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

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## 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.

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