curve between nucleate boiling and transition boiling.