Effect of the Modification of the Start-Up Sequence on the Thermal Stresses for a Microgas Turbine

Microgas turbines (MGT) are an alternative for small-scale energy production; however, their small size becomes a drawback since it enhances the heat transfer among their components. Moreover, heat transfer drives to temperature gradients which become higher during transient cycles like start-up. The influence of different start-up curves on temperature and thermal stresses of a microgas turbine was investigated. Stationary and rotational blades of the turbine were numerically simulated using CFD and FEM commercial codes. Conjugated heat transfer cases were solved for obtaining heat transfer from fluid toward the blades. Changes of temperature gradients within the blades during the start-ups were calculated under transient state with boundary conditions according to each curve to assess accurate thermal stresses calculations. Results showed that the modification of the start-up curves had an impact on the thermal stresses levels and on the time when highest stresses appeared on each component. Furthermore, zones highly stressed were located near the constraints of blades where thermal strains are restricted. It was also found that the curve that had a warming period at the beginning of the start-up allowed reducing the peaks of stresses making it more feasible and safer for the turbine start-up operation

IDETC/CIE -28219 AN ENERGY BASED METHOD FOR WEAR ANALYSIS OF A CrCoMo-UHMWPE AND DLC-UHMWPE COUPLES FOR HIP PROSTHESIS

ABSTRACT In this work, a model to evaluate the abrasive wear between two semi-cylindrical entities is presented. The entities represent the average roughness radius, of the contact surfaces formed between the femoral head and acetabular cup of a hip prosthesis. The contact couples employed in this work are CrCoMo-UHMWPE and DLC-UHMWPE. Here three different interference distances were employed: 1, 2.5 and 40 percent of the mean radius roughness of the UHMWPE. The energy method proposed here determines the maximum contact stresses, from where the maximum point of distortional energy is obtained. This is then linked to the geometry of the cylindrical entity, which then gives the initial failure point. Subsequent similar calculations provide with the trajectory of the wearing path. The percentage of the abrasive wear obtained from this method was compared to Archard´s method. It was noted that the percentage of Archard's wear is a ten in million part from the total volume, while that the percentage of Energy's wear is between 2.760% and 7.055%, when an interference distance S=0.5 µm, was employed. It was also found that the CrCoMo-UHMWPE couple exhibited 22.84 % of volume lost compared with the 2.95 % of the DLC-UHMWPE couple

Continuous Improvement Process in the Development of a Low-Cost Rotational Rheometer

The rheological characterization of fluids using a rheometer is an essential task in food processing, materials, healthcare or even industrial engineering; in some cases, the high cost of a rheometer and the issues related to the possibility of developing both electrorheological and magnetorheological tests in the same instrument have to be overcome. With that in mind, this study designed and constructed a low-cost rotational rheometer with the capacity to adapt to electro- and magneto-rheological tests. The design team used the method of continuous improvement through Quality Function Deployment (QFD) and risk analysis tools such as Failure Mode and Effect Analysis (FMEA) and Finite Element Analysis (FEA). These analyses were prepared in order to meet the customer’s needs and engineering requirements. In addition to the above, a manufacturing control based on process sheets was used, leading to the construction of a functional rheometer with a cost of USD $1500