Cold flow conditions

Under isothermal cold flow conditions only the continuity and momentum equations are required as defined by (3.417) choosing appropriate values for the generalized functions analogous to those in Table 3.1. The governing mixture equations are then expressed as ... 

During a model study, wind conditions and stack diameter are appropriately scaled down to ensure dymamic similarity. This suffices only the requirements for cold flow conditions. In a burning environment, however, parameters such as fuel pyrolysis time that depends only on fuel chemistry and temperature [66] are also important to be considered. In addition, buoyancy effects are generally neglected in model flares. For all these reasons, the model results must be compared with field test data to validate the correlations developed and develop scaling laws. Due to the unavailability of such data, quantitative scaling laws are yet to be developed. To date, only a few model test results have been compared with field test data. For instance, Schwartz and White [69] compared predictions of radiative emission from various models with field data. Gook et al. [90,91] conducted field-scale... 

Tarmy et al. [9] measured gas holdup under various cold flow conditions in order to predict the holdup for the EDS coal liquefaction process. These authors observed rather low holdup values and churn-turbulent flow in their cold flow studies while, surprisingly, under the actual conditions of the EDS process bubbly flow prevailed and gas holdup was as high as 0.5. 

If a bypass or PR valve is provided, it must also have sufficient capacity to relieve the vapor generated from the cold fluid by heat input from the hot side under design flow conditions, if vaporization could also cause the cold side to be overpressurized. 

Cold flow studies have several advantages. Operation at ambient temperature allows construction of the experimental units with transparent plastic material that provides full visibility of the unit during operation. In addition, the experimental unit is much easier to instrument because of operating conditions less severe than those of a hot model. The cold model can also be constructed at a lower cost in a shorter time and requires less manpower to operate. Larger experimental units, closer to commercial size, can thus be constructed at a reasonable cost and within an affordable time frame. If the simulation criteria are known, the results of cold flow model studies can then be combined with the kinetic models and the intrinsic rate equations generated from the bench-scale hot models to construct a realistic mathematical model for scale-up. 

Test method IP 309 is used to determine the low-temperature filterability of distillate fuels including those treated with a cold flow improver. The cold filter plugging point (CFPP) is defined as the highest temperature at which the fuel, when cooled under the prescribed conditions, will not flow through the filter or requires more than 60 seconds for 20 mL to pass through or fails to return completely to the test jar. This method is part of a series of standardized tests developed by the Institute of Petroleum. Test method IP 309 is summarized as follows ... 

The potential of structured packings as catalyst carriers for reactive stripping, film-flow-monoliths, Sulzer DX -packings, both coated with zeolite BEA, and katapak-S , filled with BEA-particles, was explored in cold-flow experiments and under reactive stripping conditions in a pilot-scale plant. 

Figure 15 ICP-MS background spectra (plotted on a logarithmic scale) for a sample containing 0.1% nitric acid (a) Conventional plasma conditions (1000 W, 0.77 L/min nebulizer gas flow rate). The Ar+ and 0+ signals are saturating the detector, so their signals are greater than 2 x 109 counts/sec. (b) Cold plasma conditions (600 W, 1.08 L/min nebulizer gas flow rate). Note that full scale in (a) is 10l° whereas in (b) it is 108. (From Ref. 147.)...

In the development of these processes and their transference into an industrial-scale, dimensional analysis and scale-up based on it play only a subordinate role. This is reasonable, because one is often forced to perform experiments in a demonstration plant which copes in its scope with a small produdion plant ( mock-up plant, ca. 1/10-th of the industrial scale). Experiments in such plants are costly and often time-consuming, but they are often indispensable for the lay-out of a technical plant. This is because the experiments performed in them deliver a valuable information about the scale-dependent hydrodynamic behavior (arculation of liquids and of dispersed solids, residence time distributions). As model substances hydrocarbons as the liquid phase and nitrogen or air as the gas phase are used. The operation conditions are ambient temperature and atmospheric pressure ( cold-flow model ). As a rule, the experiments are evaluated according to dimensional analysis. 

Just as for this model all similar approaches found in the literature suffer from the problem that not all fluid mechanical variables can be precalculated on the basis of the operating conditions. Instead, reasonable estimations or measurements in cold flow models are used... 

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