A fluid mixing device, comprising: a double pipe comprising: an inner pipe body having a first inlet and an opposing first outlet; an outer pipe body surrounding the inner pipe body, and having a second inlet and an opposing second outlet; and a plurality of stoppers disposed between the inner pipe body and the outer pipe body to form a plurality of channel openings between the inner pipe body and the outer pipe body; a feed hopper for housing the double pipe, having: a funnel-shaped channel; and a third inlet and an opposing third outlet, wherein the third outlet is positioned at a bottom of the funnel-shaped channel, and corresponding in position to the first outlet and the second outlet of the double pipe wherein the fluid mixing device is characterized by comprising: a mixing chamber disposed below the funnel-shaped channel and having: a concave disc positioned below the third outlet, a plurality of guide plates surrounding the concave disc, wherein an included angle (γ) formed between a surface of each of the guide plates and the radial direction of the concave disc ranges from 0° to 75°. a double pipe comprising: an inner pipe body having a first inlet and an opposing first outlet; an outer pipe body surrounding the inner pipe body, and having a second inlet and an opposing second outlet; and a plurality of stoppers disposed between the inner pipe body and the outer pipe body to form a plurality of channel openings between the inner pipe body and the outer pipe body; a feed hopper for housing the double pipe, having: a funnel-shaped channel; and a third inlet and an opposing third outlet, wherein the third outlet is positioned at a bottom of the funnel-shaped channel, and corresponding in position to the first outlet and the second outlet of the double pipe an inner pipe body having a first inlet and an opposing first outlet; an outer pipe body surrounding the inner pipe body, and having a second inlet and an opposing second outlet; and a plurality of stoppers disposed between the inner pipe body and the outer pipe body to form a plurality of channel openings between the inner pipe body and the outer pipe body; a feed hopper for housing the double pipe, having: a funnel-shaped channel; and a third inlet and an opposing third outlet, wherein the third outlet is positioned at a bottom of the funnel-shaped channel, and corresponding in position to the first outlet and the second outlet of the double pipe a funnel-shaped channel; and a third inlet and an opposing third outlet, wherein the third outlet is positioned at a bottom of the funnel-shaped channel, and corresponding in position to the first outlet and the second outlet of the double pipe wherein the fluid mixing device is characterized by comprising: a mixing chamber disposed below the funnel-shaped channel and having: a concave disc positioned below the third outlet, a plurality of guide plates surrounding the concave disc, wherein an included angle (γ) formed between a surface of each of the guide plates and the radial direction of the concave disc ranges from 0° to 75°. a mixing chamber disposed below the funnel-shaped channel and having: a concave disc positioned below the third outlet, a plurality of guide plates surrounding the concave disc, wherein an included angle (γ) formed between a surface of each of the guide plates and the radial direction of the concave disc ranges from 0° to 75°. a concave disc positioned below the third outlet, a plurality of guide plates surrounding the concave disc, wherein an included angle (γ) formed between a surface of each of the guide plates and the radial direction of the concave disc ranges from 0° to 75°.