A SOLAR EJECTOR COOLING SYSTEM USING REFRIGERANT R141b

A high-performance solar ejector cooling system using R141b as the working fluid was developed. We obtain experimentally a COP of 0.5 for a single-stage ejector cooling system at a generating temperature of 90°C, condensing temperature of 28°C, and an evaporating temperature 8°C. For solar cooling application, an optimum overall COP can be obtained around 0.22 at a generating temperature of 95°C, evaporating temperature of 8°C and solar radiation at 700 W m⁻².     

Experiments on vapour jet refrigeration system suitable for solar energy applications

Experiments are carried out on a R11 vapour jet refrigeration system (VJRS) to study the influence of ejector configuration and operating conditions on the performance. Eight ejector configurations, formed out of five nozzles and seven diffusers are investigated. The influence of boiler temperature, which represents the solar energy collection temperature, and that of evaporating temperature, which denotes the cooling load temperature, are studied. Overall COPs in the range of 0.08-0.33 and evaporating temperatures in the range of −3–18°C are obtained for boiler temperatures from 75 to 85°C. Ejector configuration has significant influence in deciding the operating range.     

Estimation of ejector's main cross sections in steam-ejector refrigeration system

This paper describes the calculation of main cross sections of a steam-ejector, operating in a refrigeration system. For the detailed calculation of ejector a method has been developed which employs functions describing the thermodynamic properties of steam. The influence of three major parameters: generator pressure, condenser and evaporator temperature on cross sections of ejector is discussed. The design conditions were: generator pressure (6–8 bar), condenser temperature (40–50 °C) and evaporator temperature (4–10 °C). It is confirmed that the dimensions of ejector depend on the operation conditions.     

An exergy analysis of a solar-driven ejector refrigeration system

Exergy analysis is used as a tool to analyse the performance of an ejector refrigeration cycle driven by solar energy. The analysis is based on the following conditions: a solar radiation of 700 W/m², an evaporator temperature of 10 °C, a cooling capacity of 5 kW, butane as the refrigerant in the refrigeration cycle and ambient temperature of 30 °C as the reference temperature. Irreversibilities occur among components and depend on the operating temperatures. The most significant losses in the system are in the solar collector and the ejector. The latter decreases inversely proportional to the evaporation temperature and dominates the total losses within the system. The optimum generating temperature for a specific evaporation temperature is obtained when the total losses in the system are minimized. For the above operating conditions, the optimum generating temperature is about 80 °C.     

Study on a dual-mode, multi-stage, multi-bed regenerative adsorption chiller

In this paper, a detailed parametric study on a dual-mode silica gel–water adsorption chiller is performed. This advanced adsorption chiller utilizes effectively low-temperature solar or waste heat sources of temperature between 40 and 95 °C. Two operation modes are possible for the advanced chiller. The first operation mode will be to work as a highly efficient conventional chiller where the driving source temperature is between 60 and 95 °C. The second operation mode will be to work as an advanced three-stage adsorption chiller where the available driving source temperature is very low (between 40 and 60 °C). With this very low driving source temperature in combination with a coolant at 30 °C, no other cycle except an advanced adsorption cycle with staged regeneration will be operational. In this paper, the effect of chilled-water inlet temperature, heat transfer fluid flow rates and adsorption–desorption cycle time effect on cooling capacity and COP of the dual-mode chiller is performed. Simulation results show that both cooling capacity and COP values increase with the increase of chilled water inlet temperature with driving source temperature at 50 and 80 °C in three-stage mode, and single-stage multi-bed mode, respectively. However, the delivered chilled-water temperature increases with chilled-water inlet temperature in both modes.     

Performance testing and evaluation of solid absorption solar cooling unit

Based on solid-vapour intermittent absorption system, DORNIER a German Firm designed and fabricated a solar cooling unit, which utilizes thermal energy supplied by heat pipe vacuum tube solar collectors through thermosyphonic flow of water. The unit of 1.5 kWh/day cooling capacity uses ammonia as a refrigerant and IMPEX material as absorbent and does not have any moving part requiring no auxiliary energy. The IMPEX material (80% SrCl₂ and 20% Graphite) has high heat and mass transfer coefficient as well as high absorption capacity. Detailed experiments were performed on a unit in Delhi under real field conditions followed by theoretical analysis. Theoretical maximum overall COP of the unit is 0.143, and it depends upon the climatic conditions. Under field conditions, it was found that if the maximum daytime ambient temperature was 30°C and night time temperature 20°C, it took three sunny days to freeze water in the cooling box. After the second day, the temperature inside the cooling box remained 1°C. The overall COP was found to be 0.081 only. The automatic control valve based on mechanical/thermal principles however has defects and the problem of corrosion of the sealings needs to be solved. In climates where day time temperatures are high (Delhi summer 43°C–47°C during the day, 30°C–35°C during the night) and solar radiation relatively low (4–5 kWh/m²d) because of pollution and sand in the atmosphere, it is most unlikely that pressure in the ammonia circuit can reach values at which ammonia vapours start to condense. The unit, needs to be redesigned for such conditions.     

Novel composite sorbent for resorption systems and for chemisorption air conditioners driven by low generation temperature

The utilization of a composite sorbent (NaBr and expanded graphite) in chemisorption air conditioning systems driven by low-grade heat source, and in resorption systems with simultaneous heating and cooling effects was experimentally investigated using bench-scale prototypes. The mass of ammonia desorbed and adsorbed was measured, and used to calculate the specific cooling capacity. The sorbent produced 219 kJ kg⁻¹ of cooling at 5 °C and 510 kJ kg⁻¹ at 15 °C, when the heat source temperature was 65 °C and the heat sink temperature was 30 °C. The air conditioning system mean specific cooling power (SCP), and mean coefficient of performance (COP) were calculated based on the desorbed and adsorbed masses, and on the variation of temperature in the reactors. For the same heat source and heat sink temperatures mentioned above, the air conditioning system had a SCP of 129 ± 7 W kg⁻¹ and a COP of 0.46 ± 0.01, when cooling occurred at 15 °C. Regarding the utilization of the composite sorbent in resorption machines, the prototype was tested for production of cooling/heating at −5/50 °C, and at 10/70 °C. In the former condition, the COP was only 0.02, but in the latter condition, there was a tenfold increase in the COP, and the combined coefficient of performance and amplification reached 1.11, which indicates the energy saving potential of resorption systems using the studied sorbent.     

Crystallization as a limit to develop solar air-cooled LiBr–H2O absorption systems using low-grade heat

In the present work the use of low-temperature solar heat is studied to produce cooling at 5°C, using a double-stage LiBr–H₂O air-cooled absorption cycle. A solar plant, consisting of flat plate collectors feeding the generators of the absorption machine, has been modeled. Operating conditions of the double-stage absorption machine, integrated in the solar plant without crystallization problems for condensation temperatures up to 53°C, are obtained. Results show that about 80°C of generation temperature are required in the absorption machine when condensation temperature reach 50°C, obtaining a COP equal to 0.38 in the theoretical cycle.A comparative study respect to single-stage absorption cycles is performed. Efficiency gain of the double-stage solar absorption system, over the single-stage one, will increase with higher condensation temperatures and lower solar radiation values. Single-stage cycles cannot operate for condensation temperatures higher than 40°C using heat from flat plate collectors. For higher condensation temperatures (45°C) the generation temperatures required (105°C) are very high and crystallization occurs. Condensation temperatures able to use in double-stage cycles may be increased until 53°C using heat from flat plate collectors without reaching crystallization.     

Experimental investigation and analysis on a thermoelectric refrigerator driven by solar cells

Experimental investigation and performance analysis on a solar cell driven, thermoelectric refrigerator has been conducted. Research interest focused on testing the system performance under sunshine. Experiment results demonstrated that the unit could maintain the temperature in the refrigerator at 5–10°C, and have a COP about 0.3. Further analysis indicated that the performance of the system is strongly dependent on intensity of solar insolation and temperature difference of hot and cold sides for the thermoelectric module, etc. There exist optimum solar insolation rates, which let the cooling production and COP achieve maximum value, respectively. It was expected that the refrigerator would be potential for cold storage of vaccine, food and drink in remote area, or outdoor conditions where electric power supply is absent.