TY - JOUR
T1 - A new version of a low concentration evacuated tube solar collector
T2 - Optical and thermal investigation
AU - Ribeiro Teles, Mavd de Paula
AU - Ismail, Kamal Abdel Radi
AU - Arabkoohsar, Ahmad
PY - 2019/3
Y1 - 2019/3
N2 - This work is focused on investigating the performance of a new version of evacuated tube solar collector with and without solar tracking system. The evacuated tube solar collector is composed of an absorbing copper tube positioned eccentrically inside a transparent glass cover tube which has a reflective film insert on its inner surface and vacuum in eccentric annular space. Modeling of the proposed evacuated tube collector is based on the conservation equations of mass, momentum and energy and discretized by using the finite volumes method. A home-built numerical code is developed, tested and its grid size optimized. This code is validated against available experimental and numerical results. Effects of the tilt angle and tracking systems are also evaluated. The results showed maximum and minimum daily efficiencies of the collector of about 73% and 42%, respectively. The annual efficiency of this collector was evaluated as 61.5% for the city of São Luís, Brazil. The new contributions from the present work include the reflective film, the eccentricity of the absorber and the presence of vacuum in the annular space. The reflective film helps to keep the absorber at uniform temperature and reduce thermal induced stress. The eccentricity is introduced to create concentration effect which helps to increase the outlet temperature of the working fluid and reduce the mass of the collector system. The presence of vacuum in the eccentric annular space reduces effectively the thermal losses, improves the efficiency.
AB - This work is focused on investigating the performance of a new version of evacuated tube solar collector with and without solar tracking system. The evacuated tube solar collector is composed of an absorbing copper tube positioned eccentrically inside a transparent glass cover tube which has a reflective film insert on its inner surface and vacuum in eccentric annular space. Modeling of the proposed evacuated tube collector is based on the conservation equations of mass, momentum and energy and discretized by using the finite volumes method. A home-built numerical code is developed, tested and its grid size optimized. This code is validated against available experimental and numerical results. Effects of the tilt angle and tracking systems are also evaluated. The results showed maximum and minimum daily efficiencies of the collector of about 73% and 42%, respectively. The annual efficiency of this collector was evaluated as 61.5% for the city of São Luís, Brazil. The new contributions from the present work include the reflective film, the eccentricity of the absorber and the presence of vacuum in the annular space. The reflective film helps to keep the absorber at uniform temperature and reduce thermal induced stress. The eccentricity is introduced to create concentration effect which helps to increase the outlet temperature of the working fluid and reduce the mass of the collector system. The presence of vacuum in the eccentric annular space reduces effectively the thermal losses, improves the efficiency.
KW - Solar energy
KW - Evacuated tube solar collector
KW - Collector modeling
KW - Solar tracking systems
KW - Eccentric evacuated tube collector
UR - http://www.scopus.com/inward/record.url?scp=85060168733&partnerID=8YFLogxK
U2 - 10.1016/j.solener.2019.01.039
DO - 10.1016/j.solener.2019.01.039
M3 - Journal article
SN - 0038-092X
VL - 180
SP - 324
EP - 339
JO - Solar Energy
JF - Solar Energy
ER -