Single-Phase Laminar-Flow Heat Transfer and Two-Phase Oscillating-Flow Heat Transport in Microchannels

2003 ◽  
Author(s):  
Shigefumi Nishio
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Single Phase ◽  
Local Equilibrium ◽  
Oscillating Flow ◽  
Thermal Systems ◽  
Two Phase ◽  
Flow And Heat Transfer ◽  
Flow Heat ◽  
Inner Diameter

The present review article focuses on the research field of heat transfer of single-phase laminar-flow and two-phase self-exciting oscillating-flow in microchannels. First, to make prominent the special features of Micro Thermal Systems (MTSs), the definition of the term “Nano Thermal Systems” (NTSs) is discussed from the viewpoint of local equilibrium. Next, to show the special features of flow and heat transfer in microchannels, some thermal functions appearing in microchannels are introduced. Further, focusing on flow and heat transfer characteristics of single-phase laminar liquid-flow in microchannels, researches in the literature and recent results at IIS (Institute of Industrial Science, the University of Tokyo) are introduced, and it is shown that the results obtained for tubes larger than 0.1mm in inner diameter are in good agreement with the conventional analyses. Finally, Japanese researches and recent results at IIS on micro SEMOS heat pipes (mSEMOSs) are introduced and it is shown that a mSEMOS of 0.5mm in inner diameter can transport a significant amount of heat.

Simulation of Two-Phase Flow and Heat Transfer in Mini- and Micro-Channels for Concentrating Photovoltaics Cooling

2011 ◽  
Author(s):  
Devin Pellicone ◽  
Alfonso Ortega ◽  
Marcelo del Valle ◽  
Steven Schon
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Single Phase ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Micro Scale ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Micro Channels

Advances in concentrating photovoltaics technology have generated a need for more effective thermal management techniques. Research in photovoltaics has shown that there is a more than 50% decrease in PV cell efficiency when operating temperatures approach 60°C. It is estimated that a waste heat load in excess of 500 W/cm2 will need to be dissipated at a solar concentration of 10,000 suns. Mini- and micro-scale heat exchangers provide the means for large heat transfer coefficients with single phase flow due to the inverse proportionality of Nusselt number with respect to the hydraulic diameter. For very high heat flux situations, single phase forced convection in micro-channels may not be sufficient and hence convective flow boiling in small scale heat exchangers has gained wider scrutiny due to the much higher achievable heat transfer coefficients due to latent heat of vaporization and convective boiling. The purpose of this investigation is to explore a practical and accurate modeling approach for simulating multiphase flow and heat transfer in mini- and micro-channel heat exchangers. The work is specifically aimed at providing a modeling tool to assist in the design of a mini/micro-scale stacked heat exchanger to operate in the boiling regime. The flow side energy and momentum equations have been implemented using a one-dimensional homogeneous approach, with local heat transfer coefficients and friction factors supplied by literature correlations. The channel flow solver has been implemented in MATLAB™ and embedded within the COMSOL™ FEM solver which is used to model the solid side conduction problem. The COMSOL environment allows for parameterization of design variables leading to a fully customizable model of a two-phase heat exchanger.

Performance Evaluation of Liquid Flow With PCM Particles in Microchannels

2005 ◽  
Vol 127 (8) ◽  
pp. 931-940 ◽  
Author(s):  
K. Q. Xing ◽  
Y.-X. Tao ◽  
Y. L. Hao
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Laminar Flow ◽  
Phase Change ◽  
Performance Index ◽  
Single Phase ◽  
Suspension Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase

A two-phase, non thermal equilibrium-based model is applied to the numerical simulation of laminar flow and heat transfer characteristics of suspension with microsize phase-change material (PCM) particles in a microchannel. The model solves the conservation of mass, momentum, and thermal energy equations for liquid and particle phases separately. The study focuses on the parametric study of optimal conditions where heat transfer is enhanced with an increase in fluid power necessary for pumping the two-phase flow. The main contribution of PCM particles to the enhancement of heat transfer in a microsize tube is to increase the effective thermal capacity and utilize the latent heat effect under the laminar flow condition. An effectiveness factor εeff is defined to evaluate the heat transfer enhancement compared to the single-phase flow heat transfer and is calculated under different wall heat fluxes and different Reynolds numbers. The comparison is also made to evaluate the performance index, i.e., the ratio of total heat transfer rate to fluid flow power (pressure drop multiplied by volume flow rate) between PCM suspension flow and pure water single-phase flow. The results show that for a given Reynolds number, there exists an optimal heat flux under which the εeff value is the greatest. In general, the PCM suspension flow with phase change has a significantly higher performance index than the pure-fluid flow. The comparison of the model simulation with the limited experimental results for a MCPCM suspension flow in a 3mmdia tube reveals the sensitivity of wall temperature distribution to the PCM supply temperature and the importance of characterizing the phase change region for a given tube length.

Nanotechnology as Effective Passive Technique for Heat Transfer Augmentation

2018 ◽  
pp. 1-49
Keyword(s):  
Heat Transfer ◽  
Base Fluid ◽  
Single Phase ◽  
Particle Dispersion ◽  
Two Phase ◽  
Flow And Heat Transfer ◽  
Fluid Properties ◽  
And Behaviors ◽  
Passive Technique ◽  
Definition Of

Nanofluids are fluids containing the solid nanometer-sized particle dispersion. Two main methods are introduced in this chapter, namely single-phase and two-phase modeling. In first method, the combination of nanoparticle and base fluid is considered as a single-phase mixture with steady properties, and in the second method, the nanoparticle properties and behaviors are considered separately from the base fluid properties and behaviors. Moreover, nanofluid flow and heat transfer can be studied in the presence of thermal radiation, electric field, magnetic field, and porous media. In this chapter, a definition of nanofluid and its applications have been presented.

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