Air heaters with passive ceramic radiant elements to increase the radiant component of heat transfer

Abstract

Air heater with at least one electric heating element for heating a gas stream, characterized in that at least one passive ceramic radiation element is arranged in the flow channel, which is not electrically contacted, is heated predominantly by thermal radiation from the heating element and emits heat radiatively and convectively to the gas stream through its emitting surface, wherein the radiation element increases the radiative component of the heat transfer in the air heater.

Description

Technical field

[0001] The invention relates to an electrically heated air heater for heating a gas stream, in particular an air stream, for industrial high-temperature applications, for example in industrial furnaces, drying plants or thermal process plants. State of the art

[0002] Known air heaters have at least one electric heating element arranged in a flow channel that heats a flowing gas stream. Heat transfer from the heating element to the gas is predominantly convective. The radiative component of heat transfer is limited, especially with heating elements that have a small emitting surface or with materials that have a low emissivity.

[0003] To increase heating power, the electrical power is usually increased or the geometry of the heating conductor is changed, which can lead to a higher thermal and electrical load on the heating conductor as well as a shortened service life. Object of the invention

[0004] The object of the invention is to provide an air heater in which improved heat transfer to the gas stream is achieved with the same electrical power, so that a lower thermal load on the heating conductor is possible. Solution to the task

[0005] The problem is solved by an air heater with at least one electric heating conductor, in which at least one passive ceramic radiation element is additionally arranged in the flow channel.

[0006] The radiant element is not electrically contacted and is heated primarily by thermal radiation from the heating conductor. Through its emissive surface, the radiant element transfers the absorbed heat to the flowing gas stream both radiatively and convectively. This increases the radiative component of heat transfer in the overall air heater system. The radiant element consists of an oxide ceramic with a higher emissivity than the heating conductor or its insulating material. Ceramic materials such as cordierite, mullite, aluminum oxide, or comparable oxide ceramics are preferred. Advantageous embodiments

[0007] In a preferred embodiment, the radiation element is designed as a rod-shaped, tube-shaped, profiled or plate-shaped component and is arranged to be inserted or replaced in the flow channel.

[0008] The radiant element is preferably mechanically decoupled so that thermal expansion can be accommodated without constraints. The air heater is particularly suitable for operating temperatures above 700 °C, whereby the increased radiant component provided by the radiant element leads to improved heat transfer to the gas flow.

Claims

[1] Air heater with at least one electric heating element for heating a gas stream, characterized by , that at least one passive ceramic radiation element is arranged in the flow channel, which is not electrically contacted, is heated predominantly by thermal radiation from the heating conductor and emits heat radiatively and convectively to the gas flow through its emitting surface, whereby the radiation element increases the radiative component of the heat transfer in the air heater. [2] Air heater according to claim 1, characterized by that the radiation element consists of an oxide ceramic with an emissivity of at least 0.

5. [3] Air heater according to claim 1 or 2, characterized by that the radiation element consists of cordierite, mullite, aluminum oxide or a comparable oxide ceramic. [4] Air heater according to any of the preceding claims, characterized by, that the radiation selenient is designed as a rod-shaped, tubular or profiled component. [5] Air heater according to any of the preceding claims, characterized by that the radiation element is arranged in the flow channel in a way that allows it to be inserted or replaced. [6] Air heater according to any of the preceding claims, characterized by that the radiation element is mechanically decoupled. [7] Air heater according to any of the preceding claims, characterized by that the air heater is designed for operating temperatures above 700 °C.