IMPROVING THE FILM COOLING PERFORMANCE OF A TURBINE ENDWALL WITH MULTI-FIDELITY MODELING CONSIDERING CONJUGATE HEAT TRANSFER

The gas turbine endwall is bearing extreme thermal loads with the rapid increase of turbine inlet temperature. Therefore, the effective cooling of turbine endwalls is of vital importance for the safe operation of turbines. In the design of endwall cooling layouts, numerical simulations based on conjugate heat transfer (CHT) are drawing more attention as the component temperature can be predicted directly. However, the computation cost of high-fidelity CHT analysis can be high and even prohibitive especially when there are many cases to evaluate such as in the design optimization of cooling layout. In this study, we established a multi-fidelity framework in which the data of low-fidelity CHT analysis was incorporated to help the building of a model that predicts the result of high-fidelity simulation. Based upon this framework, multi-fidelity design optimization of a validated numerical turbine endwall model was carried out. The high and low fidelity data were obtained from the computation of fine mesh and coarse mesh respectively. In the optimization, the positions of the film cooling holes were parameterized and controlled by a shape function. With the help of multi-fidelity modeling and sequentially evaluated designs, the cooling performance of the model endwall was improved efficiently.

Improving the Film Cooling Performance of a Turbine Endwall With Multi-Fidelity Modeling Considering Conjugate Heat Transfer

The gas turbine endwall is bearing extreme thermal loads with the rapid increase of turbine inlet temperature. Therefore, the effective cooling of turbine endwalls is of vital importance for the safe operation of turbines. In the design of endwall cooling layouts, numerical simulations based on conjugate heat transfer (CHT) are drawing more attention as the component temperature can be predicted directly. However, the computation cost of high-fidelity CHT analysis can be high and even prohibitive especially when there are many cases to evaluate such as in the design optimization of cooling layout. In this study, we established a multi-fidelity framework in which the data of low-fidelity CHT analysis was incorporated to help the building of a model that predicts the result of high-fidelity simulation. Based upon this framework, multi-fidelity design optimization of a validated numerical turbine endwall model was carried out. The high and low fidelity data were obtained from the computation of fine mesh and coarse mesh respectively. In the optimization, the positions of the film cooling holes were parameterized and controlled by a shape function. With the help of multi-fidelity modeling and sequentially evaluated designs, the cooling performance of the model endwall was improved efficiently.

Numerical Study in Three Dimensions of Influence of the Fluids Nature and Obstacle Position on the Electronic Component Cooling

In this work, we have studied numerically the influence of the nature of nanofluids and the obstacle position, within the mini-channel of dimensions (10 x 10 x 108 mm3) on the electronic component cooling. The power of the electronic component is constant. In these simulations we have considered the Al2O3-water, SiO2-water and TiO2-water as coolants. The numerical results are obtained by choosing a Reynolds number (Re) between 300 and 500 and considering that the flow regime is stationary. The simulation was performed using the software, ANSYS FLUENT.The analysis of the simulation results shows that the position of obstacles within the mini-channel has considerable effects on the improvement of the electronic component temperature. The results also showed that among the nanofluids studied, the liquid containing nanoparticles Al2O3-water is the best for the electronic component cooling.

Modeling Directional Brightness Temperature (DBT) over Crop Canopy with Effects of Intra-Row Heterogeneity

In order to improve the simulation accuracy of directional brightness temperature (DBT) and the retrieval accuracy of component temperature, a model considering intra-row heterogeneity to simulate the DBT angular distribution over crop canopy is proposed. At individual scale, the probability of leaf appearance is inversely proportional to the distance from central stem. On the basis of this assumption, we formulated leaf area volume density (LAVD) spatial distribution at three hierarchical scales: individual scale, row scale, and scene scale. The equations for directional gap probability and bi-directional gap probability were modified to adapt the heterogeneity of row structure. Afterwards, a straightforward radiative transfer model was built based on the gap probabilities. A set of simulated data was generated by the thermal radiosity-graphics combined model (TRGM) as the benchmark to evaluate both forward simulation and inversion ability of the new model; we compared the new DBT model against an existing model assuming row as homogeneous box. With the growth of crops, the canopy structure of row crops will gradually change from row structure to continuous canopy. The new DBT model agreed with the TRGM model much better than the homogeneous row model at the middle stage of the crop growth season. The new model and the homogeneous row model achieve similar accuracy at early stage and end stage. At the middle growth stage, the new model can improve the accuracy of soil temperature retrieval. We recommend the new DBT model as an option to improve the DBT simulation and component temperature retrieval for row-planted crop canopy. In particular, the more accurate component temperatures during the middle growth stage are fundamentally important in characterizing crop water status, evapotranspiration, and soil moisture, which are subsequently critical for predicting crop productivity.

Compact Thermal Model of the Pulse Transformer Taking into Account Nonlinearity of Heat Transfer

This paper presents a compact nonlinear thermal model of pulse transformers. The proposed model takes into account differentiation in values of the temperatures of a ferromagnetic core and each winding. The model is formulated in the form of an electric network realising electrothermal analogy. It consists of current sources representing power dissipated in the core and in each of the windings, capacitors representing thermal capacitances and controlled current sources modelling the influence of dissipated power on the thermal resistances in the proposed model. Both self-heating phenomena in each component of the transformer and mutual thermal couplings between each pair of these components are taken into account. A description of the elaborated model is presented, and the process to estimate the model parameters is proposed. The proposed model was verified experimentally for different transformers. Good agreement between the calculated and measured waveforms of each component temperature of the tested pulse transformers was obtained. Differences between the results of measurements and calculations did not exceed 9% for transformers with a toroidal core and 13% for planar transformers.

Respon Vibrasi Overall dan Temperatur Komponen Mesin Terhadap Misalignment Axial

Misalignment is one of the problems that often occurs in rotary equipment. In this paper, the observation was done to the rotary machine model in response to changes of axial misalignment by using vibration meter and infrared thermography camera. The model was a machine series, consisting of electric motor and disc which was connected by 3 Jaw flexible coupling. The shafts were positioned into several axial misalignment conditions to see the effect on the overall vibration value and its component temperature. The result of vibration observation showed that under certain conditions, by increasing shaft misalignment then the overall vibration value tends to decrease. With the decrease of overall vibration value, the machine condition was not in better condition. This was indicated by observing the temperature of the components in this condition, which showed the opposite fact. As misalignment increases, the temperature of the engine components also increases.

Gargling with Aloe vera extract is effective to prevent the Ventilator-Associated Pneumonia (VAP)

Background: Long-term use of a mechanic ventilator may cause Ventilator- Associated Pneumonia (VAP) infection, nosocomial pneumonia that occurs after 48 hours in patients using mechanical ventilation either through the endotracheal tube or the tracheostomy tube. To prevent the occurrence of VAP, antiseptic liquid (mouthwash) such as chlorhexidine 2% maybe recommended. However, gargling using chlorhexidine may also cause allergies, thus, Aloe vera extract could be an alternative. Aims: The purpose of this study was to determine the effectiveness of Aloe vera extract as mouthwash to prevent the occurrence of Ventilator-associated pneumonia. Methods: This research is a quasi-experiment case-control study with a pre- posttest control group design. The sample size in this study was 30 respondents who were equally distributed into two groups; intervention group was administered using Aloe vera extract, while chlorhexidine was practiced for the control group. To determine the occurrence of VAP, Clinical Pulmonary Infection Score (CPIS) for Ventilator-Associated Pneumonia was measured on the first day of intubation and the fourth day, enumerated by nurses in the emergency room. CPIS is a set of indicators comprised of temperature, leucocyte, trachea secretion, oxygenation (PaO2/FiO in mm Hg), and thorax photo. CPIS value below than five will be regarded non-VAP, while CPIS scored 6-9 will be diagnosed as VAP. Results: Oral hygiene with Aloe vera extract was able to prevent the occurrence of VAP (p-value = 0.001), but there was no significant difference between the control group and intervention in the CPIS component temperature, leukocytes, tracheal secretions, FiO2, and the thoracic component. Conclusions: Oral hygiene with Aloe vera extract effectively prevented the occurrence of V entilator-Associated Pneumonia (V AP) compared to chlorhexidine.