THE EFFECT OF COOLING ON MECHANICAL AND THERMAL STRESSES IN VASCULAR STRUCTURES

Abstract

Here, we show how the vascular channel configuration and its shape affect the mechanical strength which is simultaneously subjected to heating and mechanical load. The material properties were defined as functions of temperature. The effect of channel cross-section on the coolant mass flow rate, peak temperature and peak stresses are documented. The results show that the resistances to flow of stresses and fluid is minimum with the circular channels while the resistance to the heat flow is the smallest with semi-circular channels. In addition, morphing the vascular design provides almost the smallest resistance to the heat flow with circular channels (0.3% difference in the peak temperature). This shows that even the convective resistances are the smallest with circular-cross section, overall thermal resistance is smaller in semi-circular design for the fixed fluid volume. The peak stress is smaller with hybrid design than the parallel designs for the entire pressure drop range. In addition, the effects of mechanical load, heating rate and reference temperature on the stress distribution are also documented. Furthermore, the thermal and mechanical stresses are also documented separately, and then compared with the coupled solution cases. The chief result of this paper is that for a coupled system minimizing only one of the resistance terms is not sufficient, all the resistances considered simultaneously in order to uncover the best performing design. In coupled solutions, we documented the simulation results with temperature dependent material properties and the resistances to the heat and fluid flow is affected by the mechanical deformations. In addition, the results show that the designs should be free to vary, the unexpected designs can be the best performing designs for the given parameters and constraints. Therefore, the design parameters based on the experience does not always yield the best performing designs as the objectives and constraints vary.

Keywords

• Vascular,Cooling,Thermal Expansion,Smart Features

References

1. [1] Çetkin, E. (2015). Inverted fins for cooling of a non-uniformly heated domain. Journal of Thermal Engineering, 1(1), 1-9.
2. [2] Cetkin, E., & Oliani, A. (2015). The natural emergence of asymmetric tree-shaped pathways for cooling of a non-uniformly heated domain. Journal of Applied Physics, 118(2), 024902.
3. [3] Sakanova, A., Keian, C. C., & Zhao, J. (2015). Performance improvements of microchannel heat sink using wavy channel and nanofluids. International Journal of Heat and Mass Transfer, 89, 59–74.
4. [4] Minea, A. A. (2015). Numerical studies on heat transfer enhancement and synergy analysis on few metal oxide water based nanofluids. International Journal of Heat and Mass Transfer, 89, 1207–1215.
5. [5] Shafahi, M., Bianco, V., Vafai, K., & Manca, O. (2010). Thermal performance of flat-shaped heat pipes using nanofluids. International Journal of Heat and Mass Transfer, 53(7–8), 1438–1445.
6. [6] Li, Y., Xie, H., Yu, W., & Li, J. (2015). Liquid Cooling of Tractive Lithium Ion Batteries Pack with Nanofluids Coolant. Journal of Nanoscience and Nanotechnology, 15(4), 3206–3211.
7. [7] Alshaer, W. G., Nada, S. A., Rady, M. A., Del Barrio, E. P., & Sommier, A. (2015). Thermal management of electronic devices using carbon foam and PCM/nano-composite. International Journal of Thermal Sciences, 89, 79-86.
8. [8] Li, T., Lee, J.-H., Wang, R., & Kang, Y. T. (2014). Heat transfer characteristics of phase change nanocomposite materials for thermal energy storage application. International Journal of Heat and Mass Transfer, 75, 1–11.

9. [9] Ma, T., Yang, H., Zhang, Y., Lu, L., & Wang, X. (2015). Using phase change materials in photovoltaic systems for thermal regulation and electrical efficiency improvement: a review and outlook. Renewable and Sustainable Energy Reviews, 43, 1273-1284.
10. [10] Cetkin, E., Lorente, S., & Bejan, A. (2012). Vascularization for cooling a plate heated by a randomly moving source. Journal of Applied Physics, 112(8), 084906.
11. [11] Cetkin, E., Lorente, S., & Bejan, A. (2011). Vascularization for cooling and mechanical strength. International Journal of Heat and Mass Transfer, 54(13–14), 2774–2781.
12. [12] Wang, K. M., Lorente, S., & Bejan, A. (2009). The transient response of vascular composites cooled with grids and radial channels. International Journal of Heat and Mass Transfer, 52(19–20), 4175–4183.
13. [13] Rocha, L. A. O., Lorente, S., & Bejan, A. (2009). Tree-shaped vascular wall designs for localized intense cooling. International Journal of Heat and Mass Transfer, 52(19–20), 4535–4544.
14. [14] Cetkin, E., Lorente, S., & Bejan, A. (2011). Hybrid grid and tree structures for cooling and mechanical strength. Journal of Applied Physics, 110(6), 064910.
15. [15] Yenigun, O., & Cetkin, E. (2016). Experimental and numerical investigation of constructal vascular channels for self-cooling: Parallel channels, tree-shaped and hybrid designs. International Journal of Heat and Mass Transfer, 103, 1155–1165.
16. [16] Cho, K. H., Lee, J., Ahn, H. S., Bejan, A., & Kim, M. H. (2010). Fluid flow and heat transfer in vascularized cooling plates. International Journal of Heat and Mass Transfer, 53(19–20), 3607–3614.
17. [17] Cho, K. H., Chang, W. P., & Kim, M. H. (2011). A numerical and experimental study to evaluate performance of vascularized cooling plates. International Journal of Heat and Fluid Flow, 32(6), 1186–1198.
18. [18] White, S. R., Sottos, N. R., Geubelle, P. H., Moore, J. S., Kessler, M., Sriram, S. R., ... & Viswanathan, S. (2001). Autonomic healing of polymer composites. Nature, 409(6822), 794-797.
19. [19] Hamilton, A. R., Sottos, N. R., & White, S. R. (2010). Self-healing of internal damage in synthetic vascular materials. Advanced Materials, 22(45), 5159–5163.
20. [20] Bejan, A., Lorente, S., & Wang, K. M. (2006). Networks of channels for self-healing composite materials. Journal of Applied Physics, 100(3), 033528.
21. [21] Wang, K. M., Lorente, S., & Bejan, A. (2010). Vascular structures for volumetric cooling and mechanical strength. Journal of Applied Physics, 107(4), 044901.
22. [22] Çetkin, E. (2015). Constructal structures for self-cooling: microvascular wavy and straight channels. Journal of Thermal Engineering, 1(5), 166-174.
23. [23] Rocha, L. A. O., Lorente, S., & Bejan, A. (2014). Vascular design for reducing hot spots and stresses. Journal of Applied Physics, 115(17), 174904.
24. [24] Cetkin, E., Lorente, S., & Bejan, A. (2015). Vascularization for cooling and reduced thermal stresses. International Journal of Heat and Mass Transfer, 80, 858–864.
25. [25] Multiphysics, C. O. M. S. O. L. (2005). Comsol, Inc. Burlington, MA.