Whether you are the Chief Product Development Engineer for a Fortune 500 company or an Entrepreneur with a great idea for a heated finished product, determining what you need from your heater can be a daunting task. Fortunately, it doesn’t have to be that way. Below we will outline the steps necessary for the most time and cost effective method to answer the fundamental question about heating elements – what wattage will I need in my application? Before we begin, it is important to note that Watt density is the central concept upon which flexible heaters are selected, designed and perform. Watt density is simply the wattage output of a heater relative to its size, typically expressed in the US in watts per square inch (wpsi). For example, a 10 inch by 10 inch heater which is 200 watts would have a watt density of 2 wpsi. All things being equal, the watts per square inch is the primary influence that determines the heaters operating characteristics in your application. Determine Watts per Square Inch required in your application. Step One: Establish a baseline: Before setting up a test protocol, identify the basic performance characteristics you are looking for from the heater in your application. These typically include operating temperature, ambient conditions for the application and time required to reach the desired operating temperature. Step Two: Recreate the environment: As you set up your testing area, make sure to consider the actual operating environment and try to replicate that as closely as possible. For example, make sure that your test area includes adequate air-flow if the application is used in an exposed environment, or conversely, that an insulated environment is used if the heater is to be in an enclosure. Incorporate insulation, substrates and other fixtures or objects that might influence the thermal properties of the heater. Step Three: Gather Test Equipment: At this point, it is not always necessary to have an exact prototype made to fit your application – function is paramount. The basic equipment needed to evaluate watts per square inch include:
Step Four: Test to find the required Watt Density: NOTE: NEVER LEAVE HEATER OR TEST AREA UNATTENDED WHILE HEATER IS OPERATING!
Step Five: Calculate the required watt density in your application using the following formula:
WPSI = / total square inches in the heater. |