Our temperature-controlled products use the Peltier principle. When controlling the temperature of a cuvette, the cuvette sits in a black-anodized aluminum tower, pressed gently into a corner. A Peltier device is attached to either the bottom or side of the tower. A Peltier device acts as a heat pump. Run current through it in one direction and it will remove heat; run the current in the opposite direction and it will add heat.
The Peltier device is driven by a modified PID (Proportional, Integral, Derivative) temperature controller. Set a target temperature and the controller powers the transfer of heat to or from the cuvette tower. The controller reduces its effort as the temperature of the tower approaches the target, and finally maintains an adequate current to stabilize the tower at the target temperature. Our temperature controllers are “bipolar” controllers capable of heating above or cooling below ambient temperature.
A heat exchanger is placed on the other side of the Peltier device. When cooling your sample, heat is deposited into the heat exchanger; when heating, heat is drawn from the heat exchanger. Heating with a Peltier device is more efficient than cooling. Joule heat is generated in the elements of the Peltier device, as you run electrical current through them. This heat diminishes cooling capability but increases the ability to drive the temperature up.
In an “air-cooled” system, the heat exchanger attempts to come to equilibrium with the temperature of the surrounding air. With a “water-cooled” system, flowing water or other coolant provides or removes heat. Water holds about a thousand times as much heat as an equal volume of air and is thus much more efficient for heating and cooling.
The heat exchanger on a water-cooled system is a block of brass with holes running through it. Attach tubing and circulate water. Use your own circulating bath or purchase one of the options available from us. When working at high temperatures, use warm water; use colder water for lower temperatures. Water can provide heat, but mostly draws heat from the Peltier device.
For air cooling, we add copper fins and a small fan. We retain the brass water heat exchanger for times you might want to use water to change temperatures rapidly or plunge the temperature below 0 °C. You may need to purchase a special option to circulate water on an air-cooled system. Again, the air can provide heat, but mostly draws heat from the Peltier element.
Air cooling is convenient since you will not need to maintain a circulating bath near your spectrometer. If available, use it for most routine work. If you plan large frequent temperature changes or plan to push the low temperature capabilities of your cuvette holder, connect the water.
Air cooling with one of our products will give you good stable temperature control from about zero degrees C up to as high as 110 °C or 150 °C, depending on the product. You may notice that your cuvette holder performance with air cooling is as good or better than that obtained by any other company with water cooling. How we accomplish this feat is a trade secret, but you will sometimes hear us speak of “cascading Peltiers.”
Water cooling is simpler and less expensive than air cooling. It is also required, when you wish to drop the temperature of your cuvette well below the ambient temperature. You will note that our Brr 20 and Brr 30 products capable of -55 °C require water cooling.
Finally, a Peltier device is often called a thermoelectric cooler, or TEC. We use the term “Peltier device” to honor Jean Charles Athanase Peltier, who did so much for us in 1834 when he and reported the effect since named for him.