Gas heating apparatus

Abstract

A thermally sprayed gas heater comprises a gas flow apparatus that propels a gas through a housing; and a thermally sprayed heater bonded to a surface of the apparatus, the heater positioned to heat the gas flow in the housing. In other aspects, a heater system for a turbulent flow gas duct comprises a duct having a gas flow channel, the channel having a shaped surface providing turbulent gas flow in the channel, and a thermally sprayed heater positioned to heat the gas flow in the channel.

1 . A heater system of a turbulent gas flow duct, comprising:
 a duct having a gas flow channel, the channel having a shaped surface providing a turbulent gas flow in the channel; and   a thermally sprayed heater positioned to heat the gas flow in the channel.   
     
     
         2 . The heater system of  claim 4 , wherein the thermally sprayed heater is located in the channel. 
     
     
         3 . The heater system of  claim 2 , wherein the thermally sprayed heater is bonded to the shaped surface. 
     
     
         4 . The heater system of  claim 3 , wherein the shaped surface comprises a panel heater that is angled with respect to the predominant direction of gas flow in the channel. 
     
     
         5 . The heater system of  claim 1 , wherein the gas flow channel is characterized by a Reynolds number that is greater than about 2000. 
     
     
         6 . The heater system of  claim 1 , wherein the gas flow channel is characterized by a Reynolds number that is greater than about 3000. 
     
     
         7 . The heater system of  claim 1 , wherein the gas flow duct is configured to transfer heat predominantly by forced convection. 
     
     
         8 . The heater system of  claim 7 , wherein the gas flow duct is configured to minimize radiative heat loss. 
     
     
         9 . The heater system of  claim 1 , wherein the thickness of the thermally sprayed heater is less than about 0.030 inches. 
     
     
         10 . The heater system of  claim 1 , wherein the thermally sprayed heater is characterized by a material resistivity of greater than about 10 −4  Ω-cm. 
     
     
         11 . The heater system of  claim 1 , wherein the thermally sprayed heater comprises a resistive heating layer having a substantially lamellar structure. 
     
     
         12 . The heater system of  claim 11 , wherein the resistive heating layer comprises a first material and a second material, wherein the first material is an electrically conducting material and the second material is an electrically insulating material. 
     
     
         13 . The heater system of  claim 1 , wherein the thermally sprayed heater is deposited on an insulating material. 
     
     
         14 . The heater system of  claim 13 , wherein the insulating material comprises a mica material. 
     
     
         15 . The heater system of  claim 14 , wherein the mica material comprises a mixture of mica with an electrically insulating material, the mixture having a higher thermal coefficient of expansion than pure mica. 
     
     
         16 . The heater system of  claim 12 , wherein the bulk resistivity of the resistive heating layer is higher than the resistivity of the conductive material by a factor of about 10 or more. 
     
     
         17 . The heater system of  claim 12 , wherein the bulk resistivity of the resistive heating layer is higher than the resistivity of the conductive material by a factor of about 10 to about 1000. 
     
     
         18 . The heater system of  claim 12 , wherein the content of the electrically insulating material in the resistive heating layer comprises at least about 40% by volume. 
     
     
         19 . The heater system of  claim 12 , wherein the content of the electrically insulating material in the resistive heating layer comprises between about 40-80% by volume. 
     
     
         20 . The heating system of  claim 12 , wherein the electrically conductive material comprises a metallic material. 
     
     
         21 . The heating system of  claim 20 , wherein the metallic material comprises at least one of titanium (Ti), vanadium (V), cobalt (Co), nickel (Ni). magnesium (Mg), zirconium (Zr), hafnium (Hf), aluminum (Al), tungsten (W), molybdenum (Mo), tantalum (Ta); silicon (Si), a metal alloy, a metal composite, and a metalloid. 
     
     
         22 . The heating system of  claim 20 , wherein the electrically conductive material comprises aluminum. 
     
     
         23 . The heating system of  claim 20 , wherein the electrically insulating material comprises a reaction product of the metallic material. / 
     
     
         24 . The heating system of  claim 23 , wherein the reaction product comprises at least one of an oxide, a nitride, a carbide and a boride. 
     
     
         25 . The heating system of  claim 23 , wherein the electrically insulating material comprises aluminum oxide. 
     
     
         26 . The heating system of  claim 23 , wherein the electrically insulating material comprises a thermally-sprayed insulating material and a reaction product of the electrically conducting material.