Theoretical analysis to investigate thermal performance of co-axial heat pipe solar collector

Abstract

The thermal performance of co-axial heat pipe solar collector which consist of a collector 15 co-axial heat pipes surrounded by a transparent envelope and which heat a fluid flowing through the condenser tubes have been predicted using heat transfer analytical methods. The analysis considers conductive and convective losses and energy transferred to a fluid flowing through the collector condenser tubes. The thermal performances of co-axial heat pipe solar collector is developed and are used to determine the collector efficiency, which is defined as the ratio of heat taken from the water flowing in the condenser tube and the solar radiation striking the collector absorber. The theoretical water outlet temperature and efficiency are compared with experimental results and it shows good agreement between them. The main advantage of this collector is that inclination of collector does not have influence on performance of co-axial heat pipe solar collector therefore it can be positioned at any angle from horizontal to vertical. In high building where the roof area is not enough the co-axial heat pipe solar collectors can be installed on the roof as well as wall of the building. The other advantage is each heat pipe can be topologically disconnected from the manifold.

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Abbreviations

A :

Surface area (m2)

A abs :

Absorber area (m2)

C p :

Specific heat capacity (J/kg K)

d :

Diameter (m)

F R :

Heat removal factor

g :

Gravitational constant (9.81) (m/s2)

h :

Heat transfer coefficient (W/m2 K)

k f :

Thermal conductance (W/m K)

I :

Solar insolation (W/m2)

L :

Length (m)

\( \dot{m} \) :

Mass flow rate (kg/s)

Nu :

Nusselt number

Pr :

Prandtl number

Q :

Heat flow (W)

Ra :

Rayleigh number

Re :

Reynolds number

t :

Thickness (m)

T :

Temperature (°C)

T avg :

Average temperature

T v :

Vapour temperature (°C)

ΔT lm :

Suitable mean temperature difference (°C)

U L :

Overall heat-transfer coefficient (W/m2 °C)

α :

Absorptance

β :

Volumetric thermal expansion (1/K)

ε :

Emissivity

μ :

Dynamic viscosity (kg/m s)

η :

Collector efficiency

τ :

Transmissivity

λ :

Latent heat (J/kg)

ν :

Kinematic viscosity (m2/s)

ρ :

Density (kg/m3)

σ :

Stefan–Boltzman constant (5.67E−8) (W/m2 K4)

1:

Fluid

2:

Inside condenser surface

3:

Outside condenser surface

4:

Inside evaporator surface

5:

Outside evaporator surface

6:

Glass envelope inner surface

7:

Glass envelope outer surface

8:

Surrounding air

9:

Sky

abs :

Absorber

g :

Glass

conv :

Convection

rad :

Radiation

Loss :

Loss

Avg :

Average

Sol :

Solar

l :

Liquid

ν :

Vapour

w :

Wick

f :

Fluid

i:

Inside

o:

Outlet, outside

References

  1. 1.

    Azad E et al (1987) Solar water heater using gravity-assisted heat pipe. J Heat Recovery Syst CHP 7(4):341–350

    Google Scholar 

  2. 2.

    Azad E (2008) Performance analysis of wick-assisted heat pipe solar collector and comparison with experimental results. J Heat Mass Transf 45:645–649

    Google Scholar 

  3. 3.

    Azad E (2009) Interconnected heat pipe solar collector. Int J Eng Trans 22(3):233–242

    MathSciNet  Google Scholar 

  4. 4.

    Azad E (2008) Theoretical and experimental investigation of heat pipe solar collector. J Exp Thermal Fluid Sci 32(8):1666–1972

    Article  Google Scholar 

  5. 5.

    Azad E (2010) Co-axial heat-pipe solar collector Iranian Patent No. 60678-1/6/1388

  6. 6.

    Riffat SB, Zhao X, Doherthy PS (2004) Developing a theoretical model to investigate thermal performance of a thin memberane heat-pipe solar collector. J Appl Thermal Eng 25:899–915

    Article  Google Scholar 

  7. 7.

    Riffat SB, Doherthy PS, Abdel Aziz EI (2000) Performance testing of different types of liquid flat plate collectors. Int J Energy Res 24:1203–1215

    Article  Google Scholar 

  8. 8.

    Dunn PD, Reay DA (1976) Heat Pipe. Pergamon press, Oxford

    Google Scholar 

  9. 9.

    Faghri A (1995) Heat pipe science and technology. Taylor & Francis, Washington

    Google Scholar 

  10. 10.

    Kim Y, Seo T (2007) Thermal performances comparisons of the glass evacuated tube solar collectors with shapes of absorber tube. Renew Energy 32:772–795

    Article  Google Scholar 

  11. 11.

    Nada SA, El-Ghetany HH, Hussein HMS (2004) Performance of a two-phase closed thermosyphon solar collector with a shell and tube heat exchanger. Appl Thermal Eng 24:1959–1968

    Article  Google Scholar 

  12. 12.

    Duffie JA, Beckman WA (1980) Solar engineering of thermal processes. Wiley-Inter Science, New York

    Google Scholar 

  13. 13.

    Forristall R (2003) Heat transfer analysis and modelling of parabolic trough solar receiver implemented in engineering equation solver NREL/TP-550-34169

  14. 14.

    Incropera FP, DeWitt DP (1996) Fundamentals of heat and mass transfer, 3rd edn. Wiley, Toronto

    Google Scholar 

  15. 15.

    Bienert WB, Trimmer DS, Wolf DA (1975) Application of heat pipes to solar collectors. In: Proceedings of the 10th intersociety energy conversion. University of Delaware, Newark, pp 1533–1539

  16. 16.

    Holman JP (2002) Heat transfer, 9th edn. McGraw-Hill Company, New York

    Google Scholar 

Download references

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Azad, E. Theoretical analysis to investigate thermal performance of co-axial heat pipe solar collector. Heat Mass Transfer 47, 1651 (2011). https://doi.org/10.1007/s00231-011-0827-3

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Keywords

  • Heat Transfer
  • Nusselt Number
  • Heat Pipe
  • Radiation Heat Transfer
  • Solar Collector