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Precision Heat Transfer Measuring System
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| Enersyst´s heat-transfer monitors are ideal for a wide range of applications, including such industrial processes as thermosetting plastics. Other Enersyst models are used for the food service industry and applications such as commercial baking. |
On the surface, it doesn´t seem so difficult: if you want to measure how something heats up or cools down, you use a thermometer. But -- especially in a manufacturing environment -- it´s not that simple. Measuring air temperature is only part of the story.
Heating and cooling is really something called the thermal transfer process; that is, the process in which heat is transferred into (or out of) a product. This is measured by the calculation of the "h" value, or heat transfer coefficient -- the BTU per unit, per unit time, and per unit change in temperature relative to the surrounding temperature. In short, it requires much more than just a thermometer -- not only does the surrounding air temperature need to be measured, but the internal and external temperatures of the product itself, measured periodically over a specific length of time.
Why is this important? In critical heating processes -- say, the baking of bread -- heat transfer plays an important role because as the product changes (in this case, from dough to fresh bread), the chemical make-up of it changes as well, and the heat transfer process needs to be monitored to understand at what points oven temperatures and heat generation need to be adjusted to facilitate these changes. Once this is precisely understood, conditions can be replicated over and over again to assure rigid product consistency for volume production.
To accomplish this Enersyst has developed what they call a heat transfer rate target module measurement device. Simply put, this is a device consisting of one or more sensors (such as a thermocouple) embedded in a heat sink, a data logger, and a power source. The device can be either hard-wired or wireless and contained in a package robust enough to survive extremely hostile environments.
Enersyst has developed their device for use in both ovens and freezers, neither of which are limited to the food industry. For example, ovens are also used for thermosetting plastics and drying paints, while cooling is also used to preserve organic specimens and stabilize certain chemical compounds. Freezing processes -- particularly flash freezing -- are virtually impossible to characterize using time and temperature factors alone.
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| This graph shows how two drinks, when placed in the same temperature environment, will cool at different rates based on the heat transfer. Forced convection has a better heat transfer, and so it cools faster. This is why you need a heat transfer monitor and not just thermocouples in the air. |
Commercial baking often involves both types of heating: radiant and conduction, and particularly the convection form of conduction, which combines fluid mixing and the short-range interaction of atoms, molecules, and electrons. In ovens, the fluid is actually the atmosphere and the convection can be natural, forced, or hot-air impingement. Radiant heat is the transfer of heat energy by electromagnetic waves which can be absorbed, reflected, scattered, or transmitted.
To accurately measure heat transfer in ovens and freezers, Enersyst packages its device in a cylindrical or plate-shaped package about six inches in diameter and a quarter inch thick, these two shapes being the most efficient for uniform heat transfer. Both the surface area and the thickness can be adjusted to more closely match the actual product being heated (or cooled) for more accurate measurements. To further increase accuracy, specific materials or coatings can be used for the device, or "target," to more closely duplicate the thermal characteristics of the product. For example, dark gray anodized aluminum surfaces tend to absorb more radiative energy, approximating the response of many food products to heating.
The device can be used in both ovens and freezers, neither of which are limited to the food industry
Embedded in the device are several sensors, ideally set up to measure the surrounding atmospheric temperature, the surface temperatures and the internal temperature. These readings are then captured by a data logger, typically a digital memory chip, coupled with a clock and a power supply. Because the sensors (such as thermocouples) take analog readings, an analog-to-digital converter is included. The memory chip can store an average of 200 data points and the times of their readings for each of up to five different inputs. In a wireless configuration, this data is then retrieved from the device and downloaded to a personal computer for analysis and permanent storage. Data loggers can also be located remotely from the device and receive input via wiring.
To return to our baking example, by closely analyzing the data gathered by the heat transfer target module, a detailed picture of how the baking process affected the baked good can be established. A bottom sensor records how the bottom of the bread pan heated and initiated the rising of the dough, while a top sensor indicates how the change in direction and intensity of the heat from hot-air impingement browned the crust and created texture. This data, combined with the proper use of ingredients, assures consistent baked goods time after time.
This same data measuring, logging, and analysis using Enersyst´s technology can be used in a wide variety of industrial, commercial, and retail heating and cooling applications.
