Barrel Heaters - Hasmak.com.tr

Reference DataHeat Loss Factorsand GraphsHelpful Hint: The graphs for lossesfrom uninsulated and insulatedsurfaces are hard to read at lowtemperatures close to ambient. Hereare two easy-to-use calculations thatare only rule-of-thumb approximationswhen used within the limits noted.Rule #1: Losses from anuninsulated surface (with anemissivity close to 1.0): (Thisapplies only to temperaturesbetween ambient and about121°C (250°F))Losses (W/in 2 ) =∆T (°F) rise above ambient200Rule #2: Losses from an insulatedsurface: (This insulation is assumedto be one inch thick and have aK-value of about 0.5 Btu-in/hr - ft 2 -°F.Use only for surfaces less than427°C (800°F.))Losses (W/in 2 ) =∆T (°F) rise above ambient950Some Material Emissivities/MetalsSpecificEmissivityMaterial Heat Polished Medium HeavyBtu/lb-°F Surface Oxide OxideBlackbody 0.75 1.00Aluminum 0.24 0.09 0.11 0.22Brass 0.10 0.04 0.35 0.60Copper 0.10 0.04 0.03 0.65Incoloy ® 800 0.12 0.20 0.60 0.92Inconel ® 600 0.11 0.20 0.60 0.92Iron, Cast 0.12 — 0.80 0.85Lead, solid 0.03 — 0.28 —Magnesium 0.23 — — —Nickel 200 0.11 — — —Nichrome, 80-20 0.11 — — —Solder, 50-50 0.04 — — —Steelmild 0.12 0.10 0.75 0.85stainless 304 0.11 0.17 0.57 0.85stainless 430 0.11 0.17 0.57 0.85Tin 0.056 — — —Zinc 0.10 — 0.25 —Some Material Emissivities/Non-MetalsSpecificMaterial Heat EmissivityBtu/lb-°FAsbestos 0.25-0.2Asphalt 0.40-0.2Brickwork 0.22-0.2Carbon 0.20-0.2 Most non-metals:Glass 0.20-0.2 0.90Paper 0.45-0.2Plastic 0.2-0.5.-..2Rubber 0.40-0.2Silicon Carbide 0.20-0.230.-..Textiles —0.2Wood, Oak 0.57-0.2Additional information on emissivities is availablefrom Watlow.Incoloy ® is a registered trademark of SpecialMetals Corporation.Inconel ® is a registered trademark of SpecialMetals Corporation.398