# Analysis of single phase fluid flow and heat transfer at micro-scale

## (Ongoing Project)

### Groups:

### People:

- Barbaros Çetin
- Kevin D. Cole (Uni. Nebraska -- Lincoln)
- Reza Rasooli

### Project Duration:

Start Date: January 1st, 2010### Summary:

With the today’s fabrication facility, fabrications of channels with a size in the order of micrometers are not an issue (even the fabrication of microtubes with the diameters of several micro-meters/nanometers have become possible). These kinds of small channels can easily be the elements of microheat exchangers, microheat sinks, microsensors, and micropower generation systems. For an effective and economical design of microfluidic systems, fluid flow and heat transfer characteristics of flow at micro-scale need to be well understood. As fluid flow and heat transfer takes place at the micro-scale, many additional effects such as rarefaction, electro-viscous effects, viscous dissipation, and axial conduction need to be considered which can be neglected at the macro-scale. Rarefaction is important for small dimensions compared to the mean-free-path of the fluid (less than 5 um at atmospheric conditions), and is common for gas flows in microchannels. Electro-viscous effects are due to the interaction of the ions in the fluid with the electrical double layer (EDL) near the non-conducting channel wall, and is significant for liquid flow in microchannels with dimensions less than 5 lm for deionized water. Viscous dissipation is the heating of the fluid due to the work done against the viscous forces. The effect of viscous dissipation can be important for flows with Rey- nolds number (Re) greater than 100 for microchannels. Moreover, the characteristic time for convection and conduction become comparable at the micro- scale, and the convection term no longer dominates the conduction term in the longitudinal direction. This is defined by flow for which the Peclet number (Pe) is not too large. Under this condition axial conduction in the fluid cannot be neglected as in the case of mac- rochannel flow. The effect of the axial conduction in the fluid becomes more pronounced as Pe decreases. In conventional applications involving channels, the channel-wall thickness is very small compared to the hydraulic diameter of the channel; hence the heat transferred by conduction in the wall can be neglected compared to the convective heat transfer in many macroscale flows. However, in microchannels the thickness of the channel wall is usually equal in size or larger than the hydraulic diameter of the channel. Therefore the heat trans- ferred in the wall by conduction cannot be neglected for the case of convective liquid flow in a microchannel, and the heat transfer mechanism becomes conjugate. Therefore, the investigation of role of these parameters on fluid flow and heat transfer is important for a better fundamental understanding, and useful in the analysis and design of micro-scale heat transfer devices.### Related Publications:

- Cole, K.D., Çetin, B. (2017). "Modeling of Joule heating and convective cooling in a thick-walled micro-tube",
*Int. J. Thermal Sciences*(In press) - Barışık, M., Yazıcıoğlu, A.G., Çetin, B., Kakaç, S. (2015). "Analytical solution of thermally developing microtube heat transfer including axial conduction",
*Int. Comm. Heat and Mass Transfer*, v.67 p.81-88

Full Text | DOI: http://dx.doi.org/10.1016/j.icheatmasstransfer.201 - Çetin, B., Zeinali, S. (2014). "Analysis of heat transfer for a low Peclet number microtube flow using second-order slip model: An extended-Graetz problem",
*J. Engineering Mathematics*, v.89(1) p.13-25

Full Text | DOI: 10.1007/s10665-014-9704-7 - Cole, K., Çetin, B., Brettmann, L. (2014). "Microchannel heat transfer with slip flow and wall effects",
*AIAA J. Thermophysics and Heat Transfer*, v.28(3) p.455-462

Full Text | DOI: 10.2514/1.T4267 - Çetin, B. (2013). "Effect of thermal creep on heat transfer for a 2D microchannel flow: An analytical approach",
*ASME J. Heat Transfer, Special Issue on Microchannel Heat Transfer*, v.135(10) p.101007

Full Text | DOI: 10.1115/1.4024504 - Çetin, B., Cole, K. (2011). "The effect of axial conduction on heat transfer in a liquid microchannel flow",
*Int. J. Heat and Mass Transfer*, v.54 p. 2542-2549

DOI: 10.1016/j.ijheatmasstransfer.2011.02.007 - Çetin, B., Cole, K. (2015). "Modeling of conjugate heat transfer in an electrically heated microtube",
*8th International Conference on Computational Heat and Mass Transfer*(140), May 25-28, Istanbul, Turkey

Full Text - Çetin, B. (2012). "Evaluation of Nusselt number for a ﬂow in a microtube with second-order model including thermal creep",
*10th Int. Conf. Nano/Micro/Mini-channels (ICNMM’2012)*(73321) p.251-256, July 8–12, Puerto Rico, USA

DOI: 10.1115/ICNMM2012-73321