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Theoretical analysis of convective heat transfer enhancement of microencapsulated phase change material slurries

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Abstract.

This paper analyzes the convective heat transfer enhancement mechanism of microencapsulated phase change material slurries based on the analogy between convective heat transfer and thermal conduction with thermal sources. The influence of each factor affecting the heat transfer enhancement for laminar flow in a circular tube with constant wall temperature is analyzed using an effective specific heat capacity model. The model is validated with results available in the literature. The analysis and the results clarify the heat transfer enhancement mechanism and the main factors influencing the heat transfer. In addition, the conventional Nusselt number definition of phase change slurries for internal flow is modified to describe the degree of heat transfer enhancement of microencapsulated phase change material slurries. The modification is also consistent evaluation of the convective heat transfer of internal and external flows.

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Abbreviations

c:

volumetric concentration of microcapsules

cm :

mass concentration of microcapsules

cp :

specific heat, kJ kg–1 K–1

hfs :

phase change material heat of fusion, kJ kg–1

hm*:

modified convective heat transfer coefficient, W m–2 K–1

k:

thermal conductivity, W m–1 K–1

ke :

effective thermal conductivity of slurry, W m–1 K–1

kb :

slurry bulk thermal conductivity, W m–1 K–1

ML:

dimensionless initial subcooling

Mr:

dimensionless phase change temperature range

Nu:

conventional Nusselt number

Nu*:

improved Nusselt number

qw n :

wall heat flux, Wm–2

Pe:

Peclet number

Pr:

Prandtl number

Re:

Reynolds number

r:

radial coordinate, m

r0 :

duct radius, m

r1 :

dimensionless radial coordinate

Ste:

Stefan number

T:

temperature, K

T1 :

lower phase change temperature limit, K

T2 :

upper phase change temperature limit, K

Ti :

slurry inlet temperature, K

u:

axial velocity, m/s

v:

radial velocity, m/s

x:

axial coordinate, m

x1 :

dimensionless axial coordinate

α:

thermal diffusivity, m2/s

θ:

dimensionless temperature

μ:

dynamic viscosity, N·s/m2

ν:

kinematic viscosity, m2/s

δt :

width of thermal boundary, m

η:

degree of heat transfer enhancement, η = hm*/(hm*)single

b:

bulk fluid (slurry)

b0:

slurry without phase change

l:

liquid

m:

mean

s:

solid

f:

suspending fluid

p:

microcapsule particles

w:

wall

single:

single-phase fluid

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Acknowledgements.

This work was supported by the National Natural Science Foundation of China (Grant No. 50076020), the Department of Science and Technology of China (Grant no. G2000026309), and the Excellent Young Faculty Foundation of the Ministry of Education of China. The authors thank Prof. Z.Y. Guo of the Deptartment of Engineering Mechanics, Tsinghua University, Beijing, for his suggestions concerning the present paper.

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Authors and Affiliations

  1. Institute of Heating, Ventilating and Air-conditioning, Tsinghua University, Beijing 100084, P. R. China

    Yinping Zhang, Xianxu Hu & Xin Wang

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  1. Yinping Zhang
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  2. Xianxu Hu
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  3. Xin Wang
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Correspondence to Yinping Zhang.

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Zhang, Y., Hu, X. & Wang, X. Theoretical analysis of convective heat transfer enhancement of microencapsulated phase change material slurries. Heat and Mass Transfer 40, 59–66 (2003). https://doi.org/10.1007/s00231-003-0410-7

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  • DOI: https://doi.org/10.1007/s00231-003-0410-7

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