Todd A. Jankowski

Development and Validation of a Thermal Model for Electric Induction Motors

A transient lumped-parameter thermal model of an induction motor is developed. The energy balances and the expressions for the appropriate node couplings representing conduction and convection heat transfer between nodes, as well as the expressions for the heat capacity of each node, are presented. We also present expressions used in a Second Law analysis to calculate the entropy generation and exergy destruction rates at each node. An overall Second Law efficiency for heat transfer through the motor is then defined. The model is validated by comparing calculated temperatures with experimental data for a motor driving an electric submersible pump, showing that the lumped-parameter approximation is sufficient to accurately calculate temperature distributions in the motor and to capture temperature changes during warm-up and cooldown. Finally, the Second Law analysis is used to determine which components in the motor are contributing most to the inefficiency of the heat transfer process, providing a diagnostic tool for identification of areas in the motor where potential heat transfer enhancements would be most beneficial.

Laminar flow in a porous channel with large wall suction and a weakly oscillatory pressure

The laminar oscillatory flow inside a rectangular channel with wall suction is considered here. The scope is limited to large suction imposed uniformly along the permeable walls. Inside the channel, the onset of small amplitude pressure disturbances produces an oscillatory field that we wish to investigate. Based on the normalized pressure-wave amplitude, the conservation equations are linearized and split into leading-order (steady) and first-order (time-dependent) equations. The first-order set is subdivided into an acoustic, pressure-driven, wave equation, and a vortical, boundary-driven, viscous equation. For longitudinal pressure oscillations, both equations are written to the order of the wall suction Mach number. The resulting equations are then solved in an exact fashion. The novelty lies in the vortical response that reduces to a Weber equation following a Liouville–Green transformation. The emerging rotational solution is expressible in terms of confluent hypergeometric functions of the suction ...

Vortical and acoustical mode coupling inside a porous tube with uniform wall suction

This paper considers the oscillatory motion of gases inside a long porous tube of the closed-open type. In particular, the focus is placed on describing an analytical solution for the internal acoustico-vortical coupling that arises in the presence of appreciable wall suction. This unsteady field is driven by longitudinal oscillatory waves that are triggered by small unavoidable fluctuations in the wall suction speed. Under the assumption of small amplitude oscillations, the time-dependent governing equations are linearized through a regular perturbation of the dependent variables. Further application of the Helmholtz vector decomposition theorem enables us to discriminate between acoustical and vortical equations. After solving the wave equation for the acoustical contribution, the boundary-driven vortical field is considered. The method of matched-asymptotic expansions is then used to obtain a closed-form solution for the unsteady momentum equation developing from flow decomposition. An exact series expansion is also derived and shown to coincide with the numerical solution for the problem. The numerically verified end results suggest that the asymptotic scheme is capable of providing a sufficiently accurate solution. This is due to the error associated with the matched-asymptotic expansion being smaller than the error introduced in the Navier-Stokes linearization. A basis for comparison is established by examining the evolution of the oscillatory field in both space and time. The corresponding boundary-layer behavior is also characterized over a range of oscillation frequencies and wall suction velocities. In general, the current solution is found to exhibit features that are consistent with the laminar theory of periodic flows. By comparison to the Sexl profile in nonporous tubes, the critically damped solution obtained here exhibits a slightly smaller overshoot and depth of penetration. These features may be attributed to the suction effect that tends to attract the shear layers closer the wall.

FLOW OF SATURATED LIQUID NITROGEN THROUGH MICRO-SCALE ORIFICES

The flow of saturated liquid nitrogen through micro-scale orifices has been characterized experimentally. Measurements of pressure drop and flow rate were made with liquid nitrogen flowing through orifices ranging in diameter from 50 micron to 370 micron, with orifice length-to-diameter ratios ranging from 1.5 to 10. The design of the experimental apparatus, the instrumentation used, and the experimental uncertainties are presented. Obstacles encountered while attempting to obtain repeatable and reliable results at cryogenic temperatures are discussed. Finally, experimentally measured discharge coefficients are shown to agree with a model for single-phase liquid flow through micro-orifice tubes.

Apparatus for Testing Rotating Heat Pipes

*† ‡ A test apparatus, that will be used to study the heat transfer performance of rotating heat pipes, has been designed and built. The apparatus allows for simultaneous testing of a pair of crank-shaped rotating heat pipes operating near room temperature. The test rig is designed to support heat pipes with an on-axis rotating condenser section, an off-axis eccentrically rotating evaporator section, and a curved adiabatic section. Due to the length of the heat pipes (55”), the distance from the axis of rotation to the off-axis evaporator section (9.5”), and the maximum rotation speed (5500 rpm), care had to be taken in the design of a substantial support structure for the heat pipes, the selection of a drive system, and the design of the mounting frame. These design issues, as well as safety considerations associated with the test apparatus, are discussed here. Preliminary test data for stationary and low-speed tests are also presented.

Long Term Vacuum Maintenance in HTS Equipment without External Pumping

High temperature superconducting (HTS) devices being developed, such as motors, generators, and electric power transmission cables, are intended to replace conventional, room temperature equipment. As such, the cryogenic and vacuum operation of this equipment has to be nearly transparent to ensure market acceptance. The cryostat has to deliver a stable operating temperature requiring little or no maintenance for a period of years. To maintain a nearly constant and low heat load on the refrigeration system, the vacuum must be kept at less than about 7 mPa (5 × 10−5 torr), preferably with no external pumping system. This, in turn, requires the use of low outgassing materials, and adsorbers or getters that can effectively remove the residual gasses in the system. Each particular device differs in the system volume, the materials used, the fabrication and degassing techniques, the operating temperatures of the various components, and the availability and maintenance requirements, necessitating an individual a...

A ROTATING HEAT PIPE FOR COOLING OF SUPERCONDUCTING MACHINES

A curved rotating heat pipe for use in superconducting motor and generator applications is introduced here. The heat pipe shown here is built so that both the condenser and evaporator sections are parallel to the axis of rotation. The condenser section is concentric with the axis of rotation while the evaporator section can be placed in contact with off-axis heat sources in the rotating machine. The geometry is achieved by incorporating an S-shaped curve between the on-axis rotating condenser section and the off-axis revolving evaporator section. We show that because the heat pipe is a sealed, passive heat transfer device with nearly isothermal operation, the heat pipe concept may be advantageous when considering the overall refrigeration system used with the superconducting machine. High-speed, room temperature test data with this heat pipe geometry indicate that the working fluid in the heat pipe continued to circulate, resulting in heat transfer with a high effective thermal conductivity, with the heat...

Oscillatory Viscous Flow in a Porous Channel with Arbitrary Wall Suction

This paper considers a porous channel in which a suction-driven flow is modulated by arbitrary levels of fluid extraction acting uniformly along its porous boundaries. When small longitudinal oscillations are enabled, a rotational wave motion is established that this study attempts to explore. For an elongated channel, two asymptotic methods are used. The first technique is based on a two-variable multiple-scale expansion that takes into account the thin boundary layer near the wall. While retaining generality of expression, the multiplescale procedure is carried out until a closed-form solution for the velocity field is obtained for an arbitrary mean-flow function F. An alternative approach based on WKB exponentials is also employed. The WKB expansion is then pursued to arbitrary order. These asymptotic formulations are shown to agree with one another and with numeric simulations of the problem for three specific cases of F.

Imposition of Oscillatory Waves inside a Cylindrical Tube with Large Wall Suction

This study considers the laminar oscillatory flow in a porous tube with uniform wall suction. For a low aspect ratio tube, the time-dependent governing equations are decomposed following a regular perturbation of the dependent variables. The method of matched-asymp totic expansions is then used to obtain a solution for the unsteady momentum equation developing from flow decomposition. The numerically verified end results suggest that the asymptotic scheme is capable of providing a sufficiently accurate solution. This is due to the error associated with the matched-asymptotic expansion being smaller than the error introduced while linearizing the Navier-Stokes equations. A basis for comparison is established by examining the evolution of the oscillatory field in both space and time. The corresponding boundary-layer behavior is also characterized over a range of oscillation frequencies and wall suction velocities. In general, the current solution is found to exhibit features that are consistent with the laminar theory of periodic flows. By comparison to the exact Sexl profile established in nonporous tubes, the current critically-damped solution exhibits a slightly smaller overshoot and depth of penetration. These features may be attributed to the suction effect that tends to attract the shear layers closer the wall.

Electromagnetic Stirring of Plutonium Metal Part I: Theoretical Calculations and System Design (LA-UR-13-23071)

Currently one difficulty presented in the induction melting and casting of Pu is stirring of the metal during melting. Stirring is typically performed mechanically by an operator, who plunges a stir rod into the melt, or by a complex mechanical system. These methods have several inherent problems; vacuum degradation associated with mechanical actuation through containment and plunging of impurity rich skull back into the melt which has been shown to introduce casting defects.