An evaluation of the contribution of radiation diffusion to thermal conductivity in high-pressure discharge lamps from operating-voltage and wall-temperature measurements

Abstract

The contribution of the radiation diffusion κ rad to the thermal conductivity κ in high-pressure discharge lamps is evaluated from operating-voltage and wall-temperature measurements for several cylindrical ceramic discharge tubes filled with mercury and argon as the rare gas. From calculations of κ rad using spectral line data of mercury, it is shown that the electrical conductivity σ can be well represented by a linear function of the heat-flux potential S. Under this assumption, the energy balance can be solved analytically and plasma parameters, i.e. radiation-diffusion and plasma-temperature profiles, can be calculated from the operating voltage and wall temperature without knowledge of spectral lines. The results are in good agreement with numerical calculations of the energy balance involving calculation of the radiation diffusion from spectral line data. The method may also be applied to other buffer gases for which there is a linear dependency of σ (S). This may be checked qualitatively by measurement of the temporal evolution of the operating voltage using the Cassie-Francis equation.

Modeling of a xenon short arc lamp considering the behavior of tungsten vapour evaporated from electrodes

“…Shyy et al [11] used a simplified radiation model that disregarded radiative transport in a 3D model that considered the effect of gravity; they showed that the convective flow, with multiple vortices, influences the energy balance within the arc and the gas temperature. Examples of models that include radiative transport are those of Hartel et al [12], Born [13] and Galvez [14]. Hartel et al found that the optically thin radiation output can be described using the discharge current, a set of atomic data and the transport properties of the plasma using a model that includes radiative transport.…”

Investigations on the influence of pressure, current and electrode gap in high-pressure mercury lamps

“…The latter is important at high temperatures (above 4000 K in a 4 MPa mercury discharge). It is estimated by the so-called radiation diffusion approximation for the resonance lines at 185 and 254 nm (cf [3,7,14,23]). The computation of the radiation transport is based on a given temperature profile which can be extracted from the numerical simulations to improve λ P iteratively.…”

“…The diffusion of electrons from the hot plasma spots close to the electrodes (with high plasma temperatures resulting in high electron densities) is directed into the relatively cold plasma regions immediately in front of the electrodes (with low plasma temperatures resulting in extremely low local thermal equilibrium (LTE) electron densities). This creates a strongly enhanced non-LTE electrical conductivity σ in regions close to both cathode and anode (cf figures [3][4][5]. The enlarged non-LTE electrical conductivity leads to realistic values of the electric field in near-electrode regions (resulting in realistic anode and cathode fall voltages) and offers the possibility of connecting the numerical simulation of plasma and electrodes (plasma-electrode interaction).…”

Line broadening measurements and determination of the contribution of radiation diffusion to thermal conductivity in a high-pressure zinc discharge

“…Consequently, heat transfer due to radiation diffusion strongly influences the plasma properties. As reported in [5], the term κ rad may evaluated by…”