Advanced Materials Research Vols. 732-733

Abstract: Based on the forward voltage measurement principle, a test device was designed for junction temperature measurement. The voltage temperature coefficient is-1.49mV/°C according to the experimental data, and a series of junction temperatures were obtained on various ambient temperature. A numerical model was built by using the CFD software Flent, which was verified with the experimental data. The influence of the different structure parameters of the heat sink on heat dissipation performance was studied numerically. The results show that the optimal structure parameters were as following: Fin number is within 8~12. Fin height is within 170mm~190mm. Fin length is within 35mm~55mm. Fin thickness is within 1mm~3mm. Bases radius is within 33mm~40mm. With the chip junction temperature and the radiator weight as optimizing object, the optimal parameters were obtained as following: Fin number is 12. Fin height is 190mm. Fin length is 55mm. Fin thickness is 1.5mm. Bases radius is 33 mm.

Abstract: A mechanical vapor recompression heat pump driven by a centrifugal fan is designed together with falling-film evaporation. Based on theoretical analysis, experimental research is applied to study the fan type of MVR. Choosing water as the experimental medium, the operation characteristic of MVR applied to low evaporation is examined. Practically, the pressure difference of the unit is likely to keep stable while its evaporation pressure goes up. After the system performance is tested and analyzed, it shows that the total evaporation water and total input energy increase as its evaporation pressure grows. Further, some calculation is done and the result indicates that its SMER and COP decrease while the evaporation pressure rises. The reason of this phenomenon is: the leakage loss of the fan inside goes up and its displacement efficiency reduces as the evaporation temperature and pressure is high; finally, it brings forth the drop of the systems adiabatic efficiency. Finally, the trend of average input work for compressed vapor is compared in three different terms. The trend of average input work by calculation is the same as that in theory; that is to say, both of them descend when the evaporation pressure ascends. Because of displacement efficiency, the trend of average input work by measure is different from that in theory; that is to say, the average input work by measure grows slightly when the evaporation pressure goes up.

Abstract: In this paper, mathematical model for heat transfer in thermal barrier is established based on the experiment which tested apparent heat conductivity of heat insulation oil pipes. Vacuum degree influence on performance of vacuum heat insulation oil pipe is analyzed by contrasting heat insulation oil pipes in different grades. The main conclusions are as follow. When internal pressure in the thermal barrier is between 0~20Pa or greater than 40Pa, the apparent heat conductivity increases with the pressure. And when internal pressure in the thermal barrier is between 20~40Pa, the apparent heat conductivity decreases with the pressure in volatility. When internal pressure in the thermal barrier is between 30~40Pa, the apparent heat conductivity of heat insulation oil pipe is lesser.

Abstract: The ribs have been used to raise the area of convection heat transfer and consume little material simultaneously. This article adopt the analyze method of exergy transfer, with the help of gained temperature distribution in the constant-section straight ribs, derived the equation of the exergy distribution and the coefficient of exergy transfer distribution, with pay more attention to the rules of the energy quality decaying during the process of heat transfer in ribs. The solving results have been acquired in the Aluminium ribs and steel ribs with the case of same geometric parameter and same temperature parameter. The results show that the temperature, exergy value and the coefficient of exergy transfer is descending along the length direction of ribs. The parameter of Aluminium ribs is greater than the steel ribs because of the different property.

Abstract: The article points out and describes in detail the basic thermal bridges in contact thermal insulation systems and in ventilated facades. Thermal bridges are illustrated by means of thermal images of spot thermal bridges and the calculation of spot heat transfer coefficients.

Abstract: A numerical investigation of the flow and heat transfer in a two-row finned-tube heat exchanger is conducted with a three-dimensional conjugated model using the CFD software. The results show that, compared to the quadrate slotted fin, the circular slotted fin have good heat transfer performance in that the percentage increase in heat transfer is higher than that in the friction factor. Within the Reynolds number range compared ( from 1,270 to 8,892), the Nusselt number of new slit 1 is about 25.6-61.6% and 20.8-57.5%, while new slit 2 is about 26.8-33.6% and 25.8-33.0%, higher than that of the quadrate slotted fin surface at identical pressure drop and the identical pumping power, respectively. For the two-row plate fin-and-tube heat exchanger, new slit 2 is recommended for the use in air-conditioning because its integrative design.

Abstract: Aimed to optimize the design of micro combustor whose chamber based on porous medium wall surface, combustion and flame stability characteristics on porous wall surface with methane/air flat flame were investigated experimentally in this paper. The experimental results show that stable flat flame can be formed on the porous medium surface within given ranges of fuel equivalence ratio and flow rate. When mixture flow rate increasing, the thickness of flame decreases firstly and then increases, and standoff distance of flames decreases quickly and then is unchanged. At higher mean velocity of mixture, the flame moves closer to the porous plate surface, and the minimum distance needing for keeping stable flames decreases. The heat exchange between the porous plate and the mixture can not only preheat mixture but also cool the porous plate.

Abstract: Experiments of gas-solid suspension were carried out in a high-flux circulating fluidization bed with the solid mass flux up to 536 kg/(m²·s). Differential pressure fluctuation time series were obtained at different locations in the riser. Shannon entropy increment rate analysis was developed to identify the flow pattern and transformation and characterize the dynamic behavior. Effect of superficial gas velocity on the Shannon entropy increment rate was examined under high solid mass flux. It was demonstrated that a circulating fluidization bed at high solid mass flux was a deterministic chaos system and the sensitivity of the system's chaotic characteristic to operating parameters at different flow regimes was different. Shannon entropies increment rate of different flow regimes were distinct. Shannon entropy increment rate analysis method results in high degree of recognition for flow pattern and transformation.

Abstract: The general cycle model of a class of external combustion engines is established in which the influence of the multi-irreversibilities mainly resulting from the linear heat-loss model between the high and low heat reservoir, and the irreversible adiabatic processes. Some important parameters such as the power output, efficiency and the temperatures of the working substance are calculated and some important characteristic curves are given. The results obtained in this paper may provide some theoretical guidance for the optimal design of the Carnot, Brayton, Braysson and some new heat engines.

Abstract: Dynamic changing process is caused by heat and mass transfer between thermodynamic system and outside, which is not entirely judged in Traditional thermodynamics. Drawing on Modern Thermodynamic and Shell Theory, a new thermodynamic system has been conducted, which consists of inner system, border (shell) and outside. Shell is formed by shell wall and shell gates, and shell wall is insulated. On the basis of above, the opening degree and exchange rate, and the relationship between them are proposed. In the new system, the message as a physical quantity is equivalent to material and energy. The exchanging physical quantities include information, material and energy between thermodynamic system and outside. As the material flow exchange process, stability criterion (border opening degree) is derived. Traditional thermodynamics is perfected and supplemented by the research findings, which offered theory basis for thermodynamic system exact analysis.