Heat recirculation system

External recirculation is the movement of the heated air within the bay to an external duc t, where this air mixes with inlet air, and the mixture serves as the cooling fluid within the bay. Inlet air does not have direct access to the tube bundle an adequate mixing chamber is essential. Recirculation over the end of the exchanger is illustrated in Fig. 11-48. Over-the-side recirculation also is used. External recirculation systems maintain the desired low temperature of the air crossing the tube bundle. 

Remove core decay heat High pressure injection system Low pressure injection system High pressure recirculation system Core flood tanks Auxiliary feedwater system Power conversion system Remove core decay heat Auxiliary feedwal stem Power conversion m High pressure inj( i system pow. peiuicd relief valves... 

The closed recirculation system (see Fig. 8-3) is used when it is necessary or economical to produce cooling water at a temperature below that feasible with an open system, or it is important to prevent foreign matter from getting into the water.14 Here secondary heat exchangers are used to remove the energy. The only water loss is due to leaks, and since it is an isolated system, any water pretreating that is required is minimal. 

The presence of water, or water vapour, affects the chemistry of thermal modification and heat transfer within the wood (Burmester, 1981). Under dry treatment conditions, the wood is dried prior to thermal modification, or water is removed by the use of an open system, or a recirculating system equipped with a condenser. In closed systems, water evaporated from the wood remains as high-pressure steam during the process. Steam can also be injected into the reactor to act as a heat-transfer medium, and can additionally act as an inert blanket to limit oxidative processes. Such steam treatment processes are referred to as hygrothermal treatments. Where the wood is heated in water, this is known as a hydrothermal process. Hydrothermal treatments have been extensively studied as a... 

Figure 4.12 Power (V/ ) and efficiency (Titot) characteristics of a counter-current exchanger TEG system. For comparison, the intrinsic TE efficiency (t te) without heat recirculation is reported.

Multiple steady states may be expected also in other catalytic systems. Two important cases should be mentioned (i) catalytic systems with some kind of heat recirculation and (ii) trickle-bed reactors. 

Continuous water recirculation system, whereby cooling water picks up heat by being pumped through a process heat source or heat exchanger and then over a cooling tower, open to the air, whereupon the sensible heat gained is lost by an evaporation process. 

An electrical resistance heater with more turns at the tube ends (to compensate for heat losses) surrounds each tube. There is a vertical laminar flow hood over the loading area to minimize particle contamination of the wafers being loaded. As we can see, there are temperature controls for the furnace tubes, and a power module to provide the electrical power. When operated as a LPCVD system, a unit including both the gas flow and vacuum systems is positioned on the right side. Such a unit is shown in Figure 8. Here we can see the vacuum pumps on the left, and the mass flow controllers on the right. The vacuum pump oil recirculation systems are shown in the slide out drawers. As can be seen in Figure 9, this system, as well as most current similar systems, operate under computer control. 

Various levels of models can be used to describe the behavior of pilot-scale jacketed batch reactors. For online reaction calorimetry and for rapid scale-up, a simple model characterizing the heat transfer from the reactor to the jacket can be used. Another level of modeling detail includes both the jacket and reactor dynamics. Finally, the complete set of equations simultaneously describing the integrated reactor/jacket and recirculating system dynamics can be used for feedback control system design and simulation. The complete model can more accurately assess the operability and safety of the pilot-scale system and can be used for more accurate process scale-up. 

Using this approach, corrosion potentials have been calculated for various components in the heat-transport circuit of a BWR, as shown in Fig. 19, as a function of the concentration of hydrogen added to the feedwater. The calculations predict that the lower plenums and recirculation systems of many BWRs can be protected by hydrogen water chemistry, but that those components that are exposed to high radiation fields and/or high concentration of radiolysis products cannot be protected, at least under full-power operating conditions. Similar calculations have been carried out [46] for in-vessel materials in PWRs, in order to explore the susceptibility of various components to intergranular fracture. 

The heat exchanger has a recirculation bypass to ensure that the monomer-polymer sirup from the reactor and the incoming monomer are homogeneously mixed. The side arm heat exchange system provides an inventory of cooled material which can be quickly injected into the reactor to produce rapid cooling of the reactor contents. 

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