A semi-empirical formula to describe the net emission coefficient of self-absorbed spectral lines for use in modelling high-pressure discharge lamps

Self Cite

Operating wall temperature and electrode separation are important factors in the design of efficient high-pressure sodium lamps. The authors have measured and calculated how the arc efficacy varies with wall temperature and input power per unit length. In their experiments they controlled the wall temperature by passing gases with different thermal conductivities over the arc tube. Their experiments showed that the arc efficacy increases at rates of 3.75+or-0.15% per 100K rise in wall temperature and 3.5+or-0.3% per 1 Wmm-1 increase in electrical power input. The corresponding calculated average rates are 2.1% per 100K and 1.7% per 1 Wmm-1. The satisfactory agreement of their experiments with their calculations resolves a discrepancy between their computer model predictions and those of Waymouth and Wyner (1981). Their two-zone model predicted that the efficacy decreases as the electrical power input increases. Although they have found that the proportion of the total radiation emitted in the D-lines decreases as the power input increases, this is more than compensated by an increase in the total radiated power at the expense of thermal conduction.

Section: Modei Descriptionmentioning

confidence: 99%

Relationship between efficacy, arc tube temperature and power dissipation in a high-pressure sodium lamp

Denbigh¹,

Jones²,

Mottram³

1983

Self Cite

“…Lowke (1969) used time relaxation to solve the exact equations for the radiation flux density, the mean radiation intensity and the arc energy balance, while Waszink (1973) and de Groot and van Vliet (1975) used the Holstein escape probability factor (Holstein 1947) to solve the radiative transfer problem. A different approach was used by Jones and Mottram (1981) and Denbigh et a1 (1983) to describe the net emission coefficient in the arc energy equation by a semiempirical formula.…”

Section: Introductionmentioning

confidence: 99%

On the theory of radiation-dominated wall-stabilised arcs

Lee

Cram

1985

A method for computing the radial temperature distributions in wall-stabilised arcs is developed and is applied to the treatment of D-line emission from a sodium arc lamp. The method adopts a radial temperature distribution containing two free parameters whose values are derived from two coupled nonlinear equations, one describing the energy balance on the arc axis, and the other the integrated energy balance. The radiative terms in the energy balance equations are obtained from a solution of the exact transfer equation.

“…In all the theoretical models, the radiation terms are approximated during the evaluation of the energy balance: it is this evaluation which leads to the temperature profile from which spectra can be calculated. Even in cases (Jones and Mottram 1981) in which radiation transport calculations are done on several spectral lines, there is still some radiation omitted. To what extent are the resulting energy balance calculations affected?…”

Section: Introductionmentioning

confidence: 99%

Energy balance of high-pressure sodium discharges under controlled vapour conditions

Wharmby

1984

Measurements have been made of the energy balance of high-pressure sodium arcs in sapphire arc tubes under conditions of: (a) varying power from 200 to 600 W at a constant amalgam temperature of 700 degrees C; (b) varying amalgam temperature from 700 to 800 degrees C at a constant power of 400 W; and (c) varying mercury pressure from 0 to 1050 Torr at a constant power of 400 W and a sodium pressure of 65 Torr. Together with measurements of axis and wall temperatures, these results provide an excellent test of theoretical models. High radiation efficiency is favoured by high input power and mercury rich amalgam. The amalgam temperature hardly affects the radiation efficiency, despite a large change in arc temperature. A number of radiation processes which are individually insignificant contribute approximately=25% of the radiation and need to be included in model calculations. The infrared discharge continuum amounts to only 3-5% of the input power, but its origin remains a mystery.