Xinli Wei

A Study on Improving in Natural Convection Heat Transfer for Heat Sink of High Power LEDs

In this paper the natural convection heat transfer performance of horizontal heat sink was studied by numerical simulation and experiment. The numerical simulation results show that there are some interesting features in the flow field of heat sink model. 1) Among the fins, the air vertically flows only through the fins in the symmetry center of heat sink while it horizontally flows through the fins in other area. 2) There is an air stagnation zone located at the fin root in the symmetry center of heat sink. These features both caused the decrease in heat transfer temperature difference and heat transfer area in fact. The natural convection heat transfer performance of heat sink is affected at last. In order to eliminate the air stagnation zone and change in the flow way of air, some holes were perforated at the fin root. These holes play its role. In this test, the heat transfer power of heat sink with seven holes has increased by 16.7% compared with the prototype.With the increase in the number of holes, the natural convection heat transfer power of heat sink also increases. But when the number of holes reaches to a value, the increase in the number of holes will not function properly.

Selection of Working Fluids for Low-Temperature Waste Heat Recovery Using Organic Rankine Cycle

As for the industrial exhaust heat with the temperature ranging from 120°C to 200°C, 5 working fluids commonly used in organic Rankine cycle, namely R113、R123、R134a、R245fa and R600a, have been analysed from the perspective of safety, environment and economical efficiency. The results show that: R123 is of great poison, but its thermal economical efficiency is the best, especially under the condition of high temperature. The suitable ambient temperature ranges from 20-35°C. R245fa belongs to a safe and environment friendly fluid. For its best comprehensive property and wide range of ambient temperature, R245fa is very beneficial to the ORC system.

Experimental research and analysis of energy efficiency for direct radiant floor heating system with ASHP

This paper presents experimental research and analysis of energy efficiency for direct radiant floor heating system with ASHP (air source heat pump). An experimental platform was built, and the performance of ASHP, heating effect and energy consumption of heating system were studied. The results show that the indoor heat load can be well met when the output capacity of ASHP runs at 30%, in which the floor surface temperature and indoor air temperature were reached at 26 °C, 22 °C, respectively. Vertical temperature field can well met the requirements of indoor thermal comfort. Besides, the paper examines heating performance for different envelope, the results indicate that as the condensing coil spacing decreases, the indoor heating effect gets better, but the consumption of energy and tubes increase. Finally, testing the hourly energy efficiency ratio of heating system, and comparing energy efficiency of different technologies, the results point out that radiant floor heating system with ASHP has the best energy efficiency and the obvious advantage of energy saving compared with other heating technologies.

Economic Analysis of Solar Wall System in Northern China Heating Region

The economic feasibility of solar wall system was assessed with RETScreen software for 15 widespread locations in northern China heating region. Several different economic and financial indicators were calculated, such as the internal rate of return, net present value, simple payback and benefit-cost ratio. Results showed that the solar wall system was only profitable for four sites according to the current domestic price of solar wall plate and its absorptivity. When the price was reduced or the absorptivity under the condition of invariable price was improved, there were more sites profitable for this system. So, only when the price of energy increases 95% or the price of solar wall plate falls 50%, the solar wall system will be profitable for all sites in northern China heating region.

Corrosion Mechanism of Atmosphere Spacein Oil Tank Containing Sulfur

Oil tank is easily corroded by internal and external media in service. Corrosion types of gas spaces in oil tank were summarized, corrosion process was analyzed also. Through the research of corrosion mechanism of gas space of oil tank, author put forward that H2S corrosion was a dominant factor for gas space corrosion. H2S corrosion mechanism model at low temperature was obtained also. Metallic samples test showed that corrosion rate was decreased while the samples were placed in simulating atmosphere spaces of oil tank. Corrosion product iron sulfide has loose, porous, layered, and cracked structure. When ingredient of atmosphere varied with time，iron scale was produced, mixed with iron sulfide. Electrochemical test showed that the increase of acidity accelerated the cathode process and accelerated the corrosion rate of Q235-B steel.

Design of Small-Scale Radial Inflow Turbine Integrated into Organic Rankine Cycle

Organic Rankine Cycle (ORC) is dramatically suitable for low temperature waste-heat generation. The small-scale radial inflow turbine is introduced to integrate into the ORC characterized by simple structure, low parts count, high efficiency, especially getting high efficiency under the condition of smaller flow. This turbine is comprised of four main parts named by the volute, the nozzle (stator), the impeller (rotor), and the diffuser respectively. This paper introduces how to design and model the parts in detail, discusses modeling skills and shares experience. The structure of the volute and impeller is so complicated that parts are not easy to model. These 3D models can directly import to both ANSYS and FLUENT to analysis the flow field in order to achieve the optimize parameters.

The effect of floor structure on heat transfer of radiant floor heating system with air-source heat pump (ASHP)

This paper presents numerical simulation for heat transfer of radiant floor heating system, whose heat source is air-source heat pump (ASHP). The results of simulation for heat transfer show that: 1) With the increasing of the tube spacing in floor layer, the average floor surface temperature decreases and temperature fluctuations enlarge, in the same time practical experiments show that the simulation results are reliable.2) The thinner the floor layer structure, the higher the floor surface temperature, and the more thermal inertia and cost of floor, but the less capacity of heat storage. The thickness of the floor layer structure should be decided by actual design requirements for space heating.3) Floor radiant heating capacity will be significantly reduced with the decreasing of thermal conductivity of floor surface layer. The material of floor surface layer, whose heat transfer coefficient is small, should be avoided to be use in practical engineering.

Experimental study of thermal comfort for direct radiant floor heating system utilizing R22

This paper presents experimental study for direct radiant floor heating system with air-source heat pump utilizing R22. An experimental platform was established, and thermal comfort of the heating system was analyzed from floor temperature, vertical temperature field, relative humidity, operation temperature and average radiation temperature, radiation asymmetry, PMV (Predicted Mean Vote) and PPD (Predicted Percent Dissatisfied). It shows that the indoor heat load can be well met as the output capacity of ASHP runs at 30%. When the heating system steadily runs, thermal comfort is very perfect. Finally calculating the values of PMV and PPD index, the results point out that PMV is about −0.7 ∼ −0.17, and PPD is 5.58%∼15.49%, which could well meet the requirements of thermal comfort in China (PPD ⩽ 20%, −1.5 <PMV <+1.2).

Heat transfer simulation for radiant floor heating system with air-source heat pump

This paper presents numerical simulation for heat transfer of radiant floor heating system, whose heat source is air-source heat pump. According to the results of simulation for heat transfer of different tube spacing in floor layer, it can be found that with the tube spacing increases, the average floor surface temperature decreases and temperature fluctuations enlarge. The recommended tube spacing is 100mm and 150mm. Practical experiments show that simulation results are reliable. Numerical simulation on tube spacing of 100mm and 150mm showed, for the condition of tube spacing of 150mm, the average floor surface temperature is low, and temperature distribution is uneven. While the heat flux for tube spacing of 100mm is 41.35 W/m2, which is less than 47.3 W/m2 of the tube spacing of 150mm, the reason is that tube spacing is smaller, heat transfer driving force for working fluid is smaller.

Analysis and Optimization of ORC for Low-Temperature Waste Heat Power Generation

This paper presents energy analysis, thermodynamic calculation and exergy analysis for waste heat power generation system of Organic Rankine Cycle based on the first and second laws of thermodynamics. In order to improve system performance, for low-temperature waste heat of 120°C and R245fa organic working fluid, using Aspen Plus software conducted simulation, optimization and improvement. Results from these analyses show that decreasing the expander inlet temperature, increasing inlet pressure of the expander, and adding regenerative heater can increase thermal and exergy efficiencies, at the same time reduce system irreversibility.