Heat and Mass Transfer

, Volume 53, Issue 9, pp 2951–2960 | Cite as

Transient analysis of subcritical/supercritical carbon dioxide based natural circulation loop with end heat exchangers: experimental study

  • Ajay Kumar YadavEmail author
  • Maddali Ramgopal
  • Souvik Bhattacharyya


Carbon dioxide (CO2) based natural circulation loops (NCLs) has gained attention due to its compactness with higher heat transfer rate. In the present study, experimental investigations have been carried out to capture the transient behaviour of a CO2 based NCL operating under subcritical as well as supercritical conditions. Water is used as the external fluid in cold and hot heat exchangers. Results are obtained for various inlet temperatures (323–353 K) of water in the hot heat exchanger and a fixed inlet temperature (305 K) of cooling water in the cold heat exchanger. Effect of loop operating pressure (50–90 bar) on system performance is also investigated. Effect of loop tilt in two different planes (XY and YZ) is also studied in terms of transient as well as steady state behaviour of the loop. Results show that the time required to attain steady state decreases as operating pressure of the loop increases. It is also observed that the change in temperature of loop fluid (CO2) across hot or cold heat exchanger decreases as operating pressure increases.


Heat Exchanger Mass Flow Rate Tilt Angle Riser Heat Transfer Rate 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols


specific heat capacity(J/kgK)




internal diameter of inner pipe or loop diameter (m)


external diameter of inner pipe or loop diameter (m)


gravitational acceleration (m/s2)


total height of vertical pipe (m)


length of CHX (sink) and HHX (source) (m)


total length of a horizontal pipe (m)


adiabatic pipe length on horizontal pipe (m)


mass flow rate (kg/s)


heat transfer rate (W)

\(q^{{{\prime \prime }}}\)

heat flux (W/m2)


Radius of curvature for bends (m)


Stainless steel


temperature (K)


time (s)

Greek letters


loop fluid temperature difference between riser and downcomer centres (K)


temperature rise/drop of water across the CHX or HHX (K)



cold heat exchanger, sink


carbon dioxide


hot heat exchanger, source





The study has been carried out under a project sponsored by Extramural Research Division, Council of Scientific and Industrial Research (CSIR), Government of India. The financial support provided by CSIR is gratefully acknowledged.

Compliance with ethical standards

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2017

Authors and Affiliations

  • Ajay Kumar Yadav
    • 1
    Email author
  • Maddali Ramgopal
    • 2
  • Souvik Bhattacharyya
    • 2
  1. 1.Department of Mechanical EngineeringNational Institute of Technology KarnatakaSurathkalIndia
  2. 2.Department of Mechanical EngineeringIndian Institute of Technology KharagpurKharagpurIndia

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