Raja Sekhar Dondapati

Parametric Evaluation of AC Losses in 500 MVA/1.1 kA High Temperature Superconducting (HTS) Cable for Efficient Power Transmission: Self Field Analysis

High Temperature Superconducting (HTS) cables are used for efficient power transmission. In the present work, AC losses in High Temperature superconducting cable due to self field with various parameters are calculated and validated with the published results. A 500 MVA / 1.1 kArms HTS transmission cable operating at 50 Hz is considered for the AC loss (self field) calculations. The major AC losses arise due to self field in the HTS cable and can be obtained by the approximated Norris equation. Two different superconducting cables, one with BSCCO and the other with YBCO tapes are considered for the present analysis. For a transport current of 1.1 kArms, the analytically calculated self field loss is 0.4 W/m (with BSCCO tape) and 0.5 W/m (with YBCO tape) respectively are comaprable with published experimental results.

Conceptual design and cooling strategies of current lead for superconducting power transmission applications

The superconducting power transmission applications requires current lead for transferring electric current from room temperature to the cryogenic environment. The current lead being made from a normal conductor requires special cooling as high density current is passed from it. In this paper, a generalized conceptual design of the current leads for all the superconducting applications is presented. This design of the current lead is derived from the past designs used in superconducting applications. A heat balance equation that governs the quenching of the lead is derived considering all the modes of heat infiltration into the lead. The whole lead has been divided into different parts so that each aspect can be emphasized upon to achieve maximum current carrying capacity with minimum cooling load. The cooling strategies adopted for maintaining the cryogenic environment inside the lead with minimum cooling load on the refrigerator are also discussed.

Enhancement of Heat Transfer in Heat Pipes Using TiO2/Benzene Based Nano-coolants

Nowadays, the world is experiencing many challenges in solving heat transfer issues in various engineering systems. However, limited approaches are available to solve such challenges. To increase heat transfer, many researchers found that the Nanofluid is one of the feasible coolant which increase the working efficiency of many engineering devices. Electronic equipment dissipates enormous amount of heat while in operation which directly affect the work efficiency. To increase the efficiency it is mandatory to remove the heat by using proper coolant. Hence, the heat pipes are employed in electronic devices to remove the heat. To enhance the heat transfer in heat pipe nano-coolants may be used. In this present work, thermophysical properties of different types of base fluids with Titanium Dioxide (TiO2) Nanoparticles have been investigated with different concentrations of Nanoparticles (1-5 % by volume) at 300K temperature. The effective thermal conductivity of Nanofluids is compared with the base fluid and the results show enhancement in thermal conductivity. The thermal conductivity of Nanofluid is increased up to 3% at 300K with 1 % by volume concentration of nanoparticles and 15% at 5% by volume of concentration as compared to Benzene (C6H6) base fluid.

Analytical approximations for temperature dependent thermophysical properties of supercritical diesel fuel surrogates used in combustion modeling

Supercritical fluid technology is introduced to combat the critical challenges related with emissions, incomplete and clean diesel fuel combustion. The chemical kinetics of diesel fuel is a strong function of temperature. As surrogate fuels have a potential to represent a real diesel fuel, thermophysical properties of such fuels have been studied in this present work as a function of temperature. Further, two diesel surrogate fuels which have been identified as the components of actual diesel fuel for jet engines are studied and thermophysical properties of these two surrogates are evaluated as a function of temperature at critical pressure. In addition, the accuracy and reliability of the developed correlations is estimated using two statistical parameters such as Absolute Average of Relative Error (AARE) and Sum of Average Residues (SAR). Results show an excellent agreement between the standard data and the correlated property values.Supercritical fluid technology is introduced to combat the critical challenges related with emissions, incomplete and clean diesel fuel combustion. The chemical kinetics of diesel fuel is a strong function of temperature. As surrogate fuels have a potential to represent a real diesel fuel, thermophysical properties of such fuels have been studied in this present work as a function of temperature. Further, two diesel surrogate fuels which have been identified as the components of actual diesel fuel for jet engines are studied and thermophysical properties of these two surrogates are evaluated as a function of temperature at critical pressure. In addition, the accuracy and reliability of the developed correlations is estimated using two statistical parameters such as Absolute Average of Relative Error (AARE) and Sum of Average Residues (SAR). Results show an excellent agreement between the standard data and the correlated property values.

Investigation on the Crack Behaviour in Kevlar 49 Based Composite Materials using Extended Finite Element Method for Aerospace Applications

Ductile to brittle transition (DTBT) is extensively observed in materials under cryogenic temperatures, thereby observing brittle failure due to the non-resistance of crack propagation. Owing to its outstanding mechanical and thermal properties, Kevlar 49 composites are widely used in aerospace applications under cryogenic temperatures. Therefore, in this paper, involving the assumption of linear elastic fracture mechanics (LEFM), mechanical characterization of Kevlar 49 composite is done using Extended Finite Element Method (X-FEM) technique in Abaqus/CAE software. Further, the failure of Kevlar 49 composites due to the propagation of crack at room temperature and the cryogenic temperature is investigated. Stress, strain and strain energy density as a function of the width of the Kevlar specimen is predicted, indicates that Kevlar 49 composites are suitable for use under cryogenic temperatures.

Thermal Analysis on Thrust Pad Bearing with Non-Newtonian Lubricant

Hydrodynamic pad thrust bearings are widely used, due to their low friction, good load carrying capacity and high damping characteristics, in high speed rotating machines, such as pumps, compressors, turbines, turbo generators. However, the need for high load bearing capabilities and compactness of the thrust pad bearings has attracted the attention of engineers. The design of such thrust pad bearings involves selection of bearing materials, lubricants and operating conditions. As the performance of lubricants plays a vital role in the life cycle of bearings, thus the present work examines the thermophysical properties of non-Newtonian surrogate lubricants. The lubricant properties at different temperatures were extracted from NIST- Supertrapp ® and a correlation is developed which is further used in the computational analysis of thrust pad bearing. A steady state thermal analysis is done on the thrust pad bearings which are modeled and meshed in ANSYS ® 14.5. It was observed that the temperature variation on the outer surface to be varying linearly whereas a non-linear variation has been identified at inner surface of a pad in a thrust pad bearing initiating thermal stresses. Moreover, these thermal stresses may contribute finally to the reduction in performance with respect to wearing of pads. The present work also focuses on temperature dependent thermophysical properties on the temperature distribution of thrust pad bearings.

Effect of Varying Inter-Implant Distance in a Two Implant-Three Prosthetic Unit Dental System: A Finite Element Analysis Study

The objective of this study was to calculate the stress produced at the implants as well as at the bone-implant interface under axial or vertical, oblique and para-axial loading due to different distances between the implants using FEA. Research was carried out on a two implant-three prosthesis unit system. Modeling of each component was done in CAM software SOLIDWORKS. After the assembly was done, ANSYS 14.0 was used for the finite element analysis. Material properties were assigned to every component and all the loading conditions were applied individually. Von Mises stress values have been evaluated at the implants and the jawbone. Since the jawbone is made up of cortical and cancellous bone, stresses were calculated on both of them individually. Our study revealed that oblique loading was the most critical loading followed by para-axial and axial loading, maximum stresses were produced in the prosthesis followed by implants, cortical bone and cancellous bone. Moreover the buccal side of the entire system was more affected than the lingual side.