جستجوی مقالات مرتبط با کلیدواژه "refrigeration system" در نشریات گروه "مکانیک"

The supply of required cooling energy for building and industrial applications, along with simultaneous efforts to reduce environmental pollution and also reduce electricity consumption and related costs, are a concern that has been considered by researchers for years. Required cold load in most parts of Iran is higher than for heat load. In hot and humid areas where we have to use compression refrigeration systems with high power consumption, it seems more necessary to find alternative methods. In this research, a new design in the form of a cold water cycle in a copper pipe that can be installed on domestic fans has been proposed which can also significantly reduce power consumption and be able to replace the compression cooler in times of moderate temperature. The results showed that in times of moderate heat, this alternative system can be used and create similar cooling conditions with air conditioners and cusses a reduction up to 90% in electricity consumption. Also, the return on investment in this project was calculated for about one year.

Exergy and thermoeconomic analysis is an effective method for determining thermodynamic characteristics and optimizing thermodynamic-economic performance of refrigeration systems. The present study deals with exergy and thermoeconomic analysis of a variable refrigerant flow system with four evaporators used in the dairy industry. A computer code written in EEs software was used for system simulation. Impact of three refrigerants, R502, R1234ze and R134a, on thermodynamic-economic parameters of the system was investigated. In addition to calculation of exergy efficiency of refrigeration cycle for three mentioned refrigerants, effect of evaporation and distillation temperature on system exergy degradation and exergy efficiency of was also investigated. Results showed that R1234ze gas can be appropriate alternative for R502 and R134a gases. Results show that exergy destruction in compressor in reference temperature from 3.974kW for R134a refrigerant increases to 4.221 kW for refrigerant R502. Exergy destruction in the condenser in second level was calculated for all refrigerants. In thermoeconomic analysis, costs of components of variable refrigerant flow system were investigated and total costs for R134a-R502-R1234ze refrigerants were studied. It was observed that a lowest cost is related to R502 refrigerant and total annual cost for or R134a and R1234ze refrigerants are in the next ranks.

In industrial processes, there are many processes that operate below ambient temperature. Usually when these processes demand refrigeration over a very wide temperature range, cascade refrigeration systems are employed. Unfortunately, the cascade refrigeration systems are capital intensive because of major use of installed equipment and large energy requirement in operations. Therefore, the continuing development of new methods to reduce net power and capital costs of refrigeration systems is important in the design of low temperature processes. A recent advancement has been the introduction of mixtures as refrigerants in place of pure refrigerants. In mixed refrigerant cycles, the composition of the mixture can be selected such that the liquid refrigerant evaporates over a temperature range similar to that of the process cooling demand to provide the desired refrigerant characteristics. Small temperature driving force leads to near-reversible operation, thus better thermodynamic efficiency and lower power requirement. Also, a mixed refrigerant cycles feature simpler machinery configuration and fewer maintenance problems. Due to the lack of comprehensive design method for mixed refrigerant cycle, conventional approaches are largely trial-and-error and therefore operations can be far away from optimal conditions. The difficulty in design mainly stems from two aspects: one is the expensive and highly nonlinear nature of computation and the other is the sensitivity of the cycles to the operating changes, especially the change in the composition of refrigerant mixtures and, the suction and discharge pressures of compressor. In this paper, a novel method for comprehensive design of mixed refrigerant cycles is proposed by combined mathematical programming and thermodynamics approach. This method combines the power of thermodynamics and mathematical programming. While the mathematical programming can satisfactorily give the optimal choice of pressures operating conditions and refrigerant compositions, thermodynamics at the same time gives the user insights and confidence in solution. The procedure is demonstrated using a case study of design of two mixed refrigerant cycles for cold section of olefin plant of Tabriz petrochemical complex.