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Steady-State Heat Transfer Measurement Techniques
Published in Je-Chin Han, Lesley M. Wright, Experimental Methods in Heat Transfer and Fluid Mechanics, 2020
Recalling that the goal is to determine the heat transfer enhancement in the rib roughened channel, it is necessary to recognize how the heat transfer enhancement will be evaluated. In the study shown with this example, the heat transfer enhancement is presented in terms of the Nusselt number ratio (Nu/Nuo). This is a convenient method for comparing the increased heat transfer in the rib roughened channel (Nu) to that of a smooth channel (Nuo). In order to determine the Nusselt number, the heat transfer coefficient must first be calculated, and the heat transfer coefficient can be determined the convective heat transfer equation. () hx=Q˙net,x/AsTw,x−Tb,x
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
Applications
Published in Raj P. Chhabra, CRC Handbook of Thermal Engineering Second Edition, 2017
Joshua D. Ramsey, Ken Bell, Ramesh K. Shah, Bengt Sundén, Zan Wu, Clement Kleinstreuer, Zelin Xu, D. Ian Wilson, Graham T. Polley, John A. Pearce, Kenneth R. Diller, Jonathan W. Valvano, David W. Yarbrough, Moncef Krarti, John Zhai, Jan Kośny, Christian K. Bach, Ian H. Bell, Craig R. Bradshaw, Eckhard A. Groll, Abhinav Krishna, Orkan Kurtulus, Margaret M. Mathison, Bryce Shaffer, Bin Yang, Xinye Zhang, Davide Ziviani, Robert F. Boehm, Anthony F. Mills, Santanu Bandyopadhyay, Shankar Narasimhan, Donald L. Fenton, Raj M. Manglik, Sameer Khandekar, Mario F. Trujillo, Rolf D. Reitz, Milind A. Jog, Prabhat Kumar, K.P. Sandeep, Sanjiv Sinha, Krishna Valavala, Jun Ma, Pradeep Lall, Harold R. Jacobs, Mangesh Chaudhari, Amit Agrawal, Robert J. Moffat, Tadhg O’Donovan, Jungho Kim, S.A. Sherif, Alan T. McDonald, Arturo Pacheco-Vega, Gerardo Diaz, Mihir Sen, K.T. Yang, Martine Rueff, Evelyne Mauret, Pawel Wawrzyniak, Ireneusz Zbicinski, Mariia Sobulska, P.S. Ghoshdastidar, Naveen Tiwari, Rajappa Tadepalli, Raj Ganesh S. Pala, Desh Bandhu Singh, G. N. Tiwari
The dimensionless Nusselt number (NuD) is defined by the convective heat transfer coefficient, the mean hydraulic diameter (Dh), and the thermal conductivity (k) of the fluid. The Dittus–Boelter correlation (Equation 4.1.11) can be used to calculate the Nusselt number if the Reynolds (ReD) and Prandtl (Pr) numbers are known. The value of n depends on whether a fluid is being heated (n = 0.4) or cooled (n = 0.3). The subscript D on the Nusselt and Reynolds numbers indicates that the dimensionless numbers are based on a particular hydraulic diameter, which in this case may be either the hydraulic diameter of the inner pipe (Dh = d1) or the mean hydraulic diameter of the annular region (Dh= D1− d2). It is important to note that the Dittus–Boelter correlation is only valid for Re ≥ 10,000 and 0.6 ≤ Pr ≤ 160. The correlation is also only valid for smooth pipe surfaces, which is not exactly the case in this example. Finally, error is introduced if there are large differences between the pipe wall and the mean temperature of the fluid, which was used to evaluate the fluid properties. Multiple iterations can be used to solve for the wall temperature or other correlations may be useful in minimizing these errors.
Numerical investigation and experimental validation of shape and position optimisation of a static wavy flag for heat transfer enhancement
Published in International Journal of Ambient Energy, 2022
Swadesh Suman, Vineeth Uppada, Swati Singh, Sanjay Mahadev Gaikwad
All the industrial systems dealing with heat and fluid transfer involve fluid flow through channels and must deal with efficient heat dissipation problem at the same time. Heat transfer through channels is one of the classical problems in the heat transfer and fluid mechanics. The thermal behaviour of these channels has been described well by the correlations given by Bergman and Incropera (2011). These correlations imply that the Nusselt number of the fluid flowing inside the channel is a function of Reynolds and Prandtl number which represent the flow properties of the fluid. Nusselt number is used to find the average heat transfer coefficient, which gives the idea of the amount of the heat carried by the fluid. Nusselt number can be easily varied by changing the Reynolds or the Prandtl number. As it is difficult to vary flow properties (i.e. change the Prandtl number), usually the Nusselt number is controlled by varying the Reynolds number.
Experimental investigation of substrate board orientation effect on the optimal distribution of IC chips under forced convection
Published in Experimental Heat Transfer, 2021
V K Mathew, Tapano Kumar Hotta
7. The non-dimensional numbers for the IC chips affecting the laminar forced convection heat transfer are then evaluated using the Eqns. 7 and 8, respectively. The Reynolds number is the ratio of the inertia force to viscous force in fluid flow and is the product of density times velocity times characteristic length divided by the viscosity coefficient. The Nusselt number is the ratio of convective to conductive heat transfer across the fluid boundary. The characteristic length of the IC chips is a scaling parameter and is taken L = 4A/P, as reported in Bergman et al. [28]. This is defined in this manner to develop suitable correlations, as discussed under Section 3.5.3.
Numerical investigation of the non-Newtonian power-law fluid with convective boundary conditions in a non-Darcy porous medium
Published in Waves in Random and Complex Media, 2022
Hiranmoy Mondal, Arpita Mandal, Rajat Tripathi
The Nusselt number is defined as the ratio of convective heat transfer to conductive heat transfer. The Sherwood number is defined as the ratio of convective mass transport to diffusive mass transport. The behavior of Nusselt and Sherwood numbers with various parameters is shown in Figures 10 and 11, respectively. Increasing the Lewis number tends to decrease the heat transfer rate and increase the mass transfer rate in the boundary layer thickness. This aspect may be due to the direct effect of G on the velocity near the wall which significantly influences the strength of the convection mechanism in transporting heat from the wall as compared to the dispersion mechanism.