Heat exchangers

A heat exchanger is a specialized device that assists in the transfer of heat from one fluid to the other. In some cases, a solid wall may separate the fluids and prevent them from mixing. In other designs, the fluids may be in direct contact with each other. In the most efficient heat exchangers, the surface area of the wall between the fluids is maximized while simultaneously minimizing the fluid flow resistance. Fins or corrugations are sometimes used with the wall in order to increase the surface area and to induce turbulence.

The main use of heat exchangers is in industrial procedures. They are often brought to use in heating processes. They can also be applied for heat and energy saving as heat exchangers are used to recover lost heat energy in industries and the recovered heat energy is then used to heat another stream, thus eliminating the need for another heat source and putting the otherwise lost and wasted heat to use.

Heat exchangers have found their use in several industries; most importantly, the petroleum industry, food industry, waste water treatment industry and wine industry. Heat exchangers are used in chemical processing and power production. They are also used widely in spacecrafts and airplanes to heat fuel. Air conditioning and refrigeration systems are some other important fields where heat exchangers are applied.

There are three primary flow arrangements with heat exchangers: counter-flow, parallel-flow, and cross-flow. In the counter-flow heat exchanger, the fluids enter the exchanger from opposite sides. This is the most efficient design because it transfers the greatest amount of heat. In the parallel-flow heat exchanger, the fluids come in from the same end and move parallel to each other as they flow to the other side. The cross-flow heat exchanger moves the fluids in a perpendicular fashion.

There are also four different designs of heat exchangers: shell and tube, plate, regenerative, and intermediate fluid or solid. The most typical type of heat exchanger is the shell and tube design. This heat exchanger has multiple finned tubes. The tubes carry the liquids that will be processed by the exchanger. One set of tubes will carry the medium that will be in need of cooling. The other set of tubes will carry the liquid that will run through the other medium and provide the cooling for it. This process also goes the other way with the mediums either being cooled or heated.

The set of tubes present in a shell and tube heat exchanger is called a tube bundle. The tube bundle is comprised of several different tubes in all shapes and sizes. A shell and tube heat exchanger is usually used for jobs that would require high pressures. The pressures that this particular exchanger typically deals with can be around 30 bars and be as high as 260°C. The strength of the tubes that make up this particular heat exchanger enables it to handle pressures high.

In the plate heat exchanger, the fluid flows through baffles. This causes the fluids to be separated by plates with a large surface area. This type of heat exchanger is typically more efficient than the shell and tube design.

The regenerative heat exchanger takes advantage of the heat from a specific process in order to heat the fluid used in the same process. These heat exchangers can be made with the shell and tube design or the plate design. The intermediate fluid or solid heat exchanger uses the fluids or solids within it to hold heat and move it to the other side in order to be released. This method is commonly used to cool gases while removing impurities at the same time.

To ensure good condition of a heat exchanger and to prevent contamination and any blockage due to impurities collected in a heat exchanger, a regular and timely examination of heat exchangers is essential.

4. Answer the questions to the text:

1) What is a heat exchanger?

2) What separates the fluids and prevents them from mixing?

3) Why are fins or corrugations sometimes used with the wall?

4) What can heat exchangers be used for?

5) In what industries have heat exchangers found their use?

6) What are three primary flow arrangements with heat exchangers?

7) How is a shell and tube heat exchanger designed?

8) How does a regenerative heat exchanger work?

5. Choose the correct continuation to complete the following statements:

1) The fluids may be separated and prevented from mixing

a) by a solid wall

b) by a specialized device

2) In the most efficient heat exchangers, the surface area of the wall between the fluids

a) is maximized

b) is minimized

3) Heat exchangers are often brought to use in

a) heating processes

b) industrial procedures

4) Some other important fields where heat exchangers are applied.

a) air conditioning and refrigeration systems

b) spacecrafts and airplanes

5) The fluids come in from the same end and move parallel to each other as they flow to the other side

a) in the parallel-flow heat exchanger

b) in the counter-flow heat exchanger

6) For jobs that would require high pressures

a) a shell and tube heat exchanger is usually used

b) a plate heat exchanger is usually used

6. Fill in the gaps with the suitable words from the box:

a) treatment b) heat c) arrangements d) refrigeration d) tube e) spacecrafts f) finned g) flow

1. fluid _____resistance

2. waste water _______industry

3. to recover lost _______energy

4. primary flow _______with heat exchangers

5. multiple ______tubes

6. shell and _______design

7. to be used widely in______ and airplanes

8. air conditioning and______ systems

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Pick up the key words from the text “Mixing and blending”. Make up your own sentences with them.	\|	Which of the following sentences from the text contain the Passive Voice forms? Explain how you define these forms.

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