Numerical Investigation of A Novel Single-Pass All-Glass Receiver for Parabolic Trough Collector

ABSTRACT

A novel single-pass all-glass parabolic trough receiver (SPAG-PTR) that has a potential to improve the reliability of the parabolic trough collector was developed. Both heat losses with/without the ends insulation and thermal efficiency of the SPAG-PTR were numerically investigated and the bellows on the ends of the receiver were optimized. The results show that the three waves bellow SPAG-PTR with the ends insulation has a lower heat loss up to 10.5 W/m in the temperature of 540 K, which is about 15% less than the ends without insulation case. In addition, the results from the steady-state heat transfer model shows that the heat loss increases with the increase of vacuum pressure, wind velocity, and temperature. Thermal efficiency of this kind of SPAG-PTR is about 0.62 ~ 0.72 in the temperature range of 540 ~ 330 K. Furthermore, the thermal stress and heat loss of the receiver was simulated, the optimal structure with two waves of each bellow were obtained, which could decrease the heat loss about 2%~2.5% than the three waves-bellow type. All these results show that this optimized SPAG receiver is promising in the medium-low temperature solar thermal utilizations.

KEYWORDS:

• Parabolic trough collector
• single-pass all-glass evacuated tube solar receiver
• thermal performance

Nomenclature

A	=	area, m2
B	=	interaction coefficient
C	=	adaptation coefficient
c	=	optical Concentration ratio
cp	=	Oil conductively coefficient, J/(Kg K)
D	=	diameter, m
FR	=	transfer factor
Gr	=	geometric concentration ratio
K	=	gas thermal conductivity, W/(m K)
m	=	mass flow rate of the heat transfer fluid, Kg/s
Nu	=	Nusselt number
P	=	pressure of annular space, Pa
Pr	=	Prandtl number
Q	=	heat transfer, W
Ra	=	Rayleigh number
s	=	absorbed solar energy of receiver, W/m2
T	=	temperature, K
UL	=	Total heat loss coefficient, W/(m K)
$\sigma$	=	Stefan- Boltzmann constant, W/(m2 K4)
$\epsilon$	=	Emissivity
$\upsilon$	=	Kinematic viscosity, m2/s
$\gamma$	=	gas specific heat ratio
$\delta$	=	gas molecular diameter, m
$\alpha$	=	gas thermal diffusion coefficient
$\beta$	=	thermal expansion coefficient, 1/K
$\eta$	=	Efficiency
$\rho$	=	Reflectance
$\tau$	=	Transmittance
${\alpha }_0$	=	Absorbance
${\delta }_0$	=	declination angle, °
$\omega$	=	hour angle, °
$\theta$	=	incident angle of sun, °
${\gamma }_0$	=	azimuth angle of collector, °
$\phi$	=	local latitude, °
${\beta }_0$	=	inclination of collector, °

Subscripts

ab	=	absorber tube
ai	=	internal of the absorber tube
ao	=	external of the absorber tube
gi	=	internal of the glass envelope
go	=	external of the glass envelope
rad	=	Radiation
cov	=	Convection
std	=	Standard condition
a	=	Ambient
out	=	Outlet
in	=	Inlet
m	=	Average
opt	=	optical

Additional information

Funding

This work was supported by National Natural Science Foundation of China (Grant No. 51806100), Natural Science Foundation of Jiangsu Province (Grant No. BK20180706), China Postdoctoral Science Foundation(Grant No.2018M632294), The Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No.17KJA470004).