Source Inlet Research Articles

Direct Determination of Creatinine in Urine and Analysis of Pure Aniline by Extractive Electrospray Ionization Mass Spectrometry

The direct mass spectrometric determination of highly concentrated analytes in human urine was demonstrated using extractive electrospray ionization without sample dilution or complex preparation. By increasing the distance between the extractive electrospray source and ion inlet of the mass spectrometer from 5 millimeters to 15 centimeters, the fraction of free analyte ions and charged microdroplets introduced into the mass spectrometer was substantially reduced. Consequently, detector saturation, instrument contamination, and space charge effects were greatly diminished for the analysis of highly concentrated samples. Under the optimized experimental conditions, pure aniline and creatinine (>1 millimolar) in human urine were directly characterized by extractive electrospray ionization without any pretreatment. The urinary creatinine concentrations from two adults were 424 ± 30 and 635 ± 32 micrograms per milliliter and were in good agreement with those obtained by a spectrophotometric method based on the Jaffe reaction. The results show that extractive electrospray ionization is suitable for the direct determination of highly concentrated analytes or even pure compounds, allowing rapid characterization of samples in the chemical industry and clinical studies.

Humidity affects relative ion abundance in direct analysis in real time mass spectrometry of hexamethylene triperoxide diamine.

Unstable explosive hexamethylene triperoxide diamine (HMTD) is dangerous in quantity and benefits from the minimal sampling handling associated with atmospheric pressure chemical ionization for mass spectral analysis. Seasonal variation observed in HMTD mass spectra suggested a humidity dependence. Therefore, direct analysis in real time (DART) ionization mass spectra were acquired at a range of humidity values. An enclosure was designed to fit around the ion source and mass spectrometer inlet at atmospheric pressure. The enclosure was supplied with controlled amounts of humidified air from a test atmosphere generator to create programmable conditions for ambient analysis. The relative abundance and fragmentation of analyte ions were observed to change reliably with changing humidity values and, to a lesser degree, temperature. Humidity at such plasma-based ion sources should be regulated to avoid ∼90% shifts in relative ion abundance and provide stability and reproducibility of HMTD analysis.

Knudsen cell mass spectrometry using restricted molecular beam collimation. I. Optimization of the beam from the vaporizing surface.

This study analyzes molecular beam sampling by mass spectrometry by the Knudsen method using the so-called " restricted collimation device" . This device, defined by the field and source apertures, was proposed in order to eliminate any additional contribution to the genuine molecular beam of surface vaporizations coming from the vicinity of the effusion orifice as usually detected by the ion source of a mass spectrometer. The molecular transmission of the " restricted collimation device" was calculated using a vaporization law under vacuum taking into account the real surface where the molecules are emitted, i.e., the sample evaporation surface in the Knudsen cell or the effusion orifice section, towards the ion source inlet by integration of elementary solid angles. An optimum is observed depending on the pair of selected apertures that define the restricted collimation device, i.e., the field and source apertures. This optimum is different from that previously calculated when taking into account only the solid angle, as defined by the restricted collimation device. This difference is attributed to the previously approximate assumption that optimizing the restricted collimation solid angle automatically optimizes the sampling of the effused beam included in the restricted collimation angle. Moreover, the location of the evaporating surface for molecules traveling through the collimation device towards the ionization chamber remains an important factor: the distance between the sample evaporation surface and the field aperture is of paramount importance as it changes the molecular transmission to the mass spectrometer or to any target collection device in the conventional Knudsen method.

Thermodynamic analysis of organic Rankine cycle using zeotropic mixtures

In recent years, more and more attention has been paid to organic Rankine cycle (ORC), which is simply structured, highly reliable and easily maintainable. In order to improve the efficiency of ORC systems, zeotropic mixtures whose phase change process is variable temperature, are used as working fluids to match the temperature profiles of the heat source and heat sink. In this paper, a thermodynamic model which mainly includes Jacob number and the ratio of evaporation temperature and condensation temperature is proposed to forecast the thermal efficiency, output work and exergy efficiency of ORC system with zeotropic mixture. Furthermore, the proposed model programmed by Mablab 2010a is verified by the theoretical data. Then, for different heat source inlet temperature, using different zeotropic mixture pairs, output work that is objective function is maximized by optimizing the evaporation temperature. The results show that if the other working conditions are fixed, the heat source inlet temperature has a significant influence on the best composition of zeotropic mixtures at the optimal evaporation temperature. With the increase of heat source inlet temperature, there exists a heat source inlet temperature that pure working fluid has better system performance than zeotropic mixture. The extent of ORC system performance improvement has a positive correlation with zeotropic mixture’s temperature glide.

The Combined Solar with a Dual Heat Source Heat Pump Applied in a Greenhouse Heating System - An Operation Optimization of Water Source Heat Pump

Based on the finite-time thermodynamic theory, an operation optimization, of water source heat pump in the combined solar with a dual heat source heat pump which is applied in a greenhouse heating system, is made. According to the ε-NTU method and entropy theory, heat exchange and balance equations are obtained. The function relationship between COP and the indoor temperature Tn, the ambient temperature Ta, low temperature heat source inlet temperature Tie and high temperature heat source inlet temperature Tic is also obtained. By means of programming, the impact of parameters on the COP and the way of regulating this water source heat pump system are presented in this article. The results show that: when a separate water source heat pump is running, by adjusting the hot water temperature and the match status of each indoor heating system, the energy-saving operation can be realized.

SIMULATION ON THE PERFORMANCE OF CARBON DIOXIDE AND HYDROCARBON HEAT PUMPS FOR MODERATE TO HIGH TEMPERATURE HEATING

In order to compare the performance of the carbon dioxide, propane and isobutane heat pumps for moderate to high temperature heating, the three heat pump cycles were optimized using a simulation method. To fairly compare the performance of the cycles by using different working fluids, each cycle was optimized from the viewpoint of heating COP by two design parameters. The first is the gas cooler (or condenser) exit temperature and the other is the ratio of the overall heat conductance of the gas cooler to the combined overall heat conductance of the gas cooler and the evaporator. The inlet and outlet temperatures of secondary fluid of the gas cooler (or condenser) were fixed at 40/90°C and 40/150°C. The heat source inlet temperature was fixed at 10°C. The flow rates of both the heat source and the heat sink were also fixed. The results shows that the hydrocarbon heat pumps have 11–17% higher heating COP than carbon dioxide heat pump under the simulation conditions considered in the present study. However, for a high temperature heating, even though the isobutane heat pump shows the best performance, the carbon dioxide heat pump looks promising due to hydrocarbon heat pumps' high compression ratio.

Performance Analysis of an Irreversible Regenerative Brayton Cycle Based on Ecological Optimization Criterion

An ecological optimization along with a detailed parametric analysis of an irreversible regenerative Brayton cycle with finite heat capacity of external reservoirs have been carried out. The external irreversibilities due to finite temperature difference and internal irreversibilities due to fluid friction losses in compressor / turbine, regenerative heat loss, pressure loss are included in the analysis. Ecological function is thermodynamically optimized which is defined as the power output minus the product of environment temperature and entropy generation rate. A detailed analysis shows that the ecological function and corresponding power output / thermal efficiency can be maximized with judicious selection of parameters such as efficiency of turbine and compressor, effectiveness of various heat exchangers, heat source inlet temperature, pressure drop recovery coefficients and heat capacitance rate of the working fluid. It is found that the regenerative effectiveness is more prominent for maximum ecological function and corresponding thermal efficiency while cold side effectiveness is dominant factor for corresponding power output. It is also found that the effect of turbine efficiency (ηt) is more than the compressor efficiency (ηc) on the thermodynamic performance of an irreversible regenerative Brayton heat engine cycle. The model analyzed in this paper gives lower values of various performance parameters as expected and replicates the results of an irreversible regenerative Brayton cycle model discussed in the literature at pressure recovery coefficients of α1=α2=1.

Real-time detection of chemical warfare agent simulants in forensic samples using active capillary plasma ionization with benchtop and field-deployable mass spectrometers

A novel analytical technique to detect chemical warfare agent (CWA) simulants in forensic samples is presented. Three G-agent type simulants that closely mimic real CWAs, namely dimethyl methylphosphonate (DMMP), diethyl ethylphosphonate (DEEP), and diethyl phosphoramidate (DEPA), and in addition a hydrolysis product, pinacolyl methylphosphonate (PMP), were utilized. Dilute solutions spotted onto six different forensic matrices were used to evaluate the capability of an active capillary plasma ionization source, which could be attached to the inlets of either a conventional benchtop ion trap mass spectrometer or a miniaturized ion trap mass spectrometer, under ambient conditions. The sample solutions and matrix surfaces were exposed for about 10–20 seconds at a distance of 1 cm from the plasma ion source inlet. This real-time methodology was found to have a shorter analysis time than previously reported techniques. A full method validation, quantitative studies, and optimization for detection of real CWAs on forensic matrices should be done in the future.

The Effect of Thermal Diffusivity on the System Efficiency of a DOTEC Cycle

In this study, the effect of deep ocean condenser inlet temperature (T DOI ), condenser inlet pressure (P cond,in ), and thermal diffusivity on system efficiency of some selected refrigerants was analyzed using HYSYS. The proposed DOTEC cycle is similar to the reheat Rankine cycle but eliminates irreversibilities by bleeding a fraction of the steam between certain stages of the turbine. The evaporator inlet mass flow rate, inlet temperature of turbine 1, turbine efficiency and inlet and outlet temperature of heat source were imposed. The working fluids considered are sorted in ascending order of their molecular weights as R717, R600a and R152a. Results indicated that a fluid with a lower boiling point temperature like R717 needs a corresponding high heat source and/or evaporator inlet pressure. Also, the response of thermal diffusivity closely follows the change in TDOI as an increase in T DOI increases P cond,in which reduces thermal diffusivity and system efficiency. Furthermore, the fluid with the nominal boiling point temperature has the highest efficiency with efficiency decreasing with an increase in T DOI .

Applying neural networks to solve the inverse problem of indoor environment

The computational fluid dynamics (CFD) analysis and back propagation neural network (BPNN) were employed to solve the inverse problem of indoor environment (IPIE). The approaches to identify the contaminant source locations and inlet boundary conditions by the measurement data at specified observation locations were put forward separately. The inverse design of the indoor boundary conditions by the desired distribution of predicted mean vote (PMV) in the control domain was also presented. The result demonstrated the utility of our proposed method in solving the IPIE.

Thermal Characteristics in Two-Reactor Adsorption Refrigerator Using Metal Chloride Compound Adsorbent

An adsorption refrigerator using two-phase heating with chemical/physical compound adsorbent of CaCl2/ activated carbon was designed and performance-tested. Microporous activated carbon was mixed with salt to increase the mass transfer performance of the adsorbent and avoid the problem of agglomeration phenomenon. Because of the utilization of two-phase heating in the adsorption heating process, the heat transfer performance can be improved, compared with single-phase heating process. Other novelties in the design come from the fact that only three water valves were used in the system and the system always works under positive pressure status both in the heating process and cooling process, which improves the system’s reliability. The test results reveal that the mass recovery has a larger impact on the COP (Coefficient of Performance) than SCP (Specific Cooling Power). When the hot source inlet temperature is about 128 °C, and the cooling water inlet temperature is about 28 °C, the evaporating temperature can attain to −17 °C. Correspondingly, the COP and SCP are improved by 53.3% and 51.1% by mass recovery.

Adsorption cooling system employing granular activated carbon–R134a pair for renewable energy applications

An adsorption cooling system has been designed and built employing granular activated carbon (GAC)–R134a as adsorbent–refrigerant pair. The performance of the system has been determined using a cycle simulation computer program written in Fortran. The performance of the system has been determined varying driving heat source inlet temperatures and delivered evaporator temperatures. The maximum driving heat source temperature is kept below 100 °C to utilize solar thermal energy or waste heat sources. The results showed good agreement between the theoretical and experimental data. The maximum theoretical coefficient of performance (COP) is obtained as 0.35. The experimental specific cooling energy (SCE) is reached up to 70 kJ kg−1 whereas the maximum theoretical SCE of the system is 83 kJ kg−1. The pressurized-bed adsorption cooling system can effectively utilize low grade waste heat of temperature below 100 °C.

A comparative study of power optimization in low-temperature geothermal heat source driven R125 transcritical cycle and HFC organic Rankine cycles

In order to compare the power output of an R125 transcritical cycle with that of HFC subcritical ORCs for a low-temperature geothermal heat source of about 100 °C, an R125 transcritical cycle and subcritical ORCs using R134a, R245fa and R152a were optimized for power output by a simulation method. In contrast to previous studies, to fairly compare the power of different cycles, power optimizations were carried out for given heat source and sink inlet temperatures, and given flow rates based on the typical power plant thermal-capacitance-rate ratio. The total overall conductance (TOC) which implies heat exchanger cost was fixed, whereas the allocation of the overall conductance between the vapor generator and the condenser was optimized in the simulation. Results show that under simulation conditions considered in the present study, the power output of an R125 transcritical cycle was greater than that of subcritical ORCs when a TOC was higher than 35 kW/K. When a TOC was lower than that, transcritical cycle's power output was slightly less than that of subcritical cycles.

Development of nanoinjector devices for electrospray ionization - tandem mass spectrometry (ESI-MSn)

In mass spectrometric (MS) systems with electrospray ionization (ESI), the sample can be analyzed coupled to separation systems (such as liquid chromatography or capillary electrophoresis) or simply by direct infusion. The greatest benefit of the type of injection is the possibility of continuous use of small amounts of samples over a long period of time. This extended analysis time allows a complete study of fragmentation by mass spectrometry, which is critical for structure elucidation of new compounds, or when using an ion trap mass analyzer. The injector filled with the sample is placed at the ESI source inlet creating an electric field suitable for the continuous formation of a spray (solvent and sample) and consequently, the gradual and even release of the sample. For the formation of the spray, is necessary that the injector end is metalized. The formation of a bilayer of titanium and gold provided an excellent attachment of the film, resulting in a nanoinjector for ionization/spray formation in the system for MS. The nanoinjectors showed high repeatability and stability over 100 min by continuous sampling with 10 µL of sample.

Comparative analysis of series and parallel geothermal systems combined power, heat and oil recovery in oilfield

The option of combined heat, power generation and oil recovery (CHPO) was considered for the associated geothermal water ranging from 100 to 150°C. Series and parallel circuits of an organic Rankine cycle (ORC) subsystem, an oil gathering and transportation heat tracing (OGTHT) subsystem and an oil recovery subsystem were first put forward and then compared by first and second law analyses. In addition, a case study was conducted based on the data from an actual series circuit geothermal system in an oilfleld. The objective was to ascertain their respective applicabilities of the two circuit systems. Results indicate that R601a shows the highest cycle performance. The series circuit is preferable for high geothermal water inlet temperatures and low heat source inlet temperatures of the OGTHT, whereas the parallel circuit is just the reverse. Moreover, for each working condition, there exists a specific critical mass flowrate ratio, making the net power output of the parallel circuit equal to that of the series circuit.

Increasing the rate of sample vaporization in an open air desorption ionization source by using a heated metal screen as a sample holder

Rapid vaporization of sample into the ionizing gas exiting a direct analysis in real time (DART®) source has been enabled by directing a high electrical current through a metal wire screen to which sample has been applied. This direct heating of the screen enables rapid vaporization of sample as the wire temperature rises from room temperature to greater than 400°C in less than 20 s. Positioning the screen between the DART source and atmospheric pressure inlet of the mass spectrometer ensures that the ionizing gas is in close proximity to the sample molecules, resulting in efficient ionization while significantly reducing the time required for mass spectrometric analysis. The capability to modulate the electrical current flow through the wires facilitates either rapid desorption for the determination of single component samples or slower desorption where analysis of mixtures might be desired. The technology also enables deployment of strategies for the determination of chemicals present as powders that might otherwise require dissolution prior to analysis. Results from the use of this thermally assisted DART ('TA-DART') system for the analysis of pure compounds, simple mixtures, solids and low vapor pressure samples are presented.

저온 지열발전의 출력 극대화를 위한 흡수식 동력 사이클의 시뮬레이션

In this study, an absorption power cycle, which can be used for a low-temperature heat source driven power cycle such as geothermal power generation, was investigated and optimized in terms of power by the simulation method. A steady-state simulation model was adopted to analyze and optimize its performance. Simulations were carried out for the given heat source and sink inlet temperatures, and the given flow rates were based on the typical power plant thermal-capacitance-rate ratio. The cycle performance was evaluated for two independent variables: the ammonia fraction at the separator inlet and the maximum cycle pressure. Results showed that the absorption power cycle can generate electricity up to about 14 kW per 1 kg/s of heat source when the heat source temperature, heat sink temperature, and thermal-capacitance-rate ratio are 100°C, 20°C, and 5, respectively.

Humidification–dehumidification desalination system driven by geothermal energy

The work presented in this paper focuses on desalinating sea water system using a humidification–dehumidification process as it is supplied with water heated by geothermal energy as clean and renewable natural resources of energy. Computer simulation of the behavior under various working conditions of the desalination system was carried out to predict the variations of key output. Such variables include the ratio of sea water mass flow rate related to air mass flow rate, cooling water temperature difference across the condenser, geothermal source inlet temperatures to the heat exchanger and the amount of produced distilled water. To validate the computer program, a comparison between the experimental and theoretical results was conducted, and a good agreement had been obtained. The result showed that, the optimum value of the ratio between sea water mass flow rate to air mass flow rate was found to be in the range of 1.5 to 2.5. Improvement in the fresh water productivity at the optimum ratio of sea water mass flow rate to the air flow rate was observed by increasing both the geothermal source inlet temperature and the cooling water temperature difference across the condenser.

Thermodynamic analysis of a power cycle using a low-temperature source and a binary NH 3–H 2O mixture as working fluid

Two Rankine cycles, one with and one without a regenerator, both using a NH 3–H 2O mixture as the working fluid, have been analyzed for fixed source and sink inlet temperatures. A fixed mass flow rate of a hot gaseous stream is providing the thermal energy input at the heat recovery boiler (HRB). The methodology used in this work is divided in four steps: energy analysis, exergy analysis, finite size (or finite time) thermodynamics (i.e. thermodynamic calculations in the context of reasonable temperature differences in the heat exchangers) and calculation of the heat exchangers' areas. The results show that the range of evaporation pressures satisfying some basic conditions increases with the source inlet temperature and with the ammonia concentration. They also show the existence of an optimum evaporation pressure for each of the four analyses. In the first two analyses, an optimum evaporation pressure of approximately 3.2 MPa maximises the thermal and exergetic efficiency, at respectively 11% and 73%. In the last two analyses, the optimum pressure of 2.5 MPa minimises the heat exchangers' areas. The results also show that the net power output generated from a limited energy source doesn't influence the results of the energy analysis. However, an increase of the net power output decreases the exergetic efficiency while at the same time it increases the heat exchangers' surface.

Simulation of velocity and temperature distributions of displacement ventilation system with single or double heat sources

In order to obtain a better understanding of flow characteristics of displacement ventilation, the three-dimensional numerical models are developed using the CFD technology. The numerical simulation results are verified by experiments, based on this, the velocity and temperature distribution of three-dimensional displacement ventilation system with single and double heat sources are studied. Velocity and temperature fields under two different cases of heat source are analyzed and compared. The numerical results show that there are three layers in vertical temperature fields of displacement ventilation system with single or double heat sources, and the vertical temperature distribution of single heat source is different from that of double heat sources. When indoor load is large, the comfort requirement of people indoor can’t be satisfied with displacement ventilation system only, thus an additional refrigeration system is necessary. Furthermore, under the condition of two heat sources, the displacement ventilation parameters can’t be computed simply according to single heat source inlet parameters, therefore the interaction between heat sources should be considered.