Numerical evaluation of expansion loops for pipe subjected to thermal displacements

The thermal expansion can lead to the high stress on the pipe. The problem can be overcome using expansion loops in a certain length depending on the material’s elastic modulus, diameter, the amount of expansion, and the pipe’s allowable stresses. Currently, there is no exact definition for the dimension of expansion loops design both for loop width (W) and loop footing height (H) sizes. In this study, expansion loops were investigated with using ratio of width and height (W/H) variations to understand pipe stress occurring on the expansion loops and the expansion loops’ safety factor. Relationship between non dimensional stress on the expansion loop pipe was studied numerically by finite element software on several working temperatures of 400oF, 500oF, 600oF, and 700oF. It can be found that stress occurring on the pipes increases as the increases of W/H of the expansion loops and results in a lower safety factor. The safety factor of the expansion loops pipe has a value of 1 when the ratio of loop width and loop footing height (W/H) value was 1.2 for a 16-inch diameter pipe. Stress occurring on the pipe increases with the increase of the working temperature. Expansion loops pipe designed for 400oF can still work well to handle thermal extension pipe occurring on 500oF.

EXAMINATION OF HEAT PIPE BASED SYSTEMS FOR ENERGY-EFFICIENT REDUCTION OF THERMALLY INDUCED ERRORS IN MACHINE TOOLS

Variable heat sources in machine tools lead to unsteady displacement fields and hence necessitate temperature control in order to maintain the required positioning accuracy. Adding passive components that redistribute heat through heat storage and heat transport within the machine tool is one approach to compensate for thermal errors. While including latent heat storage components reduces the machine response to heat inputs in a certain temperature range, highly conductive elements like heat pipes provide the option to transport heat losses to environmental air or further components. Thereby, the temperature field around heat emitting machine components can be altered aiming for a reduction of thermal displacements of the tool center point. In order to guarantee the efficacy of corresponding compensation systems in machine tools, the performance of heat pipes under accelerating forces has to be determined. The present paper presents findings of experimental investigations on translationally moved heat pipes conducted on a linear direct drive based test rig. A simulation approach for modeling the heat transfer limits of heat pipes is proposed providing a high compatibility with finite element models. Different scenarios for the use of heat pipes in machine tools are demonstrated and evaluated by means of numerical results.

SMART SENSOR FOR ENHANCEMENT OF A MULTI-SPINDLE AUTOMATIC LATHE THERMAL ERROR COMPENSATION MODEL

The development of a smart sensor is proposed to improve the thermal error compensation model of a multi-spindle automatic lathe. The smart sensor is capable of gathering real-time information about rotating spindle drum temperatures. Thereafter, the temperature obtained by the smart sensor is applied as input to the thermal error compensation model based on the transfer function instead of an indigenous temperature measured on the stationary part of the multi-spindle automatic lathe. Using spindle drum temperature as the model input increases the prediction of thermal displacements in the X-axis by 16%.

First-Principles Study on Lattice Dynamics and Thermal Conductivity of Thermoelectric Intermetallics Fe3Al2Si3

Thermoelectric materials have been expected as a critical underlying technology for developing an autonomous power generation system driven at near room temperature. For this sake, Fe3Al2Si3 intermetallic compound is a promising candidate, though its high lattice thermal conductivity is a bottleneck toward practical applications. Herein, we have performed the first-principles calculations to clarify the microscopic mechanism of thermal transport and establish effective ways to reduce the lattice thermal conductivity of Fe3Al2Si3. Our calculations show that the lowest-lying optical mode has a significant contribution from Al atom vibration. It should correspond to large thermal displacements Al atoms. However, these behaviors do not directly cause an increase of the 3-phonon scattering rate. The calculated lattice thermal conductivity shows a typical temperature dependence and moderate magnitude. From the calculated thermal conductivity spectrum and cumulative thermal conductivity, we can see that there is much room to reduce the lattice thermal conductivity. We can expect that heavy-element doping on Al site and controlling fine microstructure are effective strategies to decrease the lattice thermal conductivity. This work suggests useful information to manipulate the thermal transport of Fe3Al2Si3, which will make this material closer to practical use.

Features of the High-Temperature Structural Evolution of GeTe Thermoelectric Probed by Neutron and Synchrotron Powder Diffraction

Among other chalcogenide thermoelectric materials, GeTe and derivative alloys are good candidates for intermediate temperature applications, as a replacement for toxic PbTe. We have prepared pure polycrystalline GeTe by using arc-melting, and investigated its structural evolution by using neutron powder diffraction (NPD) and synchrotron X-ray diffraction (SXRD), as well as its correlation with the thermal variation of the Seebeck coefficient. Besides a significant Ge deficiency (~7% Ge vacancies), the thermal evolution of the unit-cell volume and Ge-Te bond lengths in the rhombohedral phase (space group R3m), below 700 K, show unexpected anomalies involving the abrupt Ge-Te bond lengthening accompanied by increased Te thermal displacements. Above 700 K, the sample is cubic (space group Fm-3m) and shows considerably larger displacement parameters for Ge than for Te, as a consequence of the random distribution of the lone pair lobes of Ge2+. The Seebeck coefficient, reaching 120 μV K−1 at 775 K, shows a shoulder in the 500–570 K region that can be correlated to the structural anomaly, modifying the electron-phonon scattering in this temperature range.

Spatially Resolving Anharmonic Lattice Dynamics in Molecular Crystals With X-Ray Diffraction and Terahertz Spectroscopy

<div><div><div><div><p>The combination of X-ray diffraction and low-frequency vibrational spectroscopy has proven to be a powerful method for understanding the relationship between molecular and crystalline structures, dynamics, and the properties of materials. In this work, we show how information obtained from terahertz time-domain spectroscopy (THz-TDS) measurements, coupled with first-principles simulations including anharmonic effects, is able to reconcile specific vibrational motions to the experimentally observed large- amplitude thermal displacements in a pair of isomeric molecular crystals. In particular, we show that a single terahertz mode is responsible for the observed structural data, and provide a framework for predicting and interpreting the origins of related phenomena.</p></div></div></div></div>

Resolving Anharmonic Lattice Dynamics in Molecular Crystals With X-Ray Diffraction and Terahertz Spectroscopy

<div><div><div><div><p>The combination of X-ray diffraction and low-frequency vibrational spectroscopy has proven to be a powerful method for understanding the relationship between molecular and crystalline structures, dynamics, and the properties of materials. In this work, we show how information obtained from terahertz time-domain spectroscopy (THz-TDS) measurements, coupled with first-principles simulations including anharmonic effects, is able to reconcile specific vibrational motions to the experimentally observed large- amplitude thermal displacements in a pair of isomeric molecular crystals. In particular, we show that a single terahertz mode is responsible for the observed structural data, and provide a framework for predicting and interpreting the origins of related phenomena.</p></div></div></div></div>

DEFINITION OF THERMAL DISPLACEMENTS IN SHAPING OF MANUFACTURING EQUIPMENT UNITS

The paper is devoted to the development of a method for the thermal displacement definition of spindle units having the most significant impact upon parameter reliability of manufacturing equipment used in modern mechanical engineering. Investigation methods: thermal displacement measurements of spindle units at fixed timing according to a special procedure; the approximation of thermal displacement functions obtained in an experimental way by a polynomial of the fourth degree through the least-squares method with the factor computation based on the use of matrix factorization. On the basis of experimental and theoretical investigations there is formed a semi-empirical polynomial mathematical model for the thermal displacement definition of spindle units in manufacturing equipment by a calculation method.