Finite Difference Thermal Analysis Research Articles

Numerical thermal analysis of synchronous reluctance generator for wind energy application

AbstractThis paper focuses on the thermal analysis of the synchronous reluctance generator with a rating of 2.1 kW. It mainly uses explicit, and implicit finite difference methods for thermal analysis to reduce the complexity of thermal calculation for the machine's components. It compares the results with the results obtained using a finite element analysis (FEA) and includes the experimental verification of the obtained results. The explicit, and implicit finite difference thermal analysis is relatively simple and computationally fast. Once the design parameters are known, the electric losses and iron losses of the synchronous reluctance generator are evaluated. These machine parameters are utilized in developing the explicit finite difference (EFD), an implicit finite difference (IFD), and a 3D FEA model for thermal analysis. It is observed that the obtained results from the EFD, IFD, FEA, and experiments are very close to each other, and the temperature rise for the designed machine is within the desired and acceptable range.

Sliding Friction and Heat Generation in Pressurized U-Cup Seals Under Low-Speed Reciprocating Conditions

A test apparatus was designed and constructed to investigate the friction and heat generation characteristics of sliding polymeric U-cup seals used in high-pressure nitrogen gas springs. Tests were run at three speeds; and friction and temperature data were obtained. Seal specimens were examined under a scanning electron microscope before and after each test. Evidence of degradation and thermal softening of the seal material was found for the highest relative speed tests where elevated temperatures were measured. In addition, a semi-empirical transient finite-difference thermal analysis of the rod and the high-pressure chamber in the test apparatus was also developed. Numerical simulations of the three tests were performed using measured friction force data, and temperature predictions from the model were compared with those measured at different locations in the test apparatus. Predicted values exhibited reasonable agreement with the measured values, particularly under steady-state conditions. The variations observed for certain transient conditions appeared to be due to overestimated convective heat transfer coefficients at lower speeds, and due to the transient nature of thermal resistances between the seal cartridge and the high-pressure chamber, which may vary with a change in temperature.

Thermal modeling of electrical contacts in switches and relays

A thermal modeling procedure has been developed to calculate the temperature distribution of components in complex three-dimensional (3-D) switches and relays. The methods developed for dissecting the components, treating of thermal interaction among the components, and calculating of interface thermal resistance are reported. In particular, the knowledge of electrical "a-spot" is used to estimate solid-solid contact area and void area. The void areas do not contribute to electrical conductivity but do contribute to thermal conductivity. The method is used to more accurately estimate the interface thermal resistance which is very important in any thermal analysis program. Actual switches and relays were modeled using finite difference thermal analysis, and the results matched well with measured temperatures.

A thermal analysis for the use of cooled rotating drums in electron processing

The thermal response of rotating drums under an electron beam has been analyzed using a finite difference thermal analysis computer code. Rotating drums are used to convey thin webs or films under the electron beams while controlling their temperature and, in some cases, in dissipating the exotherm involved in curing coatings applied to them. Each portion of the drum surface receives one heat pulse per rotation as it passes under the beam. The drum's thermal behavior shows both an immediate response to each heat pulse and a more gradual response to the average heat acquired over many pulses. After many rotations a steady state is reached where there is only an immediate response to each heat pulse but the gradual heating has tapered off. Nevertheless the steady state temperatures are strongly dependent on the gradual heating that led to them. Slow and fast speeds of rotation are compared showing the effects of both gradual and immediate heating components. The thermal analysis is extended to include the coolant fluid inside the drum shell and the web on the drum surface. The coolant's incoming temperature, volumetric flow rate, flow speed through the coolant channels and film coefficient between the outer shell and fluid are all included in the analysis. The small air gap between the web and drum, the convective cooling of the web to the ambient air, and the exothermic reaction of any chemical reactions on the web are included. The stresses produced in the drum shell (i.e. between the outer surface and the temperature-controlling fluid within the drum) are analyzed in order to define safe e-beam powers and rotating speeds. The analysis provides the basis for many design decisions and can give an end-user a full temperature history for his product for any set of conditions.

Shuttle Entry Air Data System preflight testing and analysis

Data from the Shuttle Entry Air Data System (SEADS) port arcjet test were correlated using conventional finite difference thermal analysis methods to demonstrate the applicability of such methods to flight analyses. The arcjet tests were conducted to demonstrate the integrity of the SEADS-coated columbium port and provide data required to accomplish SEADS preflight analysis. The successful correlation of the results from finite difference thermal analysis methods and the test data demonstrated these methods for flight analysis. Using these techniques, a preflight analysis of the SEADS was performed and it was concluded that the maximum port temperature will be at a safe level for the first SEADS mission.

Nonisothermal Axisymmetric Forging

An approximate solution for nonisothermal upset forging is presented. A finite difference thermal analysis and an upper-bound deformation solution are used for this purpose. The thermal analysis is for a homogeneous state of strain, it ignores deformation heating, but accounts for all modes of heat flow during the transfer of the billet to the tooling and throughout the deformation. The upper-bound solution is based on admissible velocity field equations, the recorded temperature data from the thermal analysis, and constitutive equations for temperature, strain, and strain rate-dependence of flow stress. The size of the chilled zone is determined by minimization of total power for the deformation process. Theoretical predictions for load-displacement behavior and the size of the chilled zone are compared with the experimental results for 304 stainless and AISI 1042 steels.

Use of graphite in Langmuir-calorimeter probe heads

Graphite has become an important material in magnetically confined fusion devices, being used for components such as limiter blades, divertor plates, and Faraday shields. Langmuir-calorimeter probes on the tokamak fusion test reactor (TFTR) and the Princeton large torus (PLT) have utilized graphite in probe heads, active elements, protective shields, and in an epoxy compound for various applications. Most recently, all-graphite edge probes have been used successfully on these machines. The advantages and disadvantages of using this material as a collecting element and a heat resistant support are discussed, with reference to its survivability and usefulness in the TFTR environment. A three-dimensional finite difference thermal analysis of a TFTR graphite calorimeter is presented which calculates its temperature response to selected power inputs. This was used to estimate power densities at the edge of TFTR plasmas.

Degradation in Strength of Laminated Composites Subjected to Intense Heating and Mechanical Loading

An analytical procedure is presented for predicting the loss in integrity of composite structures subjected to simultaneous intense heating and applied mechanical loads. An in tegral part of the method is a nonlinear, two-dimensional, finite difference thermal analysis which considers the effects of surface ablation, re-irradiation losses, and temperature-dependent thermophysical properties. Another important feature of the structural survivability model is a flat-plate finite element code, based on the Mindlin theory, which is coupled to a maximum stress failure criterion. Predictions from the analysis methodology are compared with experimental results obtained on 24, 48, and 96 ply graphite epoxy tension specimens which were spot-irradiated at various intensity levels.