Heat exchangers, which are also known as heat transfers, are devices that are used to transfer heat from one fluid to another through a solid surface. Heat can be transferred through either heat absorption or dissipation. Heat exchangers are basic in concept however they have complex designs where characteristics such as material, thermodynamic laws, and liquid characteristics work together to get optimal end results.
Heat exchangers are used in both commercial and residential applications as they are found in items such as car radiators, refrigerators, boilers, air conditioners and furnaces. Industries like HVAC, petrochemicals, food, utilities, and oil and gas have a great demand for heat exchangers. These items help to cut down on expensive electricity bills by recovering wasted heat and channeling that heat more efficiently.
Hot and cold liquids enter separate chambers or tubes of the heat exchanger unit. The hot liquid transfers its heat to a conductive surface between it and the cold chamber. The partition or conductive surface then transfers the heat to the cold fluid. In a heat exchanger the hot and cold fluids are never combined. Gaseous fluids and gases are also used in heat exchangers.
Heat exchangers are available in various types such as viz., brazed; shell and tube; and shell and coil. Brazed heat exchangers include several plates that are vacuum-brazed together and they have a high turbulent flow that decreases residual deposit and maintenance. Ideally suited for hydraulic systems, brazed heat exchangers are found in water heaters, swimming pools, spas and snow-melting units. Shell and tube heat exchangers are equipped with straight or U-shaped, stainless steel tubes that are encased in a carbon steel shell. Durable and rugged, shell and tube exchangers suit adverse and abrasive conditions and materials. A coil and baffle combination ensures maximum heat exchange aiding tube expansion. Shell and coil heat exchangers are ideal for areas that have space constraints. They are high-efficiency machines which consist of corrugated tubes that are helically arranged in a lightweight compact shell.
There are three basic flow systems in heat exchangers. In the parallel method both fluids flow in the same direction. In the counter method the fluids flow from opposite directions and in the cross method the fluids flow perpendicular to one another.