What is fouling factor in heat transfer?
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 minimise the frequency of cleaning.
How do you calculate the fouling factor?
The required area ratio considering the fouling factors is calculated as follows: Ao = outer surface area of the tube (m2/m) Ai = inner surface area of the tube (m2/m) αo = outer heat transfer coefficient (W/m2 K)
Does fouling increase overall heat transfer coefficient?
Transfer Coefficients
Two probable mechanisms exist whereby the overall coefficient ofa heat exchanger can be increased when fouling occurs. These are the creation of roughness elements and restrictions to flow, both of which increase film heat transfer coefficients.
Why do we use fouling factor?
Fouling increases with increasing temperature and decreasing velocity. As we can see fouling factor decreases the overall heat transfer coefficient deteriorating the performance of the heat exchanger. Therefore, the Fouling factor is used in heat exchanger design as a safety factor.
What is the unit of fouling factor?
Hence the SI unit of fouling factor is m².°C/W. In FPS system: In the FPS system, the unit of the convective heat transfer coefficient is Btu/hr.ft².°F. Therefore unit of fouling factor is given by, Fouling factor=1h−1Btuhr.
How do you reduce fouling factor?
The best way to avoid particulate fouling is to keep the cooling water clean and thereby prevent particles from entering the heat exchanger. However, in all cooling systems, and especially when using open cooling systems (with cooling towers), there will always be particles present in the cooling water.
What is the fouling coefficient?
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.
What factors affect heat transfer coefficient?
The factors affecting the overall heat transfer coefficient are thermophysical properties such as the density, viscosity, and thermal conductivity of the fluid. Further, it is affected by the geometry and area across which the heat transfer is taking place.
Does fouling decrease heat transfer?
It occurs in all industries and most heat exchanger designs, with impacts ranging from heat transfer degradation to flow resistance and pressure drops. By forming a kind of insulation on heat-transfer surfaces and reducing heat transfer, fouling undermines heat exchange efficiency.
Can fouling factor be negative?
“Negative” fouling – 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 has highest fouling factor?
6. Which one is having the highest value of fouling factor? Explanation: Fouling factor for engine exhaust is 0.002 while that of industrial liquids, fuel oil and turbine exhaust are 0.0002, 0.0010 and 0.0002 respectively. 7.
How do you increase heat transfer coefficient?
To increase heat transfer rates, the velocity through a jacket can be increased by recirculating the cooling or heating liquid. For simple jackets without baffles, heat transfer will be mainly by natural convection, and the heat transfer coefficient will range from 200 to 400 W/m2°C.
What are the three factors that affect heat transfer?
Experiments show that the heat transferred to or from a substance depends on three factors—the change in the substance’s temperature, the mass of the substance, and certain physical properties related to the phase of the substance.
Does fouling increase with increasing temperature?
Fouling factors for corrosion fouling show a peak value as temperature increases; at low temperature, the corrosion rate increases with temperature but the corrosion requires the presence of dissolved oxygen and this dissolved oxygen content is reduced at higher temperatures due to the decreasing solubility of oxygen …
What factors affect the heat transfer coefficient?
On what factors heat transfer coefficient depends?
Heat transfer coefficient depends on both the thermal properties of a medium, the hydrodynamic characteristics of its flow, and the hydrodynamic and thermal boundary conditions.
How do you reduce fouling factor in heat exchanger?
What four factors can affect heat transfer?
The process of heat conduction depends on four basic factors: the temperature gradient, the cross section of the materials involved, their path length, and the properties of those materials.