Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Experimental Heat Transfer, pressure drop, and Flow Visualization of R-134a in Vertical Mini/Micro Tubes
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

For the application of minichannel heat exchangers, it is necessary to have accurate design tools for predicting heat transfer and pressure drop. Until recently, this type of heat exchangers was not well studied, and in the scientific literature there were large discrepancies between results reported by different investigators. The present thesis aims to add to the knowledge of the fundamentals of single- and two-phase flow heat transfer and pressure drop in narrow channels, thereby aiding in the development of this new, interesting technology with the possibility of decreasing the size of electronics through better cooling, and of increasing the energy efficiency of thermal processes and thermodynamic cycles through enhanced heat transfer.

A comprehensive experimental single-phase flow and saturated flow boiling heat transfer and pressure drop study has been carried out on vertical stainless steel tubes with inner diameters of 1.700, 1.224 and 0.826 mm, using R-134a as the test fluid. The heat transfer and pressure drop results were compared both to conventional correlations developed for larger diameter channels and to correlations developed specifically for microscale geometries.

Contrary to many previous investigations, this study has shown that the test data agree well with single-phase heat transfer and friction factor correlations known to be accurate for larger channels, thus expanding their ranges to cover mini/microchannel geometries. The main part of the study concerns saturated flow boiling heat transfer and pressure drop. Tests with the same stainless steel tubes showed that the heat transfer is strongly dependent on heat flux, but only weakly dependent on mass flux and vapor fraction (up to the location of dryout). This behavior is usually taken to indicate a dominant influence of nucleate boiling, and indicates that the boiling mechanism is strongly related to that in nucleate boiling. The test data for boiling heat transfer was compared to several correlations from the literature, both for macro- and mini-channels. A new correlation for saturated flow boiling heat transfer of refrigerant R-134a correlation was obtained based on the present experimental data. This correlation predicts the presented data with a mean absolute deviation of 8%. The frictional pressure drop results were compared to both macro- and mini channel correlations available from the literature. The correlation suggested by Qu and Mudawar (2003) gave the best prediction to the frictional two-phase pressure drop within the studied ranges.

A unique visualization study of saturated flow boiling characteristics in a vertical 1.332 mm inner diameter quartz tube, coated with a transparent heater has also been conducted. The complete evaporation process in a heated circular mini-channel has been studied visually in detail using high speed CCD camera. The study revealed the developments of the flow patterns and the behavior from bubble nucleation to the dry out of the liquid film. The bubble departure frequency, diameter, growth rate, and velocity were determined by analyzing the images. Finally, a flow pattern map for boiling flow in microchannels has been developed based on the test data.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , viii, 103 p.
Series
Trita-REFR, ISSN 1102-0245 ; 2007:59
Keyword [en]
Minichannel, microchannel, heat transfer, pressure drop, single-phase, two-phase, flow boiling, flow visualization, dry out, bubble behavior, flow pattern.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4299ISBN: 978-91-7178-594-7 (print)OAI: oai:DiVA.org:kth-4299DiVA: diva2:11699
Public defence
2007-03-26, F3, Lindstedtsvägen 26, KTH, 10:00
Opponent
Supervisors
Note
QC 20100812Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2010-08-12Bibliographically approved
List of papers
1. Experimental investigation of single-phase convective heat transfer in circular microchannels
Open this publication in new window or tab >>Experimental investigation of single-phase convective heat transfer in circular microchannels
2004 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 28, no 2-3, 105-110 p.Article in journal (Refereed) Published
Abstract [en]

In this study, the heat transfer characteristics of single-phase forced convection of R134a through single circular micro-channels with 1.7, 1.2, and 0.8 mm. as inner diameters were investigated experimentally. The results were compared both to correlations for the heat transfer in macroscale channels and to correlations suggested for microscale geometries. The results show good agreement between the classical correlations and the experimentally measured data in the turbulent region. Contrary, none of the suggested correlations for microchannels, agreed with the test data. In the laminar regime, the heat transfer coefficients were almost identical for all three diameters.

Keyword
Convection; Microchannel; Single phase heat transfer; Channel flow; Laminar flow; Turbulence; Microscale geometries; Heat transfer; convection; experimental study; heat transfer; laminar flow; microchannel; single-phase flow; turbulence
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6863 (URN)10.1016/S0894-1777(03)00028-1 (DOI)000187974600005 ()2-s2.0-0348172185 (Scopus ID)
Note
QC 20100812. 4th International Conference on Compact Heat Exchangers and Enhancement Technology for the Process Industries. GRENOBLE, FRANCE. 2002Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2017-12-14Bibliographically approved
2. Experimental investigation of single-phase pressure drop in circular minichannel
Open this publication in new window or tab >>Experimental investigation of single-phase pressure drop in circular minichannel
(English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606Article in journal (Refereed) Submitted
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6864 (URN)
Note
QC 20100812Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2017-12-14Bibliographically approved
3. Evaporative heat transfer in vertical circular microchannels
Open this publication in new window or tab >>Evaporative heat transfer in vertical circular microchannels
2004 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 24, no 8-9, 1241-1253 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents new experimental results on saturated flow boiling in microchannels. Heat transfer coefficients were measured for saturated boiling of R134a in vertical circular tubes with internal diameters of 1.7, 1.224 and 0.826 mm, and a uniformly heated length of 220 mm. Heat transfer coefficients were obtained for a heat flux range of 3-34 kW/m(2), a mass flux range of 50-400 kg/m(2) s, and vapour qualities up to 0.6. Experiments were conducted at two different pressures, 8.626 and 6.458 bars. Heat transfer coefficients were found to be a strong function of the wall heat flux and system pressure, while being fairly independent upon mass flux and vapour quality. This suggests that the heat transfer mechanism is strongly related to that in nucleate boiling.

Keyword
Flow boiling; Heat transfer; Microchannel; Enthalpy; Evaporation; Evaporators; Heat flux; Heat pump systems; Heat transfer coefficients; Nucleate boiling; Specific heat; Thermal conductivity; Thermodynamics; Viscosity; Flow boiling; Microchannels; Heat transfer
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6865 (URN)10.1016/j.applthermaleng.2003.12.030 (DOI)000221204600011 ()2-s2.0-1842576519 (Scopus ID)
Note
QC 20100812Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2017-12-14Bibliographically approved
4. Two-phase flow pressure drop of R-134a in a vertical circular mini/micro channel
Open this publication in new window or tab >>Two-phase flow pressure drop of R-134a in a vertical circular mini/micro channel
2008 (English)In: Proceedings of the 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, 2008, 343-353 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents new experimental results on saturated flow boiling pressure drop in microchannels. The two-phase pressure drops were measured for vertical saturated boiling of R-134a in circular tubes with internal diameters of 1.700, 1.224, and 0.826 mm, and a uniformly heated length of 220 mm, the total flow length is 580 mm. The total pressure drops were obtained for a heat flux range of 10-30 kW/m(2), a mass flux range of 100-400 kg/(m(2)s), and outlet vapor qualities up to 0.6. Experiments were conducted at the average saturation pressure of 8.62 bar. The experimental data was compared to predictions by correlations available in the literature both for microchannels and larger diameter tubes.

Keyword
Circular tubes, Experimental data, Flow length, Heated lengths, Internal diameters, Mass flux, Mini/micro-channel, Saturated flow boiling, Saturation pressure, Total pressure drop, Two-phase pressure drops, Vapor quality, Heat flux, Microchannels, Multiphase flow, Pressure drop
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6866 (URN)10.1115/ICNMM2008-62243 (DOI)000262925200043 ()2-s2.0-77952633929 (Scopus ID)978-0-7918-4834-0 (ISBN)
Conference
The 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, Darmstadt, Germany, Jun 23-25, 2008
Note
QC 20100812. Uppdaterad från Submitted till Published 20100812.Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2011-09-08Bibliographically approved
5. Flow boiling visualization in a vertical circular minichannel at high vapor quality
Open this publication in new window or tab >>Flow boiling visualization in a vertical circular minichannel at high vapor quality
2006 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 30, no 8, 755-763 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on an experimental study of saturated flow boiling of R134a inside a circular vertical quartz tube coated with a transparent heater. The inner diameter of the tube was 1.33 mm and the heated length 235.5 mm. The flow pattern at high vapor qualities and the dryout of the liquid film were studied using a high speed CCD camera at the mass fluxes 47.4 and 124.4 kg/m(2) s in up flow at 6.425 bar. The heat fluxes ranged from 5 to 13.6 kW/m(2) for the lower mass flux and from 20 to 32.4 kW/m(2) for the higher mass flux.

The behavior of the flow close to dryout was found to be different at low and high mass flux. At low mass flux the location of the liquid front fluctuated with waves passing high up in the tube. In between the waves, a thin film was formed, slowly evaporating without breaking up.

At high mass flux the location of the liquid front was more stable. In this case the liquid film was seen to break up into liquid streams and dry zones on the tube wall.

Keyword
Dryout; Flow boiling; Minichannel; Visualization; Charge coupled devices; Evaporation; Flow visualization; Thin films; Vapors; Dryout; Flow boiling; Mass flux; Minichannels; Pipe flow; Charge coupled devices; Evaporation; Flow visualization; Pipe flow; Thin films; Vapors
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6867 (URN)10.1016/j.expthermflusci.2006.03.005 (DOI)000241181700006 ()2-s2.0-33746459316 (Scopus ID)
Note
QC 20100812. Konferens: International Conference on Heat Transfer and Fluid Flow in Microscale, Barga, Italy, Sep 25-30, 2005. ENEA, Inst Thermal Fluid Dynam.Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2017-12-14Bibliographically approved
6. A visualization study of bubble behavior in saturated flow boiling through a vertical mini-tube
Open this publication in new window or tab >>A visualization study of bubble behavior in saturated flow boiling through a vertical mini-tube
2007 (English)In: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 28, no 10, 852-860 p.Article in journal (Refereed) Published
Abstract [en]

Forced convection saturated R-134a boiling experiments were conducted in a vertical mini-quartz tube coated with a transparent heater; the inner diameter of the tube was 1.33 mm and the heated length 235.5 mm. The dynamics of the saturated boiling process, bubble characteristics, and behavior were studied using a high-speed CCD camera at different mass fluxes in up-flow at 6.425 bar. The heat fluxes were 5 and 20 kW/m(2). The flow visualization results show that the bubble departure frequency generally inc

Keyword
Boiling liquids; CCD cameras; Flow visualization; Forced convection; Growth rate; Heat flux; Flow boiling; Saturated boiling; Bubbles (in fluids)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6868 (URN)10.1080/01457630701378275 (DOI)000249762200007 ()2-s2.0-34547366618 (Scopus ID)
Note
QC 20100812. Uppdaterad från Accepted till Published 20100812.Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2017-12-14Bibliographically approved

Open Access in DiVA

fulltext(1841 kB)19540 downloads
File information
File name FULLTEXT01.pdfFile size 1841 kBChecksum MD5
62f084b52bd9b939fa0b1d6ae6706977e9be224099fd0b6ac5406ac6fc8bb99f397cf918
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Owhaib, Wahib
By organisation
Applied Thermodynamics and Refrigeration
Energy Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 19540 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2597 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf