Begell House Inc.
Heat Transfer Research
HTR
1064-2285
50
10
2019
MIXED CONVECTION IN A LID-DRIVEN CAVITY FILLED BY A MICROPOLAR NANOFLUID WITH AN INSIDE CIRCULAR CYLINDER
921-943
10.1615/HeatTransRes.2018020175
Zehba A. S.
Raizah
Department of Mathematics, Faculty of Science, Abha, King Khalid University, Saudi Arabia
circular cylinder
lid-driven cavity
micropolar nanofluid
mixed convection
In this study, we numerically investigated steady mixed-convection flow and heat transfer in a lid-driven cavity filled by micropolar nanofluids with an inside circular cylinder by using the finite volume method. The inner circular cylinder and the vertical walls of the cavity were taken as adiabatic. The cavity is subjected to moving upper wall with constant temperatures on the top and bottom walls. Computations are carried out to investigate the effects of the Reynolds number, Richardson number, micropolar parameters, and the radius with positions of the inner circular cylinder on heat transfer, nanoparticle concentrations, microrotation, and fluid flows inside the square cavity for a strong concentration case (ζ = 0). Local results show that there is an effect of a micropolar parameter on the flow and heat transfer. The results for k = 0, which corresponds to the Newtonian fluid case, are compared with the previous published studies from the open literature and good agreement is obtained.
EFFECTS OF A MIXTURE OF CuO AND Al2O3 NANOPARTICLES ON THE THERMAL EFFICIENCY OF A FLAT PLATE SOLAR COLLECTOR AT DIFFERENT MASS FLOW RATES
945-965
10.1615/HeatTransRes.2018027822
Zahra Ouderji
Hajabdollahi
School of Mechanical Engineering, Pusan National University, Busan 609-735, Republic of Korea
Mohsen
Mirzaei
School of Mechanical Engineering, Vali-e-Asr University of Rafsanjan, Rafsanjan 7718897111,
Iran
Kyung Chun
Kim
School of Mechanical Engineering, Pusan National University, Jangjeon-dong, Gumjung-ku, Busan 609-735, South Korea
mixture of nanoparticles
flat plate solar collector
thermal efficiency
mass flow rate
volume fraction
This research experimentally investigates the effects of adding nanoparticles with a volume fraction of 0.1% on the thermal efficiency of a flat plate solar collector at different mass flow rates. CuO/water and Al2O3/water nanofluids were studied in mixtures with different mass ratios. The results show that the nanofluids increase the efficiency of the solar collector significantly. The best mass flow rate was obtained for each nanofluid to obtain the maximum collector efficiency. Compared with water, the solar collector efficiency at the optimal rate is increased by 50%, 16%, 15%, 8%, and 2% for CuO, Al2O3, 25% CuO + 75% Al2O3, 75% CuO + 25% Al2O3, and 50% CuO + 50% Al2O3, respectively. Because of the high thermal conductivity of the CuO nanoparticles, the energy received from the collector increases. The highest energy absorption occurs in the case of CuO nanoparticles, followed by Al2O3 nanoparticles. Although the Brownian motion of Al2O3particles can be a significant feature in the heat transfer properties, the high thermal conductivity of CuO had a greater effect. Finally, the heat loss and heat absorption through the solar collector were calculated for all of the nanofluids to confirm the results.
EFFECTIVE THERMAL CONDUCTIVITY OF CARBON NANOTUBE-BASED NANOFLUIDS AT HIGH TEMPERATURES
967-975
10.1615/HeatTransRes.2018025525
Haifeng
Jiang
Key Laboratory of Hydraulic Machinery Transients (Wuhan University), Ministry of Education,
School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei 430072, China
Lin
Shi
Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department
of Energy and Power Engineering, Tsinghua University, Beijing 100084, PR China
Xuejiao
Hu
Key Laboratory of Hydraulic Machinery Transients (Wuhan University), Ministry of Education,
School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei 430072, China
Qingsong
An
Key Laboratory of Efficient Utilization of Low and Medium Grade Energy of Ministry of Education,
Tianjin University, Tianjin 300072, PR China
nanofluid
thermal conductivity
high temperature
carbon nanotube
nanoparticle aggregation
This study investigated the effects of temperature (30–180°C) and CNT volume fraction (0.001–0.007) on the effective thermal conductivity of CNT-based nanofluids, which extended the temperature range of available experimental data. The experimental results agree well with the theoretical model. The thermal conductivity enhancement increases with increasing CNT volume fractions at less than 100°C. Higher volume fractions result in greater thermal conductivity enhancement with temperature. Above 120°C, the thermal conductivity enhancement decreases with increasing temperature due to various aggregate states of the nanoparticles at high temperatures. The present study demonstrates the thermal conduction mechanisms in CNT-based nanofluids at high temperatures.
FLOW BOILING HEAT TRANSFER OF R30 IN PARALLEL MICROCHANNEL HEAT SINKS
977-992
10.1615/HeatTransRes.2018026477
Zong-wei
Zhang
College of Aeronautical Engineering, Civil Aviation University of China, Tianjin, China
Wen-di
Xu
College of Aeronautical Engineering, Civil Aviation University of China, Tianjin, China
Zhao
Wang
Aerospace System Engineering Shanghai, China
Cong
Liu
College of Air Traffic Management, Civil Aviation University of China, Tianjin, China
Ke-lu
Cui
College of Aeronautical Engineering, Civil Aviation University of China, Tianjin, China
microscale heat transfer
flow boiling
R30
two-phase
horizontal channel
This study examined the flow boiling heat transfer characteristics in horizontal rectangular microchannels with hydraulic diameter of 0.5 and 1.0 mm. Experiments were performed with R30 refrigerant under the following conditions: heat flux 1-16 kW·m-2, mass flux 111-333 kg·s-1·m-2, and vapor quality 0-0.35. The results showed that heat transfer was strongly affected by heat flux and vapor quality, while the mass flux remained less influential. The effect of flow regime transition on heat transfer coefficient was discussed through parameter analysis. Previous correlations have been examined and none of them can predict new data with satisfactory accuracy.
NUMERICAL INVESTIGATION OF FILM COOLING SUBJECT TO BULK FLOW PULSATIONS
993-1006
10.1615/HeatTransRes.2018025718
Mostafa A. H.
Abdelmohimen
College of Engineering, King Khalid University, Saudi Arabia; Shoubra Faculty of Engineering,
Benha University, Egypt
film cooling; gas turbine blades; pulsation flow; numerical simulation
One of the important parameters that affects the gas turbine blades film cooling is the behavior of the main flow. Due to the blade rotation, a periodical frequency is moving through the main flow. In this study, a numerical simulation is used to investigate the effect of the bulk flow pulsations on film cooling. The study is carried out on a flat plate surface with a simple cylindrical hole inclined by 30° with the direction of the main flow stream. The study is carried out at blowing ratios of 0.5, 1.0, and 2.0. The free stream Strouhal number ranged from 0 to about 0.49, and the coolant Strouhal number ranged from 0 to 4.1 compared to 0.2-6.0 for the operating turbine range. The free stream is represented by a sinusoidal profile with pulsation velocity amplitude in the free stream of ± 20% of the time-averaged free stream velocity. The realizable k-ε model is used to solve the momentum equation. A comparison with previous experimental studies is presented to verify the numerical model. The results show that the pulsating flow has a significant effect on the film cooling performance for pulsating frequency higher than 35 Hz. For pulsating frequency higher than 35 Hz, at blowing ratio 0.5, as the pulsating frequency increases, the film cooling effectiveness decreases while at blowing ratio 2.0, the film cooling effectiveness increases with increasing pulsating frequency. The reduction in the overall-time averaged film cooling effectiveness at pulsating frequency 75 Hz with blowing ratio equal to 0.5 is about 49.7% of the film cooling at zero pulsating frequency, while the increase in it at the pulsating frequency 75 Hz with blowing ratio equal to 2 is about 108%.
THEORETICAL NONLINEAR MODEL OF FRICTIONAL HEAT GENERATION IN BRAKING
1007-1022
10.1615/HeatTransRes.2018026425
Aleksander
Yevtushenko
Faculty of Mechanical Engineering, Bialystok University of Technology (BUT), 45C Wiejska Str.,
Bialystok, 15-351, Poland
Michal
Kuciej
Faculty of Mechanical Engineering, Bialystok University of Technology (BUT), 45C Wiejska Str.,
Bialystok, 15-351, Poland
Ewa
Och
Faculty of Mechanical Engineering, Bialystok University of Technology (BUT), 45C Wiejska Str.,
Bialystok, 15-351, Poland
frictional heating
braking
thermal sensitivity
temperature
thermal stresses
A mathematical model to investigate the temperature field and thermal stresses in an essentially nonlinear pad–disk brake system has been proposed. For this purpose, a one-dimensional boundary-value heat conduction problem with friction heat generation for the strip–semispace system has been formulated. It has been assumed, that thermal contact of friction between these elements is perfect, and the thermal and mechanical properties of their materials depend on the temperature. A numerical solution to the problem by means of the method of lines with integral interpolation over the spatial variable has been obtained. Knowing the distribution of the transient temperature field, the corresponding thermal stresses were found, too. Calculations for a gray iron disk and titanium alloy pad were executed.