Bulk Heating Rate Research Articles

Simulation investigation of heating rate and temperature uniformity in fluidized bed

In this paper, the hydrodynamics and gas–solid heat transfer characteristics during bed material heating process are investigated using the CFD-DEM approach, and the heating rate and bed temperature uniformity are quantitatively analysed. After model validation, gas–solid heat transfer characteristics in a typical case is analysed. On this basis, the effects of operating conditions is further discussed. The results show that overheating phenomenon at bed bottom is weakened obviously by solid internal circulation behavior in fluidized bed. As time marches, bed temperature uniformity is effectively improved with increasing mean bed temperature. Specially, a temperature drop at particle scale is captured by tracer particle method. A simplified energy balance model is developed to explain the relationship between bulk heating rate and operating conditions, and qualitatively consistent between simulation results and model analytical solutions is captured. Furthermore, the temperature uniformity under different operating conditions is qualitatively discussed by standard deviation of particle temperature.

New insights into the role of selective and volumetric heating during microwave extraction: Investigation of the extraction of polyphenolic compounds from sea buckthorn leaves using microwave-assisted extraction and conventional solvent extraction

We report a direct comparison of microwave heating and conventional heating in solvent extraction by using exactly the same reaction conditions (including heating rate) in the extraction of polyphenols from dried sea buckthorn leaves. We have for the first time decoupled the effects of bulk heating rate and mixing regime from the fundamental microwave heating mechanism. We show that although microwave selective heating can increase the yield and quality of the polyphenols extracted, if the same bulk heating rate is applied there is no difference in treatment time and therefore theoretical energy requirements of the process. The first implication of these results for process intensification is that if microwave selective heating can be enhanced in scaled up processes through electromagnetic design, the extract yield and quality may be increased further. The second implication is that conventional extraction processes could be designed to provide the same heating rate and hence treatment time as microwave extraction, but any potential energy and space savings would have to be balanced against the increase in capital cost and complexity of the equipment. That said, the very small penetration depth of microwaves into ethanol/water solvent also poses design challenges in the scale up of microwave equipment.

Irreversible thermodynamics of transport across interfaces

With spintronics applications in mind, we use irreversible thermodynamics to derive the rates of entropy production and heating near an interface when heat current, electric current, and spin current cross it. Associated with these currents are apparent discontinuities in temperature (ΔT), electrochemical potential (Δ[Formula: see text]), and spin-dependent “magnetoelectrochemical potential” (Δ[Formula: see text]). This work applies to magnetic semiconductors and insulators as well as metals, because of the inclusion of the chemical potential, μ, which is usually neglected in works on interfacial thermodynamic transport. We also discuss the (nonobvious) distinction between entropy production and heat production. Heat current and electric current are conserved, but spin current is not, so it necessitates a somewhat different treatment. At low temperatures or for large differences in material properties, the surface heating rate dominates the bulk heating rate near the surface. We also consider the case where bulk spin currents occur in equilibrium. Although a surface spin current (in A/m2) should yield about the same rate of heating as an equal surface electric current, production of such a spin current requires a relatively large “magnetization potential” difference across the interface.

A Large-Eddy Simulation Study of the Influence of Subsidence on the Stably Stratified Atmospheric Boundary Layer

The influence of the large-scale subsidence rate, S, on the stably stratified atmospheric boundary layer (ABL) over the Arctic Ocean snow/ice pack during clear-sky, winter conditions is investigated using a large-eddy simulation model. Simulations of two 24-h periods are conducted while varying S between 0, 0.001 and 0.002 ms−1, and the resulting quasi-equilibrium ABL structures and evolutions are examined. Simulations conducted with S = 0 yield a boundary layer that is deeper, more strongly mixed and cools more rapidly than the observations. Simulations conducted with S > 0 yield improved agreement with the observations in the ABL height, potential temperature gradients and bulk heating rates. We also demonstrate that S > 0 limits the continuous growth of the ABL observed during quasi-steady conditions, leading to the formation of a nearly steady ABL of approximately uniform depth and temperature. Subsidence reduces the magnitudes of the stresses, as well as the implied eddy-diffusivity coefficients for momentum and heat, while increasing the vertical heat fluxes considerably. Subsidence is also observed to increases the Richardson number to values in excess of unity well below the ABL top.

Preliminary Neutronic Calculations for Fusion Blanket Testing in the Engineering Test Reactor

The neutronic feasibility of testing fusing firstwall/blanket systems in a fission reactor is investigated. Heating rates resulting from a 14-MeV fusion source are calculated with one-dimensional transport theory for two tokamak blanket designs and compared with heating rates computed for the same blankets in the Engineering Test Reactor (ETR). The designs studied are a gas-cooled, liquid-lithium blanket with no neutron multiplier and a water-cooled, solid lithium-aluminate blanket with a beryllium multiplier. Based on these preliminary results, it is concluded that bulk heating rate profiles expected in tokamak reactor blankets can be simulated quite well in large (65- × 76- × 91-cm) blanket experiment modules placed on one side of the ETR core. Heating rates corresponding to tokamak wall loadings of 1 MW/m2 can be achieved, and the level varied to simulate the cyclic operation typical of tokamaks.

Acoustic waves and heating due to molecular energy transfer in an electric discharge CO laser

This paper summarizes analytical studies and the interpretation of experimental results for the compression and rarefaction waves generated in the cavity of a pulsed CO electric discharge laser. A one-dimensional analysis of acoustic waves is applied to a transversely excited laser. The influences of heating in the cathode fall, heat transfer to the cathode, flow through both the anode and cathode, and bulk heating of the plasma are included. The analysis is used to relate the bulk heating rate to observable features of the pressure and density waves. Data obtained from interferograms and reported elsewhere are used to infer the bulk heating rates in a pulsed CO laser. Results are presented for CO/Ar, CO/N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , and N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> plasmas. Comparison of the data with recent theoretical results for the heating due to electron/ neutral collisions and the anharmonic defect associated with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V-V</tex> energy transfer shows substantial differences at lower values of total energy deposition. The change of heating With <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E/N</tex> is in fairly good agreement with predicted values.