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The enrichment of low concentration coalbed methane using adsorption process with activated carbon adsorbent was studied in this work. Adsorption isotherms of methane, nitrogen and carbon dioxide on activated carbon were measured by volumetric method, meanwhile a series of breakthrough tests with single component, binary components and three components feed mixture has been performed for exploring dynamic adsorption behaviors. Moreover, a rigorous mathematical model of adsorption bed containing mass, energy, and momentum conservation equation as well as dual-site Langmuir model with the Linear driving force model for gas–solid phase mass transfer has been proposed for numerical modeling and simulation of fixed bed breakthrough process and vacuum pressure swing adsorption process. Furthermore, the lumped mass transfer coefficient of methane, nitrogen and carbon dioxide on activated carbon adsorbent has been determined to be 0.3 s−1, 1.0 s−1 and 0.06 s−1 by fitting the breakthrough curves using numerical calculation. Additionally, a six bed VPSA process with twelve step cycle sequence has been proposed and investigated for low concentration coalbed methane enrichment. Results demonstrated that the methane molar fraction in feed mixture ranged from 10% to 50% could be enriched to 32.15% to 88.75% methane in heavy product gas with a methane recovery higher than 83% under the adsorption pressure of 3 bar (1 bar = 105 Pa) and desorption pressure of 0.1 bar. Energy consumption of this VPSA process was varied from 0.165 kW·h·m−3 CH4 to 0.649 kW·h·m−3 CH4. Finally, a dual-stage VPSA process has been successfully developed to upgrade a low concentration coalbed methane containing 20% methane to a target product gas with methane purity higher than 90%, meanwhile the total methane recovery was up to 98.71% with a total energy consumption of 0.504 kW·h·m−3 CH4.

In this paper, a model of activated carbon was established by molecular simulation and the separation performance of N2 and CH4 on activated carbon was studied. In order to evaluate the adsorption selectivity and diffusion selectivity of N2 and CH4, Grand Canonical Monte Carlo and molecular dynamic methods were used to obtain equilibrium adsorption isotherms and mean square displacements of N2 and CH4 on activated carbon with different pore sizes. Research results showed that the difference in adsorption isosteric heat of N2 and CH4 at the pore size of 0.46 nm is the largest, which is 5.759 and 7.03 kcal·mol−1 (1 cal=4.184 J), respectively. Activated carbon with pore size of 0.46 nm has the best N2 and CH4 adsorption selectivity, while its diffusion selectivity is not obvious.

Tetrafluoromethane (R14) is an important fluid in three-stage-cascade refrigeration and mixed-refrigerant Joule-Thomson refrigeration (MJTR). In this work, an experimental investigation on condensation pressure drop of R14 in a horizontal smooth tube with inner diameter of 4 mm was carried out. Experiments were implemented at mass fluxes from 150 to 650 kg/(m2 s), saturation pressures from 1 to 3 MPa and heat fluxes from 8.3 to 28.2 kW/m2 over the entire range of vapor quality. The effects of heat flux, mass flux, saturation pressure and vapor quality were analyzed and discussed. In addition, the frictional pressure drops were compared with twenty-nine well known frictional pressure drop correlations. An improved frictional pressure drop correlation was deduced and predicted R14 experimental data well with a mean absolute relative deviation of 12.18%. Finally, 2317 data points from nineteen published literature were adopted to evaluate the predictive ability of this new model. It achieves a satisfactory predicting result with a mean absolute relative deviation of 17.39% and 87.26% of the experimental data within the deviation bandwidth of ±30%.

Waste heat sources such as flue gas generate large temperature span during recovery process. In order to improve the temperature match with such waste heat sources, a novel absorption refrigeration system with continuous-temperature-changing generation process is proposed. Internal heat recovery process is introduced to both the generator and absorber, and a premixer is added to take the place of the solution heat exchanger in traditional system. A numerical model of the system is built, in which the continuous-temperature-changing generation process is simulated based on a stripping column with heat input at each stage. New parameters are defined and optimized to strengthen the internal heat recovery process, and thus to improve system efficiency. Simulation results show that the system can operate under a large waste heat temperature span of 67.5 K, almost twice of the conventional system. With the evaporation temperature, waste heat inlet temperature, and cooling water temperature at −15 °C, 150 °C and 20 °C, respectively, a maximum COP of 0.93 and exergy efficiency of 49.7% is acquired while the waste heat temperature span is 60 K, showing that the system can acquire larger utilization rate of waste heat with higher system efficiency.

An experimental investigation on flow condensation heat transfer characteristics of tetrafluoromethane (R14) in a horizontal smooth tube with inner diameter of 4 mm was carried out. Experiments were implemented at mass fluxes from 200 to 650 kg/(m2 s), saturation pressures from 1 to 3 MPa and heat fluxes from 8.3 to 28.2 kW/m2 over the entire range of vapor quality. The effects of saturation pressure, mass flux, heat flux and vapor quality were analyzed and discussed. In addition, R14 experimental data were compared with fifteen well-known flow condensation heat transfer correlations. Based on the comparison result and experimental data, an improved flow pattern-based heat transfer correlation was proposed and predicted R14 experimental data well with a mean absolute relative deviation of 6.26%. Finally, 1370 data points from nine published literature were adopted to evaluate the predictive ability of this new model. It achieves a satisfactory predicting result with a mean absolute relative deviation of 20.04% and 77.61% of the experimental data within the deviation bandwidth of ±30%.

Among district heating technologies, gas-fired boiler has difficulty in recovering flue gas waste heat and conventional heat pump has poor performance at low ambient temperature. In the present work, a novel gas-fired absorption heat pump is proposed. High-grade sensible heat and low-grade latent heat of the flue gas is recovered in the solution preheater and intermediate evaporator successively. Moreover intermediate evaporation and absorption processes are introduced, and the intermediate pressure is adjusted according to the ambient temperature, to improve the system adaptability in cold regions. Simulation results show that the coefficient of performance (COP), primary energy efficiency and exergy efficiency are 1.69, 1.39 and 54.5% when the evaporation, supply and return water temperature are −15, 55 and 35 °C, respectively. The COP of the proposed system has 13% and 20% improvement compared to those of the single-effect absorption system with and without waste heat recovery. Furthermore, the proposed system has energy saving potential of 11.7% and 39.6%, and payback time of 2.9 and 2.5 years compared to the single-effect absorption heat pump and the gas-fired boiler, respectively. The proposed system is suitable to provide 50 kW close range district heating for a typical urban residential building, especially in cold regions.

The absorption refrigeration system driven by low grade heat sources, especially the waste heat sources, becomes more and more attractive in recent decades. However, most traditional absorption systems cannot achieve a high utilization rate of the waste heat with limited heat capacity. These systems are usually designed to obtain heat in the generator, which means that the waste heat sources cannot be utilized to the temperature lower than the generator temperature. This paper proposed a new structure heated by heat conduction oil in the generator and electric heating rings around the stripping section. This structure can simulate the temperature-distributed heat sources when the electric heating rings work. It can also simulate a traditional generator when the electric heating rings do not work. Influences of different heat distributions are analyzed in detail in this paper. The results show that the heat sources utilization rate will increase with the increase of the heat in the stripping section, while the coefficient of performance will be negatively affected by the increasing heat in the stripping section. By optimizing the heating structure, the coefficient of performance can be similar to that of a traditional system when the heat is just added in the middle and lower part of stripping section. The optimum utilization rate of heat sources in this test model can reach 1.8 times to that of a traditional system. Under this heating model, the lowest temperature required in the heating section is 82 °C when the heat conduction oil inlet temperature is 169 °C. It is much lower than the temperature inside the generator, which is 137.3 °C.

In this paper, a detailed experimental study was carried out to investigate the two phase flow patterns of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation pressures from 0.215 to 0.415 MPa, mass fluxes from 67 to 194 kg m−2 s−1 and heat fluxes from 10.6 to 75.0 kW m−2. Based on high speed camera, four main flow regimes can be identified: plug flow, stratified-wavy flow, slug flow and annular flow. Intermittent flow (include plug and slug flow) to annular flow transition was detected and plotted on flow pattern map. Comparisons between available intermittent/annular (I/A) transition lines in the literature and the experimental data have been made. The result shows that no transition equations can fit the experimental transition curve well. By taking the surface tension, gravity force, heat flux, viscosity and density into account, four dimensionless number were introduced into the transition equation. Finally, a transition equation of intermittent/annular flow for R600a was proposed and shows good agreements with the experimental data.

This study aims to investigate the sensitivity of bubble sample size during the saturated nucleate boiling of ethane. Experiments were conducted on a horizontal flat surface, under pressures of 0.15, 0.2, and 0.3 MPa with heat fluxes varying from 14.27 kW m−2 to 81.22 kW m−2. Mathematical tools like statistical analysis were used for the standardized study on boiling. Sequential analysis and random sampling were conducted to investigate the sensitivity of bubble sample size. The trend in which parameters changed with sample size was observed. The relative deviation ( e ) was within ±10%, ±5%, and ±2% for sample sizes of 40, 95, and 215, respectively. The analytical results could provide reference to establish uniform standards in the boiling field. In addition, common statistical analysis was performed to examine the data distribution characteristics of bubble departure diameters. The Gauss function was evaluated as the best fitted probability distribution function. Data distribution changed with heat flux and pressure. The experimental results have a direct and substantial contribution to the boiling area.

An ammonia–water absorption refrigeration system with a novel generator structure driven by temperature-distributed heat sources to increase the utilization rate of waste heat is presented. The stripping section of the distillation column and generator were replaced by a generator with temperature-distributed heat sources. The heat sources were distributed throughout the entire process in the generator, so the mass and heat transfer were coupled at different temperatures, which increased the waste heat utilization at low temperatures. Compared with a traditional system, temperature–distributed heat sources increased the utilization temperature range. In the simulation of the system, the condition at cold end kept unchanged while the heating distributions and quantity inside the generator were changed. The performance of the new generator driven by temperature-distributed heat sources was analyzed while compared with a traditional system through the coefficient of performance, separation efficiency and waste heat utilization.

Heat transfer and pressure drop for two-phase flow are closely related to corresponding flow patterns. In this work, an experimental investigation on adiabatic and condensation two-phase flow patterns and their transitions of tetrafluoromethane (R14) in a horizontal tube with inner diameter of 4 mm was conducted. Experiments were implemented at mass fluxes from 200 to 650 kg/(m2 s), saturation pressures from 1 to 3 MPa and heat fluxes from 8.2 to 28.2 kW/m2. The observed adiabatic flow patterns were compared with six well-known flow pattern maps, none of them can predict all the transition lines accurately. Therefore, a new dimensionless number S1, which takes account of inertia force, gravity force, shear force and surface tension force, was proposed to develop the new adiabatic flow pattern transition criteria. Eight groups of data were compared with the new adiabatic flow pattern map, most of the flow pattern data can be accurately predicted. What’s more, in order to explain the effect of heat flux on condensation flow pattern transitions, another new dimensionless number S2 was proposed by combining the dimensionless number S1 and boiling number together. Finally, a condensation flow pattern map was proposed based on the dimensionless number S2.

In order to cover long-term but small quantity liquid nitrogen requirements of laboratory or field users, a miniature movable mixed-refrigerant liquid nitrogen generator (MRLN) was developed and tested here, based on a precooled mixed-refrigerant J-T (MRJT) refrigerator. With the full air-cooled, skid-mounted structure, this MRLN was built utilizing off-the-shelf refrigeration components like commercial single-stage oil-lubricated compressors to reduce construction cost greatly. Bottled pure N2, pressure swing adsorption (PSA) unit and mini cryogenic rectification column could be employed to supply N2 in different operation modes respectively. In pure N2 mode, N2 was directly liquefied by the MRJT refrigerator. With feed N2 at 0.8 MPa, the specific power consumption (SPC) was 1.79 kWh L−1, and figure of merit (FOM) was 6.27%. The estimated SPC in PSA mode was 2.68 kWh L−1. For column mode, the SPC was 4.59 kWh L−1, with FOM of 3.38%. A closed N2 cycle could convey cooling capacity between flammable refrigerant and air. This MRLN could be a convenient and low-costing choice for some liquid nitrogen users.

In order to meet increasingly stringent emission regulations and fuel economy requirements, the high efficient clean combustion and emission control technologies for internal combustion engine were developed rapidly in recent years. Among them, the development of basic combustion science and new combustion modes such as homogeneous compression combustion (HCCI), premix compression combustion (PCCI), low-temperature combustion (LTC), and reactive controlled compression combustion (RCCI) plays a vital role in improving the combustion and emission performance of engines.

Considering to the importance of hydrogen peroxide (H2O2) in a number of pathological processes and fluorescence sensor as a powerful tool for imaging and therapy of H2O2-related diseases, herein, a n ear-infrared fluorescent sensor for c olorimetric and r atiometric detecting H2O2 and viscosity, named NCR, was constructed and reported. Its long emission wavelength (670 nm) avoids the interference of biological autofluorescence. When NCR interacted with 10 equiv. of H2O2, colorimetric characteristic provides a clear naked eye recognition (colourless turned to green under UV light and light purple turned to colorless under visible light). In addition, NCR shows high sensitivity to viscosity with or without the addition of H2O2. It was also found alkaline environment contribute to enhance fluorescence response to H2O2. A suitable water-octanol partition coefficient (logP, 0.521 ± 0.003) and low cytotoxicity displayed that NCR is very favorable to image living cells. Furthermore, exogenous and endogenous H2O2 was detected successfully by NCR in living Hela cells. These studies indicate that NCR has great potential to develop as a practical tool for monitoring H2O2 level in biological process.

Methane (R50) and ethane (R170) are the dominated components of natural gas and the important components in mixture refrigerants for the mixture Joule–Thomson refrigeration cycle. In this a...

Recently, considerable attention has been given to new environment-friendly refrigerant mixtures for applications such as heat pumps and air conditioners. This study presents flow boiling heat transfer characteristics of environment-friendly refrigerant mixture of R1234ze(E)/R600a (0.148/0.852, 0.194/0.806, 0.371/0.629, 0.623/0.377 and 0.797/0.203 by mole fraction) in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were conducted at saturation pressures from 0.215 to 0.415 MPa, mass fluxes from 67 to 194 kg m−2 s−1 and heat fluxes from 10.6 to 74.8 kW m−2. The influences of concentration, saturation pressure, mass flux and heat flux on heat transfer were analyzed and discussed. Furthermore, the experimental data were also compared with nine well-known flow boiling heat transfer correlations. The results indicated that correlation of Liu and Winterton (1991), which is the correlation for pure fluids, gives the best fit to the experimental data with a mean relative deviation of 18.2%. Finally, a new heat transfer correlation based on power-additive model was proposed and two suppression factors Smix and Fmix were introduced into the new correlation by taking account of mass transfer resistance. The new correlation makes great progress in the prediction accuracy with a mean relative deviation of 6.4%.

Thermodynamic design and analysis of small scale liquid nitrogen generators based on mixed-refrigerant Joule–Thomson cycle (MR JT) are illustrated in this paper, providing low-cost choices for remote and field users. Bottled pure nitrogen, PSA unit or mini air separation column are utilized in different processes, with feed gases liquefied in the MR JT refrigerators driven by single-stage compressors. Problems in the application of low pressure gas source and mini column are investigated, including column simplification, air liquefaction in flammable MR JT, etc. System exergy analysis is conducted. For pure N2 at 8.0 bar, specific power consumption (SPC) of 0.53 kWh L−1 and figure of merit (FOM) of 24.46% are achieved. With PSA unit, SPC is 0.85 kWh L−1. In the process with column, a closed N2 cycle is employed to deliver cooling capacity from flammable mixed-refrigerant to air. Optimal SPC of 0.84 kWh L−1 and FOM of 19.96% are reached.

Considerable attention has recently been given to the new environment-friendly refrigerant of R1234ze(E) for applications such as heat pump and air-conditioning systems. In this study, an experiment was carried out to investigate two-phase flow patterns and flow transitions for R1234ze(E) in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation pressures from 0.215 to 0.415 MPa, mass fluxes from 130 to 258 kg/m2 s and heat fluxes from 10.6 to 74.8 kW/m2. The influences of saturation pressure, mass flux and heat flux on flow pattern transition were analyzed. Six well-known flow maps have been compared with the observed flow patterns of R1234ze(E). The results indicated that none of them can predict all the flow pattern transitions well. Thus, three dimensionless numbers K1, K2 and K3 which represent the ratio of the evaporation momentum force to the inertia force, the evaporation momentum force to the surface tension force, and the shear force to the gravity force respectively were introduced. Based on dimensionless numbers K1, K2, K3 and Xtt, a new flow pattern map for R1234ze(E) was proposed which could accurately predict the experimental data.

This study presents flow boiling heat transfer and pressure drop characteristics of R1234ze(E) in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were conducted at saturation pressures from 0.215 to 0.415 MPa, mass fluxes from 130 to 258 kg m−2 s−1 and heat fluxes from 10.6 to 74.8 kW m−2. The influences of saturation pressure, mass flux and heat flux were analyzed. Furthermore, the performance of R1234ze(E) was compared with R600a. The results show that heat transfer coefficient and pressure drop of R600a are larger than R1234ze(E). Several well-known correlations were evaluated and the results indicate that the correlation of Fang (2013) and Yang et al. (2017) give the best fit to the heat transfer coefficient and pressure drop respectively. Finally, a new heat transfer correlation was proposed and it makes great progress in the prediction accuracy.

An experimental investigation on condensation flow pattern and heat transfer coefficient of methane/ethane mixtures (0.27/0.73, 0.54/0.46 and 0.7/0.3 by mole) in a horizontal smooth tube with inner diameter of 4 mm was carried out. The tests were conducted at saturation pressure of 1.5–2.5 MPa with mass flux of 98–257 kg m −2 s −1 and heat flux of 15.1–44.4 kW m −2 over the entire vapor quality range. The effects of concentration, saturation pressure, heat flux, mass flux and vapor quality were analyzed and discussed. A new annular/non-annular flow pattern transition criteria on condensation for zeotropic mixtures was carried out. The new transition criteria took the influence of mass transfer resistance into consideration and had satisfactory predictive ability in present study. Moreover, the experimental data were compared with many condensation heat transfer correlations of mixtures. An improved heat transfer correlation for zeotropic mixtures based on flow patterns was proposed. The new correlation combined with the equilibrium method and introduced a new correction factor ( F m ). It achieves better predicting results with a mean absolute relative deviation of 8.02%.

As a critical facility, spiral-wound heat exchanger (SWHE) has been widely used in many industrial applications. A computational fluid dynamics (CFD) model was employed with the smallest periodic element and periodic boundary conditions to examine the characteristics of the shell side of SWHE. Numerical simulation results show that the heat transfer coefficients around the tube initially increase and subsequently decrease with radial angle because of the influence of backflow and turbulent separation. The mean absolute deviation between simulated heat transfer coefficients and measured values for methane, ethane, nitrogen and a mixture (methane/ethane) is within 5% when Reynolds number is over 30000. For the pressure drop, the simulated values are smaller than the measured values, and the mean absolute deviation is within 9%. Numerical simulation results also indicate that the pressure drop and heat transfer coefficients on the shell side of SWHE decrease as the winding angle of the tubes increases. Considering the effect of winding angle on pressure drops and heat transfer coefficients, the modified correlations of Nusselt number N u = 0.308 R e 0.64 P r 0.36 ( 1 + sin θ ) − 1.38 and friction factor f = 0.435 R e − 0.133 ( sin θ ) − 0.36 , are proposed. Comparing with the experimental data, the maximum deviations for heat transfer coefficients and pressure drops are less than 5% and 11% respectively.

In this work, a facile hemicyanine-naphthalene-based fluorescent sensor for colorimetric and ratiometric sensing of pH was constructed via a simple synthesis process. Significantly, sensor 3 showed a high sensitivity to extremely alkaline solution and had a notably large Stokes shift (145 nm). Its absorbance and fluorescence enhanced or quenched obviously in the pH range of 5.0–12.0, accompanying with colour change. In addition, the fluorescence intensity increased 727-fold (F440/F710) when the pH was adjusted to 12, indicating that sensor 3 showed great potential in the detection of extremely alkaline solution.

With the growing concern of environment problems, there are urgent demands for environment-friendly refrigerants in the refrigeration industry. As a natural refrigerant, R600a not only has zero ozone depletion potential and quite low global warming potential, but also has better cooling performance than other refrigerants. Due to its good cooling performance and environment-friendly characteristics, R600a has been used as an alternative refrigerant in heat transfer applications such as refrigerators, freezers, and heat pumps. It is known that accurate prediction of two phase flow pattern transition and frictional pressure drop of R600a in a horizontal tube play an important role in design and optimization of refrigerators, freezers, and heat pumps. According to this issue, a detailed experimental study was carried out to investigate the two-phase flow pattern transition and frictional pressure drop characteristics of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation temperature from 282.4 to 304 K, mass fluxes from 67 to 194 kg/(m2 s). Based on a high speed camera, four main flow regimes can be observed: plug flow, stratified-wavy flow, slug flow and annular flow. The flow map of R600a has been drawn and comparisons between the experimental data of flow patterns and transition lines in the literature have been made. The results showed that with the increase of mass flux, the inception of the annular flow regime occurs earlier. The intermittent flow regime takes place over a narrow range of vapor quality and annular flow regime occupies a wide range of vapor quality. In addition, the trend of Barbieri and Ong and Thome I / A transitions lines are consistent with the experimental data. However, both of them overestimate the inception of the annular flow regime. After taking the influence of vapor inertia, liquid viscous and surface tension forces into account, a modified Weber number We * has been introduced to the new flow pattern transition model. Based on the relationship of X tt and We *, a new correlation has been proposed and it can well fit with the experimental data of flow pattern. Furthermore, a detailed discuss of frictional pressure drop of annular flow and non-annular flow has been made. The results indicated that frictional pressure drop increases with the increases of vapor quality. The tendency of frictional pressure drop presents different the changing laws in different flow regime. The frictional pressure drop increases slowly in the non-annular flow regime while it increases rapidly when the flow pattern turns into the annular flow regime. The reason is that the vapor-phase pressure drop often dominates the total two-phase frictional pressure drop. The annular flow regime owns higher void fraction than the non-annular flow regime. Nine classic prediction correlations of pressure drop were evaluated and the results showed that the correlation of Gronnerud and Muller-Steinhagen and Heck give the best fit to the experimental frictional pressure drop of annular flow and non-annular flow with a mean absolute relative deviation of 38.5% and 19.7% respectively.

Boiling heat transfer exists in many industrial heat exchangers such as the evaporator of the refrigerator and the air conditioner, the reboiler of the chemical equipment and steam generator of the nuclear reactor. In the process of boiling, bubble movement can speed up the heat transfer between liquid and solid, leading to the improvement in heat transfer efficiency. Traditional refrigerants used in the industrial facilities have serious environmental problems, therefore, new substitutes are needed. Hydrocarbons are good alternatives. Ethane was suggested as one component of a mixed- refrigerant for its zero ozone depletion potential, low global warming potential and high thermodynamic properties. Therefore, it is important to investigate the bubble behavior of ethane in saturated nucleate pool boiling to design and optimize the industrial equipment like evaporator, improve natural gas liquefaction technology, and research characteristics of heat transfer and multiphase flow as well. Although there are a lot of researches on the heat transfer characteristics of pool boiling, the research on the bubble behavior in ethane is still lacking. In this paper, visualization experiments on the pool boiling heat transfer characteristics of ethane were carried out at 0.2 MPa. The heat fluxes varied from 14.65 kW m−2 to 80.79 kW m−2. Boiling occurred on the upward facing side of a smooth vertical copper cylinder with 20 mm diameter, connected to a DC power supply to control the heat flux on the surface. The measured roughness of the surface was 68.1 nm (root mean square average of the height deviations) and 50.7 nm (the arithmetic average of the absolute values of the surface height deviations). Acquisition of the temperature and pressure was accomplished by using a Keithley 2700 and six thermocouples. The experimental apparatus has a steel ruler inside the pool as the reference length to measure the bubble sizes and the maximum uncertainty for length measurement is 0.060 mm. Some conclusions can be drawn. (1) According to the change of diameter with time, the growth process was divided into three stages. The bubble growth process has obvious segmentation characteristics, and piecewise prediction models are recommended. (2) The bubbles in boiling pool exhibit the characteristics of axial symmetry and uneven distribution; the shape of separation of ethane bubbles has ellipsoidal and irregular shapes relative to normal temperature liquids. (3) There were trail changes and additional movements of large bubbles. Compared to normal temperature liquids, the trail changes were relatively simple; and the bubbles are bubbly and slug flow of two flow regimes. (4) System pressure, heating wall properties like surface roughness, liquid properties like contact angle and surface tension have an important influence on bubble behavior. This paper suggests that the heat transfer prediction equation should consider them.

In recent years, due to the environmental issues, suitable substitutes are being searched to replace the traditional chlorinated refrigerants. With zero ozone depleting potential, low global warming potential and high thermodynamic performance, the hydrocarbons are suitable selections in refrigerators and heat pump systems. As hydrocarbons, R50 and R170 are also the important parts of the natural gas and often-used components in mixture refrigerants for the low-temperature Joule-Thomson refrigerator. As the flow characteristics play important parts in the design and optimization of the heat exchangers in refrigerators and air-conditioning systems, the two-phase frictional pressure drop should be well examined and analyzed. Although there are massive experimental studies on two-phase frictional pressure drop of hydrocarbons in horizontal tubes, the published experimental investigations for zeotropic mixtures of R50/R170 are rare. Therefore, it′s desirable to conduct an experimental investigation on two-phase frictional pressure drop of zeotropic mixtures of R50/R170 in a horizontal tube and find a suitable correlation. In this paper, two-phase frictional pressure drop of R50/R170 mixtures (0.27:0.73, 0.54:0.46 and 0.7:0.3 by mole) was studied experimentally in a horizontal tube with inner diameter of 4 mm. The tests were carried out at saturation pressures from 1.5 MPa to 2.5 MPa for mass fluxes from 99 kg m−2 s−1 to 255 kg m−2 s−1, vapor qualities from 0 to 0.9. The uncertainty for the pressure drop was 40 Pa and the uncertainties for the vapor quality with a 95% confidence interval were less than 11.74% under the employed operation conditions. The effects of mass flux, saturation pressure, vapor quality and concentration on two-phase frictional pressure drop were examined and analyzed. Some conclusions can be drawn that (1) the frictional pressure drops increase with the increasing mass flux and the impact becomes more obvious when the vapor quality increases; (2) the frictional pressure drops decrease with the increasing saturation pressure and the impact enhances when the vapor quality increases; (3) the frictional pressure drops increase with the increasing vapor quality and then change to be smooth even decline at high vapor qualities. And the effect of vapor quality enhances as the mass flux increases and the saturation pressure decreases; (4) the frictional pressure drops of pure R50 are lower than that of all R50/R170 mixtures and the frictional pressure drops of the initial concentration of R50/R170 mixtures at 0.27:0.73 are also lower than that of other two initial concentrations of R50/R170 mixtures. Their differences are not obvious at low vapor qualities, while the differences enhance when the mass flux and vapor quality increase as well as the saturation pressure decreases. The influence of concentration may be mainly related to the difference of the vapor densities. In addition, the experimental data were compared with twenty well-known frictional pressure drops correlations. The comparison results showed that the Friedel correlation showed the best agreement with a mean absolute relative deviation of 19.26% and 87.45% of points in the deviation bandwidth of ±30%.

In this work, bubble departure diameters and bubble departure frequencies on saturated nucleate pool boiling of methane were studied. The experiments were conducted on the upper surface of a smooth vertical copper cylinder, at pressures of 0.15 MPa, 0.2 MPa, 0.3 MPa and 0.4 MPa with heat fluxes varying from 10.64 kW m−2 to 79.25 kW m−2. Bubble departure diameters were measured from the images captured by a high-speed digital camera at lower heat fluxes less than 79.25 kW m−2, at which isolated bubbles were obtained. Bubble departure frequencies were calculated by counting the numbers of the detachment bubbles and the corresponding time intervals. Their relationship with Jacob number (Ja) was analyzed. With an increase in Ja at a given pressure, bubble departure diameter increases while bubble departure frequency tends to decrease. After the comparisons with six most used correlations for bubble departure diameter, a new correlation was developed within ±20% deviation from most of the experimental data. Additionally, a new correlation for the relationship between bubble departure diameter and departure frequency was also proposed within ±20% deviation from most of the experimental fDd2.

Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in throttling process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.

A detailed experimental study was carried out to investigate the flow boiling heat transfer and pressure drop characteristics of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation pressures from 0.215 to 0.415 MPa, mass fluxes from 67 to 194 kg m −2 s −1 and heat fluxes from 10.6 to 75.0 kW m −2 . Based on an high speed camera, four main flow regimes can be observed: plug flow, stratified-wavy flow, slug flow and annular flow. Intermittent to annular flow transition was detected and plotted on flow pattern maps. Comparisons with available transition lines in the literature have been made. Furthermore, the influences of saturation pressure, mass flux and heat flux on heat transfer coefficient were analyzed. The experimental data was compared with the calculated data of seven well-known correlations. The results indicated that, the correlation of Liu and Winterton showed the best agreement with a mean absolute relative deviation of 11.5%. For two-phase frictional pressure drop, mass flux had obviously positive effect on frictional pressure drop, while negative effect was found for saturation pressure. Eight correlations were evaluated and the correlation of Muller-Steinhagen and Heck gave the best fit to the experimental data with a mean absolute relative deviation of 32.9%. A new correlation of pressure drop which accounted for the influence of surface tension and gravitational force was developed on the basis of Muller-Steinhagen and Heck correlation and its mean absolute relative deviation was about 16.6% for the experimental data.

An experimental investigation of two-phase flow patterns and their transitions for R170 in a horizontal smooth tube was presented. The tests were conducted at various saturation pressures from 1.5 MPa to 2.5 MPa for different mass fluxes from 100 kg m−2 s−1 to 250 kg m−2 s−1 over the entire vapor quality range. The effects of mass flux and saturation pressure on two-phase flow pattern transitions were investigated and analyzed. The physical properties of velocity, viscosity and surface tension are important to the flow pattern transition criteria under our experimental conditions. Several two-phase flow pattern maps in horizontal tubes were compared with the experimental data. Finally, a new flow pattern map for R170 in a horizontal tube based on the Kim et al. (2012) map was carried out.

In recent years, due to the environmental problems of traditional chlorinated refrigerants, it has become an urgent task to search for suitable substitutes. Hydrocarbons, with zero ozone depleting potential, low global warming potential and high thermodynamic performance, are good alternative refrigerants in refrigerators and heat pump systems. In addition, hydrocarbons also the important parts of the natural gas. As one kind of hydrocarbons, ethane and its mixtures have been widely applied in the mixed refrigerant throttling refrigeration systems and recommended to be used in the cascade refrigeration systems to replace R13 and R503. As the heat transfer characteristics of ethane play important parts in the design of the heat exchangers in refrigeration cycles, the heat transfer coefficients during condensation should be well examined and analyzed. Although there are massive experimental studies of heat transfer on flow condensation of hydrocarbons in horizontal tubes, the published experimental investigations for ethane are rare. Therefore, it’s desirable to conduct an experimental investigation on condensation heat transfer of ethane in a horizontal tube and find suitable correlations. In this paper, condensation heat transfer of ethane was studied experimentally in a horizontal tube with inner diameter of 4 mm. The heat transfer test section was a copper plate (100 mm× 20 mm× 200 mm) embedded twelve four-wire PT100 platinum resistance thermometers. Using the assumption of two-dimensional heat conduction for the copper plate, both the wall temperature and heat flux could be obtained. The tests were carried out at saturation pressures from 1.01 MPa to 2.56 MPa for mass fluxes from 100 kg/(m2 s) to 257 kg/(m2 s) and vapor qualities from 0 to 0.8. The uncertainties for the heat transfer coefficient with a 95% confidence interval were less than 3.33% under the employed operation conditions. The effects of mass flux, vapor quality and saturation pressure on condensation heat transfer coefficient were examined and analyzed. Some conclusions can be drawn that (1) in relative high mass fluxes and vapor qualities, the condensation heat transfer coefficients increased with the increasing mass flux and vapor quality while decreased with the increasing saturation pressure; (2) in relative low mass fluxes and vapor qualities, the vapor quality, mass flux and saturation pressure had a little influence on condensation heat transfer coefficients. In addition, the experimental data were compared with nine well-known correlations of condensation heat transfer coefficient. The comparison results showed that Chato (1962) correlation and Wang et al. (2002) correlation relatively agreed well with the experimental data with the mean absolute relative deviations less than 35%. The other correlations showed larger predicted results than the experimental data with the mean absolute relative deviations more than 55%. And the Chato correlation and Wang et al. correlation were both in good agreement with the relative low heat transfer coefficients rather than the relative high heat transfer coefficients.

Condensation heat transfer and pressure drop of R170 were studied experimentally in a horizontal tube with inner diameter of 4 mm. The tests were conducted at saturation pressures from 1 MPa to 2.5 MPa, mass fluxes from 100 kg (m2∙s)−1 to 250 kg (m2∙s)−1 and average heat fluxes from 55.3 kW m−2 to 96.3 kW m−2 over the entire vapor quality range. The effects of vapor quality, mass flux and saturation pressure on condensation heat transfer and pressure drop were examined and analyzed. The experimental data were compared with various well-known correlations of condensation heat transfer coefficient and pressure drop. The comparison results showed that Koyama et al. correlation agreed with the experimental heat transfer coefficient with a mean absolute relative deviation less than 25%, and the Yan and Lin correlation can accurately predict the experimental pressure drop with a mean absolute relative deviation less than 18%.

The thermodynamic comparison of small mixed-refrigerant J-T (MRJT) and gas expansion (Kapitza cycle) LN2 generators are conducted by the exergy method in this paper. Both of two types are employed for low pressure N2 liquefaction and air separation (< 9.0 bar). Pure N2, PSA units or cryogenic air separation columns are used for LN2 production. The MRJT type is driven by single-stage compressors. It is indicated that the efficiency of MRJT type is higher than Kapitza type. With pure N2 at 8.0 bar, the figures of merit (FOM) of MRJT and Kapitza types are 26.86% and 12.79%, respectively. With mini air separation columns, the FOM of MRJT and Kapitza types are 21.42% and 11.34%, respectively. The large exergy losses in the compressor unit and non-isentropic expansion are the main reasons of the inferior efficiency of the Kapitza type. In addition, the Kapitza type requires larger total compressor displacement than the MRJT type. The MRJT type is recommended to be used in small LN2 generators.

Despite being efficient means of district heating, conventional single-effect absorption heat pumps suffer significant performance deterioration at low ambient temperatures. To solve this problem, an ammonia-water absorption heat pump prototype with intermediate process is designed and built. It utilizes both low-grade heat from the ambient and exhaust heat from natural gas combustion, through the evaporator and intermediate evaporator, respectively. To perform comparison study, the prototype also has the single-effect mode. Experimental results indicate that when the evaporation temperature is 0 °C, the prototype with intermediate process can provide 30 kW heating capacity to heat the water in sequence through the rectifier, condenser and absorber, from 34.24 to 55.09 °C, and the coefficient of performance and primary energy efficiency are 1.66 and 1.28, respectively. When evaporation temperatures reduce to −5, −10 and −15 °C, the coefficient of performances are 1.51, 1.40 and 1.28, respectively, reaching 77%–90% of the simulation values under corresponding working conditions. Compared to the conventional single-effect system, the prototype with intermediate process performs better at lower evaporation temperature, with the coefficient of performance improved by 11%. By replacing the original heat exchangers, the proposed system can be easily applied to the existing heat networks based on gas-fired boilers to improve energy efficiency, and the favorable experimental performance proves that it is a more efficient way of residential district heating, especially in cold regions.

Chloride (Cl-), a primary anion in the extracellular fluid, plays an important role in a variety of physiological and pathological processes, such as cell apoptosis and proliferation. However, the information about Cl- in cancer cell apoptosis and chemoresistance is poorly understood. In the present study, we found that temozolomide (TMZ) treatment led to a decrease in intracellular concentration of Cl- ([Cl-]i) in both U87 and TMZ-resistant U87/R glioma cells. The decrease in [Cl-]i was more noticeable in U87 cells than in U87/R cells. Moreover, the expression of LRRC8A was reduced in U87/R cells compared with U87 cells. LRRC8A downregulation inhibited TMZ, induced the decrease in [Cl-]i and abolished the difference of [Cl-]i between U87 cells and U87/R cells. Knockdown of LRRC8A using small interfering RNA attenuated TMZ-induced U87 cell growth inhibition and apoptosis, while overexpression of LRRC8A by adenoviral infection enhanced the effect of TMZ on U87 and U87/R cell viability and apoptosis. Furthermore, LRRC8A downregulation inhibited TMZ-induced mitochondria-dependent apoptosis, including elevated Bcl-2 expression, reduced Bax expression, cytochrome c release, and caspase nine and caspase three activation. On the contrary, upregulation of LRRC8A augmented the activation of mitochondria-dependent apoptotic pathway in U87 and U87/R cells. In conclusion, this study demonstrates that LRRC8A potentiates TMZ-induced glioma cell apoptosis via promoting mitochondria-dependent apoptosis, suggesting that LRRC8A can be represented as a novel target for drug resistance treatment in glioma cells.

Three miniature Joule-Thomson cryogenic coolers and a testing set up were built to investigate the cooling performance in this work. Shell-and-tube heat exchanger and plate fin heat exchangers with rectangular micro channels were designed to achieve high specific surface area. The main processing technology of micro mixed refrigerant cooler (MMRC) was described. The design and fabrication processing of the plate fin heat exchangers were also described. The new developed micro plate-fin type heat exchanger shows high compactness with the specific heat surface larger than 1.0x104 m 2 /m 3 . The results of experimental investigations on miniature mixed refrigerant J-T cryogenic coolers driven by a Mini-Compressor were discussed. The performance evaluation and comparison of the three coolers was made to find out the features for each type of cooler. Expressions of refrigeration coefficient and exergy efficiency were pointed out. No-load temperature of about 112 K, and the cooling power of 4.0W at 118K with the input power of 120W is achieved. The exergy efficiency of the SJTC is 5.14%.

The hydrocarbons and its mixtures are suitable for environment-friendly refrigerant alternatives because of their good environmental criteria and high thermodynamic performances. Based on the experimental results of the hydrocarbon mixtures, a correlation was developed earlier by Zou (2010) to predict saturated flow boiling heat transfer coefficients inside horizontal smooth tubes. In this article, the proposed correlation is extended to predict evaporation of some more mixtures (such as R50/R170) inside a horizontal tube by evaluating the mixture factor for that fluid. The comparisons of the present model and other classic models with the previous experimental data are made to evaluate the mean deviation for the hydrocarbon mixtures. It reveals that the new model is better to predict the flow boiling heat transfer for the hydrocarbon mixtures.

In this work, the entire pool boiling curve of tetrafluoromethane (R14) under 0.1 MPa was experimentally acquired on a horizontal copper surface, and the nucleate boiling, critical heat flux (CHF) point, transition boiling, Leidenfrost point (the minimum film boiling point) and film boiling were observed. In the nucleate boiling regime, boiling heat transfer data and bubble images depicting the boiling behavior at different heat fluxes were obtained from the measurements. The measured heat flux at the CHF point is 220.39 kW m−2, and the corresponding surface superheat temperature is 16.1 K. The measured CHF data were also compared to several existing correlations, including the Bailey and Lienhard & Dhir correlations, both of which show good agreement. We also measured the boiling heat transfer data in the transition and film boiling regimes. The measured heat flux and surface superheat temperature of the Leidenfrost point were 126.83 kW m−2 and 87.1 K, respectively.

Comprehensive heat transfer coefficient and pressure drop data of the two-phase saturated flow boiling for propane were obtained in a smooth horizontal tube at conditions covering mass fluxes from 62 to 104 kg m−2 s−1, heat fluxes from 11.7 to 87.1 kW m−2, and saturated temperatures from −35.0 to −1.9 °C. Results indicate that heat transfer coefficients increase with mass and heat flux. For saturation temperature and vapor quality, distinct variation trends were observed depending on different test conditions. The heat transfer experimental data were compared with five well-known correlations. Among those, Liu–Winterton correlation shows the best agreement with a mean absolute relative deviation less than 10%. For two-phase frictional pressure gradients, the influences of saturation temperature, mass flux and vapor quality were also presented. The predicted method of Muller-Steinhagen & Heck correlation gives the best fit to the data with a mean absolute relative deviation less than 20%.

Thermal design shows significant effects on energy conversion efficiency, lifespan and beam quality of high-power laser diode arrays (HPLDAs). In this study, a slot jet array heat sink (SJAHS) is designed to improve the cooling performance of HPLDAs, and numerical simulations were conducted to optimize the flow and heat transfer in the heat sink. Flow passages inside the heat sink ensured that the coolant is allocated to every jet uniformly. The jet geometry is optimized to enhance the heat transfer. When the working fluid is assumed as water at 293 K inlet temperature and at a flowrate of 800 mL/min, the heat sink is capable of removing 150 W heat over an area of 15 mm2 with a maximum temperature increase of 52.75 K from the coolant inlet to emitters. It means that the emitter-to-coolant thermal resistance is 0.35 K/W without considering the interface thermal resistance. The corresponding pressure drop is 361 kPa. Compared with the existing microchannel heat sink, the numerical results implied that this new heat sink possesses a better cooling performance.

An experimental study on the saturated flow boiling heat transfer for a binary mixture of R290/R152a at various compositions is conducted at pressures ranging from 0.2 to 0.4 MPa. The heat transfer coefficients are experimentally measured over mass fluxes ranging from 74.1 to 146.5 kg/(m2·s) and heat fluxes ranging from 13.1 to 65.5 kW/m2. The influences of different parameters such as quality, saturation pressure, heat flux, and mass flux on the local heat transfer coefficient are discussed. Existing correlations are analyzed. The Gungor-Winterton correlation shows the best fit among experimental data for the two pure refrigerants. A modified correlation for the binary mixture is proposed based on the authors’ previous work on pool boiling heat transfer and the database obtained from this study. The result shows that the total mean deviation is 10.41% for R290/R152a mixtures, with 97.6% of the predictions falling within ±30%.

Saturated flow boiling heat transfer coefficients in a horizontal tube of the binary mixtures of R170/R290 were measured. The experiments were performed at three different mixture compositions and various saturation pressures from 0.35 to 0.57 MPa. The results were obtained over the mass fluxes ranging from 63.6 to 102.5 kg m−2 s−1 and heat fluxes ranging from 13.1 to 65.5 kW m−2. The influences of quality, saturation pressure, heat flux and mass flux on the heat transfer characteristic were examined and discussed. The flow pattern of mixture was shown and the transitions of flow pattern occur at higher mass flux and quality for mixtures than for pure substance. A modified correlation was developed based on the previous research of our group on the pool boiling heat transfer and the database obtained from this study. The comparison of the experimental heat transfer coefficient with the predicted value using the present correlation shows that the total mean deviation is 15.97% for R170/R290 mixtures.

Objective To study ultra-early pathophysiological changes of rabbit acute lung injury (ALI) caused by paraquat (PQ) and discuss the ultra-early protective effect of ulinastatin on rabbit ALI due to PQ. Methods 30 New Zealand white rabbits were randomly divided into a control group, a paraquat group and an ulinastatin intervention group with 10 rabbits in each group. For paraquat group and intervention group a single dose of paraquat (35mg/kg) was injected intraperitoneally to establish rabbit models of ALI. The control group was injected an equal volume of saline. The intervention group was treated with 100Ku/kg ulinastatin immediately after the establishment of the ALI model. The respective experimental groups underwent 320-slice CT perfusion scan of pleural at 2h, 4h and 6h time point after modeling to get CTP (CT Perfusion) images and related parameters. 2mL blood was collected in the marginal ear vein to determine the mass concentration of the vascular endothelial growth factor (VEGF). The animals were killed by air embolism after 6h and lung tissue was taken for pathology observation. Results The reginal blood flow (rBF) and reginal blood volume (rBV) of paraquat group at 2,4,6 h time point were significantly (P Conclusion In the ultra-early stage of rabbit ALI induced by PQ, pulmonary vascular endothelial cell is damaged and serum VEGF mass concentration and pulmonary vascular permeability increase. Early ulinastatin intervention can reduce serum VEGF level and PQ-induced vascular permeability amplitude, indicating that ulinastatin has a protective effect on pulmonary vascular endothelial cells.

In this paper, an experimental study on two-phase flow patterns (evaporation) for propane in a horizontal smooth tube is presented. The tests were conducted at various saturation pressures from 0.2 MPa to 0.4 MPa for different mass velocities from 70 kg/(m 2 s) to 180 kg/(m 2 s) and two heat fluxes (20.16 kW/m 2 and 37.1 kW/m 2 ) in the entire ranges of vapour qualities. Several flow pattern maps were compared with the experimental flow pattern data, especially for the intermittent/annular (I/A) transition line. Finally, a transition equation of intermittent/annular flow for propane was modified with an improved flow pattern map.