Jorge I. Hernández

Study of a Solar Booster Assisted Ejector Refrigeration System With R134a

The studies of ejector refrigeration systems employing refrigerant R134a for air conditioning are scarce and nonexistent for ice making when its potential application in developing countries will lessen their refrigeration needs. So, a parametric study for an ice making solar booster assisted ejector refrigeration system operating with R134a is carried out. System energy and exergy efficiencies as well as ejector efficiency are presented as a function of generator and condenser temperatures and booster discharge pressure. A discussion on maximum ejector efficiency and its effect in system behavior is also carried out. With results indicating that for an evaporator temperature of -10°C, the system can operate at a generator temperature of 85°C with average energy efficiencies between 0.21 and 0.58, depending on the condenser temperature. Consequently, these systems could be a solution for solar refrigeration using off-the-shelf components.

The evaluation of a small capacity shell and tube ammonia evaporator

Abstract The use of ammonia as refrigerant is widespread in vapour compression and ammonia/water absorption systems. Ammonia is not actually used in low capacity applications mainly because of the lack of economical available equipment. For this reason, the objective of this study is the numerical and experimental evaluation of a small capacity ammonia shell and tube evaporator with enhanced heat transfer surfaces. An experimental system to evaluate small capacity heat exchangers was developed. A shell and tube evaporator with external low fin tubes was successfully tested. The experimental uncertainty for the evaporator capacity has been estimated within ±5.5%. The experimental results were used to validate a heat exchanger numerical tool that predicts reasonably well the cooling capacity and load outlet temperatures. The methodology presented in this work can be applied to evaluate other refrigerants in similar shell and tube evaporators and to optimize the design of an evaporator for a specific application.

Efficient Operation of a Booster Assisted Ejector Refrigeration System

The procedure to define the efficient operation of a booster assisted ejector refrigeration system is presented. This procedure assures efficient system and ejector operation and keeps constant design refrigeration capacity. The system produces ice at a rate of 100 kg in 6 h at a temperature of −10°C using refrigerant R134a. This system is powered with solar energy and operates at a generation temperature below 90°C. This procedure includes the criterion to select the system design point, the methodology that determines system behavioral maps and the criterion of system operation. The criterion of design point selection considers an adequate generation temperature, the lower condensation temperature and the higher booster discharge pressure, considering the system energy and exergy efficiencies and the supplied energy and compression work ratios. The methodology considers system behavior in steady state with ejector operation in transition regime. The criterion for system operation considers a fixed refrigeration capacity. This implies to work in two operational regimes, one corresponds to condensation temperatures lower than its design value and other to higher values. In the first region, the system efficiency increases and the ejector works efficiently and more than the booster. In the second region, the system efficiency decreases slightly and the booster works more than the ejector despite of that the ejector has a higher efficiency. In any case, the system and ejector operate efficiently in any region.Copyright