Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • 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
Investigation of the heat transfer of enhanced additively manufactured minichannel heat exchangers
KTH, School of Industrial Engineering and Management (ITM).
2019 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Mini-/microchannel components have received attention over the past few decades owing to their compactness and superior thermal performance. Microchannel heat sinks are typically manufactured through traditional manufacturing practices (milling and sawing, electrodischarge machining, and water jet cutting) by changing their components to work in microscale environments or microfabrication techniques (etching and lost wax molding), which have emerged from the semiconductor industry. An extrusion process is used to produce multiport minichannel-based heat exchangers (HXs). However, geometric manufacturing limitations can be considered as drawbacks for all of these techniques. For example, a complex out-of-plane geometry is extremely difficult to fabricate, if not impossible. Such imposed design constraints can be eliminated using additive manufacturing (AM), generally known as three-dimensional (3D) printing. AM is a new and growing technique that has received attention in recent years. The inherent design freedom that it provides to the designer can result in sophisticated geometries that are impossible to produce by traditional technologies and all for the redesign and optimization of existing models.

The work presented in this thesis aims to investigate the thermal performance of enhanced minichannel HXs manufactured via metal 3D printing both numerically and experimentally. Rectangular winglet vortex generators (VGs) have been chosen as the thermal enhancement method embedded inside the flat tube. COMSOL Multiphysics, a commercial software package using a finite element method (FEM), has been used as a numerical tool. The influence of the geometric VG parameters on the heat transfer and flow friction characteristics was studied by solving a 3D conjugate heat transfer and laminar flow. The ranges of studied parameters utilized in simulation section were obtained from our previous interaction with various AM technologies including direct metal laser sintering (DMLS) and electron-beam melting (EBM).

For the simulation setup, distilled water was chosen as the working fluid with temperaturedependent thermal properties. The minichannel HX was assumed to be made of AlSi10Mg with a hydraulic diameter of 2.86 mm. The minichannel was heated by a constant heat flux of 5 Wcm−2 , and the Reynolds number was varied from 230 to 950. A sensitivity analysis showed that the angle of attack, VG height, VG length, and longitudinal pitch have notable effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and the distance from the sidewalls do not have a significant influence on the HX performance over the studied range. On the basis of the simulation results, four different prototypes including a smooth channel as a reference were manufactured with AlSi10Mg via DMLS technology owing to the better surface roughness and greater design uniformity. A test rig was developed to test the prototypes. Owing to the experimental facility and working fluid (distilled water), the experiment was categorized as either a simultaneously developing flow or a hydrodynamically developed but thermally developing flow. The Reynolds number ranged from 175 to 1370, and the HX was tested with two different heat fluxes of 1.5 kWm−2 and 3 kWm−2 .

The experimental results for the smooth channel were compared to widely accepted correlations in the literature. It was found that 79% of the experimental data were within a range of ±10% of the values from existing correlations developed for the thermal entry length. However, a formula developed for the simultaneously developing flow overpredicted the Nusselt number. Furthermore, the results for the enhanced channels showed that embedding VGs can considerably boost the thermal performance up to three times within the parameters of the printed parts. Finally, the thermal performance of the 3D-printed channel showed that AM is a promising solution for the development of minichannel HXs. The generation of 3D vortices caused by the presence of VGs ii can notably boost the thermal performance, thereby reducing the HX size for a given heat duty.

Place, publisher, year, edition, pages
2019. , p. 85
Series
TRITA-ITM-EX ; 2019:413
Keywords [en]
Minichannel; Microchannel; Heat exchanger; Additive manufacturing; 3D printing; Numerical simulation; CFD; Comsol
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-264278OAI: oai:DiVA.org:kth-264278DiVA, id: diva2:1372868
External cooperation
KTH
Supervisors
Examiners
Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2019-11-25Bibliographically approved

Open Access in DiVA

fulltext(16774 kB)32 downloads
File information
File name FULLTEXT01.pdfFile size 16774 kBChecksum SHA-512
aa27d41f90ac40637210b6dd70b19c63e6dc288394e350192dfd78580a0cbaa6343269821f88136aa53e27d6f40d8bb871cfc8f6859bfc2d90aad0b47547ad10
Type fulltextMimetype application/pdf

By organisation
School of Industrial Engineering and Management (ITM)
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 32 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

urn-nbn

Altmetric score

urn-nbn
Total: 139 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • 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