A new low global warming refrigerant, CF3CF=CH2 (HFO‐1234yf), has been developed to replace HFC‐134a in automotive air conditioning systems. HFC‐134a is being phased out in the European Union due to high global warming potential. HFO‐1234yf is highly energy efficient, exhibits low toxicity, and can potentially be used in systems currently designed for refrigerant HFC‐134a with minimal modifications. Significant work has been completed to assess the flammability characteristics of HFO‐1234yf. Though it is flammable per ASTM E‐681, it is significantly less so than HFC‐152a which has also been considered as an HFC‐134a alternative. HFO‐1234yf has a relatively high lower flammability limit at 6.2 vol% in air. Computational Fluid Dynamics (CFD) modeling has shown it is very unlikely the lower flammability limit will be reached when the refrigerant is leaked into the passenger compartment of a vehicle. HFO‐1234yf also has a high minimum ignition energy (MIE) from 5,000 to 10,000 mJ which indicates there may be very few potential ignition sources in a vehicle. It also has very low burning velocity at 1.5 cm/sec indicating low potential for damage should an ignition occur. Several automotive industry groups have completed extensive risk assessments which have concluded HFO‐1234yf is safe to use as a refrigerant in vehicles. This article will review flammability test results and challenges that were overcome to measure flammability of a mildly flammable refrigerant as well as CFD modeling work for vehicle leakage scenarios. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2010

HFO‐1234yf (Hydrofluoro‐Olefin) is a new, low global warming refrigerant developed for automotive air‐conditioning (A/C) systems [Nielsen et al., Chem Phys Lett 439 (2007), 18–22]. It was developed to replace R‐134a, which is being phased out in the European Union because of its high global warming potential (IPCC, Intergovernmental Panel on Climate Change Fourth Assessment Report—Climate Change 2007: Synthesis Report, 2007). HFO‐1234yf is highly energy efficient, exhibits low toxicity, and can be potentially used in direct expansion automotive A/C systems with minimal design modifications. Significant work has been previously completed to confirm the mild flammability characteristics of HFO‐1234yf. To understand the impact of accidental releases of HFO‐1234yf into a garage environment, computational fluid dynamics (CFD) modeling was used to simulate releases of HFO‐1234yf under various A/C line rupture scenarios. In particular, releases were simulated using a leak source in a calm open area, a room with no forced ventilation and the same space but impinging on a flat plate. The refrigerant concentration was determined as function of distance (x, y, and z directions) from the leak point during leak event. The size and shape of the portion of the refrigerant plume above the lower flammability limit was also determined. This work enforces the benefit of using the inherently safer practice of minimization of refrigerant quantities. This article will review CFD modeling results for given refrigerant leak scenarios. © 2010 American Institute of Chemical Engineers Process Saf Prog, 2011

This article provides an overview showing the value of CFD for the study of explosions. Although computational fluid dynamics finds a great deal of use in solving very complex problems, its value is not limited to complex problems. Many relatively simple problems can be solved quickly and economically with the use of CFD. The intent of this article is to show industry the possibilities that exist for improving safety when the physics of explosions are better understood.