Browsing by Author "Tian, Y."

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    Automating business intelligence recovery from a web-based system.
    (2010) Kang, Jian; Li, J.; Huang, J.; Tian, Y.; Yang, Hongji
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    Comprehensive Evaluation of Paraffin-HDPE Shape stabilized PCM with Hybrid Carbon Nano-additives
    (Elsevier, 2019-09-17) Qu, Y; Wang, S; Zhou, D; Tian, Y.
    Thermal energy storage using phase change materials (PCMs) is of great interests in many fields, especially in solar thermal applications. To overcome the leakage problem caused by phase change and the low thermal conductivities of most PCMs, especially paraffin, the current study prepared and tested two Paraffin-HDPE-based composites by adding two hybrid Carbon Nano-additives (CNs) fillers: Expanded Graphite-Multi-walled Carbon Nanotube (EG-MWCNT) and Expanded Graphite-Carbon Nanofiber (EG-CNF). A comprehensive evaluation method was first proposed based on the Efficacy Coefficient Method (ECM) to assess the thermal performance of Paraffin-HDPE shape stabilized PCM (SSPCM). Seven individual indexes, including phase change temperature, latent heat, thermal conductivity, leakage rate, specific heat of both solid and liquid phase, and heat storage/heat release rates, were measured and applied to obtain the overall efficacy coefficients of the prepared SSPCM composites. The results showed that in all studied composites, n-octadecane-HDPE/EG-MWCNT composite exhibited the best comprehensive thermal performance with an optimal mass ratio of EG and MWCNT being 4:1.
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    Computational and experimental investigations of an omni-flow wind turbine
    (Elsevier, 2015-03-15) Ying, P.; Chen, Y.K.; Xu, Y.G.; Tian, Y.
    Both numerical and experimental studies were conducted to evaluate the performance of an omni-flow wind turbine designed to provide renewable electricity on the top of urban buildings like skyscrapers. The numerical approach was based on Finite Volume Method (FVM) and the turbulence flow was studied with several commonly used Reynolds-averaged Navier–Stokes turbulence models. The results of the study were evaluated with the wind tunnel test results over a range of tip speed ratios. The numerical results showed the effect of blade number on both power output and starting capability. Although both the power and torque coefficient were improved significantly by the optimisation of the blade number, there was only a slight change when the blade number was greater than twenty. The results from wind tunnel testing also showed excellent starting capability with a starting wind velocity as low as 1.6 m/s. A numerical simulation was also conducted for the wind turbine working under non-uniform flow conditions. The numerical results have shown that the peak power coefficient of such a wind turbine under non-uniform flow, was lower than that under the uniform flow. Additionally, the applied thrust on a blade was subject to frequent and periodical changes. However, the effect of the change of thrust in magnitude and frequency was not significant. Therefore the omni-flow wind turbine has the potential to meet the challenge of unpredictable wind velocity and direction as a consequence of the urban environment.
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    Effects of multiple sintering parameters on the thermal performance of bi-porous nickel wicks in Loop Heat Pipes
    (Elsevier, 2016-08-01) Qu, Y.; Zhou, Kan; Zhang, Kunfeng; Tian, Y.
    The thermal performances of a bi-porous nickel wicks in Loop Heat Pipe (LHP) including porosity, permeability, capillary pumping head and effective thermal conductivity (ETC) have been examined theoretically and experimentally, based on five key sintering parameters including the content of pore forming agent, compacting pressure, sintering holding time, sintering temperature and the particle size of pore forming agent. Firstly, a total number of 16 orthogonal tests are carried out with five key sintering factors and four levels of each factor. The optimal level of five sintering factors is obtained from the point of acquiring the most desirable overall performance of bi-porous nickel wicks, which can be used as the reference sintering process for bi-porous nickel wicks. Then, the experimental values of ETC were compared with eleven theoretical models. The results showed that the Alexander model and the Maxwell model overestimated and underestimated the experimental results of bi-porous nickel wicks, respectively. In the porosity range of 0.5–0.7, an average of the Chernysheva and Maydanik model and the Chaudhary and Bhandari model was found to be the best fit to the experimental data, providing an accurate method to predict ETC values of bi-porous nickel wicks of LHP.
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    An experimental and numerical examination on the thermal inertia of a cylindrical lithium-ion power battery
    (Elsevier, 2019-03-28) Wang, S.; Tian, Y.; Li, K.; Wang, J.; Wu, Y.; Ji, S.
    Thermal issues are increasingly critical for the scaling-up and integrated deployment of lithium-ion batteries (LIBs). To make battery temperature control more accurate, a concept of thermal inertia was proposed to cylindrical power batteries in the current study. Experimental results showed that the thermal inertia of the battery can greatly affect the thermal behavior during battery discharging process, based on which a battery thermal model was created by COMSOL Multiphysics with infrared imaging technology adopted to experimentally investigate the thermal inertia for a LiFePO4 (LFP) battery. It is evidenced that the model and the corresponding simulation can provide helpful guidance for the thermal behavior control and improve thermal performance. Furthermore，the temperature distribution and variation of the slack period (after discharge) were studied, including internal temperature, surface temperature and temperature difference. Results showed that the battery radius (R) and discharge rate (C) were the major factors that influenced the thermal inertia. In addition, a thermal inertial calculation model was proposed for predicting battery thermal inertia under different operating conditions.
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    Experimental study on thermal conductivity of paraffin-based shape-stabilized phase change material with hybrid carbon nano-additives
    (Elsevier, 2019-08-20) Qu, Y; Wang, S; Zhou, D; Tian, Y.
    Thermal energy storage with Phase Change Materials (PCMs) is one of the most potential technologies for energy storage. However the low thermal conductivity of PCMs reduces the heat exchange rate during melting and solidification cycles. This paper studied the effects of two hybrid Carbon Nano-additives (CNs) fillers, that is, Expanded Graphite-Multi-walled Carbon Nano-tube (EG-MWCNT) and Expanded Graphite- Carbon Nano-fiber (EG-CNF), on the thermal conductivity of Paraffin-HDPE SSPCM. From the viewpoints of synergistic thermal enhancement effect and the interfacial thermal resistance, the principle of enhancing thermal conductivity of Paraffin-HDPE/EG-MWCNT and Paraffin-HDPE/EG-CNF composite PCMs was analyzed. A modified Maxwell-Garnett model with a synergy factor η was proposed, which found excellent agreement between model prediction and the experimental data. Compared with the 5wt% loading of single CN additive EG, the thermal conductivities of hybrid CNs fillers (EG-MWCNT and EG-CNF) Paraffin-HDPE SSPCM had increased by 60% and 21.2% respectively. Within the scope of mass ratios of hybrid CNs fillers in this paper, Paraffin-HDPE/EG-MWCNT composite PCM exhibited superior performance than Paraffin-HDPE/EG-CNF in thermal conductivity with the optimal mass ratio of EG and MWCNT being 4:1.
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    Improved thermal performance of a large laminated lithium-ion power battery by reciprocating air flow
    (Elsevier, 2019-02-14) Wang, S.; Tian, Y.; Li, K.; Wang, J.; Wu, Y.; Ji, S.
    Thermal safety issues are increasingly critical for large-size laminated Lithium-Ion Batteries (LIBs). Despite a number of investigations conducted on the Battery Thermal Management System (BTMS) with reciprocating air-flow cooling, large laminated power LIBs are still not sufficiently investigated, particularly in the view of battery thermal characteristics. The present study investigates the thermal behaviors of an air-cooled NCM-type LIB (LiNi1−x−yCoxMnyO2 as cathode) from an experimental and systematic approach. The temperature distribution was acquired from different Depth of Discharge (DOD) by the infrared imaging (IR) technology. A reciprocating air-flow cooling method was proposed to restrict the temperature fluctuation and homogenize temperature distribution. Results showed that there was a remarkable temperature distribution phenomenon during the discharge process, the temperature distribution was affected by direction of air-flow. Forward air-flow (from current collector side to lower part of battery) was always recommended at the beginning of the discharge due to the thermal characteristics of the battery. After comprehensive consideration on battery temperature limit and cooling effect, the desired initial reversing timing was about 50% DOD at 3 C discharge rate. Different reversing strategies were investigated including isochronous cycles and aperiodic cycles. It was found that the temperature non-uniformity caused by heat accumulation and concentration was mitigated by reciprocating air-flow with optimized reversing strategy.
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    Infrared imaging investigation of temperature fluctuation and spatial distribution for a large laminated lithium ion power battery
    (Elsevier, 2019-02-18) Tian, Y.; Li, K.; Wang, J.; Wu, Y.; Ji, S.
    The present study investigates the thermal behaviors of a naturally cooled NCM-type LIB (LiNi1−x−yCoxMnyO2 as cathode) from an experimental and systematic approach. The temperature distribution was acquired for different discharge rates and Depth of Discharge (DOD) by the infrared imaging (IR) technology. Two new factors, the temperature variance ( ) and local overheating index (LOH index), were proposed to assess the temperature fluctuation and distribution. Results showed that the heat generation rate was higher on the cathode side than that on the anode side due to the different resistivity of current collectors. For a low-power discharge, the eventual stable high-temperature zone occurred in the center of the battery, while with a high-power discharge, the upper part of the battery was the high temperature region from the very beginning of discharge. It was found that the temperature variance ( ) and local overheating index (LOH index) were capable of holistically exhibiting the temperature non-uniformity both on numerical fluctuation and spatial distribution with varying discharge rates and DOD. With increasing the discharge rate and DOD, temperature distribution showed an increasingly non-uniform trend, especially at the initial and final stage of high-power discharge, the heat accumulation and concentration area increased rapidly.
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    MDA-based Development of Music-learning System
    (2008) Landy, Leigh; Tian, Y.; Yang, Hongji
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    An ontology-based model driven approach for a music learning system.
    (2010) Tian, Y.; Chen, Feng; Yang, Hongji; Landy, Leigh
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    Parametric analysis of influencing factors in Phase Change Material Wallboard (PCMW)
    (Elsevier, 2014-01-25) Zhou, D.; Shire, G.S.F; Tian, Y.
    Incorporating Phase Change Materials (PCMs) into traditional building structures has been considered as an effective way to reduce the mismatch between energy supply and demand and in turn to minimise energy consumption (cooling/heating energy). For building applications, Phase Change Material Wallboards (PCMWs) are of particular interest due to their easy installation to existing buildings for refurbishment. Both interior and exterior PCMWs are investigated in this paper, with a numerical study examining the effects of wallboard thermal properties on its thermal performance. These influencing factors include melting temperature, melting range, latent heat, thermal conductivity and surface heat transfer coefficient. An effective heat capacity model is adopted to consider latent heat with the model validated by an experiment. Inner surface temperature and diurnal energy storage are chosen as the evaluation criteria when comparing the thermal performance between different PCMWs. By analysing the effects of influencing factors on the system thermal performance, this study serves as a useful guide for selection of PCMs in energy-efficient buildings.
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    A review of thermal performance in multiple evaporators loop heat pipe
    (Elsevier, 2018-07-20) Qu, Y.; Wang, S.; Tian, Y.
    Multi-evaporator loop heat pipe (ME-LHP), as one of the typical two-phase closed capillary circulation systems, exhibits tremendous potential in applications which involve high heat flux and multi-heat sources, and is especially attractive to spacecraft and electronics packaging thermal control. This paper provides a comprehensive review of ME-LHP research and developments for the past 20 years covering four aspects: design theory, mathematical models, steady-state operational performance and start-up performance. ME-LHP design theory contains three key problems including the number limit for evaporators, sizing of the compensation chamber (CC) and calculation of the working fluid charge. Three peculiar features in steady performance have been discussed, which are the heat load sharing feature, the control rules of the operation temperature among multiple CCs, and the capillary limit of ME-LHP. Two influencing factors of start-up performance have been taken into account, including the required superheat on ME-LHP start-up and the initial fluid distribution in evaporators.
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    Thermal analysis of phase change material board (PCMB) under weather conditions in the summer
    (Elsevier, 2016-04-25) Zhou, D.; Tian, Y.; Qu, Y.; Chen, Y.K.; Tian, Y.
    Phase Change Material Board (PCMB) has been considered as an effective way to improve the thermal comfort in either new or existing buildings. In this work, firstly the optimal melting temperatures of internal and external PCMB are given, and the optimal heat storage capacities are obtained under the idealised circumstance of considering sinusoidal changes of the room and outdoor temperatures during a day. Secondly, to study the potential energy saving from applying a PCMB, a case study of a lightweight office with real environmental conditions is carried out. The air conditioning is switched on in the model to keep the indoor temperature within thermal comfort. Using the daily energy consumption and daily thermal comfort rate as the performance criteria, the effects of major influencing factors including melting temperature, latent heat and thermal conductivity of PCMB are studied parametrically. The results show that both the external and internal PCMB can achieve better performance when the melting temperature is chosen to be slightly higher than the average indoor air temperature. In the summer, the external PCMB has a better performance than the internal PCMB because the external PCMB works not only as a heat storage system whose function is similar to the internal PCMB, but also as a thermal connection between the outdoor and indoor environment due to its thermal insulation function, which reduces the influence of the changing outdoor environment.