Heat Flow Calorimetry Research Articles

The Effect of the Angle of Inclination on the Efficiency in a Medium-Temperature Flat Plate Solar Collector

In this experimental work, the effects of the inclination angle β and the (Ti − Ta)/G on the efficiency and the UL-value were investigated on a medium-temperature flat plate solar collector. The experiments were based on steady-state energy balance, by heat flow calorimetry at indoor conditions and considering the standard American National Standard Institute/American Society of Heating Refrigerating and Air Conditioning Engineers (ANSI/ASHRAE) 93-2010. The solar radiation was emulated by the Joule effect using a proportional integral derivative (PID) control considering two conditions of the absorber temperature, Case 1: (To − Ti) > 0, and Case 2: (To − Ti) = 0. The inclination angles were 0°–90° and the (Ti − Ta)/G were 0.044–0.083 m2·°C/W and 0.124–0.235 for Case 1 and Case 2, respectively. The variations of β and (Ti − Ta)/G cause efficiency changes up to 0.37–0.45 (21.6%) and 0.31–0.45 (45.0%), respectively, for Case 1. Also, the UL(β) reached changes up to 10.1–12.0 W/m2·°C (19.2%) and 8.4–12.0 W/m2·°C (41.7%), respectively, for Case 1. The most significant changes of UL(β)/UL(90°) vs. β were 8.0% at the horizontal position for Case 1, while for Case 2, the maximum change was 1.8% only. Therefore, the changes of the inclination angle cause significant variations of the convective flow patterns within the collector, which leads to considerable variation of the collector efficiency and its UL value.

Modifying Cement Hydration with NS@PCE Core-Shell Nanoparticles

It is generally accepted that fine particles could accelerate cement hydration process, or, more specifically, this accelerating effect can be attributed to additional surface area introduced by fine particles. In addition to this view, the surface state of fine particles is also an important factor, especially for nanoparticles. In the previous study, a series of nano-SiO2-polycarboxylate superplasticizer core-shell nanoparticles (NS@PCE) were synthesized, which have a similar particle size distribution but different surface properties. In this study, the impact of NS@PCE on cement hydration was investigated by heat flow calorimetry, mechanical property measurement, XRD, and SEM. Results show that, among a series of NS@PCE, NS@PCE-2 with a moderate shell-core ratio appeared to be more effective in accelerating cement hydration. As dosage increases, the efficiency of NS@PCE-2 would reach a plateau which is quantified by various characteristic values. Compressive strength results indicate that strength has a linear correlation with cumulative heat release. A hypothesis was proposed to explain the modification effect of NS@PCE, which highlights a balance between initial dispersion and pozzolanic reactivity. This paper provides a new understanding for the surface modification of supplementary cementitious materials and their application and also sheds a new light on nano-SiO2 for optimizing cement-based materials.

Measurement of Li-Ion Battery Electrolyte Stability by Electrochemical Calorimetry

Recent work describing the use of high precision coulometry combined with isothermal heat flow calorimetry has shown promise in studying electrolyte reactivity in Li-ion batteries. In this paper we describe what we term an “integration/subtraction” technique for determining the electrolyte reactivity as a function of cell voltage in Li-ion full pouch cells. We apply this method to the characterization of a base electrolyte blend of ethylene carbonate and ethyl methyl carbonate (EC/EMC 3/7 w/w) with 1 M LiPF6. We then show how the parasitic thermal power and coulombic efficiency are affected by the addition of the reactive carbonates vinylene carbonate and 1-fluoro-ethylene carbonate to the base electrolyte. We show how this method can discriminate the effectiveness of additives used in Li-ion cells as a function of cell voltage and cycle life.

Surface Area Increase of Silicon Alloys in Li-Ion Full Cells Measured by Isothermal Heat Flow Calorimetry

Li-ion pouch cells utilizing a negative electrode formulated with 15 wt% of an engineered Si alloy in a graphite composite electrode were cycled in an isothermal heat flow calorimeter against a LiCoO2 positive electrode. Two different electrolytes were investigated: a blend of ethylene carbonate and ethyl methyl carbonate (3EC:7EMC) and a blend of ethylene carbonate, ethyl methyl carbonate and 1-fluoro ethylene carbonate (27EC:63EMC:10FEC). Both electrolytes were 1 M in LiPF6 salt. The parasitic thermal power and coulombic efficiency was derived from isothermal heat flow measurements and high precision current-source meters. Cells without FEC showed high parasitic thermal power which increased with cycle number indicative of a surface area increase which was confirmed by post-cycling scanning electron micrographs and surface area measurements. Cells with FEC showed relatively stable parasitic thermal power. These measurements demonstrate the surprising function of FEC in controlling or attenuating the evolution of surface area in Si alloys. Vinylene carbonate was also found to be effective at controlling the increase in alloy surface area.

Studies on the early hydration of two modifications of ye'elimite with gypsum

Two modifications of ye'elimite (namely orthorhombic ye'elimite (stoichiometric C4A3$) and iron-containing cubic ye'elimite (C4A2,7F0,3S¯)) were synthesized and the reactions without additional sulfate and with gypsum were tracked by means of heat flow calorimetry. Without gypsum the reaction differs significantly for both modifications while the addition of gypsum leads to almost comparable reactions. With addition of gypsum two distinct heat flow maxima could be detected while the reaction without gypsum showed only one distinct maximum for both modifications. For the systems with gypsum additional experiments were performed namely in-situ XRD, NMR, thermodynamic modeling, TGA and pore solution composition. It could be shown that the reaction with gypsum shows two steps of ettringite precipitation for both modifications. The two steps show significant differences. During the first step of ettringite precipitation gypsum and ye'elimite and free water are consumed forming ettringite and a highly hydrated AHx. The second ettringite precipitation is powered by ye'elimite consumption but no further gypsum dissolution. In addition, water is removed from the AHx used up for the second ettringite precipitation. The two modifications of ye'elimite react comparable with gypsum but show slightly different heats of hydration when reacting with the same calcium sulfate (gypsum) during early hydration; this is due to slightly lower reaction turnover of the cubic, iron-containing modification leading to slightly reduced ettringite formation.

Influence of crystallinity and surface area on the hydration kinetics of CA2

The hydration of CA2 (CaAl4O7) is usually a slow process. However, we found that CA2 is easily grindable and that the BET surface area and the amount of X-ray amorphous phase highly influence the hydration kinetics. Tempering of ground samples significantly decreased the BET surface area and the amount of X-ray amorphous phase. The hydration of tempered CA2 started later and proceeded much more slowly. A different degree of crystallinity of CA2 explains the wide range of different hydration kinetics and especially the occurrence of the often observed exothermic heat flow peak prior to the CA2 main reaction. By different grinding procedures and tempering we were able to prepare samples that were completely hydrated within 24h and such samples which did not react within 24h. Using heat flow calorimetry, in-situ XRD and in-situ 1H-TD-NMR we show that X-ray amorphous CA2 reacts prior to crystalline CA2.

The effect of d-gluconic acid as a retarder of ground granulated blast-furnace slag pastes

Ground granulated blast-furnace slag (GGBFS) is a latent hydraulic binder, which has also the ability to hydrate autonomously after contact with water. The rate of hydration strongly depends on the composition of the slag and the pH-value of the mixing water or activator. The retarded GGBFS suspension and an alkali activator can be used in a special two-component binder system for variable applications. d-gluconic acid (C6H12O7) was found to be a suitable retarder for GGBFS, which retarded the hydration at least 28days. The retarder extends the dormant period of the hydration process and prevents mainly the formation of strength-giving phases. The interaction of GGBFS and retarder was investigated by heat flow calorimetry, measurement of non-purgeable organic carbon (NPOC), inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetry (TG) and scanning electron microscopy (SEM). The basis for this study was a constant binder content, various concentrations of the retarder and different durations for the retarding effect. The concentrations were 0.05, 0.25 and 1.00% by weight of the mixing water. The samples were investigated between 0 and 28days. At the end, one mixture was optimized for a shelf time of at least 28days without separation.

Influence of the reactivity of the amorphous part of mechanically activated alite on its hydration kinetics

The hydration of one mechanically activated alite passing through different drying procedures is examined by heat flow calorimetry and quantitative in-situ XRD analysis. The reactivity of the alite powders is strongly affected by the drying technique. It is shown that the reactivity of the amorphous part of the activated alite sample is particularly affected. Due to the fast initial dissolution of the amorphous “alite” part, the hydration progression is speeded up significantly. However, if the hydration is not speeded up by the amorphous “alite” dissolution, as in the case of surface passivation, the heat released until the transition to the deceleration period will increase. It is discussed that a crystalline alite dissolution by etch pit opening could increase the reactive alite surface and therefore increase the reaction degree at the transition to the deceleration period.

Chemical kinetics on thermal decompositions of cumene hydroperoxide in cumene studied by calorimetry: An overview

Study on chemical kinetics related to the thermal decomposition of cumene hydoperoxide (CHP) in cumene is summarized in this work. It is of great importance to gather and compare the differences between these kinetic parameters for further substantial applications in the chemical industry and process safety. CHP has been verified to possess an autocatalytic behavior by using microcalorimetry (such as TAM and C-80) operated at isothermal mode in the temperature range from 70°C to 120°C. However, it exhibits a reaction of n-th order detected by non-isothermal DSC scanning and adiabatic calorimeter. By the isothermal aging tests, activation energy and frequency factor in logA(s−1) were averaged to be (117.3±5.9) kJmol−1and (11.4±0.3), respectively. Kinetic parameters acquired from data of interlaboratories by using heat-flow calorimetry, the averaged activation energy and frequency factor in logA(s−1) were (119.3±11.3) kJmol−1and (12.0±0.2), respectively. On the analogy of results from adiabatic calorimetry, the activation energy and frequency factor in logA(s−1) were respectively averaged to be (122.4±9.2) kJmol−1and (11.8±0.8). Five sets of kinetic models in relation to autocatalytic reactions are collected and discussed as well.

Application of heat-flow calorimetry for developing mathematical models of reactor processes

The paper discusses the possibility of using heat-flow calorimetry and differential scanning calorimetry to study the kinetics and modeling of industrial multistage reactions. The informativity of the obtained experimental data was studied and the methodology of applying them to solve inverse kinetic problems has been demonstrated. The results of using calorimetry to develop mathematical models of complicated chemical processes and applying them to optimize the operating conditions of industrial processes have been considered.

Oxidation of Magnesium: Implication for Aging and Ignition

Magnesium is widely used in pyrotechnic formulations; it is also a component of reactive alloys, e.g., Al—Mg and B—Mg, which are potential fuels for explosives and propellants. Despite its widespread applications, the kinetics of oxidation of Mg powders are not well quantified. Such kinetics are of fundamental importance for the models aimed to describe thermally induced ignition of metal powders. In addition, for Mg the issue of aging is important because its oxide, MgO, is porous. In this work, magnesium oxidation by both oxygen and steam was studied by thermo-analytical measurements for micron-sized spherical powders. Heat flow calorimetry and thermogravimetric analysis were used to quantify reaction rates for low and elevated temperature ranges, respectively. Experiments with spherical powders with different but overlapping particle size distributions were used to identify the location of the reaction interface. The reaction was found to occur at the interface of metal and the growing oxide layer for ...

Influence of the specific surface area of alumina fillers on CAC hydration kinetics

For refractory application inert alumina fillers frequently are mixed with calcium aluminate cements to improve particle packaging and to reduce the demand of water for low-cement castables. This finally results in decreased porosity and higher strength. Investigations by isothermal heat flow calorimetry show that the presence of alumina filler material with high specific surface area leads to a shortening of the induction period of calcium aluminate cement hydration. The study also demonstrates that the specific surface area of the chosen alumina filler changes the starting point of the main hydration reaction and in consequence the setting time of the calcium aluminate cement mixture is strongly influenced. During the dormant period the heat flow of calcium aluminate cement hydration with coarse alumina filler material of lower specific surface area is characterised by negative values. By addition of filler with higher specific surface area, the surface available for heterogeneous nucleation can be increased. Owing to more available surfaces the critical energy barrier for stable nuclei formation can be reduced. This results in a positive heat flow during the dormant period and a shift of the main reaction to earlier points in time.

In situ 1H-TD-NMR: Quantification and microstructure development during the early hydration of alite and OPC

An in situ framework for 1H time-domain nuclear magnetic resonance analysis was developed and applied on alite and OPC hydration. Highly time-resolved quantitative data on the evolution of proton reservoirs during hydration was collected for up to 40h. Reservoirs could be clearly assigned to mobile (mix water), intermediate (C-S-H) and rigid fractions (CH, ettringite). Comparison of determined fraction quantities with data from in situ XRD measurements and heat flow calorimetry show very good agreement. During alite hydration at 23°C, a bulk water content of 4 H2O in C1.7SHx was confirmed. T2 relaxation times of the mobile fraction shifted towards shorter times from the start of the main reaction until the maximum of the heat flow. Microstructure evolution is nearly finished at that point in time. T2 relaxation times are severely shortened for iron-containing OPC, but are still evaluable.

Influence of carboxylated styrene–butadiene latex copolymer on Portland cement hydration

The influence of carboxylated styrene–butadiene (SB) latex on the hydration of ordinary Portland cement was investigated by means of isothermal heat flow calorimetry, in-situ X-ray diffraction, electroacoustic zeta potential measurement and ion analysis of the cement pore solution. In particular, to assess the influence of the spraying aids polyvinyl alcohol (colloidal stabilizer) and kaolin (anti-caking agent) on cement hydration, the impact of the liquid SB latex was compared with that of its re-dispersible powder. It was found that anionic SB generally retards both the aluminate and silicate reactions. This effect can be ascribed to adsorption of SB particles onto positively charged clinker or hydrate phases and the chelation of calcium ions present in cement pore solution by the carboxylate groups of the SB sample. SB powder exhibits a lower anionic charge density due to PVOH coating, thus interacts less strongly with cement and retards slightly less, compared to liquid SB latex.

Mechanically activated alite: New insights into alite hydration

For superior understanding of alite hydration an investigation of mechanically activated alite (M3 modification) was performed by XRD and heat flow calorimetry. Activation resulted in reduced particle size, a decreased mean crystallite size and partial amorphization. For the samples of activated alite a significantly accelerated and intensified hydration was observed and complete conversion of alite was found after 24h. The enthalpy of reaction for crystalline alite was determined to be −548J/g from measured heat of hydration after 24h. The enthalpy of reaction of amorphous “alite” was found to be less exothermic (−386J/g). The main hydration period is controlled by nucleation of C–S–H, while the transition from acceleration to deceleration period takes place after consumption of the small alite particles. XRD amorphous C–S–H phase is indicated to precipitate in considerable amount even in the highest activated alite before “long-range ordered”, XRD detectable C–S–H was observed.

Assessment of Stability of Propellants and Safe Lifetimes

AbstractThe surveillance of gun propellants is basically performed either by an investigation into the thermal behavior of the propellant or by the determination of its remaining effective stabilizer content. Over the years it is shown that the surveillance of NC based gun propellants is necessary. NC based materials are intrinsically unstable, and can cause many accidents. Some accidents were caused by old unstable material, other ones were initiated by the extreme conditions during storage, like during expeditionary operations of military forces. And in quite a few cases it was a combination of these. Surveillance tests have changed over the years, and the last philosophy is to test the propellants as close as possible in comparison to the way they are stored [1] for this way of testing the Heat Flow Calorimetry (or microcalorimetry) method is the optimum. Older methods like the Abel heat test, Methyl Violet Test, Bergman‐Junk stability test, are test methods an analysis of the current status, without or very limited prediction behavior. Besides that the temperatures are relatively high, the measuring value is quite strongly dependent of the observer/operator. In general these tests are applied for propellants and sometimes explosives, although the general application worldwide (as far they are in use by countries) is propellants.

Application of isothermal calorimetry and thermal analysis for the investigation of calcined gypsum–lime–metakaolin–water system

The calcined gypsum–lime–metakaolin–water system and its subsystems consisting of two and three components are analyzed using the isothermal heat flow calorimetry, differential scanning calorimetry, and thermogravimetry. The hydration heat development in the initial hydration phase up to several hours is monitored in a common way, on the samples having a mass of about 1 g. In later time intervals up to 1 week when the values of the specific hydration heat power are very low, a large-volume calorimeter with better resolution is used for 300 g samples. The thermal analysis is carried out with the specimens undergoing hydration for the time periods of one to 8 days. The isothermal heat flow calorimetry shows that in the analyzed system and its subsystems, the majority of hydration heat is evolved during ~1.5 h after beginning of the hydration process. After 25 h, measurable amounts of hydration heat are produced in the gypsum–lime–metakaolin and metakaolin–lime mixes only, indicating a pozzolanic reaction in progress. In both these mixes, the differential scanning calorimetry reveals seven endothermic peaks corresponding to the thermal decomposition processes occurring during the heating up to 1000 °C. After 8 days of hydration, all Ca(OH)2 is found missing in the gypsum–lime–metakaolin and metakaolin–lime mixtures, which points to the completion of the pozzolanic reaction. The results obtained by the differential scanning calorimetry are well correlated with the mass changes measured by thermogravimetry and derivative thermogravimetry.

Enhanced thermal property measurement of a silver zinc battery cell using isothermal calorimetry

The push for increased energy density of electrochemical cells highlights the need for novel electrochemical techniques as well as additional characterization methods for these cells in order to meet user needs and safety requirements. To achieve ever increasing energy densities and faster controlled release of that energy, all materials of construction must be constantly evaluated from electrode to casing and everything in-between. Increasing the energy density of the cell improves its utility, but it also increases the waste heat and maximum potential uncontrolled energy release. Design agents and system developers need new ways to monitor and classify the probability and severity of the catastrophic failures as well as the system characteristics during intended operation. To support optimization of these battery cells it is necessary to understand their thermal characteristics at rest as well as under prescribed charge and discharge cycles. One of the many calorimetric tools available to observe and record these characteristics is heat flow calorimetry. Typically, a heat flow calorimeter is operated isothermally and measures the sum heat released or consumed by a sample material inside of a calorimetric measuring cell. For this study an improved calorimetric measuring cell for a modified Hart 6209 precision temperature bath was designed and constructed to measure the heat flow of larger electrochemical cells (18×8×16cm). This new calorimetric measuring cell is constructed to allow independent measurements of heat flow among each of the sample’s six sides in contrast to the typical one measurement of the average heat flow. Heat flows from 0.01 to 7.00 Watts were measured by the calorimeter with an average signal noise less than 1mW during the charge and discharge cycles of the batteries under test. The heat capacities of the samples were also determined with experimental deviation of less than 2%. This paper provides a description of the calorimeter, calibration test results on its performance, and test results from two cells tested.

Thermal Property Measurements of Stratigraphic Units with Modeled Implications for Expected Performance of Vertical Ground Source Heat Pumps

Ground temperature and lithology influence ground source heat pump (GSHP) performance; however, typical design for residential systems uses estimated handbook values that are not necessarily representative of local geology. The incorporation of true ground temperature and thermal property measurements into design models would yield a more optimal design and thus decrease life cycle cost. A two-part study was conducted, first focusing on recording thermal properties of specific lithofacies in a particular region (Wisconsin, USA), then modeling how these measurements could change expected GSHP design and performance in a typical residential setting. Representative sedimentary, igneous, and metamorphic rocks from Wisconsin were characterized using guarded-comparative-longitudinal heat flow experiments (ASTM E1225), calorimetry, and weight-volume assessments. X-ray diffraction was also performed on some samples to assess the effect of mineralogy. Across all rock types, thermal conductivity ranged from 1.84 to 6.71 W m−1 K−1, and specific heat capacity ranged from 713 to 891 J kg−1 K−1. The indexed values were used to construct a hypothetical vertical heat exchange loop penetrating vertically consecutive Paleozoic strata. The hypothetical loop was examined using the rate of system temperature drop under full load as a measure of performance during the heating season. Expected system performance was compared between commonly cited thermal conductivity values of their general lithologies (e.g. sandstone, dolomite, shale) and the laboratory-measured thermal properties of the specific formations. Thermal conductivity indexed by general lithology proved to be insufficient as a design parameter to generate accurate assessments of GSHP performance.

Controlling cement hydration with nanoparticles

Nanoparticles have recently become a focus in the development of new accelerators for cement hydration. We have produced nanoparticles of different materials like Al2O3, C–S–H-phase, and quartz by different top-down and bottom-up production methods. The effect of these particles on the cement hydration was followed by heat flow calorimetry to evaluate their acceleration potential as a function of the particles material, particles size and their percentage in the cement paste. In this work we will demonstrate which particles have the best potential as accelerators for cement hydration and therefore are most suitable for further investigations. Interestingly, nanoparticles which have a retarding effect on cement hydration were also found.