Radiation from gases

Whilst the calculation of the radiant heat flux from a gas to an adjoining surface embraces inherent spectral and directional effects, a simplified approach has been developed by Hottel and Manglesdorf which involves the determination of radiation emission from a hemispherical mass of gas of radius L, at temperature Tg to a surface element, dL4i, near the centre of the base of the hemisphere. Emission from the gas per unit area of the surface is then  

A black surface will not only absorb all of this radiation but will also emit radiation, and the net rate at which radiation is exchanged between the gas and the surface at temperature 

In this equation, the absorptivity may be obtained from the emissivity using expressions of the form  

Geometry Characteristic length Mean beam length, Le 

Infinite circular cylinder— radiation to curved surface Diameter, D 0.95D 

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Radiation from gases containing suspended particles... 

RADIATION FROM GASES AND SUSPENDED PARTICULATE MATTER... 

Radiation from Gases and Suspended Particulate Matter. 5-30... 

Rg. 2.16 Comparison of direct gas radiation from gases to load (lower curve) with radiation from gases to refractory to load (gray area between curves). At the peaks, 66% is direct gas radiation and the remaining 34% is gas radiation to refractory that is then re-radiated to the load. (See also fig. 5.5.)... 

The two phases are coupled explicitly with mass flux and energy flux preserved. Thermal radiation from gas phase reaction is neglected in this model only laser radiation and conductive heat feedback from adjacent gas phase grids are taken into account as energy source terms for the condensed phase, which is critical to realize the pressure dependence of the mass burning rate. 

In the dense interstellar medium characteristic of sites of star fonuation, for example, scattering of visible/UV light by sub-micron-sized dust grains makes molecular clouds optically opaque and lowers their internal temperature to only a few tens of Kelvin. The thenual radiation from such objects therefore peaks in the FIR and only becomes optically thin at even longer wavelengths. Rotational motions of small molecules and rovibrational transitions of larger species and clusters thus provide, in many cases, the only or the most powerfiil probes of the dense, cold gas and dust of the interstellar medium. 

On metals in particular, the dependence of the radiation absorption by surface species on the orientation of the electrical vector can be fiilly exploited by using one of the several polarization techniques developed over the past few decades [27, 28, 29 and 30], The idea behind all those approaches is to acquire the p-to-s polarized light intensity ratio during each single IR interferometer scan since the adsorbate only absorbs the p-polarized component, that spectral ratio provides absorbance infonnation for the surface species exclusively. Polarization-modulation mediods provide the added advantage of being able to discriminate between the signals due to adsorbates and those from gas or liquid molecules. Thanks to this, RAIRS data on species chemisorbed on metals have been successfidly acquired in situ under catalytic conditions [31], and even in electrochemical cells [32]. 

Figure 5.13 shows a typical experimental arrangement for obtaining the Raman spectmm of a gaseous sample. Radiation from the laser source is focused by the lens Lj into a cell containing the sample gas. The mirror Mj reflects this radiation back into the cell to increase... 

Excimer lamps have opened the possibiHty of cost-effective large-area direct photochemical vapor deposition (PCVD). PCVD of stoichiometric, insulating Si02 onto Si wafer has been reported using SiH and N2O as gas-phase precursors and the 172-nm radiation from a Xe 2 lamp (54). Deposition... 

Carbon Dioxide—Water-Vapor Mixtures When these gases are present together, the total radiation due to both is somewhat less than the sum of the separately calculated effects, because each gas is somewhat opaque to radiation from the other in the wavelength regions 2.7 and 15 [Lm. 

Description A tray or compartment diyer is an enclosed, insulated housing in which solids are placed upon tiers of trays in the case of particulate solids or stacked in piles or upon shelves in the case of large objects. Heat transfer may be direct from gas to sohds by circulation of large volumes of hot gas or indirect by use of heated shelves, radiator coils, or refractoiy walls inside the housing. In indirec t-heat units, excepting vacuum-shelf equipment, circulation of a small quantity of gas is usually necessary to sweep moisture vapor from the compartment and prevent gas saturation and condensation. Compartment units are employed for the heating and diying of lumber, ceramics, sheet materi s (supported on poles), painted and metal objects, and all forms of particulate solids. 

Equation (12-57) does not account for gas radiation at high temperature when the kiln charge can see the burner flame hence, the method will yield a conservative design. When a kiln is fired internally, the major source of heat transfer is radiation from the flame and hot gases. This occurs directly to both the sohds surface and the wall, and from the latter to the product by reradiation (with some conduction). 

At X-ray fluorescence analysis (XRF) of samples of the limited weight is perspective to prepare for specimens as polymeric films on a basis of methylcellulose [1]. By the example of definition of heavy metals in film specimens have studied dependence of intensity of X-ray radiation from their chemical compound, surface density (P ) and the size (D) particles of the powder introduced to polymer. Have theoretically established, that the basic source of an error of results XRF is dependence of intensity (F) analytical lines of determined elements from a specimen. Thus the best account of variations P provides a method of the internal standard at change P from 2 up to 6 mg/sm the coefficient of variation describing an error of definition Mo, Zn, Cu, Co, Fe and Mn in a method of the direct external standard, reaches 40 %, and at use of a method of the internal standard (an element of comparison Ga) value does not exceed 2,2 %. Experiment within the limits of a casual error (V changes from 2,9 up to 7,4 %) has confirmed theoretical conclusions. 

Height of flame center above flare tip, m h = Height of flare tip above grade, m F = Fraction of heat release radiated from the flame m = Mass flaring rate, kg/s H = Lower heating value of the flare gas, MJ/kg r = Relative humidity, percent The following are the calculation steps ... 

The carbon/hydrogen ratio of gas is considerably lower than oil or coal, which results in a flame of very low luminosity. Radiation from the flame is therefore low and furnace design must allow for heat transfer to be primarily by convection and conduction, together with re-radiation from hot surfaces. 

A bare thermocouple is used to measure the temperature of a gas flowing through a hot pipe. The heat transfer coefficient bet ween the gas and the thermocouple is proportional to the 0.8 power of the gas velocity and the heat transfer by radiation from the walls to the thermocouple is proportional to the temperature difference. 

H. 10 An important role of stratospheric ozone, Os, is to remove damaging ultraviolet radiation from sunlight. One result is the eventual dissociation of gaseous ozone into molecular oxygen gas. Write a balanced equation for the dissociation reaction. 

Here, we shown a "conventional" system. It consists of a light source, an etched, transparent circuit diagram and a lens to focus the pattern upon the wafer which has a photoresist layer. Upon exposure, the unexposed part of the photoresist is wzished off. Sometimes, the exposed area is removed, depending upon weather the photoresist is positive or negative. Contrast this simple system with a method under development is the "Extreme Ultraviolet (EUV) system, using radiation from excited Xe gas, i.e.- 157 nm. The EUV system is shown in the following ... 

Mossbauer resonance of Zn to study the influence of the gravitational field on electromagnetic radiation. A Ga ZnO source (4.2 K) was used at a distance of 1 m from an enriched ZnO absorber (4.2 K). A red shift of the photons by about 5% of the width of the resonance line was observed. The corresponding shift with Fe as Mossbauer isotope would be only 0.01%. The result is in accordance with Einstein s equivalence principle. Further gravitational red shift experiments using the 93.3 keV Mossbauer resonance of Zn were performed later employing a superconducting quantum interference device-based displacement sensor to detect the tiny Doppler motion of the source [66, 67]. 

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