An apparatus for mixing a second fluid into a first fluid, the apparatus comprising: a chamber enclosing a flow path of the first fluid, the chamber having a first inlet for receiving the first fluid and a second inlet arranged downstream of the first inlet for receiving the second fluid, an outlet, arranged downstream of the second inlet, for discharging a mixture of said first fluid and said second fluid, wherein the flow path of the first fluid extends from the first inlet to the outlet and the second inlet opens into the flow path of the first fluid; a vertically adjustable throttle body having a first end disposed at a bottom portion of the chamber and a second end comprising an end portion; wherein the throttle body is arranged inside the chamber, downstream of the first inlet and upstream of the second inlet, for controlling the flow area of the flow path, wherein the throttle body is adapted to be vertically adjustable in such a way that the flow area of the flow passage decreases with a decreasing flow rate of the first fluid and increases with an increasing flow rate of the first fluid, characterized in that the end portion of the throttle body comprises three parts, the first part being upstream of the second part, the third part being downstream of the second part; wherein, in an operating position, the second inlet is upstream of the third part of the throttle body and downstream of the first inlet; and wherein the first part and the third part of the end portion are protrusions and the second part is an indentation, wherein the first part and the third part of the end portion are adapted to achieve a higher flow velocity than the second part. a chamber enclosing a flow path of the first fluid, the chamber having a first inlet for receiving the first fluid and a second inlet arranged downstream of the first inlet for receiving the second fluid, an outlet, arranged downstream of the second inlet, for discharging a mixture of said first fluid and said second fluid, wherein the flow path of the first fluid extends from the first inlet to the outlet and the second inlet opens into the flow path of the first fluid; a vertically adjustable throttle body having a first end disposed at a bottom portion of the chamber and a second end comprising an end portion; wherein the throttle body is arranged inside the chamber, downstream of the first inlet and upstream of the second inlet, for controlling the flow area of the flow path, wherein the throttle body is adapted to be vertically adjustable in such a way that the flow area of the flow passage decreases with a decreasing flow rate of the first fluid and increases with an increasing flow rate of the first fluid, characterized in that the end portion of the throttle body comprises three parts, the first part being upstream of the second part, the third part being downstream of the second part; wherein, in an operating position, the second inlet is upstream of the third part of the throttle body and downstream of the first inlet; and wherein the first part and the third part of the end portion are protrusions and the second part is an indentation, wherein the first part and the third part of the end portion are adapted to achieve a higher flow velocity than the second part.