Heat Ex changers Fouling factor
Heat ex changers:
Heat ex changers are devices used to transfer heat energy from one fluid to another. Typical heat ex changers experienced by us in our daily lives include condensers and evaporators used in air conditioning units and refrigerators. Boilers and condensers in thermal power plants are examples of large industrial heat ex changers. There are heat ex changers in our automobiles in the form of radiators and oil coolers. Heat ex changers are also abundant in chemical and process industries.
There is a wide variety of heat ex changers for diverse kinds of uses, hence the construction also would differ widely. However, in spite of the variety, most heat ex changers can be classified into some common types based on some fundamental design concepts. We will consider only the more common types here for discussing some analysis and design methodologies.
Fouling
Material deposits on the surfaces of the heat ex changer tubes may add more thermal resistances to heat transfer. Such deposits, which are detrimental to the heat exchange process, are known as fouling. Fouling can be caused by a variety of reasons and may significantly affect heat ex changer performance. With the addition of fouling resistance, the overall heat transfer coefficient, Uc, may be modified as:
1/Ud=(1/Uc)+R"
where R” is the fouling resistance.
Fouling can be caused by the following sources:
1) Scaling is the most common form of fouling and is associated with inverse solubility salts. Examples of such salts are CaCO3, CaSO4, Ca3(PO4)2, CaSiO3, Ca(OH)2, Mg(OH)2, MgSiO3, Na2SO4, LiSO4, and Li2CO3.
2) Corrosion fouling is caused by chemical reaction of some fluid constituents with the heat ex changer tube material.
3) Chemical reaction fouling involves chemical reactions in the process stream which results in deposition of material on the heat ex changer tubes. This commonly occurs in food processing industries.
4) Freezing fouling is occurs when a portion of the hot stream is cooled to near the freezing point for one of its components. This commonly occurs in refineries where paraffin frequently solidifies from petroleum products at various stages in the refining process. , obstructing both flow and heat transfer.
5) Biological fouling is common where untreated water from natural resources such as rivers and lakes is used as a coolant. Biological micro-organisms such as algae or other microbes can grow inside the heat ex changer and hinder heat transfer.
6) Particulate fouling results from the presence of micro scale sized particles in solution. When such particles accumulate on a heat ex changer surface they sometimes fuse and harden. Like scale these deposits are difficult to remove.
Heat ex changers are devices used to transfer heat energy from one fluid to another. Typical heat ex changers experienced by us in our daily lives include condensers and evaporators used in air conditioning units and refrigerators. Boilers and condensers in thermal power plants are examples of large industrial heat ex changers. There are heat ex changers in our automobiles in the form of radiators and oil coolers. Heat ex changers are also abundant in chemical and process industries.
There is a wide variety of heat ex changers for diverse kinds of uses, hence the construction also would differ widely. However, in spite of the variety, most heat ex changers can be classified into some common types based on some fundamental design concepts. We will consider only the more common types here for discussing some analysis and design methodologies.
Fouling
Material deposits on the surfaces of the heat ex changer tubes may add more thermal resistances to heat transfer. Such deposits, which are detrimental to the heat exchange process, are known as fouling. Fouling can be caused by a variety of reasons and may significantly affect heat ex changer performance. With the addition of fouling resistance, the overall heat transfer coefficient, Uc, may be modified as:
1/Ud=(1/Uc)+R"
where R” is the fouling resistance.
Fouling can be caused by the following sources:
1) Scaling is the most common form of fouling and is associated with inverse solubility salts. Examples of such salts are CaCO3, CaSO4, Ca3(PO4)2, CaSiO3, Ca(OH)2, Mg(OH)2, MgSiO3, Na2SO4, LiSO4, and Li2CO3.
2) Corrosion fouling is caused by chemical reaction of some fluid constituents with the heat ex changer tube material.
3) Chemical reaction fouling involves chemical reactions in the process stream which results in deposition of material on the heat ex changer tubes. This commonly occurs in food processing industries.
4) Freezing fouling is occurs when a portion of the hot stream is cooled to near the freezing point for one of its components. This commonly occurs in refineries where paraffin frequently solidifies from petroleum products at various stages in the refining process. , obstructing both flow and heat transfer.
5) Biological fouling is common where untreated water from natural resources such as rivers and lakes is used as a coolant. Biological micro-organisms such as algae or other microbes can grow inside the heat ex changer and hinder heat transfer.
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