Nozzle limitations

The top spray system has been used to coat materials as small as 100 microns. Smaller substrates have been coated, but agglomeration is almost unavoidable due to nozzle limitations and the tackiness of most coating substances. Batch sizes range from a few hundred grams to approximately 1,500 kg. Typically, a single nozzle wand with up to six liquid delivery ports is used, but multiple nozzle systems have been applied. 

A model for electrically pulsed jets has been described (26). The viscous drag in a thin nozzle limits the flow rate and leads to intrinsic pulsations of the cone jet. Scaling laws for intrinsic cone jet pulsations have been derived to establish the operating regime for drop deployment. The scaling laws are applicable to similar electro-hydrodynamic processes in miniaturized electrospraying systems. 

Argon purging of the upper tundish nozzle is common when aluminum killed steels are cast. This practice is effective in reducing the rate of alumina buildup on the nozzle bore, but it does not prevent it. Clogging of the upper nozzle limits tundish life in some steel plants. 

In order to maintain high energy efficiency and ensure a long service life of the materials of construction in the combustion chamber, turbine and jet nozzle, a clean burning flame must be obtained that minimizes the heat exchange by radiation and limits the formation of carbon deposits. These qualities are determined by two procedures that determine respectively the smoke point and the luminometer index. 

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

Jet Aerators. Jet aerators are a cross between the diffused and mechanical aerators. Air and water are pumped separately under the water surface into a mixing chamber and ejected as a jet at the bottom of the tank or pond (Fig. 3f). Jet aerators are suited for deep tanks and have only moderate cost. Disadvantages include high operational costs, limitations caused by tank geometries, and nozzles that can clog. Additionally, they require blowers. 

Figure 7 shows nozzle locations and support arrangements for a typical horizontal vessel (7). The saddles used for support are sustained by concrete pedestals or steel stmctures. Sufficient clearance between the bottom nozzles and the support saddles needs to be provided for access to the nozzle flange bolts. The manway can be located on the end head of the vessel, the topside of the vessel, or the side of the vessel. The preference is for an end manway wherever possible for accessibiHty, except when it is limited by the level gauges and controls that are commonly mounted off the heads. 

Normally, zircon sand is readily available as a by-product of mtile and ilmenite mining at ca 150 per metric ton. However, zircon and baddeleyite are obtained as by-products of their operations, and therefore, the supply is limited by the demand for other minerals. In 1974, when a use for zircon in tundish nozzles developed in the Japanese steel industry, a resulting surge in demand and stockpiling raised zircon prices to 500/t. Worldwide production by country is given in Reference 80. 

Feedstocks. Feedstocks are viscous aromatic hydrocarbons consisting of branched polynuclear aromatics with smaller quantities of paraffins and unsaturates. Preferred feedstocks are high in aromaticity, free of coke and other gritty materials, and contain low concentrations of asphaltenes, sulfur, and alkah metals. Other limitations are the quantities available on a long-term basis, uniformity, ease of transportation, and cost. The abiUty to handle such oils in tanks, pumps, transfer lines, and spray nozzles are also primary requirements. 

Appendix 4 gives definitions and rules for stress analysis for shells, flat and formed heads, and tube sheets, layered vessels, and nozzles including discontinuity stresses. Of particular importance are Table 4-120.1, Classification of Stresses for Some Typical Cases, and Fig. 4-130.1, Stress Categories and Limits of Stress Intensity. These are veiy useful in that they clarify a number of paragraphs and simphfy stress analysis. 

The smaller framed hot gas expanders are often equipped with two control valves, each controlling a segment of 30% and 20%, respectively, of the total inlet. It is possible to vary the inlet cross-sectional area of these segments, within limits, by later replacing individual nozzles with blind fillers or vice-versa. Other machines may feature full arc admission without control valves. 

Injection of Steam in the Combustor of the Gas Turbines Utilizing Present Dual Fuel Nozzles. Steam injection in the combustor has been commonly used for NO control as seen in Figure 2-43. The amount of steam, which can be added, is limited due to combustion concerns. This is limited to about 2-3% of the airflow. This would provide an additional 3-5% of the rated power. The dual fuel nozzles on many of the industrial turbines could easily be retrofitted to achieve the goal of steam injection. The steam would be produced using an HRSG. Multiple turbines could also be tied into one HRSG. 

Nozzle Area of the First Turbine Stage Expander Stage). This is a very eritieal parameter and limits the total airflow into the turbine seetion, thus this limits the amount of steam injeetion or the amount of the heated and humidified eompressed air injeetion. 

The uniformity of the eombustor outlet profile affeets the useful level of turbine inlet temperature, sinee the average gas temperature is limited by the peak gas temperature. This uniformity assures adequate nozzle life, whieh depends on operating temperature. The average inlet temperature to the turbine affeets both fuel eonsumption and power output. A large eombustor outlet gradient will work to reduee average gas temperature and eonse-quently reduee power output and effieieney. Thus, the traverse number must have a lower value—between 0.05 and 0.15 in the nozzle. 

Table 12-4 is a summary of liquid fuel speeifieations set by manufaeturers for effieient maehine operations. The water and sediment limit is set at 1% by maximum volume to prevent fouling of the fuel system and obstruetion of the fuel filters. Viseosity is limited to 20 eentistokes at the fuel nozzles to prevent elogging of the fuel lines. Also, it is advisable that the pour point be 20 °F (11 °C) below the minimum ambient temperature. Failure to meet this speeifieation ean be eorreeted by heating the fuel lines. Carbon residue should be less than 1% by weight based on 100% of the sample. The hydrogen eontent is related to the smoking tendeney of a fuel. Lower... 

With heavy fuels, the ambient temperature and the fuel type must be considered. Even at warm environmental temperatures, the high viscosity of the residual could require fuel preheating or blending. If the unit is planned for operation in extremely cold regions, the heavier distillates could become too viscous. Fuel system requirements limit viscosity to 20 centi-stokes at the fuel nozzles. 

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