Browse Topic: Refrigerants
R-1234yf is used in almost every new car sold in the U.S., but the EU is discussing a ban and the industry is investigating alternatives like CO2 and propane. According to its manufacturer, Chemours, use of R-1234yf has grown so much since the refrigerant replaced the long-established R-134a that it's now used in 95% of new cars sold in the U.S. An estimated 220 million cars on global roads are also using it. The problem with R-134a, which came in cars and trucks in the 1990s, is that it's a gas with “a global warming potential (GWP) that is 1,430 times that of CO2,” according to the EPA. Since 2017, EU legislation has banned the use of any refrigerant in new vehicles with a GWP higher than 150. That rule doomed R-134a but opened the door for R-1234yf, which has a GWP of only four. The EU is currently revisiting R-1234yf emissions rules and may ban the substance in a few years. In the U.S., the EPA stands by its use.
The oil circulation rate (OCR) is a deciding factor for the performance of automotive air conditioning systems at both the system and component levels. OCR is defined as the percentage by mass of oil present in a representative sample of oil-refrigerant mixture drawn from the system at steady state. In recent years, many industries are opting for low-OCR compressors, and so the OCR values are getting smaller, making it even more important to be able to accurately measure the OCR in the system. All the different OCR measurement techniques rely on the ASHRAE Standard 41.4 for proper calibration. This standard describes OCR measurement using a sampling technique which involves connecting an evacuated sampling cylinder at the liquid line of the system at steady state to draw a sample containing the liquid mixture of refrigerant and oil. However, several factors such as orientation of sampling cylinder and valve opening speed can affect the OCR results. The flow entering the sampling cylinder initially consists of both liquid refrigerant and liquid oil. As the valve on the sampling cylinder is opened, the refrigerant undergoes flashing followed by recompression and re-condensation of vapor refrigerant, and simultaneous filling up with liquid mixture until pressure equalization between the system supply line and evacuated sampling cylinder is achieved. This two-phase, two-component, phase changing flow is complex, and for the present study, flow visualization using a high-speed camera and analytical tools are used to study the flashing flow of pure refrigerant entering an evacuated sampling cylinder. The obtained results are used to compare with those obtained with oil-refrigerant mixture to shed light on how parameters such as sampling cylinder orientation and valve opening speed can affect the measured OCR values.
As one of the key components of the heat pump system, the electronic expansion valve mainly plays the role of throttling and reducing pressure in the heat pump system. The refrigerant flowing through the orifice will produce complex phase change. It is of great significance to study the internal flow field by means of CFD calculations. Firstly, a three-dimensional fluid model is established and the mesh is divided. Secondly, the phase change model is selected, the material is defined and the boundary conditions are determined. According to the principle of the fluid passing through thin-walled small holes, the flow characteristics of electronic expansion valve are theoretically analyzed. Then the flow characteristics of expansion valve are numerically calculated, and a bench for testing mass flow rate of the expansion valve is built. Then the theoretical value, CFD value and experimental value are compared to verify the correctness of the established three-dimensional fluid model. The flow rate changes of expansion valve are studied under the condition of changing geometric parameters such as the cone angle of the valve spool and the radius of circular arc at the end of the valve seat. According to the momentum theorem, the steady hydraulic force is theoretically deduced. Then the changes of steady hydraulic force are studied under the conditions of different inlet pressure and outlet pressure. At the same time, there also analyzes the effects of the conditions of different valve spool cone angle and valve seat arc radius on steady hydraulic force on the valve spool. Finally, transient analysis is carried out by using dynamic mesh technology. The speed of spool movement is defined by User Defined Function (UDF). Under constant pressure difference conditions, the influence of the spool movement on the hydraulic force and outlet flow of the valve is studied. And the change of the internal pressure field are shown.
The scope of this document is to aid in the selection of hose and hose assembly titles.
Mobile Vehicle Air Conditioning (MVAC) systems are a substantial source of greenhouse gas (GHG) emissions. The use of high-GWP R-134a in MVAC systems contributes a lot to the inflated climate footprint of the segment. In recent years, with the Kigali Amendment in 2016, there has been an increasing push from the regulators in the US and EU to make a shift from R-134a to more climate friendly refrigerants such as olefins (R-1234yf), low-GWP HFCs (R-152a) and carbon dioxide (CO2). In terms of development and demonstration, these alternative technologies have come a long way in the last few years and are almost ready to be implemented. However, barring a few instances, the uptake and deployment-at-scale of these technologies have not really taken place till now in India, and in other parts of the world despite the regulatory push. In this context, this paper will take stock of the challenges in deploying and implementing these technologies at scale, particularly with an eye to domestic realities in India, as well as the ideal policy landscape which can facilitate the mainstreaming of alternative refrigerant technologies.
The automotive application places very special demands on the air conditioning system. As is the case with any other process, system efficiency is very important and the automotive air-conditioning application is no exception. While the characteristics of all the major components in the air conditioning system like compressor, condenser, evaporator and blower contribute to overall system efficiency, localized inefficiencies do play a part and so must be kept to a minimum, especially in this day and age when extra emphasis is being laid on sustainability. One such phenomenon that contributes to the system inefficiency is heat pick-up in suction line. Since the temperature at the evaporator-outlet is quite lower than ambient and also its surroundings (steering system pipes and hoses, engine, air intake pipes and so on), the refrigerant picks up heat as it moves along the suction line up to the compressor inlet. This heat pick-up is detrimental to the overall system performance. Even though most of the automotive HVAC engineers are fairly aware of the undesirable effects of heat pick-up in suction line, many a times the heat picked up in suction line is seen only in terms of °C rise in temperature from evaporator-outlet to compressor-inlet and thus we are not able to visualize or quantify the extent of its impact on other parameters. With the help of case studies, this paper aims at providing a methodology for determining and arriving at the conservative estimate of the impact of heat pick up in suction line on parameters like compressor-outlet temperature, refrigerant mass flow rate, work of compression, refrigeration effect and COP. The results thus obtained provide a greater understanding of the said undesirable effects of heat pick-up in suction line, so that necessary actions could be taken to address the same.
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