An apparatus suitable for mixing intensification comprising: - A plate reactor provided with a reactor vessel provided with smooth periodic constrictions, the reactor vessel comprising a bundle of reactors having alternatively straight sections and convergent - divergent sections, each convergent - divergent section consisting of a convergent section and a divergent section, wherein a distance L between consecutive convergent sections is defined by: a length L 2 of the straight section of width D w and a length L 1 of the convergent-divergent section; said length L 1 comprising a radius R c of curvature of a sidewall of the convergent section, a radius of curvature R d of a sidewall of the divergent section, and a radius of curvature R t at the convergent - divergent section centre; said length L 1 further comprising an open area α defined as the shortest tube width d 0w of the convergent - divergent section divided by the width D w, wherein: - the distance L is 1 to 5 times the width D w; - L 1 is 0.5 to 3 times the width D w; - the width d 0w of the convergent-divergent section is 0.1 to 0.5 times the width D w; - R c is 0.1 to 0.5 times the width D w; - R d is 0.1 to 0.5 times the width D w; - R t is 0.1 to 0.5 times the width D w; - the open area α has values between 10 and 50%; - wherein said smooth periodic constrictions are present in two parallel faces of a rectangular or square cross section tube, defining the 2D smooth periodic constrictions; - A mixing chamber; - Oscillation means to oscillate a liquid or multiphase fluid within the reactor vessel. - A plate reactor provided with a reactor vessel provided with smooth periodic constrictions, the reactor vessel comprising a bundle of reactors having alternatively straight sections and convergent - divergent sections, each convergent - divergent section consisting of a convergent section and a divergent section, wherein a distance L between consecutive convergent sections is defined by: a length L 2 of the straight section of width D w and a length L 1 of the convergent-divergent section; said length L 1 comprising a radius R c of curvature of a sidewall of the convergent section, a radius of curvature R d of a sidewall of the divergent section, and a radius of curvature R t at the convergent - divergent section centre; said length L 1 further comprising an open area α defined as the shortest tube width d 0w of the convergent - divergent section divided by the width D w, wherein: - the distance L is 1 to 5 times the width D w; - L 1 is 0.5 to 3 times the width D w; - the width d 0w of the convergent-divergent section is 0.1 to 0.5 times the width D w; - R c is 0.1 to 0.5 times the width D w; - R d is 0.1 to 0.5 times the width D w; - R t is 0.1 to 0.5 times the width D w; - the open area α has values between 10 and 50%; a length L 2 of the straight section of width D w and a length L 1 of the convergent-divergent section; said length L 1 comprising a radius R c of curvature of a sidewall of the convergent section, a radius of curvature R d of a sidewall of the divergent section, and a radius of curvature R t at the convergent - divergent section centre; said length L 1 further comprising an open area α defined as the shortest tube width d 0w of the convergent - divergent section divided by the width D w, wherein: - the distance L is 1 to 5 times the width D w; - L 1 is 0.5 to 3 times the width D w; - the width d 0w of the convergent-divergent section is 0.1 to 0.5 times the width D w; - R c is 0.1 to 0.5 times the width D w; - R d is 0.1 to 0.5 times the width D w; - R t is 0.1 to 0.5 times the width D w; - the open area α has values between 10 and 50%; - the distance L is 1 to 5 times the width D w; - L 1 is 0.5 to 3 times the width D w; - the width d 0w of the convergent-divergent section is 0.1 to 0.5 times the width D w; - R c is 0.1 to 0.5 times the width D w; - R d is 0.1 to 0.5 times the width D w; - R t is 0.1 to 0.5 times the width D w; - the open area α has values between 10 and 50%; - wherein said smooth periodic constrictions are present in two parallel faces of a rectangular or square cross section tube, defining the 2D smooth periodic constrictions; - A mixing chamber; - Oscillation means to oscillate a liquid or multiphase fluid within the reactor vessel.