Secondary Heat Source Research Articles

A mixed solution for the three-dimensional temperature distribution in turning inserts using finite and boundary element techniques

It is an established fact that critical thermal aspects would have a significant influence on any metal cutting process. The possible improvement in the overall efficiency that might arise out of any refinements in the thermal fields would naturally attract the attention of the industry. At the same time, the very complex nature of the problem poses serious problems when the true influence of the critical parameters is sought for. While the numerous analytical, experimental and numerical investigations reported earlier show the interest and challenges associated with the process, it appears there is still some scope for further research and refinement. This paper presents another method of solving the thermal fields of metal cutting tools combining certain classical techniques suggested in the past with some relatively new methods of the continuum approach. The moving work piece and the chip are considered as one domain and the stationary cutting tool as another domain to simulate the material flow conditions. The iterative solution sufficiently takes care of the distribution of the primary and secondary heat sources and the need to assume a heat partition coefficient is eliminated. A mixed finite element and boundary element method finally enables the estimation of the cutting temperatures. While the thermal fields analysed in carbide turning inserts show considerable amount of agreement with previous data, the approach seems to be quite simple and reliable and can be readily applied to any metal cutting problem.

Parameterization of solar heating by the near IR CO 2 bands in the mesosphere

Absorption of solar energy by CO 2 bands at wavelengths shorter than 5 μm provides a secondary source of heating in the mesosphere. This source is essential between 65 and 85 km where it can exceed 1 K/day and contribute up to 30 % to the total solar heating, provided the mesospheric ozone heating has a local minimum in this region. A proper calculation of the solar heating in the near-infrared CO 2 bands involves consideration of complicated NLTE processes in the CO 2 molecule. This circumstance and the relatively small energy effect account for the absence of parameterizations for the near-infrared CO 2 solar heating in the mesosphere suitable for use in GCMs. In this paper we present what we believe is the first such parameterization. It has been developed for use in GCMs as a daytime correction to the 15 μm CO 2 band cooling previously parameterized only for nighttime conditions. At any given height level this parameterization has an explicit dependence on both the volume mixing ratio of CO 2 at the altitude in question and the CO 2 column density along the solar radiation path. Dependence on a variety of other parameters is quite complicated but of less importance and has been taken into account through statistics. The accuracy of the parameterization is examined for a wide variety of atmospheric conditions. Between 70 and 80 km, where the near-infrared CO 2 solar heating is of the most importance, the error of daily averaged values of this heating does not generally exceed 0.1 K/day or less than 10 %.

Cutting forces modeling considering the effect of tool thermal property—application to CBN hard turning

Force modeling in metal cutting is important for a multitude of purposes, including thermal analysis, tool life estimation, chatter prediction, and tool condition monitoring. Numerous approaches have been proposed to model metal cutting forces with various degrees of success. In addition to the effect of workpiece materials, cutting parameters, and process configurations, cutting tool thermal properties can also contribute to the level of cutting forces. For example, a difference has been observed for cutting forces between the use of high and low CBN content tools under identical cutting conditions. Unfortunately, among documented approaches, the effect of tool thermal property on cutting forces has not been addressed systemically and analytically. To model the effect of tool thermal property on cutting forces, this study modifies Oxley’s predictive machining theory by analytically modeling the thermal behaviors of the primary and the secondary heat sources. Furthermore, to generalize the modeling approach, a modified Johnson–Cook equation is applied in the modified Oxley’s approach to represent the workpiece material property as a function of strain, strain rate, and temperature. The model prediction is compared to the published experimental process data of hard turning AISI H13 steel (52 HRc) using either low CBN content or high CBN content tools. The proposed model and finite element method (FEM) both predict lower thrust and tangential cutting forces and higher tool–chip interface temperature when the lower CBN content tool is used, but the model predicts a temperature higher than that of the FEM.

High-Power CO2 Laser Welding Characteristics of Hot Steel Samples.

The present paper describes experimental results of the high power laser welding characteristics of hot steelsamples. Using laser induced plasma as a secondary heat source, the penetration depth of 1000°C steelsamples improve about 30% compared to that of room temperature samples. The maximum depth is 38mmat lm/min welding velocity using 40 kW power. A beam weaving method is adopted to enlarge bead width without degrading fusion efficiency. It is also effective for suppressing bead depth deviation.

Effect of mechanical tissue properties on thermal damage in skin after IR-laser ablation

The damage created instantaneously in dorsal skin and in the subjacent skeletal muscle layer after CO2 and Er3+ laser incisions is histologically and ultrastructurally investigated. Light microscopical examinations show an up to three times larger damage zone in the subcutaneous layer of skeletal muscle than in the connective tissue above. The extent of thermally altered muscle tissue is classified by different zones and characterized by comparison to long time heating injuries. The unexpectedly large damage is a result of the change of elastic properties occurring abruptly at the transition between different materials. This leads to a discontinuity of the cutting dynamics that reduces the ejection of tissue material. We show that the degree of thermal damage originates from the amount of hot material that is not ejected out of the crater acting as a secondary heat source.

Thermal structure of accreting neutron stars and strange stars

view Abstract Citations (78) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Thermal Structure of Accreting Neutron Stars and Strange Stars Miralda-Escude, J. ; Haensel, P. ; Paczynski, B. Abstract Steady-state models of accreting neutron stars and strange stars are presented, and their properties as a function of accretion rate are analyzed. The models have steady-state envelopes, with stationary hydrogen burning taken into account, the helium shell flashes artificially suppressed, and the crust with a large number of secondary heat sources. The deep interiors are almost isothermal and are close to thermal equilibrium. A large number of models were calculated for many values of the accretion rates, with ordinary, pion-condensed, and strange cores, with and without secondary heat sources in the crust, and with the heavy element content of the accreting matter in the range Z = 0.0002-0.02. All models show a similar pattern of changes as the accretion rate is varied. For low accretion rates, the hydrogen burning shell is unstable; for intermediate rates, the hydrogen burning shell is stable, but helium burning is not; for high rates, the two shell sources burn together and are unstable. Publication: The Astrophysical Journal Pub Date: October 1990 DOI: 10.1086/169295 Bibcode: 1990ApJ...362..572M Keywords: Neutron Stars; Steady State; Stellar Interiors; Stellar Mass Accretion; Stellar Models; Temperature Distribution; Cobalt Isotopes; Heat Sources; Helium; Hydrogen; Iron Isotopes; Nickel Isotopes; X Rays; Astrophysics; STARS: ACCRETION; STARS: INTERIORS; STARS: NEUTRON; X-RAYS: BURSTS full text sources ADS |

A model of the solar chromosphere-corona transition region based on classical thermal conduction

view Abstract Citations (40) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Model of the Solar Chromosphere-Corona Transition Region Based on Classical Thermal Conduction Athay, R. Grant Abstract A hot corona cooled by inward thermal conduction very likely results in a transition region whose isotherms follow a highly roughened surface. Assuming a checkerboard of cool peaks and hot valleys in surfaces of constant temperature and using the observed emission measure at T = 60,000 K, the ratio of the mean height of the cool peaks to the mean separation of peaks and valleys has a value of 160. By allowing nearly all of the parallel conduction flux of 1 million ergs/sq cm per sec at 1 million K in the hot valleys to flow across magnetic field lines into the cool peaks, a predicted emission measure in very good agreement with the low-temperature branch of the observed emission measure, including the Ly-alpha region, is found. This purely conductive model has the advantages of explaining both the observed emission measure curve and the wide vertical extent of the transition region at the limb without introducing ad hoc secondary heat sources. Publication: The Astrophysical Journal Pub Date: October 1990 DOI: 10.1086/169272 Bibcode: 1990ApJ...362..364A Keywords: Chromosphere; Solar Atmosphere; Solar Corona; Surface Roughness; Thermal Conductivity; Heat Sources; Lyman Alpha Radiation; Magnetic Field Configurations; Solar Magnetic Field; Solar Physics; SUN: ATMOSPHERIC MOTIONS; SUN: TRANSITION REGION full text sources ADS |

Residential wood burning and air pollution

The use of wood as a primary or secondary source of residential heating has been increasing rapidly in Australia, U.S.A., and elsewhere since the early 1970s. This sharp increase in wood burning is having a detrimental impact on air quality, the effects being quite acute in some areas. The emissions normally include particulates, organic compounds, polycyclic organic materials, nitrogen oxides, sulphur oxides, and carbon monoxide. The nature and amounts of compounds emitted into the atmosphere are highly variable and depend on many factors such as fuel type, operating conditions, and combustor designs. Concerned by the health implications of wood smoke, a number of environmental agencies and research groups are working towards characterizing and quantifying emissions and to identify the factors affecting emissions. This paper reviews the literature available to date, which is quite extensive, and presents information pertinent to the different pollutional aspects of wood burning.

Theory of current-direction dependence of normal-zone propagation velocity in multifilamentary composite conductors

We develop a theory for the current-direction dependence of the normal-zone propagation velocity observed in multifilamentary composite superconductors. Normal-zone propagation is known to be driven primarily by Joule heating in both the normal zone and the current-sharing zone, which lies between the normal (T>T c ) and superconducting (I c ) zones. We show, however, that the Peltier effect is an important secondary source of heating and cooling in the current-sharing zone and accounts for essentially all of the current-direction dependence of the normal-zone propagation velocity observed in a Nb 3 Sn/Cu composite conductor. For one current direction Peltier heat is deposited in the current-sharing zone, thereby adding to the Joule heat and increasing the normal-zone propagation velocity, while for the other current direction Peltier heat is absorbed, thereby cooling the current-sharing zone and thus decreasing the normal-zone propagation velocity. Contrary to the claim of Gurevich and Mints, we find that the Thomson effect is about an order of magnitude too small to account for the current-direction dependence observed in a Nb 3 Sn/Cu composite conductor.

Convective heat transfer enhancement produced by secondary heat sources in a liquid nitrogen pool

This paper studies the influence of secondary heat sources on the convective heat transfer from a vertical cylindrical heater immersed in a LIN pool. Two types of secondary heat source have been used. In the first case, the heat leak through the vessel walls into the pool was varied without causing nucleation, so as to retain convective heat transfer. It was found that the convective flow loops induced in the pool produced a small enhancement of the heat transfer from the cylindrical heater. In the second case, a small horizontal heater loop was introduced into the pool below the cylindrical heater. The secondary heat flux used was such that boiling occurred at the loop to give rising bubbles surrounding the cylindrical heater. This produced a large enhancement of the convective heat transfer from the cylindrical heater. The enhancement ratio is presented as a function of the power supplied to the loop heater.

Druhotné zdroje tepla v pivovarsko-sladařském průmyslu.

Pivovarsko-sladařský průmysl je velmi náročný na spotřebu tepla, jejíž trend stoupá v souvislosti se zvyšováním výroby, zaváděním nových technologií i mechanizací a automatizací procesů. Autor diskutuje, převážně na podkladě vlastních měření, dosažitelné možnosti maximálních úspor ve varnách a teplovodních hospodářství pivovarů a u sladovnických hvozdů, využitím tepla brýdových par, kondenzátů a spalin.