How can you determine the view factor F12 when the view factor F21 and the surface areas are available?
The view factors for the heat exchange between the top and bottom surfaces, F12 and F21, are the same because the areas of both surfaces are the same; F12 = F21. We can find this common view factor from Figure 13-5 with L1/D = L2/D = 1 since all sides of the cube are the same.
What does the view factor represent when is the view factor from a surface to itself not zero?
When the view factor from a surface to itself not zero. The view factor represents the fraction of radiative energy that is diffused from one surface element and strikes the other surface element directly with no intervening reflections.
What is meant by view factor?
From Wikipedia, the free encyclopedia. In radiative heat transfer, a view factor, , is the proportion of the radiation which leaves surface that strikes surface. . In a complex ‘scene’ there can be any number of different objects, which can be divided in turn into even more surfaces and surface segments.
What is the significance of shape factor?
The shape factor explains the angle ratio under which two surfaces appear with respect to one another. Its applications include heat exchange computations caused by thermal radiation, lighting engineering, and the parameterization of isothermal knot models in space thermodynamics.
What is conduction shape factor?
One of the common and practical ways to calculate steady conduction heat flow in an enclosure between two surfaces with constant temperatures is to use the concept of conduction shape factor (CSF). Indeed, CSF is defined as the ratio of a heat-transfer-area to a heat-transfer-length.
Which of the following is a wrong statement the shape factor is equal to one?
1. Which of the following is a wrong statement according to the shape factor is equal to one? Explanation: For a flat or convex surface, the shape factor with respect to itself is zero. This aspect stems from the fact that for any part of flat or convex surface, one cannot see any other part of the same surface.
What is the relation between the rate of convection heat transfer and the rate of mixing in turbulent fluid flow?
The intense mixing of the fluid in turbulent flow enhances heat and momentum transfer between fluid particles, which in turn increases the friction force and the convection heat transfer coefficient.
How can you increase the rate of heat transfer?
Factors that affect rate of heat flow include the conductivity of the material, temperature difference across the material, thickness of the material, and area of the material. Different materials have greater or lesser resistance to heat transfer, making them better insulators or better conductors.
What does the rate of heat transfer depend on?
The rate of heat transfer depends on the material through which heat is transferred. The effect of a material upon heat transfer rates is often expressed in terms of a number known as the thermal conductivity. Thermal conductivity values are numerical values that are determined by experiment.
Why counter flow heat exchanger is most efficient?
Counter flow heat exchangers are inherently more efficient than parallel flow heat exchangers because they create a more uniform temperature difference between the fluids, over the entire length of the fluid path. For example, one fluid may make 2 passes, the other 4 passes.
What is counter flowing flowing?
A counter-flow heat exchanger is one in which the direction of the flow of one of the working fluids is opposite to the direction to the flow of the other fluid. In a parallel flow exchanger, both fluids in the heat exchanger flow in the same direction.
What affects heat exchanger efficiency?
Heat exchanger efficiency is highly affected by the velocity of the operating fluid so it is recommended that the flow rate should be increased from time to time. The increased turbulence works to retard fouling tendencies that otherwise impact heat exchanger performance and impede the flow of fluids.
How do you calculate heat exchanger performance?
4.0 – HEAT EXCHANGERS CALCULATIONS:
- The main basic Heat Exchanger equation is: Q = U x A x ΔTm =
- The log mean temperature difference ΔTm is: ΔTm =
- (T1 – t2) – (T2 – t1) = °F.
- T1 = Inlet tube side fluid temperature; t2 = Outlet shell side fluid temperature;
- ln (T1 – t2) (T2 – t1)