During steady-state working conditions, in small capacity mechanical vapour-compression refrigerating systems using capillary tubes and without refrigerant accumulators, refrigerant charge affects the values of the main operating parameters. In order to establish the influence of refrigerant charge distribution on working conditions, the results of an experimental investigation for a vertical freezer of 320 dm3 with diabatic capillary tube are reported, varying the charge of isobutane between 55 g and 200 g at constant ambient temperature. The results showed that, increasing the charge, the subcooling degree at condenser exit, the evaporating and the condensing pressures, the mass flow rate increase, while superheating degree at evaporator exit decreases. An optimum charge with respect to energy consumption was found.
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