期刊：
INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW,2020年30(8):4025-4065 ISSN：0961-5539
通讯作者：
Zhao, Fu-Yun
作者机构：
[Liu, Run-Zhe; Zhao, Fu-Yun; Wang, Wei-Wei; Wang, Lei; Cai, Yang] Wuhan Univ, Sch Power & Mech Engn, Wuhan, Peoples R China.;[Liu, Di] China Univ Petr East China, Coll Pipeline & Civil Engn, Dongying Campus, Dongying, Peoples R China.;[Wang, Hanqing] Univ South China, Sch Civil Engn, Hengyang, Peoples R China.
通讯机构：
[Zhao, Fu-Yun] W;Wuhan Univ, Sch Power & Mech Engn, Wuhan, Peoples R China.
关键词：
Nanofluids;Heat transfer enhancement;MHD natural convection;Porous fins;Topology and morphology
摘要：
Purpose - This paper aims to numerically investigate the magnetohydrodynamic (MHD) convection heat transfer of nanofluid inside a differentially heated enclosure with various fin morphologies. Design/methodology/approach - The fluid flow within the cavity was governed by N-S equations while it within porous medium was solved by the non-Darcy model, called the Darcy-Forchheimer model based on representative element-averaging method. Empirical correlations from experimental data are used to evaluate the effective thermal conductivity and dynamic viscosity. Relevant governing parameters, including thermal Rayleigh number (10~5-10~7), Hartmann number (0-50), Darcy number (10~(-6)-10~(-1)), thermal conductivity ratio of porous matrix (1-10~3), nanoparticles volume fraction (0-0.04) and topology designs of porous fins, are sensitively varied to identify their effects and roles on the fluid flow and heat transfer. Particularly, heatlines are used to investigate the mechanism of heat transport. Findings - Numerical results demonstrate that the predictions of average Nusselt number are augmented by using more porous fins with high permeability, and this effect becomes opposite in tiny Darcy numbers. Particularly, for high Darcy and Rayleigh numbers, the shortest fins could achieve the best performance of heat transfer. In addition, the prediction of average Nusselt number reduces with an increase in Hartmann numbers. An optimal nanoparticles concentration also exists to maximize heat transfer enhancement. Finally, numerical correlations for the average Nusselt number were proposed as functions of these governing parameters. Practical implications - Present work could benefit the thermal design of electronic cooling and thermal carriers in nanofluid engineering. Social implications - Present work could benefit the thermal design of electronic cooling and thermal carriers in nanofluid engineering. In addition, optimum thermal removals could enhance the lifetime of electronics, therefore reducing the cost of energy and materials. Originality/value - To the best knowledge of authors, there are not any studies considering the synergetic effects of porous fins on MHD convection of nanofluids. Present work could benefit the thermal design of electronic cooling and thermal carriers in nanofluid engineering.
摘要：
The capillary ceiling radiation cooling panel (C-CRCP) is a newly developed terminal device for air conditioning to provide indoor thermal comfort for occupants and to save energy. In this paper, numerical modelling of a room with a C-CRCP system was used to analyze radiant heat transfer under non-steady-state conditions. Experiments were conducted in an environmental chamber to verify simulation results. The chamber was equipped with a C-CRCP, which was covered with gypsumboard. The results showed that the inlet water temperature had a significant influence on ceiling surface temperature. The ceiling surface temperature and the steady-state time were increased with higher inlet water temperature. A vertical gradient in indoor air temperature was found. Ceiling surface temperature and indoor air temperature were increased with an increase in inlet air temperature. The energy supply rate of the radiant panel had a positive correlation with chilled water velocity. The amount of radiation was double the amount of convection, and the thickness of the gypsumboard had virtually no effect on the proportions of radiation and convection. The model was considered validated since the maximum relative errors between experimental data and simulation results of inlet water temperature and supply air conditions were within 10%.
作者机构：
[Zhao, Fu-Yun; Cai, Yang; Zhang, Dong-Dong] Wuhan Univ, Minist Educ, Key Lab Hydraul Machinery Transients, Wuhan, Hubei, Peoples R China.;[Zhao, Fu-Yun; Cai, Yang; Zhang, Dong-Dong] Wuhan Univ, Hubei Key Lab Waterjet Theory & New Technol, Wuhan, Hubei, Peoples R China.;[Zhao, Fu-Yun; Cai, Yang; Zhang, Dong-Dong] Wuhan Univ, Sch Power & Mech Engn, Wuhan, Hubei, Peoples R China.;[Liu, Di] China Univ Petr, Coll Pipeline & Civil Engn, Qingdao, Shandong, Peoples R China.;[Wang, Han-Qing] Univ South China, Sch Civil Engn, Hengyang, Hunan, Peoples R China.
通讯机构：
[Zhao, Fu-Yun] W;[Liu, Di] C;Wuhan Univ, Sch Power & Mech Engn, Wuhan, Hubei, Peoples R China.;China Univ Petr, Coll Pipeline & Civil Engn, Qingdao, Shandong, Peoples R China.
关键词：
Air source energy;Domestic water heating;Low energy built ventilation;Thermoelectric heat pumps
摘要：
An air-source thermoelectric heat pump (AS-THP) system is proposed in the present work, and it actively exploits ambient air source energy serving for cold air delivery and hot water supply simultaneously. A mathematical model, combining thermoelectric theory and the effectiveness-number of transfer units (ε-NTU), is firstly conducted to predict the performance of AS-THP system. Subsequently, the effects of thermoelectric input current, inlet air/water temperatures, thermal conductance, mass flow rate in both cold and hot sides, and the number of thermoelectric coolers on the performance of AS-THP system are sensitively investigated. Modeling results demonstrate that the thermal conductance and specific heat allocations in heat exchanger hot and cold sides could put heavy effects on the total cooling capacity (Qc,all), coefficient of performance (COP), outlet water temperature (Tc,out) and outlet air temperature (Th,out). Further modeling on the thermal parameters in both sides has shown that overall efficiency of AS-THP system could be achieved to nearly 90%. Also, with the increase of unit number, the cooling load for each thermoelectric unit would be reduced while the input power increases inversely. Present research could be beneficial for extensive utilization of thermoelectric heat pump in daily life by the use of ambient air source energy.
期刊：
Numerical Heat Transfer, Part B: Fundamentals,2019年75(4):265-288 ISSN：1040-7790
通讯作者：
Zhao, Fu-Yun
作者机构：
[Wang, Lei; Zhang, Dong-Dong; Zhao, Fu-Yun] Wuhan Univ, Minist Educ, Key Lab Hydraul Machinery Transients, Wuhan, Hubei, Peoples R China;[Wang, Lei; Zhang, Dong-Dong; Zhao, Fu-Yun] Wuhan Univ, Hubei Key Lab Waterjet Theory & New Technol, Wuhan, Hubei, Peoples R China;[Wang, Lei; Zhang, Dong-Dong; Zhao, Fu-Yun] Wuhan Univ, Sch Power & Mech Engn, Wuhan 430072, Hubei, Peoples R China;[Liu, Di] China Univ Petr, Coll Pipeline & Civil Engn, Qingdao, Shandong, Peoples R China;[Wang, Han-Qing] Univ South China, Sch Civil Engn, Hengyang, Hunan, Peoples R China
通讯机构：
[Zhao, Fu-Yun] W;Wuhan Univ, Sch Power & Mech Engn, Wuhan 430072, Hubei, Peoples R China.
摘要：
In former theoretical researches of nanofluid flows, numerical investigations could not agree with experimental observations, particularly regarding whether the mixing nanoparticles will enhance or deteriorate the heat transfer. In the present work, thermal driven buoyancy flows of nanofluids in a square enclosure were modeled by the use of homogeneous assumptions and the effective kinematic viscosity and thermal conductivity formulas. Thoroughly developed heat transfer coefficient is subsequently proposed, aiming to critically evaluate the performance of nanofluid heat transport. Numerical results are presented over a wide range of thermal Rayleigh number (10(3) <= Ra <= 10(6)) and nanoparticles volume fraction (0.001 <= phi <= 0.04). Present modeling results accurately predict both the enhancement and deterioration of the natural convection heat transfer, fully validated by former experimental observations. Overall, mathematical models and Nusselt number definitions proposed in the present work effectively enhance the reliability of numerical modeling researches on the nanofluid heat transfer. Present clarification research on the Nusselt unifications could benefit future development of thermal carrier fluid enhanced by nano-particles.
摘要：
This paper presents a study on the impact of incoming wind velocity magnitudes and horizontal aperture separations on natural ventilation flows in a single-sided wind-driven naturally ventilated building with two apertures (SS2) on the rear wall or the front wall. Both the velocity fields and the contaminant concentration fields were simulated and investigated. The present study is based on CFD simulations with unsteady Reynolds-averaged Navier-Stokes (URANS) SST k-ω model. A vortex shedding flow mechanism has been identified when the two apertures are mounted either on the rear wall or on the front wall, through which the air flow oscillates at a certain rate. CFD results further demonstrate that the oscillating frequency increases with the incoming wind magnitude and is nearly independent of the horizontal aperture separations. For the same building configuration, the root mean square (r.m.s) of the non-dimensional ventilation flow rate is independent of the incoming wind speed, whereas it decreases when the horizontal aperture separation is reduced. The time-averaged contaminant concentration fields also validated the different ventilation performance of different aperture configurations. This novel ventilation mechanism could be applied to alleviate the poor ventilation performance of buildings with single-sided apertures.
