3/13/2021 12:46:18 PM
A)What is Heat Exchanger?
A heat exchanger is a device used to transfer thermal energy between two or more fluids, which are at different temperatures.
A heat exchanger is a system used to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes.
Heat exchangers are devices that transfer heat from one medium to another. The purpose of the heat transfer typically is to lower or raise temperatures in a device or within a specified area. The two media can be the same — for example, air-to-air — or different — air-to-water.
Heat Transfer Mechanism:
There are two types of heat transfer mechanisms involved in heat exchangers—single-phase or two-phase heat transfer.
In single-phase heat exchangers, the fluids do not undergo any phase change throughout the heat transfer process,meaning that both the warmer and cooler fluids remain in the same state of matter at which they entered the heat exchanger.
For example, in water-to-water heat transfer applications, the warmer water loses heat which is then transferred to the cooler water and neither change to a gas or solid.
In two-phase heat exchangers, fluids do experience a phase change during the heat transfer process. The phase change can occur in either or both of the fluids involved resulting in a change from a liquid to a gas or a gas to a liquid. Typically, devices that employ a two-phase heat transfer mechanism require more complex design considerations than ones that employ a single-phase heat transfer mechanism. Some of the types of two-phase heat exchangers available include boilers, condensers, and evaporators.
B)What are the types of Heat Exchanger?
1)Shell and tube heat exchangers
Shell and tube heat exchangers are a device that puts two working fluids in thermal contact using tubes housed within an outer cylindrical shell. These two integral pathways are usually built out of thermally conductive metals that allow easy heat transfer The tubes carry a fluid from their inlet to their outlet (tube-side flow), while the shell passes a separate fluid over these tubes (shell-side flow). The number of tubes, known as the tube bundle will dictate how much surface area is exposed to the shell-side flow, and therefore determines how much heat is transferred.
2)Double pipe heat exchangers
The double pipe heat exchanger is, in its simplest form, one pipe held concentrically inside of a larger pipe (thus the name “double pipe”). The inner pipe acts as the conductive barrier, where one fluid flows through this inner pipe and another flows around it through the outer pipe, forming an annulus shape. The outside or “shellside” flow passes over the inside, or “tubeside” flow, which will cause heat exchange through the inner tube’s walls. They are also often referred to as hairpin, jacketed pipe, jacketed u-tube, and pipe-in-pipe exchangers The double pipe heat exchanger is one of the easiest designs to fabricate, add on to, and repair.
3)Plate heat exchangers
A plate exchanger consists of a series of parallel plates that are placed one above the other so as to allow the formation of a series of channels for fluids to flow between them.The space between two adjacent plates forms the channel in which the fluid flows.Inlet and outlet holes at the corners of the plates allow hot and cold fluids through alternating channels in the exchanger so that a plate is always in contact on one side with the hot fluid and the other with the cold
The size of a plate can range from a few square centimeters (100 mm x 300 mm side) up to 2 or 3 square meters (1000 mm x 2500 mm side). The number of plates in a single exchanger ranges from just ten to several hundred, so reaching surface exchange areas up to thousands of square meters.
4)Condensers, evaporators, and boilers
Condensers are heat exchanging devices that take heated gas or vapor and cool it to the point of condensation, changing the gas or vapor into a liquid.
An evaporator is a device in a process used to turn the liquid form of a chemical substance such as water into its gaseous-form/vapor.
Boilers are used to produce steam. The generation part of a steam system uses a boiler to add energy to a feedwater supply to generate steam. The energy is released from the combustion of fossil fuels or from process waste heat.
C)What are materials used for making Heat Exchanger?
Heat exchangers with shell diameters of 10 inches to more than 100 are typically manufactured to industry standards. Commonly, 0.625 to 1.5" tubing used in exchangers is made from low carbon steel, Admiralty, copper, copper-nickel, stainless steel, Hastelloy, Inconel, or titanium.