In frost-free refrigerator typical two compartments, the flow is induced by a fan which directs air to a plenum where it is distributed to the refrigerated compartments by the action of a damper. The air returning from the compartments is mixed at the evaporator inlet, closing the cycle. The pressure difference generated by fan must be high enough to balance the pressure drop imposed by the air circuit, and it defines the air flow in circulation, the cooling capacity and efficiency of the fan. Unfortunately, the air circuit of most refrigerators is still designed by the method of trial and error. A procedure not as sophisticated as the PIV and CFD techniques but reliable and practical, is to use a wind tunnel.

POLO has an open cycle tunnel air, built in a circular modular structure, following the standards of ASHRAE-51 standard, to meet the flow and pressure ranges commonly found in domestic applications. The computation of the flow is done indirectly by measuring the pressure drop through the nozzle by means of a differential pressure transducer. The tunnel has an auxiliary fan that is used to vary the flow rate in a range from 15 to 200 m3 / h. By coupling the refrigerator tunnel can measure the air flow and the installation of perforated hoses at specific points can measure the impedance of the air cooler circuit. The fan performance can also be evaluated, and in this case it must be removed from the refrigerator and installed in a tunnel of outputs.