0
Research Papers

A Transient Immersed Coil Heat Exchanger Model

[+] Author and Article Information
William R. Logie

e-mail: william.logie@solarenergy.ch

Elimar Frank

Institut für Solartechnik SPF,
HSR Hochschule für Technik Rapperswil,
Oberseestrasse 10, 8640, Rapperswil, Switzerland

A side effect of this higher temperature is a drop in the collector efficiency.

All reference to low flow refers to the flow conditions of the collector and not the immersed heat exchanger.

While all Pt 100Ω sensors were regularly calibrated, the error implied here is that of resolution, seeing as a maximum of 12 sensors were used to collect local wall temperature information.

Neumann boundary conditions with surface heat flux set to zero.

In the TRNSYS environment it is typical to evaluate an average power over the time step, in which case the average is used for both the old and new power densities.

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received September 12, 2012; final manuscript received February 14, 2013; published online June 25, 2013. Assoc. Editor: Werner Platzer.

J. Sol. Energy Eng 135(4), 041006 (Jun 25, 2013) (7 pages) Paper No: SOL-12-1225; doi: 10.1115/1.4023928 History: Received September 12, 2012; Revised February 14, 2013

The aim of this paper is to present a transient one-dimensional (1D) radial immersed coil heat exchanger model that accounts for the effect that geometry and operating conditions have on heat transfer performance. Insights gained through its use in both an analysis of experimental data and an implementation in the simulation environment TRNSYS are shown and discussed. While variation in the external convection coefficient of immersed coil heat exchangers has little effect on the annual solar fraction of a generic solar domestic hot water system, variation in collector side flow can influence the solar fraction as great as ±5%, in particular low collector side flow improves stratification inside the store.

FIGURES IN THIS ARTICLE
<>
Copyright © 2013 by ASME
Your Session has timed out. Please sign back in to continue.

References

Farrington, R. B., and Bingham, C. E., 1986, “Testing and Analysis of Immersed Heat Exchangers,” Tech. Rep. 254-2866, Solar Energy Research Institute, National Renewable Energy Laboratory, Golden, CO.
Mote, R., and Probert, S. D., 1991, “The Performance of a Coiled Finned-Tube Heat Exchanger Submerged in a Hot Water Store: The Effect of the Exchangers Orientation,” Appl. Energy, 38, pp. 1–19. [CrossRef]
Ali, M. E., 1994, “Experimental Investigation of Natural Convection From Vertical Helical Coiled Tubes,” Int. J. Heat Mass Transfer, 37(4), pp. 665–671. [CrossRef]
Xin, R. C., and Ebadian, M. A., 1996, “Natural Convection Heat Transfer From Helicoidal Pipes,” J. Thermophys. Heat Transfer, 10(2), pp. 297–302. [CrossRef]
Prabhanjan, D. G., Rennie, T. J., and Vijaya Raghavan, G. S., 2003, “Natural Convection Heat Transfer From Helical Coiled Tubes,” Int. J. Thermal Sciences, 43, pp. 359–365. [CrossRef]
Reindl, D. T., Beckman, W. A., and Mitchell, J. W., 1992, “Transient Natural Convection in Enclosures With Application to Solar Thermal Storages Tanks,” ASME J. Solar Energy Eng., 114, pp. 175–181. [CrossRef]
Su, Y., 2006, “Numerical Study of Natural Convection of Heat Exchangers Immersed in a Thermal Storage Vessel,” Ph.D. thesis, University of Minnesota, Minneapolis, MN.
Boetcher, S. K. S., Kulacki, F. A., and Davidson, J. H., 2010, “Negatively Buoyant Plume Flow in a Baffled Heat Exchanger,” ASME J. Solar Energy Eng., 132(3), p. 034502. [CrossRef]
Shah, L. J., and Furbo, S., 1998, “Correlation of Experimental and Theoretical Heat Transfer Mantle Tanks Used in Low Flow SDHW Systems,” Solar Energy, 64(4–6), pp. 245–256. [CrossRef]
Drück, H., 2007, “Mathematische Modellierung und Experimentelle Prüfung von Warmwasserspeichern für Solaranlagen,” Ph.D. thesis, Universtität Stuttgart, Institut für Thermodynamik und Wärmetechnik, Stuttgart, Germany.
Davidson, J. H., Mantell, S. C., and Francis, L. F., 2007, “Thermal and Material Characterization of Immersed Heat Exchangers for Solar Domestic Hot Water,” Advances in Solar Energy, Vol. 17, D. Y. Goswami, ed., Routledge, London, pp. 99–129.
Hahne, E., Kübler, R., and Kallweit, J., 1989, “The Evaluation of Thermal Stratification by Exergy,” Energy Storage Systems, Kluwer Academic. New York, pp. 465–485.
Messerschmid, H., 2002, “Entwicklung und Validation Eines Numerischen Verfahrens zur Beurteilung von Trinkwasserspeichern,” Ph.D. thesis, Universtität Stuttgart, Lehrstuhl für Heiz- und Raumlufttechnik, Stuttgart, Germany.
van Koppen, C. W. J., Thomas, J. P. S., and Veltkamp, W. B., 1979, “The Actual Benefits of Thermally-Stratified Storage in a Small and Medium Size Solar System,” Proceedings of ISES Solar World Congress, Atlanta, GA, May 28–June 1, pp. 579–580.
Scheuren, J., Pujiula, F., and Eisenmann, W., 2004, “Comparative Measurements of Two Identical Thermal Solar Systems With High-Flow and Low-Flow Rates,” Proceedings of ISES EuroSun, Freiburg, Germany, June 20–24.
Davidson, J. H., Adams, D. A., and Miller, J. A., 1994, “A Coefficient to Characterize Mixing in Solar Water Storage Tanks,” ASME J. Solar Energy Eng., 116, pp. 94–99. [CrossRef]
Rosengarten, G., Morrison, G., and Behnia, M., 1999, “A Second Law Approach to Characterising Thermally Stratified Hot Water Storage With Application to Solar Hot Water,” ASME J. Solar Energy Eng., 121, pp. 194–200. [CrossRef]
Rosen, M. A., 2001, “The Exergy of Stratified Thermal Energy Storages,” Solar Energy, 71(3), pp. 173–185. [CrossRef]
Huhn, R., 2007, “Beitrag zur Thermodynamischen Analyse und Berwertung von Wasserwärmespeichern in Energieumwandlungsketten,” Ph.D. thesis, Technischen Universität Dresden, Deresden, Germany.
Hampel, M., 2008, “Rechnergestützte Entwicklung von Warmwasser Wärmespeichern für Solaranlagen,” Ph.D. thesis, Universität Stuttgart, Stuttgart, Germany.
Haller, M. Y., Yazdanshenas, E., Andersen, E., Bales, C., Streicher, W., and Furbo, S., 2010, “A Method to Determine Stratification Efficiency of Thermal Energy Storage Processes Independently From Storage Heat Losses,” Solar Energy, 84, pp. 997–1007. [CrossRef]
van Berkel, J., Veltkamp, W. B., and Shaap, A. B., 1991, “Thermal Behaviour of a Heat Exchanger Coil in a Stratified Storage,” Proceedings of ISES Solar World Congress, Denver, CO, August 19–23.
van Berkel, J., Veltkamp, W. B., and Shaap, A. B., 1993, “Heat Transfer Phenomena in a Stratified Storage With Integrated Heat Exchanger Coils,” Proceedings of ISES Solar World Congress, Budapest, August 23–27.
Eichhorn, R., Lienhard, J. H., and Chen, C. C., 1974, “Natural Convection From Isothermal Spheres and Cylinders Immersed in a Stratified Fluid,” 5th International Heat Transfer Conference, Tokyo, September 3–7, Vol. 3, pp. 10–14.
Drück, H., 2006, MULTIPORT Store—Model for TRNSYS, 1.99f ed., Institut für Thermodynamik und Wärmetechnik, Universität Stuttgart, Pfaffenwaldring 6, 70550 Stuttgart, Germany.
Drück, H., Bachmann, S., and Müller-Steinhagen, H., 2006, “Testing of Solar Hot Water Stores by Means of Up- and Down-Scaling Algorithms,” Proceedings of ISES EuroSun, Glasgow, UK, June 27–30.
Haberl, R., Frank, E., and Vogelsanger, P., 2009, “Holistic System Testing—10 Years of Concise Cycle Testing,” Proceedings of ISES Solar World Congress, Johannesburg, South Africa, October 11–14.
Klein, S., Newton, B. J., Thornton, J. W., Bradley, D. E., Mitchell, J. W., and Kummert, M., 2006, TRNSYS Reference Manual: Mathematical Reference, 16.1 ed., Solar Energy Laboratory, University of Wisconsin-Madison, Madison, WI.
Logie, W., and Frank, E., 2011, “Experimental and Numerical Investigations on Thermal Energy Storages—Indirect Charging Via Immersed Coil Heat Exchangers,” Tech. Rep. BFE/102958, Institut für Solartechnik SPF, Rapperswil, Switzerland.
Duffie, J. A., and Beckman, W. A., 2006, Solar Engineering of Thermal Processes, 3rd ed. John Wiley and Sons, New York.
Cadafalch, J., 2009, “A Detailed Numerical Model for Flat Plate Solar Thermal Devices,” Solar Energy, 83, pp. 2157–2164. [CrossRef]
Carbonell, D., Cadafalch, J., and Consul, R., 2011, “A Transient Model for Radiant Heating and Cooling Terminal Heat Exchangers Applied to Radiant Floors and Ceiling Panels,” Proceedings of ISES Solar World Congress, Kassel, Germany, August 28–September 2.
Gnielinski, Y., 1986, “Heat Transfer and Pressure Drop in Helically Coiled Tubes,” Proceedings of the 8th International Heat Transfer Conference, San Francisco, CA, August 17–22, pp. 2847–2854.
Morgan, V. T., 1975, “The Overall Convective Heat Transfer From Smooth Circular Cylinders,” Adv Heat Transfer, 11, pp. 199–264. [CrossRef]
Churchill, S. W., and Chu, H. H. S., 1975, “Correlating Equations for Laminar and Turbulent Free Convection From a Horizontal Cylinder,” Int. J. Heat Mass Transfer, 18, pp. 1049–1053. [CrossRef]
Henderson, J. B., and Caolo, A. C., 1983, “Optimization of Radial Finned Tube Heat Exchangers for Use in Solar Thermal Storage Systems,” Tech. Rep. DOE/R1/25247-T1, Dept. of Mechanical Engineering and Applied Mechanics, Rhode Island University, Kingston, RI.
Heimrath, R., and Haller, M. Y., 2007, “The Reference Heating System, the Template Solar System,” Tech. Rep., IEA SHC Task 32 Subtask A.
Crank, J., and Nicolson, P., 1996, “A Practical Method for Numerical Evaluation of Solutions of Partial Differential Equations of the Heat-Conduction Type,” Adv. Comput. Math., 6, pp. 207–226. [CrossRef]

Figures

Grahic Jump Location
Fig. 1

A temperature array used for modeling stratification in thermal energy stores

Grahic Jump Location
Fig. 2

Illustration of a TES with an IHX showing an exploded view of a discrete IHX section with tube length ∂L and surface area ∂A

Grahic Jump Location
Fig. 3

Varied flow (Reynolds number) overall heat exchange characteristics of a stainless steel tube coiled through a diameter of 0.49 m to a length of 20.45 m and an area of 1.69 m2; internal fluid is 33% ethylene-glycol, storage fluid is water parametrically set at a constant 30 °C and a collector power of 2 kW is assumed to be leaving the heat exchanger

Grahic Jump Location
Fig. 4

Plots of local heat transfer information over the height of a discretized exemplary IHX helix (dimensions and operating conditions as in Fig. 3)

Grahic Jump Location
Fig. 5

Overall heat transfer area coefficient of seven immersed heat exchangers tested over three mass flow rates with a constant power of 2 kW

Grahic Jump Location
Fig. 6

Plot of external Nusselt numbers against the respective Rayleigh numbers. The correlation from Morgan [34] and two variations either side of this are also plotted for comparison.

Grahic Jump Location
Fig. 7

Illustration of Crank–Nicolson discretization

Grahic Jump Location
Fig. 8

Illustration of horizontal tube cross section showing development of the convection thermal boundary layer given the presence of heat exchange from the internal to the external fluid

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In