Free Convection, Forced Convection, and Acoustic Vibrations in a Constant Temperature Vertical Tube

1959 ◽  
Vol 81 (1) ◽  
pp. 68-74 ◽  
Author(s):  
T. W. Jackson ◽  
W. B. Harrison ◽  
W. C. Boteler
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Sound Pressure ◽  
Experimental Studies ◽  
Experimental System ◽  
Vertical Tube ◽  
Acoustic Vibrations ◽  
Average Temperature ◽  
Comparison Of The Results ◽  
The Heat Transfer Coefficient

Experimental studies of heat transfer to air with superposed forced and free convection were reported in a previous paper [1]. In studies reported in this paper, the same experimental system was employed, but a complication was added in the form of acoustic vibrations in the flow field. By comparison of the results with and without acoustic vibrations under conditions which were otherwise the same, an effort has been made to determine the effect of acoustic vibrations on heat transfer. The Nusselt modulus, based on the log mean temperature difference, ranged from 17.2 to 50.6; the Graetz modulus, based on the bulk or average temperature of the air, ranged from 40.2 to 1633; and the Grashof-Prandtl D/L modulus, based on properties of air at the wall temperature, ranged from 0.967 × 105 to 1.26 × 106. The results indicated that sound pressure levels below approximately 118 decibels had little effect on the heat-transfer coefficient. Below 118 decibels free convection forces were evident. Above 118 decibels free convection forces were apparently negligible and the effect of sound appeared to be considerable.

scholarly journals Theoretical Studies of the Vibration Process of the Dryer for Waste of Food

2020 ◽  
Vol 44 (339) ◽  
pp. 32-45
Author(s):  
Volodymyr Bulgakov ◽  
Ivan Sevostianov ◽  
Gryhoriy Kaletnik ◽  
Ihor Babyn ◽  
Semjons Ivanovs ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Food Waste ◽  
Experimental Studies ◽  
The Body ◽  
Fluidised Bed ◽  
Technological Parameters ◽  
Heating Pipes ◽  
Maximum Stiffness ◽  
Low Energy Consumption ◽  
The Heat Transfer Coefficient

AbstractAn urgent problem is drying and processing of the wet dispersed waste, obtained in the production of food products, which can then be efficiently used as a fertiliser, for feeding livestock or as biofuel. A new design of a vibrating fluidised bed dryer has been developed, which, with low energy consumption, provides a pre-set productivity and the required final moisture content. The process of vertical oscillations of the body of a vibration dryer, together with the food waste contained in it, is analysed analytically, the necessary equivalent scheme is built, on the basis of which differential equations of the vertical oscillations of the body are compiled, their analytical solutions are obtained, and a numerical calculation is performed on a PC using the developed program. Rational parameters of the vibration dryer, providing vibroboiling of the mass of the food waste, have been determined: the body mass m = 250 ... 510 kg; the debalance mass md= 10… 15 kg; the number of revolutions of the debalance electric motor nd= 1950 ... 2650 rpm ∙ min∙1; maximum stiffness of the support springs Cp= 8∙105 N∙m–1; the diameter of the centre of mass of the debalances dd= 0.01 m. In addition, as a result of the thermophysical theoretical and experimental studies of the vibration drying process, the following optimal design and technological parameters of the vibration dryer were obtained: the heat transfer area St.p.n= 4.15 m2; the radius of the heating pipe rt= 0.1 m; the length of the heating pipe lt = 3 m; the number of heating pipes nt= 50; the heat transfer coefficient Kp= 2500; the final temperature of the dried waste to2= 100 ºС.

scholarly journals EFFECT OF CAVITY RATIO ON HEAT TRANSFER BY FREE LOAD FROM HEATED PLATES UPWARD WITH CONSTANT HEAT FLUX

2021 ◽  
Vol 9 (12) ◽  
pp. 686-695
Author(s):  
Waleed Abdulhadiethbayah ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Free Convection ◽  
Electronic Devices ◽  
Experimental Studies ◽  
Constant Heat Flux ◽  
Rate Of Change ◽  
Constant Heat ◽  
The Difference

Many engineering and industrial applications always seek to find ways to dissipate heat from heated surfaces used in these industries. As it is involved in the cooling of electronic parts and electrical transformers, as well as the design of solar collectors, in addition to being a process of heat exchange between hot surfaces and the fluids in contact with them. Since most electronic devices or their parts are cooled by removing the heat generated inside them by using air as a heat transfer medium and in a free convection way, and the fact that heat transfer by free convection occurs in many fields, so there were many studies that dealt with this topic. The free load is generated by the buoyant force (Bouncy force) As a result of the difference in the density of the fluid adjacent to the heated surface due to the difference in temperatures between the fluid and the surface. The laminar flow along surfaces has been extensively studied analytically [1,2,3,4] In the horizontal, inclined and vertical case, whether by constant heat flux or constant surface temperature, there are also many experimental studies of heat transfer by free convection from horizontal, inclined and vertical surfaces with constant heat flux or constant surface temperature [5,6,7,8]. Some experimental studies have also been conducted on heat transfer by convection from heated surfaces in the form of a disk (ring)The outcome of these studies was to extract an exponential mathematical relationship between the average of Nusselt number and the Kirchhoff number or Rayleigh number and the following formula: (Nu=C(Ra) n It is one of the most suitable formulas for heat transfer by free convection from heated surfaces in all its forms and over a wide range of Rayleigh number . It is noted that not all of these studies dealt with the study of the effect of the cavity ratio on heat transfer by free convection from square-shaped surfaces, which is the form that is more applied in electronic devices. Therefore, the current research means studying the rate of change in the average of Nusselt number, which represents a function of the rate of change in the rate of heat transfer by convection, as well as studying the thermal gradient above the surface, and this was done through using three hollow surfaces in proportions (0.25,0.5,0.75) of the total area.

Numerical Analysis of Supercritical Water Heat Transfer in Vertical Tube With Different Obstacles

2009 ◽  
Author(s):  
Bo Zhang ◽  
Jianqiang Shan ◽  
Jing Jiang
Keyword(s):  
Heat Transfer ◽  
Critical Point ◽  
Supercritical Water ◽  
Transfer Characteristic ◽  
Vertical Tube ◽  
Bulk Temperature ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Water Reactors ◽  
The Heat Transfer Coefficient

Supercritical Water Reactors (SCWRs) are essentially water reactors operating at pressure and temperature above critical point. The heat transfer coefficient is relative low when the bulk temperature is above the pseudo-critical point due to the properties of vapor-like fluid. To obtain better heat transfer characteristics, increasing the fluctuation using obstacles is the conventional method. Heat transfer characteristic in vertical tube with different obstacles is numerically investigated under supercritical condition. Numerical simulation is carried out with commercial CFD code Fluent 6.1 and adaptive grid. The results show that The RNG k-ε model with enhanced wall treatment can obtain a reliable result; the blockage ratio and the local temperature have large influence on the heat transfer enhancement. The influence region and decay trend of obstacles are also studied and compared with existing correlations.

scholarly journals Measurement of Heat Transfer Coefficients in an Agitated Vessel with Tube Baffles

10.14311/1171 ◽  
2010 ◽  
Vol 50 (2) ◽  
Author(s):  
M. Dostál ◽  
K. Petera ◽  
F. Rieger
Keyword(s):  
Heat Transfer ◽  
Cold Water ◽  
Vertical Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Steady State Method ◽  
Classic Approach ◽  
Large Heat ◽  
Common Operation ◽  
The Heat Transfer Coefficient

Cooling or heating an agitated liquid is a very common operation in many industrial processes. A classic approach is to transfer the necessary heat through the vessel jacket. Another option, frequently used in the chemical and biochemical industries is to use the heat transfer area of vertical tube baffles. In large equipment, e.g. fermentor, the jacket surface is often not sufficient for large heat transfer requirements and tube baffles can help in such cases. It is then important to know the values of the heat transfer coefficients between the baffles and the agitated liquid. This paper presents the results of heat transfer measurements using the transient method when the agitated liquid is periodically heated and cooled by hot and cold water running through tube baffles. Solving the unsteady enthalpy balance, it is possible to determine the heat transfer coefficient. Our results are summarized by the Nusselt number correlations, which describe the dependency on the Reynolds number, and they are compared with other measurements obtained by a steady-state method.

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