DESIGN AND CONSTRUCTION OF A U-TUBE HEAT EXCHANGER
ABSTRACT
In buses, fluid used to cool down the diesel engine is often passed through a heat exchanger and the heat it reclaims is used to warm cold air from outside that is pumped up from the floor of the passenger compartment. That saves the need for having additional, wasteful electric heaters inside the bus. A car radiator is another kind of heat exchanger. Water that cools the engine flows through the radiator, which has lots of parallel, aluminum fins open to the air. As the car drives along, cold air blowing past the radiator removes some of the heat, cooling the water and heating the air and keeping the engine working efficiently.
Heat exchangers are devices whose primary responsibility is the transfer (exchange) of heat, typically from one fluid to another. However, they are not only used in heating applications, such as space heaters, but are also used in cooling applications, such as refrigerators and air conditioners. Many types of heat exchangers can be distinguished from on another based on the direction the liquids flow. All heat exchangers do the same job—passing heat from one fluid to another—but they work in many different ways. In U tube heat exchangers, one fluid flows through a set of metal tubes
CHAPTER ONE
1.0 INTRODUCTION
The purpose of a heat exchanger is just that--to exchange heat. Most processes require the heating or cooling of streams to produce a desired temperature before the stream can be fed to operations. In any heat exchanger there must be a fluid that requires a change in energy (heating or cooling) and a fluid that can provide that energy change. One fluid is sent through a pipe on the inside of the heat exchanger while the other fluid is sent through a pipe on the outside. In this configuration, no mixing of the hot and cold fluids needs to take place. This is very convenient for many processes, especially when product purity needs to be ensured. This arrangement also allows for large quantities of heat to be transferred quickly, and it is relatively easy to maintain consistent operating conditions.
There are three principle means of achieving heat transfer, conduction, convection, and radiation. Heat exchangers run on the principles of convective and conductive heat transfer. Radiation does occur in any process. However, in most heat exchangers the amount of contribution from radiation is miniscule in comparison to that of convection and conduction. Conduction occurs as the heat from the hot fluid passes through the inner pipe wall. To maximize the heat transfer, the inner-pipe wall should be thin and very conductive. However, the biggest contribution to heat transfer is made through convection.
There are two forms of convection; these are natural and forced convection. Natural convection is based on the driving force of density, which is a slight function of temperature. As the temperature of most fluids is increased, the density decreases slightly. Hot fluids therefore have a tendency to rise, displacing the colder fluid surrounding it. This creates the natural “convection currents” which drive everything from the weather to boiling water on the stove. Forced convection uses a driving force based on an outside source such as gravity, pumps, or fans. Forced convection is much more efficient, as forced convection flows are often turbulent. Turbulent flows undergo a great deal of mixing which allow the heat to be transferred more quickly.
In this particular apparatus, water is used as both the hot and cold fluid. The purpose of this heat exchanger is to cool a hot stream. Heat transfer occurs in both directions; the hot water is cooled, and the cooling water is heated. This arrangement is called a u-tube” heat exchanger. There are many other forms of heat exchangers; most notably, the double-pipe heat exchanger. In this arrangement a cold fluid flows through a pipe in the center of the apparatus and is heated by a hot fluid on the outside of that pipe. The hot water used in the U-tube heat exchanger is produced by means of a double-pipe heat exchanger. The discharge from the shell of the U tube heat exchanger is circulated through the inner pipe of the double pipe heat exchanger. Low-pressure steam condenses on the outside of the pipe, heating the water before it enters the tubes of the U-tube heat exchanger.
1.2 SIGNIFICANCE OF THE PROJECT
- Simple and Compact in size
- Heat transfer efficiency is more
- Can be easily cleaned
- No extra space is required for dismantling
- Capacity can be increased by introducing plates in pairs
- Leaking plates can be removed in pairs, if necessary without replacement
- Maintenance is simple
- Turbulent flow help to reduce deposits which would interfere with heat transfer
1.3 LIMITATION OF THE PROJECT
- Initial cost is high since Titanium plates are expensive
- Finding leakage is difficult since pressure test is not as ease as tube coolers
- Bonding material between plates limits operating temperature of the cooler
- Pressure drop caused by plate cooler is higher than tube cooler
- Careful dismantling and assembling to be done
- Over tightening of the clamping bolts result in increased pressure drop across the cooler
- Joints may be deteriorated according to the operating conditions
- Since Titanium is a noble metal, other parts of the cooling system are susceptible to corrosion.
1.4 APPLICATION OF THE PROJECT
Saving energy is a huge and costly problem for factory bosses and it's one reason they often install devices called heat exchangers to salvage as much heat as possible from waste gases. Heat exchangers have lots of other familiar uses too. Engines in cars, ships, and planes use heat exchangers to work more efficiently, and if you have a refrigerator or an air-conditioner in your home, those are using heat exchangers too.****************************************************************
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