Journal of Thermal Analysis and Calorimetry

The oxidation of organic compounds with nitric acid has the potential to undergo a runaway hazardous reaction and explosion after the thermal–neutral induction period. The purpose of this study is to obtain a better understanding of the oxidation reaction mechanism to clarify the specific conditions under which the exothermic reaction occurs. In this study, the oxidation reactions of formic acid with nitric acid were investigated to represent a typical mixture of organic compound and nitric acid. From the results of thermal analysis, the overall reaction rate in a 15% nitric acid and 10% formic acid aqueous solution was formulated using an autocatalytic reaction model. The apparent activation energy was 75.2 kJ mol−1, and the pre-exponential factor was 7.87 × 108 s−1. The reaction rate increased with either nitric or formic acid concentrations, emphasizing that it is important to treat the mixture at lower concentrations for thermal safety. As a result of the thermal and in situ Raman spectroscopic analyses, it was found that the concentration of nitrous acid increased with the progress of the reaction as nitric acid and formic acid changed into NO2, N2O4, HCO(O)NO, HCO(O)NO2, and so on. The reaction mechanism started from nitrous acid and the oxidation of formic acid with nitric acid is an autocatalytic reaction involving this nitrous acid-initiated cycle.

This study examined the efficacy of PCM implementation in the wall on the thermal performance of the air handling unit (AHU). For this, a PCM layer (2 cm) was incorporated into the base wall with a thickness of 23 cm to investigate the PCM presence efficacy on heat transfer reduction. Considering the solar radiation effects on the building envelope, the sensitivity of the heat transfer reduction to the wall positions toward the cardinal direction was inspected. Based on the numerical results, placing PCM close to the outside space outperformed the PCM close to the interior space. Owing to PCM incorporation, the maximum and minimum heat transfer reduction was 27% and 5%, respectively. To examine the effect of PCM properties, eighteen PCMs were utilized and it was found that the effectiveness of the PCM within the wall in reducing heat transfer intensified with reducing the thermal conductivity. By adding PCM to the wall, less heat is transferred to the interior space in July and therefore the AHU cooling coil load is diminished. Calculations show that installing PCM on the wall can reduce the cooling coil power up to 33%. The effect of wall direction on the usefulness of installing PCM inside the wall is significant.

The core goal of the current theoretical exertion is to explore the impacts of step and sinusoidal bottom heating patterns on the buoyancy-driven flow and their heat flow aspects that are triggered by the temperature gradient inside the cavity which is commonly essential for many engineering applications like solar cells, food processing unit, materials processing unit, nuclear reactor core, etc. The domain of study is an air-filled cavity with an aspect ratio of 1, while the bottom wall is subjected to these two types of boundary conditions. The vertical walls are retained at reasonably lower temperatures whereas the top wall is kept insulated. The thermal and flow properties have been perceived with the aid of pertinent parameters like entropy generation, Nusselt number, non-dimensional temperature profiles and stream functions. The Ra is varied in the range of 103 ≤ Ra ≤ 106. The SIMPLE algorithm is applied to solve the governing differential equations by using a commercial software Ansys Fluent 2019. A significant observation found from the work is that the heat transfer rate is greater in the case of the step temperature profile. The average Nusselt number enhances 1.7 times from Ra = 105 to Ra = 105 for both the heating cases. Additionally, the heat transfer irreversibility is more near the wall as related to far from the wall due to high temperature gradients. The total entropy generation is 1.4 times more for step temperature profile as related to sinusoidal heating.

High-density polyethylene (HDPE) nanocomposites were prepared by a melting-compounding process with a polymethylsilsesquioxane (PMSQ) as nanofiller. In this process, the PMSQ nanoparticles were swollen in an organic solvent using a Ultra-Turrax system and sonication and blended with molten HDPE using a twin-screw extruder. This was followed by solvent removal. Nanocomposites with different PMSQ mass contents from 0 to 1% were prepared. The nanocomposites were characterized with Fourier transformed infrared, transmission electron microscopy, differential scanning calorimetry, scanning electron microscopy and by thermal conductivity. The mechanical and thermomechanical properties of the materials were studied. The HDPE–PMSQ nanocomposites presented a remarkable increase in the elastic modulus (E′) compared to the neat HDPE. The obtained mechanical and thermomechanical properties of HDPE–PMSQ nanocomposites were found to be related to the barrier effect of the PMSQ nanoparticles.

In this paper, the flow pattern and thermal characteristics of free convection of a Newtonian magnetohydrodynamic fluid flow inside a square enclosure are compared against two different non-Newtonian power-law (PL) fluids. The enclosure with horizontal insulated walls has two constant-temperature obstacles, while two sidewalls are differentially heated with sinusoidal pattern. Boussinesq approximation is used to consider the effect of hydrodynamic field on the thermal field. The problem is grounded using lattice Boltzmann method, and D2Q9 function is used to describe distribution of the density and energy. The effects of Rayleigh number, PL index, the aspect ratio of constant-temperature obstacles, Hartmann number, and periodicity of sinusoidal boundary condition on the hydrodynamic and thermal characteristics are investigated. The results showed that with increasing Rayleigh number, the Nusselt number increases but with increasing power-law index and Hartmann number, the Nusselt number decreases for shear thinning, Newtonian and shear thickening fluids. In addition, it was shown that increasing the aspect ratio of obstacles increases the Nusselt number. Also, it was reported that the Nusselt number of Newtonian and shear thinning fluids increases with increasing the periodicity of the sinusoidal boundary condition from 2π to 4π, while it reduces by further increase in periodicity.

The XIV International conference on thermal analysis and calorimetry held in St Petersburg, Russia 2013, which would restarted the regular periodicity of these meetings in Russia, is described including history of these conferences. The paper portrayed in details highlighting plenary lectures. Two addressed subjects dealing with yet unaccepted theory of thermal decomposition of solids and the overlooked impact of DTA heat inertia are discussed.

In this study, thermal performance of an impingement jet with the presence of porous block is numerically investigated. The study is comprised of two main parts. At first, a parametric study is conducted on the steady impingement jet with porous block. Later, the effect of porous block is assessed on the pulsative impingement jet. The effect of different pulsation frequencies and amplitudes is analyzed on the heat transfer between the jet and porous block. In order to model the thermal performance, the local thermal non-equilibrium model is applied to the system. An entropy generation study was also conducted in order to investigate the system’s performance from second law of thermodynamics point of view. In addition to the mentioned studies, by utilizing the energy density flux vector, different regimes of heat transfer in various cases are demonstrated and some of the trends obtained in parametric study are justified. The results suggest that porous block can change the Nusselt number distribution on the target plate. A more flattened Nusselt number distribution is observed with the presence of porous blocks. While lower frequencies and amplitudes of pulsation do not affect the thermal performance of the jet, higher ones have a moderate effect on the heat transfer rate of the impinging jet.

Organic peroxides combined with ionic liquids had a high application value in the desulfurization process. However, thermal stability between organic peroxides and ionic liquids displayed a significant difference. Moreover, it was of great significance to investigate the thermal hazard of organic peroxides due to the influence of ionic liquids. In this study, a common organic peroxide cumene hydroperoxide (CHP) and two imidazole ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([Bmim]BF4 and Bmim[NTf2]), with good desulfurization performance were selected for experiments. The thermal stability of [Bmim]BF4 and Bmim[NTf2], respectively, mixed with cumene hydroperoxide in air and nitrogen conditions was studied by thermogravimetry (TG) analysis. The kinetic data of CHP which was mixed with two ionic liquids were evaluated using two different isoconversional methods: Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS). Furthermore, their gas decomposition products were investigated by thermogravimetry coupled with Fourier-transform infrared spectroscopy (TG-FTIR) analysis. The experimental and calculated results demonstrated that the apparent activation energy was decreased after CHP was mixed with the two ionic liquids. The main decomposition stage ranged from 350.0 to 480.0 K with a mass loss of CHP under air and nitrogen conditions. The thermal decomposition behavior of the CHP under air conditions displayed higher apparent activation energy compared with that in nitrogen atmosphere. The experimental results provide an important reference for organic peroxides combined with ionic liquids applicated in the desulfurization process.