The present invention relates to a photo bio-reactor for cultivating and harvesting a bio-mass suitable for producing hydrocarbon comprising: (i) a helical tubular system having a plurality of substantially coaxial helical transparent tubular coils(l,..), which could be easily autoclaved, for flow of a culture medium containing micro algae to be cultivated, each coil being hydraulically connected to its adjacent coaxial coil, said coils having annular spaces interposed between the adjacent coils and a space enclosed by the inner diameter of innermost coil, the first and the last coil each having a free end (ii) a means (2) of providing periods of light and darkness on each point alternately for predetermined time periods on the inner and outer surfaces of each of said coil (iii) a de-gasser chamber (4) having hydraulic connection with said free end of first coil (1) for removing unwanted gases from said culture medium (iv) optionally, a stirrer (5) or perfusion air-lift reactor (5) provided in said de-gasser chamber(4) for keeping the bio-mass in suspension in said culture medium (v) said de-gasser chamber (4) having hydraulic connection with a heat exchanger (6) for controlling temperature of said culture medium (vi) a means (7) for causing flow of said culture medium in said coils without said means coming into direct contact with said medium and (vii) a gas injection means (8) connected to said de-gasser chamber (6) on one end and said free end of last coil on the other end.
