Flow Calorimeter Research Articles

The isobaric heat capacity of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) at temperatures from (230 to 285) K and pressures up to 8 MPa using a new flow calorimeter

In this paper, a new flow calorimeter was developed to measure the isobaric specific heat capacity (cp) of liquids. The uncertainties of temperature, pressure, and cp were estimated to be less than 11 mK, 0.02 MPa and 1.26%, respectively. The pure 1,1,1,2-tetrafluoroethane (R134a) was measured at temperatures from (230 to 285) K to quantitatively calculated the heat leakage at different temperatures. In order to verify the reliability of apparatus, the cp for R134a and difluoromethane (R32) were obtained at temperatures from (230 to 285) K and pressures up to 8 MPa. Measurements of R134a and R32 show good agreement with the reported data and the high-precision Helmholtz energy equations of state (EoSs). Finally, a total of 33 cp data for 2,3,3,3-Tetrafluoroprop-1-ene (R1234yf) were obtained at temperatures from (230 to 285) K and pressures up to 8 MPa. The presented cp data show good agreement with the published data and two Helmholtz energy EoSs developed by Akasaka et al. and Richter et al. with the average absolute relative deviations (AARDs) of 0.92% and 1.80%, respectively. The Helmholtz energy EoS developed by Akasaka et al. gives a better prediction performance for the cp of R1234yf at low temperature than the other EoS.

Continuous milli-scale reaction calorimeter for direct scale-up of flow chemistry

Reaction calorimetry of flow processes is important for scale-up and safety in flow chemistry. Due to the increasing number of flow processes, corresponding flow calorimeters are required as an alternative or addition to high-precision batch calorimeters. In this work, a milli-scale isoperibol continuous flow calorimeter was used to measure the heat of reaction based on an elaborated heat transfer model. This allows for reaction calorimetry without calibration. The model was tested with a selective, fast and exothermic neutralization reaction of acetic acid and sodium hydroxide at different flow rates, concentrations and viscosities. Deviations of the mean heats of reaction from the literature values were only about 2%. The calorimetric data can further be used for direct scale-up with tube bundle mixer heat exchangers having similar heat transfer characteristics. In addition, a reaction screening at different flow rates allows to find the maximum temperature and maximum heat generation. This data is useful in safety analyses of continuous processes. For these reasons, continuous reaction calorimetry provides a practical scale-up tool for flow processes.

Coffee Wastes as Sustainable Flame Retardants for Polymer Materials

Development of green flame retardants has become a core part of the attention of material scientists and technologists in a paradigm shift from general purpose to specific sustainable products. This work is the first report on the use of coffee biowastes as sustainable flame retardants for epoxy, as a typical highly flammable polymer. We used spent coffee grounds (SCG) as well as SCG chemically modified with phosphorus (P-SCG) to develop a sustainable highly efficient flame retardant. A considerable reduction in the peak of heat release rate (pHRR) by 40% was observed in the pyrolysis combustion flow calorimeter analysis (PCFC), which proved the merit of the used coffee biowastes for being used as sustainable flame retardants for polymers. This work would open new opportunities to investigate the impact of other sorts of coffee wastes rather than SCG from different sectors of the coffee industry on polymers of different family.

Boil-off calorimetry enthalpy measurements and equation of state of an aqueous pyridine azeotrope

We present measurement and modeling of the thermo-physical properties of an aqueous pyridine azeotrope for evaluation as a working fluid for power and thermal management applications. The enthalpy values of the Pyridine/water azeotrope were measured using an electrical matching boil-off flow calorimeter in the range of P = 0.101 to 11 MPa and T = 373 to 575 K. A Peng-Robinson equation of state model for mixtures was fitted to the experimental data using a temperature-dependent binary interaction parameter. The results were used to develop a pressure-enthalpy diagram with isotherms in both the liquid and vapor states.

Flame retardancy effect of phosphorus graphite nanoplatelets on ethylene‐vinyl acetate copolymer: Physical blending versus chemical modification

AbstractA novel modified exfoliated graphite nanoplatelets (GNP‐g‐APP), resulting from grafting ammonium polyphosphate (APP) on exfoliated graphite nanoplatelets (GNP) was prepared and evaluated as flame retardant for ethylene‐vinyl acetate copolymer (EVA). The effect of modification on the thermal stability and flame retardancy of EVA was discussed. Thermogravimetric analysis (TGA), UL‐94, pyrolysis combustion flow calorimeter (PCFC), and mass loss calorimeter (MLC) analyses were employed for the evaluation of the thermal stability and flame retardancy of composites. The introduction of 20 wt.% GNP‐g‐APP into EVA resulted in significant enhancement in flame retardant properties with respect to the system containing physical mixture of GNP and APP. The former blend exhibited 57% decrease in the peak of heat release rate (pHRR), and 35% reduction in the total heat release (THR) than the latter one in MLC test. Thus, pHRR was decreased from 940 kW.m−2 for neat EVA to 403 kW.m−2 for EVA containing GNP‐g‐APP. V0 rating (auto‐extinguishable behavior) was also observed in UL 94 chemically modified sample. According to the present study, chemical modification of GNP with APP is more effective than a physical mixing of GNP and APP in improving the flame retardant properties of EVA.

Effectiveness of Silanization and Plasma Treatment in the Improvement of Selected Flax Fibers' Properties.

The study investigated the effectiveness of the combination of chemical and physical methods of natural fibers’ modification. The long flax fibers were subjected to various types of modification. These were silanization, plasma modification and a combination of these methods. For the silanization process, two types of silanes were used: amino- and vinylsilane. The application of structurally different compounds allowed us to acquire knowledge about the effect of the modifier structure on its properties. Various properties of flax fibers were investigated, comparing the results before and after different modification processes. The flammability of prepared samples were tested by pyrolysis combustion flow calorimeter (PCFC). In the effect of the natural fibers’ modifications, flammability was reduced even by 30%. The thermal stability of modified fibers increased. The FTIR tests of the gases released during thermal degradation of the tested fibers allowed us to determine the important compounds and prove a lower degree of flax-fiber decomposition after modification. Flax fibers were also tested to evaluate their physical properties (linear mass, average diameter, aspect ratio and hygroscopicity). Changes in surface morphology were observed by scanning electron microscope (SEM). The properties of natural fibers improved significantly, thus contributing to an increase in their suitability for the use in composites.

Heat Release Kinetics upon Water Vapor Sorption Using Cation-Exchanged Zeolites and Prussian Blue Analogues as Adsorbents: Application to Short-Term Low-Temperature Thermochemical Storage of Energy

In view of potential uses in short-term thermochemical heat storage by sorption of water vapor, the capacity to release a sufficient heat amount at the appropriate rate of a Prussian blue analogue (PBA) containing hexacyanocobaltate vacancies has been compared with those of 13X type zeolites possessing Na+, Ce3+, Ce4+, or Tb3+ extra-framework compensating cations. The extended structural and surface characterization demonstrated good reproducibility of the preparation procedures performed on a 10-g scale. The adsorbents were tested under dynamic conditions of gas flow with the aid of either a gas flow calorimeter (120 mL h−1 helium flow) to measure the amount and rate of the integral heat release or a laboratory-scale test rig (15,000 to 22,800 mL h−1 nitrogen flow) to monitor the outlet temperature of nitrogen heated by adsorption. For a regeneration temperature of 353 K and a partial H2O pressure of 2.8 kPa in helium, the PBA sample yielded an integral heat ranging between 900 and 1020 kJ kg−1 with a very slow heat release lasting for even 12–14 h. The zeolite-based materials generated between 350 and 950 kJ kg−1 more rapidly (up to 6–7 h), depending on the nature and the content of compensating cations, as well as on the dehydration state achieved during regeneration. With the laboratory-scale test rig, the efficiency of heat extraction by convection was about 65% for Na-13X and only 38% for PBA, and it diminished with decreasing flow rate.

Fire behavior of lead-containing PMMA based Kyowaglas

In the present work, the flammability of Kyowaglas is characterized experimentally. Kyowaglas is a lead-based composite used in glove boxes of nuclear facilities as a biological protection against radiation. It consists of 70%wt PMMA (Poly(Methyl Methacrylate)) and 30%wt leaded compounds. The aim of the study is to understand the role and impact of lead during the combustion of Kyowaglas in order to deepen knowledge of its thermal and fire behavior. A comparative study between Kyowaglas and virgin PMMA is conducted to better understand the effect of lead on the combustion process of these materials. Fire behavior is studied using cone calorimeter, pyrolysis-combustion flow calorimeter and thermogravimetric analysis. At different stages of cone calorimeter test, the samples and residues were examined and characterized using different experimental techniques like microscopy, spectroscopy, X-ray diffraction and calorimetry. Thermal analysis data show that lead seems to slightly accelerate the decomposition of PMMA under inert atmosphere. However, it confers significant thermal stability during a cone test due to the accumulation of lead on the surface of the sample. As the Kyowaglas burns, metallic lead is formed and accumulated at the top surface slowing down the heat transfer. At the end of the cone calorimeter test, lead oxide beads start to form on the surface of the residue due to the oxidation of metallic lead.

Implications of the Heat Generation of LMR-NCM on the Thermal Behavior of Large-Format Lithium-Ion Batteries

Lithium- and manganese-rich NCM (LMR-NCM) cathode active materials exhibit a pronounced energy inefficiency during charge and discharge that results in a strong heat generation during operation. The implications of such a heat generation are investigated for large-format lithium-ion batteries. Small laboratory cells are generally considered isothermal, but for larger cell formats this heat cannot be neglected. Therefore, the heat generation of LMR-NCM/graphite coin cells and NCA/graphite coin cells as a reference is measured for varying charge/discharge rates in an isothermal heat flow calorimeter and scaled to larger standardized cell formats. With the aid of thermal 3D models, the temperature evolution within these cell formats under different charge/discharge operations and cooling conditions is analyzed. Without an additional heat sink and any active cooling of larger LMR-NCM/graphite cells, discharge C-rates lower than C/2 are advisable to keep the cell temperature below a critical threshold. If the loads are increased, the cooling strategy has to be adapted to the specific cell format, otherwise critical temperatures above 60 °C are easily reached. For the investigated convective surface cooling and base plate cooling scenarios, thick prismatic cell formats with LMR-NCM are generally unfavorable, as the large amount of heat cannot be adequately dissipated.

Heat of Absorption of CO2 in Aqueous Solutions of 1-Methylpiperazine (1MPZ) and 3-(Dimethylamino)-1-propylamine (DMAPA)

The main objective of this study is to measure the heat of absorption of CO2 in two promising aqueous amine solutions at different operating conditions. The heat of absorption of CO2 in aqueous 3-(Dimethylamino)-1-propylamine (DMAPA) and 1-Methylpiperazine (1MPZ) were measured using a flow calorimeter at (313.15 and 343.15) K and at (1, 2 and 2.6) MPa. Measurements were performed at two concentrations of aqueous amine solutions (15 and 30) wt. %. A mixing flow CELL was integrated inside a C-80 heat calorimeter was manufactured for us by Setaram (Caluire, France). Aqueous amine and CO2 were transferred to the mixing flow cell at pre-determined flow-rates in order to measure the heat of absorption at given temperatures and pressures. Different flow-rates of aqueous amine solutions and CO2 were used to reach different CO2 loadings (mole of CO2/ mole of amine). The heat of absorptions per mole of CO2 at infinite dilution for aqueous solutions of DMAPA and 1MPZ were estimated from the experimental heat of absorption data. Heats of absorption for 1-MPZ were much lower than those of Monoethanolamine (MEA) at all concentrations. Values for aqueous DMAPA solutions were identical to those for MEA.

Software-guided microscale flow calorimeter for efficient acquisition of thermokinetic data

Fast chemical process development is inevitably linked to an optimized determination of thermokinetic data of chemical reactions. A miniaturized flow calorimeter enables increased sensitivity when examining small amounts of reactants in a short time compared to traditional batch equipment. Therefore, a methodology to determine optimal reaction conditions for calorimetric measurement experiments was developed and is presented in this contribution. Within the methodology, short-cut calculations are supplemented by computational fluid dynamics (CFD) simulations for a better representation of the hydrodynamics within the microreactor. This approach leads to the effective design of experiments. Unfavourable experimental conditions for kinetics experiments are determined in advance and therefore, need not to be considered during design of experiments. The methodology is tested for an instantaneous acid-base reaction. Good agreement of simulations was obtained with experimental data. Thus, the prediction of the hydrodynamics is enabled and the first steps towards a digital twin of the calorimeter are performed. The flow rates proposed by the methodology are tested for the determination of reaction enthalpy and showed that reasonable experimental settings resulted.Graphical abstractA methodology is suggested to evaluate optimal reaction conditions for efficientacquisition of kinetic data. The experimental design space is limited by thestepwise determination of important time scales based on specified input data.

Dual UV-Thermal Curing of Biobased Resorcinol Epoxy Resin-Diatomite Composites with Improved Acoustic Performance and Attractive Flame Retardancy Behavior

This study has developed novel fully bio-based resorcinol epoxy resin–diatomite composites by a green two-stage process based on the living character of the cationic polymerization. This process comprises the photoinitiation and subsequently the thermal dark curing, enabling the obtaining of thick and non-transparent epoxy-diatomite composites without any solvent and amine-based hardeners. The effects of the diatomite content and the compacting pressure on microstructural, thermal, mechanical, acoustic properties, as well as the flame behavior of such composites have been thoroughly investigated. Towards the development of sound absorbing and flame-retardant construction materials, a compromise among mechanical, acoustic and flame-retardant properties was considered. Consequently, the composite obtained with 50 wt.% diatomite and 3.9 MPa compacting pressure is considered the optimal composite in the present work. Such composite exhibits the enhanced flexural modulus of 2.9 MPa, a satisfying sound absorption performance at low frequencies with Modified Sound Absorption Average (MSAA) of 0.08 (for a sample thickness of only 5 mm), and an outstanding flame retardancy behavior with the peak of heat release rate (pHRR) of 109 W/g and the total heat release of 5 kJ/g in the pyrolysis combustion flow calorimeter (PCFC) analysis.

Эффективная мощность сжатой сварочной дуги с разнополярными импульсами тока

The authors reviewed the research works on the effective power of direct and reverse polarity welding arcs with a non-consumable electrode in argon. The study shows that it is difficult to use the arc effective efficiency for effective power determination. It applies to the constricted arc more than to the free one. Based on data analysis for the effective power of polarities and the effective efficiency of a constricted arc burning toward the cooper heat flow calorimeter, the authors calculated the specific effective power of polarities and arc stresses. The maximum values are 23.2 W/A for the reverse polarity arc; and 14.2 W/A for the direct polarity arc. The study identified that the decrease in the specific effective power of polarities at the current increase within 100–150 A is well described by linear dependencies. With the current increase, there is a linear decrease in the direct polarity arc stress, while the reverse polarity arc stress remains constant. The spread of data for the specific effective power of polarities is about two times less than the spread for effective efficiency. Using a 2D mathematical model of the constricted arc column in a closed area, the authors calculated the power absorbed by plasma-forming argon and nozzle walls. As a result, the authors obtained the dependencies of the power transferred by argon on the nozzle channel length and the arc current. The specific effective power of argon flow for analyzed current densities and argon consumption shows poor dependence on the arc current and is equal to 5.5 W/A approximately. The power contribution of plasma-forming argon to the effective power of the constricted arc increases with the current increase.

Combined effect of palygorskite and melamine polyphosphate on flame retardancy properties of polyamide 11 nanocomposites

Pyrolysis and fire behaviour of palygorskite (Pal) fibrous clay (5 wt%) reinforced polyamide 11 nanocomposites prepared by melt compounding were investigated in combination with melamine polyphosphate (MPP). Palygorskite was modified by 3-amino-propyl-triethoxysilane (APTES). Thermal stability and combustion behaviour of the materials were studied by thermogravimetric analysis (TGA), pyrolysis combustion flow calorimeter (PCFC) and cone calorimeter. TGA data showed that MPP reduced the thermal stability of PA11 nanocomposites, whereas the addition of both unmodified and modified palygorskite improved this property. Further, the cone calorimeter and PCFC results indicated a significant decrease in the peak of heat release rate (pHRR) and the total heat release (THR) of PA11 nanocomposites. This also means that the PA11 combustion was strongly reduced in the presence of combined Pal with MPP, being however more pronounced for the modified palygorskite. The improved fire behaviour could be attributed to a synergistic effect between Pal and MPP.

Reaction Calorimetry for Studying Kinetics in Bulk Phase Polymerization of Propene

AbstractPolypropylene is one of the commercially most important polymers and is produced via coordinative polymerization with supported metal‐organic catalysts in different processes. While kinetic measurements for slurry and gas‐phase polymerization of propene are well‐established, for bulk phase polymerization of propene, often the only kinetic information obtained from an experiment is the yield. In this paper, two calorimetric methods and their application for measurement of kinetics of bulk phase polymerization of propene are discussed. On the one hand a special calibration‐free heat flow calorimeter and on the other hand power compensation calorimetry coupled with a software sensor for online baseline correction.

AC loss and contact resistance in REBCO CORC®, Roebel, and stacked tape cables

Many high-temperature superconductor (HTS) applications require superconducting cables with high currents while operating in an alternating magnetic field. HTS cables should be composed of numerous superconducting tapes to achieve the required current capacity. Alternating current and magnetic fields cause AC losses in such cables and can provoke conductor instability. AC losses and contact resistances were measured of several cable designs based on commercially available REBCO tapes at the University of Twente. The AC loss was measured under identical conditions for eight REBCO conductors manufactured according to three types of cabling methods—CORC® (Conductor on Round Core), Roebel, and stacked tape, including a full-size REBCO CICC (cable in conduit conductor). The measurements were done at T = 4.2 K without transport current in a sinusoidal AC magnetic field of 0.4 T amplitude and frequencies from 5 to 55 mHz. The AC loss was measured simultaneously by calibrated gas flow calorimeter utilizing the helium boil-off method and by the magnetization method using pick-up coils. Also, the AC loss of two CORC® conductors and a Roebel cable was measured at 77 K. Each conductor was measured with and without background field of 1 T. The measured AC coupling loss in the CORC® and Roebel conductors is negligible at 4.2 K for the applied conditions while at 77 K coupling loss was observed for all conductors. The absence of coupling loss at 4.2 K can be explained by shielding of the conductor interior; this is confirmed with measurement and calculation of the penetration field of CORC® and Roebel cables. The inter-tape contact resistance was measured for CORC® and stacked tape samples at 4.2 and 77 K. It was demonstrated that a short heat treatment of CORC® conductor with solder-coated tapes activates tape-to-tape soldering and decreases the contact resistance. The reduction of contact resistance by two orders in magnitude to tens of nΩm is comparable with the interstrand contact resistance in ITER Nb3Sn type conductors.

Uncertainty analysis of a water flow calorimeter while welding in short-circuit and spray transfer regimes

The thermal efficiency of arc welding influences the cooling rate, peak temperature, and microstructures of a weld, which affects the material properties of the welded joint. This work quantifies the uncertainty of thermal efficiency measurements on gas metal arc welds using low (2.5 kW) and high (9.5 kW) arc powers. In order to understand the effect of calorimeter parameters on the measured efficiency, a two-factor, two-level full factorial design was carried out for each arc power condition. In this study, the factors are flow rate (2 l/min and 5 l/min) and plate thickness (0.25 in. [6.35 mm] and 0.375 in. [9.53 mm]). The results show that the uncertainty in the thermal efficiency measurements increases when both higher flow rates and plate thickness are used. Moreover, the use of a thick plate causes the heat transfer regime to change, increasing the cooling rate and decreasing the observed thermal efficiency. Uncertainty is also influenced by the metal transfer mode during welding.

Parametric Analysis of the In-bed gas flowing calorimetry of metal hydride bed employed in CFETR SDS

Gas flowing calorimetry is considered to be one of the most promising tritium measurements method in fusion fuel cycles, yet the parametric study of the structure design is still insufficient. In this study, three-dimensional models, combining with commercial computational fluid software, has been used to evaluate the calorimetric performance of tritium storage beds. The effects of structural geometry and cooling method on the heat transfer behavior have been systematically studied. The results show that the proposed model can effectively characterizes the evolution of the temperature difference of the cooling gas with time during the calorimetric process. Typically, increasing number of the U-shaped cooling tubes, thickness of the metal hydride layer and flow rate of the cooling liquid are beneficial for reducing the thermal equilibrium time. When the number of calorimeter bed cooling tubes is 12, the thickness of the metal hydride layer is 23, and the cooling gas is 20 SLMP of CO2, the thermal equilibrium time is only 4.5h. Furthermore, through optimizing the structural parameters, which can have an important influence on calorimetric performance, highly efficient and accurate gas flow calorimeter can be developed in the future.

The determination of isobaric heat capacities of liquid by the new flow calorimeter

A new flow calorimeter is developed to analyze the isobaric heat capacity of liquid. The characteristics of calorimeter have been studied at temperatures from 293 K to 353 K and pressures from 0.1 MPa to 15 MPa. The design of the calorimeter includes the innermost part of the calorimeter with two thick-walls, aluminum shields and microheater. The function of thick-walls with aluminum shields is to replace the conventional constant temperature bath for minimizing heat loss and precisely controlling the temperature of calorimeter. In order to verify the feasibility and reliability of the apparatus, the heat loss is checked by pure water under given pressure and various temperatures. The heat capacity of toluene, heptane and cyclohexane are measured at various temperatures and pressures. The experimentally measured data as a whole is in good agreement with the literature values available. Compared with the literature data, the experimental results by using the new calorimeter show that the deviations are less than 2%.

Influence of Sepiolite and Lignin as Potential Synergists on Flame Retardant Systems in Polylactide (PLA) and Polyurethane Elastomer (PUE).

A comparison of the influence of sepiolite and lignin as potential synergists for fire retardant (FR) systems based on ammonium polyphosphate (APP) has been carried out in polyurethane elastomer and polylactide. Different ratios of kraft lignin and sepiolite were tested in combination with APP in both polymers. The thermal stability and the fire behavior of the corresponding composites were evaluated using Thermogravimetric Analysis (TGA), a Pyrolysis Combustion Flow Calorimeter (PCFC) and Cone Calorimeter (CC). The mechanisms of flame retardancy imparted by APP and other components were investigated. Synergistic effects were highlighted but only for specific ratios between APP and sepiolite in polyurethane elastomer (PUE) and polylactide (PLA) on one hand, and between APP and lignin in PLA on the other hand. Sepiolite acts as char reinforcement but through the formation of new phosphorus compounds it is also able to form a protective layer. Conversely, only complementary effects on fire performance were noted for lignin in PUE due to a dramatic influence on thermal stability despite its action on char formation.