Numerical simulation of a fuel nozzle's spray

The aim of this thesis is to examine the boundary conditions that must be input into the computational fluid dynamic software, FLUENT in order to model spray. This can then be used to advance the current computational fluid dynamic models used to model an engine's combustor. This will save the industry time and money, in the design development stages. The parameters that were studied in this thesis included, changing the angle the spray is injected at and the Rosin-Rammler parameters: number of droplet diameters contained within the spray and the droplet diameters spread, determining the uniformity of the spread. The results found that it was possible to predict the Rosin-Rammler plot with a minor change of the Rosin-Rammler parameter, spread, q. It was also found that the initial assessments of the spray parameters provide reasonable trends in the axial and radial velocities.

Numerical simulation of a fuel nozzle's spray

The aim of this thesis is to examine the boundary conditions that must be input into the computational fluid dynamic software, FLUENT in order to model spray. This can then be used to advance the current computational fluid dynamic models used to model an engine's combustor. This will save the industry time and money, in the design development stages. The parameters that were studied in this thesis included, changing the angle the spray is injected at and the Rosin-Rammler parameters: number of droplet diameters contained within the spray and the droplet diameters spread, determining the uniformity of the spread. The results found that it was possible to predict the Rosin-Rammler plot with a minor change of the Rosin-Rammler parameter, spread, q. It was also found that the initial assessments of the spray parameters provide reasonable trends in the axial and radial velocities.

Thermal-hydraulic performance prediction of two new heat exchangers using RBF based on different DOE

Thermal performance prediction with high precision and low cost is always the need for designers of heat exchangers. Three typical design of experiments (DOE) known as Taguchi design method (TDM), Uniform design method (UDM), and Response surface method (RSM) are commonly used to reduce experimental cost. The radial basis function artificial neural network (RBF) based on different DOE is used to predict the thermal performance of two new parallel-flow shell and tube heat exchangers. The applicability and expense of ten different prediction methods (RBF + TDML9, RBF + TDML18, RBF + UDM, RBF + TDML9 + UDM, RBF + TDML18 + UDM, RBF + RSM, RBF + RSM + TDML9, RBF + RSM + TDML18, RBF + RSM + UDM, RSM) are discussed. The results show that the RBF + RSM is a very efficient method for the precise prediction of thermal-hydraulic performance: the minimum error is 2.17% for Nu and 5.30% for f. For RBF, it is not true that the more of train data, the more precision of the prediction. The parameter “spread” of RBF should be adjusted to optimize the prediction results. The prediction using RSM only can also obtain a good balance between precision and time cost with a maximum prediction error of 14.52%.

SiC MOSFET Device Parameter Spread and Ruggedness of Parallel Multichip Structures

This paper presents a preliminary study of the impact of device electro-thermal parameter spread and temperature variation on the robustness of SiC MOSFET parallel multi-chip power switch architectures. Reference is made to 1200 V – 80 mΩ rated commercial devices. Some major parameters are identified and selected, presenting experimental evidence of their impact during transient overload events. An advanced physics-based simulation model is then employed to extend the analysis to a more comprehensive set of parameters and operational conditions.

Modeling of the Impact of Parameter Spread on the Switching Performance of Parallel-Connected SiC VJFETs

Operation of parallel-connected 4H-SiC VJFETs from SemiSouth was measured and modeled using numerical simulations. The unbalanced current waveforms in parallel-connected VJFETs were related to spread in the critical parameters of the device structure and to the influence of the parasitic inductances in the measurement circuit. The physical device structure was reconstructed based on SEM analysis, electrical characterization, and device simulations. The two hypothetical critical design parameters that were studied with respect to spread were the p-gate doping profile (Case 1) and the emitter doping (Case 2). Variation in both parameters could be related to variation in the emitter breakdown voltage, the on-state characteristics, and the threshold voltage of the experimental devices. The switching performance of the parallel-connected JFETs was measured using a single gate driver in a double pulse test and compared with simulations. In both investigated cases a very good agreement between measurements and simulations was obtained. The modeling of the transient performance relies on good reproduction of transfer characteristics and circuit parasitics.

Fine-Line Structuring of Microwave Components on LTCC Substrates

Low temperature co-fired ceramics (LTCC) are used in a wide range of RF and microwave applications. The ceramic multilayer technology provides a truly three-dimensional circuit technology, hermetical sealing, hybrid integration, and favorable microwave properties at moderate costs. In order to take full advantage of millimeter wave frequencies, resolutions of lines and spaces below the typical, screen printable 50 μm are desired. This paper describes the technological development of a fine-line structuring process based on resinate thin films and electroplating on LTCC. A combination of thin-film technology and thick-film technology leads to a novel resinate technology. This new process replaces the commonly used expensive sputtered layers, usually required for thin-film structuring combined with standard LTCC technology. The initial layer is replaced by a screen-printed metallo-organic paste (resinate paste). Resinate pastes consist of metallo-organic noble metal compounds (e.g. gold and silver), which are dissolved in organic suspensions. The film thickness after firing is typically below 1 μm. This layer can be used to define structures with high precision using photolithography and electroplating followed by an etching process. The etching processes investigated here showed promising resolutions of 25 μm for lines and spaces. But wet-chemical processes can be applied to sintered LTCC surfaces only. Buried fine structures may be achieved with tape-on-substrate (ToS) technology which allows for laminating and subsequent sintering of structured greensheets onto sintered ceramics. The benefits of this technology for microwave applications are obvious, given an improved resolution and parameter spread, and an accordingly reduced variation of the resulting structures.