Advertisement

Heat and Mass Transfer

, 47:1651 | Cite as

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

Original

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.

Keywords

Heat Transfer Nusselt Number Heat Pipe Radiation Heat Transfer Solar Collector 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

A

Surface area (m2)

Aabs

Absorber area (m2)

Cp

Specific heat capacity (J/kg K)

d

Diameter (m)

FR

Heat removal factor

g

Gravitational constant (9.81) (m/s2)

h

Heat transfer coefficient (W/m2 K)

kf

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)

Tavg

Average temperature

Tv

Vapour temperature (°C)

ΔTlm

Suitable mean temperature difference (°C)

UL

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

Greek symbols

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)

Subscripts

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):341–350Google Scholar
  2. 2.
    Azad E (2008) Performance analysis of wick-assisted heat pipe solar collector and comparison with experimental results. J Heat Mass Transf 45:645–649Google Scholar
  3. 3.
    Azad E (2009) Interconnected heat pipe solar collector. Int J Eng Trans 22(3):233–242MathSciNetGoogle Scholar
  4. 4.
    Azad E (2008) Theoretical and experimental investigation of heat pipe solar collector. J Exp Thermal Fluid Sci 32(8):1666–1972CrossRefGoogle Scholar
  5. 5.
    Azad E (2010) Co-axial heat-pipe solar collector Iranian Patent No. 60678-1/6/1388Google Scholar
  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 25:899–915CrossRefGoogle 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 24:1203–1215CrossRefGoogle Scholar
  8. 8.
    Dunn PD, Reay DA (1976) Heat Pipe. Pergamon press, OxfordGoogle Scholar
  9. 9.
    Faghri A (1995) Heat pipe science and technology. Taylor & Francis, WashingtonGoogle 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 32:772–795CrossRefGoogle 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 24:1959–1968CrossRefGoogle Scholar
  12. 12.
    Duffie JA, Beckman WA (1980) Solar engineering of thermal processes. Wiley-Inter Science, New YorkGoogle Scholar
  13. 13.
    Forristall R (2003) Heat transfer analysis and modelling of parabolic trough solar receiver implemented in engineering equation solver NREL/TP-550-34169Google Scholar
  14. 14.
    Incropera FP, DeWitt DP (1996) Fundamentals of heat and mass transfer, 3rd edn. Wiley, TorontoGoogle 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 1533–1539Google Scholar
  16. 16.
    Holman JP (2002) Heat transfer, 9th edn. McGraw-Hill Company, New YorkGoogle Scholar

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Advanced Materials and Renewable Energy DepartmentIranian Research Organization for Science and Technology (IROST)TehranIran

Personalised recommendations