Charge reduction analysis in a water-cooling machine working with R290

• A sensitivity analysis on the geometric parameters of a water cooler is performed. • New correlations between geometric factors and refrigerant charge are identified. • Strategies are implemented to reduce the subcooling ensuring the system's ongoing. • The right blend between different condenser and capillary tube sizes is investigated. • A condenser pipes diameter reduction of 74% allows a 34.7% refrigerant charge drop. The objective of the present study is to investigate potential strategies for reducing the refrigerant charge in a cooling system. The machine under analysis is a water-cooling machine comprising a compact condenser, a capillary tube, an evaporator submerged in a tank filled with water, and a reciprocating fixed-speed compressor. A thermodynamic model, experimental validated with measured data, is used to perform sensitivity analysis on the identified most relevant design parameters: capillary tube length and condenser dimensions (fins size and pipes diameter). Key findings indicate significant reductions in refrigerant charge (up to 34.7%) by adjusting condenser pipes diameter and fins width, with minimal impact on thermal power and COP (Coefficient of Performance). Specifically, increasing capillary tube length and decreasing condenser dimensions demonstrated to be an effective strategy for reducing refrigerant charge while maintaining system efficiency. The results emphasize the critical role of managing subcooling levels as practical approaches to reduce the refrigerant charge of the system. As result, correlations, that link the reduction in refrigerant charge to changes in condenser geometry and variations in capillary tube length, are derived. The changes in the capillary tube length in accordance with the condenser size variation, ensure that the machine performance remains within a 5% range of the design cooling capacity with a proper degree of subcooling. The current methodology can be applied to similar systems to support a low charge design.