What types of heat exchangers coolers and heaters used onboard?
20 Jun '17, 02:31
A heat exchanger is any device used to transfer heat from one substance (liquid, gas or vapor) to another substance while preventing the two from intermixing. There is a metal wall partition between the two substances, such as that of a plate, tube or pipe, which acts as a conducting wall. A hot solution flowing on one side of the heat exchanger’s barrier transfers its heat to a cooler solution flowing on the other side. Thermal energy only flows from the hotter to the cooler. The size of a heat exchanger’s surface area affects its speed and efficiency. With shell and tube designs, the larger surface area transfers heat faster and more efficiently. The tubes in a heat exchanger may be finned to enlarge its surface area. One fluid flowing through the tubes and a second fluid flowing around the finned tubes to be heated or cooled accomplish the transfer of heat. In plate type designs, less surface area is recommended in order to prevent fouling. The plate corrugation create turbulence, which keeps the unit cleaner and plays a vital role in increasing the efficiency of heat transfer. Heat exchangers are typically constructed of steel, copper, bronze, stainless steel, aluminum, or cast iron.
The three main types of heat exchangers, differentiated by their structure, used on board of ships: - tube-and-shell - plate - air-cooled.
A tube-and-shell heat exchanger consists of tubes that are run through a large circular tank – the shell. Tube-and-shell (or tubular) heat exchangers are used in applications in which pressure and temperature demands are high. Tubular heat exchangers are also used when fluid contains particles that would block the channels of a plate heat exchanger. There are several types of tube-and-shell heat exchangers including U-tube, straight, spiral, and finned tube.
Plate heat exchangers utilize corrugated plates that are mounted within a frame and fastened together. They are designed so that the flow of the hot and cool liquids always run countercurrent to each other. Plate heat exchangers are used when temperature and pressure demands are moderate. It is common that a plate heat exchanger will have the same thermal capacity as a tube-and-shell five - seven times its size.
There are several types of plate heat exchangers including:
- semi-weld or hybrid types.
The gasketed is the most common. Included in the plates of these are elastomer gaskets, which contain the pressure and control the flow of each medium.
Brazed plate heat exchangers are made up of specially formed plates, vacuum brazed together.
Welded plate heat exchangers are fully welded and require no gaskets; they are usually constructed of one material (usually stainless steel.)
Semi-weld or hybrid plate exchangers consist of pairs of plates that are laser welded together into cassettes. This allows one fluid to flow in a welded channel and the other to flow in a gasketed channel.
Air-cooled heat exchangers have a cartridge of tubes with fins and a central motor fan for cooling or heat removal.
20 Jun '17, 02:54