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  Multi-passage electric heater using ceramic foam as a diffuser and method of useUSPTO Application #: 20080085105Title: Multi-passage electric heater using ceramic foam as a diffuser and method of use Abstract: A multi-passage electric heater for heating a gas flowing through the passages uses electric heating elements disposed in the passages for gas heating. One of both of the inlet and outlet of the heater includes a ceramic foam material as a diffuser. The diffuser on the inlet side effectively distributes gas evenly to the passages for heating and insulates against radiated heat loss through the inlet. When located on the outlet side of the heater, a more homogenous outlet stream of heated gas is created, with the outlet diffuser minimizing loss of radiated heat from the outlet side and acting as a heat exchange medium for improved heater efficiency. (end of abstract) Agent: Clark & Brody - Washington, DC, US Inventor: Dexter E. Diepholz USPTO Applicaton #: 20080085105 - Class: 392488 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080085105. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001]The present invention is directed to a multi-passage electric heater, and in particular, to an electric heater that employs one or more diffusers made from a ceramic foam material to modify the inlet and outlet flow characteristics of the heater and enhance the heater operation. BACKGROUND ART [0002]The use of process heaters for heating fluids is well known in the industry. One manufacturer of these types of heaters is Farnam Custom Products of Arden, N.C., with one example being their "heat torch family". This product as well as other heaters can be seen on their website, www.farnam-custom.com and in company literature. Other examples of this art are demonstrated by product literature published by Farnam Custom Products. Process heaters are used primarily to heat a gas with the most common use being to heat air. The gas is forced through the heater by pressure difference between the heater inlet and the heater outlet. As the gas is directed through the heater its temperature is raised as it comes in contact with the heated internal surfaces of the process heater. [0003]It is well known in the prior art to build process heaters for heating gas that directs the gas stream from the inlet to the outlet through multiple passages, normally a parallel path, within the heater. Within each passage, the gas is heated by means of some heat exchange mechanism such as electric heating elements. [0004]One type of multi-passage electric heater commonly used in the industry is to have separate, individual tubes made of material suitable for the application, e.g., a ceramic material. The tubes are preferably aligned so each is parallel to one another and parallel to the direction of the incoming and outgoing gas flows. The entire group of parallel tubes is contained within an external cover or housing of the process heater assembly. Some means for heating, such as properly configured heating element material powered by an electric current, is used to transfer thermal energy as the gas moves through each tube thereby raising the outlet temperature to a desired level. [0005]A second method is to use a heater core employing a honeycomb configuration having parallel channels for directing the gas from the inlet to the outlet. The honeycombed heater core is made of a material with properties appropriate for the intended use. The most common material is an extruded ceramic. The cross section area of each channel is sized so as to permit an appropriate flow of gas and to accommodate a means of heating. The most common means of heating in these types of heater cores is a properly configured electric heating element wire that when energized will properly heat the gas to a desired temperature. The honeycombed heater core is contained within the outer housing of the process heater. [0006]A typical use of a process heater is to place it in line for heating a gas flowing through a pipe or tube. Other uses may be to use the process heater for directing a hot gas stream in an intended direction to accomplish a given function. [0007]The prior art process heaters for heating gases have significant shortcomings. One ongoing problem with these multi-passage electric heaters is that the exiting gas stream tends to have a non-uniform distribution of temperature and velocity across the opening. This is a result of a non-uniform distribution of the velocity and volume of the gas across the face of the heater inlet. It is desirable to have the heated gas stream to be relatively uniform in velocity and temperature for the most effective use in applications. [0008]Further, the non-distribution of velocities across the cross-section of the inlet fluid stream results in temperature problems further downstream. To solve this problem, certain heaters use metallic screens and/or grids located in the inlet and outlet, which also double as barriers for entry of foreign or unwanted objects. However, these remedies are ineffective as means to yield either uniform temperatures or velocities [0009]The problems with velocity for these types of multi-passage electric heaters create yet another serious shortcoming. As noted in the above description of the prior art, process heaters for heating gas are made up with a collection of paths or passages, for example separate parallel tubes or a body with parallel extruded holes. A means for heating the gas is placed inside the tubes or openings thus raising the temperature during operation. [0010]For proper operation, it is desirable that the velocity and volume flow rate of the gas being heated be uniform over the cross section of the entrance of the heater. If this is not the case, the velocity and thus the volume rate of flow through the tubes or passages will not be uniform. This non-uniform gas flow will result in uneven heating whereby those passages having the lowest velocity or volume rate of flow will operate at higher temperatures than those with the higher velocity or volume flow rate. This is because a lesser fluid flow rate in some tubes or passages results in higher temperatures since the fluid mass to extract thermal energy is less than desirable. [0011]There are deleterious consequences of this type of uneven heating. One already mentioned is that the heated fluid has an undesirable and uneven temperature distribution as it exits the heater outlet and is delivered for its intended use. Other consequences of the uneven heating involve the heater construction. The materials used for the passages and the materials used to generate energy for heating the gas can irreversibly degrade at higher temperatures. Since the ultimate temperature required of the heated fluid is normally high, higher-than-specified temperatures in passages as a result of uneven flow through the heater can have adverse effects on the materials of the heater. [0012]One such undesirable effect will be in that the metallic components of the heater, especially those using electric heating elements, will be degraded and experience a shortened useful life and in some cases premature burnout. This is even more of a problem when the gas is air, given its propensity to oxidize metallic materials. The excessive temperatures will ultimately oxidize the heater materials at a rate greater that for which the product was designed. [0013]Another undesirable effect of the overheating is that ceramic materials, such as the extruded honeycombed heater core or parallel tubes, may operate at sufficiently high temperatures so as to compromise the ceramic material's dielectric properties. This will result in current leakage and deterioration of any electric current carrying parts such as heating elements. [0014]Accordingly, improvements are needed in the field of process electric heaters which employ multiple passages to heat a flowing gas. The present invention responds to this need by improving the construction and operation of these types of heaters through the use of a ceramic foam material, which is utilized at least as flow diffusers for control of the inlet and outlet flow characteristics of the heater. SUMMARY OF THE INVENTION [0015]A first object of the present invention is an improved multi-passage electric heater. [0016]Another object of the invention is an improvement in the method of using multi-passage electric heaters for heating gas. [0017]Yet another object of the invention is the use of a ceramic foam material as a diffuser for one or both of the inlet and outlet of the multi-passage electric heater. [0018]Other objects and advantages of the present invention will become apparent as the description thereof proceeds. [0019]The invention is an improvement in multi-passage electric heaters having a heater core, an inlet and an outlet, wherein at least some of passages of the heater core each include an electric heater for heating a gas passing therethrough. The improvement of the invention comprises employing a ceramic foam material that is placed over at least a portion of one or both of the inlet and the outlet of the heater. The ceramic foam material can be used for both the inlet and the outlet of the heater, and can cover the inlet and outlet in their respective entireties. [0020]The ceramic foam material can take any shape consistent with the heater inlet and outlet configuration, and can include openings for service wiring. The opening can also account for dead spots in the heater core and provide weight reduction and the like. [0021]The ceramic foam material can be any type of a ceramic foam that would provide diffusing and distribution characteristics for the incoming and outgoing gas stream passing through the heater. As well, the foam can be any type that provides an insulating property and heat retention property to function as a heat exchange medium, particularly when used as an outlet diffuser. One example of such a ceramic foam is a magnesia-stabilized zirconia. Continue reading... Full patent description for Multi-passage electric heater using ceramic foam as a diffuser and method of use Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Multi-passage electric heater using ceramic foam as a diffuser and method of use patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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