scholarly journals Heat Transfer Performance of R-1234ze(E) with the Effect of High-Viscosity POE Oil on Enhanced GEWA-B5H Tube

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2285
Author(s):  
Abhishek Kumar ◽  
Miao-Ru Chen ◽  
Jung-Hsien Wu ◽  
Kuo-Shu Hung ◽  
Li-Kang Su ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Fraction ◽  
Heat Transfer Performance ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
High Viscosity ◽  
Heat Fluxes ◽  
Transfer Performance ◽  
Oil Viscosity ◽  
Low Viscosity

In this study, the heat transfer performance of high-viscosity polyol ester (POE) oil POEA-220 (220 cSt) with low-GWP (global warming potential) refrigerant R-1234ze(E) on enhanced GEWA-B5H tube was investigated at saturation temperatures of 10 °C, 0 °C, and −6 °C. The mass fraction of oil varied from 0.25% to 10%, and all the nucleate pool boiling data were measured at heat fluxes ranging from 10 kW/m2 to 90 kW/m2. The experimental results showed that the heat transfer performance of the R-1234ze(E)/POEA-220 mixtures were superior to the R-1234ze(E)/POEA-68 mixtures. At saturation temperatures of 0 °C and −6 °C, even a 10% mass fraction of the POEA-220 oil showed an enhancement in the HTC (heat transfer coefficient) compared to the pure refrigerant in the moderate heat flux range. On the other hand, for the R-1234ze(E)/POEA-68 mixtures, a 5% mass fraction of oil showed no enhancement in the HTC compared to pure refrigerant at the same saturation temperature. Moreover, at low saturation temperatures (0 °C and −6 °C), the enhancement in the HTC decreased with increasing mass fraction of low-viscosity oil POEA-68, whereas high-viscosity oil POEA-220 showed the highest enhancement in the HTC for a 5% mass fraction of oil at −6 °C saturation temperature compared to the pure refrigerant. The results indicate that for nucleate boiling, the effect of oil viscosity on heat transfer performance is negligible if it contains comparatively high thermal conductivity and low surface tension. In addition, the effect of surface aging on heat transfer performance for the GEAW-B5H tube with pure refrigerant was also reported.

scholarly journals Entropy Generation and Heat Transfer Performance in Microchannel Cooling

Entropy ◽  
2019 ◽  
Vol 21 (2) ◽  
pp. 191 ◽  
Author(s):  
Jundika Kurnia ◽  
Desmond Lim ◽  
Lianjun Chen ◽  
Lishuai Jiang ◽  
Agus Sasmito
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Heat Transfer Performance ◽  
Second Law Of Thermodynamics ◽  
High Heat ◽  
Heat Fluxes ◽  
Transfer Performance ◽  
Cooling Channel ◽  
High Heat Transfer ◽  
Microchannel Cooling

Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250–1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.

Comparison of Droplet Evaporation and Nucleate Boiling Mechanisms on Nanoporous Superhydrophilic Surfaces

2019 ◽  
Author(s):  
Samuel Cabrera ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Droplet Evaporation ◽  
Transfer Performance ◽  
Nanostructured Surface ◽  
Nanostructured Surfaces ◽  
Droplet Vaporization

Abstract Recent studies have indicated that at slightly superheated surface temperatures, droplet evaporation on a nanoporous superhydrophilic surface exhibits onset of nucleation and nucleate boiling effects similar to pool boiling processes. This paper discusses water droplet evaporation experiments and pool boiling experiments conducted on nanostructured surfaces of a 45° downward facing pyramid copper and aluminum substrate. The nanostructured surfaces were used to conduct both droplet evaporation experiments and pool boiling experiments and thus allow direct comparison of the underlying heat transfer performance and mechanisms for these two different processes. The four surfaces tested were the following: bare copper surface, nanostructured surface on copper, bare aluminum surface, and nanostructured surface on aluminum. Mean heat flux values at varying superheats were obtained through temperature and time measurements. To better understand the heat performance of each surface, the wetting and wicking characteristics of each surface were also tested. Experimental results indicate that many of the mechanisms associated with pool boiling may also play a role in droplet vaporization, and their presence can produce levels of heat transfer performance comparable to, or even higher than, that observed in pool boiling at a comparable wall superheat. The results demonstrate that the nanostructured surface affects onset of nucleate boiling and maximum heat flux in both droplet vaporization and nucleate boiling on these surfaces. The implications of these results for strategies to enhance spray cooling and pool boiling are also discussed.

Experimental Investigation of Area Ratio on Microjet Array Heat Transfer

2009 ◽  
Author(s):  
Gregory J. Michna ◽  
Eric A. Browne ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Area Ratio ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
High Heat Transfer

Electronics cooling is becoming increasingly difficult due to increasing power consumption and decreasing size of processor chips. Heat fluxes in processors and power electronics are quickly approaching levels that cannot be easily addressed by forced air convection over finned heat sinks. Jet impingement cooling offers high heat transfer coefficients and has been used effectively in conventional-scale applications such as turbine blade cooling and the quenching of metals. However, literature in the area of microjet arrays is scarce and has not studied arrays of large area ratios. Hence, the objective of this study is to experimentally assess the heat transfer performance of arrays of microjets. The microjet arrays were fabricated using MEMS processes in a clean room environment. The heat transfer performance of several arrays using deionized water as the working fluid was investigated. Inline and staggered array arrangements were investigated, and the area ratio (total area of the jets divided by the surface area) was varied between 0.036 and 0.35. Reynolds numbers defined by the jet diameter were in the range of 50 to 3,500. Heat fluxes greater than 1,000 W/cm2 were obtained at fluid inlet-to-surface temperature differences of less than 30 °C. Heat transfer performance improved as the area ratio was increased.

NUMERICAL STUDY ON FLOW BOILING IN A TREE-SHAPED MICROCHANNEL

Fractals ◽  
2019 ◽  
Vol 27 (07) ◽  
pp. 1950111
Author(s):  
WEI YU ◽  
LUYAO XU ◽  
SHUNJIA CHEN ◽  
FENG YAO
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Flow Rate ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Performance ◽  
The Heat Transfer Coefficient

A two-dimensional model is developed to numerically study the water flow boiling through a tree-shaped microchannel by VOF method. In this work, the bubble dynamics and flow patterns along the channel are examined. Additionally, the pressure drop, heat transfer performance and the effects of mass flow rate and heat flux on the heat transfer coefficient are analyzed and discussed. The numerical results indicate that, there are three main bubble dynamic behaviors at the wall, namely coalesce-lift-off, coalesce-slide and coalesce-reattachment. At the bifurcation in high branching level, the slug bubbles may coalesce or breakup. The flow patterns of bubbly, bubbly-slug flows occur at low branching level and slug flow occurs at high branching level. The passage of bubbles causes the increasing of fluid temperature and local pressure. Additionally, the pressure drop decreases with the branching level. The flow pattern and channel confinement effect play a vital role in heat transfer performance. The nucleate boiling dominant heat transfer is observed at low branching level, the heat transfer performance is enhanced with increasing branching level from [Formula: see text] to 2. While, at high branching level, the heat transfer performance becomes weaker due to the suppression of nucleate boiling. Moreover, the heat transfer coefficient increases with the mass flow rate and heat flux.

The Effects of Wettability and Surface Morphology on Heat Transfer for Zinc Oxide Nanostructured Aluminum Surfaces

2017 ◽  
Author(s):  
Claire M. Kunkle ◽  
Jordan P. Mizerak ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Heat Transfer Performance ◽  
Nucleate Boiling ◽  
Contact Angles ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wetted Area ◽  
Aluminum Surfaces

The development of hydrophilic surface coatings for enhanced wetting characteristics has led to improvement in heat transfer metrics like impinging droplet vaporization time and the heat transfer coefficient. Hydrothermal synthesis, a method of developing hydrophilic surfaces, has been previously shown to produce high performing heat transfer surfaces on copper substrates [1]. Our study applied this production method to aluminum substrates, which have the advantage of being cheaper, lighter, and a more widely used for heat sinks than copper. Previous experiments have shown that water droplets on ZnO nanostructure coated surfaces, at low superheats, evaporate via thin film evaporation rather than nucleate boiling. This leads to heat transfer coefficients as much as three times higher than nucleate boiling models for the same superheat. Our nanocoated aluminum surfaces exhibit superhydrophilicity with an average droplet liquid film thickness of 20–30 microns, which can produce heat transfer coefficients of over 25 kW/m2K. This study discusses characterization of ZnO nanostructured aluminum surfaces to better understand the related mechanisms which lead to such high heat transfer performance. All ZnO nanostructured aluminum surfaces produced for this study exhibited superhydrophilicity, with sessile droplet contact angles of less than 5 degrees. The challenge of achieving accuracy for such low contact angles led to the development of a new wetting metric related to the droplet’s wetted area on a surface rather than the contact angle. This new metric is predicated on the the fact that heat transfer performance is directly related to this wetted area, thickens, and shape of the expanding droplet footprint. Shape irregularity of droplets on these superhydrophilic surfaces is discussed in this study, where there appears to be advantages to irregular spreading compared with surfaces that produce symmetric radial spreading. One form of irregular spreading consists of liquid droplets spreading out both on top of the surface and within the microstructure of the surface coating. The liquid within the microstructure forms films less than 5 microns thick, making local heat transfer coefficients of greater than 100 kW/m2K possible. SEM microscope imaging provided additional insight to the underlying mechanisms which cause these surfaces to produce such exceptional spreading as well as irregular spreading, resulting in very good heat transfer performance. Experimental work was coupled with computational analysis to model the contact line of the droplet footprint. Image processing of experimental photos helps to analyze spreading characteristics, which can be directly related to heat transfer due to film thickness at various points during spreading. Approaches used to characterize these superhydrophilic surfaces advance understanding of the connections between nanoscale structural elements and macroscale performance characteristics in heat transfer. This understanding can reveal key insights for developing even better high performance surfaces for a broad range of applications.

Nucleate Pool Boiling on Tubes With Subsurface Mini and Micro Channels

2008 ◽  
Author(s):  
Peter Stephan ◽  
Frank Wondra
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Standard Procedure ◽  
Model Development ◽  
Heat Fluxes ◽  
Optical Measurements ◽  
Transfer Performance ◽  
Performance Measurements ◽  
Micro Channels ◽  
Physically Based

Tubes with subsurface mini- and micro channels are widely used in boiling devices. Today, the design of these tubes is based on empirical investigations because reliable theoretical or numerical design methods are not available, and the heat transfer performance characteristics vary strongly e.g. for different fluids, system pressures and heat fluxes. The presented study approaches the subject of interest from 3 different paths: (i) macroscopic heat transfer performance measurements; (ii) optical measurements of the thermal and hydrodynamic phenomena inside the subsurface channels with very high spatial and temporal resolution; (iii) development of a computational model. While path (i) is a standard procedure in the scientific community, path (ii) is a completely new approach, and only the combination of (i) and (ii) is a solid basis for the physically based model development in path (iii). Tubes with different subsurface channels and micro pin-fins are used in combination with different fluids at different system pressures. The results are presented and discussed.

scholarly journals Experimental Investigation on Heat Transfer of Supercritical Water Flowing in the Subchannel with Grid Spacer in Supercritical Water-Cooled Reactor

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1016
Author(s):  
Weishu Wang ◽  
Lingwei Guo ◽  
Ge Zhu ◽  
Xiaojing Zhu ◽  
Qincheng Bi
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Supercritical Water ◽  
Heat Transfer Performance ◽  
Heat Fluxes ◽  
Experimental Investigations ◽  
Grid Function ◽  
Transfer Performance ◽  
Supercritical Water Cooled Reactor ◽  
The Impact

Experimental investigations on the heat transfer performance of supercritical water flowing in the subchannel of supercritical water-cooled reactor (SCWR) simulated by a triangular channel were conducted at pressures of 23–28 MPa, mass flow rates of 700–1300 kg·m−2·s−1, and inner wall surface heat fluxes of 200–600 kW·m−2. An 8 mm diameter fuel rod with a 1.4 pitch to diameter ratio was used. The effects of pressure, mass flow rate, and heat flux on the heat transfer performance under the resistance of a standard grid spacer were analyzed. Experimental results showed the significant positive influence of the grid spacer on the supercritical water in the subchannel. Moreover, in the presence of the grid spacer, the parameters influenced the heat transfer with different degrees of strengthening reaction. In view of the phenomenon in the tests, the rule of the supercritical heat transfer was further revealed by the comparison between empirical formulas and experimental data. This paper mainly studied the positioning grid function and the fluid flow characteristics downstream of the subchannel under the influence of the standard grid spacer and the impact mechanism of each parameter on the whole heat transfer process coefficient.

Sign in / Sign up

Export Citation Format

Share Document