How do you determine the required power for a silicone rubber heater ?
A flexible heater is designed to adapt to the surface to be heated, providing great versatility. Among the many varieties available are silicone heating elements, polyimide films, heating strips, heating strips with thermostat, heating cords, heating tank wraps, gas cylinder heaters, as well as solutions custom made. Flexible silicone heating elements are distinguished by their robustness, reliability, precision, and resistance to humidity and chemicals, in addition to their ease of installation and adaptation to other system components.
They therefore find wide applications in the industrial, commercial and military sectors, where reliability, cost-effectiveness, compactness, resistance to wear and flexibility are essential criteria. Precise determination of your power needs is crucial to guarantee peak performance of the heating system. Let’s see this in more details !
Empowering your heating solutions starts with a thorough understanding of your power requirements. Powering Up offers the roadmap to ensure your silicone flexible heater performs at its best.
How to determine the required power for a silicone rubber heater?
Selecting the appropriate heater entails careful consideration of critical aspects.
About your project
- Temperature Requirements. The desired operating temperature of the application is pivotal. The temperature differential between the target temperature and ambient conditions dictates the required heat output.
- Operating Environment. Considering ambient temperature and operational conditions is essential in wattage determination.
- Surface Area. The size of the area necessitating heating significantly impacts wattage calculation. Larger surfaces typically demand higher wattage to achieve the desired temperature.
- Insulation/Heat Loss. Evaluating insulation effectiveness and potential heat loss is crucial. Applications experiencing rapid heat dissipation may require elevated wattage to offset losses.
- Safety Margins. Incorporating safety margins is customary to ensure the heater can withstand unexpected variations or environmental changes without risking overheating.
How to determine the required power for a silicone rubber heater – ohmvo.comAbout the heater
- Temperature Range. Ensure the heater can operate within your application’s required temperature range, typically between -60°C to 200°C, with some models capable of higher temperatures.
- Material Thermal Conductivity. Material properties influence the wattage requirement. Materials with lower thermal conductivity may necessitate increased power input to reach the desired temperature.
- Size and Shape. Consider the dimensions of the heater to ensure it fits within the available space in your application.
- Watt Density. Select a heater that matches the desired watt density, ensuring it delivers the necessary power output relative to the surface area to attain your target temperature.
- Voltage. Ensure compatibility with your power supply voltage when selecting a heater.
- Chemical/Moisture Resistance. Select a waterproof or water-resistant heater if it will be exposed to moisture. If exposed to chemicals, opt for a heater compatible with the substances encountered.
Understanding heat transfer
Before we dive into the calculations, let’s clarify the difference between energy and power, and how they relate to wattage requirements.
In simple terms, power is measured in watts (W), while energy is measured in watt-hours (W x hr) in the metric system.
To determine wattage requirements, two values need to be calculated: warm-up and operating heat. If heat loss is negligible, the power required for warming up a material follows a linear function involving the material’s mass, specific heat, temperature change, and desired warm-up duration:
Where:
- 𝑃 = Heater power (W)
- 𝑚 = Mass of material (g)
- 𝐶𝑝 = Specific heat of material (J/kg·K) from Table 1
- 𝑇𝑓 = Final Temperature of material (°C)
- 𝑇𝑖 = Initial temperature of material (°C)
- 𝑡 = Desired warm-up time (min)
This equation provides a straightforward way to estimate power if warming up is the main concern and heat loss is minimal. However, it usually gives a cautious estimate. To be more accurate, add about 10% to account for any potential heat losses you’re unsure about.
Understanding heat transfer – ohmvo.comOhm’s Law
Understanding Ohm’s Law is essential for calculating the load when using a thermostat or digital controller, as it illustrates the connection between voltage, power, current, and resistance. For instance, if you choose a flexible heating element rated at 200 Watts with a 120 Vac supply, the current would be 1.6 amps according to Ohm’s Law.
A is equal to W /V where: A = amps; W = power; V = voltage. For example, 200 Watts/120 Vac = 1.6 amps.
Finally, to determine the kW required to heat a solid, the following formula is used.
kW = (WT x Cpx Δ T)/3412 x h
Where :
WT= material weight, lb
Cp= specific heat, BTU/lb- °F
Δ T = temperature rise, °F
3412 = BTU/kWh conversion factor
h = heating time, hours
Estimating the required wattage
For silicone rubber heaters, the following guidelines are commonly used :
- Low Heat-Up: 2.5 watts per square inch (w/in²).
- Average Heat-Up: 5 watts per square inch (w/in²).
- High Heat-Up: 7.5 watts per square inch (w/in²) and above.
The equation will depend on the material :
- To heat water in a tank : Watts = 3.1 x Gallons x ΔT (in °F) / Heat-Up Time (in hrs).
- To heat oil/viscous liquids in a tank : Watts = 1.35 x Gallons x ΔT (in °F) / Heat-Up Time (in hrs).
- To head solids : Watts = 0.05 x Lbs of Steel x ΔT (in °F) / Heat-Up Time (in hrs).
An example ? Let’s say you want to heat a block of material :
- Mass (m): 500 grams.
- Specific heat (Cp): 0.5 J/kg·K.
- Initial temperature (Ti): 20°C.
- Final temperature (Tf): 80°C.
- Desired warm-up time (t): 30 minutes.
Using the formula :
Substituting the values :
Add a safety margin of 25%, the required wattage reaches here 625 watts.
Temperature sensors for flexible heaters
While calculations are valuable tools in designing thermal equipment, experimentation remains indispensable for achieving optimal performance. Making practical testing is indeed essential. Mounting a heater and powering it up allows for firsthand assessment of its effectiveness. If you’ve used our guide to estimate power and added a sufficient safety margin, the specified wattage should suffice; otherwise, redesign may be necessary.
Temperature sensors for flexible heaters – ohmvo.comA variety of temperature controllers and sensors can be selected depending on the specific needs of the application. Among the most commonly used sensor types for applications involving flexible heating elements are surface temperature sensors. These sensors, such as thermocouples, RTDs or thermistors, are available with a built-in adhesive or can be attached to the heated surface. Additionally, simple thermostats are also available for basic applications while digital temperature controllers come in different sizes, offering a variety of input and output options. Thermocouple and RTD inputs are the most common, accompanied by mechanical relays or DC pulse outputs. DC pulse outputs allow the user to activate a more powerful relay to control the heating load.
For intricate heating requirements, the Ohmvo engineering team is readily available to offer assistance with calculations and tailor solutions to meet your specific heating demands !