Mass flow ratio

Conveying systems normally use air as the transport medium to convey granular, crushed, or pulverized materials. Modelling the flow of pneumatic conveying and calculating its pressure loss is a problematic task. The greatest problem arises from the fact that different mass flow ratios, solid flow rate divided by the gas flow rate, imply different flow types in pneumatic conveying. Each of these flow types, which can be classified in many different ways, requires its own specific model in order to provide a concrete calculation method. 

The mass flow ratio p, sometimes also called mixture ratio, is defined as... 

Obviously, the closer the particles are to each other, the more likely it is that they will stick together and form larger clumps, which usually means that the flow is not uniform. This view combined with Eq. (14.18) is a greatly simplified explanation of why the mass flow ratio q, for dry wood chips can rise to five or even higher and still the flow of the mixture of air and large chip particles can be handled as a uniform suspension, a uniform dilute-phase flow, although it is not actually dilute. The mass flow ratio for fine coal powder, however, has to be much less than five in order for the flow to be handled as a uniform dilute flow. 

Equation (14.91) contains only the mass flow ratio /u as a characteristic number of the mechanics of similitude of the mixture. All the other irnpor rant factors, such as particle size, solid density, etc., are contained in the additional pressure-loss coefficient of the solid particles, A, which is determined separately for each material. 

In Figure 264 the dehumidification potential A7 of a 40% LiCl-F O solution is plotted as a function of the air to solution mass flow ratio MR for certain operating conditions and ideal mass exchange, solid line (1). In addition the energy storage capacity SC is plotted, dotted line (2). Up to a... 

It should be noted that the acceleration component is dominant in the last part of the pipe, where, because of the rapid pressure drop and the low absolute pressure, the specific volume of the gas increases sharply. This effect is more pronounced at high mass flow rates with large values of mass flow ratio, 3 (= mjm,). As shown in Figures 3.44a and 3.446, the average friction coefficient is affected by the mixture mass flow rate m, the mass flow ratio 3, and the diameter of the pipe D. The Re is defined as... 

The mass fraction (a) of the less dense phase (which, for gas-liquid flows, is called the quality) is x = mL/(ms + mL), so the mass flow ratio can be written... 

Powder (in spray drying tower) Mean particle size, Air / liquid mass flow ratio, Dmean Mr Kim-Marshall equation [26] 0.4 0.32... 

K Adsorption equilibrium constant trtj Mass flow ratio in section , defined by Eq. (6) n Adsorbed phase weight concentration... 

The non-linearity effect can easily be demonstrated by the following theoretical separation of a binary mixture. Let us assume that the concentrations of A and B are the same and correspond each to half of the overall feed concentration. The feed concentration is in addition assumed to be the only parameter necessary to characterize the feed composition. The mass flow ratio in section 1 (constrained by Eq. (8)) does not depend on the feed composition. On the contrary, the upper Emit on the flow rate ratio m4 given by Eq. (10) is a function of the feed composition. Both dependencies are illustrated in Fig. 5. 

For sufficiently large heat flux to mass flow ratios, the nucleation mechanism predominates and the heat transfer becomes independent of the two-phase flow characteristics of the system. Thus at large values of the boiling number, the heat transfer coefficients are virtually independent of the Lockhart-Martinelli parameter, Xn. 

The larger the value for cr, the greater the scattering of the size distribution, and, correspondingly, the poorer the uniformity of the droplet sizes. Part of the data measured at various air-to-liquid mass flow ratio, m.JmL, are shown in Table 5.1. It can be seen that, normally, the impingement between opposing droplets-in-gas suspension streams makes cr smaller. Only those obtained at in the third column of the... 

For the ball-probe measurement of charge current in a dilute gas-solid suspension, prove that, for a given type of particle and a given mass flow ratio, the current measured is independent ofthe particle size for db 3> dp. It is assumed that the charge transfer coefficient is constant. 

The flow pattern in a horizontal gas-solid pipe flow varies with the solids concentration. In a horizontal pipe flow at a given gas flow rate, the following flow patterns sequentially occur as the particle loading, defined as the mass flow ratio of particles to gas, increases ... 

Three carbonaceous materials were employed in the experiments i) commercial (Degussa) amorphous carbon black (CB-330) with specific surface area (s.s.a.) of 82 m /g (BET) and apparent density of 375 kg/m ii) Diesel Soot (DS), collected at the exhaust of a Lombardini, single cylinder, D.I., 325 cm displacement, 18 1 compression ratio Diesel engine, operated at an air/fuel mass flow ratio of about 20. The BET s.s.a. of fi esh soot was 90 m /g and the apparent density 375 kg/m iii) soot (BS) generated by an heating gas-oil burner. The fuel mass flow rate fed to the burner was 1.6 kg/h while the air/fuel mass flow rate ratio was 18 and, correspondingly, the soot concentration in the exhaust gas was about 1000 ppm. 

The shock wave acts as a liquid atomizer up to the point at which the momentum of the shock wave is able to disperse the liquid stream. By analogy with two-phase flow in packed columns, such hydrodynamic conditions can be construed as flooding. Hence, the region of stable atomization is mapped in terms of a flooding coefficient, defined as the mass flow ratio of undispersed liquid to the total liquid subject to the shock-wave field... 

For each steady state heat flux, seven ten eratures were measured for every condition of velocity and water/air mass flow ratio investigated to ensure that a reliable trend could be determined. The radial profiles of tenqierature at 500°C widiout water addition and with 4.75% water/air mass flow ratio are shown in Figure 3. The ten erature profiles are flat or sUghdy increasing toward the edges and have errors of 2.2% and 5.2% for no water addition and 4.75% water/air mass flow ratio respectively. The steady state ten erature was chosen to be that of the center zone of the plate, 2.54 cm in diameter. The three thermocouples used to record the temperatures in this zone exhibited a uniform temperature profile. 

These results suggest that fee heater enclosure losses are more important for lower heat transfer rates. For a given plate temperature, as the heat transfer through the plate to fee flow increases, the heater enclosure losses increase slowly and become less significant For singlephase flows, the curves obtained for heater enclosure losses are more linear at lower temperatures and more curved at higher temperatures due to radiation. Heater enclosure losses increase as the air velocity increases at a constant plate steady state temperature, or as fee plate tenqterature increases fin a constant air velocity. For two-phase flows the heat losses increase as fee water/air mass flow ratio increases for a given steady state temperature. 

Figure 7 shows the same corrections for a two-phase flow with a water/air mass flow ratio of 4.75% at 3.9m/s. The top curve corresponds to the preliminary results. Like the singlephase flow, as the heater input increases steady state temperature rises, however, the tenq)erature is lower for the two-phase flow. This augmentation of heat transfer is attributed to latent heat of evaporation of water droplets within the boundary layer. As the water/air mass flow ratio increases, the steady state temperature decreases for the same heater input... 

Figure 12 shows the effect of water/air mass flow ratio on heat transfer enhancement for a jet exit velocity of 3.9m/s. The heat transfer enhancement is defined as the ratio of the two-pWe Nusselt number over the single-phase Nusselt number at die same jet exit velocity. Conqiressed air is used in the water nozzle to atomize water into small droplets. This additional air flow also has a cooling effect. To quantify the compressed air effect, a set of experiments were performed for single-phase flow adding conqtressed air fimn the water nozzle. 

F nre 12 Effect of watei/air mass flow ratio on two-phase flow heat transfer enhancement... 

For a two-pbase flow of mjm 1.64% the time needed to reach 3S°C was 900 seconds. If the water/air mass flow ratio is increased to 2.81% only 600 seconds are needed, and for mw/nia 4.75% the cooling time is reduced to 300 seconds, three times lower than that for 1.64%. These results indicate that the water/air mass flow ratio can be used to change the cooling curve. 

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