The quality of teaching and learning is determined not just by the quality of teachers, but also the quality of the environment where they are working. This study aims to track the motivational factors of basic education educator. The results show th
some key factors which affect language learningFull description
theory
Full description
Heat Exchanger Fouling Factors
Heat Exchanger Fouling Factors Compressed air is a dirty gas service and it is very difficult to avoid the effects of the impurities continuously ingested by the compressor. These impurities in the air and coolant eventually deposit on heat exchanger tube surfaces, impeding heat transfer. A heat exchanger uses the principle that h eat transfer occurs when there is a difference in temperature between the two fluids. In an air compressor heat exchanger, there is a coolant stream and a hot air stream. The two streams are separated by a thin, solid wall. The wall must be thin and conductive in order for the exchange of heat to occur. Yet, the wall must be strong enough to withstand withstand any pressure by the fluids. Copper is a common common choice for construction. Here is a simple flow diagram showing how heat transfers in a heat exchanger.
This flow arrangement is called co-current. co-current. If the direction of one of the streams is reversed, the arrangement is called counter-current flow. counter-current flow. Air compressor heat exchangers are typically counter-current flow. Here are the temperature profiles along the heat exchanger. Note that the temperature profiles are different for co-current flow and for counter-current flow.
Heat Exchanger Fouling Factors
The area between the curve is the heat transfer rate (Q). We can see that the heat transfer rate for counter-current flow is larger than the rate for co-current flow. Counter flow heat exchangers provide more effective heat transfer. Most of the air compressor heat exchangers we encounter are counter-current flow design.
A perfectly clean exchanger will have three components tha t make up the total thermal resistance (R): R1 = Thermal resistance of inside flow R2 = Thermal resistance of exchanger tube R3 = Thermal resistance of outside flow
Heat Exchanger Fouling Factors
Therefore: R = R1 + R2 + R3 When your new compressor is being tested in the factory the exchangers can come close to this performance, but it does not accurately represent real world operation. During normal heat exchanger operation, surfaces are often subject to fouling by fluid impurities, rust formation, scale or other reactions between the fluid and the wall material. The subsequent deposition of a film or scale on the surface can greatly increase the resistance to heat transfer between the fluids. This effect can be considered during the design phase by introducing an additional thermal resistance, termed as fouling factor (Rf ). Its value depends on the operating temperature, fluid velocity and length of service of the heat exchanger. Fouling also impacts fluid temperature. To account for the fouling that will occur there will be two additional components in the total thermal resistance (R): R4 = Thermal resistance of fouling on inside surface R5 = Thermal resistance of fouling on outside surface You can plan for the effects of fouling by requiring that a fouling factor be used when the compressor manufacturer quotes compressor performance. If the effect of fouling is not considered, exchangers will be undersized when placed in a real world, dirty environment. Now rather than deriving heat transfer coefficients, we are going to give the fouling factors you should use based on the fluid. Please follow this link to the Fouling Factor table. Remember, you need to specify a fouling factor for both the coolant side and the air side of the heat exchanger. If you are using a fluid not listed in the table, please post a request in the Open Air Forum. We will try to get you an answer. Home Links
Solutions Articles Search IT Jargon Legal Terms Contents Reference Glossary Company Questions Privacy Webmaster This page was last updated December 29, 2000
Fouling Factors
Fouling Factors For Heat Exchangers Water Temperatures 125 °F (51.7 °C) or less Types of Water
Water Velocity 3 ft/sec (1 m/sec) and less
h - ft2 - °F / Btu 0.0005 0.0005
Seawater Distilled Treated boiler 0.001 feedwater Engine jacket 0.001 Great Lakes 0.001 Cooling Tower and Spray Pond - Treated 0.001 makeup - Untreated 0.003 Boiler blowdown 0.002 Brackish water 0.002 River Water - Minimum 0.002 - Mississippi 0.003 - Delaware / 0.003 Schuylkill - E. River / New 0.003 York Bay - Chicago 0.008 Sanitary Canal Muddy or silty 0.003 Hard (over 15 0.003 grains/gal) Type of Fluid Air Nitrogen
Water Velocity over 3 ft/sec (1 m/sec)
h - ft2 - °F / m - °C / W m - °C / W Btu 0.000088 0.0005 0.000088 0.000088 0.0005 0.000088 0.00018
0.0005
0.000088
0.00018 0.00018
0.001 0.001
0.00018 0.00018
0.00018
0.001
0.00018
0.00053 0.00035 0.00035
0.003 0.002 0.001
0.00053 0.00035 0.00018
0.00036 0.00053
0.001 0.002
0.00018 0.00035
0.00053
0.002
0.00035
0.00053
0.002
0.00035
0.00141
0.006
0.00106
0.00053
0.002
0.00035
0.00053
0.003
0.00053
h - ft2 - °F / Btu 0.002 0.0005
m - °C / W 0.00035 0.000088
Fouling Factors
Home Links
Source: Tubular Exchanger Manufacturer Association Solutions Articles Search IT Jargon Legal Terms Contents Reference Glossary Company Questions Privacy Webmaster This page was last updated April 01, 2001
