Internal Heat Sink Research Articles

Heat transfer characteristic of oil shale particle during the retorting

The heat transfer occurring within oil shale particle is a dominant fundamental cause affecting shale oil yield and energy consumption of industrial oil shale retorts. For exploring this property, the shape of crushed Gonglangtou oil shale particle is first investigated, showing very obvious platy structure especially in the equivalent diameter range of 4–25mm. So, it is more appropriate to describe oil shale particle with thin rectangle model. And then, a mathematical heat transfer model is developed to analyze the thermal behavior within oil shale particle in the process of the retorting, incorporating the pyrolytic heat as an internal heat sink. Previous experimental data are applied to validate this model. Furthermore, the central temperature history and heating time of oil shale particles with different sizes are predicted at various heating rates using this heat transfer model, showing that platy structure characteristic offers an important role for the heat transfer process and even for the particle fragmentation. In order to improve retorting efficiency and reduce energy loss, it is recommended at last that the residence time of oil shale in the retorting reactors should fully consider the heating time of oil shale particle.

Superimposition of Elementary Thermodynamic Cycles and Separation of the Heat Transfer Section in Energy Systems Analysis

In a wide variety of thermal energy systems, the high integration among components derives from the need to correctly exploit all the internal heat sources by a proper matching with the internal heat sinks. According to what has been suggested in previous works to address this problem in a general way, a “basic configuration” can be extracted from the system flowsheet including all components but the heat exchangers, in order to exploit the internal heat integration between hot and cold thermal streams through process integration techniques. It was also shown how the comprehension of the advanced thermodynamic cycles can be strongly facilitated by decomposing the system into elementary thermodynamic cycles which can be analyzed separately. The advantages of the combination of these approaches are summarized in this paper using the steam injected gas turbine (STIG) cycle and its evolution towards more complex system configurations as an example of application. The new concept of “baseline thermal efficiency” is introduced to combine the efficiencies of the elementary cycles making up the overall system, which demonstrates to be a useful reference to quantify the performance improvement deriving from heat integration between elementary cycles within the system.

A uniform source-and-sink scheme for calculating thermal conductivity by nonequilibrium molecular dynamics

A uniform source-and-sink (USS) scheme, which combines features of the reverse [F. Müller-Plathe, J. Chem. Phys. 106, 6082 (1997)] and improved relaxation [B. Y. Cao, J. Chem. Phys. 129, 074106 (2008)] methods, is developed to calculate the thermal conductivity by nonequilibrium molecular dynamics (NEMD). The uniform internal heat source and sink are realized by exchanging the velocity vectors of individual atoms in the right half and left half systems, and produce a periodically quadratic temperature profile throughout the system. The thermal conductivity can be easily extracted from the mean temperatures of the right and left half systems rather than by fitting the temperature profiles. In particular, this scheme greatly increases the relaxation of the exited localized phonon modes which often worsen the calculation accuracy and efficiency in most other NEMD methods. The calculation of the thermal conductivities of solid argon shows that the simple USS scheme gives accurate results with fast convergence.

Penetrative convection via internal heating in anisotropic porous media

Penetrative convection in an anisotropic porous medium is simulated via internal heating. We consider both internal heat sources and sinks, where the porous medium has constant anisotropic thermal diffusivity and non-homogeneous permeability. Both linear instability and global nonlinear energy stability analyses are performed. By adopting a differential constraint approach, the nonlinear stability boundaries are shown to be sharp when compared with the linear instability thresholds. In contrast, it is shown that adopting a standard energy analysis does not yield sharp results.

Thermal management system for loudspeaker having internal heat sink and vented top plate

A thermal management system promotes cooling effects of a loudspeaker. The thermal management system includes an internal heat sink having a tubular shape and mounted between a pole piece and a magnet of the loudspeaker, the internal heat sink having pleat portions to form a plurality of air passages on an inner surface from top to bottom thereof; and a back plate connected to the pole piece and having ventilation holes that vertically penetrate through the back plate, the internal heat sink and the magnet being mounted on the back plate. A lower end of the air passage on the internal heat sink is positionally matched with an upper opening of the ventilation hole on the back plate, thereby allowing an air flow through the air passage and the ventilation hole.

Effect of Internal Cooling on Tool-Chip Interface Temperature in Orthogonal Cutting

A numerical method to study the effect of internal heat sink variables on the tool-chip interface temperature in orthogonal cutting was presented. The analytical method is based on two main assumptions that the chip can be treated as a semi-infinite body with a moving heat source at the tool-chip interface and the tool can be treated as a semi-infinite body with a stationary heat source at the tool-chip interface and a uniform plane heat sink inside the semi-infinite body. An approach using the point heat partition coefficient is employed to obtain the tool-chip interface temperature distribution. The temperature distributions along the tool-chip interface with different heat sink intensities, heat sink distances from the tool-chip interface, and heat sink areas were presented. The effects of the heat sink intensity, heat sink distance from the tool-chip interface, and heat sink area on the tool-chip interface temperature were investigated. It was found that the internal cooling with a heat sink in the cutting tool could greatly affect the tool-chip interface temperature. Presented at the STLE Annual Meeting in Toronto, Ontario, Canada May 17-20, 2004 Review led by Jane Wang

Penetrative convection in a horizontally isotropic porous layer

Penetrative convection in a horizontally isotropic porous layer is investigated primarily using an internal heat sink model and alternatively, a quadratic density temperature law. Employing the heat sink model, we show that the temporal growth rate for the linearised system is real, which allows us to perform a linear instability analysis. A nonlinear energy analysis is also presented, yielding a global stability threshold. We compare the heat sink model to the quadratic density model and find that the linearised systems are adjoint, implying that the instability boundaries which can be derived from the two models are the same.

A study of flank wear in orthogonal cutting with internal cooling

Internal cooling is being paid more and more attention as a means to overcome the limitations of cutting fluids. The purpose of this paper is to investigate the effects of internal cooling on the flank wear of cutting tools in orthogonal cutting. A flank wear model for a cutting tool in orthogonal cutting is presented which is based on previous wear models and includes the normal stress and the effect of thermal softening. The effects of internal heat sink intensity and heat sink area on the flank wear of the cutting tool in orthogonal cutting are demonstrated.

Numerical modeling of thermal stratification in a lake reservoir. Methodology and case study

A numerical model of the hydrodynamic and thermal structure of an artificial lake was designed and developed as a basis for an ecological water-quality model. It allows the quantification of the vertical mixing processes that govern not only the thermal structure but also the nutrient exchanges, and more generally the distribution of dissolved and particulate matter between the different parts of the lake. The vertical temperature profiles were calculated by solving the one-dimensional heat transfer equation that takes into account the internal heat sources and sinks, advection due to inflow and outflow and the molecular and eddy diffusions. A finite-difference discretization of first-order in time and second-order in space was chosen. The numerical time-step was three hours and layers were one-meter in thickness. These time- and space-scales are well-suited to perform a precise simulation of the different processes occurring over a seasonal period. Moreover, this simulation requires only a reasonable amount of computer time.¶This model was used to study an artificial lake, (i.e. a reservoir), located in the high Loire valley (Roanne, France). To precisely identify the physical processes followed with an accurate numerical modeling, on-site data were acquired intensively over three years. Temperatures were monitored hourly at 11 different levels in the three main reaches of the reservoir to study the lake hydrodynamics and thermal behaviour. Meterological measurements were made every 20 minutes. One-year data were used for calibration, whereas the model was validated using the data collected over the other two years.

Mixed convection in a low rotation horizontal cylinder

In this paper, the effect of rotation imposed to a horizontal cylinder containing a fluid is studied. A uniform temperature is imposed on the circular boundary of the enclosure while a uniform internal heat sink is applied to cool down the system. The resulting convective heat transfer is studied using both perturbation methods and numerical procedures. Only the weak rotation regime, in which the centrifugal force is negligible compared to gravity, is considered. Results indicate that the rotation significantly affects the flow and temperature fields, and thus the overall heat transfer.

Effect of weak rotation on natural convection in a horizontal porous cylinder

Natural convection in a fluid saturated porous medium confined in a horizontal circular cylinder and rotating about its axis, with isothermal boundary conditions and uniform internal heat sink, is studied by both numerical and perturbation methods. No symmetry with respect to the vertical diameter is expected for the flow and temperature fields and the whole region must be involved in the computation. Only the weak rotation regime, for which the centrifugal force is negligible compared to gravity, is considered. Governing equations for the two-dimensional flow field are solved in both rotating and non-rotating coordinate systems. Results indicate that rotation significantly decreases the radial amplitude of fluid particle trajectories in the radial direction and thus reduces the overall heat transfer.

A Stefan problem in a Bridgman crystal grower

We discuss a one-dimensional model for a Bridgman crystal grower, where the removal of heat is described by an internal heat sink. A consequence is the apparent existence of mushy regions for relatively large velocities of the cooling machine; these mushy regions are an artefact of the one-dimensional approximation. We show that for some types of cooling profiles there exists a critical speed for the existence of mushy regions, whereas for different cooling profiles no such critical speed exists. The presence of a mushy region may indicate a strong curvature of the liquid/solid interface in the real situation.

Caecal function provides the energy of fermentation without liberating heat in the poikilothermic mammal, Heterocephalus glaber

This paper presents the first report of a mammalian internal organ with a lower temperature than its abdominal surrounds. Heterocephalus glaber, the naked mole-rat, is a poikilothermic mammal that leads a strictly subterranean existence and consumes a high proportion of fibre in its diet. The fermentation chamber in these animals appears to absorb rather than generate heat and the temperature in it was consistently 1.2 +/- 0.5 degrees C (n = 17) lower than rectal temperature. A caecum with a lower temperature than its abdominal surrounds provides an internal heat sink which could be advantageous for metabolic heat dissipation in the plugged humid burrows in which the naked mole-rat permanently resides.

Observation of swelling-irradiation creep interaction at low values of swelling with CW 316 SS

Swelling and irradiation creep interaction occurs under irradiation in cylindrical tubing containing an internal heat source and external heat sink. The swelling and irradiation creep interaction can be measured by axially slitting the tubing while constrained and measuring the slit width change after the constraint is removed. Swelling and irradiation creep interaction data have been obtained from an EBR-II irradiation test. The test consists of encapsulated fuel pins wherein the capsules comprise the test samples and provide the swelling and irradiation creep interaction data. Slit tube data have been obtained on two 20% cold-worked AISI 316 stainless steel capsules irradiated to a peak fluence level of 7.0 × 10 22 n/cm 2 ( E ⩾0.1 MeV). An assessment of the slit tube data was made by comparing the data with performance calculations using empirical swelling and irradiation creep equations.

Calculation of the boundary layer of a transparent gas on a radiating surface

Heat transfer in the laminar boundary layer of a transparent gas flowing aroud a plane radiating surface is studied. Radiative heat-transfer processes in gases may be divided into two main groups. The first involves heat transfer in absorbing and radiating media. In this case, the effect of radiation lies in the introduction of new terms into the energy equation, representing internal heat sources and sinks. The second group embraces heat-transfer processes in a transparent gas when the effect of radiation on convection expresses itself solely by way of the boundary conditions. Here we study a case of practical importance belonging to the second group: heat transfer in the laminary boundary layer of a transparent gas flowing around a flat plate with the thermal flux qw specified on its surface.

Boundary layers with prescribed heat flux—application to simultaneous convection and radiation

An analysis is carried out to determine the distribution of surface temperature along a flat plate experiencing simultaneous convective heat transfer, radiative exchange with the environment, aerodynamic heating, and internal heat sources or sinks. Both laminar and turbulent boundary layer flows are considered. Numerical results are presented for a wide range of the governing parameters; these are compared with simplified solutions based on local application of heat-transfer coefficients for uniform wall temperature and for uniform heat flux. The problem is treated within the framework of the thermal boundary layer with prescribed heat flux. The initial part of the paper is devoted to establishing certain general results for such boundary layers. Exact solutions are obtained for power-law and series heat flux distributions. An approximate solution for arbitrarily varying surface heat flux is derived by superposing step-function solutions furnished by the integral energy equation.

Stability of Compressible Laminar Boundary Layer with Internal Heat Sources or Sinks

A solution of the equations of the compressible laminar boundary layer with heat sources or heat sinks is presented. The solution is limited to the flow over a flat plate with arbitrary surface temperature and constant Prandtl Number. I t is assumed that the additional mass associated with the heat sources or sinks is negligible. Stability calculations indicate that the boundary laj^er can be stabilized by heat withdrawal near the aircraft surface (e.g., by evaporation of liquid droplets) or by heat addition near the outer edge of the boundary layer (e.g., by condensation of a vapor). In addition, heat withdrawal near the surface is shown to provide an effective means of surface cooling.