Convective Heat Transfer of Laminar Single-Phase Flow in Randomly Rough Microtubes

2005 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Single Phase ◽  
Phase Flow ◽  
Wall Roughness ◽  
Single Phase Flow ◽  
Cross Sectional ◽  
Surface Areas

Convective heat transfer of laminar, single-phase flow in rough microtubes is studied. Wall roughness and slope are assumed to possess Gaussian, isotropic distributions. Fractal concepts are used to model the rough microtube. It is shown that due to the existence of wall roughness, both cross-sectional and inside surface areas are increased. A new concept is defined as a figure of merit for assessing thermal performance of rough microtubes. As a result of increasing roughness, an enhancement is observed in the thermal performance of microtubes. The present model can be extended to analyze other geometries such as rectangular and trapezoidal microchannels.

Convective Heat Transfer of Laminar Droplet Flow in Thermal Entrance Region of Circular Tubes

1979 ◽  
Vol 101 (3) ◽  
pp. 480-483 ◽  
Author(s):  
Shi-chune Yao
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Single Phase ◽  
Entrance Region ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Droplet Flow ◽  
Thermal Entrance Region ◽  
Thermal Entrance

Connective heat transfer of laminar droplet flow is calculated numerically for the thermal entrance region of circular tube with constant wall temperature. The heat transfer contribution of saturated droplets in the superheated vapor stream is considered as distributed heat sink. In the thermal entrance region, the size and the population density of the droplets are considered as constants. The heat transfer of droplet flow is found to be considerably higher than that of single phase flow. The effects of the droplet characteristics and the wall superheat to the convective heat transfer are studied. Fundamental differences of heat transfers in single phase flow and droplet flow are revealed.

A New Thermodynamic and Heat Transfer Model for Nanolubricants and Refrigerant Heat Transfer Processes in Smooth Copper Tubes

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Pratik S. Deokar ◽  
Lorenzo Cremaschi ◽  
Andrea A. M. Bigi
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Single Phase ◽  
Flow Boiling ◽  
Heat Transfer Model ◽  
Forced Flow ◽  
Transfer Model ◽  
Phase Flow ◽  
Two Phase

Abstract In air conditioning systems, lubricating oil leaves the compressor and circulates through the other system components. This lubricant acts as a contaminant affecting heat transfer in heat exchangers. The literature indicated that mixtures of refrigerants and nanolubricants, that is, nanoparticles dispersed in the lubricant oils, have potentials to augment heat transfer exchange effectiveness. However, the nanoparticle mechanisms leading to such heat transfer changes are still unclear and not well included in the models. In this work, an existing single-phase forced flow convective heat transfer model, originally developed for water-based nanofluids, was modified to include the effects of diffusion and mass balance of different shape nanoparticles within the laminar sublayer and turbulent layer of the flow. A new physics-based superposition heat transfer model for saturated two-phase flow boiling of refrigerant and nanolubricants was also developed by integrating the modified forced flow convective heat transfer model and a semi-empirical pool boiling model for nanolubricants. The new model included the several physical effects that influenced heat transfer, such as slip mechanisms at the nanoparticles and base fluid interface and its influence on the laminar sublayer thickness, momentum transfer from the nanoparticles to the growing bubbles, and formation of lubricant excess concentration at the tube surface and its influence on bubble growth and tube wetting. The new model was validated for single-phase convective heat transfer and two-phase flow boiling of refrigerant R410A with two nanolubricants, having nonspherical ZnO nanoparticles and spherical Al2O3 nanoparticles.

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