Book - School of Science and Technology

Direct systems ± gaseous fuels (primarily convective) 103Burner andSafety ControlsEmitterTubeReflectorExtractFanFigure 4.6 Gas-fired radiant tube (Gas-Rad)the form of a `U' tube with the suction fan adjacent to the burner box, as shown in Figure4.6; similar arrangement with a single straight tube is available up to 15 m length with 50 kWrating. The cascade arrangement is thus not practicable, the units requiring a flue for each.Direct systems ± gaseous fuels (primarily convective)Natural convectorsAs in the case of luminous fires, the better types of convector are designed to providemeans for dispersal of the products of combustion via a conventional outlet or a balancedflue arrangement, as in Figure 4.7. In terms of construction, convectors consist of a heatexchanger so mounted within a casing as to provide a passage for the movement ofconvected air from a low level inlet to a top or top-front outlet. In most cases there willbe some heat transfer to the front of the casing and a small radiant output may result.Designs aimed at the institutional building have ratings of up to 10 kW but 3 kW is a morerepresentative average.Convectors without flue connections are available but should not be used in domesticpremises, unless these are of the most modern design incorporating effective catalyticconvertors to make, relatively, safe the products of combustion.