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Units and Dimensions
Published in C. Anandharamakrishnan, S. Padma Ishwarya, Essentials and Applications of Food Engineering, 2019
C. Anandharamakrishnan, S. Padma Ishwarya
Dimensionless quantities: a dimensionless quantity can be defined as a number or expression which does not possess a unit but has a fixed value. It is a combination of dimensions such that it eventually cancels out to unity. For example: π or pi ( = 3.14159) and e (Euler’s number, a mathematical constant equal to 2.71828).
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
In SI units hx is measured in W/m2∘C. The heat transfer coefficient is often expressed via an important dimensionless quantity known as the Nusselt number. The Nusselt number is defined as Nux=hxxκf
Gas Flow at Vacuum Conditions
Published in Igor Bello, Vacuum and Ultravacuum, 2017
The Reynolds number is a dimensionless quantity. When Reynolds number Re is larger than 2100 (Re > 2100), gas flows in a turbulent regime, and when Re < 1100, gas may flow in a viscous laminar regime. Apparently, the transition region between the turbulent and laminar regimes is gradual, and it occurs between Reynolds numbers of 2100 and 1100. The boundary values of Reynolds number at which the flow character changes relate to the states of duct surfaces, particularly surface roughness, as well as experimental factors. As a result, slightly different boundary values of the Reynolds number can be found in different publications. However, mostly the values of Reynolds numbers as given above are considered to be transition boundaries for turbulent and transition turbulent–laminar gas flows.
Numerical modeling of bioconvection and heat transfer analysis of Prandtl nanofluid in an inclined stretching sheet: A finite difference scheme
Published in Numerical Heat Transfer, Part A: Applications, 2023
The influence of and over the Nusselt number has been illustrated in Figure 9(a–c). In heat transfer studies, the Nusselt number (), a dimensionless quantity, is used to describe the convective heat transfer rate. It shows how much heat is transferred over a boundary layer via convection as opposed to conductive heat transfer and these plotting curves indicate that the conductive heat is more dominant over the convective heat. is an increasing function of Prandtl fluid parameters and and The at the surface decreases with augmented values of Eckert number. Figure 9(b) reveals the impact of and over the surface cooling rate. The nusselt number diminishes with an increase in the Brownian motion, this decline is also being assisted by strong thermophoretic forces. But, the Prandtl fluid parameter enhances the rate of heat transfer at the surface. asserts that the convective heat transfer rate, therefore, becomes more significant than the conductive heat transfer rate when the fluid’s thermal diffusivity becomes comparatively less compared to its momentum diffusivity. This behavior is seen when the thermal boundary layer is more substantial than the momentum boundary layer and vice-versa for
Numerical modeling of heat transfer performance and optimization of car radiator using (H2O/Al2O3) nanofluids as coolant
Published in Numerical Heat Transfer, Part B: Fundamentals, 2022
S. O. Oyedepo, D. Ezeuduji, A. O. Araoyinbo, O. Kilanko, U. K. Efemwenkiekie, J. O. Dirisu, A. K. Aworinde, P. O. Babalola, R. O. Leramo, Mohamed H. Ahmed, B. Saleh
Nusselt number is a dimensionless quantity used for analyzing the heat transfer in both free and forced convection systems. It is the ratio of the convective to conductive heat transfer across the boundary of a flowing fluid. From the simulation results, the Nusselt number for both the coolant in the radiator can be calculated as follows; where is the heat transfer coefficient (coolant side).
Numerical study on structure optimization and heat transfer characteristic of distributed pulsating flow heat exchanger
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Lei Chen, Hongxin Zhang, Song Huang, Jianjun Li
Nusselt number(Nu) is a dimensionless quantity indicative of the ratio of heat conduction resistance to heat transfer resistance in fluid convection heat transfer. The calculation equation for Nu is as follows: