Fouling has a significant impact on heat transfer
across the heat exchanger surface
, and therefore on the overall operational performance and the economics of the process. … These side effects combine to increase the pressure drop across the heat exchanger, reducing flow rates and aggravating the problem further.
Does fouling increase heat transfer?
Fouling
has a significant impact on heat transfer across the heat exchanger surface
, and therefore on the overall operational performance and the economics of the process. … These side effects combine to increase the pressure drop across the heat exchanger, reducing flow rates and aggravating the problem further.
What is fouling in heat transfer?
Fouling is
the formation of unwanted material deposits on heat transfer surfaces during process heating and cooling
. It occurs in all industries and most heat exchanger designs, with impacts ranging from heat transfer degradation to flow resistance and pressure drops.
How can fouling or scaling affect heat transfer performance of heat exchangers?
Scaling. Scaling is a type of fouling caused by inorganic salts in the water circuit of the heat exchanger. It
increases the pressure drop and insulates the heat transfer surface
, thus preventing efficient heat transfer.
What is fouling factor and which effect does fouling have on overall heat transfer coefficient explain overall heat transfer coefficient with thermal circuit Sketch?
Fouling
changes the surface of the wall between hot and cold fluids
. As a result, the overall heat transfer rate through that surface is reduced. Correspondingly, the heat transfer coefficient at the surface is drastically reduced, since the heat conducting wall metal is not in contact with the fluids any more.
What are the cause and source of fouling?
Biological fouling is caused by
the growth of organisms, such as algae
, within the fluid that deposit onto the surfaces of the heat exchanger. … Corrosion fouling occurs when a layer of corrosion products builds up on the surfaces of the tube, forming an extra layer of material that often has thermal resistance.
What is a fouling factor?
The fouling factor represents
the theoretical resistance to heat flow due to a build-up of a layer of
dirt or other fouling substance on the tube surfaces of the heat exchanger, but they are often overstated by the end user in an attempt to minimize the frequency of cleaning.
Can fouling resistance negative?
The application of these findings to the analogous case of heat transfer across a fouled surface explains the existence of apparently negative fouling resistances which are often observed shortly after start-up from clean conditions.
Can fouling factor be negative?
This can occur
when fouling rate is quantified by monitoring heat transfer
. Relatively small amounts of deposit can improve heat transfer, relative to clean surface, and give an appearance of “negative” fouling rate and negative total fouling amount.
Which is not an example of heat exchanger?
6. Which of the following is not an example of
recuperators
type heat exchanger? Explanation: Recuperators are not used in chemical factories. 7.
Which one has the highest value of overall heat transfer coefficient?
Which one is having highest value of overall heat transfer coefficient? Explanation: Overall heat transfer coefficient for
feed water heaters
is 8500 W/m
2
K while that of steam, alcohol condensers and ammonia condensers are 5000 W/m
2
K, 630 W/m
2
K and 1400 W/m
2
K.
How do you calculate fouling factor?
- Alcohol vapors : R
d
= 0.00009 (m
2
K/W) - Boiler feed water, treated above 325 K : R
d
= 0.0002 (m
2
K/W) - Fuel oil : R
d
= 0.0009 (m
2
K/W) - Industrial air : R
d
= 0.0004 (m
2
K/W) - Quenching oil : R
d
= 0.0007 (m
2
K/W) - Refrigerating liquid : R
d
= 0.0002 (m
2
K/W) - Seawater below 325 K : R
d
= 0.00009 (m
2
K/W)
What are the causes of fouling?
Several variables contribute to fouling, including
water pH, product viscosity, and the roughness of component surfaces
, among many others. Together, the variables can be expressed as a fouling factor that numerically represents resistance to heat transfer — or thermal resistance — in your system.
How can fouling be controlled?
Increasing flow velocity increases
the fluid shear stress which causes more removal. This results in lower fouling rates which resulting to lower fouling resistance. For weak deposits (particulate fouling), increasing the flow velocity may completely eliminate fouling.
What is the effect of fouling?
Fouling is a dynamic phenomenon which changes with time. Fouling
increases the overall thermal resistance and lowers the overall heat transfer coefficient of heat exchangers
. Fouling also impedes fluid flow, accelerates corrosion and increases pressure drop across heat exchangers.
