Heat exchanger fluid location

A commercial design based on semicontinuous operation was developed for manufacture of silicate powders (27). A slurry, prepared containing the feed materials and water, is fed to the reactor tank and heated by circulating a heat-exchange fluid in channels located on the outside vessel wall. A six-bladed stirrer is operated at about 100 rpm in order to keep reagents well mixed. Once the slurry reaches the operating temperature, the vessel heat is maintained until reaction is complete. For most fine-particle products, this time is less than 1 hr. 

A schematic for one microchannel configuration is shown in Figure 6, where catalytic monoliths are located at the center of an array of reaction channels, interleaved with heat exchange channels. A heat exchange fluid flowing co- or counter-current (shown in Figure 6) to the reaction flow removes the heat of reaction and cools the gas, thereby... 

Distance-Velocity Lag (Dead-Time Element) The dead-time element, commonly called a distance-velocity lag, is often encountered in process systems. For example, if a temperature-measuring element is located downstream from a heat exchanger, a time delay occurs before the heated fluid leaving the exchanger arrives at the temperature measurement point. If some element of a system produces a dead-time of 0 time units, then an input to that unit,/(t), will be reproduced at the output a.s f t — 0). The transfer function for a pure dead-time element is shown in Fig. 8-17, and the transient response of the element is shown in Fig. 8-18. 

The most direct way to reject heat above ambient temperature to the environment is by the use of aircooled heat exchangers, as discussed in Chapter 151. These coolers exploit a flow of ambient air across the outside of tubes through which process fluids are flowing that require cooling. Such air coolers are very common in some industries, particularly when the plant is located in a region where water is scarce. 

Distance-Velocity Lag (Dead-Time Element) The dead-time or time-delay element, commonly called a distance-velocity lag, is often encountered in process systems. For example, if a temperaturemeasuring element is located downstream from a heat exchanger, a time delay occurs before the heated fluid leaving the exchanger... 

Problem A long fin of 0.02 m diameter is one of the fins conducting heat away from a heat exchanger. The steady-state temperature at two different locations along the fin 0.09 m apart are 130°C and 100°C, respectively. The environment is at 20°C. If the thermal conductivity of the fin is 100 W/(m.K), calculate the heat transfer coefficient between the fin and the environmental fluid. 

C Can the temperature of the cold fluid rise above the inlet lemperature of the hot fluid at any location in a heat exchanger Explain. 

It is very important that a melt-out riser be installed whenever tank contents are ejq)ected to freeze on prolonged shutdown. The purpose is to provide a molten chimney through the crust for relief of thermal expansion or cavitation if fluids are to be pumped out or recirculated through an external exchanger. An external heat tracer, properly located, will serve the same purpose but may require more remelt time before pumping can be started. 

Two pressure transducers are located upstream of the stack to monitor anode and cathode pressure during the experimental runs. A spiral heat exchanger, using external water at room temperature as second fluid, is used to control the temperature of the cooling water. The FCS humidification strategy is based on the deionized water injection method (see Sect. 4.5), activating the injection when the outlet air temperature is higher than 60°C. 

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