An introduction to heat transfer

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Numerical Heat Transfer And Fluid Flow

Part I: Background and Fundamentals Introduction, Mohamed Gad-el-Hak, University of Notre Dame Scaling of Micromechanical Devices, William Trimmer, Standard MEMS, Inc., and Robert H. Stroud, Aerospace Corporation Mechanical Properties of MEMS Materials, William N. Sharpe, Jr., Johns Hopkins University Flow Physics, Mohamed Gad-el-Hak, University of Notre Dame Integrated Simulation for MEMS: Coupling Flow-Structure-Thermal-Electrical Domains, Robert M. Kirby and George Em Karniadakis, Brown University, and Oleg Mikulchenko and Kartikeya Mayaram, Oregon State University Liquid Flows in Microchannels, Kendra V. Sharp and Ronald J. Adrian, University of Illinois at Urbana-Champaign, Juan G. Santiago and Joshua I. Molho, Stanford University Burnett Simulations of Flows in Microdevices, Ramesh K. Agarwal and Keon-Young Yun, Wichita State University Molecular-Based Microfluidic Simulation Models, Ali Beskok, Texas A&M University Lubrication in MEMS, Kenneth S. Breuer, Brown University Physics of Thin Liquid Films, Alexander Oron, Technion, Israel Bubble/Drop Transport in Microchannels, Hsueh-Chia Chang, University of Notre Dame Fundamentals of Control Theory, Bill Goodwine, University of Notre Dame Model-Based Flow Control for Distributed Architectures, Thomas R. Bewley, University of California, San Diego Soft Computing in Control, Mihir Sen and Bill Goodwine, University of Notre Dame Part II: Design and Fabrication Materials for Microelectromechanical Systems Christian A. Zorman and Mehran Mehregany, Case Western Reserve University MEMS Fabrication, Marc J. Madou, Nanogen, Inc. LIGA and Other Replication Techniques, Marc J. Madou, Nanogen, Inc. X-Ray-Based Fabrication, Todd Christenson, Sandia National Laboratories Electrochemical Fabrication (EFAB), Adam L. Cohen, MEMGen Corporation Fabrication and Characterization of Single-Crystal Silicon Carbide MEMS, Robert S. Okojie, NASA Glenn Research Center Deep Reactive Ion Etching for Bulk Micromachining of Silicon Carbide, Glenn M. Beheim, NASA Glenn Research Center Microfabricated Chemical Sensors for Aerospace Applications, Gary W. Hunter, NASA Glenn Research Center, Chung-Chiun Liu, Case Western Reserve University, and Darby B. Makel, Makel Engineering, Inc. Packaging of Harsh-Environment MEMS Devices, Liang-Yu Chen and Jih-Fen Lei, NASA Glenn Research Center Part III: Applications of MEMS Inertial Sensors, Paul L. Bergstrom, Michigan Technological University, and Gary G. Li, OMM, Inc. Micromachined Pressure Sensors, Jae-Sung Park, Chester Wilson, and Yogesh B. Gianchandani, University of Wisconsin-Madison Sensors and Actuators for Turbulent Flows. Lennart Loefdahl, Chalmers University of Technology, and Mohamed Gad-el-Hak, University of Notre Dame Surface-Micromachined Mechanisms, Andrew D. Oliver and David W. Plummer, Sandia National Laboratories Microrobotics Thorbjoern Ebefors and Goeran Stemme, Royal Institute of Technology, Sweden Microscale Vacuum Pumps, E. Phillip Muntz, University of Southern California, and Stephen E. Vargo, SiWave, Inc. Microdroplet Generators. Fan-Gang Tseng, National Tsing Hua University, Taiwan Micro Heat Pipes and Micro Heat Spreaders, G. P. "Bud" Peterson, Rensselaer Polytechnic Institute Microchannel Heat Sinks, Yitshak Zohar, Hong Kong University of Science and Technology Flow Control, Mohamed Gad-el-Hak, University of Notre Dame) Part IV: The Future Reactive Control for Skin-Friction Reduction, Haecheon Choi, Seoul National University Towards MEMS Autonomous Control of Free-Shear Flows, Ahmed Naguib, Michigan State University Fabrication Technologies for Nanoelectromechanical Systems, Gary H. Bernstein, Holly V. Goodson, and Gregory L. Snider, University of Notre Dame Index

The MEMS Handbook

An Introduction to Magnetohydrodynamics

Geometry: shape, size, aspect ratio and orientation Flow Type: forced, natural, laminar, turbulent, internal, external Boundary: isothermal (Tw = constant) or isoflux (q̇w = constant) Fluid Type: viscous oil, water, gases or liquid metals Properties: all properties determined at film temperature Tf = (Tw + T∞)/2 Note: ρ and ν ∝ 1/Patm ⇒ see Q12-40 density: ρ ((kg/m) specific heat: Cp (J/kg ·K) dynamic viscosity: μ, (N · s/m) kinematic viscosity: ν ≡ μ/ρ (m/s) thermal conductivity: k, (W/m ·K) thermal diffusivity: α, ≡ k/(ρ · Cp) (m/s) Prandtl number: Pr, ≡ ν/α (−−) volumetric compressibility: β, (1/K)

Convection Heat Transfer

A micro-tube passage is a basic and important element in the design of micro heat exchangers and for this reason during the last decade a series of investigations have been made with the aim to clarify the main scaling effects playing an important role in microtubes. In this paper, a combined analysis of numerically and experimentally obtained average friction factors in microtubes under the situation of under-expanded (choked) gas flow is presented. The working fluid (nitrogen) passes through the microtube and discharges into the atmosphere under an increasing inlet pressure. Experiments and numerical computations are performed for microtubes with 249 and 528.9 mm in diameter, by varying the aspect ratio (i.e. length/diameter) from 100 to 200. The numerical methodology to solve the governing equations is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. In order to capture the under-expansion characteristics of the flow during choking, the computational domain is extended in the downstream region beyond the microtube outlet. Both experimental and numerical results were obtained for a wide range of Mach number and Reynolds number. In the previous study, it was demonstrated how the outlet Mach number can be expressed as a function of the tube diameter under choked conditions. In this paper, a data reduction procedure for the estimation of the average friction factor between the inlet and the outlet of the microtube is proposed for choked flows in which the outlet gas temperature and pressure are obtained by using the outlet Mach number calculated numerically as a function of the microtube diameter. It is demonstrated how this data reduction method allows an accurate calculation of the average friction factors in microtubes by using a limited number of parameters which are easy to measure. The results obtained in this way are in good agreement with the numerical predictions as well as with the most common empirical correlations.

Average Friction Factors of Choked Gas Flow in Microtubes

Three methods for predicting pressure loss of gaseous flow in a conduit-system of microchannel heat exchanger are proposed and discussed. In the experiment, the heat transfer plate which is the core of the heat exchanger has 34 rectangular microchannels. The microchannels are 330 m in width, 200 m in depth and 20 mm in length. The working fluid is air at room temperature, which is compressed to flow in the heat exchanger and flows out to atmospheric surroundings. The static pressures were measured at the inlet and outlet of the conduit-system. The conduit-system, namely, the heat exchanger and the piping system, includes several factors of pressure loss such as pipe friction, sudden expansion or contraction at the joints of piping system, besides the conventional loss at the heat exchanger core. These additional losses cannot be ignored because the hydraulic diameters of piping system tend to be small for microchannel heat exchangers. The prediction methods are formulated with the assumption that the pressure loss coefficients (such as pipe friction factor) have the same value of those of incompressible flow. One of the methods is simply formulated assuming isothermal flow and constant densities in each conduit-element, and another one is based on one-dimensional adiabatic flow theory. These two methods adopted pressure loss correlation of incompressible flow as approximation. The third method adopted modified pressure loss correlation where the essence of pressure loss is considered as internal heat generation by dissipation, and total pressure loss is calculated based on isobaric curves on h-s chart using entropy increase by the heat generation. When the measured outlet pressure is used as initial value of prediction, the third method gives the best prediction of static pressure difference between the inlet and outlet of the conduit-system within 3.9% difference from the experiment in the range of 371-1460 of channel Reynolds number.

Pressure loss prediction of gaseous flow in a conduit-system of microchannel heat exchanger

Abstract The coarse graining parameter has been used to determine parameter values of the dissipative particle dynamics (DPD). However, it is known that the self-diffusivity obtained by the DPD simulation reduces with increasing the coarse graining parameter. In this study, an alternative expression for Boltzmann temperature of the DPD particles is proposed. The self-diffusivity and the dynamic viscosity of water were obtained by using the proposed expression for Boltzmann temperature of the DPD particles and the standard weight function. The obtained self-diffusivity was slightly higher than the measured value in the temperature range from 280 K to 330 K, however, it was independent of the coarse graining parameter. The obtained dynamic viscosity agreed well with value obtained by REFPROP in the temperature range from 280 to 370 K.

Alternative expression for Boltzmann temperature of dissipative-particle-dynamics particles

Combined heat transfer characteristics were obtained numerically for three-dimensional natural convection and thermal radiation in a long and wide vertical porous layer with a hexagonal honeycomb core. We assumed that the porous layer was both homogeneous and isotropic. The pure Darcy law for fluid flow and Rosseland's approximation for radiation were used. The numerical methodology was based on an algebraic coordinate transformation technique and the transformed governing equations were solved using the SIMPLE algorithm. The effect of radiation on the heat transfer characteristics was investigated over a wide range of radiation numbers and temperature ratios for two Darcy-Rayleigh number values (Ra * = 100 and 1000) and for a fixed aspect ratio of H/L = 1. The results are presented in the form of combined radiation and convection heat transfer coefficients and are compared with the corresponding values for pure natural convection.

Natural convection and radiation heat transfer in a vertical porous layer with a hexagonal honeycomb core (Part 1: Numerical analysis)

Discussion: “Friction Numbers and Viscous Dissipation Heating for Laminar Flows of Water in Microtubes” (El-Genk, M., and Yang, I., 2008, ASME J. Heat Transfer, 130, p. 082405)

Yutaka Asako

Papers

Average Friction Factors of Choked Gas Flow in Microtubes

Pressure loss prediction of gaseous flow in a conduit-system of microchannel heat exchanger

Alternative expression for Boltzmann temperature of dissipative-particle-dynamics particles

Natural convection and radiation heat transfer in a vertical porous layer with a hexagonal honeycomb core (Part 1: Numerical analysis)

Discussion: “Friction Numbers and Viscous Dissipation Heating for Laminar Flows of Water in Microtubes” (El-Genk, M., and Yang, I., 2008, ASME J. Heat Transfer, 130, p. 082405)