# Forced convective boiling in vertical tube for binary refrigerant mixtures of R11 and R113

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## Abstract

An experimental study was carried out on convective boiling heat transfer for mixtures of R11 and R113 flowing in a uniformly heated vertical tube by measuring the wall and bulk temperatures, and the results were compared with an existing correlation. A reduction of the average heat transfer coefficient for mixtures was verified for flow boiling. It was observed that two kinds of boiling behavior existed depending on mass flux. It was also found that the Chen's correlation was particularly successful for the case of high mass rate flow in which convective boiling prevailed. However in the case of low mass rate flow where nucleate boiling was dominant, the Chen's correlation was found to be inappropriate. Mass transfer resistance in the liquid film played a vital role for determining the heat transfer coefficient of refrigerant mixtures. It has been also found that the equilibrium assumption was hardly applicable to the convective boiling phenomena.

## Key Words

Convective Boiling Refrigerant Mixtures Mass Transfer Resistance## Nomenclature

*C*_{p}Specific heat (

*J/kgK*)*D*Molecular diffusion coefficient (

*m*^{2}/*s*)*d*Inside diameter of heating tube (

*m*)*F*Two phase multiplier defined by Chen

*G*Mass flux (

*kg/m*^{2}*s*)*h*_{tg}Latent heat of vaporization (

*J/kg*)*h*_{m}Mass transfer coefficient (

*m/s*)*k*Thermal conductivity (

*W/mK*)*P*Pressure (

*kPa*)*Pr*Prandtl number

*P*_{s}Saturation pressure (

*kPa*)- ΔP
_{s} Different in saturation pressure corresponding to Δ

*T*_{ s }=*T*_{w}−*T*_{s}- α
Heat flux (

*W/m*^{2})*Re*Reynolds number

*S*Nucleate boiling suppression factor defined by Chen

*Sc*Schmidt number

*T*Temperature (

*K*)*x*_{m}Local liquid mass fraction of the less volatile component

*y*_{m}Local liquid vapor fraction of the less volatile component

*z*Distance from the inlet of test section (

*m*)

## Greek Letters

*α*_{s}Nucleate boiling heat transfer coefficient (

*W/m*^{2}*K*)*α*_{c}Total heat transfer coefficient (

*W/m*^{2}*K*)*α*_{L},*α*_{LO}Forced convection heat transfer coefficient (

*W/m*^{2}*K*)*α*_{m}Measured heat transfer coefficient (

*W/m*^{2}*K*)*α*_{T}Thermal diffusivity (

*m*^{2}/*s*)- μ
Viscosity (

*pa·s*)- ϱ
Density (

*kg/m*^{3})- σ
Surface tension (

*N/m*)

## cripts

*Binary*Binary liquid

*l*Liquid component

*m*Mixture

*s*Saturated

*TP*Two-phase

- ρ
Vapor

*w*Wall

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## References

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