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.
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) |
= | Stefan- Boltzmann constant, W/(m2 K4) | |
= | Emissivity | |
= | Kinematic viscosity, m2/s | |
= | gas specific heat ratio | |
= | gas molecular diameter, m | |
= | gas thermal diffusion coefficient | |
= | thermal expansion coefficient, 1/K | |
= | Efficiency | |
= | Reflectance | |
= | Transmittance | |
= | Absorbance | |
= | declination angle, ° | |
= | hour angle, ° | |
= | incident angle of sun, ° | |
= | azimuth angle of collector, ° | |
= | local latitude, ° | |
= | 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 |