Numerical Simulations of Natural Convective Heat Transfer in Vertical Concentric and Eccentric Annular Channels

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
A. A. Busedra ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Mass Flow Rate ◽  
Convective Heat ◽  
Mass Flow ◽  
Flow Rate ◽  
Annular Channel ◽  
Diameter Ratio ◽  
Fluid Temperature ◽  
Annular Channels

Natural convective heat transfer in a concentric and a highly eccentric, vertical, open ended, annular channel has been investigated numerically. The inner to outer diameter ratio was 0.61, and the height to hydraulic diameter ratio was 18:1. Three heating modes were considered, all having uniform heat flux applied to one or both of the two walls, while the unheated wall was kept adiabatic. The wall temperature distribution, mass flow rate, and midchannel Nusselt number for the case with both walls heated were found to be in excellent agreement with available experimental results. For the same heating conditions, the heat transfer rate in the concentric annular channel was found to be greater than that in the highly eccentric channel, while the mass flow rate was higher in the eccentric channel. A novel finding for the eccentric channel was that the location of maximum velocity was intermediate between the narrow and wide gaps. Another novel observation, which was attributed to radiation effects, was that the fluid temperature in the wide gap region was lower than that of an adiabatic wall. The paper contains additional observations that would be of interest to designers of systems containing annular channels.

Numerical Investigation of Convective Heat Transfer on a Dynamic Wall Heat Exchanger With Varying Amplitude and Frequency

2020 ◽  
Author(s):  
Md. Habibur Rahman ◽  
Emdadul Haque Chowdhury ◽  
Didarul Ahasan Redwan ◽  
Hasib Ahmed Prince ◽  
M. Ruhul Amin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Mass Flow Rate ◽  
Convective Heat ◽  
Mass Flow ◽  
Flow Rate ◽  
Convective Heat Transfer Coefficient ◽  
Liquid Temperature

Abstract The current work aims to investigate the thermo-hydraulic performances of a dynamic wall heat exchanger by varying amplitude and frequency of the oscillating waveform. The lower wall of the channel is exposed to constant heat flux, the upper insulating wall is deforming in a sinusoidal waveform, and water is taken as the working fluid. The governing partial differential equations are solved by using the Arbitrary Lagrangian-Eulerian finite element method. The study has been performed in the transient regime for up to 1.0 second. At first the effects of frequency variation over the average mass flow rate, convective heat transfer coefficient, and the average liquid temperature have been observed for a particular amplitude of the dynamic wall. It has been found that the mass flow rate of water increases linearly with increasing frequency. Convective heat transfer coefficient decreases with increasing frequency up to 50 Hz, then starts to increase notably. Interestingly, the fluctuating average liquid temperature decreases and reaches a steady-state faster with increasing frequency. To explore the effect of amplitude over heat transfer characteristics, the amplitude ratio of the sinusoidal wave is varied maintaining a constant frequency of oscillation. It has been observed that with increasing amplitude, both mass flow rate and convective heat transfer coefficient increase exponentially. Increasing amplitude ratio from 0.5 to 0.9 results in an increment in the convective heat transfer coefficient by about 5 times. Although, the average liquid temperature decreases and reaches a steady state faster with increasing amplitude, initially the peak temperature of the water is recorded for the highest amplitude.

Convective Heat Transfer Performance of FC-72 in a Pin-Finned Channel

2008 ◽  
Author(s):  
Liang-Han Chien ◽  
S.-Y. Pei ◽  
T.-Y. Wu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flow Rate ◽  
Smooth Surface ◽  
Heat Transfer Performance ◽  
Fluid Temperature ◽  
Transfer Performance ◽  
Finned Surface

This study investigates the influence of the heat flux and mass velocity on convective heat transfer performance of FC-72 in a rectangular channel of 20mm in width and 2 mm in height. The heated side has either a smooth surface or a pin-finned surface. The inlet fluid temperature is maintained at 30°C. The total length of the test channel is 113 mm, with a heated length of 25mm. The flow rate varies between 80 and 960 ml/min, and the heat flux sets between 18 and 50 W/cm2. The experimental results show that the controlling variable is heat flux instead of flow rate because of the boiling activities in FC-72. At a fixed flow rate, the pin-finned surface yields up to 20% higher heat transfer coefficient and greater critical heat flux than those of a smooth surface.

Experimental Study on Heat Transfer of Supercritical Kerosene in a Vertical Upward Tube

2013 ◽  
Author(s):  
Dan Huang ◽  
Wei Li ◽  
Wei Zhang ◽  
Guo-Qiang Xu ◽  
Zhi Tao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Temperature ◽  
Physical Properties ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Supercritical Pressure ◽  
Fluid Temperature ◽  
Thermo Physical Properties

A research on the heat transfer performance of kerosene flowing in a vertical upward tube at supercritical pressure is presented. In the experiments, insights are offered on the effects of the factors such as mass flow rate, heat flux and pressure. It is found that increasing the mass flow rate could enhance the heat transfer performances, while increasing the working pressure will deteriorate the heat transfer. Besides, the effect of heat flux on heat transfer is complicated. Based on the analysis of experimental data, enhancement of heat transfer occurs when the inner wall temperature of tube is higher than pseudo-critical temperature while the bulk fluid temperature is lower than the pseudo-critical temperature. At the supercritical conditions, heat transfer is influenced by the significant changes in thermo-physical properties, thus accurate evaluations of the thermo-physical properties become the key for the supercritical heat transfer calculations. The extended corresponding-state principle could be used for evaluating the density and the transport properties of kerosene, including its viscosity and thermal conductivity, at different temperatures and pressures. In order to obtain the numerical values of the heat capacity, a Soave–Redlich–Kwong (SRK) equation of state is used. The correlation for predicting heat transfer in kerosene at supercritical pressure is established, the calculation results from this correlation are in good agreement with the experimental results.

Convective Heat Transfer to CO2 at a Supercritical Pressure Flowing Vertically Upward in Tubes and an Annulus Channel

2008 ◽  
Author(s):  
Yoon-Yeong Bae ◽  
Hwan-Yeol Kim ◽  
Deog-Ji Kang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Annular Channel ◽  
Supercritical Pressure ◽  
Internal Diameter ◽  
Test Results ◽  
Annular Channels ◽  
Normal Heat

Extensive experiments on heat transfer at a supercritical pressure to CO2 in tubes and annular channels have been performed. The geometries of the test sections include tubes of an internal diameter of 4.4 and 9 mm and an annular channel (8 × 10 mm). Based on the test results a set of correlations, which covers a deteriorated heat transfer regime as well as a normal heat transfer regime, was developed.

Effect of pre-swirl nozzle closure modes on unsteady flow and heat transfer characteristics in a pre-swirl system of aero-engine

2021 ◽  
pp. 095441002110191
Author(s):  
Gaowen Liu ◽  
Zhao Lei ◽  
Aqiang Lin ◽  
Qing Feng ◽  
Yan Chen
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Temperature Drop ◽  
Thermodynamic Characteristics ◽  
Circumferential Direction ◽  
Temperature Changes ◽  
Air Supply ◽  
Cooling Air

The pre-swirl system is of great importance for temperature drop and cooling air supply. This study aims to investigate the influencing mechanism of heat transfer, nonuniform thermodynamic characteristics, and cooling air supply sensitivity in a pre-swirl system by the application of the flow control method of the pre-swirl nozzle. A novel test rig was proposed to actively control the supplied cooling air mass flow rate by three adjustable pre-swirl nozzles. Then, the transient problem of the pre-swirl system was numerically conducted by comparison with 60°, 120°, and 180° rotating disk cavity cases, which were verified with the experiment results. Results show that the partial nozzle closure will aggravate the fluctuation of air supply mass flow rate and temperature. When three parts of nozzles are closed evenly at 120° in the circumferential direction, the maximum value of the nonuniformity coefficient of air supply mass flow rate changes to 3.1% and that of temperature changes to 0.25%. When six parts of nozzles are closed evenly at 60° in the circumferential direction, the maximum nonuniformity coefficient of air supply mass flow rate changes to 1.4% and that of temperature changes to 0.20%. However, different partial nozzle closure modes have little effect on the average air supply parameters. Closing 14.3% of the nozzle area will reduce the air supply mass flow rate by 9.9% and the average air supply temperature by about 1 K.

Heat Transfer and Flow Friction Characteristics for Compact Cold Plates

2003 ◽  
Vol 125 (1) ◽  
pp. 104-113 ◽  
Author(s):  
Chang-Yuan Liu ◽  
Ying-Huei Hung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Thermal Resistance ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Average Nusselt Number ◽  
Cold Plate ◽  
Air Mass

Both experimental and theoretical investigations on the heat transfer and flow friction characteristics of compact cold plates have been performed. From the results, the local and average temperature rises on the cold plate surface increase with increasing chip heat flux or decreasing air mass flow rate. Besides, the effect of chip heat flux on the thermal resistance of cold plate is insignificant; while the thermal resistance of cold plate decreases with increasing air mass flow rate. Three empirical correlations of thermal resistance in terms of air mass flow rate with a power of −0.228 are presented. As for average Nusselt number, the effect of chip heat flux on the average Nusselt number is insignificant; while the average Nusselt number of the cold plate increases with increasing Reynolds number. An empirical relationship between Nu¯cp and Re can be correlated. In the flow frictional aspect, the overall pressure drop of the cold plate increases with increasing air mass flow rate; while it is insignificantly affected by chip heat flux. An empirical correlation of the overall pressure drop in terms of air mass flow rate with a power of 1.265 is presented. Finally, both heat transfer performance factor “j” and pumping power factor “f” decrease with increasing Reynolds number in a power of 0.805; while they are independent of chip heat flux. The Colburn analogy can be adequately employed in the study.

scholarly journals Thermal Characteristics Analysis on Multi- Heat Pipe Induced Heat Exchanger

2019 ◽  
Vol 9 (2S2) ◽  
pp. 143-147 ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Pipe ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Cold Water ◽  
Hot Water ◽  
Working Fluid ◽  
Physical Parameters

In this investigation of multi heat pipe induced in heat exchanger shows the developments in heat transfer is to improve the efficiency of heat exchangers. Water is used as a heat transfer fluid and acetone is used as a working fluid. Rotameter is set to measure the flow rate of cold water and hot water. To maintain the parameter as experimental setup. Then set the mass flow rate of hot water as 40 LPH, 60LPH, 80 LPH, 100LPH, 120 LPH and mass flow rate of cold water as 20 LPH, 30 LPH, 40 LPH, 50 LPH, and 60 LPH. Then 40 C, 45 ºC, 50 ºC, 55 C, 60 ºC are the temperatures of hot water at inlet are maintained. To find some various physical parameters of Qc , hc , Re ,, Pr , Rth. The maximum effectiveness of the investigation obtained from condition of Thi 60 C, Tci 32 C and 100 LPH mhi, 60 LPH mci the maximum effectiveness attained as 57.25. Then the mhi as 100 LPH, mci as 60 LPH and Thi at 40 C as 37.6%. It shows the effectiveness get increased about 34.3 to the maximum conditions.

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