The volumetric flow rate of the air can also be expressed in terms of the conveying air velocity and the pipeline bore. Fig. 0000003049 00000 n
It can be seen that initially a large amount of power is used to cool the hot air that has accumulated within the cabin during the initial soak phase. Let’s simplify things and pretend that the air is completely dry, with no humidity, and that it is an ideal gas.
As shown in Fig. Solids loading ratio, ϕ, is defined as the ratio of the mass flow rate of the material conveyed, to the mass flow rate of the air used to convey the material and was presented in the introductory chapter with Eqn. 13.9b data are presented without hindrance of the test results in Fig. Number of tubes, length of tubes, mass flow rate of air, mass flow rate of liquid-desiccant solution. trailer
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19.3. Why Do Objects Have Mass? In the high-velocity dilute phase conveying region, the performance and behavior of the material is no different from that of any other material conveyed in dilute phase flow. 0000066672 00000 n
Figure 10.2 illustrates the variation of exergy efficiency with inlet air mass flow rate for several values of the product mass. The ideal gas law, for a steady flow situation, however, presented in Eqn. Over time the cabin starts to cool and the capacity falls to a steady ~ 2.75kW as the returned air temperature approaches that of the outlet. 21.1: m˙p = mass flow rate of material, tonne/h. When only a single point is used the intermediate stage of the data scaled to the plant pipeline, of the test pipeline bore, is not available. 13.1 pipeline. It will be in the region of 13 to 16 m/s for fine granular materials, being closer to 13 m/s if the material has a wide particle size distribution. Fig. 0000057860 00000 n
For the scaling up of the conveying characteristics in Fig. 13.2 they are shown with the inclusion of lines of constant conveying-line inlet air velocity, because this is a critical parameter in distinguishing between dilute and dense phase flows for this type of material. However, the exergy efficiency increases considerably with increasing product mass. The design here is based on a conveying-line inlet air velocity of 17 m/s and Eqn. In addition, increasing the mass of product considerably influences the exergy efficiency, i.e., exergy efficiency increases with increasing product mass due to more of the input exergy being utilized in the drying operation rather than flowing through the dryer unchanged. 38.6°C DBT/26.0°C WBT. This also includes materials that are capable of being conveyed in dense phase. 13.5. This is reproduced here as Eqn. 20.1, as for the test pipeline, or scaling the 0.330 kg/s for the test pipeline in proportion to the larger pipe section area. Variation of process exergy efficiency with mass flow rate of drying air for several product weights. It is located at the correct value of conveying-line inlet air velocity and the solids loading ratio is about 5. 0000033836 00000 n
About air; 1.2929 kilogram [kg] of air fits into 1 cubic meter; 0.00075 ounce [oz] of air fits into 1 cubic inch; Air weighs 0.0012929 gram per cubic centimeter or 1.2929 kilogram per cubic meter, i.e. 20.5.
0000048154 00000 n
When the conveying characteristics are scaled in total these features can be seen, as with Figs 16.2b, 16.5b and 16.6bFig 16.2bFig 16.5bFig 16.6b.
share | cite | improve this question | follow | edited Jul 16 '16 at 23:01. peterh - Reinstate Monica . The mass flow rate of liquid solution in the regenerator cannot be taken as independent variable since this is the same as the liquid flow rate at the exit of the absorber. This is presented in Fig. With this material there is a complete reversal in slope of the constant pressure drop curves at low values of airflow rate.
Ordinary Portland cement has been selected as being representative of materials conveyed in dense phase in a sliding bed mode of flow and the conveying characteristics are presented in Fig. The impact of preconditioning technologies is to reduce the initial vehicle temperature, and thus the air recirculated to the evaporator is also reduced, leading to a reduced capacity requirement (as the output temperature remains fixed for all simulations). Figure 10.6 shows the exergy efficiency variation with product mass as the mass flow rate of drying air is varied. 16.4 and is reproduced here in Eqn. Increasing the specific exergy difference decreases the exergy efficiency. The equations for evaluating airflow rate were developed in Chapter 9. In the first stage scaling is with respect to conveying distance, and this includes both pipeline orientation and bends. From: Pneumatic Conveying Design Guide (Third Edition), 2016, David Mills, in Pneumatic Conveying Design Guide (Third Edition), 2016. Figure 8.3 shows the variation of exergy efficiency with inlet drying air temperature for several values of product mass. 0000057655 00000 n
7,114 10 10 gold badges 35 35 silver badges 51 51 bronze badges. Is there a formula?
0000107203 00000 n
The actual length of the plant pipeline is 325 m and it is this length that needs to be used to evaluate the air-only pressure drop for the plant pipeline having the same bore as the test pipeline, in the first instance. Increasing the specific exergy difference decreases the exergy efficiency. Thus, this liquid desiccant-based system seems to be feasible only if ample amount of waste heat is available. 16.8: subscripts 1 and 2 = the appropriate pipe bores of the two pipelines. The initial cost of the plant was estimated (in 1994) to be Rs. 13.5. It also means that the conveying air velocity will vary along the length of a pipeline. T 1 = conveying-line inlet air temperature, K = 288 K (15 °C) Substituting these values in Eqn. Variation of process exergy efficiency with product moisture content for different moisture evaporation rates. 13.2 for the granulated sugar, if the conveying-line inlet air velocity is below 16 m/s, nothing will be conveyed because the pipeline will block, and if it is greater than about 30 m/s, almost nothing will be conveyed because all of the available energy is lost to friction. Figure 13.7 shows that the change in slope of the constant pressure drop curves occurs approximately at a velocity of about 15 m/s. Fig. Ibrahim Dincer, Marc A. Rosen, in Exergy (Second Edition), 2013. 0000107921 00000 n
The exergy efficiency increases with increasing moisture content of the products. The exergy efficiency increases linearly with product mass. 13.10. Variation of process exergy efficiencies with mass of product. 16.2, with the materials conveyed over 95 m through an 81 mm bore pipeline, to a pipeline of larger bore, the datum pressure drop should first be changed throughout by the appropriate values obtained from Fig. – Calculated evaporator capacity curves. The minimum value of conveying air velocity will be of the order of 10 to 12 m/s for fine powders, being closer to 10 m/s for ground materials, such as flour and cement, because of the particle shape. Increasing drying air temperature reduces the exergy efficiency, since exergy efficiency is inversely proportional to the exergy rate of drying air. Figure 13.6 shows that the conveying limit can cut across constant pressure drop conveying lines of low value. FIGURE 10.8. 0000001902 00000 n
Because the pressure drop line has been chosen as 0.85 bar and the conveying-line inlet air velocity has been determined as 17 m/s, the appropriate, Exergy Analysis of Drying Processes and Systems, illustrates the variation of exergy efficiency with inlet, EXERGY ANALYSIS OF DRYING PROCESSES AND SYSTEMS, The outlet gas properties of the CC are a function of, Exergy Analysis of Crude Oil Distillation Systems, and assuming an adiabatic process, the hot, International Journal of Heat and Mass Transfer, Supply air conditions: 15.3°C/0.0067 kg/kg da. Optimized design of a 20 TR LDAC system. The plot in Figure 7 shows that when the optimised configuration is combined with good duct insulation, the overall capacity reduction is of the order ~ 0.8kW (~ 22%). These two elements were considered in Chapter 16, “Pipeline Scaling Parameters.” This procedure was considered at this point in the previous case study and an expression for the equivalent length, Le, of a pipeline was given with Eqn. Tests were undertaken with nylon pellets in a similar pipeline to that used earlier for the polyethylene pellets except that it was 81 mm bore and so required about twice the amount of air for conveying.
10.6) for each of nine bends, gives: Substituting this value, the airflow rate of 0.330 kg/s and the pipeline bore of 0.105 m into Eqn. A very much longer pipeline is used for this purpose in order to magnify the extent of the transitional region. 20.5 therefore needs to be reduced by this amount for scaling purposes, to take account of the difference in air-only pressure drop values. 33 1 1 gold badge 1 1 silver badge 6 6 bronze badges $\endgroup$ $\begingroup$ Here is an ideal gas formula calculator. 13.9. 0000096421 00000 n
This is shown on Fig. Interestingly, we note that exergy efficiency varies little (decreasing slightly) with increasing humidity ratio of the drying air. This is in addition to the reduction as a consequence of scaling to a longer pipeline. Finally we need to fix the extent of “cooling” that the new system should provide. The duct insulation study also reduced the heat pick-up of air flowing into the cabin and again a reduced capacity is obtained. 21.2): An alternative, and more direct, expression for volumetric flow rate is derived from the flow situation: This is the actual volumetric flow rate. These were presented earlier in Fig.
This means that instead of having 0.747 bar for conveying material, it is now reduced to 0.747 – 0.195 = 0.552 bar.
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