Heat Transfer Studies in Ejector-induced Downflow Bubble Column

2016 ◽  
Vol 14 (5) ◽  
pp. 955-964
Author(s):  
Rohit B. Meshram ◽  
Gautam Kundu ◽  
Dibyendu Mukherjee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Liquid Velocity ◽  
Bubble Column ◽  
Research Work ◽  
Experimental Studies ◽  
Heat Removal ◽  
Axial Position ◽  
The Heat Transfer Coefficient

Abstract Temperature control in bubble columns is of great importance, since chemical reactions in many of the chemical, pharmaceutical, fertilizer, etc. industries are usually accompanied by heat supply or heat removal operations. In the present research work, the heat transfer coefficient of a two-phase co-current vertical downflow bubble column (i.d. 0.05 m×1.6 m height) was evaluated. Experimental studies were carried out to calculate the heat transfer coefficient for operating temperature ranges from 60 °C to 90 °C. The effects of the superficial gas velocity (4.25×10–3 to 9.58×10–3 m/s), liquid velocity (8.50×10–2 to 16.98×10–2 m/s), gas holdup, and axial position were investigated. Empirical correlation was developed, based on a multiple regression analysis to calculate a heat transfer coefficient as a function of dimensionless numbers, including the Reynolds number, the Prandtl number, and the Froude number.

Development of a Heat Transfer Coefficient Model via Experimental Validation

2008 ◽  
Vol 3 (1) ◽  
Author(s):  
Adel A. Al-Hemiri ◽  
Nada Sadoon Ahmedzeki
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Standard Deviation ◽  
Transfer Coefficient ◽  
Bubble Column ◽  
Mechanistic Model ◽  
Bubble Column Reactor ◽  
Ann Model ◽  
Liquid Bubble ◽  
The Heat Transfer Coefficient

Knowledge of the heat transfer coefficient is an essential prerequisite for any industrial gas/liquid bubble column reactor design. In this paper, experiments were carried out in a laboratory scale bubble column using air–water and 10wt% glycerin–air solution systems. Experimental values of the heat transfer coefficient were compared with some of the previous published correlations and were also compared with the model predicted by ANN in our previous work (Ahmedzeki, 2007). The ANN model was found to be better than all previous published correlations. %AARE was 8.2 and %standard deviation was 7.85. A mechanistic model was also developed to analyze the system. The resulting correlation was a %AARE of 17.5 and %standard deviation of 15. Both the above models and the experimental results compared well with the previous published correlations.

scholarly journals Experimental Investigation on Condensation of Vapor in the Presence of Non-Condensable Gas on a Vertical Tube

2018 ◽  
Author(s):  
Shengjun Zhang ◽  
Feng Shen ◽  
Xu Cheng ◽  
Xianke Meng ◽  
Dandan He
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Total Pressure ◽  
Mass Fraction ◽  
Heat Removal ◽  
Heat Transfer Process ◽  
Transfer Model ◽  
Operation Conditions ◽  
The Heat Transfer Coefficient

According to the operation conditions of time unlimited passive containment heat removal system (TUPAC), a separate effect experiment facility was established to investigate the heat transfer performance of steam condensation in presence of non-condensable gas. The effect of wall subcooling temperature, total pressure and mass fraction of the air on heat transfer process was analyzed. The heat transfer model was also developed. The results showed that the heat transfer coefficient decreased with the rising of subcooling temperature, the decreasing of the total pressure and air mass fraction. It was revealed that Dehbi’s correlation predicted the heat transfer coefficient conservatively, especially in the low pressure and low temperature region. The novel correlation was fitted by the data obtained in the following range: 0.20~0.45 MPa in pressure, 20% ~ 80% in mass fraction, 15°C ~ 45°C in temperature. The discrepancy of the correlation and experiment data was with ±20%.

scholarly journals DEVELOPMENT OF HIGH EFFICIENT SHELL-AND-TUBE HEAT EXCHANGERS BASED ON PROFILED TUBES

2020 ◽  
Author(s):  
Djamalutdin Chalaev ◽  
◽  
Nina Silnyagina ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Hydraulic Resistance ◽  
Heat Exchangers ◽  
Experimental Studies ◽  
Corrugated Tube ◽  
The Heat Transfer Coefficient

The use of advanced heat transfer surfaces (corrugated tubes of various modifications) is an effective way to intensify the heat transfer and improve the hydraulic characteristics of tubular heat exchangers. The methods for evaluating the use of such surfaces as working elements in tubular heat exchangers have not been developed so far. The thermal and hydrodynamic processes occurring in the tubes with the developed surfaces were studied to evaluate the efficiency of heat exchange therein. Thin-walled corrugated flexible stainless steel tubes of various modifications were used in experimental studies. The researches were carried out on a laboratory stand, which was designed as a heat exchanger type "tube in tube" with a corrugated inner tube. The stand was equipped with sensors to measure the thermal hydraulic flow conditions. The comparative analysis of operation modes of the heat exchanger with a corrugated inner tube of various modifications and the heat exchanger with a smooth inner tube was performed according to the obtained data. Materials and methods. A convective component of the heat transfer coefficient of corrugated tube increased significantly at identical flow conditions comparing with a smooth tube. Increasing the heat transfer coefficient was in the range of 2.0 to 2.6, and increased with increasing Reynolds number. The increase in heat transfer of specified range outstripped the gain of hydraulic resistance caused by increase of the flow. Results and discussion. CFD model in the software ANSYS CFX 14.5 was adapted to estimate the effect of the tube geometry on the intensity of the heat transfer process. A two-dimensional axially symmetric computer model was used for the calculation. The model is based on Reynolds equation (Navier-Stokes equations for turbulent flow), the continuity equation and the energy equation supplemented by the conditions of uniqueness. SST-turbulence model was used for the solution of the equations. The problem was solved in the conjugate formulation, which allowed assessing the efficiency of heat exchange, depending on various parameters (coolant temperature, coolant velocity, pressure). The criteria dependences were obtained Nu = f (Re, Pr). Conclusions. The use a corrugated tube as a working element in tubular heat exchangers can improve the heat transfer coefficient of 2.0 - 2.6 times, with an increase in hydraulic resistance in the heat exchanger of 2 times (compared with the use of smooth tubes). The criteria dependences obtained on the basis of experimental studies and mathematical modeling allow developing a methodology for engineering calculations for the design of new efficient heat exchangers with corrugated tubes.

scholarly journals Physical and numerical simulation of the thermal and mechanical characteristics of stationary flows in the gasair paths of piston engines

2019 ◽  
Vol 21 (5) ◽  
pp. 22-28
Author(s):  
L. V. Plotnikov ◽  
Yu. M. Brodov ◽  
B. P. Zhilkin ◽  
A. M. Nevolin ◽  
M. O. Misnik
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Sections ◽  
Experimental Studies ◽  
Hydraulic Systems ◽  
Reciprocating Engines ◽  
The Heat Transfer Coefficient ◽  
Exhaust Systems

Thermomechanical perfection of intake and exhaust systems largely determine the efficiency of the working process of reciprocating engines (ICE). The article presents the results of numerical simulation and experimental study of the heat transfer of gas flows in profiled gas- air systems of ICEs. A description of the numerical simulation technique, experimental setup, configurations of the studied hydraulic systems, measuring base and features of the experiments are given. On the basis of numerical modeling, it has been established that the use of profiled sections with cross sections in the shape of a square or a triangle in exhaust systems of an ICEs leads to a decrease in the heat transfer coefficient by 5-11%. It is shown that the use of similar profiled sections in the intake system of reciprocating engines also leads to a decrease in the heat transfer coefficient to 10 % at low air flow rates (up to 40 m/s) and an increase in the heat transfer coefficient to 7% at high speeds. Experimental studies qualitatively confirm the simulation results.

Thermal-Hydraulic Analytical Models of Split-Flow Microchannel Liquid-Cooled Cold Plates With Flow Impingement

2021 ◽  
Author(s):  
Deogratius Kisitu ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Experimental Studies ◽  
Base Plate ◽  
Analytical Models ◽  
Split Flow ◽  
Wide Range ◽  
Cold Plates ◽  
The Heat Transfer Coefficient

Abstract Impingement split flow liquid-cooled microchannel cold plates are one of several flow configurations used for single-phase liquid cooling. Split flow or top-in/side-exit (TISE) cold plates divide the flow into two branches thus resulting in halved or reduced flow rates and flow lengths, compared to traditional side-in /side-exit (SISE) or parallel flow cold plates. This has the effect of reducing the pressure drop because of the shorter flow length and lower flow rate and increasing the heat transfer coefficient due to thermally developing as opposed to fully developed flow. It is also claimed that the impinging flow increases the heat transfer coefficient on the base plate in the region of impingement. Because of the downward impinging and turning flow, there are no exact analytical models for this flow configuration. Computational and experimental studies have been performed, but there are no useful compact analytical models in the literature that can be used to predict the performance of these impingement cold plates. Results are presented for novel physics-based laminar flow models for a TISE microchannel cold plate based on an equivalent parallel channel flow approach. We show that the new models accurately predict the thermal-hydraulic performance over a wide range of parameters.

scholarly journals Transient behavior of a plate-fin-and-tube heat exchanger taking into account different heat transfer coefficients on the individual tube rows

2019 ◽  
Vol 137 ◽  
pp. 01036
Author(s):  
Dawid Taler ◽  
Jan Taler ◽  
Katarzyna Wrona
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Experimental Studies ◽  
Analytical Formula ◽  
Cfd Modeling ◽  
Individual Tube ◽  
The Heat Transfer Coefficient

Plate-fin and tube heat exchangers (PFTHE) are made of round, elliptical, oval or flat tubes to which continuous fins ( lamellas) are attached. Liquid flows inside the tubes and gas flows outside the tubes perpendicularly to their axes and parallel to the surface of continuous fins. Experimental studies of multi-row plate-fin and tube heat exchangers show that the highest average heat transfer coefficient on the air side occurs in the first row of tubes when the air velocity in front of the exchanger is less than approximately 3.5 m/s when a Reynolds number based on an equivalent hydraulic diameter equal to the distance between tube rows in the direction of air flow is less than 10,000. In the subsequent rows of tubes up to about the fourth row the heat transfer coefficient decreases. In the fifth and further rows, it can, that the heat transfer coefficient is equal in each tube row. It is necessary to find the relationships for the air-side Nusselt number on each tube row to design a PFTHE with the appropriate number of tube rows. The air-side Nusselt number correlations can be determined experimentally or by CFD modeling (Computational and Fluid Dynamics). The paper presents a new mathematical model of the transient operation of PFTHE, considering that the Nusselt numbers on the air side of individual tube rows are different. The heat transfer coefficient on an analyzed tube row was determined from the equality condition of mass- average air temperature differences on a given tube row determined using the analytical formula and CFD modeling. The results of numerical modeling were compared with the results of the experiments.

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