Thermoelectrics Unlimited, Inc.
Using Cold Plates

    Heat radiates; cooling power does not.  This simple property of thermodynamics has a huge effect on the effective use of cold plates in the laboratory.  If you are used to using hot plates, mostly what you have to do is set the vessel on the plate, turn the power on and wait.  Heat will emanate from the plate, the vessel will absorb it and the contained sample will warm up.  At equilibrium, you can expect a relatively small temperature differential between the plate and the sample because heat is flowing in a natural, favorable direction.  Not so with cold plates.
    Transfer of cooling power depends almost entirely on contact.  An irregularly shaped contact surface at the junction to the plate blocks the conductivity of cooling power and makes it very difficult for the instrument to extract heat from the sample.  The flatter the mating surface, the better, such as, ground bottom glassware and machined aluminum blocks.  A few drops of a heat conducting oil, such as silicone oil, can make a huge difference in the rate of heat pumping.  
    Thermal gradients are also a problem when cooling.  Since heat rises, a warmed sample will usually maintain a fairly good vertical equilibrium.  A cooled sample, however, will be cold at the junction to the plate and can be close to the initial temperature at the top.  This problem is addressed in several ways: stirring of a liquid sample (hence the Stir-Kool), using the minimum  possible sample size, or inserting the vessel in an aluminum block.  These methods will contribute to vertical thermal equilibrium in a cooled sample.
    Condensation is anathema to cooling.  An uninsulated vessel at the dewpoint acts as a room dehumidifier; the cooling power goes into converting ambient humidity into water droplets, virtually stopping any further cooling of the sample.  To get low temperatures, it is imperative that the vessel be insulated. Polyfoam jackets and acrylic chambers are several ways of limiting condensation.  
    Thermoelectrics Unlimited, Inc. offers a full line of ground bottom glassware and machined aluminum blocks, heat transfer fluid and thermal grease, and insulating devices.  These products can significantly increase the performance of a cooling process. For specific product applications, we can recommend products and methods of use to make your particular process efficient and effective.  Put us to work for you!

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