Hi guys, can I get all of these texts re-written to prevent plagiarism. Please.

Question

Hi guys, can I get all of these texts re-written to prevent plagiarism. Please. Thank you

INTRODUCTION

A heat exchanger is a device designed to efficiently transfer or "exchange" heat from one matter to another. When a fluid is used to transfer heat, the fluid could be a liquid, such as water or oil, or could be moving air. The most well-known type of heat exchanger is a car radiator. In a radiator, a solution of water and ethylene glycol, also known as antifreeze, transfers heat from the engine to the radiator and then from the radiator to the ambient air flowing through it. This process helps to keep a car's engine from overheating.

There are three primary classifications of heat exchangers according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is the most efficient, in that it can transfer the most heat from the heat (transfer) medium per unit mass due to the fact that the average temperature difference along any unit length is higher

Shell and Tube Heat Exchanger

Shell and tube heat exchangers consist of series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc. Shell and tube heat exchangers are typically used for high-pressure applications (with pressures greater than 30 bar and temperatures greater than 260 °C). This is because the shell and tube heat exchangers are robust due to their shape.
Several thermal design features must be considered when designing the tubes in the shell and tube heat exchangers: There can be many variations on the shell and tube design. Typically, the ends of each tube are connected to plenums (sometimes called water boxes) through holes in tube sheets. The tubes may be straight or bent in the shape of a U, called U-tubes.

Corrugated Plate Heat Exchanger

The plate heat exchanger (PHE) is a specialized design well suited to transferring heat between medium- and low-pressure fluids. Welded, semi-welded and brazed heat exchangers are used for heat exchange between high-pressure fluids or where a more compact product is required. In place of a pipe passing through a chamber, there are instead two alternating chambers, usually thin in depth, separated at their largest surface by a corrugated metal plate. The plates used in a plate and frame heat exchanger are obtained by one piece pressing of metal plates. Stainless steel is a commonly used metal for the plates because of its ability to withstand high temperatures, its strength, and its corrosion resistance.

The plates are often spaced by rubber sealing gaskets which are cemented into a section around the edge of the plates. The plates are pressed to form troughs at right angles to the direction of flow of the liquid which runs through the channels in the heat exchanger. These troughs are arranged so that they interlink with the other plates which forms the channel with gaps of 1.3–1.5 mm between the plates. The plates are compressed together in a rigid frame to form an arrangement of parallel flow channels with alternating hot and cold fluids. The plates produce an extremely large surface area, which allows for the fastest possible transfer. Making each chamber thin ensures that the majority of the volume of the liquid contacts the plate, again aiding exchange. The troughs also create and maintain a turbulent flow in the liquid to maximize heat transfer in the exchanger. A high degree of turbulence can be obtained at gerchangerlow flow rates and high heat transfer coefficient can then be achieved.

As compared to shell and tube heat exchangers, the temperature approach in a plate heat exchangers may be as low as 1 °C whereas shell and tube heat exchangers require an approach of 5 °C or more. For the same amount of heat exchanged, the size of the plate heat exchanger is smaller, because of the large heat transfer area afforded by the plates (the large area through which heat can travel). Increase and reduction of the heat transfer area is simple in a plate heat-exchanger, through the addition or removal of plates from the stack.

Explanation / Answer

INTRODUCTION:

Heat exchanger works on the principle of conductive heat transfer. It acts as an interface that transfer heat from high temperature medium to low temperature medium. Depending on the material thermal conductivity, the rate of heat transfer decided. The medium can be liquid or gas. In many applications the medium is water or oil. In nuclear power plants water used as a coolant in heat exchanger. Radiator in cars is an another example for heat exchanger. The radiator takes away heat produced in car engine which is a heat exchanger. The medium in radiator is solution of water and ethylene glycol. The mixture is also known as anti-freeze. Here the mixture absorb heat from engine that flows in the radiator and in-turn leaves the heat to ambient air flowing over it.

Depending on the flow of medium, the heat exchangers are classified as.

Parallel flow Heat exchanger: Here the fluids enter the tubes at the same end and travels parallel to each other and leaves from the other end.

Counter-flow heat exchanger: Hot and cold fluid enter at the opposite ends and travel opposite to each other.

Counter-flow heat exchangers are more effective than parallel flow because they create more uniform temperature difference between the fluids, over the entire length of the fluid path. It can also be explained from the LMTD method. LMTD is more for counter flow heat exchanger. So for same amount of heat to be transferred counter flow heater exchanger requires lesser surface.

Shell and Tube Heat Exchanger: From the name itself it can be justified that one medium flow in shell and the other in bundle of tubes which are called as tube bundle. These are generally used for high pressure applications (with pressures greater than 30 bar and temperatures greater than 260 °C). The design of this heat exchanger has tubes which ends are connected to plenums. The design can also be improvised to increase the temperature drop by using bent tubes in place of straight tubes and baffles are also used.

Corrugated plate heat exchanger: One of the heat exachanger used for transferring heat when medium and low pressurized fluids are plate heat exchanger (PHE). Generally for heat transfer between high-pressure fluids welded, Brazed heat exchangers are used or more compact product should be used.

In PHE if we replace pipe passing through a chamber with two alternating chambers that are thin in depth and separated at their largest surface by a corrugated metal plate. The plates in PHE are made by one piece pressing of metal plates, The material commonly used for this plates is stainless steel which has high temperature resistance, strength and corrosive resistance.

The space given between the plates by rubber sealing gaskets that are cemented into a section around the edge of the plates. To make liquid runs through the channels in the heat exchanger, these plates are pressed so that they form troughs at right angles to flow direction of liquid. To interlink the other plates which forms channel with gaps of 1.3–1.5 mm between the plates these troughs are arranged. To form an arrangement of parallel flow channels with alternating hot and cold fluids, these plates are compressed together. for the fastest possible transfer, the plates are to be produce an extremely large surface area. The troughs also create and maintain a turbulent flow in the liquid to maximize heat transfer in the exchanger. A high degree of turbulence can be obtained at gerchangerlow flow rates and high heat transfer coefficient can then be achieved.

As compared to shell and tube heat exchangers, the temperature approach in a plate heat exchangers may be as low as 1 °C whereas shell and tube heat exchangers require an approach of 5 °C or more. In PHE increase and reduction of the heat transfer area is simple by addition or removal of plates from the stack.

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