Finned Tubular Heaters
In applications where tubular heaters are exposed to forced convection, placing fins around tubular heaters increases their surface area and thus improves their heat transferring capacity. Finned tubular heaters, compared to regular tubular heaters, run at lower surface temperatures for the same watt densities when placed in identical air streams. Graph1 compares watt density, outlet air temperature, and the speed of air flow for regular and finned tubular heaters respectively. Despite their advantages, finned tubular heaters are not recommended for applications where outlet air temperatures exceed 600°F.
The physical characteristics of a finned tubular heater play a major role in the effectiveness of its heat transfer. The table below specifies the outside diameter of fins, their thickness, the spacing between consecutive fins, as well as the element sheath and fin material.
Threaded fittings, if required, are the standard mounting attachments supplied with finned tubular heaters. These fittings are brazed or crimped onto the heaters. For special applications, finned tubular heaters can be made with mounting brackets that have special designs.
|TUBE DIAMETER||FIN THICKNESS||FINS PER INCH||FIN WIDTH||*TOTAL SQ.INCH PER LINEAR INCH||*MAX SHEATH LENGTH||*OUTSIDE DIAMETER OF FINS|
|*Dimensions are subject to change|
STAINLESS STEEL FINS AND TUBULAR SHEATH MATERIAL
SPECIAL MOUNTING ACCESSORIES
The sheath material of a finned tubular heater and its watt density are two critical factors that affect its durability. The standard finned tubular heaters are made of steel sheath and steel fins (750°F max. surface temperature) since steel is very efficient in heat transfer. These heaters have a plain-surface finish. For corrosive environments or high temperature applications (above 750°F), finned tubular heaters could be made with stainless steel sheath and stainless steel fins.
Safe watt densities that keep surface temperatures below allowable limits depend on the speed of the incoming air and its outlet temperature. Graph 2 shows maximum watt densities recommended for a specific sheath temperature and air velocity.
Kilowatts to Heat Air