5 Fundamental Rules for Designing Efficient Heat Transfers
Considering these basic rules for designing thermal heat transfers will expand a project’s productivity, enhance your process, and diminish energy loss.
An electric heater can distribute heat where needed and when connected with a properly placed thermocouple will ensure control in your process and provide a constant state. However, a poor design or improper placement of the sensor for the heating system could result in a concept that is not ideal and could produce an increase in premature failures. Following the fundamental rules for design will eliminate costly rebuilds or modifications to designs when it comes to best utilizing your industrial electric heater.
An adequate comprehension of the fundamental conventions of heat transfer is imperative for any project’s success. The properties of heat transfer are similar to that of a sound wave. Heat, like all elements of energy must follow physics laws.
By adhering to the fundamental rules for designing heat transfers, you are more apt to achieve the desired end state for your project and avert costly errors.
1. Heat Must Have a Straight Path
When a radiator vent is closed or obstructed, a room will get cold. The same is true for any heat path, suffice it to say, it must remain unobstructed and heat does not magically bend around obstacles. Likewise, holes, pockets, slots or other misdirection could create an opportunity for the heat to stray from its intended destination.
In illustration, examine the application wherein a thermocouple’s location in a packaging jaws set blocks a portion of the heat transfer. An (FEA) or finite-element analysis would show that only two-thirds of the area within a seal face meets the temperature band of 6°F or 3.3°C.
A redistribution of wattage could assist to make the profile more even, though not 100 percent. A change to the watt density at the heater’s end will increase the area to 86 percent of the temperature band. Although a hole still exists, the compensation of an increase in wattage could make the design more feasible. Occasionally, difficult designs have no functional alternative; however, an expert could provide an adequate alternative when facing challenges that others might not have considered.
2. Examine Design Alternatives for Accurate Temperature Bands
In order to avoid further expenses, all options must be looked at in the design stage to preclude cost and time over runs or production of an inadequate design. Heating experts are aware of available designs that will fit your needs and reduce costs, if asked. When a standard heater does not fit the design or will not produce the correct temperature band requirements, it may require a non-standard heater.
In the packaging jaw case, a conversion to an energy-focused design could significantly reduce power requirements. The use of state-of-the art FEA software could allow a designer to evaluate thermal needs and produce a solution that offers better uniformity, a faster cycle and slashed power consumption. The change to a design utilizing a focused heater will reduce the power requirements from 650 W to 125 W. That is a significant savings and ultimately results in lower expenses for materials. In addition, this method offers easier heater replacement than a seized cartridge heater.
3. The Basic Rules for Designing: Affirm that Energy Must Be Controlled
One of the basic rules for designing any heater is to ensure the temperature can be controlled. When a thermocouple is too close to a heater or to the surface where the temperature band will be measured, its reading could be skewed and an inaccurate controller set point returned. In an ideal situation, you will want an accurate measure of the temperature on the working surface. Correct thermal placements reduce temperature differentials (Δ) between the working temperature and the set point. This will provide a more accurate analysis of the true process environments.
A second scenario involves how web thickness and mass affect the distribution of heat. When web thickness is not enough, the heat does not radiate evenly. On the other hand, when the web is thicker than necessary, process recovery could be slowed and efficiency diminished.
Therefore, both the temperature sensing location and the web thickness determine accurate heat transfer. When the thermocouple temperature band matches the working surface temperature, the heating process is better controlled. When the process is not sufficiently controlled, the heat distribution will not be ideal.
4. Preserve Groove and Bore Integrity
Longer heater life and increased savings can be attained by excellent fits. Electric heat, by definition is efficient to 100 percent; however, the heat transfer process is not efficient to 100 percent. There is a loss between the heater and the product which needs heating.
Getting top performance from the electric heater means an intimate connection within the process. Design conditions must ensure a tight, smooth fit.
Optimal heat transfer is realized when the heater is pushed into the tool, when possible. This permits a watt density that is higher, which allows a longer life for the heater. Care must be used when pushing the heater into the tool. Some deformation may be acceptable, but not compression. Check with a thermal solution partner for proper installation procedures to provide a longer lifespan for the heater.
5. More Wattage Does Not Always Equal Better
You might have heard that more watts are better however, that may not always be the case. The bulk of the energy expended is used while bringing the heat up to the desired temperature from the room temperature. To maintain a set point, only 20 percent of that initial output in watts is needed. Therefore, when you introduce more wattage into the process to increase the temperature, it will probably make no difference whatsoever during actual operations at temperature. However, rapid rises in temperatures leave the tool susceptible to warpage and a shorter lifespan for the heater.
In summary, although heat is a powerful tool when utilized efficiently, there is no magic. It is up to the operator to properly control heat distribution and designers to draft more efficient applications to better use heat transfers by utilizing the previous five fundamental rules.
It is imperative to any industrial heater’s lifespan and energy conservation to consider the basic rules during development and design. A small change can substantially impact heater life expectancies, processor speeds, and tool quality.
A thermal solution partner and/or heat transfer experts can propose expertise to ensure a better design, which includes a more efficient system.
（content from the wattco）