Charge optimisation of a solar milk chiller with direct current compressors

In view of promoting the utilization of solar photo-voltaic energy for milk chilling application a custom designed milk chiller with DC compressors was fabricated. Two different DC compressors were used operating with HFC-134a and HC-600a refrigerants to ascertain the performance of HFC and HC refrigerants when used in solar powered application. In view of optimizing the performance of both refrigerants, charge optimization was experimentally carried out for both refrigerant circuits. The optimum charge was obtained based on the maximum coefficient of performance and exergy efficiency. When comparing ice formation and coefficient of performance, the HC-600a refrigerant circuit was lower than that of HFC-134a circuit. It was also observed that the total exergy destruction experienced was maximum in the HFC-134a circuit than that of the HC-600a circuit. The magnitude of exergy destruction was found to be maximum in the compressor and then followed by the condenser, evaporator and finally the capillary for both refrigeration circuits. This study showed an efficient way for using the solar power for operating a milk chiller with DC compressors and with ice bank tank to avoid the dependency on batteries.

Simulation and Validation of a Two-Phase Pumped Loop Cooling System

Two-phase refrigerant pumped loop cooling systems have seen wider use in recent years because of higher power density electronics and the need for increased heat transfer capability. However, two-phase systems are difficult to model because they operate in a closed-loop and both liquid and vapor phases exist and change with time throughout the system. A two-phase “test-bed” system was constructed in order to explore the various operating regimes and limitations of this technology. Additionally, physical results from this test-bed were used to determine if the system performance could be accurately modeled using a commercially available software package such as SINDA/FLUINT. The refrigerant circuit uses R134a as the cooling fluid that is pumped around a complete loop using a positive displacement pump. Heat is added at the evaporator using ceramic heaters on the outside of the housing that boils the fluid, resulting in a liquid/vapor mix in the transport tube. Heat is removed at the condenser which is a commercial flat plate heat exchanger that uses building water for cooling. A closed-loop fluid-thermal model of the test-bed was created in Thermal Desktop®, which is the pre and post-processor for the SINDA/FLUINT analyzer, and compared to several tests conducted on the physical system at varying heat loads. The model successfully predicted the system performance after adjustments to the model for refrigerant mass charge and condenser performance. The maximum difference between the measured evaporator temperature and the modeled temperature was only 6.1°F; which occurred at the highest heat input level (1400 Watts). Explanations for differences between model and test results will be discussed. In particular, modeled system temperatures were found to have a very non-linear sensitivity to the total refrigerant mass charge.

Stand-Alone Battery Thermal Management for Fast Charging of Electric Two Wheelers—Integrated Busbar Cooling

This paper presents a thermal interface for cylindrical cells using busbar-integrated cooling channels. This interface is available due to the use of a stand-alone refrigerant circuit for the thermal management of the battery. A stand-alone refrigerant circuit offers performance and efficiency increases compared to state-of-the-art battery thermal management systems. This can be achieved by increasing the evaporation temperature to the requirements of the Li-ion cells and the use of alternative refrigerants. The solution proposed in this paper is defined for electric two-wheelers, as the thermal management of these vehicles is currently insufficient for fast charging where high heat losses occur. Three channel patterns for the integrated busbar cooling were examined regarding their thermal performance to cool the li-ion cells of a 16p14s battery pack during fast charging. A method of coupling correlation-based heat transfer and pressure drop with thermal finite element method (FEM) simulations was developed. The symmetric channel pattern offers a good compromise between battery temperatures and homogeneity, as well as the best volumetric and gravimetric energy densities on system level. Average cell temperatures of 22 °C with a maximum temperature spread of 8 K were achieved.

Mathematical Simulation of the Thermodynamic Processes Associated with the Vapour-Injected Scroll Compressor

Both the major energetic crisis and the global warming, which influence the worldwide economy and the future of the society, determine the development of energetic and ecological performances of both the refrigeration equipment and air conditioning systems. Thus, there is a worldwide supported effort made in order to decrease the carbon dioxide emissions resulted from the burning of fossil fuels and the other greenhouse effect gas emissions. This article presents a refrigeration system design model using a vapour injection scroll compressor and tube in tube evaporators working with refrigerant R407C. The refrigerant circuit comprises of a main evaporator, a secondary evaporator (for the injection process), scroll compressor, condenser and five expansion valves. Furthermore it uses R407C as refrigerant. The secondary refrigerant for both the main and the secondary evaporator is a 50% concentration solution of propylene-glycol and water. Secondary circuit comprises of a pump, an electric boiler, an expansion vessel and a by-pass circuit made of many stop valves. The condenser is cooled with mains water.

Study of Ground – Water Heat Pump Parameters during 3 Years of Operation

The manuscript presents results of a 3 years experiment, concerning in the monitoring of working parameters of a ground – water heat pump with horizontal collectors. The measured working parameters of the refrigerant circuit are: evaporating pressure, condensing pressure, superheating temperature, discharge temperature, sub cooling temperature. There were also measured the flow rate and the temperatures on the heating circuit of water and on the horizontal collectors circuit with antifreeze. The methodology of data processing, described in the manuscript, allowed calculation of evaporating temperature and condensing temperature, based on measured corresponding pressures. The main obtained results consist in a complete set of working and performance parameters and their variation in 3 years of operation. Details are presented for operating conditions characteristic for different cases: middle of heating season, end of heating season, middle of non-heating season, beginning of heating season. Some practical conclusions of the study are also presented in the manuscript. It was indicated how the outside temperature is influencing the values of working and performance parameters, but mainly on the effective number of running periods.

Performance Study of a Solar Adsorption Refrigeration System

This paper presents the simulation of a solar-powered continuous adsorption air-conditioning system with the working pair of silica gel and water. In order to make the adsorption system more suitable to use solar energy to supply cooling continuously during daytime, a new adsorption system without refrigerant valves is being developed in SJTU recently. By using this system, the problem such as pressure drop along refrigerant circuit can be resolved. The frequent switches of refrigerant valves can also be omitted. The daytime long simulation results (ranging from 6:00 to 18:00) demonstrate that the solar-powered adsorption system can supply a fairly steady cooling output all the time. Based on the results, parametric study is also undertaken to optimize the design.