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Generally, a heat exchanger functions to transfer heat between two fluids. In a large number of industries, a concentric tube heat exchanger is utilized for such processes as air-conditioning, the preparation of food, material processing, waste heat recovery, pharmaceutical industries, chemical processing, transport, cryogenics distillation and power production. They operate by developing a driving force of temperature when passing streams of fluid of varying temperatures, all parallel to one another and separated by some physical boundary such as a pipe. Three different heat transfer operations occur; the convective transfer of heat from the fluid to the tube's inner wall, a conductive transfer of heat passig from the tube's wall, and the convective transfer of heat from the tube's outer wall to the fluid on the outside. What this achieves is a forced convection that will transfer heat from and to the product. These heat exchangers are produced in a number of designs and flow arrangements and the double-pipe or the concentric tube design is one of the simplest. In this design, a pipe is located within another, and outlet and inlet ducts are present for the fluids. In this design, one part contains the hot flowing fluid that transfers its heat across the metal's wall, which is often made of stainless steel or copper, to a cold fluid. The diameter size of the tubes with relative to one another is the most critical factor that influences the size of the heat exchanger. 
The flow is called a parallel flow if both of the inlets are flowing in the same direction and on the same side. The opposite configuration is called a counter flow. Both of these flows are quite commonly used, but because the counter flow can provide a greater temperature differential when cooling and heating a liquid, it is the most often used. The most common use for the parallel flow is to create a common temperature for the two liquids. |
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