This invention concerns forced air or gas heaters. Examples thereof are shown in U.S. Pat. Nos. 3,783,236, 3,654,431, 3,551,643 and 3,094,606.
This invention provides a forced gas heater that prevents premature heater element burnout due to overheating.
A major problem with any process heat application involving forced air or gas heaters is premature heater element burnout. Heater elements oxidize with heat, the higher the temperature, the faster the oxidation, and if the heater element gets hotter still, it will melt. Premature burnout can occur if gas flow is too low and the heater element gets hotter than it should. In this invention a built-in controller keeps the heater element from burning out prematurely, even if gas flow is completely stopped.
Because premature burnout is a common problem with gas heater use, external controllers, which are sometimes expensive, have been used in the past. These controllers normally operate by measuring exit gas temperature from the heater, and, if the exit temperature is too great, the controller will cut power to the heater. This works, but it can take too long to react if the thermocouple used to measure the gas is to massive or if it was moved somehow from the exit of the heater. Also, if the gas flow is suddenly cut off, the thermocouple will read an increasingly lower temperature, because the hot gas will not pass over the junction. Therefore, the controller actually puts more power to the element, when, in fact, the element itself is too hot already. One way users have eliminated this problem is by adding yet another component to the controller.
By using a flow-sensor/switch or a pressure-sensor/switch, the controller will cut power when there is an interruption or reduction in the gas flow. This must be used with the thermocouple temperature control to make the system work. It can fail easily, if there is too much pressure for the sensor/switch to take, for instance, if there is an unintentional burst of flow, the sensor may be pushed beyond its designed limits, and break. The user may also set these controllers to the wrong settings, and end up burning out the element because the controller was working, but within the wrong parameters.
Besides the added cost of all of this equipment to control, the space requirement often becomes a problem. Many users need to fit this equipment into small spaces, or into machines that they sell. There are heaters available that will control in a small space, but will not work when the gas flow is completely cut off.