It may seem strange to write an article about sample conditioning systems when they have been with us for so long in one form or another, stranger yet to include them under future trends on the website. Yet, the newer brands of instrument are becoming ever more dependent on such additions due to the advent of the portable infrared analyzer and generally more sensitive measuring systems. This means that external equipment such as sample conditioners will increase in importance in times to come.
Sample conditioners can be separated into three rough categories:
The refrigerant type will always be with us for a number of reasons. It is more efficient. Although no form of refrigerant system can be seen as particularly efficient in normal engineering terms, this type of cooler requires the least power input for a given cooling effect. They can be built to produce very high levels of cooling, making them ideal for stationary installations and similar use. The construction principles are well-known, making maintenance less of a problem. There are, nevertheless, some important drawbacks to the use of this type of equipment. The refrigerant used can become a problem for ecological reasons. The traditional R12 coolant that was used in refrigerators for years is out of popularity due to its contribution to the greenhouse effect. This change can only be applauded but has caused a number of problems in the refrigerant branch. Using propane as a coolant in electrical equipment can only be viewed with horror. Not only is it a highly flammable gas, but its contribution to the greenhouse effect is possibly greater than that of the earlier refrigerant. There are now other refrigerants on the market, but the price and efficiency have both undoubtedly suffered from the change.
The next disadvantage is weight. Anyone who has carried a household refrigerator up a few flights of steps will need no extra explanation to this point! A motor, compressor and evaporator have a certain weight, regardless of what you do. Related to this is the problem of bulk. The evaporator requires a certain area and the heat exchanger must be physically separated from the cooling unit to increase efficiency. There is no point in trying to cool your own waste heat energy!
Such a refrigeration unit has moving parts and, as we all know, anything that moves is subject to wear. Motors and compressors will wear out in time and require replacement, making routine maintenance essential.
The heat exchanger of a refrigerator is a fragile unit. Of necessity it consists of thin pipes or similar containing the hot fluid try to give up its heat energy. These can be easily damaged, leading to loss of refrigerant and, naturally, dysfunction.
Shaking the refrigerant in transport will lead to vapour locks which must be left to settle before the unit is used. Using the unit immediately after transport will lead to premature failure of the pump and other parts.
From the comments above perhaps produce the question of why anyone would use a refrigerant type when there is a Peltier element available. The answer is, of course, power and efficiency. A Peltier element requires an immense amount of current to produce the cooling effect needed and must generally be cascaded to produce any useful cooling at all. It simply has the advantage of relatively low cost, light weight and no moving parts. It can be instantly used after transport with out any fear of failure and will cool down more rapidly than the refrigerant type.
The last type, the catch-pot and its brethren, also have a place. They are perfectly acceptable where there is no fear of loss of sample due to solubility and have the great advantage of low cost and negligible maintenance, except for regular emptying!
This is naturally not everything that is required for sample conditioning, but cooling of the sample is the first stage. The next step is to remove the condensate quickly and efficiently from the unit before any effect on the gas becomes unavoidable. The most common method is the use of a peristaltic pump or similar to remove the water from the lowest point of the condensing chamber. Careful use of geometry can ensure that there is little contact between gas and condensate and, hence, minimal interaction.