Determination of the diameter ratios for minimum entropy generation in a borehole geothermal heat exchangers using numerical simulation of the flow and heat transfer

Authors

Semnan universiyy

Abstract

In this paper, diameter ratio of a geothermal borehole heat exchanger is determined in a manner that the entropy generation is minimized. The SST k-ω model is used to model the turbulent flow. Pressure loss calculation for different diameter ratios of the heat exchanger shows that for diameter ratio of 0.7, the total pressure loss is minimum. Results of the bulk flow temperature showes that the outlet temperature increases at higher heat resistance of the internal wall. The total entropy generation for different diameter ratios at different heat resistance of internal wall are also presented. Results show that when the heat resistance of internal wall increases, the minimum entropy generation occurs at higher diameter ratios. On the other hand, reduction in heat transfer coefficient of the outer wall and increment in heat transfer coefficient of internal wall are not favorable. Increment in heat resistance of the internal wall at higher diameter ratios of the heat exchanger, reduces both of these unfavorable effects.

Keywords

Main Subjects

References

[1] Barbier E (2002) Geothermal energy technology and current status: an overview. Renew Sust Energ Rev 6(1-2): 3-65.
[2] Kagel A, Bates D, Gawell K (2007) A guide to geothermal energy and the environment. Geothermal Energy Association, Washington.
[3] Egg J, Howard B (2011) Geothermal HVAC Green Heating and Cooling. 1st edn. McGraw-Hill, New York.
[4] Boyle G (2004) Renewable Energy: Power for a Sustainable Future. 2nd edn. Oxford University Press.
[5] Dipippo R (2008) Geothermal power plants: principles, applications, case studies and environmental impact. 3rd edn.  Butterworth-Heinemann (an imprint of Elsevier), Waltham.
[6] Nalla G, Shook G, Mines L, Bloomeld K (2004) Parametric sensitivity study of operating and design variables in wellbore heat exchanger. Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA.
[7] Al-Khoury R, Bonnier PG, Brinkgreve BJ (2005) Efficient finite element formulation for geothermal heating systems. Part I: steady state. Int J Numer Meth Eng 63 (7): 988-1013.
[8] Al-Khoury R, Bonnier PG, Brinkgreve BJ (2005) Efficient finite element for- mulation for geothermal heating systems. Part II: transient. Int J Numer Meth Eng, 67(5): 725-74.
[9] Feng Y (2012) Numerical study of downhole heat exchanger concept geothermal energy extraction. Ph.D. Thesis, Louisiana state university.
[10] Parisch P, Mercker O, Oberdorfer P, Bertram E, Tepe R, Rockendorf G (2015) Short-term experiments with borehole heat exchangers and model validation in TRNSYS. Renew Energ 74: 471-477.
[11] Funabiki A, Oguma M, Yabuki T, Kakizaki T (2014) The effects of groundwater flow on vertical-borehole ground source heat pump systems. ASME 12th Biennial Conference on Engineering Systems Design and Analysis, June 25-27, Copenhagen, Denmark.
[12] Beier RA, Acuna J, Mogensen P, Palm B (2013) Borehole resistance and vertical temperature profiles in coaxial borehole heat exchangers. Applied Energy 102: 665-675.
[13] Sliwa T, Gonet A (2004) Theoretical model of borehole heat exchanger.  J  Energy Resour  Technol 127(2): 142-148.
[14] Mastrulla R, Mauro AW, Menna L, Vanoli GP (2014) A model for a borehole heat exchanger working with CO2. Energ Proc 45: 635-644.
[15]Masalias MD (2011) Thermodynamic optimization of downhole coaxial heat exchanger for geothermal applications. M.Sc. thesis, Warsaw University of Technology, Faculty of Power and Aeronautical Engineering, Warsaw.
[16] Gnielinski V (2009) Heat Transfer coefficients for turbulent flow in  concentric annular ducts.  Heat Transfer Eng 30(6): 431-436.
[17] Menter FR (1994) Two-equation eddy-viscosity turbulence models for engineering applications. AIAA J 32(8): 1598-1605.
[18] Van Doormal JP, Raithby GD (1984) Enhancements of the SIMPLE method for predicting incompressible fluid flows. Numer Heat Transfer 7(2): 147-163.
[19] White FM (2011) Fluid mechanics. 7th edn. McGraw-Hill, New York.
[20] Bejan A, Kraus AD (2003) Heat transfer Handbook. John Wiley & Sons, New York.
[21] Bejan A, Tsatsaronis G, Moran M (1996) Thermal design & optimization. John Wiley & Sons, New York.
[22] Bergman TL, Levine AS, Incropera FP, Dewitt DP (2011) Fundamentals of heat and mass  transfer. 7th edn. John Wiley & Sons, New York.
[23] Van Wylen GJ, Sonntag RE (1985) Fundamentals of Classical Thermodynamics. 3rd edn. John Wiley & Sons, New York.
Journal of Solid and Fluid Mechanics
Volume 6, Issue 1
March and April 2016
Pages 249-258

Files

Share

How to cite

Statistics