Monday, 23 August 2021 10:46

Understanding the factors affecting heat loss

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Understanding the factors that influence heat loss allows design engineers to better calculate the insulation and power needed to heat a product. Troubleshooting any inefficiencies and reducing heat loss can improve the efficiency of heating systems and save costs. Here, Johann Lainer, senior marketing communications specialist at industrial technology company Watlow, breaks down the factors related to heat loss and explains how to calculate predicted heat loss for your application.

Heat loss is the intentional or unintentional movement of heat from one material to another, which can happen through conduction, convection or radiation. Conduction often occurs when an insulated or uninsulated component is in direct contact with another component, convection occurs when a pipe, electric heater or other component has an air barrier around it, while radiation is when there is no contact and heat moves as waves.

How heat loss happens 

With an understanding of how heat loss occurs, it’s important to then select power and temperature controllers that best suit your heating situation. One way to do this is to account for common heat loss factors. While every scenario will have different factors affecting heat loss and transfer, uninsulated surfaces, vertical or horizontal insulated surfaces and oil, paraffin or water surfaces are common areas of heat loss that design engineers must account for when selecting heating products.

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Factors that influence heat loss can change when relocating a process or make changes to an assembly line. Targeting a facility’s heat loss factors and making necessary adjustments with controlling equipment or insulation strategies keeps your operations running at the same quality and consistency as it was before the change.

In addition, adjusting the temperature of a heater or protecting it from one or more of these heat loss factors can reduce the wattage usage of the system, saving a considerable amount in daily operating expenses.

Emissivity and heat loss

Emissivity is defined as the ability of a particular object or material to emit infrared energy. The emissivity of a heater, thermocouple and insulation can affect the heat loss by radiation. 

This is another piece of the puzzle when determining how much heat is required for a specific application. It’s important to explore the emissivity of the material in the heating process and identify whether the material is a polished surface or has medium or heavy oxide. Even non-metals are emissive, so the specific heat of insulation materials must be checked to see how it can affect overall heat loss.

Calculating heat loss

When working to reduce heat loss, adopting a predictive mindset is advised. Watlow recommends calculating a process or piece of equipment’s expected heat loss based on the location, insulation type and material being heated.

To understand how to calculate heat loss, multiply the convection curve value by a factor of 1.29 for horizontal heating products, whereas vertical pipes should use the direct value of the curve. For bottom surfaces, multiply the curve by 0.63. However, this offers a rough guide and the calculation does not consider other heat loss factors that may affect your product. Original equipment manufacturers (OEMs) need a more accurate way to measure heat loss for their specific product, so alterations known as emissivity values need to be made.

Using the graph is helpful at high temperatures, but as the temperature reaches ambient, or over 21 degrees Celsius, it can be difficult to read. There are two general rules that can help you arrive at a more precise temperature reading.

Firstly, calculate losses from an uninsulated surface close to 1.0 emissivity by dividing the temperature rise above ambient by 200, and secondly, calculate losses from an insulated surface with the approximate thickness of one inch and a thermal conductivity K- value of 0.5 by dividing the rise above ambient temperature by 950.

From controllers to heaters, or whether you’re looking to improve the efficiency of your process, Watlow offers a range of industrial heating equipment and technical guides to help design engineers understand and manage heat loss factors.

Heat loss is influenced by various reasons dependent on the material and application. However, the result remains the same — increased costs and more inefficiencies. Understanding what causes heat loss and knowing how to calculate the predicted loss of your application is key to maintaining productivity.

To find out more about Watlow’s products or to calculate heat loss, visit watlow.com/heat-loss-factors-and-graphs/.

About Watlow:

Watlow is a global industrial technology company that uses its world-class engineering expertise, advanced thermal systems and manufacturing excellence to enrich everyday life. Many of the world’s leading companies leverage our technology in vital applications such as semiconductor processing, environmentally-friendly energy solutions and lifesaving medical and clinical equipment, to name a few. Founded in 1922, Watlow’s culture is driven by our purpose of “Enriching Lives Through Inspired Innovation,” enabling us to deliver high-impact solutions that improve our customers’ competitive advantage.

 

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