Heat Transfer in Vapour-Liquid Flow at High Reduced Pressures

2010 ◽  
Author(s):  
Victor Yagov ◽  
Maria Minko
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Co2 Flow ◽  
Reduced Pressures ◽  
Good Agreement

During the last decade a number of studies of boiling heat transfer in carbon dioxide notably increase. As a field of CO2 practical using corresponds to high reduced pressures, and a majority of available experimental data on CO2 flow boiling even in submillimetric channels relate to turbulent liquid flow regimes, a possibility arises to develop sufficiently general method for HTC predicting. Under the above conditions nucleate boiling occurs up to rather high flow quality, even in annular flow regime due to extremely small size of an equilibrium vapour bubble. This conclusion is in agreement with the available experimental data. The predicting equation for nucleate boiling heat transfer developed by one of the present authors in 1988 is valid for any nonmetallic liquid. A contribution of forced convection in heat transfer is calculated according to the Petukhov et al. equation with correction factor, which accounted for an effect of velocity increase due to evaporation. This effect can be essential at relatively small heat fluxes and rather high mass flow rates. The Reynolds analogy and homogeneous model are used in order to account for the convective heat transfer augmentation in two-phase flow. Due to low ratio of liquid and vapour densities at high reduced pressures the homogeneous approximation of two-phase flow seems to be warranted. A total heat transfer coefficient is calculated as an interpolated value of boiling and convective HTCs. The experimental data on CO2 flow boiling related to regimes before heated wall dryout incipience are in rather good agreement with the calculations. Besides the data on carbon dioxide flow boiling, the results on water, helium, nitrogen and some refrigerants were used for comparison; at rather high reduced pressures the computed and the measured values of HTCs are in a good agreement. The data include results obtained in the channels of a diameter from 0.6mm up to 18mm. It is clear that at high reduced pressures there is no strong variation in boiling heat transfer with channel size decrease, it means that a classification on channel size has no sense if it does not consider liquid/vapour densities ratio.

Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Leyuan Yu ◽  
Aritra Sur ◽  
Dong Liu
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Instabilities ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer

Single-phase convective heat transfer of nanofluids has been studied extensively, and different degrees of enhancement were observed over the base fluids, whereas there is still debate on the improvement in overall thermal performance when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3–water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the changes in available nucleation sites and surface wettability as well as thinning of thermal boundary layers in nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in two-phase flow of nanofluids, but with reduced amplitude in pressure, temperature, and mass flux oscillations.

Proposed Correlation for Forced Convection Boiling Heat Transfer in Mini and Micro Channels With CO2 as a Fluid

2014 ◽  
Author(s):  
Mayank I. Vyas ◽  
Salim A. Channiwala ◽  
Mitesh N. Prajapati
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer ◽  
Micro Channels

After reviewing the available literature on flow boiling heat transfer in mini/micro tubes and channels, it is felt that there is need for predictive correlations which is applicable over wide range of parameters. In present work a new correlation for two-phase flow boiling heat transfer coefficient is developed, which has considered nucleate boiling and convective boiling heat transfer effect. To develop this correlation we have considered total 651 data points, which have been collected from the open available literature covering different operational conditions and different dimensions of channels. We have selected CO2 as a working fluid because it does not contain chlorine, hence an efficient and environmentally safe refrigerant and would be potential replacement for R-22. CO2 has unusual heat transfer and two-phase flow characteristics, and is very different from those of conventional refrigerant. Also a comparison of present correlation with the best published correlation for CO2 is done. The results of this comparison indicate that the new developed correlation is superior to published best correlation for CO2. Present correlation is also compared with best published correlation for all fluids and with the correlation developed by using CO2 data. The results of these both case, indicate that the present correlation is superior.

Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

2013 ◽  
Author(s):  
Leyuan Yu ◽  
Dong Liu
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Instabilities ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer

Recent studies of single-phase convective heat transfer of nanofluids reveal that, unlike the promising hypohesis in the early works, there is no significant improvement in the overall thermal performance of nanofluids over that of the base fluids when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3-water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the change of surface wettability and the thinning of thermal boundary layer in the nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in nanofluid two-phase flow, however, the oscillation amplitudes of the pressure, temperature and mass flux measurements are reduced.

scholarly journals The effect of reduced pressure on carbon dioxide flow boiling heat transfer in minichannels

2018 ◽  
Vol 70 ◽  
pp. 02012
Author(s):  
Dariusz Mikielewicz ◽  
Blanka Jakubowska
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Carbon Dioxide ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Reduced Pressure ◽  
Flow Boiling Heat Transfer

In the paper presented are the results of the study on the effect of reduced pressure on flow boiling heat transfer data in minichannels as well as conventional ones. That effect renders that most of heat transfer correlations fail to return appropriate results of predictions. Mostly they have been developed for the reduced pressures from the range 0.1-0.3. The special correction has been postulated to the in-house model of flow boiling and condensation which modifies the two-phase flow multiplier as well as the temperature gradient in pool boiling. Four two-phase flow multiplier models were tested for this purpose, i.e. due to Friedel, Tran, Müller-Steinhagen and Heck and finally its in-house modification for applicability to minichannels. The model has been tested against a large selection of experimental data collected from various researchers to investigate the sensitivity of the in-house developed model. The collected experimental data came from various studies from literature and were conducted for the full range of quality variation and a wide range of mass velocity and saturation temperatures. In the work are presented the results of calculations obtained using the in-house developed semi empirical model on selected experimental flow boiling data related to carbon dioxide.

21821 Study on Flow Boiling Heat Transfer and Two-Phase Flow in Flat Mini-Channel

2007 ◽  
Vol 2007.13 (0) ◽  
pp. 97-98
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Tomonari Yamada ◽  
Naoki Uchida
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer

Modifications and Extensions to the Annular Flow Model

2006 ◽  
Author(s):  
Priyadarshan U. Patankar ◽  
Bhalchandra P. Puranik
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Model ◽  
Heat Sinks ◽  
Phase Flow ◽  
Uniform Heating ◽  
Two Phase

Boiling heat transfer to fluid flow in microchannel heat sinks is being looked upon as a promising solution to the problem of cooling microprocessors with large power densities. In the present work, an annular flow model [1] is implemented to investigate the boiling heat transfer and two-phase flow characteristics in microchannel heat sinks. A modification in the model for the deposition mass transfer coefficient is proposed to better compare the existing experimental data [2]. The deposition mass transfer coefficient affects the distribution of liquid in the form of entrained droplets and the liquid film. The liquid film thickness is the most significant parameter in the determination of the heat transfer coefficient. The suggested change ensures consistent results for the behavior of the entrained fraction. We further report pressure drop results obtained using the modified annular flow model and a comparison with existing experimental data. Finally, we present results predicted by the annular flow model for non-uniform heating of a microchannel, in an effort to simulate hot spots on a microprocessor chip. A few preliminary results obtained from the modified model to simulate boiling and two-phase flow in a parallel microchannel device with non-uniform heating are presented.

Two-Phase Flow Phenomena for Boiling in Two Parallel Microchannels

2004 ◽  
Author(s):  
H. Y. Li ◽  
P. C. Lee ◽  
F. G. Tseng ◽  
Chin Pan
Keyword(s):  
Heat Transfer ◽  
Slug Flow ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Nucleate Boiling ◽  
Vapor Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Silicon Bulk ◽  
Flow Phenomena

Boiling heat transfer and corresponding two-phase flow phenomena are of significant interest for the design of a compact evaporator. The present work investigates experimentally, using a high-speed digital CCD camera, the two-phase flow phenomena for boiling in a silicon-based, two parallel trapezoid microchannels, which were prepared by the combination of silicon bulk micro machining and Pyrex-silicon wafer bonding. Onset of nucleate boiling, bubbly flow, slug flow, and partial dry out slug flow are typically observed along the flow direction. The appearance of the partial dryout slug flow may degrade the nucleate boiling heat transfer in the microchannel. At a low flow rate, reversed vapor flow is observed. In such a flow pattern, liquid droplets are formed intermittently on the inner wall of top Pyrex glass due to vapor condensation. Moreover, the reversed vapor flow usually accompanies with large magnitude two-phase flow oscillations.

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