Calculation of the heat-transfer coefficient in block-graphite heat exchangers

1979 ◽  
Vol 15 (3) ◽  
pp. 199-202
Author(s):  
V. S. Novopavlovskii
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Graphite Heat ◽  
The Heat Transfer Coefficient

scholarly journals Experimental Research and Simulation of Fin and Tube Heat Exchanger

2017 ◽  
Vol 9 (4) ◽  
pp. 451-461
Author(s):  
Artur Rubcov ◽  
Sabina Paulauskaitė ◽  
Violeta Misevičiūtė
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Ventilation System ◽  
Experimental Tests ◽  
Maximum Heat ◽  
Tube Heat Exchanger ◽  
The Heat Transfer Coefficient

The paper provides the results of experimental and theoretical test of a wavy fin and tube heat exchanger used to cool air in a ventilation system when the wavy fin of the heat exchanger is dry and wet. The experimental tests, performed in the range of 1000<Re<4500 of the Reynolds number applying LMTD-LMED methodology, determined the dependency of the heat transfer coefficient on the supplied air flow rate with the varying geometry of the heat exchanger (the number of tube rows, the distance between fins, the thickness of the fin and the diameter of the tube). The experimental tests were performed on 9 heat exchangers in heating and 6 heat exchangers in cooling mode. After processing the results of the experimental tests, empirical equation defining the characteristics of the heat transfer coefficient of all heat exchangers were derived. The maximum heat transfer coefficient deviation is 11.6 percent. The correction factor of the wet fin (Lewis number) depending on the number of Reynolds, which ranges from 0.75 to 1.1 also is determined. Maximum capacity deviation equals 3.7 percent. The obtained equations can only be applied to a certain group of heat exchangers (with the same shape of fins or the distance between the tubes). The results of the experimental test and simulation with ANSYS program are compared and the heat transfer coefficients vary from 6.5 to 11.4 percent.

Numerical Simulation about Heat Transfer Coefficient for the Double Pipe Heat Exchangers

2011 ◽  
Vol 71-78 ◽  
pp. 2577-2580 ◽  
Author(s):  
Hui Fan Zheng ◽  
Jing Bai ◽  
Jing Wei ◽  
Lan Yu Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Total Heat Transfer ◽  
Double Pipe ◽  
Heat Exchanges ◽  
The Heat Transfer Coefficient ◽  
Pipe Heat

Based on the EES software, a heat transfer coefficient calculation program about double pipe heat exchanges is established. Some experimental data are compared to the simulation data for proving that the program can predict the heat transfer coefficient of the double pipe heat exchangers, and then the change of heat transfer coefficient is calculated and analyzed with relevant parameters. The results show that the heat transfer coefficient of heat exchanger are increasing with the flow of the shell side, the tube side and the logarithmic mean temperature difference, and when the temperature difference equals to 12°C, the total heat transfer coefficient can up to 2400W/m2.K or so.

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.

Effect of Inlet Flow Angle on Performance of Multilouvered Fin Heat Exchangers

2003 ◽  
Author(s):  
Dahai Guo ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Inlet Flow ◽  
Flow Angle ◽  
The Heat Transfer Coefficient ◽  
Effective Reynolds Number

The effect of inlet flow angles on flat tube multilouvered fin heat exchangers is studied. Five inlet flow angles, α= ±25, ±45 and 0 degrees are employed with respect to the face of the heat exchanger. One louver angle θ = 25 degrees, and three fin pitches, Fp = 1.0, 1.5 and 2.0 are considered. There is a strong correlation between the response of the flow efficiency and heat transfer coefficient to inlet flow angle. Positive flow angles, which are in the same direction as the louver angle, have to undergo a smaller rotation to be aligned with louver directed flow in the bank, and exhibit better performance characteristics than negative inlet flow angles. The first-order effect of inlet flow angles is to reduce the effective mass flow rate and Reynolds number through the heat exchanger. For positive flow angles and small fin pitches, the heat transfer coefficient correlates well with the effective Reynolds number {Reeff = Re(cosα)}. However, this is not the case when flow angles are negative and the fin pitch increases. Under these conditions, the Nusselt number deviates considerably from the effective Reynolds number analogy, with a subsequent loss in heat transfer capability. For large negative inlet flow angles (α = −45), the heat transfer coefficient drops as much as 50% for a fin pitch Fp = 2.

An Experimental Study on Convective Boiling Heat Transfer in Micro Heat Exchangers

2010 ◽  
Author(s):  
Chien-Yuh Yang ◽  
Wei-Chi Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
High Heat ◽  
Vapor Quality ◽  
Straight Flow ◽  
The Heat Transfer Coefficient

Attributed to its high heat transfer coefficient, evaporating cooling involving the use of micro heat exchangers is considered a possible thermal management solution for cooling of high heat flux electronic devices. The desire to develop high-performance micro heat exchangers operating in the evaporation regime provides a major motivation for the present work. Methanol evaporated in two micro heat exchangers with chevron flow passages and straight flow passages respectively were tested in the present study. The test results show that the heat transfer coefficient increased with increasing flow rate in both chevron and straight flow passages micro heat exchangers. However, the effect of vapor quality on the heat transfer coefficient in the straight passages heat exchanger is in adverse to that in the chevron passages heat exchanger. The heat transfer coefficient increased with increasing vapor quality in the chevron passages heat exchanger but decreased in the straight passages heat exchanger. The flow visualization through transparent cover heat exchangers showed that the liquid film inside channel is partially dry out in the straight passages heat exchanger. The dryout portion area increased with increasing heating rate and exit vapor quality. This degraded the average heat transfer performance for evaporation in the straight passages heat exchanger. Because of the surface tension effect, the liquid film was dragged at the intersection corner of the upper and lower plate chevron passages. There is no significant dryout portion in the chevron passages heat exchanger. The relation of vapor quality with heat transfer performance in chevron passages heat exchanger is therefore similar to the boiling in a single channel prior to critical heat flux condition.

scholarly journals Evaluation of selected methods of the heat transfer coefficient determination in fin-and-tube cross-flow heat exchangers

2018 ◽  
Vol 240 ◽  
pp. 02004 ◽  
Author(s):  
Tomasz Bury ◽  
Małgorzata Hanuszkiewicz Drapała
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Cross Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Heat ◽  
The Heat Transfer Coefficient

The work is a part of a thermodynamic analysis of a finned cross-flow heat exchanger of the liquid-gas type. The heat transfer coefficients on the liquid and the gas side and the area of the heat transfer are the main parameters describing such a device. The basic problem in computations of such heat exchangers is determination of the coefficient of the heat transfer from the finned surfaces to the gas. The differences in the heat transfer coefficient local values resulting from the non-uniform flow of mediums through the exchanger complicates the analysis additionally. Six Nusselt number relationships are selected as suitable for the considered heat exchanger, and they are used to calculate the heat transfer coefficient for the air temperature ranging from 10°C to 30°C and for the velocity values ranging from 2 m/s to 20 m/s. In the next step, the gas-side heat transfer coefficient is determined by means of numerical simulations using a numerical model of a repetitive fragment of the heat exchanger under consideration. Finally, the Wilson plot method is also used. The work focuses on an analysis of the in-house HEWES code sensitivity to the method of the heat transfer coefficient determination. The authors believe that the analysis may also be useful for the evaluation of different methods of the heat transfer coefficient computation.

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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