Kettle element

Putting water into an electric kettle does not cause the water to get hot. The water stays cold until we turn on the power to the kettle element, which converts electrical energy from the mains into heat energy. The heat energy from the kettle element is then absorbed by the water, which gets hot as a direct consequence. 

We want to turn up the radio because it s noisy outside, and we want to hear what is broadcast. We therefore turn the volume knob toward loud . At its most basic, the volume control is a variable resistor, across which we pass a current from the battery, acting much like a kettle element. If we turn up the volume control then a larger current is allowed to flow, causing more energy to be produced by the resistor. As a listener, we hear a response because the sound from the speakers becomes louder. The speakers work harder. 

The resistance of a kettle element which takes 12 A from a 230 A main supply is ... 

In addition to the type description code there is also a shorthand that is used for classifying heat exchangers. The first element of the shorthand is the nominal diameter, which is the inside diameter of the shell in inches, rounded off to the nearest integer. For kettle reboilers and chillers ii emember the kettle has a narrow end and a fat end), the nominal diame-tci is the port diameter (the narrow end) followed by the shell diameter, each rounded off to the nearest integer. 

Most modem kettles contain a powerful element (the salesman s word for heater ), operating at a power of 1000 W or more. A heater emits 1 W if it gives out 1 Js-1 so, a heater rated at 1000 W emits 1000 Js-1. We may see this power expressed as 1 kW (remember that a small k is shorthand for kilo, meaning 1000). By contrast, an electrical ring on the stove will probably operate between 600 and 800 W, so it emits a smaller amount of heat per second. Because the water absorbs less heat energy per unit time on a stove, its temperature rises more slowly. 

In a modem, automatic kettle, an electric heater warms the water inside the kettle - we call it the element . The electric circuit stops when the water reaches 100 °C because a temperature-sensing bimetallic strip is triggered. But the energy for a more old-fashioned, whistling kettle comes from a gas or a coal hob. The water boils on heating and converts to form copious amounts of gas (steam), which passes through a small valve in the kettle lid to form a shrill note, much like in a football referee s whistle. 

One compound that becomes less soluble at higher temperatures is calcium carbonate, CaCOa. If you have an electric kettle, you have probably noticed a build-up of scale on the heating element. The scale is mostly calcium carbonate, which precipitates out of the water as it heats up. 

The carbonate ions recombine with calcium ions to form calcium carbonate deposits. These deposits form a coating on heating elements in kettles and boilers, and build up inside hot water pipes. The coating is commonly called boiler scale. (See Figure 9.9.) It not only reduces the flow of water in pipes, but it also increases the cost of heating the water. 

Water baths are the more common of the two, and the steam is generated by heating water with an electric element - just like a kettle. The element may have a thermostatic control, which can control the temperature of the water to some extent. Most water baths have a constant level device on the side of the bath, which supplies water to the bath to a fixed level above the heating element and prevents the water bath from boiling dry. Water baths are single hole or multiple hole types, and the holes are covered by concentric metal or plastic rings, which allows you to vary the size of the hole. 

The controlling elements include the controller and its accessories and the final control element, which in this case and in most process cases is a valve. A single block represents the controlled system, which is the jacketed, agitated kettle. 

Kettle (1969)). The matrix elements can be expressed in terms of the radial parameters ao, 2 and m where... 

The last stage of the process is the final caustic clean, which removes any trace impurity of elements such as antimony, calcium, magnesium, and zinc that may have passed through from the previous processes. The metal is pumped from the de-bismuthizing area to the final kettles where it is held at about 500°C. Caustic soda is added and stirred into the lead for about one hour. Samples are taken at regular intervals to ensure that the product meets the required lead specifications. Once the lead is in specification, it is cast in the required shape and either sold to the market or used internally for production of calcium and antimonial alloys. 

Antimony, arsenic, tin, and sulfur. Two methods of reducing/removing these elements from lead are available. The choice depends on the final level required in lead product. If the elements are to be removed from the bullion, the softening process is used. Alternatively, to reduce these elements to a specified level, caustic soda and/or sodium nitrate is stirred into the kettle held at about 500°C. This latter method is commonly referred to as the Harris process. 

Secondary producers often employ the same kettles for alloy formation as are used in the refining process. This is because the equipment needed to alloy certain elements is common to both processes. High-speed stirring and correct fume... 

Alloying elements such as copper, silver, and antimony have a much higher melting point than lead and thus require continuous agitation, or stirring, in the kettle to promote dissolution. Tin, on the other hand, has a lower melting point and is the easiest element to alloy with lead. 

S.F.A. Kettle (1996) Physical Inorganic Chemistry, Spektrum, Oxford - Chapter 11 gives an excellent introduction to orbital, spectroscopic and magnetic properties of the /-block elements. 

Berg T, Petersen A, Pedersen GA, Petersen J and Madsen C (2000) The release of nickd and other trace elements from electric kettles and coffee machines. Food Addit Contam 17 189-196. 

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