Category: CFD

Since the introduction of the digital computer in the 1950s, computational fluid dynamics (CFD) has increasingly been used to study and solve complex problems in fluid flow and heat transfer. With the rising popularity of sophisticated computing tools, many challenging engineering problems tend to be assigned to the CFD simulation world...
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Header flow maldistribution and pressure loss in air-cooled heat exchangers may significantly affect performance. Most relevant literature focuses on plate-fin and cylindrical channel headers for tubular heat exchangers. The flow in the header is affected by its internal geometry, the orientation of the nozzles on the header, and inlet flow velocity....
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This webinar will discuss Xist and CFD predictions of three NTIW exchanger configurations – 2 baffle, 4 baffles, and 6 baffles. The discussion will focus on the contributions of crossflow and longitudinal flow on heat transfer, which is due to varied baffle spacing for the same baffle cut. During the webinar,...
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Compact plate-fin heat exchangers are widely used for electronics, aerospace, and automotive cooling because of the light weight and small size. The majority of open-literature data use air as the test fluid; thus, the application of the ensuing air-based methods to higher Prandtl number, liquid services is dubious. In some applications,...
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API-compliant air coolers are modeled in two- and three-dimensional computational fluid dynamics (CFD) simulations to see what improvements are needed in Xace with regard to the airside maldistribution. We validated the CFD model using Xace base cases. We then used CFD to simulate non-ideal airside flow situations that can potentially affect...
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HTRI currently runs fouling experiments on the High Temperature Fouling Unit (HTFU) which recirculates a 27 liter sample of crude for periods up to one month. As we plan to expand our crude oil fouling test program, we are investigating alternate test methods to screen crude oil fouling with smaller sample...
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Xist can predict unexpected performances of shellside viscous fluids in laminar regimes, where thermal maldistribution is present. The heat transfer of viscous flows across vertical baffles is analyzed by CFD to determine impact of such non-uniformity. Maldistribution can be monitored using a viscosity-independent Richardson number. The Richardson relates the impact of...
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During this webinar, we discuss the basics of sealing devices, including common practices and design guidelines. Further, we review the basic flow resistance equation for sealing strips used in Xist Version 7 and compare the measured performances of HTRI research-scale heat exchanger using sealing strips to CFD and Xist predictions....
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Over the past several decades, the accuracy and usability of computational methods have substantially improved. This report reviews the complicated physics of two-phase flow and phase change, presents the equations of motion for a two-phase flow with various closure models, and compares current computational approaches. Although inadequate for the entire spectrum of...
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We completed a multiphysics computational simulation of a shell-and-tube exchanger, where simultaneous fluid flow and heat transfer of both fluid streams occurred. Temperature-induced mechanical stress also acted on the solid structures. A weak coupling of a finite-volume CFD Navier-Stokes model with a finite-element computational solid mechanics model underlies the multiphysics simulation....
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HTRI experimentally evaluated the thermal-hydraulic performance of a water-water plate-and-shell heat exchanger at the Research & Technology Center and then used the results to calibrate a solution approach through computational fluid dynamics. The tortuous flow paths through the corrugated channels of the plate pack were modeled effectively using porous media. Inertial resistance...
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HTRI gathered experimental data for a plate-and-shell exchanger at the Research & Technology Center (RTC). These data provided the opportunity for HTRI to extend its CFD simulation experience to plate heat exchanger types. The results provide additional insights about the flow distribution and port pressure drops. In this webinar, we discuss...
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When increasing longitudinal pitch, methods for both pressure drop and heat transfer predictions for inline and staggered high-finned tube bundles are evaluated. When we compare the behavior simulated through computational fluid dynamics (CFD) to results from Xace and ESCOA for a characteristic tube geometry, the CFD results show that the effect...
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A new Stream Analysis Method option is available in Xace® 6 to model flow bypassing in air-cooled heat exchangers with larger gaps at the edge of the bundle than those required by the API 661/ISO 13706-1:2005 standard. The heat transfer and pressure drop of the bundle can be less than predicted...
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Xace has limited capabilities for predicting maldistributed airside heat transfer because the software does not consider inter- and intra-air cooler proximity, turn-down and fan off/on operation, or ground effects. To improve our software methods, we examined the performance of an API-compliant air cooler through computational fluid dynamics (CFD) simulations, calibrating the...
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In 2014 HTRI contracted with the Institute of Process and Environmental Engineering (IPEE) at Brno University of Technology, Brno, Czech Republic, to complete CFD simulations on six configurations of a two-pass horizontal air cooler, differing only in the number and type of inlet and outlet nozzles. Results showed the impact of...
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To gain further insight into kettle reboiler operation and improve Xist® models, we simulated several kettle reboilers in two dimensions using CFD. The two-phase simulation results show good agreement with pressure drop and vapor volume fraction measurements from the literature. However, recirculation ratios calculated from the CFD results are substantially greater...
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Three-dimensional computational fluid dynamics (CFD) simulations of experimental kettle reboiler slices from the literature, as well as from the HTRI kettle reboiler, allow examination of fluid flow behavior on a fine spatial scale—significantly beyond the resolution of available experimental measurements. Interestingly, our simulations of kettle slices yield recirculation ratios that agree...
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After briefly surveying the challenges of modeling condensation with computational fluid dynamics (CFD), we apply two relevant two-phase models in ANSYS® FLUENT® with varying degrees of success. Homogeneous nucleation in a Laval nozzle is well predicted, while the more interesting and relevant intube film condensation is plagued by grid resolution, model...
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Our ongoing analysis of the HTRI crude oil fouling data revealed an unacceptably high degree of scatter. A computational fluid dynamics (CFD) model of the High Temperature Fouling Unit (HTFU) test section demonstrated that the flow over the heated portion was undeveloped and asymmetrical, resulting in wall shear stress variations of...
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Anecdotal and laboratory evidence suggest that high shear stresses mitigate fouling. This report presents methods for calculating isothermal and diabatic shear stresses for single-phase fluids on both the tube side and the shell side of shell-and-tube heat exchangers. There are limitations to these methods, however. The tubeside shear stress calculation technique...
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Using CFD simulations of laminar flow in an offset-strip fin geometry validated with experimental data, we have confirmed that the Colburn j-factor can be substantially overpredicted for fluids whose Prandtl number is significantly greater than that of air. In addition, we determined that the j-factor varies inversely with a Prandtl number...
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Numerical design optimization and the prerequisite statistical Design of Experiments (DOE) method lead to more effective CFD parametric studies and increase our confidence that the ensuing recommendations do indeed present the best design....
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Computational fluid dynamics (CFD) analysis was used to calculate the nozzle pressure drop K-values for spiral plate heat exchangers. Results of this analysis resolved the discrepancy between K-values from the Minton method and in PHE-11. The K-values from PHE-11 compared better with the CFD results in the region of Reynolds numbers...
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Computational fluid dynamics solutions of the Reynolds-averaged Navier-Stokes equations often employ wall functions to capture the behavior of the near-wall boundary layer flow without excessive grid refinement. While the applicability of these functions has strong support from physical reasoning and dimensional arguments, they are nonetheless empirical. In this article, we review...
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During winter or in turndown conditions when full design duty is not required, air-cooled heat exchangers commonly run with one or more fans off. Xace® models this operation by allowing users to specify an inlet flow maldistribution. This article provides guidelines for modeling fans-off operation in Xace and describes a computational...
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ASME Code 2007 Section VIII - Division 1 UHX requires an average tubesheet metal temperature for calculating the allowable thermal stresses between the shell and header flanges of a shell-and-tube heat exchanger. The Xist® tubesheet temperature calculations do not take into account the contribution of the heat transfer coefficients on both...
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Under contract from HTRI, university researchers simulated the fluid flow and heat transfer characteristics in the inlet zone of a shell-and-tube exchanger using computational fluid dynamics (CFD). Results revealed that the ratio of heat transfer to pressure drop for parallel baffle cut orientation was as low as 71 percent of that...
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The thermal hydraulic performance of a gas-gas no-tubes-in-window (NTIW) field exchanger was studied parametrically using computational fluid dynamics (CFD). The tubes were modeled using porous media with velocity-dependent volumetric heat generation. An important performance indicator among the design variants was the ratio of the window velocity to the crossflow velocity. When...
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Flow distribution in a TEMA X-shell exchanger was studied parametrically through computational fluid dynamics (CFD). Using design rules for manifolds and a lumped, linear circuit analysis of the exchanger, we identified the number of nozzles and the cross-sectional distribution area as key parameters. Our CFD results quantify the improvement in the...
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TRICO Metal Products, Inc. manufactures Square One™ baffles, a strip baffle or egg crate tube support technology for square pitch layouts. This report documents heat transfer and pressure drop methods for shellside flow using Square One baffles. Based on the existing Xist® window flow model, the methods have been adjusted for...
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High fidelity, tube-by-tube computational fluid dynamics (CFD) simulations of the turbulent, multistream shellside flow within a 9-crosspass, 591-mm diameter, 2276-mm long E shell were completed at four flow rates. The shellside water flow was heated by a full bundle at a uniform tube wall temperature. Computational results for duty and pressure...
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A shellside helical flow path in a shell-and-tube exchanger can provide a number of distinct advantages over the reversing, serpentine flow path of conventional segmental baffles; however, current open literature prediction methods do not provide the confidence engineers need to make sound design decisions. Several fundamental geometric parameters either are not...
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Disk-and-doughnut baffled heat exchangers can generate more heat transfer with less pressure drop than conventional segmental exchangers in certain industrial applications. Unfortunately, little information is available on these units in service. This report introduces new methods for analyzing and rating a disk-and-doughnut baffled heat exchanger. Using three-dimensional computational fluid dynamics (CFD)...
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HTRI conducted computational fluid dynamics (CFD) simulations to investigate leakage and bypass stream behavior under various flow regimes in an industrial-scale heat exchanger with single-segmental baffles. To cover a wide range of Reynolds numbers, the simulations tested single-phase water and Alta-Vis oil. Both concentric and eccentric configurations of the exchanger’s tube-to-baffle...
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Using computational fluid dynamics (CFD) and Xist, HTRI simulated three configurations of no-tubes-in-window (NTIW) bundles in shell-and-tube heat exchangers. Our analysis of the trends in pressure drop and heat transfer underscores the importance of window friction and window momentum losses, even without tubes in this region, as well as the existence...
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After a brief overview of the evolution of the Stream Analysis Method, we use CFD simulation results to compare A-stream, tube-to-baffle leakage flow geometry and pressure drop models. We propose a modified A-stream pressure drop model for the refactored software that, contrary to current usage in HTRI Xchanger Suite 7, calculates...
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This report documents two approaches to analyze the performance of different sealing devices. The first approach examines an exchanger with a fixed sealing device count and varied baffle spacing. The second approach considers an exchanger with fixed shellside geometry but different sealing device types and arrangements. Comparisons are made between experimental...
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For shellside diabatic flows of highly viscous fluids, Xist can predict inconsistent pressure drops and heat transfer coefficients. HTRI examined the transition between forced and natural convection in single-segmental and double-segmental exchangers with Alta-Vis oil and an asphalt blend as test fluids. Comparisons were made between experimental data, open literature, computational...
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To gain insight into the physical characteristics of single-phase liquid tubeside laminar diabatic flows, we used computational fluid dynamics (CFD) to analyze laminar data acquired with the HTRI Tubeside Single-Phase Unit (TSPU). This numerical approach generated local tubeside data that were validated by the associated experimental measurements. Twenty-seven experimental conditions for...
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Impingement rods are more effective than plates in protecting entrance tubes from damage. HTRI developed a method to assess the relative impact of a variety of competing flow conditions produced by each impingement configuration. For the conditions established in this study, a two-row grid of rods with a diameter slightly smaller...
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Both the value and distribution of velocity along each span are important for proper assessment of tube vibration potential. Because of the disparity in spatial resolution between the small-scale finite element structural model of Xvib® and the larger scale incrementation scheme of Xist®, engineering judgment is required to populate the important...
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The challenges of a rules-based vibration screening in Xist® have often led to excessive conservatism for U-tubes positioned near the inlet nozzle. In this study, we simulated shellside diabatic flow over the U-bend portion of the bundle for a number of nozzle locations using computational fluid dynamics (CFD). Using the simulation...
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This report discusses multiphase computational fluid dynamics (CFD) simulations of turning flows in U-bends and turnaround headers. After brief descriptions of the numerical models, simulations of both single-phase and two-phase flows in the MBU serpentine test section are described to validate the CFD models for turning two-phase flows. The computed U-bend...
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To evaluate the thermal-hydraulic effectiveness of twisted tape inserts, we used computational fluid dynamics (CFD). After validating plain tube performance, we computed heat transfer (heating and cooling) and pressure drop for several twisted tape configurations in a 25.4-mm diameter tube with single-phase flow at laminar and turbulent Reynolds numbers from 102...
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To gain insight into the thermal-hydraulic phenomena associated with mixed convection in internal flows, we used computational fluid dynamics (CFD) to conduct a parametric study of single-phase laminar liquid flows in inclined tubes with isothermal, uniform wall temperatures (UWT). Both heating and cooling processes were simulated to isolate the effects of...
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The results of a computational fluid dynamics (CFD) study of impingement devices for inlet nozzles on shell-and-tube heat exchangers reveal the deleterious effects of increased velocity and pressure drop for a number of configurations. Simulations of entry flows with round and square solid plates as well as with rod grids were...
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Unlike exchangers with conventional nozzles and nozzles with impingement devices, heat exchangers with annular distributors utilize full tube bundles while increasing end zone effectiveness and reducing the pressure drop and tube vibration potential. The uniformity of flow at the bundle entrance is controlled by the size and geometric aspect ratio of...
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