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Due to the consensus on energy conservation and environmental protection in the international community, and considering the environmental protection and thermophysical properties, R290 has great advantages as an alternative working fluid compared with R22 in the field of air conditioner and heat pump. In the promotion process of the R290 air source heat pump (ASHP), the potential safety hazard caused by flammability can be controlled, but effective control methods are needed to ensure the reliability of the low-temperature heating process. In this paper, a new modified control strategy (MST) was proposed for R290 ASHP. The experimental results showed that the lubricating oil discharged from the compressor with MST was 10.55g less than the original control strategy (OST). In addition, when the temperature judgment condition for starting to adjust the opening of MST was 4°C, the performance was improved (using the MST) by about 1%. Whether from the point of view of reducing the discharge of lubricating oil from the compressor or the storage of refrigerant in the compressor and accumulator, the MST can effectively eliminate the oil blockage, thus improving the reliability of the heat pump system, while having beneficial impacts on the performance of the R290 heat pump.

Propane has been suggested as one of the alternative working fluids for room air conditioners in hot climate areas because of its excellent environmental properties and lower discharge temperature though there still is concern about its flammability. The lubricating condition of rotor bearings system should also be emphasized because a heavier load and lower viscosity in the oil sump could impair the reliability of rotary compressor under high ambient temperature. In this study, in order to obtain the input of simulation, the dynamic pressures and viscosity of a R290 air conditioner are experimentally measured under several conditions. On these bases, lubricating characteristics are numerically simulated by coupling the dynamics equation of crank shaft and the modified Reynolds equation of oil film using finite element method. The results show that the load on crank under 50 °C is twice as large as that of 30 °C while the viscosity of bottom oil sump decreases from 1.89 to 1.59 mPa⋅s. Simulation results imply that the minimum oil film thickness decreased to 0.44 µm under 50 °C, in which asperity contact force peaks at 3 N when arithmetic mean roughness is 0.2 µm. Asperity contact force would significantly increase to 174 N if surface roughness is 0.6 µm and boundary lubrication regime is reached. Strategies to increase oil sump viscosity is recommended to avoid adhesive wear in this case.

With the extensive use of room air conditioners, their refrigerants have a greater impact on the environment. Among many alternative refrigerants, R290 is environmentally friendly and energy-saving. Furthermore, the dynamic characteristics of R290 split room air conditioners are different from those of HFCs and HCFCs air conditioners. In previous research of R290 split room air conditioners, abnormal system parameters frequently occurred in heating and defrosting process. In this paper, the abnormal phenomena are determined to be caused by the oil blockage of throttle component. Especially, the failure often leads to safety problems of air conditioner. In addition, the abnormal phenomena of a R290 split room air conditioner was reproduced in the enthalpy difference chamber. The influence factors of the failure were studied experimentally and the experimental results showed that the oil blockage of EEV are mainly affected by the working conditions, the type of lubricating oil and the opening of EEV, which will provide experimental basis for further mechanism analysis and solution.

At present, a variety of lubricating oils are available for R290 room air conditioners (RACs). R290 is highly miscible with mineral oils (MOs), while it is partially miscible with some alkylene oils (PAGs). In this paper, the oil retention behavior of a 1.5 HP R290 RAC with two miscible MOs and two partially miscible PAGs was studied. Firstly, the OCR of a R290 rotary compressor with PAG VG60 or MO VG100 was measured in compressor performance test platform, and it was 0.66–0.88%. Then the oil retention and its mass distribution within the RAC using PAG VG60 or MO VG100 were measured by Remove and Weight Technique (RWT) and Mix and Sample Technique (MST). And then, the oil retention when using PAG VG40 or MO VG56 was measured by RWT for further comparison. Results showed that the oil retention was 1.9–8.2 g, only 0.79%–3.9% of the total oil quantity. The oil mass in heat exchangers was nearly proportional to the local refrigerant mass, while that in gas line was greatly affected by the viscosity grade of oil. It was verified that the miscibility effect of the R290/PAG mixture was mild on this R290 RAC, and the viscosity grade of oil was the most critical parameter for the oil retention in the gas line.

Propane (R290) has been considered as one of the alternatives for air conditioner system because of its zero ODP, low GWP and favourable thermo-physical properties. In this paper, experiments were conducted to investigate the dynamic characteristics and to evaluate the safety issues during the startups of a R290 room air conditioner under various outdoor ambient temperatures. Results indicate that the sub-atmospheric suction pressures occurred and lasted during the cold startup in heating mode under an extreme lower ambient temperature, which were potential hazards due to the high flammability of R290. Moreover, if air conditioner started with a smaller EEV opening and the compressor reached higher frequency much earlier, minimum suction pressures drastically declined. As soon as air conditioner started, almost all of liquid R290 stored in outdoor heat exchanger was drawn into accumulator in tens of seconds and some R290 accumulated in the cold compressor shell within a few minutes, resulting in the “starved” outdoor heat exchanger and “enriched” compressor. Additionally, the superheated R290 at EEV inlet greatly influenced the refrigerant supply to low pressure side, which retarded the increase of suction pressure.

Portable monitors such as MicroPEM can accurately characterize personal exposure of pollutants, which is critical for linking exposure and health effects of air pollution. The RTI (RTI International, Research Triangle Park, NC, USA) MicroPEM V3.2A provides both real-time fine particulate matter (PM2.5) concentrations and time-integrated PM samples collected onto Teflon filters that can be used to correct real-time data as well as allow further lab chemical analysis of species on filters (e.g., metal, black carbon). Due to the optical reflectivity of local PM sources can be very different from available standard reference particles used for calibration by RTI, there is a need for gravimetric correction and validation at each study location. However, assessments of MicroPEM have been limited in locations with severe air pollution, such as Beijing. We selected a variety of weather and air quality conditions, including both clear and hazy days in Beijing, to compare PM2.5 data among MicroPEMs as well as between MicroPEM and other types of samplers. We also compared MicroPEM real-time PM2.5 concentrations with data from nearby fixed-sites. The results show MicroPEM performed well across a wide range of PM2.5 concentrations (6–461 μg/m3) and MicroPEM data, after gravimetric correction, were consistent with those from moderate-volume samplers. Good agreement was also found between real-time data from MicroPEM and fixed-site data. The present study covered a wide range of pollution levels in actual environments and validated the usage of MicroPEM as a PM2.5 monitor in locations with elevated PM2.5 levels.

Considering the importance of the laser wavelength response and the difficulty in its real-scenario measurement in WMS, a high-accuracy and universal method was developed to characterize the relative wavelength response (RWR) by analyzing the laser current response. A coupling term that depends on both the current scan and the modulation characteristic was introduced to describe the coupling effect between the wavelength scan and modulation. The accuracy of the proposed method was verified with different laser working conditions and scan waveforms. All fitting residuals of the RWR result from the proposed method are smaller than 0.1% of the total scan range and the fitting residual of the ramp scanned WMS is twice smaller than the minimum value from literature. The better calibration-free 2f/1f fitting and more accurate CO2 concentration results also suggest the high accuracy and superiority of the proposed method. Finally, based on the precise prediction of RWR with small scan and modulation indices, the spectral parameters, including line strength and self-collisional broadening coefficient, of CO2 transition at 6976.2026 cm−1 were successfully measured using WMS.

The absorbance is of great importance in the tunable diode laser absorption spectroscopy (TDLAS) as it contains information of both gas properties and spectroscopic parameters. A novel, calibration-free wavelength modulation-direct absorption spectroscopy (WM-DAS) is proposed and experimentally verified in this two-part paper. This method combines the capability of absorbance measurement from DAS and the advantages of enhanced noise rejection and high sensitivity from WMS. In this Part I, we focus on the full theoretical basis and procedures of this method from the following three aspects: the high-accuracy characterizations of laser frequency and intensity, noise rejection ability by extracting the characteristic spectra through the fast Fourier transform (FFT) of the light intensity, and the simultaneous fitting strategy for both baseline and absorbance. The preliminary validation experiment of CO transition at 4300.6999 cm−1 in a static gas cell shows the high accuracy of the proposed method.

Ignition-delay times of syngas mixtures (H2/CO/O2/Ar) were measured using a shock tube in the following conditions: temperatures of 910–1290 K, pressures of approximately 1.0 atm, an equivalence ra...

The southwestern mountains of Hainan Island are the southernmost region with tropical karst landform in China. The frequent alternation of dry and wet seasons leads to the loss of the mineral nutrients of limestone, creating karst fissure habitats. Plants living in karst fissure habitats for long periods of time have developed local adaptation mechanisms correspondingly. In the paper, hydrogen–oxygen stable isotope technology was applied to determine the water-use sources of Impatiens hainanensis in the dry and wet seasons, hoping to expound the adaptation mechanism of I. hainanensis in karst fissure habitats to the moisture dynamics in the wet and dry seasons. In the wet season (May to October, 2018), the air humidity is relatively high in the I. hainanensis habitat, in the dry season (November 2018 to April 2019), there is a degree of evaporation. In the wet season, fine-root biomass increases with soil depths, while coarse-root biomass decreases with soil depths, in the dry season, fine-root biomass is lower and coarse-root biomass is higher compared with the wet season. It was found that the average rainfall reached 1523 mm and the main water-use sources were shallow (0–5 cm) and middle (5–10 cm) soil water, epikarst water, and shallow karst fissure water during the wet season, the average rainfall reached 528 mm, and the deep (10–15 cm) soil water and shallow karst fissure water were the main water-use sources during the dry season. Fog water has a partial complementary effect in the dry season. The differences in the distribution of root biomass and each source of water in the wet and dry seasons of I. hainanensis also reflect the different water-use strategies of I. hainanensis in the wet and dry seasons. In both dry and wet seasons, I. hainanensis formed a water-use pattern dominated by soil water and shallow fissure water (0–15 cm) under the influence of the “fissure-soil-plant” system in the karst region.

We report temperature and hydroxyl (OH) concentration measurements in methane/air premixed flat flames based on ultraviolet (UV) broadband absorption spectroscopy (BAS) of the OH electronic transitions ( X 2 Π - A 2 Σ + ). The temperature and OH mole fraction distributions were obtained at different heights above the burner for various equivalence ratios ( ϕ = 0.6, 0.7, 0.8, 0.93, and 1.06). The results agreed well with computational fluid dynamics (CFD) simulations using the AramcoMech 1.3 skeletal mechanism, which verifies the BAS measurement accuracy. For stable flames ( ϕ = 0.6, 0.7, and 0.8), the root-mean-square differences above the flat flames were all less than 16 K for the temperature and 150 ppm for the OH mole fraction. The BAS results also agreed with tunable diode laser absorption spectroscopy (TDLAS) measurements with a root-mean-square temperature difference of 31.5 K. Experimental and theoretical analysis demonstrates that the UV BAS OH detection limit is more than two orders of magnitude lower than that for infrared (IR) TDLAS, and the OH BAS temperature sensitivity is much higher than that for most line pairs in TDLAS measurements. These advantages make the UV BAS method an accurate method for combustion diagnostics, with more accurate temperature and OH concentration than IR TDLAS.

CO2 containing plasmas are of growing interest for greenhouse gas remediation and dry gas reforming. In this paper, we show that the optical emission spectrum of CO(B-A) transition can be used for gas temperature determination in CO2 containing plasmas. The study was performed in a packed-bed reactor and compared with previously published results for a MW discharge. The CO emission is mainly produced by direct electron excitation from ground state CO. The rotational temperature is determined by a fitting algorithm of the CO(B-A) (0-1) spectrum and the accuracy of the deduced rotational temperature is shown to be better than 30 K. Meanwhile, we also compared the results with the widely used Boltzmann plots of the CO(B-A) (0-1). The rotational lines corresponding to Q(18–24) yield accurately the gas temperature for spectra with a resolution in excess of 0.05 nm FWHM. Rotational lines with N

As a viable alternative for HCFCs and HFCs in the refrigeration and air conditioning industry, R290 has obvious advantages in aspects of environmental protection and thermal properties. At present, the application of R290 in air source heat pumps (ASHPs) is still in the stage of exploration and promotion. In this paper, the dynamic behaviors of an R290 ASHP were experimentally investigated during defrosting process, and an experimental platform of an R290 ASHP system was built to conduct defrosting experiments in a multifunctional enthalpy-difference laboratory. The variation of pressure and temperature of main components and the refrigerant status in the accumulator during defrosting process are shown in this paper. Experimental data was analyzed by combining the physical characteristics of R290, and the dynamic characteristics under three different working conditions were compared. The defrosting time of the three working conditions was 420 s, 435 s and 865 s respectively. In addition, there was a point M that the temperature difference between the inlet and outlet of outdoor heat exchanger (ODHE) approached zero at 370 s of condition II. The results and analysis of this research can provide effective guidance for improving the reliability of R290 ASHPs.

In the defrosting process, it is not that the larger the opening of throttle valve is, the better for defrosting. Especially in the defrosting process of R290 heat pump, too small opening or large opening will affect the defrosting performance, and even cause oil blockage. In this paper, the defrosting characteristics of an R290 air source heat pump (ASHP) with different throttle valve opening are studied. The experimental results show that the defrosting duration will increase with the increase of the throttle valve opening. In addition, when the throttle valve opening was 120, oil blockage occurred in defrosting process, while when the opening was 480, oil blockage occurred in startup of reheating process. The factors that affect the reliability of R290 ASHP in heating-defrosting operation include not only the migration of lubricating oil, but also the thermal inertia of the system after defrosting process. In the defrosting process of R290 ASHP, the selection of throttle valve opening is very important for its safety and reliability under the heating-defrosting condition. The results of this paper will provide an effective guidance for the selection of throttle valve opening of R290 ASHP in defrosting process.

The operation of R290 air conditioners at cold ambient temperatures can lead to sub-atmospheric suction pressures, risking the safety and reliability of such air conditioners. In this study, the effects of several system control strategies on the startup characteristics were investigated, with the goal of avoiding vacuums in air conditioners. The variations in the degrees of superheating and the changes in the flow patterns at key points were analyzed. The refrigerant migrations and pressure variations indicated that owing to the higher initial temperatures in a warm startup, the heat inertia of the compressor and indoor heat exchanger contributed to the formation of liquid refrigerant at the expansion valve inlet, as well as an increase in the suction pressure. Moreover, using larger initial expansion valve openings or a bypass tube between discharge and suction could increase the minimum suction pressures, by providing more R290 refrigerant to the low-pressure side at the beginning of startup.

As an alternative refrigerant for HCFCs, R290 has been gradually applied in commercial refrigerators and humidifiers because of its excellent environmental and thermodynamic properties. The application of R290 in room air conditioner (RAC) is still in the stage of promotion. Abnormal failure of throttle component in heating and defrosting process frequently occurred during developments of R290 RACs. In this paper, the mechanism of abnormal failure of electronic expansion valve (EEV) of a R290 RAC during heating-defrosting process was experimentally investigated in enthalpy-difference laboratory. The compressor and system pipeline were visualized and a viscometer was performed to measure the variation of viscosity in oil sump. The experimental results showed that the EEV failure in the startup stage of heating process, was caused by oil blockage. The oil blockage was mainly caused by much more oil and lower temperature at after-throttling during defrosting and heating-defrosting mode conversion process. The results and analysis of this research can provide an effective guidance for alleviating and eliminating the throttle component failure and improving the reliability of R290 RACs.

Ratios of the 2nd and 1st harmonics at the line center are very sensitive to absorbance, but not to line profiles when the modulation index is set to 0.94. Based on this characteristic, we proposed a method which uses the 1st and 2nd harmonics to measure the absolute absorbance, and then obtain gas pressure and concentration. Some transitions of CO2 and H2O molecules near 6980 cm−1 are selected to verify this method. The satisfactory agreement between measurement results and theoretical values validates the proposed method.

The measurement of absolute densities of reactive species and radicals such as OH is of growing interest for many plasma applications. In this paper, we extend the use of a self-absorption model for atomic emission spectroscopy to molecular emission spectroscopy. The proposed analysis of self-absorbed molecular emission spectra is a simple and inexpensive method to determine OH(X) densities and rotational temperatures compared to laser induced fluorescence. We compare the recorded absolute OH density in a non-equilibrium diffuse atmospheric-pressure RF glow discharge by this method with broadband UV absorption considering a number of rotational lines with J' ≤ 6.5, the detection limit of the line integrated OH(X) density with this method is of the order of 2 × 1019 m−2. The accuracy of the density is sensitive to the rotational temperature of the OH(A) state and the non-equilibrium rotational population distribution.

The measurement of absolute densities of ubiquitous OH radicals and gas temperatures in water containing plasmas has recently drawn a lot of attention. In this paper, we extend the self-absorption model introduced in Du et al 2016 Plasma Sources Sci. Technol. 25 04LT02 with a description of the excited state by a superposition of two Boltzmann distributions to take the non-thermal rotational distribution of the excited state into account. This technique is applied to a diffuse He + H2O RF discharge and it is shown that in addition to the determination of the ground state OH density and rotational temperature, the properties of the excited state OH(A) can also be simultaneously determined. A model of the steady-state distribution of the hot and cold group density of OH(A) is able to describe the dependence of the rotational population distributions of the excited state as a function of the water concentration. The method is also applied to a filamentary Ar + H2O DBD. While the non-homogeneous nature of the DBD leads to complications, the production of OH(A) by multiple production mechanisms leading to a complex nascent rotational population distribution causes the fitting procedure of the emission spectrum (with self-absorption) to break down.