Effect of initial temperature on explosion characteristics of 2, 3, 3, 3–Tetrafluoropropene

Highlights

• Explosion characteristics of R1234yf under various ambiences were investigated.

• P_max decreased with the temperature rise while the (dP⁄dt)_max and S_L increased.

• P_max, (dp⁄dt)_max, and S_L increased first and then declined with rising concentration.

• Elevated temperature led to a larger flammable range in experiments and simulations.

Abstract

The flammability of refrigerants is a major cause of refrigerant explosion incidents. Studying the explosion characteristics of refrigerants at different initial temperatures can provide significant benefits for solving the safety problems of refrigerants under actual working conditions. This paper studied the effects of the initial temperature and refrigerant concentration on the explosion characteristics of refrigerant 2, 3, 3, 3-tetrafluoropropene (R1234yf) at 0.1 MPa. The curves of explosion characteristics with different initial temperature revealed the same variation trend ranged from 25 °C to 115 °C. Specifically, as the refrigerant concentration was raised, the peak overpressure, the maximum rate of pressure rise, and laminar burning velocity increased initially and decreased afterwards, along with maximum values at the refrigerant concentration of 7.6%. When the refrigerant concentration was 7.6%, the peak overpressure declined exponentially with the initial temperature rise, while the maximum rate of pressure rise increased linearly. The laminar burning velocity calculated from the spherical expansion method indicated that the flame propagation was gradually accelerated by the increase of initial temperature, which coincided with the change of the maximum rate of pressure rise. Meanwhile, experiments and CHEMKIN simulation results demonstrated the effects of elevated temperature from 20 °C to 50 °C on the explosion limits of R1234yf. The lower explosion limit reduced and the upper explosion limit increased with rising initial temperature. In general, R1234yf exhibited moderate combustion and lower explosion risk, compared with traditional refrigerants.

Introduction

With the continuous development of society and living standards, air conditioners and refrigerators have become very common in our daily life. The constantly increasing demand for refrigerants inevitably leads to a rapid increase of refrigerant production. However, numerous new refrigerants are flammable hydrocarbons or hydrofluorocarbons, which have potential explosive risks and have caused many refrigerant explosion incidents in factories and residential buildings over the past few years. On January 9, 2013, two workers were killed by a violent explosion at the Hong Kong Fuan Garden Hotel of China because of a refrigerant leakage (Refrigeration Express, 2013). On March 19, 2013, four workers were injured when a refrigerant packaging plant exploded in Pekin, Illinois, USA, (ACR News, 2013). On June 22, 2015, a refrigerant explosion occurred at a factory in Dongguan City, China, and 11 workers in the workshop were injured by the shockwave (Dongguan Municipal People's Government, 2015). On March 7, 2016, an explosion occurred at a residence in Kentucky, USA, when highly flammable isobutylene and propane refrigerants leaked from a refrigerator (The Expert Institute, 2016). According to the statistics, there were nine incidents caused by the explosion of air-conditioning refrigerants in China from 2016 to 2018, resulting in six deaths and nine injuries. Therefore, a comprehensive study of the safety properties of refrigerants, including explosion characteristics and flammability, may help to prevent explosion incidents.

Zhang et al. (2015) tested the explosion pressure and the maximum rate of pressure rise of difluoromethane (R32) and propane (R290) through a 20 L sphere under various concentrations. The variation of the explosion pressures of R290/air with initial temperature from 25 °C to 150 °C and initial pressure from 0.03 MPa to 0.12 MPa in a closed container was investigated by Razus et al. (2010). Yu et al. (2019) delved into the explosion limit of chlorodifluoromethane (HCFC-22) at an elevated pressure of 1 MPa, and found that the flammable range was significantly larger than that at 0.6 MPa. Papas et al. (2017) determined the laminar burning velocities of R32, a binary mixture of R32/R1234yf, and R290/R1234yf with air at a stoichiometric concentration. Takizawa et al. (2009) and Minor et al. (2010) assessed the flammability of R1234yf. Kondo et al. (2011) measured the explosion limits of R1234yf under different pressure with and without the ammonia addition. Askar et al. (2018) studied the effect of ignition energy on the lower explosion limit of the refrigerant. The results showed that the minimum ignition energy of R1234yf was higher than that of R32 when the flame propagates at the lower explosion limit, which indicated that the explosion probability of R1234yf was lower.

R1234yf is a new synthetic refrigerant with lower Global Warming Potential (GWP), zero Ozone Depletion Potential (ODP), mild flammability, and similar thermodynamic properties to 1,1,1,2-tetrafluoroethane (R134a), a type of unsaturated fluorinated olefins. R1234yf is considered as an alternative to traditional chlorofluorocarbons (CFCs) refrigerants in the field of vehicle refrigeration system (Babushok and Linteris, 2017; Li et al., 2019a, ). The molecular structure of R1234yf is shown in Fig. 1. Further comparisons of the main physical properties between R1234yf, R134a, difluorochloromethane (R22), and 1,1-difluoroethane (R152a) are listed in Table 1. Of the above four refrigerants, R1234yf has the best environmental protection performance, while the safety of R1234yf is not satisfactory due to its inherent flammability.

Researchers have focused on the physicochemical properties of R1234yf regarding its thermodynamic performance, toxicity, environmental impact, materials compatibility, oil compatibility and so on (Mylona et al., 2019; Rangel-Hernández et al., 2019). In contrast, few studies were implemented on the explosion characteristics of R1234yf. From previous studies, the explosion characteristics of combustible gas are closely related to the environment, such as temperature, pressure, and vessel size, which are markedly varied with different conditions. Some researchers have conducted the research on the effect of initial pressure on gas explosion in vessel or pipe. Wang et al. (2013) established a connected container device composed of a 22 L spherical vessel, a 113 L spherical vessel, and a linked pipeline, so as to test the explosion pressure of methane. They found that the peak overpressure increases with raising initial pressure whether in an isolated state or a connected state. Similar experiments were adopted to analyze hydrogen explosion, which revealed a linear relationship between the peak overpressure and initial pressure at the adjacent large vessel when the ignition position is in the smaller vessel (Zhang et al., 2017). Zhen et al. (2017) and Ma et al. (2020) indicated that the promotion effect of initial pressure on the peak overpressure is greater in a closed explosion than in a vented explosion, and the increase of vacuum degree restrains the peak overpressure in the dumping vessel. Zhang et al. (2020a, found that the rising initial pressure enhances the explosion severity of hydrogen in the spherical vessel. Shen et al. (2019) observed that the hydrogen flame propagation in a closed duct tends to be milder with decreasing initial pressure. Moreover, N₂ and CO₂ can inhibit the propagation of hydrogen/air premixed flame and methane/hydrogen/air premixed flame (Zhang et al., 2019, , 2020b).

Fig. 2 shows a typical refrigeration process of R1234yf. When refrigerants are used in a normal working cycle, especially in the compression unit and throttle expansion unit, they experience periodic temperature changes. Studying the effect of temperature on the explosion characteristics of R1234yf is significant in evaluating the intrinsic safety of refrigerants and determining the explosion hazard in the refrigeration process. This paper aims to research the explosion characteristics and flammability of R1234yf through a 20 L sphere under various concentrations and initial temperatures. Furthermore, the laminar burning velocities and explosion limits of R1234yf at different temperatures were predicted by the spherical expansion method and CHEMKIN simulation, respectively. The results obtained were used to enrich the material data of R1234yf and guide the public to properly choose refrigerants from a safety perspective.