Apparatus comprising a fuel cell unit with a plurality of fuel cells arranged in parallel defining a longitudinal axis of the apparatus and defining a main flow direction coaxial to the longitudinal axis of the apparatus, wherein fuel cell inlets and fuel cell outlets are arranged at opposite ends of the fuel cell unit and in line with the main flow direction; and further comprising a stack component (1,3) being one of a heat exchanger, reformer, afterburner or preheater, the stack component comprising first fluid conduits arranged parallel to the main flow direction, and the first fluid conduits comprising first fluid inlets and first fluid outlets arranged at opposite ends of the component and in line with the main flow direction, wherein the stack component (1,3) is arranged adjacent the fuel cell unit such that at least one of the first fluid inlets and the first fluid outlets of the stack component are arranged adjacent at least one of the fuel cell outlets and the fuel cell inlets such that a fluid flow entering the apparatus may flow substantially parallel to the longitudinal axis of the apparatus in the first fluid conduits of the stack component and in the fuel cell unit and when passing from the component to the fuel cell unit or vice versa; the component (1,3) further comprising second fluid conduits with a second fluid inlet and a second fluid outlet, the second fluid conduits for a second fluid to pass through the component; wherein the second fluid inlet is arranged in an upstream region of a side of the stack component (1,3) and the second fluid outlet is arranged at a downstream region of an opposite side of the stack component such that the second fluid may flow essentially parallel to the main flow direction in a central zone (13,33) of the second fluid conduits; characterized in that obstruction means are arranged in the central zone (13,33) of the second fluid conduits, such that a pressure drop of the second fluid caused by the obstruction means in the central zone (13,33) is higher than a pressure drop caused in an inlet distribution zone (11,31) and in an outlet collection zone (12,32) of the second fluid conduits, and in that the apparatus further comprises a main inlet with an inlet distribution portion, for distributing a main fluid inside the inlet distribution portion over an entire height and width of the apparatus, wherein a depth of the inlet distribution portion varies along the height of the apparatus with an end region of the inlet distribution portion being wider versus a main inlet opening than an end region of the inlet distribution portion opposite the main inlet opening. a fuel cell unit with a plurality of fuel cells arranged in parallel defining a longitudinal axis of the apparatus and defining a main flow direction coaxial to the longitudinal axis of the apparatus, wherein fuel cell inlets and fuel cell outlets are arranged at opposite ends of the fuel cell unit and in line with the main flow direction; and further comprising a stack component (1,3) being one of a heat exchanger, reformer, afterburner or preheater, the stack component comprising first fluid conduits arranged parallel to the main flow direction, and the first fluid conduits comprising first fluid inlets and first fluid outlets arranged at opposite ends of the component and in line with the main flow direction, wherein the stack component (1,3) is arranged adjacent the fuel cell unit such that at least one of the first fluid inlets and the first fluid outlets of the stack component are arranged adjacent at least one of the fuel cell outlets and the fuel cell inlets such that a fluid flow entering the apparatus may flow substantially parallel to the longitudinal axis of the apparatus in the first fluid conduits of the stack component and in the fuel cell unit and when passing from the component to the fuel cell unit or vice versa; the component (1,3) further comprising second fluid conduits with a second fluid inlet and a second fluid outlet, the second fluid conduits for a second fluid to pass through the component; wherein the second fluid inlet is arranged in an upstream region of a side of the stack component (1,3) and the second fluid outlet is arranged at a downstream region of an opposite side of the stack component such that the second fluid may flow essentially parallel to the main flow direction in a central zone (13,33) of the second fluid conduits; characterized in that obstruction means are arranged in the central zone (13,33) of the second fluid conduits, such that a pressure drop of the second fluid caused by the obstruction means in the central zone (13,33) is higher than a pressure drop caused in an inlet distribution zone (11,31) and in an outlet collection zone (12,32) of the second fluid conduits, and in that the apparatus further comprises a main inlet with an inlet distribution portion, for distributing a main fluid inside the inlet distribution portion over an entire height and width of the apparatus, wherein a depth of the inlet distribution portion varies along the height of the apparatus with an end region of the inlet distribution portion being wider versus a main inlet opening than an end region of the inlet distribution portion opposite the main inlet opening.