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Split and Concat - Elongated Thermoelectric Cooling Solutions
May 14, 2009
In a certain amount of applications a thermoelectric (Peltier) cooler with elongated shape is required. For instance, DPSS (Diode Pumped Solid State Lasers) may need TEC with rectangular shape to fit pump module and a holder with crystal, and some of them may need more space than typical telecom TEC dimensions can provide. Or another example - thermoelectric cooling for some CCD matrixes with long planar shape, like 10x110mm2 or so.
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Three TE coolers connected in parallel form TEC Stack with 12x30mm size.
However, too long shape of thermoelectric cooler may cause a problem in application because of thermal stress. In a thermoelectric cooler operational mode there are significant temperature changes of TE module elements, caused by the gradient of temperature between the cold and hot sides of the design.
The materials of the design have different coefficients of temperature expansion (CTE) resulting in inevitable mechanical strains that may destroy the thermoelectric cooler. It is shown on the picture below.
If typical elongated telecom thermoelectric cooler dimensions like 6.0x12.2mm2 or 7.0x15.0mm2 usually avoid such a problem of thermal stress with a proper mounting methods, but any longer shape with width/length proportion 1:3 or higher may have this problem. And the most optimal method is to apply TEC Stacks - several equal thermoelectric coolers, assembled in line. Being connected in serial or parallel, several TE coolers will operate as a single unit, providing the required size, temperature difference and cooling capacity. Moreover, with a parallel connection between thermoelectric coolers such TEC stack has advanced reliability, because any failure of single unit won't cause a failure of a whole assembly.
The materials of the design have different coefficients of temperature expansion (CTE) resulting in inevitable mechanical strains that may destroy the thermoelectric cooler. It is shown on the picture below.
If typical elongated telecom thermoelectric cooler dimensions like 6.0x12.2mm2 or 7.0x15.0mm2 usually avoid such a problem of thermal stress with a proper mounting methods, but any longer shape with width/length proportion 1:3 or higher may have this problem. And the most optimal method is to apply TEC Stacks - several equal thermoelectric coolers, assembled in line. Being connected in serial or parallel, several TE coolers will operate as a single unit, providing the required size, temperature difference and cooling capacity. Moreover, with a parallel connection between thermoelectric coolers such TEC stack has advanced reliability, because any failure of single unit won't cause a failure of a whole assembly.
There is another sort of applications, particularly in DPSS lasers, where two channels operating is required for temperature control - two separate TECs in different operating modes - one for pump laser and another - for crystal temperature stabilization. For DPSS laser cooling it is usually solved simply by two different (or equal) thermoelectric coolers installed in one package (like Butterfly or HHL), having each TEC with it's own temperature control. But even at visible simplicity of such solution, there are some important moments - optical adjustment of the assembled components and electrical power consumption in high power applications.
The optimal optical adjustment can be achieved by applying of the same material with good thermal conductivity and small thermal expansion for all mounting elements in the assembly (pump laser holder, crystal holder, photoresistor and etc). Also in terms of assembly it is also more convenient to have thermoelectric coolers pre-assembled for mounting, without a necessity to mount each TEC separately. It allows to avoid possible height differences, like different solder thicknesses under TECs.
RMT Ltd provides such solution, where two different TECs have one mutual ceramics for hot side - it can say "TEC split and concat" solution.
The power consumption can be an issue in high power laser applications, for example in HHL packages. In case of two TECs applied - one of them is high power unit for pump laser, and another one usually is less powerful, required for temperature stabilization of a crystal only. In case of both of them mounted on package bottom, high power TEC will heat up the package while transferring the heat from pump laser. And smaller TEC may operate at not optimal conditions, having bottom side at high temperature already. It may increase power consumption for smaller TEC. In this case, there is more intelligent solution.
For example, a common two channels thermoelectric cooling solution for HHL, provided by RMT Ltd, has two TECs, assembled in a sandwich. Smaller and less powerful thermoelectric cooler for crystal temperature stabilization is mounted on top of powerful TEC. In this case it will operate in optimal conditions, having the bottom side already pre-cooled. It decreases total power consumption, and is more convenient by compact form factor.
The optimal optical adjustment can be achieved by applying of the same material with good thermal conductivity and small thermal expansion for all mounting elements in the assembly (pump laser holder, crystal holder, photoresistor and etc). Also in terms of assembly it is also more convenient to have thermoelectric coolers pre-assembled for mounting, without a necessity to mount each TEC separately. It allows to avoid possible height differences, like different solder thicknesses under TECs.
RMT Ltd provides such solution, where two different TECs have one mutual ceramics for hot side - it can say "TEC split and concat" solution.
For example, a common two channels thermoelectric cooling solution for HHL, provided by RMT Ltd, has two TECs, assembled in a sandwich. Smaller and less powerful thermoelectric cooler for crystal temperature stabilization is mounted on top of powerful TEC. In this case it will operate in optimal conditions, having the bottom side already pre-cooled. It decreases total power consumption, and is more convenient by compact form factor.
RMT Ltd provides all above mentioned solutions and assistance in design and estimations of the most optimal cooling systems, based on miniature thermoelectric coolers.
