Numerical simulation of solar parabolic trough collector with arc-plug insertion

ABSTRACT

This paper investigates the effect of insertion of arc-plug within the absorber tube for the thermal improvement of the solar parabolic trough collector (PTC). In order to check the optimized dimension of the arc-plug, eleven different cases have been compared. Ansys-Discovery-Aim 2019 R1 has been used for the evaluation of required thermodynamic and hydraulic properties for these distinct cases of the modified PTC (MPTC). SOLTRACE-7.9 is used for the evaluation of heat flux boundary condition need in the Ansys physics condition. The arc-plug with eleven factor R values that are taken into consideration are 0.394, 0.515, 0.636, 0.757, 0.879, 1, 1.121, 1.242, 1.364, 1.485, and 1.6060. Under the usual sets of operating conditions, the thermal efficiency (η) for factor R = 1 and R = 1.6060 are seen to be varying from 73.09% to 67.55% and 67.78% to 65.37% respectively. Whereas, under the same sets of operating conditions, the highest thermal enhancement index (TEI) for factor R = 1 and R = 1.6060 are observed to be 1.1039 and 1.3016 respectively. The arc-plug can be considered as a triangular fin with its base attached to the high thermal flux region within the absorber tube. Therefore, it cannot be taken as granted that high TEI leads to high thermal efficiency; there may occur that the fins or obstructions may act as insulators at some point of operation. It is observed that for arc-plug with factor R = 1 and R = 0.879; the PTC shows the highest thermal efficiency. Whereas, for the arc-plug with factor R = 1.6060; the PTC shows the highest heat transfer performance.

Abbreviations: CFD: Computational fluid dynamics; CPTC: Concentrated parabolic trough collector; MPTC: Modified parabolic trough collector; NUHF: nonuniform heat flux; PFAI-PTC: Pin fin array inserts parabolic trough collector; PTC: Parabolic trough collector; PTR: Parabolic trough receiver; SAT: Smooth absorber tube; SPTC: Smooth parabolic trough collector; SNL: Sandia national laboratory; TEI: Thermal enhancement index; UHF: Uniform heat flux; UMLVE: Unilateral milt-longitudinal vortexes enhanced; USR:Unilateral spiral ribbed

KEYWORDS:

• Arc-plug insert
• enhanced heat transfer
• heat transfer oil
• receiver tube
• solar parabolic trough collector

Nomenclature

A	=	Area (${\mathrm{m}}^2)$
${\mathrm{C}}_{\mathrm{p}}$	=	Specific heat capacity (J/kg. K)
d	=	Diameter of absorber tube (m)
D	=	Diameter (m)
f	=	Friction factor
I	=	Solar beam radiation (W/${\mathrm{m}}^2)$
k	=	Thermal conductivity (W/${\mathrm{m}}^2\mathrm{K})$
R	=	Ratio of radius of arc-plug to the radius of the receiver tube
T	=	Temperature (K)
l	=	Length of absorber tube (m)
L	=	Height of the fin from its base to tip (m)
W	=	Width of the parabolic concentrator (m)
$̇$	=	Mass flow rate (kg/s)
$\mathrm{P}$	=	Parameter
q	=	Heat flux (W/${\mathrm{m}}^2)$
Q	=	Heat transfer rate (W)
h	=	Convective film heat transfer coefficient (W/${\mathrm{m}}^2\mathrm{K})$
Re	=	Reynold’s number
Nu	=	Nusselt number
Pr	=	Prandtl number
u, v, w	=	Components of velocity magnitude in x, y and z
x, y, z	=	Cartesian coordinate system (m)
$\mathrm{\Delta }\mathrm{p}$	=	Pressure difference (Pa)
Subscript	=
0	=	Reference-conventional parabolic trough collector
a	=	Absorber
b	=	Base
bottom	=	Bottom lateral surface of absorber
c	=	Concentrator
cs	=	Cross-section
fin	=	Extended surface
g	=	Glass cover
i	=	Inlet
in	=	Inner surface
loss	=	Loss of heat
m	=	Mean
o	=	Outlet
op	=	Operating conditions
ou	=	Outer surface
p	=	Produced
pa	=	Profile area
pr	=	Present
r	=	Receiver
s	=	Solar intensity
soltrace	=	Soltrace software
top	=	Top lateral surface of absorber
Greek letters	=
$\mu$	=	Dynamic viscosity (Pa-s)
${\mu }_{\mathrm{t}}$	=	Turbulent viscosity (Pa-s)
$\kappa$	=	Kinetic energy
$\epsilon$	=	Emissivity or turbulent dissipation rate
$\tau$	=	Transmissivity
$\alpha$	=	Absorptivity
$\lambda$, $\beta$	=	Fin parameters
$\sigma$	=	Stefan-Boltzmann constant (W/$m^{-2}{K}^{-4}$)
${\sigma }_{\mathrm{T}}$	=	Turbulent Prandtl number
${\sigma }_{\kappa }$	=	Diffusion turbulent Prandtl number for k
${\sigma }_{\epsilon }$	=	Diffusion turbulent Prandtl number for ε
ρ	=	Density (kg/${\mathrm{m}}^3$)
η	=	Collector efficiency

Additional information

Notes on contributors

Mukundjee Pandey

Mukundjee Pandey continues his Ph.D. in the Department of Mechanical Engineering at International Institute of Information Technology, Bhubaneswar, India. He is currently working as an Assistant Professor in the Department of Mechanical Engineering at Centurion University of Technology and Management, Odisha, India. His research area includes Solar thermal energy, Computational fluid dynamics, Convective heat transfer and Finite element analysis.

Biranchi Narayana Padhi

Biranchi Narayana Padhi is presently working as faculty of Mechanical Engineering at International Institute of Information Technology, Bhubaneswar, India. His research area includes Conjugate heat transfer, Solar energy, and Energy, Exergy analysis.

Ipsita Mishra

Ipsita Mishra is currently working as an Assistant Professor in the Department of Mechanical Engineering at Centurion University of Technology and Management, Odisha, India. Her research area includes Biofuel, Solar thermal energy, and Computational fluid dynamics.