# Experimental investigations on heat transfer characteristics of pulsating single-phase liquid flow and two-phase Taylor bubble flow through a minichannel

- 87 Downloads

## Abstract

Experimental investigations are reported for pulsating Taylor bubble (PTB) flow through a 2.12 mm horizontal circular minichannel. Air and water are used as working fluids. A T-junction is used to generate Taylor bubble flow in a minichannel. The superficial gas velocity (*U*_{ SG }) is kept as 0.0472 m/s. The superficial liquid velocity (*U*_{ SL }) is kept as 0.0472 and 0.0708 m/s. The pulsating liquid flow is generated by developing a pulse generator circuit. The investigations are carried out for various pulsating flow frequencies of 0 Hz (continuous flow), 0.1, 0.25, 0.5, 1 and 2 Hz, which correspond to Womersley number (*W*_{ o }) 0, 0.84, 1.39, 1.88, 2.65 and 3.75, respectively. Heat transfer enhancement is found to be negligible (less than 1%) for pulsating laminar liquid flow through the minichannel. On the contrary, heat transfer is observed to decrease by 35% for PTB flow compared with continuous Taylor bubble (CTB) flow for imposed frequency of pulsation up to 1 Hz.

## Keywords

Taylor bubble flow pulsation frequency heat transfer minichannel## List of symbols

*c*specific heat, J kg

^{−1}K^{−1}*d*_{h}diameter of circular pipe, m

*f*frequency, Hz

*h*heat transfer coefficient, W m

^{−1}K^{−1}*k*thermal conductivity, W m

^{−2}K^{−1}*L*length of heating section, m

*L*^{*}non-dimensional axial length

*m*^{·}mass flow rate, kg s

^{−1}*Q*heat input, W

*q*^{′}heat flux, W m

^{−2}*t*time, s

*T*imposed time period of fluctuation, s

*T*^{*}non-dimensional time period

*T*_{f}^{*}non-dimensional fluid temperature

*T*_{w}^{*}non-dimensional wall temperature

*U*velocity, m s

^{−1}*t*_{c}thermal diffusivity time scale, s

*x*distance from heating section

## Greek symbol

*ω*angular velocity, rad s

^{−1}*α*thermal diffusivity, m

^{2}s^{−1}*μ*dynamic viscosity, Pa s

*ρ*mass density, kg m

^{−3}*β*homogeneous void fraction

## Non-dimensional numbers

*Re*Reynolds number

*Nu*Nusselt number

*W*_{o}Womersley number \( \left( {0.5d_{h} \sqrt {\frac{\omega }{\upsilon }} } \right) \)

*x*^{*}inverse Graetz number

## Subscripts

*g*gas (air)

*l*liquid

*tp*two phase

*sl*superficial liquid

*sg*superficial gas

## Superscripts

- *
dimensionless

## Notes

### Acknowledgements

The authors would like to thank the authorities of the Sardar Vallabhbhai National Institute of Technology, Surat, for providing financial support for the development of Advanced Fluid Dynamics Lab, where this minichannel-based experiments were conducted.

## References

- 1.Akachi H 1990 Patent No. 4,921,041, May 1, United States of AmericaGoogle Scholar
- 2.Akachi H 1993 Patent No. 5,219,020, June 15, United States of AmericaGoogle Scholar
- 3.Zhang Y and Faghri A 2002 Heat transfer in pulsating heat pipe with open end.
*Int. J. Heat Mass Transf.*45: 755–764CrossRefMATHGoogle Scholar - 4.Khandekar S, Gautam A P and Sharma P K 2009 Multiple quasi-steady states in a closed loop pulsating heat pipe.
*Int. J. Therm. Sci.*48: 535–546CrossRefGoogle Scholar - 5.Khandekar S and Groll M 2004 An insight into thermo-hydraulic coupling in pulsating heat pipe.
*Int. J. Therm. Sci.*43(1): 13–20CrossRefGoogle Scholar - 6.Patel V M, Gaurav and Mehta H B 2017 Influence of working fluids on startup mechanism and thermal performance of a closed loop pulsating heat pipe.
*Appl. Therm. Eng.*110: 1568–1577Google Scholar - 7.Zhang Y and Faghri A 2008 Advances and unresolved issues in pulsating heat pipe.
*Heat Transf. Eng.*29(1): 20–44CrossRefGoogle Scholar - 8.Mehta B and Khandekar S 2014 Taylor bubble flows and heat transfer in the context of pulsating heat pipes.
*Int. J. Heat Mass Transf.*79: 279–290CrossRefGoogle Scholar - 9.Mehta H B and Banerjee J 2016 Experimental investigations on thermo-hydrodynamics of continuous Taylor bubble flow through minichannel.
*Int. J. Heat Mass Transf.*94: 119–137CrossRefGoogle Scholar - 10.Kline S J and McClintock K N 1953 The descriptions of uncertainties in single sample experiments.
*Mech. Eng.*75: 3–8Google Scholar - 11.Muzychka Y S and Yovanovich M M 2004. Force convection heat transfer in the combined entry region of non-circular ducts.
*ASME J. Heat Transf.*126: 54–61CrossRefGoogle Scholar - 12.Womersley J R 1955 Method for the calculation of velocity rate of flow and viscous drag in arteries when the pressure gradient is known.
*J. Physiol.*127: 553–563CrossRefGoogle Scholar - 13.Yu J and Zhao T S 2004 An analytical study of pulsating laminar heat convection in circular tube with constant heat flux.
*Int. J. Heat Mass Transf.*47: 5297–5301CrossRefMATHGoogle Scholar