Pressure drop heating medium

For column analysis and troubleshooting it is important to have pressure drop measured with a DP cell. The differential pressure can also be used to control column traffic. A good way to do this would be to let the differential pressure control the heating medium to the reboiler. The largest application for differential pressure control is with packed columns where it is desirable to run at 80 to 100% of flood for best efficiency. 

In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

In addition to the shaft power needed to raise the water heat transfer medium from the low to high loop pressure, additional compressor power is needed to overcome frictional pressure drop around the loop. The power associated with this loss has been compared with that of the high temperature process loop in the reference design. To understand the role of the different heat transport fluid -water in the alternate design versus helium in the reference design - the pumping power is expressed as a fraction of the pumping power per unit thermal power transported. This permits a consistent comparison between the two loops even if they differ in total thermal power transported. 

Of course, the concept of complete similarity does not guarantee that a process will be the same in the model as in the full-scale version in every respect it is only the same with respect to particular aspect under examination, which has been described by the appropriate pi- relationship. In order to demonstrate this fact with the help of the above example, it should be remembered that the flow conditions in two smooth pipes of different scales should be considered similar when Re = idem and, according to the pressure drop characteristics, will therefore have the same numerical value of t, = Eu d/1. However, this does not mean that heat transfer conditions prevalent in the two pipes are the same. For that to be the case, the relevant pi-relationship, Nu=/(Re, Pr), requires that both the Reynolds number and the Prandtl number have the same numerical value (temperature-independent physical properties of the medium being supposed). 

The pressure drop through one channel and therefore across the heat exchanger when the porous medium is in the channel is given by ... 

The bottoms pressure is usually selected to permit use of a readily available heating medium (steam or hot oil), as well as to stay below a temperature that could cause product degradation. In the ECH-EB system, degradation is not considered a problem, and column bottoms pressure is solely a function of the pressure drop across the tower internals. Because, as seen in step 1, relative volatility can vary appreciably with pressure, it is advantageous in this case to install low-pressure-drop, high-efficiency tower internals. 

Let the medium between the flat surfaces of two bodies (now a fluid because of practical reasons) flow with a mean velocity V (Fig. 1.13). This flow results from either an imposed pressure drop or an induced buoyancy, respectively called forced and natural convection. Lettheinlettemperatureofthefluidbe72. (Note that the fluid temperature need not be Tz- Selection of Tz for this temperature eliminates temperature gradient near plate 2 and simplifies the following development.) The convection heat transfer from plate 1 is defined as the conduction in the fluid next to plate 1 (in view of the fact... 

The shell-side coefficient would therefore be hg = 123/0.573 = 215 Btu/hr. sq. ft. °F at the permissible pressure drop, and in this example the heat exchanger size could be reduced by about 35% if the weaker medium is passed through the shell side of the exchanger. 

If steam is the heating medium, the pressure drop of condensing steam is ... 

Heat is usually applied in various amounts and in different locations, whether in a metal plasticating barrel (extrusion, injection molding, etc.) or in a metal mold/die (compression, injection, thermoforming, extrusion, etc.). With barrels a thermocouple is usually embedded in the metal to send a signal to a temperature controller. In turn, it controls the electric power output device regulating the power to the heater bands in different zones of the barrel. The placement of the thermocouple temperature sensor is extremely important. The heat flow in any medium sets up a temperature gradient in that medium, just as the flow of water in a pipe sets up a pressure drop, and the flow of electricity in a wire causes a voltage drop. 

The authors modeled the microchannel heat sink, subject to an impinging jet, as a porous medium. Based on their experimental results, they suggested correlatiOTis for the pressure drop across a microchannel heat sink subject to an impinging jet as well as its thermal resistance as follows ... 

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