High Emissivity Materials

Emisshield Will Increase Heat Transfer

Emissivity is the measurement of how well a body absorbs or emits energy when compared to a perfect black body. This is measured on a scale from zero to one; one being a perfect black body. For a material to preform as a black body its emissive value must remain constant with changes in temperature. Around the world industries use refractory, ceramic fiber and metal throughout processes to increase heat transfer. These components have many different issues based on their environment but their emissivity values substantially decrease at high operational temperatures. For example, the best ceramic fiber, refractories and metals on the market have emissivity values of 0.3, 0.4 and 0.6 respectively. Applying Emisshield’s Coating Systems will increase the emissivity value of these components to between 0.85 and 0.95, remaining constant up to 3,100°F (1700°C).

Emisshield is not an insulator. It is not a barrier to the conduction of thermal energy through a furnace wall. Insulating refractories are generally placed behind dense refractories at the cold face of refractory linings. While this reduces heat loss from a furnace, the amount of heat stored in the refractory is increased and the refractory materials must withstand higher mean temperatures. When Emisshield is used, it is applied to the hot face of the furnace. Radiant and convective energy from the burners and hot furnace gases are absorbed at the surface of the coating and re-radiated to the cooler furnace load.

High temperature process furnaces are used in a variety of industrial processes. A key to process efficiency and throughput is efficient heat transfer from flames to the process material or process tubes. For gas-fired furnaces, normal furnace refractories tend to reflect a majority of arriving energy back into the furnace flue gas at the same spectral wavelength at which it is emitted from the flue gas. This energy is then again absorbed by the flue gas, limiting the amount of energy transferred to the process (tubes or materials). Emisshield Coatings on furnace walls absorb more of the incident radiant energy and reemit this energy across the wavelength spectrum, including emission through transparent windows in the spectrum. This spectral redistribution of emitted energy allows more radiant energy to pass through the flue gas and be transferred to the process surface.


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