Enhancement Of Thermal Resistance Research Articles

New Dimensionless Correlations for the Evaluation of the Thermal Resistances of a District Heating Twin Pipe System

The heat losses from pre-insulated double-pipe district heating (DH) systems buried in a homogeneous soil are studied numerically. The study is conducted using the diameter of the pipes and their distance, the size of the insulation, the thermal conductivity ratio between the insulation and the soil, as well as the burial depth of the double-pipe system, as controlling parameters. A computational code based on a control-volume formulation of the finite-difference method has been developed using the open-source framework OpenFOAM with the purpose to compute the heat transfer rate across adjacent solid regions with different thermophysical properties. The main scopes of the study are: (a) to investigate in what measure the geometry and the relative position of the warm and cold pipes, as well as the temperature imbalance, the burial depth and the physical properties of both the insulation and the soil, affect the heat losses; (b) to analyze the existence of an optimal configuration of the DH system by the thermal resistance enhancement viewpoint; and (c) to develop accurate correlating equations for the evaluation of the thermal resistance existing between each pipe and its surroundings, useful for practical thermal engineering applications.

Polylactides Bearing Vanillin at Chain End Provided Dual Dynamic Interactions: Stereocomplex Formation and Nanostructure Control

The chemical modification of the polymer chain end group of polylactide is important for the development of nanostructural materials. Herein, the first example of dual dynamic functionality in polylactides bearing vanillin at the chain end is first demonstrated. The first function, stereocomplex formation of both enantiomeric polymers, results in an enhancement in thermal resistance, while the second creates reversibility through amine–imine transformation. This transformation self‐assembles into interesting morphologies, including raindrop‐like nanoparticles observed on imine formation, and spider‐web‐like fibrous ones observed on aldehyde formation from hydrophobic–hydrophilic stimuli by acid. These properties indicate that the present polymer shows dual dynamic building block moiety properties, composed of the natural products. image

Polypropylene/Poly(trimethylene terephthalate) Blend Nanocomposite: A Thermal Properties Study

In this article, thermal properties of polypropylene/poly(trimethylene terephthalate) melt-mixed blends containing organically modified montmorillonite nanoclays and interacting compatibilizers are studied. Dynamic mechanical analysis showed an enhanced elastic modulus and reduced damping upon nanoclay fillers incorporation, also α-relaxation peak was shifted up while β-relaxation was not affected. Thermogravimetry exhibited a synergistic effect in thermal stability of the blend accompanied by a reduction in decomposition rate. This effect was more pronounced in presence of compatibilizers. The addition of nanoclay fillers generally led to an enhancement of thermal resistance; however, a dual function was evident, namely preventive and catalytic, respectively prior to and after onset of degradation.

Modification of cellulose by UV-grafting of an organopolysilazane oligomer

AbstractThe modification of cellulose fibers by grafting specific functions could improve their quality and allow their use for the development of new products. In this work we report about the functionalization of a cellulose fiber network (filters) with organo-polysilazane oligomers by UV-irradiation. Photo-induced grafting, as assessed by contact angle and TGA measurements, was successful: an interesting enhancement of thermal resistance and mechanical properties was obtained. Water repellency was also achieved.

Effect of glycosylation on the stability of α1-antitrypsin toward urea denaturation and thermal deactivation

The effects of glycosylation on the stability of human α 1-antitrypsin were investigated. The transition midpoints in urea-induced equilibrium unfolding of a non-glycosylated recombinant, a yeast version of glycosylated, and human plasma α 1-antitrypsin were 1.8 M, 2.2 M, and 2.5 M at 25°C, respectively. Kinetic analyses of unfolding and refolding revealed that glycosylation retarded the unfolding without affecting the refolding rate significantly, suggesting that the stability increase is due to the stabilization of the native state as opposed to the destabilization of the unfolded state. In thermal deactivation, which is a heat-induced aggregation process, the ungycosylated recombinant α 1-antitrypsin was deactivated most easily, which was followed in order by the yeast, and the plasma form. The results indicate that glycosylation confers the increase in stability of α 1-antitrypsin, and that the oligomannose sugars present on the yeast form produce a less stable molecule than the complex type sugars on the plasma form. It appears that the effect of glycosylation on the enhancement of thermal resistance is exerted through the increase in conformational stability. However, a stable recombinant variant (Phe 51→Cys) that showed the same conformational stability as the plasma form was less resistant to thermal denaturation than the plasma α 1-antitrypsin. The results suggest that the existence of carbohydrate moiety per se as well as the conformational stability contribute to the kinetic stability of α 1-antitrypsin toward aggregation.

Thermal impedance of pressed contacts at temperatures below 4 K

Enhancement of thermal resistance at mechanical contacts between cryogenic components by using a thin plate of sapphire is described.