TIP 1: Understand How Heat Affects the Application
Understanding how heat affects your application is the first step toward selecting a heater. Factors such as heat response time, maximum heat transfer, life expectancy requirements and ease of service must be considered. While all factors are important, an overriding factor such as maximum possible operating temperature may be most important when determining final heater design.
TIP 2: Determine the Best Heater Design
A number of process heater designs are offered on the market, including tubular, immersion, cast-in, mineral-insulated cable, silicone rubber and cartridge. Variety ensures there will be several process heating solution options. Premature failures or inadequate heat distribution problems with one style may be eliminated by an alternative heat source better suited for the application's operating parameters. When problems persist, explore alternative heating options.
TIP 3: Ensure the Design Supplies Wattage for Adequate Heating
Basic physics dictates different media will heat at different rates. This typically is referred to as the specific heat value of the material (BTU/lb ?F). Using this value, calculations can be made to determine the wattage required to heat up and maintain operating temperature for specific materials. Once the correct wattage required for the application has been determined, review optional heater designs to determine the best overall solution.
TIP 4: Carefully Select Electrical Termination
A heater's electrical termination typically is the most sensitive design area. A predominant failure mode is failure of not the heating element itself but the termination point of the electrical terminals or lead wires to the element. When deciding on a specific heater design, special attention should be given to the application's functional requirements and how they will impact the termination selection. Factors such as vibration, flexing, high temperature, moisture or other environmental variables can significantly impact the electrical termination and cause heater failure.
TIP 5: Ensure Heater Design Provides Adequate Heat Transfer
To be effective, a heater must deliver adequate energy to the application medium. This involves not only sufficient wattage but also the heater's ability to provide sufficient heat distribution across the process area. Even though wattage may be calculated accurately for the specific material being processed, the heater design must be able to disburse heat properly. Physical features such as how the heater will be mounted, the amount of area that will be covered or the possibility of multiple heat zones should be considered. Also, consider any heat sink effects that may draw heat away from the application medium.
Heaters typically are constructed of stainless steel, nickel alloys, aluminum, bronze, ceramic or silicone rubber. Lead wires are insulated with various fiberglass or polymer materials. Ensure that all materials used in heater construction are rated to handle the maximum application temperatures to which they will be subjected. The heater also must be designed to handle the application environment, which may include caustic liquids, high humidity or washdown maintenance conditions.
TIP 7: Consider Field Service Issues
To avoid premature failure or downtime, a heater must be installed and maintained properly. To minimize the amount of time spent solving heater problems later on, consider access to electrical terminations, heater removal and installation, and general maintenance procedures during the selection process. Understanding how a particular design will be serviced and maintained will leave you better prepared to handle eventual replacements and develop better predictive maintenance schedules.
TIP 8: Ensure Proper Temperature Control
Accurate temperature control is vital to process heating applications. The heater's design should allow a temperature sensor to be integrated into the heating system to monitor process temperature. Some designs such as cartridge or immersion heaters can have a temperature sensor as an integral component. Other designs such as cast-in or band heaters can be designed with mounting holes for accurate sensor placement. Regardless of heater type, accurate temperature control is required for optimal performance.
TIP 9: Verify if Any Modifications To Wiring Will Be Required
In addition to the actual performance, it is important to consider existing electrical wiring issues when choosing a heater. Determine if existing wiring can sufficiently handle the heater's electrical requirement. Factors such as the service voltage, current draw and ambient operating temperature will determine the wire gauge required, conductor material and wire insulation selection. To be absolutely certain, consult the National Electric Code Handbook.
TIP 10: Make Sure The Heater Can Be Installed and Operated Safely
The primary concern when specifying a heater design must be installation and operation safety. As all heaters pose a risk for injury or damage, it is critical to understand the safety requirements involved. A simple common sense practice involves avoiding fire hazards by installing heaters away from combustible materials or gases.
Choose an element watt density that will not exceed the maximum operating temperature of the application medium. Make sure the design has the proper electrical enclosures, particularly in hazardous locations. In addition, all heaters should be installed and maintained by trained electrical personnel in accordance with the standards set forth in the National Electrical Code.
A number of design factors can affect heater performance. Look closely before choosing a specific design for your process.