This cut-off defines I max for thethermoelectric. For each device, Q max is the maximum heat load that can beabsorbed by the cold side of the thermoelectric. The T max value is the maximum temperature difference across the thermoelectric.
These values of Q max and T max are shownon the performance curve Figure 3 as the end points of the I max line. Suppose a designer has an application with an estimated heat load of 22watts, a forced convection type heat sink with a thermal resistance of 0. The cold side of the thermoelectric will be in direct contact with the object.
The designer has a Melcor CP1. The specifications for theCP1. To determine if this thermoelectric is appropriate for this application, itmust be shown that the parameters T and Q c arewithin the boundaries of the performance curves. The parameter Tfollows directly from T h and T c. Without knowing the power into the thermoelectric, an exact value of T h cannot be found.
Equation 3 gives the temperature difference across thethermoelectric:. Figures 2 and 3 show performance curves for the CP1. Performance Curve T vs. Once thepower into the thermoelectric is determined, Equations 1 and 2 can be used tosolve for T h and to determine whether the original estimate of T h was appropriate. The input power to the thermoelectric, Pin, is the product of the currentand the voltage. Using the 3. The calculated T h is close enough to the original estimate of T h ,to conclude that the CP1.
If an exact solution needs to be known, the process of solving forT h mathematically can be repeated until the value of T h does not change. The material used for the assembly components deserves careful thought. Theheat sink and cold side mounting surface should be made out of materials thathave a high thermal conductivity i. However, insulation and assembly hardware should be made of materialsthat have low thermal conductivity i. For the sake of argument, it might turn out that to move 1W out of a junction, you have to add an additional 1 W, meaning that your final heatsink has to reject 2 W to the environment instead of the original 1 W.
Whence does the extra energy come? Through those nice, quiet, electrical terminals. Indeed, that problem is why your T j was hotter than you wanted to begin with. For instance, your PC board resistance might have to be 2x lower than it was before bigger heat spreader, larger fan, etc. Now I can think of a couple of situations where a TEC might be an excellent choice, but you need to be very sure of your calculations. Whether heat is absorbed or expelled depends upon the direction of both the electric current and temperature gradient.
This phenomenon, known as the Thomson Effect, is of interest in respect to the principles involved but plays a negligible role in the operation of practical thermoelectric modules.
For this reason, it is ignored. Power Semiconductor Substrate. Process Tool Parts Cleaning. Opto-electronics, Laser, and Infrared Applications. All rights reserved. Legal Information. Do You Need More Information? The Peltier effect describes what happens when an electric current flows through two different types of conductors for example, different types of metal like copper, zinc or bismuth telluride.
When DC voltage is applied and direct current runs from one conductor to the other, there's a change in temperature where the two conductors join. If you run electricity from a bismuth wire to a copper wire, the temperature will drop at the junction where the wires meet. When you take this small thermoelectric effect and multiply it, you can create a cooling effect strong enough to keep electronic components in a computer cool — or chill the inside of a wine fridge.
This is typically done by creating many such junctions between two ceramic plates. When electricity runs through the whole thing, one plate is the "cool side" while the other is the "hot side. Thermoelectric cooling TEC is also known as solid-state cooling, because there is no liquid refrigerant running through the machine.
Instead, solid metal is used to transfer thermal energy. In general, Peltier coolers work best in small spaces, particularly for electronic devices where there simply isn't enough space to put a compressor-based cooler. In a small size cooler, these systems are also quite efficient and may use less electricity than a compressor-based unit of the same size. Thermoelectric cooling also allows for very fine temperature control, to within 0.
Solid state cooling units are also have no moving parts, so they are far less likely to break than a traditional compressor, which requires several fans and lengthy coils through which refrigerant must pass. The refrigerant itself is also problematic from an environmental standpoint: Chlorofluorocarbons CFCs and hydrochlorofluorocarbons HCFCs are known to damage the ozone layer if they leak from a faulty machine.
Peltier devices, on the other hand, are no more harmful to the environment than a light bulb or basic fan you plug into an electrical outlet. Finally, thermoelectric cooling is silent. Unlike a compressor, which vibrates when running and can be quite loud when it cycles on, the simple electric current required to run a TEC makes no sound at all, unless a fan is present to improve air circulation.
Thermoelectric cooling units quickly become costly when used in large spaces. This is because you need to add more ceramic plates to cover a larger area, and this will require higher input voltage to operate. The more ceramic plates you have, the more electricity you'll need to use to run the machine, whereas a slightly larger compressor doesn't use that much more electricity than a smaller one. Thermoelectric cooling is entirely dependent on the ambient temperature for its ability to cool.
Unlike a compressor system, which can maintain sub-freezing temperatures in certain applications, a thermoelectric device can only bring down the temperature to a certain point below room temperature. That means that if it's 65 degrees outside, and your TEC can bring down temperatures by 30 degrees, you can achieve a low temperature of 35 degrees.
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