Shell-side Heat Transfer Coefficient Research Articles

Modeling for Shell-Side Heat Transfer Coefficient and Pressure Drop of Helical Baffle Heat Exchangers

This study has suitably modified the existing heat transfer and pressure drop correction factors of the modified Bell–Delaware method used for heat exchangers with segmental baffles, taking into consideration the helical baffle geometry. These correction factors are presented in parametric formulas based on the Taborek presented procedure for segmental baffles. These formulas are functions of the geometrical and physical parameters of discontinuous helical baffles. In addition, the parametric formulas are presented graphically based on the Stehlik method. The correction design method proposed by Stehlik for the helical baffle is presented in detail and a theoretical model for shell-side heat transfer and pressure drop is developed. In general, the results show that the present model matches more closely with the graphically proposed correction factors of Stehlik. In order to calculate the shell-side heat transfer coefficient and pressure drop using the present method, a computational code has been developed by the authors. In addition, in order to examine the validity, the results of the code for a case study are compared with the results obtained from EXPRESS software and experimental formulas presented by Zhang. The results of comparison show that the proposed method is accurate and can be used by designers confidently.

Investigation on combined multiple shell-pass shell-and-tube heat exchanger with continuous helical baffles

A combined serial two shell-pass shell-and-tube heat exchanger (CSTSP-STHX) with continuous helical baffles has been proposed to improve heat transfer performance. This CSTSP-STHX separates the shell side into two individual shell passes. The inner shell pass is conventional segmental baffled, and the outer shell pass is continuous helical baffled. The working fluid flows through the outer and inner shell passes in sequence. The thermo hydraulic performances of CSTSP-STHX are experimentally compared with the double shell-pass shell-and-tube heat exchanger with segmental baffles (SG-STHX). The results show that the CSTSP-STHX gets greater shell-side heat transfer coefficient and pressure drop, furthermore it also has better heat transfer coefficient under the same pressure drop than those of the SG-STHX. Finally it should be emphasized that the leakage on annulus separator has to be as possible as reduced. The present studies are beneficial for the design and practical operation of CSTSP-STHX.

Heat transfer and performance analysis of nanofluid flow in helically coiled tube heat exchangers

In the present paper, heat transfer characteristics of Al2O3 nanofluid flow inside shell and helical tube heat exchangers are numerically investigated. The numerical computations are performed by using SST turbulence model as well as by implementing conjugate heat transfer from hot fluid in the tube to cold fluid in the shell. The thermo-physical properties of the fluids were considered to be temperature dependent. The coil-side Reynolds number, the shell-side Reynolds number and the Prandtl number ranged between 9000 and 36,000, 600 and 2600 and 2.2 and 8.3, respectively. The effects of nanoparticle volume concentration on the temperature of coil- and shell-side flows, heat transfer rate and convective heat transfer coefficients are presented. The results indicate that the presence of 0.2% and 0.3% nanoparticle volume concentration increases the mean heat transfer rate by approximately 14% and 18%, respectively. The results also show that with the increase in particle volume concentration the coil-side, shell-side and overall heat transfer coefficients enhance. It is indicated that for the same mass flow rate, the heat transfer rate of nanofluid enhances noticeably compared to water and it increases marginally with the further increase in the nanoparticle volume concentration. The performance of the heat exchanger was evaluated and the results reveal that the effectiveness enhances by decreasing the mass flow rate and increasing the particle volume concentration, tube diameter and coil diameter. Moreover, the performance index enhances by increasing the tube diameter and reducing the coil diameter.

CFD simulations of shell-side flow in a shell-and-tube type heat exchanger with and without baffles

Shell-and-tube heat exchanger has been extensively used in industrial and research fronts for more than a century. However, most of its design procedures are based on empirical correlations extracted from experimental data of long length shell and tube heat exchanger. In this paper, an attempt has been made to investigate the complex flow and temperature pattern in such a short shell and tube type heat exchanger, with and without baffles in the shell side. Heat exchangers of length by hydraulic diameter ratio between 7<L/Dh<21(0.15m<DS<0.6m) for unbaffled and L/Dh<7(DS=0.09m) for baffled heat exchangers are analysed using CFD code OpenFOAM-2.2.0 for different mass flow rates. It was observed that the cross flow near the nozzle region has a significant contribution towards the heat transfer, hence the conventional heat transfer correlations do not apply to these short heat exchangers. Furthermore, a sensitivity study of turbulence models was performed and it was observed that the standard k–ε model gives best results for the velocity profile as well as heat transfer, provided average y+ of the first node adjacent to the heat transfer surface is maintained greater than 15. The commonly used boundary conditions at the exit are not realistic, as it tends to give either incorrect flow and temperature fields, or the solution was found to diverge. Through a sensitivity study of the exit length, it was found that exit length to shell side velocity ratio of 2.5 is required for proper convergence. Finally the effect of flow field on shell side heat transfer coefficient and a comparison with analytical methods are presented.

Numerical simulation on the performance of trisection helical baffle heat exchangers with small baffle incline angles

ABSTRACTNumerical simulation was conducted on oil–water heat transfer in five circumferential overlap trisection helical baffle shell–and–tube heat exchangers (cothSTHXs) with 16 tubes and incline angles of 12°, 16°, 20°, 24°, and 28° and a segmental baffle heat exchanger of the identical tube layout for comparison under laminar flow calculation conditions. The local images represent shell-side flow patterns, and heat transfer properties are presented showing the detailed “secondary vortex flow” and “shortcut leakage flow” patterns to explain the different characteristics of the six schemes. The simulation curves of the heat transfer coefficient and pressure drop are compared with those of the experimental ones, with satisfactory agreement. The average values of the shell-side heat transfer coefficient and the comprehensive index ho/Δpo of the 12° helical scheme are respectively 47% and 51% higher than those of the segmental baffle scheme with about the same pressure drop.

Investigations on the Condensation Heat Transfer Performance of Stainless Steel Edge-Shaped Finned Tubes

The third-generation enhanced heat transfer technologies, such as three-dimensional fin and dimple, are still important means of improving energy efficiency. This paper analyzes the condensation heat transfer performances of three edge-shaped finned tubes that were fabricated using the plowing–extruding process. Experimental results show that the shell-side heat transfer coefficient decreases with increases of heat flux and temperature difference between wall and vapor. The edge-shaped finned tubes exhibit better heat transfer performance than smooth tubes. At the identical temperature difference between the wall and the vapor, the shell-side heat transfer coefficient of the edge-shaped finned tubes is approximately 1.7–2.6 times larger than that of the smooth tubes. At the identical temperature difference between the wall and the vapor, the shell-side heat transfer coefficient of edge-shaped finned tubes is also higher than the reported value in the literature. The excellent performance of the edge-shaped finned tubes comes from the coordination of enhancement from the three-dimensional fins, dimples, and grooves. Finned tubes with grooves fabricated along the left direction have higher and thinner fins and therefore show better heat transfer performance. The shell-side heat transfer coefficients of edge-shaped finned tubes increase with plowing–extruding depth and feed increasing.

Effect of Coil Torsion on Heat Transfer and Pressure Drop Characteristics of Shell and Coil Heat Exchanger

The present work introduces an experimental study of horizontal shell and coil heat exchangers. Characteristics of the convective heat transfer in this type of heat exchangers and the friction factor for fully developed flow through their helically coiled tube (HCT) were investigated. The majority of previous studies were performed on HCTs with isothermal and isoflux boundary conditions or shell and coil heat exchangers with small ranges of HCT configurations and fluid-operating conditions. Here, five heat exchangers of counterflow configuration were constructed with different HCT torsions (λ) and tested at different mass flow rates and inlet temperatures of both sides of the heat exchangers. In total, 295 test runs were performed from which the HCT-side and shell-side heat transfer coefficients were calculated. Results showed that the average Nusselt numbers of both sides of the heat exchangers and the overall heat transfer coefficient increase by decreasing coil torsion. At lower and higher HCT-side Reynolds number (Ret), the average increase in the HCT-side average Nusselt number (Nu¯t) is of 108.7% and 58.6%, respectively, when λ decreases from 0.1348 to 0.0442. While, at lower and higher shell-side Reynolds number (Resh), the average increase in the shell-side average Nusselt number (Nu¯sh) is of 173.9% and 69.5%, respectively, when λ decreases from 0.1348 to 0.0442. In addition, a slight increase of 6.4% is obtained in the HCT Fanning friction factor (fc) at lower Ret when λ decreases from 0.1348 to 0.0442, and this effect vanishes with increasing Ret. Furthermore, correlations for Nu¯t, Nu¯sh, and fc are obtained.

CONDENSATION OF WATER VAPOR IN A VERTICAL TUBE CONDENSER

&lt;p&gt;This paper presents an analysis of heat transfer in the process of condensation of water vapor in a vertical shell-and-tube condenser. We analyze the use of the Nusselt model for calculating the condensation heat transfer coefficient (HTC) inside a vertical tube and the Kern, Bell-Delaware and Stream-flow analysis methods for calculating the shell-side HTC from tubes to cooling water. These methods are experimentally verified for a specific condenser of waste process vapor containing air. The operating conditions of the condenser may be different from the assumptions adopted in the basic Nusselt theory. Modifications to the Nusselt condensation model are theoretically analyzed.&lt;/p&gt;

Conjugate heat and mass transfer in a skewed flow hollow fiber membrane bank used for liquid desiccant air dehumidification

Hollow fiber membrane tube bank has been increasingly used in various industries. Fluid flow in shell side is often projected at an impinging angle to the fiber bank due to the complicate structure of heat mass exchangers. However most previous researches concerned only on two ideal flow conditions, pure parallel flow or pure cross flow. The effects of skewed flow were not mentioned. In this research, fluid flow and transport phenomena in a skewed flow hollow fiber membrane bank for liquid desiccant air dehumidification are investigated. The boundary conditions on the membrane surfaces are determined by coupled heat and moisture transfer from tube side, through the membranes, and to the shell side. The governing differential equations of continuity, momentum, energy and concentration are solved by a finite volume method to obtain the shell-side convective heat and mass transfer coefficients, which are then experimentally validated. The influences of skewed angles from 0° to 90° on the heat mass transfer and friction properties are investigated. Correlations are proposed for the prediction of convective transfer coefficients and friction factors at different skewed angles.

Improvisation of Shell Side Heat Transfer Coefficient in Shell and Tube Heat Exchangers using Different Configurations – A Mini Review

Improvisation of Shell Side Heat Transfer Coefficient in Shell and Tube Heat Exchangers using Different Configurations – A Mini Review

Experimental investigation on performances of trisection helical baffled heat exchangers for oil/water–water heat transfer

The trisection helical baffled shell-and-tube heat exchangers have structural features of more suitable to the equilateral triangular tube layouts and less baffle parts. In particular the circumferential overlap trisection helical baffled shell-and-tube heat exchangers are of anti-shortcut structure that accommodates one row tubes in each circumferential overlapped zone between adjacent baffles for dampening shortcut leakage. The performance tests were conducted on both oil–water and water–water heat transfer in heat exchangers with equilateral triangle tube layout of 16 tubes including five helical baffle schemes with incline angles of 12°, 16°, 20°, 24°, 28° and a segmental baffled one for comparison. The test results show that both the shell side heat transfer coefficient ho and pressure drop Δpo increase but the comprehensive index ho/Δpo decreases with the increase of the mass flow rate of all schemes; and that the shell side heat transfer coefficient, pressure drop and the comprehensive index ho/Δpo decrease with the increase of the baffle incline angle at certain mass flow rate, except that the curves of comprehensive index ho/Δpo of 12° and 16° helical baffle schemes are almost coincide. The average values of shell side heat transfer coefficient, the comprehensive index ho/Δpo of the 12° helical baffled scheme are about 50% higher than those of the segmental one with almost same pressure drop. The correlation equations for shell side Nusselt number and axial Euler number are presented varying with axial Reynolds number, Prandtl number and helical baffle incline angle.

Experimental study of effects of baffle helix angle on shell-side performance of shell-and-tube heat exchangers with discontinuous helical baffles

Flow resistance and heat transfer of several shell-and-tube heat exchangers with discontinuous helical baffles are experimentally studied and compared at the five helix angles of 8°, 12°, 20°, 30° and 40°. The second-law based thermodynamic analysis is employed to analyze the effects of baffle helix angle on the irreversible loss of heat exchangers. The results indicate that the shell-side pressure drop and heat transfer coefficient of the heat exchanger with smaller helix angle are higher than those with larger helix angle at a given shell-side volume flow rate. However, in the condition of the same shell-side Reynolds number, the flow resistance with larger helix angle is lower and the heat transfer performance is better. The heat exchanger with helical baffles at 40° helix angle presents the best comprehensive performance among the five testing heat exchangers. In the second-law thermodynamic comparisons, the irreversibility of heat exchanger is estimated by the theories of entropy generation and entransy dissipation. Experimental analysis shows that in the same heat transfer area and under the same working conditions, the shell-and-tube heat exchanger with smaller helix angle baffles produces less irreversibility in the heat exchange process. In addition, the heat exchangers with helical baffles are more effective under certain conditions of low shell-side Reynolds number.

Optimal nozzle spray cone angle for triangular-pitch shell-and-tube interior spray evaporator

The present study proposed a triangular-pitch shell-and-tube spray evaporator featuring an interior spray technique. In the proposed approach, the nozzle tubes are positioned within the tube bundle in such a way that the surface of each heater tube is sprayed simultaneously by two cooling sprays. As a result, the dry-out phenomenon is prevented, and thus the heat transfer performance is improved. An analytical expression is derived for the optimal spray cone angle for the proposed evaporator. It is shown that the optimal spray cone angle increases with an increasing diameter of the heater tubes, but decreases with an increasing distance between the heater tubes and nozzle tubes. The analytical expression for the optimal spray cone angle was validated by experimental spray tests using spray cone angles of 0°, 30°, 40°, 45° and 60°, respectively. It is shown that a good agreement exists between the experimental results for the optimal spray cone angle and the theoretical results. Furthermore, the experimental results confirm that the shell-side heat transfer coefficient obtained using the interior spray technique is significantly higher than that achieved in a conventional flooded-type evaporator over a wide range of surface heat fluxes.

Experimental investigation on performance comparison for shell-and-tube heat exchangers with different baffles

An improved structure of ladder-type fold baffle is proposed to block the triangular leakage zones in original heat exchangers with helical baffles. The numerical results showed that the distribution of shell-side velocity and temperature in improved heat exchanger are more uniform and axial short circuit flow is eliminated. The experimental results showed that the shell-side heat transfer coefficient α0 and overall heat transfer coefficient K are improved by 22.3–32.6% and 18.1–22.5%, respectively. The increment in shall-side pressure drop is about 0.911–9.084kPa, while the corresponding pumping power penalty is about 2–80W. The thermal performance factor TEF enhances by 18.6–23.2%, which demonstrates that the ladder-type fold baffles can effectively improve the heat transfer performance of heat exchangers with helical baffles. The results of this paper are of great significance in the optimal design of the heat exchanger.

Experimental Study on Oil to Water Heat Transfer Performance of Circumferential Overlap Trisection Helical Baffle Heat Exchangers

Experimental study on heat transfer performance of circumferential overlap trisection helical baffle heat exchangers of tilt angles 12°, 16°, 20°, 24°and 28° compared with a segmental baffle heat exchanger are conducted. The testing heat exchangers are constructed of a common cylinder case and replaceable tube bundle cores. The hot fluid is heat transfer oil with about 70 ℃ in the shell side and the cold fluid is cooling water with about 11 ℃ in the tube side. The results show that within the testing range, the overall heat transfer coefficient, the shell side heat transfer coefficient, pressure drop as well as comprehensive indexes ho/Δpo and ho/Δpo1/3 decrease with the increase of the tilt angle of the baffles, and the optimum scheme is the one with baffle tilt angle of 12°, and the ratios of the mean values of the shell side heat transfer coefficient ho, comprehensive index ho/Δpo and ho/Δpo1/3 of the helical scheme with baffle tilt angle of 12° over those of the segmental baffle scheme are 1.253, 1.391 and 1.285, respectively.

Comparison of heat transfer performances of helix baffled heat exchangers with different baffle configurations

Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers, the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as well as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20° (20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure drop Δpo, the highest overall heat transfer coefficient K, shell-side heat transfer coefficient ho and shell-side average comprehensive index ho/Δpo.

Experimental Investigation of Coil Curvature Effect on Heat Transfer and Pressure Drop Characteristics of Shell and Coil Heat Exchanger

The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to friction factor for fully developed flow through the helically coiled tube (HCT). The majority of previous studies were performed on HCTs with isothermal and isoflux boundary conditions or shell and coil heat exchangers with small ranges of HCT configurations and fluid operating conditions. Here, five heat exchangers of counter-flow configuration were constructed with different HCT-curvature ratios (δ) and tested at different mass flow rates and inlet temperatures of the two sides of the heat exchangers. Totally, 295 test runs were performed from which the HCT-side and shell-side heat transfer coefficients were calculated. Results showed that the average Nusselt numbers of the two sides of the heat exchangers and the overall heat transfer coefficients increased by increasing coil curvature ratio. The average increase in the average Nusselt number is of 160.3–80.6% for the HCT side and of 224.3–92.6% for the shell side when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, for the same flow rate in both heat exchanger sides, the effect of coil pitch and number of turns with the same coil torsion and tube length is remarkable on shell average Nusselt number while it is insignificant on HCT-average Nusselt number. In addition, a significant increase of 33.2–7.7% is obtained in the HCT-Fanning friction factor (fc) when δ increases from 0.0392 to 0.1194. Correlations for the average Nusselt numbers for both heat exchanger sides and the HCT Fanning friction factor as a function of the investigated parameters are obtained.

Heat Transfer Performance of an Edge-Shaped Finned Tube

The third-generation heat transfer technologies, such as three-dimensional fin and dimple, are still important means of improving energy efficiency and will continue to be challenging issues. This paper presents condensation heat transfer performance of an edge-shaped finned tube fabricated by a ploughing–extruding process. The edge-shaped finned tube integrates more than one heat transfer enhancement technology and can enhance the heat transfer capacity greatly. It is seen that the overall heat transfer coefficient and heat flux increase with inlet velocity of cold water increasing, and decrease with inlet temperature of cold water increasing, whereas the shell-side heat transfer coefficient decreases with inlet velocity of cold water increasing and increases with inlet temperature of cold water increasing. At the same inlet velocity, the shell-side heat transfer coefficient for the edge-shaped finned tube is improved by 5–7 times compared to that of a smooth tube. At the same temperature difference between wall and vapor, the shell-side heat transfer coefficient is also higher than what had been reported in the literature. The shell-side heat transfer coefficient of the edge-shaped finned tube decreases with the increase of fabrication parameter feed at the same inlet velocity or inlet temperature of cold water.

Numerical investigation on baffle configuration improvement of the heat exchanger with helical baffles

An improved structure of ladder-type fold baffle is proposed to block the triangular leakage zones in original heat exchangers with helical baffles. The numerical results showed that the shell-side tangential velocity and radial velocity in improved heat exchanger increase significantly and the shell-side fluid becomes approximately continuous spiral flow. And the configuration of ladder-type fold baffles was optimized. The numerical results showed that the shell-side heat transfer coefficient of the improved heat exchanger increases by 82.8–86.1%, when the folding ratio φ is 0.3, the baffle height ω is 60%, and the folding angle α is 37°. The associated pumping power penalty is about 21–549W due to the increased shell-side pressure drop. The thermal performance factor TEF enhances by 28.4–30.7%, which demonstrates that the ladder-type fold baffle effectively improves the heat transfer performance of heat exchangers with helical baffles. The results of this paper are of great significance in the optimal design of heat exchanger.

Effectiveness of evolutionary algorithms for optimization of heat exchangers

This paper comprehensively investigates performance of evolutionary algorithms for design optimization of shell and tube heat exchangers (STHX). Genetic algorithm (GA), firefly algorithm (FA), and cuckoo search (CS) method are implemented for finding the optimal values for seven key design variables of the STHX model. ∊-NTU method and Bell-Delaware procedure are used for thermal modeling of STHX and calculation of shell side heat transfer coefficient and pressure drop. The purpose of STHX optimization is to maximize its thermal efficiency. Obtained results for several simulation optimizations indicate that GA is unable to find permissible and optimal solutions in the majority of cases. In contrast, design variables found by FA and CS always lead to maximum STHX efficiency. Also computational requirements of CS method are significantly less than FA method. As per optimization results, maximum efficiency (83.8%) can be achieved using several design configurations. However, these designs are bearing different dollar costs. Also it is found that the behavior of the majority of decision variables remains consistent in different runs of the FA and CS optimization processes.