Modulated temperature DSC measurements relating to the cold crystallization process of poly(ethylene terephtalate)

The modulated temperature differential scanning calorimetric method (MT-DSC) yields three temperature dependent signals, an underlying heat capacity curve from the underlying heat flow rate (corresponding to the conventional DSC signal), and a complex heat capacity curve with a real part (storage heat capacity) and an imaginary part (loss heat capacity). These curves have been measured in the cold crystallization region for poly(ethylene terephtalate) with a modified Perkin-Elmer DSC-7. The underlying curve shows the well known large exothermic crystallization peak. The storage heat capacity shows a step change which reproduces the change in heat capacity during crystallization. This curve may be used as baseline, to separate the crystallization heat flow rate from the underlying heat flow rate curve. The loss heat capacity curve exhibits a small exothermic peak at the temperature of the step change of the storage curve. It could be caused by changes of the molecular mobility during crystallization.Dedicated to Professor Wunderlich on the occasion of his 65th birthday     

Modulated temperature differential scanning calorimetry

Modulated temperature differential scanning calorimetry (MTDSC) is used to study simultaneously the evolution of heat flow and heat capacity for the isothermal and non-isothermal cure of an epoxy-anhydride thermosetting system. Modelling of the (heat flow related) chemical kinetics and the (heat capacity related) mobility factor contributes to a quantitative construction of Temperature-Time-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams for the thermosetting system.     

Some elements in specific heat capacity measurement and numerical simulation of temperature modulated DSC (TMDSC) with R/C network

One important application of temperature modulated DSC (TMDSC) is the measurement of specific heat of materials. In this paper, a thermal resistance/capacitance (R/C) numerical model is used to analyze the effects of experimental parameters and calibration on the measurement of specific heat in TMDSC under isothermal conditions. The actual TMDSC experiments were conducted with sapphire and pure copper samples, respectively. Both simulation and experiments showed that in TMDSC, the measured sample specific heat is a non-linear function of many factors such as sample mass, the heat transfer properties of the TMDSC instrument, temperature modulation period, the heat capacity difference between calibration material and the test material, but modulation amplitude has very little effect on the results. The typical behavior of a heat flux type TMDSC can be described as a low pass filter in terms of specific heat capacity measurement when the instrument heat transfer properties are taken into account. At least for metallic materials, where the temperature gradient inside the sample can normally be ignored, the sample should be chosen in such a way that its total heat capacity (mass times specific heat) is close to that of the calibration material in order to get a more accurate result. Also, a large modulation period is beneficial to improving the test accuracy.     

耐热聚氯乙烯的耐热机理研究

用悬浮聚合方法制得了氯乙烯 N 苯基马来酰亚胺 ( 丙烯腈 )共聚物 ,研究了该共聚物的维卡软化点、玻璃化温度、动态力学行为以及形态结构 .发现当耐热组分达到一定含量时 ,耐热性能的增加幅度发生变化、出现两个动态力学内耗峰、形态上出现双连续相结构 .基于这些实验现象 ,提出了“刚性有效网架”可以使耐热性能大幅度提高的观点 ,并探讨了耐热机理 ,给出了物理模型 .讨论了相容性对“刚性有效网架”形成的影响     

Vapor compression CuCl heat pump integrated with a thermochemical water splitting cycle

In this paper, the feasibility of using cuprous chloride (CuCl) as a working fluid in a new high temperature heat pump with vapor compression is analyzed. The heat pump is integrated with a copper–chlorine (Cu–Cl) thermochemical water splitting cycle for internal heat recovery, temperature upgrades and hydrogen production. The minimum temperature of heat supply necessary for driving the water splitting cycle can be lowered because the heat pump increases the working fluid temperature from 755 K up to ～950 K, at a high COP of ～6.5. Based on measured data available in past literature, the authors have determined the T–s diagram of CuCl, which is then used for the thermodynamic modeling of the cycle. In the heat pump cycle, molten CuCl is flashed in a vacuum where the vapor quality reaches ～2.5%, and then it is boiled to produce saturated vapor. The vapor is then compressed in stages (with inter-cooling and heat recovery), and condensed in a direct contact heat exchanger to transfer heat at a higher temperature. The heat pump is then integrated with a copper–chlorine water splitting plant. The heat pump evaporator is connected thermally with the hydrogen production reactor of the water splitting plant, which performs an exothermic reaction that generates heat at 760 K. Additional source heat is obtained from heat recovery from the hot reaction products of the oxy-decomposer. The heat pump transfers heat at ～950 K to the oxy-decomposer to drive its endothermic chemical reaction. It is shown that the heat required at the heat pump source can be obtained completely from internal heat recovery within the plant. First and second law analyses and a parametric study are performed for the proposed system to study the influence of the compressor's isentropic efficiency and temperature levels on the heat pump's COP. Two new indicators are presented: one represents the heat recovery ratio (the ratio between the thermal energy obtained by internal heat recovery, and the energy needed at the heat pump evaporator), and the other is the specific heat pump work per mole of hydrogen produced. This new heat pump with CuCl as a working fluid can be attractive in other industrial contexts where high temperature heat is needed. One may replace a common heating technology (combustion or electric heating) with the present sustainable method that uses heat recovery and high efficiency temperature upgrading for heating applications.     

Application of a novel type of adiabatic scanning calorimeter for high-resolution thermal data near the melting point of gallium

A novel type of adiabatic scanning calorimeter (ASC) based on Peltier elements (PEs) is used to obtain high-resolution enthalpy and heat capacity data on the melting transition of gallium. The accuracy of the specific heat capacity and specific enthalpy is about 2 %, for a sub-mK temperature resolution. The simultaneously determined equilibrium specific heat capacity and specific enthalpy are used to determine the heat of fusion and the purity. In addition, the use of the PE-based ASC as a classical heat step calorimeter and as a constant rate (DSC-type) calorimeter is discussed. A comparison of the ASC results with literature data and DSC data shows the advantages of ASC for the study of phase transitions.     

Modulated‐temperature differential scanning calorimetry study of temperature‐induced mixing and demixing in poly(vinylmethylether)/water

The heat capacity or reversing heat flow signal from modulated‐temperature differential scanning calorimetry can be used to measure the onset of phase separation in a poly(vinylmethylether)/water mixture, clearly showing the special type III lower critical solution temperature demixing behavior. Characteristic of this demixing behavior is a three‐phase region, which is detected in the nonreversing heat flow signal. Stepwise quasi‐isothermal measurements through the phase transition show large excess contributions in the (apparent) heat capacity signal, caused by demixing/remixing heat effects on the timescale of the modulation (fast process). These excess contributions and their time‐dependent evolutions (slow process) are useful in understanding the kinetics of phase separation and the morphology (interphase) development. Care has to be taken, however, in interpreting the heat capacity signal derived from the amplitude of the modulated heat flow because nonlinear effects lead to the occurrence of higher harmonics. Therefore, the raw heat flow signal for quasi‐isothermal demixing and remixing measurements is also examined in the time domain. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1824–1836, 2003     

热处理对煤焦反应性及微观结构的影响

用热天平和XRD考察了热处理对二种煤(河北蔚县褐煤、四川湔江烟煤)镜质组半焦微观结构和反应活性的影响。TGA结果表明，热处理温度增加，蔚县煤镜质组(YXV)与湔江煤镜质组(JJV)焦炭的反应性降低；YXV焦炭的反应性随着热处理时间的增加而急剧下降，但一定热处理时间(60 min)后，其下降趋势变缓；热处理时间对JJV焦炭的影响较小。XRD结果表明，在热处理温度为900 ℃，初焦热处理时间为60 min时，YXV焦炭晶格结构发生明显改变，900 ℃以上，YXV焦炭芳香堆垛高度Lc随着热处理时间的增加而增加；热处理时间对JJV焦炭的影响不如YXV显著，而只有在较高的热处理温度(1 200 ℃)下，碳的微观结构才出现明显的有序化。热处理导致的焦炭微观碳结构趋于有序化是焦炭反应性下降的主要原因。     

Heat of adsorption of naphthalene on Pt(111) measured by adsorption calorimetry

The heat of adsorption of naphthalene on Pt(111) at 300 K was measured with single-crystal adsorption calorimetry. The heat of adsorption on the ideal, defect-free surface is estimated to be (300 - 34 - 199(2)) kJ/mol. From this, a C-Pt bond energy for aromatic hydrocarbons on Pt(111) of approximately 30 kJ/mol is estimated, consistent with earlier results for benzene on Pt(111). There is higher heat of adsorption at very low coverage, attributed to step sites where the adsorption heat is >/=330 kJ/mol. Saturation coverage, = 1 ML, corresponds to 1.55 x 10(14) molecules/cm(2). Sticking probability measurements of naphthalene on Pt(111) give a high initial value of 1.0 and a Kisliuk-type coverage dependence that implies precursor-mediated sticking. The ratio of the hopping rate to the desorption rate of this precursor is approximately 51. Naphthalene adsorbs transiently on top of chemisorbed naphthalene molecules with a heat of adsorption of 83-87 kJ/mol.     

Calorimetric sensing in bioanalytical chemistry: Principles, applications and trends

Calorimetry has shown great potential in bioanalytical chemistry as most biochemical processes involve a change in enthalpy. Two types of approach have been developed: (1) adiabatic calorimetry, which relies on the absence of heat exchange between the reaction vessel and the external environment, and (2) heat conduction calorimetry, involving measurement of the heat transferred from the vessel to a surrounding heat sink. Both principles, with their respective advantages and drawbacks, have been applied to microcalorimetry for the analysis of (bio)chemical compounds. Immobilization of the biomaterial in the vicinity of, or directly onto a small temperature or heat sensitive transducer has led to the concept of a calorimetric biosensor. In comparison to the traditional calorimeter, the calorimetric biosensor is better suited to continuous monitoring and size reduction. This simplified but sensitive device is expected to solve numerous problems in various fields of analytical chemistry.     

Reversible and irreversible heat capacity of poly(trimethylene terephthalate) analyzed by temperature‐modulated differential scanning calorimetry

The heat capacity of poly(trimethylene terephthalate) (PTT) has been analyzed using temperature‐modulated differential scanning calorimetry (TMDSC) and compared with results obtained earlier from adiabatic calorimetry and standard differential scanning calorimetry (DSC). Using quasi‐isothermal TMDSC, the apparent reversing and nonreversing heat capacities were determined from 220 to 540 K, including glass and melting transitions. Truly reversible and time‐dependent irreversible heat effects were separated. The extrapolated vibrational heat capacity of the solid and the total heat capacity of the liquid served as baselines for the analysis. As one approaches the melting region from lower temperature, semicrystalline PTT shows a reversing heat capacity, which is larger than that of the liquid, an observation that is common also for other polymers. This higher heat capacity is interpreted as a reversible surface or bulk melting and crystallization, which does not need to undergo molecular nucleation. Additional time‐dependent, reversing contributions, dominating at temperatures even closer to the melting peak, are linked to reorganization and recrystallization (annealing), while the major melting is fully irreversible (nonreversing contribution). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 622–631, 2000     

Leak detection in a high-pressure heat exchanger system in a refinery using radiotracer technique

A radiotracer investigation was carried out in a diesel hydrotreater (DHDT) unit in a refinery for leak detection in a breech-lock heat exchanger system. The main objectives of the study were to identify the leaking heat exchanger in a system with six heat exchangers and estimate the leak rate. Bromine-82 as dibromobiphenyl was selected and used as radiotracer for the investigation. The radiotracer was instantaneously injected into the suction end of the feed pump line to the heat exchanger of the DHDT unit. The movement of the tracer was measured at strategically selected locations using NaI(Tl) scintillation detectors. Based upon the results of the radiotracer investigation, it was found that out of six heat exchangers, exchanger E-1F was leaking.     

Deuterium isotope effect on molar heat capacities and apparent molar heat capacities in dilute aqueous solutions: A multi-channel heat-flow microcalorimeter study

The molar heat capacities of chloroform, dichloromethane, methanol, acetonitrile, acetone, dimethyl sulfoxide, benzene, dimethylformamide, toluene, and cyclohexane, as well as their deuterated isotopologues, were measured using a multi-channel heat conduction TAM (Thermal Activity Monitor) III microcalorimeter. In addition, the apparent molar heat capacities of some of the associated dilute aqueous solutions (0.0039 < solute mole fraction, x_i < 0.0210) were also measured. A temperature drop method from (298.15 to 297.15) K at 0.1 MPa was employed. The corresponding heat capacities were determined from the integration of the measured heat flow. The heat capacity results are shown to be in good to very good agreement with the available literature values. In addition, good correlations were obtained for the effect of isotopic substitution on both molar heat capacity and apparent molar heat capacity in aqueous solutions. These correlations should be useful in the prediction of the molar heat capacities or the apparent molar heat capacities of other deuterated compounds. Since these measurements were conducted with ampoules, the effects of heat of condensation and/or vapor space on the accuracy of the heat capacity determinations are discussed. The overall results from this study demonstrate the utility of a multi-channel heat conduction microcalorimeter in obtaining good reproducibility and good accuracy for molar heat capacities as well as apparent molar heat capacities from simultaneous samples.     

A nonequilibrium molecular dynamics method for thermal conductivities based on thermal noise

We developed a nonequilibrium molecular dynamics (NEMD) method for calculating thermal conductivities. In contrast to other NEMD algorithms, here only the heat sink is localized, whereas the heat source can be uniformly distributed throughout the system. The noise due to cutting off the pair forces or to integration errors is such a uniform heat source. In traditional NEMD methods it is normally considered a nuisance factor. The new algorithm accounts for it and uses it. The algorithm is easy to derive, analyse and implement. Moreover, it circumvents the need to calculate energy fluxes. It is tested on the enhanced simple-point charge model for liquid water and reproduces the known thermal conductivity of this model liquid of 0.81 W m(-1) K(-1). It can be generalized to situations, where the thermal noise is replaced by another uniform heat source, or to the inverse situation, where the heat source is localized but the heat sink extends over the entire system.     

Thermal analysis of loop heat pipe used for high-power LED

The goal of this study is to improve the thermal characteristics of high-power LED (light emitting diode) package by using a loop heat pipe. The heat-release characteristics of high-power LED package are analyzed and a novel loop heat pipe (LHP) cooling device for high-power LED is developed. The thermal capabilities, including start-up performance, temperature uniformity and thermal resistance of loop heat pipe under different heat loads and incline angles have been investigated experimentally. The obtained results indicates that the thermal resistance of the heat pipe heat sink is in the range of 0.19–3.1 K/W, the temperature uniformity in the evaporator is controlled within 1.5 °C, and the junction temperature of high-power LED could be controlled steadily under 100 °C for the heat load of 100 W.     

Particle dynamics and particle heat and mass transfer in thermal plasmas. Part II. Particle heat and mass transfer in thermal plasmas

This paper is concerned with a review of heat and mass transfer between thermal plasmas and particulate matter. In this situation various effects which are not present in ordinary heat and mass transfer have to be considered, including unsteady conditions, modified convective heat transfer due to strongly varying plasma properties, radiation, internal conduction, particle shape, vaporization and evaporation, noncontinuum conditions, and particle charging. The results indicate that (i) convective heat transfer coefficients have to be modified due to strongly varying plasma properties; (ii) vaporization, defined as a mass transfer process corresponding to particle surface temperatures below the boiling point, describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas; (iii) particle heat transfer under noncontinuum conditions is governed by individual contributions from the species in the plasma (electrons, ions, neutral species) and by particle charging effects.     

Simulation of temperature-modulated DSC of transitions represented by abrupt changes in heat capacity

Computer simulations have been applied to elucidate the response of a sample to temperaturemodulated differential scanning calorimetry (tm-DSC) during transitions. Two cases have been simulated; a latent heat without supercooling (represented by an abrupt heat capacity pulse with perfect reversibility) and a latent heat with perfect supercooling or large hysteresis (an abrupt heat capacity change without reversibility, i.e. the change in heat capacity is seen on heating, but not on cooling). Because the simulation was applied to these well-characterized phenomena, the results are useful to reveal actual sample thermal responses during transitions. The non-reversible component was observed in both cases and has no distinct difference. Higher harmonics due to non-linearity of the transitions were also observed. Furthermore, by inspecting thermal response of the sample and the essential feature of tm-DSC, a new method of data analysis has been devised.     

Reversible Melting of Semi-crystalline Polymers Frequency dependence of the reversible melting enthalpy

Modulated DSC (MDSC) has been used to study the heat flow during melting and crystallisation of some semi-crystalline polymers i.e. different grades of polyethylene (LDPE, LLDPE and HDPE), and polypropylene (PP). The heat capacities measured by MDSC are compared with the hypothetical complex heat capacities of Schawe and it is shown that numerically they are equivalent; nevertheless, the concept of the complex heat capacity is problematic on a thermodynamic basis. A reversing heat flow (proportional to the experimental heat capacity of the material) was present at all conditions used for the study. In the melting zone of the polymers it depends on the modulation frequency and on the amplitude. Higher amplitude and frequency of modulation reduce the ratio of the reversing heat flow to the total heat flow, the latter is nearly independent on these parameters. The reversible component of the melting enthalpy of polymers depends on the modulation frequency, the modulation amplitude and the type of the polymer. It increases by increasing the branching in polyethylene. The existence of the reversible heat flow during the crystallisation and melting is contrary to the current hypotheses and theories of polymer crystallisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat Transfer Performance of Milk Pasteurization Plate Heat Exchangers Using MWCNT/Water Nanofluid

Increasing efficacy of plate heat exchanger (PHE) is a method of reducing energy consumption of milk pasteurization and sterilization in dairy industries. In order to enhance heat transfer capability of water as a hot stream in PHEs, multiwalled carbon nanotubes (MWCNT) were added to water. An experimental setup was designed and manufactured to measure heat transfer coefficient and Nusselt number (Nu) as two key parameters for convective heat transfer. This system had two individual loops for hot and cold fluids. The experimental results clearly indicated that heat transfer coefficient and Nu number of pure water increased by adding MWCNT with weight concentration of less than 1 wt%. With increasing weight concentration of the nanoparticles, heat transfer coefficient and Nu number increased. This augmentation was intensified at higher Peclet numbers which showed more effective presence of them at high flow rates of nanofluids. Moreover, at constant weight concentration, both heat transfer coefficient and Nu number increased. Augmentation of heat transfer capability resulted in more heat exchange with milk fluid in a short time; thus, before occurrence of fouling in plates of exchanger, pasteurization of milk and production of the products would be easier.