POLYMERS AND PLASTIC USE FOR THE HEAT-EXCHANGE EQUIPMENT (REVIEW)

The possibility of use of the heat-exchangers in whole or in part manufactured with use of polymers and plastics is considered. Despite obvious, at first sight, inexpediency of use of polymeric materials in the heat-exchange equipment (low coefficient of heat conductivity, and also low, in comparison with metals, the strength properties of the majority of the most widespread polymers), «polymeric» heat-exchangers find application in various areas of the industry more and more surely. Classification of heat-exchange apparatuses which constructive elements are executed with use of polymeric materials is proposed. The following signs are the basis for classification: polymer type, a type of polymer meric material, type of the heat-exchange apparatus (a form of heat-exchange elements), reliance on polymeric materials in apparatuses, motion freedom of polymeric heat-exchange elements, level of assembly of a design, and also diameter of tubular elements. Critical analysis the most characteristic designs developed by domestic and foreign designers and inventors is carried out. Ref. 21, Fig. 13.

The nomogram establishment of thermal conductivity and strength of insulating concrete for high temperature mine

The insulating concrete can be effectively reduced heat exchange between surrounding rock and ventilation air, which is of positive significance to mine cooling and energy conservation. The law of the mixing amount of insulation material on thermal conductivity and strength was discovered through testing 75 specimens of insulating concrete used for mine. Based on new effective medium theory, calculation model of coefficient of heat conductivity is deduced, and its parameters are acquired with the surface regression analysis method, then the mixing threshold of insulation material is determined. The resulting experimental data and calculational results make up data sample, and then the nomogram of thermal conductivity and strength of insulating concrete is plotted. The nomogram curve can be divided into regions with the main intensity and heat insulation as the auxiliary, the mutual influence region and the main intensity and heat insulation as the auxiliary. The constructed nomogram would not only provide the basis for determining porosity of compound concrete, but also determine thermal conductivity and strength according to porosity. It can simplify calculation step for the engineering and technical staffs, and help to guide design of insulating concrete.

Technological Processes for Manufacturing Cellular Concrete Products for Construction

Cellular concrete occupies one of the leading places in world practice of a high-rise construction as the constructional heat-insulating material used in case of construction and reconstruction of buildings and constructions of different purpose. In this artificial stone construction material pores (air cells with diameter 0.1-3.0mm) are distributed rather regularly and occupy from 20 to 90% of amount of concrete, providing high heatphysical qualities (coefficient of heat conductivity of 0.07-0.2 W/ms) that allows cellular concrete houses to keep heat well. Excessive (reserve) porosity of cellular concrete provides its frost resistance (compensates expansion of water when freezing and the formed ice without material destruction). Vapor permeability of cellular concrete provides fast removal of technological moisture from material and maintenance of normal moisture conditions in rooms, and rather high air permeability promotes preserving in rooms of fresh air. Significant growth in production the cellular concrete of products is caused by use of rather simple technologies allowing (due to change of degree of porosity and properties of interstitial material) to receive cellular concrete for thermal insulation or sound insulation, to make wall constructional heat-insulating products with a density 250-1200 kg/ m3 and strength of a 1-25 MPa.

Thermal Conductivity of Different Colored Compomers

Background Compomers are mostly used in primary dentition. The thermal conductivity properties of traditional or colored compomers have not been investigated in detail so far. The aim of this in vitro study was to assess and compare the thermal conductivities of traditional and colored compomers. Method Two sets of compomers – namely, Twinky Star (available in berry, lemon, green, silver, blue, pink, gold and orange shades) and Dyract Extra (available in B1, A3 and A2 shades) –were included in this study. All of the traditional and colored compomers were applied to standard molds and polymerized according to the manufacturers’ instructions. Three samples were prepared from each compomer. Measurements were conducted using a heat conduction test setup, and the coefficient of heat conductivity was calculated for each material. The heat conductivity coefficients were statistically analyzed using Kruskal-Wallis and Duncan tests. Uncertainty analysis was also performed on the calculated coefficients of heat conductivity. Results Statistically significant differences were found (p<0.05) between the thermal conductivity properties of the traditional and colored compomers examined. Among all of the tested compomers, the silver shade compomer exhibited the highest coefficient of heat conductivity (p<0.05), while the berry shade exhibited the lowest coefficient (p<0.05). Uncertainty analyses revealed that 6 out of 11 samples showed significant differences. Conclusions The silver shade compomer should be avoided in deep cavities. The material properties could be improved for colored compomers.

Thermal-Structure Analysis and Engineering Calculation for Double Tubesheets of Heat Exchanger

Structure’s features and current engineering design situation of double tubesheet are introduced in this paper. TEMA code plays an important role in double tubesheet design, but no more information concerning how to get metal temperature is presented in TEMA code. Engineering calculation shows that the temperature distribution in double tubesheet does not meet the hypothesis in TEMA code completely. In this paper, the thermal-field feature is shown by finite element analysis, important factors of boundary conditions such as contact resistance, slot air etc. are put forward, which will affect thermal-analysis of double tubesheet. It is pointed out that thermal-field analysis is the significant step in design of double tubesheet. It was found that the total heat transfer effect in expansion joint has greater influence on stress distribution. An example of equivalent coefficient of heat conductivity method based on thermal-structure coupling is presented to demonstrate a simplified boundary treatment method in expansion joint between tubes and sheet. This paper gives suggestions for double tubesheet design finally.

RESEARCH OF DIFFICULT HEAT EXCHANGE IN THE MULTILAYERED CYLINDRICAL СONSTRUCTION INCLUDING ENERGY SAVING GAS LAYERS

Pilot and theoretical studies of difficult heat exchange in a gas layer which allowed to carry out the analysis of process of transfer of warmth are conducted to define a contribution of each component of heat exchange (convective heat exchange and radiation), to find equivalent coefficient of heat conductivity of a vertical cylindrical air layer on various operating modes of laboratory installation in the wide range of temperatures (from 0 -to 3000 C). Results of research will be useful to modeling of heatexchange processes in gas layers, at a choice of the most optimum (power effective) thickness of a layer, a material of walls, environment structure, etc.

Fabrication and Properties of New Building Materials by Reutilization Refractory Materials

The utilization of domestic waste refractory materials are reviewed, and points out that China exists to the comprehensive utilization of waste refractory material in question, discusses the necessity of recycling of waste refractory material; focuses on the composite insulation board has the advantages of organic heat preservation material strength coefficient of heat conductivity of inorganic insulation materials of high and low flame retardant, for example discusses the feasibility of waste refractory materials used in building materials field, comprehensive recycling of waste refractory material resources and corresponding to focus attention on the utilization of the problems put forward their views.

A Study of Poor Conductor’s Thermal Conductivity Coefficient Measurement

When measuring the thermal conductivities of poor conductor with steady-state method, some errors should be introduced through the process of the experimental principle derivation to the experimental data measurement. To satisfy the need of measurement, this study aims to improve the structure of the “TC-I1 Type thermal conductivity measuring apparatus” correspondingly: we placed two fans at the side of the cooling plate, thus effectively control the stability of the strong-force convection cooling environment. This study chose digital thermometer of UT325 Type to collect temperature signals, storing the data on computer and putting such data under fitting process with the software Matlab. Compared with the traditional measurement, the post-modification apparatus successfully achieves lower errors in the coefficient of heat conductivity measurement and thus the results are closer to the inherent attribute values of the sample plate. It’s very satisfactory to the requirements of teaching and scientific research oriented measurements.