Advanced Materials Research Vols. 614-615

Abstract: This work present the experimental evaluation of the energy performance of trans-critical CO₂ refrigeration and heat pump systems. The optimal gas cooler pressure and the optimal COP have been analysed from a thermodynamic point of view. The experimental evaluation covers five evaporating levels (-10 to 10°C) and in a wide range of gas cooler outlet pressures (75 to 120bar). It is concluded that: With the the internal heat exchanger (IHX) system compressor power is relatively low, when the high side pressure is over 100bar, and the evaporation temperature is below 0°C. The COP of the system without IHX is slightly higher than the system with the IHX, it is increase about 3% to 5%, when the evaporation temperature is over 5°C.

Abstract: Detailed prediction of steam flow field and heat transfer process is significant for the condensers. The flow and heat transfer performance of the condenser of 600MW power unit is numerical simulated. A model of porous media with distributed resistance and mass sink is used to simulate the function of the tube bundle. The equations including the continuous, momentum and air concentration are numerically solved using the finite control-volume integration method and SIMPLE algorithm. The distribution of steam velocity, pressure, heat transfer coefficient and air concentration are obtained and analyzed. On the basis of results, the condenser is evaluated.

Abstract: Vapor-liquid-solid phase change is a common phenomenon in nature and engineering technology. In this paper, the three-phase circulating fluidized bed evaporator was applied to concentrate Pineapple juice according to the structure and characteristics of it. Inert particles, as fluidizing medium, are put in the heating tube, increased the turbulence of the fluid, destroyed the boundary layer, and strengthened the convection, it had a good antifouling and descaling performance. Based on the experimental values derived from the circulating fluidized bed heat transfer experiments, the heat transfer experimental correlations of corrugated-tube in laminar flow regime and turbulent flow regime were obtained.The results show that the experimental value was in good agreement with the theoretical value.

Abstract: Metal Honeycomb (MH) is a plug-in unit for heat transfer enhancement, which has a large specific surface adjustable range, high heat conductivity and excellent geometric plasticity. The continuous waste heat recovery processes are simulated by FLUENT with inserted MH and ceramic honeycomb(CH) at the same shape and dimension. By comparing the heat exchange of MH with CH, it is found that the heat recovery device with MH has better performance and smaller pressure loss than that with CH.

Abstract: In order to control the attemperation water demand, the superheater heating ability is calculated by enthalpy increment. According to the changed enthalpy of the superheater outlet, the attemperation water demand is estimated. To simplify calculation, the changing steam flow is regarded as linear process during a certain time. Thus, the attemperation water calculation method is obtained. Basis on this, Matlab software is used to perform computer simulation to the system.

Abstract: The article presents a new kind of shell and tube phase change heat storage exchanger using vertical fins. And select paraffin as phase change materials, Fluent6.3 software was used to study the melting process. Some conditions of different fin height, different fin width and different fin numbers of axial direction were investigated. The results show that the higher and the wider of the fins, and the more the fin number of axial direction, the shorter is the melting time, the better is the effect of heat transfer

Abstract: Circular cooler is deployed for sinter cooling process in sintering industry. According to the sinter cooler from HBIS, an experimental study was conducted and a bench of the heat exchange body was built. Under the same initial temperature of the sinter, the experimental results of nine conditions are compared, which reveals the effect of particle size, material thickness, air flow rate and inlet air temperature on sinter sensible heat extraction, adopting orthogonal experimental method. Experiment results show that, at the mixing condition of material thickness 1400 mm, air flow rate 921 m³•h^-1 and inlet air temperature 90 °C, the unit of sinter available exergy reaches 313.55 kJ•kg^-1. The conclusions provide theoretical and experimental basis for the sensible heat extraction process of the sinter.

Abstract: This paper mainly studies the falling film evaporator in the field of water desalination. Using the method of fluent simulates the process of the liquid flowing and heat-transfer on the horizontal-tube falling film evaporation. The author analyses the distribution of the liquid film, and obtain the rule that spray density, evaporation temperature, temperature difference and pipe diameter affect the performance of heat-transfer in a certain range. So the paper plays a guiding role in heat transfer enhancement in the falling film evaporator.

Abstract: This paper describes the Fuzzy control of circular cooling water in a twin-roll strip cast, joins a feed-forward compensation to solve the time lag in conveying water. Because of the large time lag, multivariable system and hard modeling, this paper presents a Fuzzy controller for them. Based on the synthesis reasoning rules and Fuzzy logic, the Fuzzy model of circular cooling water is established. Then the simulation results show that the strip can effectively keep a constant temperature. And it has a good tracking performance, robust, strong anti-interference ability, and the cooling water can in time exchange heat with the liquid metal to get high quality strip.

Abstract: In low-middle temperature porous geothermal field, precipitation of carbonate from solution to form carbonate scale is confirmed as the main obstacle to efficient reinjection from the used hot fluids in Xianyang city, NW China. The carbonate deposits cause operational problems and may even clog pipeline and reinjection drillholes. For this reason, it's important to understand how impact of carbonate precipitation on the second-hand geothermal water before reinjection has been operated, which concern sustainable utilization of the geothermal water in Xianyang, the famous porous geothermal field in China. In this paper, firstly, different possible minerals precipitation from used geothermal fluid were discussed, and carbonate scaling was regarded as mineral for chemical clog by using combined with lab and chemical simulation method. Secondly, the key impacts of carbonate scaling on clog in reinjection holes such as temperature, degassing, pH, mixing, mineralization were demonstrated based on coupled simulation both in lab experiment and theoretical method. Lastly, the distribution of carbonate scaling and its degree in study area were calculated. The results show that, as the main mineral for precipitation, carbonate exist in most thermal-water wells of study area with the minor or medium scaling, and the carbonate scaling vary increasingly from bottom to top in a single reinjection drillhole, north to south in the study area. According to mineral-dissolution-precipitation equilibrium calculation carbonate saturated tend growth with the temperature and pH increases in study area. The influence of mineralization on carbonate clog is different, common-ion effect in the south of study area is given priority, but in the north salt effect is showed main effect. The analysis for impacts on carbonate clog reflect that carbonate deposit effect are very complicated, which interact each other.