Nozzle heat transfer

Within the framework of component development, CFD is used for scientific modeling and model validation in addition to the classical engineering parameter studies and optimization processes. Both approaches are based on the use of HPC calculation capacity. Within the framework of modeling and vahdation, HPC facilitates a complex representation of the physical phenomena with fine space and time discretization. With the aid of such submodels and appropriate laboratory experiments, models for nozzles, heat transfer phenomena, two-phase flow, and so on can be derived and vahdated. CFD models thus selected and validated form the basis for the CFD-based design and optimization of flow systems. The classical engineering problem of parameter variation and optimization requires a large number of simulation calculations and therefore leads to an extremely high cost of computation. HPC allows the parallelization of individual simulations, which in turn makes it possible to calculate several simulations simultaneously and thus enables comprehensive parameter studies and flow optimizations to be completed in an acceptable time frame. In the ATR 10 development process, CFD simulations were conducted on up to 16 cores of the JuRoPA supercomputer simultaneously. This meant that when two simulation... 

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

Gas impingement from slots, orifices, and nozzles at 10—100 m/s velocities is used for drying sheets, films, coatings (qv), and thin slabs, and as a secondary heat source on dmm dryers and paper (qv) machine cans. The general relationship for convection heat transfer is (13,14) ... 

Refrigeration units modified for free cooling do not include the hq-uid-refrigerant pump and cooler spray header nozzles. Without the cooler refrigerant agitation for improved heat transfer, this arrangement allows up to about 20 percent of rated capacity. Expected capacities for both tnermocycle and free cooling are indicated in Fig. 12-21. 

For air flow impinging normally to the surface from slots, nozzles, or perforated plates, the heat-transfer coefficient can be obtained from the data of Friedman and Mueller (Proceedings of the General Discussion on Heat Transfer, Institution of Mechanical Engineers, London, and American Society of Mechanical Engineers, New York, 1951, pp. 138-142). These investigators give... 

Stirred Vessels Gases may be dispersed in hquids by spargers or nozzles and redispersed by packing or trays. More intensive dispersion and redispersion is obtained by mechanical agitation. At the same time, the agitation will improve heat transfer and will keep catalyst particles in suspension if necessaiy. Power inputs of 0.6 to 2.0 kW/m (3.05 to 10.15 np/1,000 gal) are suitable. 

Talceislii, K., Matsuura, M., Aoki, S., and Sato, T., 1989, An Experimental Study of Heat Transfer and Film Cooling on Low Aspect Ratio Turbine Nozzles, ASME paper 89-GT-187. 

The temperature is approximately 20°F below the 265°F temperature limit. The sections differ by less than 1 F. This is probably just luck because that good a balance is not really necessary. Also, it should be noted that to maintain simplicity the additional factors were ignored, such as the 10°F temperature pickup in the return stream due to internal wall heat transfer. Also, nozzle pressure drops for the exit and return were not used. Balance piston leakage was not used as it was in Example 5-3. When all the factors are used, the pressures for each section would undoubtedly need additional adjustment as would the efficiency. However, for the actual compression process, the values are quite realistic, and for doing an estimate, this simpler approach may be quite adequate,... 

The earliest injection moulding machines were of the plunger type as illustrated in Fig. 4.30 and there are still many of these machines in use today. A predetermined quantity of moulding material drops from the feed hopper into the barrel. The plunger then conveys the material along the barrel where it is heated by conduction from the external heaters. The material is thus plasticised under pressure so that it may be forced through the nozzle into the mould cavity. In order to split up the mass of material in the barrel and improve the heat transfer, a torpedo is fitted in the barrel as shown. 

Heni, R. E. and H. K. Fauske, 1971, The Two-Phase Critical Flow of One-Component Mistuies in Nozzles, Orifices, and Short Tubes, J. Heat Transfer, pp 179-187, May. 

The simplest type of shell-and-tube heat exchanger is shown in Eigure 3-1. The essential parts are a shell (1), equipped with two nozzles and having tube sheets (2) at both ends, which also serve as flanges for the attachment of the two channels or beads ( 3) and their respective channel covers (4). The tubes are expanded into both tube sheets and are equipped w nil transverse baffles (5) on the shell side for support. The calculation of the effective heat transfer surface is based on the distance between the inside faces of the tube sheets instead of the overall tube length. 

L the shell-side fluid makes one pass from inlet to outlet. With a longitudinal baffle, and with the nozzles placed 180° around the shell, the shell-side fluid would be forced to enter at the left, flow to the right to get around the baffle, and flow to the left to reach the exit nozzle. This would be required to approximate true counter-current flow, which was assumed in the heat transfer equations of Chapter 2. 

The arrangement of baffle plates and nozzles. Figure 10-96C, are important to prevent (a) tube vibration, (b) maldistribution of the process boiling fluid, and (c) poor heat transfer coefficients due to uneven and stratified flow resulting in uneven and dry spot heat transfer from nonuniform tube wetting, and others. ... 

Note that the liquid inlet must be inline at bottom, and the vapor out must be inline at top (Figure 10-105). For a side oudet vapor nozzle, increase the heat transfer area by 30%. b. Horizontal or vertical shell-side boiling, size for low velocities and pressure drops. 

There are a variety of igniter designs which are currently employed in solid-propellant rockets. These types include rocket-exhaust (pyrogen), pyrotechnic, and hypergolic igniters, each of which can be located in the head-end closure of the motor or in the exhaust nozzle at the aft-end of the motor. The heat-transfer information appropriate to each of these possible combinations is discussed in the following sections. 

They also considered the depth of penetration of the igniter jet into the motor. They found that the motor L/Dp ratio had little effect on the heat transfer provided L exceeded the depth of penetration of the igniter jet. Their results also showed that high penetration is desirable and can be achieved by the use of high igniter mass-flow rates in conjunction with supersonic igniter-exhaust nozzles. 

The pressure drop in the HAGO nozzle quickly reaches impractical values. There is always a combination of jet diameter and jet spacing that yields the same heat transfer coefficient as the spray, but at a much lower energy cost. 

The tube velocity needs to be reduced. This will reduce the heat transfer coefficient, so the number of tubes must be increased to compensate. There will be a pressure drop across the inlet and outlet nozzles. Allow 0.1 bar for this, a typical figure (about 15% of the total) which leaves 0.7 bar across the tubes. Pressure drop is roughly proportional... 

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