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Arabian Journal for Science and Engineering

, Volume 43, Issue 9, pp 4549–4559 | Cite as

Effect of Pressure Drop and Air Mass Flow Rate on the Performance of Concentric Coaxial Glass Tube Solar Air Collector: A Theoretical Approach

  • Vishal Dabra
  • Avadhesh Yadav
Research Article - Mechanical Engineering

Abstract

The aim of this research work is to study the combined effects of constant pressure drop and air mass flow rate on concentric coaxial glass tube (CCGT) dimensions of concentric coaxial glass tube solar air collector. A mathematical model is developed in JAVA simulation program to optimize the length and diameter of CCGT by keeping the pressure drop constant for different air mass flow rates. The results show that absorber tube diameter of 0.028, 0.030 and 0.032 m has less dependency on the CCGT length instead of diameter range from 0.034 to 0.048 m for an air mass flow rate of 0.0053 kg/s as compared to 0.0074, 0.0095 and 0.0118 kg/s at a constant pressure drop. The air mass flow rate increases from 0.0053 to 0.0118 kg/s which leads to decrease in forced heat transfer coefficient and exit air temperature. More pumping power is required at high pressure drop with air mass flow rates of 0.0053, 0.0074, 0.0095 and 0.0118 kg/s.

Keywords

Collector Glass tube Heat transfer coefficient Mass flow rate Pressure drop 

List of symbols

\({C}_{p}\)

Specific heat of air (J/kg K)

\({D}_{1}\)

Transparent glazing radius (m)

\({D}_{2}\)

Absorber tube radius (m)

f

Friction factor (–)

G

Solar intensity \((\hbox {W/m}^{2})\)

\({h}_{1 }\)

Heat transfer coefficient from absorber coating to transparent glazing \((\hbox {W/m}^{2}\,\hbox {K})\)

\({h}_{2}\)

Heat transfer coefficient from absorber glass tube to exit air \((\hbox {W/m}^{2}\,\hbox {K})\)

\({h}_{\mathrm{a}}\)

Heat transfer coefficient from transparent glazing to ambient air \((\hbox {W/m}^{2}\,\hbox {K})\)

j

Element along the tube axis (–)

\({K}_{\mathrm{g}}\)

Thermal conductivity of glass (W/m K)

L

Length of CCGT (m)

\(\dot{m}\)

Mass flow rate of air (kg/s)

N

Total number of elements (–)

Nu

Nusselt number (–)

Pr

Prandtl number (–)

Re

Reynolds number (–)

\({r}_{1}\)

Transparent glazing radius (m)

\({r}_{2}\)

Absorber tube radius (m)

t

Thickness of absorber tube (m)

\({{T}}_{\mathrm{a}}\)

Ambient temperature \((^{\circ }\hbox {C})\)

\({T}_{\mathrm{inlet}}\)

Inlet air temperature \((^{\circ }\hbox {C})\)

\({T}_{\mathrm{outlet}}\)

Exit air temperature \((^{\circ }\hbox {C})\)

\({T}_{\mathrm{exp}}\)

Experimentally calculated exit air temperature \((^{\circ }\hbox {C})\)

\({T}_{\mathrm{sim}}\)

Simulated calculated exit air temperature \((^{\circ }\hbox {C})\)

\({T}_{1}\)

Transparent glazing temperature \((^{\circ }\hbox {C})\)

\({T}_{2}\)

Absorber coating temperature \((^{\circ }\hbox {C})\)

\({T}_{3}\)

Absorber glass tube \((^{\circ }\hbox {C})\)

\({T}_{4}\)

Fluid temperature \((^{\circ }\hbox {C})\)

\({u}_{\mathrm{wind}}\)

Wind speed (m/s)

Greek symbols

\(\alpha _{1}\)

Absorptivity of transparent glazing (–)

\(\alpha _{2 }\)

Absorptivity of absorber tube (–)

\(\rho \)

Density of air (kg/m\(^{3})\)

\(\Delta P\)

Pressure drop (Pa)

\(\varepsilon _{1 }\)

Emissivity of transparent glazing (–)

\(\varepsilon _{2 }\)

Emissivity of absorber coating (–)

\(\mu \)

Kinematic viscosity of the air (kg/ms)

\(\Delta x\)

Length of a slice along the tube axis (m)

K

Thermal conductivity of air (W/m\(^{2}\) K)

\(\tau _{1}\)

Transmissivity of transparent glazing (–)

\(\sigma \)

Stefan’s Boltzmann constant (W/m\(^{2}\) K\(^{4})\)

Abbreviations

CCGT

Concentric coaxial glass tube

CPC

Compound parabolic concentrator

HTF

Heat transfer fluid

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Copyright information

© King Fahd University of Petroleum & Minerals 2017

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringNational Institute of Technology, KurukshetraKurukshetraIndia

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