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Enhanced Air Cooling of Electronic Equipment
Published in Sung Jin Kim, Sang Woo Lee, for Electronic Equipment, 2020
Roughness elements, either random in nature or in a repeated-rib configuration, have been extensively studied as a technique for heat transfer enhancement in channel flows. The roughness elements considered are typically much smaller than the ribs and obstructions of the preceding section—at least an order of magnitude less than the boundary layer thickness, and in tubes, one or two orders of magnitude less than the tube diameter. Nakayama [1982] reviewed the influence of roughness Reynolds number, Prandtl number, and geometrical parameters on the momentum and heat transfer roughness functions, for both granular, three-dimensional surface roughness and for repeated-rib roughness. It was concluded from comparing a large number of studies in the literature that the relative merits of roughening a surface are large when the roughness Reynolds number is small; granular (3-D) roughness provided more favorable results than rib (2-D) roughness. The heat transfer enhancement is also larger for higher Prandtl-number fluids. It should be pointed out that in implementing roughness as a heat transfer enhancement technique variable physical properties have a more pronounced effect on heat transfer in rough passages than in smooth passages [Wassel and Mills, 1979]. Since fairly large temperature variations are experienced in electronic applications, care should be taken to account for variable-property effects.
Preliminary Concepts and Basic Equations
Published in Gautam Biswas, Amaresh Dalal, Vijay K. Dhir, Fundamentals of Convective Heat Transfer, 2019
Gautam Biswas, Amaresh Dalal, Vijay K. Dhir
The Prandtl number varies in a wide range from value of order of 0.01 for liquid metals to a value of order of 1000 for viscous oils. Simplifications are possible for very small or very large Prandtl numbers. We shall avoid such simplifications in order to keep the boundary layer equations general. However, Re is always large in our consideration. We can finally write the thermal boundary layer equation as () u∗∂θ∂x∗+v∗∂θ∂y∗=1RePr[∂2θ∂y∗2](nondimensional)
Human Thermoregulation System and Comfort
Published in Guowen Song, Faming Wang, Firefighters’ Clothing and Equipment, 2018
Regarding forced convection, Reynolds number (Re) is a dimensionless number used to describe the flow pattern of fluid around the object. It is defined as proportional to the ratio of inertial forces to viscous forces. Nusselt number (Nu) is used to describe heat exchange. It is defined as proportional to the ratio of the heat transfer by convection to that by conduction in the same fluid at rest. Prandtl number (Pr) is used to describe fluid’s thermal properties. It is defined as the ratio of the kinematic viscosity to the thermal diffusivity. These three dimensionless numbers can be calculated by (Parsons, 2014b) Re=VLv;v=μpNu=hcLKPr=μpKpc=μcK
Simulation of the laminar thermal boundary layer problem over a flat plate by exploring the local non-similarity technique
Published in International Journal of Modelling and Simulation, 2023
Matthew O. Lawal, Yusuf O. Tijani, Suraju O. Ajadi, Kazeem B. Kasali
The influence of Prandtl number is displayed in Figure 6. It is discovered that increase in decreases the temperature profile. The behaviour is as a result of being strongly dependent on thermal diffusivity of fluid from the definition meaning that larger has frail thermal diffusivity. In other words, the fluid is more viscous and conducts heat more slowly. As a result, an increment in the Prandtl number reduces the temperature profile of the fluid. The physical implication of this phenomenon is that rapid cooling or heating will be on the disadvantage. Consequently, a lower Prandtl number leads to more efficient heat transfer rate. These findings further corroborated what is in literature as reported by Olanrewaju et al. [29] and Koriko et al. [30].
Keller Box procedure for stagnation point flow of EMHD Casson nanofluid over an absorbent stretched electromagnetic plate with chemical reaction
Published in Numerical Heat Transfer, Part A: Applications, 2023
Wuriti Sridhar, Talla Hymavathi, Sameh E. Ahmed, Abdulaziz Alenazi, Ganugapati Raghavendra Ganesh
The effects of numerous parameters are analyzed by plotting graphs using MATLAB. For increasing observations of the modified Hartmann parameter, the velocity enhances because of the augmentation of the Hartmann parameter, it amplifies external forces and consequently, the flow velocity increases as it is depicted in Figure 2. Prandtl number is defined as a ratio of kinematic viscosity to thermal diffusivity and it is used to measure heat transfer rate. for progressive observations of the Prandtl number, the velocity decreases which is portrayed in Figure 3. Figure 4 shows the velocity profiles for various values of On increasing the non-dimensional parameter related to the magnets and electrodes, the velocity enhances. Figure 5 represents the velocity profiles for various values of the permeability parameter. For the augmented observations of the permeability parameter, the frictional force increases near the pores and therefore the velocity of fluid decreases. From Figure 6, enhancing the Casson parameter increases the dynamic viscidness of fluid and so the velocity of the fluid reduces. Figure 7 shows the temperature graphs for various values of the radiation constraint. With augmented observations of radiation factor, more heat is produced inside the fluid and boundary layer thickness increases as a result the temperature profiles increase. For incremental observations of the heat source parameter Q, the thermal boundary layer enhancement is noted then the temperature increases as it was depicted in Figure 8.
Volumetric chemical reactive Casson fluid flow over a nonlinear extended surface
Published in Waves in Random and Complex Media, 2023
Muhammad Shuaib, Muhammad Anas, Hijab ur Rehman
The heat transfer rate can be depicted in Figure 10(a–d). The heat transfer rate is increased for both the chemical reaction parameter R Figure 10(a), and Casson fluid parameter β Figure 10(c), against Eckert number Ec and Brownian motion parameter Nb, respectively. One can see that the Casson parameter has an inverse relation with fluid's viscosity within the temperature equation. Due to this inverse relation, the dynamic viscosity will be decreased with the increasing values of β and as a result much more heat will be transferred. Figure 10(b,d) shows that the heat transfer rate decline for the increasing values of Prandtl number Pr and heat source parameter λ, respectively. This increase in heat transfer rate is due to the reduction of thermo diffusivity of the fluid by Prandtl number.