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Core and Fuel Assembly Fluid Flow
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
Here, the value of CDRAG is also a function of the aspect ratio (see Figure 18.32). At low Reynolds numbers, most of CDRAG is the result of frictional drag on the object. Since the frictional drag is proportional to the surface area A, objects with large surface areas tend to have more drag than objects with smaller surface areas. The drag coefficient is independent of the surface roughness for laminar flows, but it is a strong function of the surface roughness for turbulent flows. Not surprisingly, rough surfaces tend to break apart the turbulent boundary layer, and the breakup of the boundary layer transfers more momentum to the surface. The pressure drop which also contributes to the total drag is due to a pressure difference between the front and the back of the object over which the fluid is flowing. Therefore, the pressure coefficient is usually largest for blunt objects, and it is normally smallest for streamlined objects such as nuclear fuel rods and aircraft wings. The drag coefficients for laminar and turbulent flow over a plate-type fuel rod (see Figure 18.33) are given by
Principles of Physics
Published in Arthur T. Johnson, Biology for Engineers, 2019
All heat is transferred from a surface area. The larger the surface area, the more heat that can be transferred. When an animal needs to conserve heat, it curls into a ball with low surface area. When an animal needs to lose heat, it spreads out to expose as much surface area as possible to the environment.
Friction
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
The frictional force that is created between the contact of two objects is independent of (not connected with) the surface area of contact. For example, place a book on a table and try to push it horizontally. Now open the outside covers of the book, place it flat on the table and try to push it again, as shown in the diagrams on the left of Figure B3.8. The book with its covers closed will create the same frictional force as the book open with both its outside covers in contact (effectively doubling its contact area). The reason for this is that although there is increased surface area of contact (i.e. when you opened the book), the same mass is distributed over a larger area of contact. In other words, you have maintained the mass of the book but spread it over a larger area, thus reducing each of the small contact forces.
Airflow through the supraglottis during inspiration
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
L. Reid, M. Hayatdavoodi, S. Majumdar
Figure 10(a) shows the pressure force acting on the regions of interest presented in Figure 2. The pressure force is obtained by , where p is the pressure, and A is the surface area. The pressure forces in all hypopharyngeal subdivisions are positive at Q = 30 L/min then become negative at higher flow rates Q > 120 L/min in the UH and MH. The LH region exhibits a positive normal force at all flow rates in the LH, which peaks at 180 L/min with an average pressure of 84 Pa over the region. The high-pressure observed in the LH, occurs due to collision of the epiglottic jet against the downstream wall before it is redirected anteriorly through laryngeal inlet. The maximal negative forces were observed in the ULA and URA regions at all flow rates, shown in Figure 10(a). These regions include the lateral margins of the epiglottic tip where peak velocities are observed in Figure 6. In Figure 10(a), the URP and ULP regions demonstrate inconsistency in their normal force values as higher flow rates are applied to the inlet. The URP has relatively low positive normal force at flow rates up to Q = 180 L/min, but at Q = 240 L/min drops significantly and becomes negative. The normal force of the ULP region is positive at low flow rates, which become negative at Q > 120 L/min and reaches a peak negative value at Q = 180 L/min.
A numerical framework for heat transfer and pressure loss estimation of matrix cooling geometry in stationary and rotational states
Published in Numerical Heat Transfer, Part A: Applications, 2019
S. Mostafa Hosseinalipour, Parisa Afkari, Hamidreza Shahbazian, Bengt Sundén
A matrix cooling geometry is composed of two layers of longitudinal ribs at an opposite angle that forming a system of crossing sub-channels. In the rotational state, according to the direction of rotation, the two layers are representing the suction side as the leading surface and the pressure side as the trailing surface, respectively. The fluid that passes the sub-channels, turns at the dead end of the side wall and moves into the sub-channel on the opposite layer with some mixing with the fluid from the other sub-channels. The flow should turn by the angle 2b (b is angle of sub-channels inclination) switching from one sub-channel to another sub-channel in the opposite layer or vice versa. These flow movements make a swirl motion and the interaction with the cross flow increased the turbulence of the flow. This also increases the heat transfer coefficient. Moreover, according to the significant increase of surface area, the heat transfer is also more increased. The longitudinal ribs in this structure have several benefits, such as improvement in structural strength, heat transfer and uniform heat transfer distribution along sub-channels both axially and laterally.
Effect of sample rugged surface on energy consumption and quality of plant-based food materials in convective drying
Published in Drying Technology, 2021
Mohammad U. H. Joardder, Reham Alsbua, Washim Akram, M. A. Karim
According to the principle of heat transfer, with the increased surface area, the rate of heat transfer is increased.[43] Use of rugged surfaces instead of the plane ones give more surface area to transfer the heat. Apart from this, due to the rugged shape, the airflow over the sample develops turbulence that results in higher heat transfer. Similarly, the rate of mass transfer increases due to the same reasons. Taken all these into consideration, waviness of the sample surface contributes to saving significant amount of energy.