Heat exchangers temperature profile

Temperature control, 42,45-47 Temperature difference, 172 logarithmic mean, 172 multipass exchangers, 173, 175-177 Temperature profiles, heat exchangers,... 

If the objective in design or operation were optimizing catalyst utilization, then Figure 82 shows that the converter temperature-composition profile should follow curve (a), which corresponds to maximum reaction rate at all points. It is also obvious that in reality this ideal temperature - concentration profile cannot be achieved. For example, a synthesis gas with about 3 % ammonia concentration entering the converter cannot be heated to the ideal temperature by heat exchange because the very high temperature required does not exist in the converter system. To reach the ideal temperature, the first portion of the catalyst must initially operate adiabatically. Consideration of the service life of the catalyst requires that this maximum initial temperature not exceed that recommended by the manufacturer, usually 530 °C (cf. Section... 

F ure 4 Counter flow heat exchanger temperature profile Heat transfer (Q) across a heat exchanger is directly proportional to AThx ... 

Basic Heat-Transfer Equations. Consider a simple, single-pass, parallel-flow heat exchanger in which both hot (heating) and cold (heated) fluids are flowing in the same direction. The temperature profiles of the fluid streams in such a heat exchanger are shown in Figure 2a. 

Fig. 2. Fluid temperature profiles in (a) a parallel flow heat exchanger and (b) a counterflow heat exchanger. Terms are defined in text.

If U varies along the tube length or the stream temperature profile is not a smooth curve, then divide the entire tube length into a number of small heat-exchange elements, apply steps (2) through (8) to each element, and sum up the resulting area requitements as follows ... 

Adl b tic Converters. The adiabatic converter system employs heat exchangers rather than quench gas for interbed cooling (Fig. 7b). Because the beds are adiabatic, the temperature profile stiU exhibits the same sawtooth approach to the maximum reaction rate, but catalyst productivity is somewhat improved because all of the gas passes through the entire catalyst volume. Costs for vessels and exchangers are generally higher than for quench converter systems. 

From Tolmin s theory and experimental data (e.g., Reichardtthe relationship between velocity profile and temperature profile in the jet cross-section can be expressed using an overall turbulent Prandtl number Pr = v /a, where Vf is a turbulent momentum exchange coefficient and a, is a turbulent heat exchange coefficient ... 

In Fig. 9.6 the temperature profiles in a counterflow heat exchanger are shown when C/, >. ... 

FIGURE 9.6 Counterflow heat exchanger temperature profiles when... 

Example 8.9 Find the temperature distribution in a laminar flow, tubular heat exchanger having a uniform inlet temperature and constant wall temperature Twall- Ignore the temperature dependence of viscosity so that the velocity profile is parabolic everywhere in the reactor. Use art/P = 0.4 and report your results in terms of the dimensionless temperature... 

An example of integrated heat-transfer modehng and reactor design is shown in Figure 11.6. A predicted thermal profile for the reactor section of a combined reactor-heat exchanger is the solid line, while the discrete points are experimentally measured temperatures along the reactor length. The thermal profile is controlled... 

With decreasing cell size, the temperature difference between the wall of the cell and the eatalyst partiele in the cell would decrease to zero. For sufficiently small cell dimensions, we may assume the two temperatures are the same. In this case, the heat conduction through the wall becomes dominant and affects the axial temperature profile. As the external heat exchange is absent and the outside of the reactor is normally insulated, the temperature profile is flat along the direction transverse to the reactant flow, and the conditions in all channels are identical to each other. The energy balance is... 

Figure 2.31 Characteristic temperature profiles in a counter-current micro heat exchanger for a very low (left), intermediate (middle) and very high (right) thermal conductivity of the wall material and equal volume flows inside the two channels, reproduced from [125],...

If the heat exchange involves desuperheating as well as condensation, then the exchanger can be divided into zones with linear temperature-enthalpy profiles in each zone. Figure 15.12a illustrates desuperheating and condensation on the shell-side of a horizontal condenser. The total heat transfer area is the sum of the values for each zone ... 

Techniques for approaching optimum temperature profiles for exothermic reaction, (a) Adiabatic operation of reactors with interstage cooling, (b) Countercurrent heat exchange. (Adapted from Chemical Reaction Engineering, Second Edition, by O. Levenspiel. Copyright 1972. Reprinted by permission of John Wiley and Sons, Inc.)... 

As discussed in Section 2.3.1.2, SEDEX [103, 104] and SIKAREX [106] instruments are also used isothermally. In the case of the SIKAREX, the temperature of the sample is held by a heating coil at constant temperature by establishing a constant rate of heat exchange to the jacket (held about 50 to 100°C below the sample temperature). By measuring the electrical input, a negative copy of the reaction heat profile is obtained. Typical sensitivity of the equipment is 0.5 W/kg operating with a sample size of 10 to 30 g and in a temperature range of 0 to 300°C. 

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