Heating cycle

The transformation is beHeved to occur by a diffusionless shear process (83). It is often referred to as martensitic transformation, having a thermal hysteresis between the cooling and heating cycles. The transformation is dependent on particle size finer particles transforming at a lower temperature than... 

Most modem coke ovens operate on a regenerative heating cycle in order to obtain as much surplus gas as possible for use on the works, or for sale. If coke-oven gas is used for heating the ovens, the majority of the gas is surplus to requirements. If producer gas is used for heating, much of the coke-oven gas is surplus. 

Medium-sized loads are often processed ia a beU furnace, as shown ia Figure 2. The operation of this furnace is opposite to that of an elevator furnace the work load is placed on a stationary hearth and the furnace is lowered over the hearth. BeU furnaces are often arranged with two or more bases (hearths) which permit more efficient use of the furnace because one base can be unloaded/loaded as the furnace carries out a heating cycle on another base. 

It is not practical to determine the contact resistance in power connectors. The resistance of the connection of a specified length of conductor on each side of the connector is measured and is called the overall resistance or the connection resistance. One industry specification (32) defines the included lengths and requites the stabiUty of the connection resistance to be within 5% of its average value throughout the heat-cycle test. 

A long heating cycle is necessaiy because the size of the solid objects or permissible heating temperature requires a long holdup for internal diffusion of heat or moisture. This case may apply when the cycle will exceed 12 to 24 h. 

Uniform depth of loading in dryers and furnaces handling particulate solids is essential to consistent operation, minimum heating cycles, or control of final moisture. After a tray has been loaded, the bed should be leveled to a uniform depth. Special preform devices, noodle extruders, pelletizers, etc., are employed occasionally for preparing pastes and filter cakes so that screen bottom trays can be used and the advantages of through circulation approached. 

Rotor Heat Cycle. As part of the rotor construction, Elliott conducts a heat cycling test of the rotor at the shaft-to-disk... 

If there is a spare rotor sold with the order, the spare rotor is also heat cycled. If the customer requests, it too can be mechanically tested prior to shipment. If a motor drive is required, the initial run-up is... 

Basic oxygen furnaces (BOFs) have largely replaced open hearth furnaces for steelmaking. A water-cooled oxygen lance is used to blow high-purity oxygen into the molten metal bath. This causes violent agitation and rapid oxidation of the carbon, impurities, and some of the iron. The reaction is exothermic, and an entire heat cycle requires only 30-50 min. The atmospheric emissions from the BOF process are listed in Table 30-16. 

The ASME, Performance Test Code on Overall Plant Performance, ASME PTC 46, was designed to determine the performance of the entire heat cycle as an integrated system. This code provides explicit procedures to determination of power plant thermal performance and electrical output. 

In time-dependent problems, all the above conditions can be time-dependent functions, such as a machine heating cycle or another time-dependent process under study. 

Assume the inlet temperature of regeneration gas is 400°F. In the beginning the initial outlet temperature of the bed will be the bed temperature of 110°F at the end of the heating cycle, the outlet temperature will be the design value of 350°F. So the average outlet temperature is (350 -i-110)/- or 230°F Then the volume of gas required for heating will be... 

For design, add 25% for heat losses and non-uniform flow. Assuming a 3-hour heating cycle, the regenerator gas heater must be sized for... 

Figure 1 DSC curves of P7MB representing a cooling cycle (lower) starting from the isotropic melt, and the subsequent heating cycle (upper). Scanning rate 10°C/min.

Schematic of an outdoor heat pump s heating cycle.

This efficiency can be improved by the use of a feed heating cycle whereby bled steam can be taken from the turbine after certain stages of expansion and then used to raise the feedwater temperature via use of feed heat exchangers. By such means the feedwater temperature. 

The power fed to the fan shaft (or the total electrical power fed to the motor if within the duct) appears as sensible heat in the system. During a heating cycle this is useful. As a mle of thumb, fan shaft power is 17 x flow m x mm swg watts. This commonly lies between 2 per cent of the cooling duty for small systems to 10 per cent for large systems. 

The SO2 in the atmosphere is derived from two sources. Firstly, from the aerial oxidation of H2S produced naturally (see later) and secondly from the combustion of sulphur-containing fuels. In industrialised countries the second source predominates, but on a global scale only about one-fifth of the total sulphur pollution is derived from human activity. In 1969, the total sulphur emission, expressed in terms of SO2, from burnt fuel in the UK was 6-06 X 10 tons. In densely populated countries sulphur pollution levels arc very much related to the domestic heating cycle, and in the UK maximum... 

The effect of the welding process on the severity of weld decay varies according to the process and the plate thickness so that no single recommendation is possible for every thickness of plate if resistance to attack is essential. The severity of weld decay correlates quite well with sensitisation times as calculated from recorded weld heating cycles. 

Methods of adding moisture to the airstream (see Sections 24.4 and 24.5) are difficult to control, since a lot of water remains in the apparatus at the moment of switching off humidihcation. For this reason, the heat-humidify-re-heat cycle as shown in Figure 24.12 is to be preferred, as the hnal heater control can compensate for overshoot. 

Figure 25.2 Pre-heat, humidify, re-heat cycle - apparatus...

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