Radiation loss

Heat produced in these cells operating at voltages of >2.31 V is generally removed by water evaporation and radiation losses. 

When the partial pressures of the radicals become high, their homogeneous recombination reactions become fast, the heat evolution exceeds heat losses, and the temperature rise accelerates the consumption of any remaining fuel to produce more radicals. Around the maximum temperature, recombination reactions exhaust the radical supply and the heat evolution rate may not compensate for radiation losses. Thus the final approach to thermodynamic equiUbrium by recombination of OH, H, and O, at concentrations still many times the equiUbrium value, is often observed to occur over many milliseconds after the maximum temperature is attained, especially in the products of combustion at relatively low (<2000 K) temperatures. 

This technique is based on the Dewar flask, which is a donble-walled vessel with reflective surfaces on the evacuated side to reduce radiation losses. Figure 11-66 shows a typical laboratory-size Dewar. Figure 11-67 shows a semiportable type. Radiation losses can be further reduced by filling the cavity with powders such as perlite or silica prior to pulling the vacuum. 

There will also be heat loss from tire substrate due to convection cuiTents caused by the teirrperamre differential in the suiTounding gas phase, but this will usually be less than the radiation loss, because of the low value of the heat transfer coefficient, / , of gases. The heat loss by this mechanism, Qc, can be calculated, approximately, by using tire Richardson-Coulson equation... 

In all of these systems, the rate of generation at the gas-solid interface is so rapid that only a small fraction is canied away from the particle surface by convective heat uansfer. The major source of heat loss from the particles is radiation loss to tire suiTounding atmosphere, and the loss per particle may be estimated using unity for both the view factor and the emissivity as an upper limit from tlris source. The practical observation is that the solids in all of these methods of roasting reach temperatures of about 1200-1800 K. 

In an effort to account for this effect, Spalding and Johnson have considered the effect of radiation losses from the solid surface. Johnson has also included a provision for a volume rate of energy loss, but he does not state the basis for the term. In the case of surface pyrolysis, the resulting equations predict the relations of burning-rate versus pressure as shown in Fig. 16. 

Neglecting radiation losses, calculate the mass of dry air passing through the dryer and the humidity of the air leaving the dryer. 

For simplicity of the model, it is assumed that the natural convection, radiation, and ionic wind effect are ignored. The ignorance of the radiation loss from the spark channel during the discharge may be reasonable, because the radiation heat loss is found to be negligibly small in the previous studies [5,6]. The amount of heat transfer from the flame kernel to the spark electrodes, whose temperature is 300 K, is estimated by Fourier s law between the electrode surface and an adjacent cell. 

V. N. Kurdyumov and M. Matalon, Radiation losses as a driving mechanism for flame oscillations, Proc. Combust. Inst. 29(1) 45-52,2002. 

Platt, J.A. and T ien, J.S., Flammability of a weakly stretched premixed flame The effect of radiation loss. Fall Technical Meeting of the Eastern States Section of the Combustion Institute, Orlando, Florida, 1990. 

S.S. Shy, S.I. Yang, W.J. Lin, and R.C. Su 2005, Turbulent burning velocities of premixed CH4/diluent/air flames in intense isotropic turbulence with consideration of radiation losses. Combust. Flame 143 106-118. 

With all these cold finger traps the rate of loss of refrigerant is much greater than from the Dewars whose inner siufaces are silvered to cut down radiation losses. 

If we assume a radiation loss of the sun of 25-30% in comparison with today s values, the primeval Earth would have had a surface temperature below the freezing point of water (provided that all other factors which influence the surface temperature remained basically unchanged). 

Assuming that radiation losses amount to 20 kJ/kg of dry air used, determine the mass flow of dry air supplied to the dryer and the humidity of the outlet air. The latent heat of water vapour at 295 K = 2449 kJ/kg, the specific heat capacity of dried material = 0.88 kJ/kg K, the specific heat capacity of dry air = 1.00 kJ/kg K, and the specific heat capacity of water vapour = 2.01 kJ/kg K. 

The detection limit of the microresonator-based refractive index sensing device is directly related to the g-factor of the resonator and the sensitivity of the resonant mode discussed above. The g-factor of a microtube resonator is determined by the total loss of a resonant mode, including radiation loss, absorption loss, and surface roughness scattering loss. The overall g-factor can be expressed as... 

Fig. 13.6 Optics of radiation losses in a MF taper, which shows the splitting of the guiding and radiating components of the propagating electromagnetic field near focal circumferences...

Here L is the characteristic length of the taper and 70 and 7w are the values of transversal propagation constants in the center of the taper waist and on the infinity, respectively. For this taper, the analytical expression for the radiation loss was found in Ref. 13. In particular, for a strong taper, when y0 IToJ, the radiation loss has the form ... 

This expression is useful for estimating of the radiation loss of an adiabatic taper with characteristic length L. Figure 13.7 shows the distribution of the evanescent electromagnetic field intensity in the vicinity of the taper for 0 = 0.2 pm 1,yao = 0.4 pm 1, L = 500 pm, and / 4 pm In agreement with illustration in... 

As mentioned in Sect. 15.2, sometimes a 4th thin layer (M) of metal or die is incorporated between the substrate and waveguide film to decrease the radiation loss into the substrate of the substrate radiation modes. These modes are referred to as leaky modes and the obtained structure is the MCLW. This configuration is also broadly used in evanescent wave sensor systems. 

Note that the re-radiation loss from the methanol surface at 7b = 64 °C is only about 0.3 kW/m2. 

In this case, all of the radiation loss from the flame is accounted for by XT, including that received by the surface of the condensed phase. Therefore flame radiation heat flux does not show up here. 

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