We come across heat management and controlling during a design of any mechanical or chemical unit equipments. A physical and chemical change involves somehow the application of heat exchanger in order to maintain the temperature as per the condition to run the system. Exchange of heat of the fluid system from a point to other point of interest is done using a piece of equipment called heat exchanger and of course it may differ from the application but ultimate principle behind it working is same.
Theory behind heat exchanger is simple, just the allowing heat energy to flow in perfectly designed system by means of conduction, convection in case of fluids and when dealt with direct firing radiation will be involved. We discuss about four main types of heat exchangers by comparing their application, capacity and range of duty which are classified based on the flow pattern of fluid in them.
- Plate heat exchanger
- Shell and tube heat exchanger
- Fin type heat exchanger
- Tubular heat exchanger
Plate type heat exchanger
It is an arrangement of plates side by side fixed along with gaskets. Each plate will be having four opening ports, a gasket which is fitted between two adjacent plate will make the fluid to flow between two ports by block remaining ports, to imagine a rectangle plate having four holes near at its edges and these are fixed in such a way that gasket between plate make a enough room for fluid to flow and change the direction of as required. This operates fluids in counter current wise for attaining maximum heat exchange.
It has advantages which overcome other heat exchanger are:
- Negligible heat loss
- overall weight of set is less
- Fits in less space
- Less maintenance cost and
- Overall heat transfer coefficient is more
- Easy installation
- Not compatible for higher temperature and pressure say above 200oC and 20 bars.
Application: Used in oil cooling system in automobiles, steam condensations, swimming water cooling systems, refrigeration systems.
Shell and tube heat exchanger
It contains tubes inside a shell which is basic and basic design of heat exchangers, it is heavy duty equipment which is widely used in process industries it can handle higher temperature up to 900 degree centigrade’s even more.
Temperature of fluids are maximum at wall than the flowing stream and the heat has to redistribute evenly, baffle arrangement make the flow somewhat turbulent for better heat transfer disturbing the boundary layer and supporting the tube also. In most cases hot fluid like steam if fed towards tube side and cold fluid is sent into shell side of shell and tube heat exchanger.
Based on the design and pattern of flow of fluid internally it can be classified as single pass, 1-2 pass, 2-4 pass, floating head heat exchangers(internal floating head and outside packed floating head), fixed tube sheet, U-tube types . It accomplish the duty of condenser when it function is to cool a stream and similarly it operates as reboiler when used for changing the phase of the stream. It operates in countercurrent and cocurrent flow pattern and their approach will differ for same equipment. SHELL AND TUBE HEAT EXCHANGER CALCULATOR
- Can handle heavy duty and high temperature and pressures
- Easy control and operate-able
- Required large space
- Maintenance cost is more
Application: Used as regular heat exchanger for distillation columns, chemical equipment’s stream cooling and heating purpose. Used internally in reboilers and evaporators.
Fin type heat exchanger
These are called as extended surface exchangers it is used in the conditions where when a process fluid is having very low heat transfer coefficient when compared to other fluids because the overall heat transfer coefficient decreases which affect the capacity of heat transfer by the available surface area so the area of contact is to be increase. We come across this type of problem when heat transfer is dealt with heating of air or gas streams and for cooling viscous liquids like engine oil.
A metal piece is welded to the surface of the tube to increase the surface are which are called as fin and mostly found on outside of the tube. Fin type heat exchanger is classified to longitudinal fins type and transverse fins type
- Use to handle low heat transfer coefficient fluids
- Used for cooling and heating of vast quantity of gases
- Slurry fluids cannot be handled
- Deposition of particle at fin corner
- Cleaning difficulty
- High pressure drop
Application: Used as economizers, automobile radiators, air cooled condensers
Tubular heat exchanger
It is a pipe in pipe heat exchanger commonly known as double pipe heat transfer equipment which is named by its construction because two pipes are pipes are fitted in such way that one pipe is fitted into other inside space. By cross section they look concentric by coaxial view. It is extended to the required length and bent like hair pin shape at the edges to make it fit in particular area. Hot fluid is fed into the inner tube and cold fluid is fed into the space between inner and outer pipes.
The tubular condenser consists of:
- A bundle of parallel tubes whose ends are expanded into tube sheets.
- The tube bundle is inside a cylindrical shell and is provided with two channels, one at each end ,and two channel covers.
- Steam or other pure vapour is introduced into the shell-side surrounding the tubes, condensate is withdrawn from the shell.
- Any non-condensable gas is removed through vent.
- The fluid to be heated is pumped through the tubes.
- Two fluids (fluid, steam) are physically separated but are in thermal contact with the thin metal tube separating them.
- Heat flows through the tube walls from the condensing vapor to the cooler fluid in the tubes.
- Fluid flowing in the tube side gain heat and increase it temperature from inlet to outlet of the tubes.
- The temperature of the shell side fluid is constant for the pressure maintained on the shell side.
- Types of flows in heat exchanger
- Easy in construction
- Can handle slurries
- Can be used at low heat transfer areas
- Easy cleaning
- Concurrent and counter current flow can be adjusted easily
- Leakage corners
- Maintenance is time consuming
- Occupy more floor space compared to others
Application: Used for refrigeration process in appliance like refrigerators, domestic heating systems and car radiators etc.