Individual nozzles, 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... 

There are basically three possible designs of nozzle arrays which differ with regard to the spent flow of the air (Fig. 1.2). In a field of individual nozzles the aft-can flow unimpeded between almost all nozzles however, in a hole channel the air can flow only between those above. In a perforated plate the air can only continue to flow laterally and then escape. Hole channels and perforated plates are easier to produce than single nozzles, as they only require holes to be perforated. However, the heat transfer is the highest for nozzle fields and the lowest for perforated plates, as will be subsequently shown. 

Fig. 1.8 Average heat transfer dependent on the pitch of the individual nozzles.

The influence of the relative distance and the nozzle pitch is shown in Fig. 1.15, where heat transfer is seen to decrease continuously with the relative distance. The maximum heat transfer occurs in the case of pitches in the range of 3 to 5, depending on the distance. The heat transfer is lower than that of an array of individual nozzles. As the maximum occurs at a smaller pitch than 6 (as for singlenozzle arrays), a higher flow rate must also be applied. 

Based on the given Nusselt fimctions for the required heat transfer coefficient in Eq. 1.9, nozzle arrays can now be designed. It is again assumed that the heat is predominantly transferred for evaporation, while the enthalpy to heat up the dry material is again neglected. First, an array of individual nozzles will be considered for which a distinct maximum in the heat transfer results at a pitch of t = 6d. Thus,... 

To analyze the individual heat transfer kinetics of droplet clusters within the spray of twin-fluid atomizers, the local correlations between the droplet concentration and the heat and flow conditions are evaluated. Numerical simulations of the spray flow analyzed in this paper have been carried out with Large-Eddy-Simulation (LES) models with Lagrangian particle tracking (discrete particle method) for the droplet motion. A synthetic perturbation generator [30] for the inflow conditions for the gas flow and simple perturbations are added to the dispersed phase to induce realistic vortex patterns at the nozzle and in the consequent spray. 

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