Begell House Inc.
Heat Transfer Research
HTR
1064-2285
46
10
2015
NUMERICAL INVESTIGATION OF SPECIES DISTRIBUTION AND THE ANODE TRANSFER COEFFICIENT EFFECT ON THE PROTON EXCHANGE MEMBRANE FUEL CELL (PEMFC) PERFORMANCE
881-901
Nima
Ahmadi
Department of Mechanical Engineering, Urmia University of Technology, Urmia, Iran
Vahid
Ahmadpour
Department of Mechanical Engineering, Urmia University of Technology, Urmia, Iran
Sajad
Rezazadeh
Department of Mechanical Engineering, Urmia University of Technology, Urmia, Iran
A full numerical, three-dimensional, single phase computational fluid dynamics model of a proton exchange membrane fuel cell (PEMFC) with both the gas distribution flow channels and the Membrane Electrode Assembly (MEA) has been developed. A single set of conservation equations which are valid for the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region are developed and solved numerically using a finite volume-based computational fluid dynamics technique. The present simulated single straight channel PEMFC model, accounts for the major transport phenomena and performance. Additionally, the effect of the anode transfer coefficient, αan, reduction on the fuel cell performance and species distribution has been investigated. The results showed that a decreasing anode transfer coefficient leads to a lower magnitude of oxygen and water mass fraction. In this way the current density, generated by the cell, decreases too. Finally, the numerical results are validated by available experimental data.
CFD METHOD STUDY OF THE INFLUENCE OF PULSATING FREQUENCY ON ENHANCEMENT OF HEAT TRANSFER FROM A RECTANGULAR FLAT PLATE IN LAMINAR PULSATING FLOWS INSIDE A VERTICAL CIRCULAR CHANNEL
903-921
Guoneng
Li
Zhejiang University of Science and Technology, Hangzhou, 310023, P. R. China
Y.
Zheng
Zhejiang University of Science and Technology, Hangzhou, 310023, P. R. China
G.
Hu
Zhejiang University of Science and Technology, Hangzhou, 310023, P. R. China
Zh.
Zhang
Zhejiang University of Science and Technology, Hangzhou, 310023, P. R. China
The effect of pulsating frequency on heat transfer from a rectangular flat plate in laminar pulsating flows inside a vertical circular channel was studied numerically to explore the controlling mechanism for heat transfer enhancement. Quantitatively accurate, second-order schemes for time, space, momentum, and energy were employed, and fine meshes were used. The unsteady, incompressible Navier−Stokes equations along with the energy equation were solved by the ANSYS® 13.0 segregated solver. The numerical results agreed well with the data from the experiment. It is found that the spatial averaged surface temperature of the rectangular flat plate fluctuates with time, and the temperature field around the rectangular flat plate oscillates in special modes at the same frequency as the flow pulsations. The heat resistance was observed to be larger during flow reversal than that during forward flowing, and it fluctuates in phase with the pressure waves. In addition, a detailed analysis found that the RMS (root-mean-square) value of the axial velocity controls the heat transfer enhancement in pulsating flows at different pulsating frequencies when the pressure amplitude and the Reynolds number remain unchanged.
PREDICTION OF THE RATE OF MOISTURE EVAPORATION FROM JAGGERY IN GREENHOUSE DRYING USING THE FUZZY LOGIC
923-935
Om
Prakash
Department of Mechanical Engineering, Birla Institute of Technology, Mesra Ranchi-835215, India
Anil
Kumar
Energy Technology Research Center, Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand; Department of Energy (Energy Center), Maulana Azad National Institute of Technology, Bhopal-462003, India
Ajay Kumar
Kaviti
Department of Mechanical Engineering, Sagar Institute of Science and Technology, Gandhinagar, Bhopal, M.P., India
P. Vishwanath
Kumar
Institute of Fronter Materials, Deakin University, Waurn Campus, 3216 Australia
In this study an attempt has been made to predict the rate of moisture evaporation by natural and forced convection from jaggery in a controlled environment. For this purpose, we have adopted simulating software called Fuzzy logic in MATLAB software (Version 7.0.1). Initially the input values from the literature, namely the jaggery temperature (Tj), surface temperature (Te), and the relative humidity (RH), were taken corresponding to different jaggery dimensions (0.03 × 0.03 × 0.01 m3, 0.03 × 0.03 × 0.02 m3, and 0.03 × 0.03 × 0.03 m3) with a total quantity of jaggery of a (0.75 kg and 2.0 kg) that are fed in the software tool box and the output values of moisture evaporation (me) were predicted. These values were compared with the experimental values and it was seen that there is close accuracy between the values. The results from this investigation indicate that the Fuzzy tool predicts the moisture evaporation rate with an absolute error varying from no error in the case of a jaggery piece of dimensions 0.03 × 0.03 × 0.01 m3 to a maximum error of 0.27 for a jaggery piece of 2 kg and of dimensions 0.03 × 0.03 × 0.02 m3 in the forced convection mode. The values of root mean square error and coefficient of determination are calculated and they are found to be 0.112 and 0.986, respectively. Thus it is concluded that the Fuzzy logic can be used to accurately predict the results with a minimum error and the present model can be extended to different places corresponding to different weather conditions, namely ambient temperature, solar radiation, and relative humidity.
STUDY OF DROPLET HEAT AND MASS TRANSFER IN FORCED CONVECTION TURBULENCE FLUCTUATIONS USING THE VOLUME-OF-FLUID MODEL
937-954
Peng
Zhao
Beijing Jiaotong University, Beijing, China
Guoxiu
Li
Beijing Jiaotong University, Beijing, China
A two-dimensional analysis for droplet heat and mass transfer in forced convection turbulence fluctuations is presented. The computational model is based on the volume-of-fluid method and PLIC free-surface tracking method, which can capture the droplet deformation accurately. The rate of droplet evaporation is computed by the gradient of vapor mass fraction in the interface cells. Numerical predictions of lifetime of droplet evaporation match experimental data quite well. The effects of turbulent intensity and oscillatory flow frequency on heat and mass transfer of a droplet are investigated. Furthermore, much attention is paid to the droplet deformation and wake length. The numerical results show that the droplet lifetime decreases with increasing turbulence intensity and decreasing oscillatory frequency. In addition, droplet deformation due to the turbulence fluctuations in forced convection plays an important role in affecting droplet evaporation.
COUPLED SIMULATION OF MULTIPHASE FLOW AND HEAT TRANSFER IN A JACKETED VESSEL
955-969
Meili
Liu
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China; School of Mechanical Engineering, Beijing Institute of Petrochemical Technology, Beijing 102249, China
Y.
Mao
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China
J. Y.
Wang
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China
J.
Wang
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249, China
This paper presents a coupled method to simulate flow and heat transfer in jacketed vessels, in which the complicated interactions between the vessel and the jacket are taken into account. The coupled simulation of a jacketed vessel of 2.00 m in diameter is carried out to investigate the heat transfer process. The results show that thermal boundary conditions of the fluids are nonuniform. When compared with simulation using uniform boundary conditions, significant differences are observed in the distribution of heat flux and heat transfer coefficient. The comparison results indicate that the thermal boundary condition has a significant influence on heat transfer in jacketed vessels.