A method for the determination of the specific heat and heat of decomposition of composite materials

A method has been developed to determine the specific heat of a material during thermal decomposition using a combination of DSC and TGA data obtained at the same heating rate. The heat of decomposition is calculated simultaneously using the same data. This technique was used to determine the specific heat and heat of decomposition of a widely used fiberglass-filled phenol—formaldehyde resin and a fiberglass-filled acrylonitrile—butadiene (AB) copolymer. Experimental data are presented for the specific heat of both the virgin and char components for temperatures between 60 and 730°C. The calculated specific heat of the mixture during decomposition for both materials is also presented.     

Thermodynamics and heat transfer study of a circular tube embedded with novel perforated angular-cut alternate segmental baffles

Journal of Thermal Analysis and Calorimetry - Baffles are used for heat transfer enhancement in heat exchanger tubes. However, they also increase the friction factor in the flow channel....     

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.     

How do the mathematical models of calorimeters really work?

In the paper methods of the analysis of heat effects occurring in the calorimeter as well as mathematical models applied for the determination heat effects involved in these devices are discussed. It was demonstrated that often mathematical models of the determination of heat effects are rather poor. Whereas, more sophisticated, existing models are relatively rarely used in calorimetric practice. The range of application of thermal–electrical and thermal–dynamic analogy methods were presented.     

Experimental analyses on heat transfer performance of TiO2–water nanofluid in double-pipe counter-flow heat exchanger for various flow regimes

Journal of Thermal Analysis and Calorimetry - Nanofluids are widely used in heat transfer applications. This article presents the effect of heat transfer and pressure drop of the TiO2–water...     

Bilanz-reaktionskalorimetrie

Reaction calorimetry is used to investigate chemical or physical reactions under realistic process conditions.The capabilities of the measuring system and the versatility of the evaluation principle are described at a simple example: dosing of cold water into the warmer reactor and heating up of the reactor content.The base of the calorimetric computations are the complete mass and heat balances. Hence the known heat fluxes can be used to give the true heat production rate of the reaction, as the example shows.The results demonstrate that even for chemical systems which produce (or consume) rather small amounts of heat, still high precision of the calorimetric data can be achieved.     

Enhancement of convective heat transfer in smooth air channels with wall-mounted obstacles in the flow path

The topic is of paramount importance. Heating, cooling, or solar air ducts are used in several sectors and in very diverse fields. The improvement in their performance has been and is still of major concern to theorists and practitioners. The issue of exchanging heat between fluid and the heated surfaces within a smooth air channel relies mainly on the value of the heat transfer coefficient. This coefficient is a mine of factors that affect the heat exchange between working fluid and heated walls. Therefore, it is an ambitious attempt to work on such a topic. Obstacles, such as staggered or in-line, transverse, or longitudinal baffles, fins, or ribs have long been utilized in several thermal systems like shell-and-tube heat exchangers with segmental baffles, compact heat exchangers, flat-plate solar air collectors, microelectronics, and various other industrial applications, because of their high thermal loads and reduced structural parameters. The channels, through which the cooling or heating fluid is supplied, are generally mounted with several obstacles in order to increase the cooling or heating level. This configuration is mostly used in designing heat exchangers and solar air collectors. Through this contribution, we present a comprehensive literature review of the various heat transfer strategies used to improve the performance of smooth air channels (SACs). Various research works were made on (SACs) either numerical or experimental in order to improve their performance. Different models and configurations of obstacles are reviewed and discussed, including attached, semiattached, or detached; parallel, orthogonal or inclined; solid, perforated, or porous; and simple, corrugated, or shaped, of various sizes, positions, attack angles, perforations, porosities, arrangements, and orientations. In these studies, the obstacles are principally used to change the direction of the flow field, to modify the distribution of the local heat transfer coefficient, and also to increase the turbulence levels, thus resulting in larger heat transfer between the fluid and the heated walls.

     

Heterogeneous/homogeneous and inclined magnetic aspect of infinite shear rate viscosity model of Carreau fluid with nanoscale heat transport

The study of the inclined flow along with the heterogeneous/homogeneous reactions in the fluid has been widely used in many industrial and engineering applications, such as petrochemical, pharmaceutical, materials science, heat exchanger design, fluid flow through porous media, etc. The purpose of this study is to present an infinite shear rate viscosity model using the inclined Carreau fluid with nanoscale heat transport. The model considers the effect of inclined angle on the fluid’s viscosity and the transfer of heat at the nanoscale. The result shows that the viscosity of the fluid decreases by increasing the inclination angle and the coefficient of heat transfer also increases with the inclination. The model can be used to predict the viscosity and heat transfer fluid’s behavior in the inclined systems that is widely used in the industrial and engineering applications. The results provide a better understanding of the inclined flow behavior of fluids and the heat transfer at the nanoscale, which can be useful in heat exchanger design, fluid flow through porous media, etc. Greater Infinite shear rate viscosity parameter gives the higher magnitude of Carreau fluid velocity. Moreover, inclined magnetic field reduces the velocity due to Lorentz force. Two numerical schemes are used to solve the model, BVP4C and Shooting.     

On-line Calibration and Determination of the Heat of Reaction for Laboratory Scale Heat Transfer Calorimeters

A simple method for the on-line calibration, in which both the heat transfer coefficient and the heat capacity of the reactor contents are determined, is described for laboratory scale heat transfer calorimeters. The calorimeter is operated in the isoperibolic mode for the calibration and a constant power is supplied to a resistor placed inside the reactor. The reactor heat balance differential equation is used to produce a set of linear simultaneous equations with each data acquisition cycle giving one equation. The heat transfer coefficient and the heat capacity are obtained from this set of equations by linear least squares. The application of the calibration procedure is illustrated by experiments in which the heat of reaction is determined on-line fora simulated reaction with first order kinetics and for the hydrolysis of acetic anhydride. This revised version was published online in July 2006 with corrections to the Cover Date.     

Review of heat transport properties of solar heat transfer fluids

The present article reviews the test techniques for some of the important heat transport properties of oils such as viscosity, density, specific heat capacity and thermal conductivity mainly used for characterization of heat transfer fluids. It can be seen that while density of oils can be tested at higher temperatures, the other heat transport properties of oils like viscosity, specific heat capacity and thermal conductivity have a limitation of being tested at low temperatures below 100–150 °C. While quite a few number of researchers have reported evaluation of heat transfer properties like specific heat capacity and thermal conductivity of oils by different methods, there remains a huge scope of debate and discussions on the repeatability and reproducibility of such tests, especially in case of oils used in high-temperature applications. A lot of insight has been gathered with respect to testing of thermal conductivity of oils, and several common test methods have been compared with each other. Lastly, two mathematical models, reported in the literature in open domain, have been reviewed and compared with each other. If the oils are to be used at elevated temperatures, like heat transfer fluids used in concentrated solar power generation where temperatures go as high as 400 °C and beyond, there is an urgent need to standardize a laboratory test method for performance evaluation of heat transport properties, which can help in formulating new generation oils based on novel chemistries and technologies like nanofluids, synthetic oils of novel chemistries, molten salts and molten metals.     

Absolute calibration of flow calorimeters used for measuring differences in heat capacities. A chemical standard for temperatures between 325 and 600K

Two methods for the absolute calibration of flow calorimeters (used for measuring the differences in heat capacities of two fluids) have been investigated. In the recommended method of calibration, a change in the flow rate of the fluids is used to minic a change in the heat capacity of the fluid. In the other method of calibration, heat loss is measured using a fluid of known heat capacity, and it is assumed this heat loss is constant. This calibration method is not recommended because the heat loss is, in general, not constant. For some calorimeters the difference between the two methods of calibration is negligible, while for others erros as high as 40% are caused by choosing the wrong method. A detailed analysis of the heat losses in this kind of calorimetry shows why the two calibration methods give different results and leads to various methods of improving calorimeter construction and operation. Because chemical standardization is far more convenient for routine use, the recommended absolute calibration method has been used to establish 3.00 mol-kg^–1 aqueous NaCl as a chemical standard for temperatures between 325 and 600K at 17.7 MPa.     

Determination of equilibrium constants by titration calorimetry : Part II. Data reduction and calculation techniques

Techniques of data reduction and methods of calculation have been given for the determination of equilibrium constants by titration calorimetry. It has been shown how, starting with typical titration calorimetry data, the apparent heat liberated in the reaction vessel can be calculated, corrected for extraneous heat effects, and used to solve for the equilibrium constant and enthalpy change value(s) for the reaction(s) under investigation. Equations are given for calculating the energy contributed to the overall heat effects measured in the reaction vessel by processes other than chemical reactions such as heat of stirring, heat losses, heat of dilution, etc., and by chemical reactions other than the one(s) for which equilibrium constant(s) are sought. Mathematical techniques and equations are presented for calculating equilibrium constants and enthalpy change values from titration data by least squares analysis.     

Thermodynamic investigation of n-hexane thin films adsorbed on magnesium oxide

The thermodynamic properties of n-hexane adsorption on MgO(100) were determined using high-resolution volumetric adsorption isotherms in the temperature range 195-255 K. Two distinct layering transitions are observed in the isotherms. The isotherms are used to calculate the two-dimensional compressibility, the differential enthalpy and entropy, the heat of adsorption, and the isosteric heat of adsorption. Neutron Diffraction is used to identify where melting of the n-hexane monolayer takes place.     

Synthesis of new substituted thiazoles containing aminooxadiazole ring

Heat exchangers of circulating type are used extensively in the heat exchange processes. Circulation of liquid in these devices is ensured by mechanical mixing devices, and heat exchange is enhanced by the increase of the heat exchange surface. The application of the upright heat exchange elements like double pipes providing a cross-flow regime in the device is the most effective. Calculation of the apparatus with the vertical heat-exchange elements for determination of constructive and regime parameters at maximum output of the device was presented.     

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.     

Heats of solution of gaseous hydrocarbons in water at 15, 25, and 35°C

Calorimetrically measured heats of solution of eleven hydrocarbon gases into water are reported at 15 and 25°C. Gases studied are methane, ethane, propane, n-butane, 2-methylpropane, 2,2-dimethylpropane, cyclopropane, ethene, propene, 1-butene, and ethyne. These values in combination with previous results are used to derive heat capacity changes at 25°C. Comparison of enthalpy and heat capacity values with those from other studies shows satisfactory agreement. Correlation of the heat capacity change with the number of water molecules in the first solvation shell of the solute suggests that the observed heat capacity changes are primarily due to changes in the water molecules in this solvent shell.     

Fire hazard assessment on polyurethane sandwich panels for temporary accommodation units

Fire hazard assessment on sandwich panels used for constructing temporary accommodation units (TAUs) is discussed. The requirements imposed by the three responsible local government departments, i.e. Buildings Department, Fire Services Department and Labour Department, are outlined. A typical sandwich panel used for constructing TAUs was assessed by a cone calorimeter. Four radiative heat fluxes of 20, 25, 50 and 65 kW m⁻² were applied to study the sustained ignition time, peak heat release rate, average heat release rates in 60 and 180 s after ignition, total heat release rate, mass loss percentage, total smoke release, carbon monoxide and carbon dioxide yields. From these data, the possibilities of flashover and smoke aspects were studied. Preliminary recommendations on what should be considered in specifying fire tests for new regulations on the use of these sandwich panels are made.     

Computation of the generalized Debye functionsδ(x,y) andD(x,y)

Automatic computer programs (BASIC-PLUS) are developed to calculate Debye functions also for non integer exponents. Functions of this type occur in the heat capacity analysis of polymer crystals, if simple continuum approximations are used. The heat capacity of completely crystalline polyethylene is calculated and compared with experimental data.     

一种用于研究金属氢化反应的量热系统

将RD-1型量热计的样品管改装成能测量金属氢化反应热效应的量热系统,量热计常数经电能标定,峰高法和面积法所测结果的相对精度为0.5-1％。     

Absolute Measurements of the Combustion Heat of Natural Gas

A new isothermal calorimetric method for measuring the combustion heat of gas, relying upon the operation principle of the heat pipe, is considered together with the sequence of thermal processes occurring when this method is used. The functional diagram of the calorimeter is analyzed. Two procedures for measuring the heat effects are presented.