Heat Transfer Configuration

If the system consists of a series of adiabatic reactors, there are two basic configurations. The first has heat exchangers or furnaces between each of the reactors to cool or heat the reactor effluent before it enters the next reactor. The second configuration uses cold shot cooling. Some of the cold reactor feed is bypassed around the upstream reac-tor(s) and mixed with the hot effluent from the reactor to lower the inlet temperature to the downstream catalyst bed. 

---

The heat transfer configuration within the bed (for the exothermic reaction) and other internal features are ignored. 

The reason illustrates the true nature of the shell-and-tube heat exchanger. It is a compromise between an ideal heat-transfer configuration and practical mechanical limitations. In this case, the difficulty is preventing leakage around the longitudinal baffle. Such leaks permit the shell-side fluid to short-circuit the tube bundle that is, a percentage of the inlet flow, may flow directly to the outlet nozzle. In extremely serious cases, I have seen the bell head (shown in Fig. 19.8) 100°F colder than the shell-side outlet temperature. 

Less commonly used arc the heat-transfer configurations shown in Figs. 5 through 9. 

All the heat transfer configurations used on CSTRs can be applied to batch reactors. 

This chapter presents a comparison of the steady-state economics of four alternative tubular reactor systems. The entire process will be considered, not just the reactor in isolation, because the optimum economic steady-state design can be determined only for the entire plant. The type of recycle, the phase of the reaction, and the heat transfer configuration all affect the optimum design. 

Reactor Parameters These include the reactor volume, space time (reactor volume/inlet volumetric flowrate), and reactor configuration. For given kinetics, thermodynamics, reactor and heat transfer configuration, and space time, the reactor volume needed to achieve a given conversion of reactants is determined. This is the design problem. For a fixed reactor volume, the conversion is affected by the tenperature, pressure, space time, catalyst, and reactor and heat transfer configuratiom This is the performance problem. 

Therefore, as the heat transfer configuration becomes more conplex, it becomes very difficult to solve the necessary equations to predict reactor performance. Because process simulators are already programmed to do this, they are a logical choice for analyzing reactor performance with heat transfer. 

Discussion. It has been shown that there are a number of options that provide increased acetone production. Except for Option 2, the options provided can be combined. The heat transfer configuration. Option 3, can be combined with an increase in HTM temperature. Option 1. In addition, the reactor feed... 

The reason illustrates the true nature of the shell-and-tube heat exchanger. It is a compromise between an ideal heat-transfer configuration and practical mechanical limitations. In this case, the... 

The stainless steel plates are separated (ca 3 pm between) by nonabsorbent vulcanized gaskets. Various profiles and configurations, including raised knobs, crescents, channels, or diamonds, provide a rapid, uniform heat-transfer plate surface. During operation the plates must be pressed together to provide a seal, and mounted and coimected in such a manner that air is eliminated and that the product drains from the plates without opening. 

Various arrangements and configurations are available for the HTST pasteurizer. For regeneration, the milk-to-milk regenerator is most common. A heat-transfer medium, usually water, provides a milk—water—milk system. Both sides may be closed (Fig. 5) or the raw milk supply may be open. 

Fig. 34. Internal cod configurations for heat-transfer surfaces (a) hehcal cod where = 0.02T, = 0.15T, and = 0.65Z (b) baffle cod...

Equation 2 defines the basic mode of operation of the dryer. The heat-transfer coefficient is a key property of the dryer configuration. 

Eigenvalue problems. These are extensions of equilibrium problems in which critical values of certain parameters are to be determined in addition to the corresponding steady-state configurations. The determination of eigenvalues may also arise in propagation problems. Typical chemical engineering problems include those in heat transfer and resonance in which certain boundaiy conditions are prescribed. 

When heat transfer occurs during immersed flow, the rate is dependent upon the configuration of the body, the position of the body, the proximity of other bodies, and the flow rate and turbulence of the... 

Laminar Flow Normally, laminar flow occurs in closed ducts when Nrc < 2100 (based on equivalent diameter = 4 X free area -i-perimeter). Laminar-flow heat transfer has been subjected to extensive theoretical study. The energy equation has been solved for a variety of boundaiy conditions and geometrical configurations. However, true laminar-flow heat transfer veiy rarely occurs. Natural-convecdion effects are almost always present, so that the assumption that molecular conduction alone occurs is not vahd. Therefore, empirically derived equations are most rehable. 

For annuli containing externally Hnned tubes the heat-transfer coefficients are a function of the fin configurations. Knudsen and Katz (Fluid Dynamics and Heat Transfer, McGraw-Hill, New York, 1958) present relationships for transverse finned tubes, spined tubes, and longitudinal finned tubes in annuli. 

The fin efficiency is found from mathematically derived relations, in which the film heat-transfer coefficient is assumed to be constant over the entire fin and temperature gradients across the thickness of the fin have been neglected (see Kraus, Extended Suiface.s, Spartan Books, Baltimore, 1963). The efficiency cui ves for some common fin configurations are given in Figs. Il-3(k7 and 11-30 ,... 

---