Maximum Allowable Pressure Drop Research Articles

Adaptive design methodology of segmented non-uniform fin arrangements for trans-critical natural gas in the printed circuit heat exchanger

As the core heat transfer equipment of a floating storage regasification unit (FSRU), the printed circuit plate heat exchanger (PCHE) has a significant impact on the gasification performance of liquefied natural gas (LNG). During LNG regasification process, natural gas undergoes a trans-critical process and its thermal properties such as density, viscosity and specific heat capacity vary considerably especially near the pseudo-critical point, which will probably lead to more volatile flow heat transfer mechanism. The traditional design scheme of uniform finned channel is difficult to give full play to the efficiency and compactness of PCHE because of lacking considering the local fluid thermodynamic variation. Therefore, this paper provides a novel design method for optimizing the flow channel profile of PCHE by applying adaptive segmented non-uniform finned micro-channels. Firstly, the entire flow channels are segmented by qualifying the gradient of density with temperature ∂ρ/∂t of trans-critical natural gas. Subsequently, within the constraints of heat exchange requirements, maximum allowable pressure drop, existing manufacturing techniques and structural strength, a mathematical optimization design model considering non-uniform fin arrangements and interlinked thermal states among these segmented channels is established. Then, to comprehensively improve entropy generation number and volume, Pareto solutions covering local flow channel parameters are obtained based on multi-objective genetic algorithm. Finally, the actual performance differences between two optimization methods respectively derived from the conventional uniform fin channels and the proposed non-uniform fin arrangements are compared based on distributed parameter model. The results show that the deviation of the entropy generation number between the optimized and validated values for the non-uniform design is very small at 6.5%, much less than that of 31.4% in the uniform design. Moreover, under the premise of the similar heat transfer efficiency, the volume for the PCHE by the non-uniform design can be reduced by 9.3%. These indicate that the proposed design methodology of segmented non-uniform fin arrangements indeed makes the PCHE more compact and enables the thermal-hydraulic performance better. The current work will serve as a framework for the design and optimization of PCHEs with drastic changes in fluid physical properties.

Spirally wound tubular heat exchanger optimisation using Genetic Algorithm

• Spirally coiled (Giauque-Hampson) type heat exchanger optimization. • Thermal analysis of optimum tube geometry predicted by Genetic Algorithm. • Design aimed at minimum exchanger weight under pressure drop constraints. • Design aimed at minimum exchanger height under pressure drop constraints. • Effect of different process parameters on the optimum heat exchanger design. A Genetic Algorithm based optimization of spirally wound two-fluid stream exchanger is presented. The proposed method elaborates a design methodology consistent with the user-defined specifications while simultaneously fulfilling a design objective linking optimization of either weight, height or thermo-hydraulic performances, etc., depending on the customer requirement. Optimization variables include tube material, tube size, normalized transverse and longitudinal pitches, number of tubes in the innermost layer, increment in the number of tubes with each successive layer, and the total number of tube layers. The effectiveness-NTU approach is adopted for design calculations, including fluid property variations with temperature. This paper explores the effect of optimization criteria like minimum weight or height and variation in pressure drop constraints on the optimized design. A compromise in exchanger effectiveness can substantially reduce its weight. Among the exchangers of the same effectiveness, the one handling 10 times larger flow could be 35 times heavier (subjected to other constraints). Exchanger designed with the minimum height criterion is nearly two times shorter than the one created on a minimum weight basis, while the shorter unit could be two times heavier. The optimum design is a trade-off between achievable minimum mass and maximum allowable pressure drop.

A composite superconducting energy pipeline and its characteristics

A superconducting energy pipeline cooled during its clean energy transferring becomes attractive recently to be a promising alternative way for combined green energy transmission to meet the ever-rising energy demand across the world. Though, study on superconducting energy pipelines gets into the conceptual design of single energy integration, the critical multi-composite structure and its characteristics have not yet been systematical. A novel high-temperature superconducting (HTS) energy pipeline integrated with power cable and liquid hydrogen (LH2) and liquefied natural gas (LNG) is proposed in this paper. The maximum allowable temperature difference and pressure drop methods are adopted to design the pipeline. A two-dimensional axisymmetric electromagnetic thermal coupling model has been established using the finite element method. The interface magnetic field formulation, heat transfer modeling, and multiphysics interface has been applied to conduct a detailed analysis of the designed superconducting energy pipeline (LH2-LNG-HTSEP). The results show that the designed LH2-LNG-HTSEP is feasible for practical operation and has more favorite characteristics to suit the HTS cable for the composite pipeline operation. The model and analysis method provide a theoretical base for the composite superconducting energy pipeline design and structural optimization.

Size optimization of heat exchanger and thermoeconomic assessment for supercritical CO2 recompression Brayton cycle applied in marine

When the state-of-the-art supercritical CO2 cycle is applied to the marines, priority should be given to the feasibility of its component size. In this study, a thermodynamic model of the marine supercritical CO2 recompression cycle was developed. To evaluate the thermoeconomic and component size of the system, the recuperator and precooler with a microtube structure were designed. After quantitatively discussing the impact of the two-stage compression mode on the component scale, the sizes of the heat exchangers were optimized based on the maximum allowable pressure drop. The parameter analysis demonstrates that increasing the speed of the power turbine is beneficial to the system thermoeconomic. Not only can an efficiency improvement of 1.73% and a cost saving of 1.77 $/MWh be achieved, but also the implementation of two-stage compression reduces the volume of the high-temperature recuperator, low-temperature recuperator, and precooler by 4.62%, 6.33%, and 37.4%, respectively. The size optimization analysis suggests that the direction with the longest distance should be regarded as the length constraint of the heat exchanger design in the absence of multi-objective optimization. Moreover, this study has guiding significance for the size optimization of the supercritical CO2 cycle used in a limited space.

A comprehensive sensitivity analysis on the performance of pseudo‐steady propane thermal cracking process

AbstractThe propane thermal cracking reactor process is investigated in an industrial furnace with an alternative wall burner arrangement. Temperature and heat distribution of the furnace is obtained by three‐dimensional computational fluid dynamics (CFD) simulation technique using Ansys Fluent software. Ten calculation domains are adopted to decrease calculation costs. Different fuel rate ratios are selected as the main effective parameter on reactor performance. Different ratios of base fuel rate (0.0695 kg/s) have been considered. The obtained reactor tube wall temperature profile is used for a one‐dimensional pseudo‐steady reactor operation. By the proposed new arrangement, the created coke layer thickness is lower about 3 mm compared with the base case after 700 h. Meanwhile, Propane conversion is increased by 4%. Besides, reactor feed flow rate variations are considered one of the essential parameter on reactor operation. Despite surging in propylene yield after coke formation, ethylene yield decreases during the process. By increasing the fuel rate in each reactor flow rate, ethylene increased while propylene yield descended. The maximum allowable pressure drop is 2.7 bar. At 0.5ṁ fuel rate and 0.85 kg/s reactor flow rate, pressure drop, reactor lifetime, and ethylene yield are 1.23 bar, 1444 h, and 28%; respectively. In the reactor flow of 0.85 kg/s, by raising fuel rate 0.5–2ṁ ethylene yield is increased from 28% to 46.83%, while process operating time is reduced to 780 h. According to the results, 0.8–0.85 kg/s could be considered as an appropriate range for reactor feed flow rate.

Test and Modeling of the Hydraulic Performance of High-Efficiency Cooling Configurations for Gyrotron Resonance Cavities

The design and manufacturing of different full-size mock-ups of the resonance cavity of gyrotrons, relevant for fusion applications, were performed according to two different cooling strategies. The first one relies on mini-channels, which are very promising in the direction of increasing the heat transfer in the heavily loaded cavity, but which could face an excessively large pressure drop, while the second one adopts the solution of Raschig rings, already successfully used in European operating gyrotrons. The mock-ups, manufactured with conventional techniques, were hydraulically characterized at the Thales premises, using water at room temperature. The measured pressure drop data were used to validate the corresponding numerical computational fluid dynamics (CFD) models, developed with the commercial software STAR-CCM+ (Siemens PLM Software, Plano TX, U.S.A.) and resulting in excellent agreement with the test results. When the validated models were used to compare the two optimized cooling configurations, it resulted that, for the same water flow, the mini-channel strategy gave a pressure drop was two-fold greater than that of the Raschig rings strategy, allowing a maximum flow rate of 1 × 10−3 m3/s to meet a maximum allowable pressure drop of 0.5 MPa.

Application of compact thermoelectric generator to hybrid electric vehicle engine operating under real vehicle operating conditions

A compact thermoelectric generator is developed for waste-heat recovery in a sedan-type hybrid electric vehicle. The shape and dimensions of the thermoelectric generator are precisely determined by performing a series of theoretical analyses to meet spatial and maximum allowable pressure drop restrictions. The waste-heat recovery performance of the thermoelectric generator is experimentally evaluated using a hybrid electric vehicle engine under the nine most commonly experienced driving conditions. One surface of the thermoelectric modules is heated by the exhaust gas flow, whereas the other surface is cooled by the engine coolant flowing at 10 L/min and 353 K. A maximum power output of ~118 W and an energy conversion efficiency of ~2.1% are obtained using 12 thermoelectric modules under the engine operating conditions that led to the highest exhaust gas flow rate and temperature. The waste-heat recovery characteristics of the present thermoelectric generator are systematically analyzed, and the results corresponding to thermal energy flow and heat recovery efficiency, as well as the voltage output–current output and power output–load resistance curves, are presented.

Concept Design of 1 GW LH2-LNG-Superconducting Energy Pipeline

A 1 GW LH2-LNG-superconducting energy pipeline has been designed, and the design parameters under the consideration of the maximum allowable temperature difference and pressure drop are verified to achieve high efficiency.

Strategy and consequence of intermittent segmented pulse-jet cleaning for long-box-shaped filter dust collector

This study investigated the influence of the intermittent segmented pulse-jet cleaning strategy for dust collectors on their filtration pressure drop, dust emission concentration, and detached dust migration. An experimental pulse-jet cleaning dust collector with 6 filter cartridges in line was designed. The intermittent segmented pulse-jet cleaning was simulated. The air volume, filtration pressure drop, and dust emission concentration were tested, and the resistance to airflow through the cartridge was calculated. The pulse-jet cleaning parameters, including positive and reverse cleaning orders, online and offline conditions, single-row and dual-row pulse-jet modes, and maximum allowable pressure drop, were analyzed. Re-capture (captured again by the just cleaned filter) and sec-capture (secondary captured by other filters) rates of the detached dust from the cleaned filter cartridge were defined and calculated. This study has demonstrated that the cleaning order has remarkable influence on the operation performance. The positive cleaning order leads to lower residual pressure drop, more uniform residual dust on the cartridges, and higher dust emission concentration during the cleaning affected stage. More obvious re-capture and sec-capture phenomena are found in the reverse cleaning order, with re-capture and sec-capture rates of 17.86% and 10.00%, respectively. This study is useful for optimizing the design of dust collector cleaning.

Efficient calculation of constraint back-offs for optimization under uncertainty: A case study on maleic anhydride synthesis

In the present work we propose an efficient and general algorithm for optimization under uncertainty based on the work of Srinivasan et al. (2003). We use specialized cubature rules to speed up the uncertainty propagation step which results in a significant reduction of the overall computational effort. The approach is illustrated by studying the optimal design of a fixed bed reactor for the synthesis of maleic anhydride from raffinate II feedstock, where the amount of n-butane and n-butenes in the feed is assumed to be uncertain. Applying the algorithm results in a robustified reactor design which shows significantly less temperature constraint violations and runaway conditions while still satisfying reactor performance criteria such as minimally required conversion and maximum allowable pressure drop.

Optimal design of microtube recuperators for an indirect supercritical carbon dioxide recompression closed Brayton cycle

This paper presents a baseline design and optimization approach developed in Aspen Custom Modeler (ACM) for microtube shell-and-tube exchangers (MSTEs) used for high- and low-temperature recuperation in a 10 MWe indirect supercritical carbon dioxide (sCO2) recompression closed Brayton cycle (RCBC). The MSTE-type recuperators are designed using one-dimensional models with thermal-hydraulic correlations appropriate for sCO2 and properties models that capture considerable nonlinear changes in CO2 properties near the critical and pseudo-critical points. Using the successive quadratic programming (SQP) algorithm in ACM, optimal recuperator designs are obtained for either custom or industry-standard microtubes considering constraints based on current advanced manufacturing techniques. The three decision variables are the number of tubes, tube pitch-to-diameter ratio, and tube diameter. Five different objective functions based on different key design measures are considered: minimization of total heat transfer area, heat exchanger volume, metal weight, thermal residence time, and maximization of compactness. Sensitivities studies indicate the constraint on the maximum number of tubes per shell does affect the number of parallel heat exchanger trains but not the tube selection, total number of tubes, tube length and other key design measures in the final optimal design when considering industry-standard tubes. In this study, the optimally designed high- and low-temperature recuperators have 47,000 3/32 in. tubes and 63,000 1/16 in. tubes, respectively. In addition, sensitivities to the design temperature approach and maximum allowable pressure drop are studied, since these specifications significantly impact the optimal design of the recuperators as well as the thermal efficiency and the economic performance of the entire sCO2 Brayton cycle.

Finding a criterion for the pressure loss of energy recovery exchangers in HVAC systems from thermodynamic and economic points of view

Heat recovery devices can help ventilation systems conserve energy; However, they cause a pressure drop in the system, and hence the system incurs an electricity consumption. In the present paper, the maximum allowable pressure drop of the recovery units is achieved from thermodynamic and economic points of view. The novelty of the research is that, unlike the existing criterion which does not differ for different cities, the introduced criteria can be calculated for each city with individual weather, economic, power plants, and energy conditions. Although the methods presented to calculate the criteria consider a broad range of effective parameters, there is no need to use complex energy simulation methods. Moreover, for each city, four types of criteria are introduced, which allows the city authorities to choose the best ones according to their city conditions, and then calculate the chosen criteria by the data of the city. In order to gain the criteria, modified enthalpy-hours and bin method variables are introduced to calculate sensible and latent energy consumption due to ventilation. The criteria are numerically calculated for Kerman city in Iran, and the results show that the recovery type and the chosen viewpoint has a considerable effect on the allowable pressure drop. The sensitivity of the results to different variables is analyzed in the end.

Optimal design of the first stage of the plate-fin heat exchanger for the EAST cryogenic system

The size of the heat exchanger is an important factor determining the dimensions of the cold box in helium cryogenic systems. In this paper, a counter-flow multi-stream plate-fin heat exchanger is optimized by means of a spatial interpolation method coupled with a hybrid genetic algorithm. Compared with empirical correlations, this spatial interpolation algorithm based on a kriging model can be adopted to more precisely predict the Colburn heat transfer factors and Fanning friction factors of offset-strip fins. Moreover, strict computational fluid dynamics simulations can be carried out to predict the heat transfer and friction performance in the absence of reliable experimental data. Within the constraints of heat exchange requirements, maximum allowable pressure drop, existing manufacturing techniques and structural strength, a mathematical model of an optimized design with discrete and continuous variables based on a hybrid genetic algorithm is established in order to minimize the volume. The results show that for the first-stage heat exchanger in the EAST refrigerator, the structural size could be decreased from the original 2.200 × 0.600 × 0.627 (m3) to the optimized 1.854 × 0.420 × 0.340 (m3), with a large reduction in volume. The current work demonstrates that the proposed method could be a useful tool to achieve optimization in an actual engineering project during the practical design process.

Laboratory measurements of slippage and inertial factors in carbonate porous media: A case study

Two important issues for accurate modeling of gas reservoir performance are the gas slippage and the inertia flow within porous media. Depending on the flow condition, these factors can make the gas permeability differ from the true (liquid) permeability. Nevertheless, since the gas flow tests are cheaper and less time consuming than the liquid flow tests, a reservoir engineer may choose to estimate the true (liquid) absolute permeability from the results of a single gas permeability test utilizing a valid empirical correlation. Although many such correlations exist in the literature, most of them have been developed for unconsolidated porous media or sandstone core samples. Therefore, using them for a specific formation will result in erroneous predictions.This paper is presented in three parts. In the first part, an empirical equation is developed to estimate the gas slippage factor using the results of laboratory measurements on 49 samples of Iranian carbonate reservoirs of Kangan and Dalan. In the second part, a correlation is developed to estimate the inertia factor for the samples. In the last part of the paper, an equation is derived to estimate maximum allowable pressure drop per length to maintain the laminar (Darcy) flow regime in the samples.The developed models in the first and the second parts of the current paper match the experimental data more accurately than the popular existing correlations. The derived equation in the last part is applicable in proper design of gas flow tests, where a laminar flow must be maintained in porous media.

High-performance strategy of a simulated moving bed chromatography by simultaneous control of product and feed streams under maximum allowable pressure drop

In this study, a novel operating strategy was developed to improve the separation performance of simulated moving bed (SMB) chromatography by the simultaneous control of product outlet streams and feed inlet stream (SimCon). The SimCon operation can achieve a high separation performance without exceeding the maximum allowable pressure drop in an SMB system. The SimCon operation consisted of three steps within a single switching period: the initial, middle, and last steps. The extract port and feed-inlet port were closed at the initial step, but the raffinate port was closed at the last step. Therefore, in the SimCon strategy, we introduce two additional operating variables in a switching period, namely the middle time and middle length. In the SimCon operation, the middle step is a key factor to achieving a good separation performance because concentration profiles can be well controlled by two new middle-step variables. The SimCon operation showed outstanding results compared with those of the corresponding conventional SMB and other stream-control strategies in terms of purity, recovery, productivity, and eluent consumption. Because the SimCon operation can be operated with smaller flow and pressure fluctuations than other flow-rate-control strategies and improves the column efficiency, it is expected that the strategy can be practically adapted to real SMB processes with a good separation performance.

A new optimization approach for shell and tube heat exchangers by using electromagnetism-like algorithm (EM)

This study proposes a new procedure for optimal design of shell and tube heat exchangers. The electromagnetism-like algorithm is applied to save on heat exchanger capital cost and designing a compact, high performance heat exchanger with effective use of the allowable pressure drop (cost of the pump). An optimization algorithm is then utilized to determine the optimal values of both geometric design parameters and maximum allowable pressure drop by pursuing the minimization of a total cost function. A computer code is developed for the optimal shell and tube heat exchangers. Different test cases are solved to demonstrate the effectiveness and ability of the proposed algorithm. Results are also compared with those obtained by other approaches available in the literature. The comparisons indicate that a proposed design procedure can be successfully applied in the optimal design of shell and tube heat exchangers. In particular, in the examined cases a reduction of total costs up to 30, 29, and 56.15 % compared with the original design and up to 18, 5.5 and 7.4 % compared with other approaches for case study 1, 2 and 3 respectively, are observed. In this work, economic optimization resulting from the proposed design procedure are relevant especially when the size/volume is critical for high performance and compact unit, moderate volume and cost are needed.

Distillation in special chemistry

In the final product, special chemicals are minor ingredients by volume, but essential for performance and function. Distillation is the separations workhorse. Specific challenges arise from the nature of special chemicals. High product purity or tight control of trace impurities have to be achieved in non-ideal, often aqueous systems. Foaming, fouling and three-phase systems are often encountered. This paper addresses two typical challenges in special chemicals distillation and practical solution methods.One example is distillation in deep vacuum in order to minimize thermal degradation of temperature-sensitive components. Enlarging column diameter to meet a maximum allowable pressure drop specification instead of a certain flooding factor entails designs with low liquid loads well below the limits given in literature. Special care should be given to distributor design to ensure acceptable efficiency.In multi-step special chemicals synthesis, reactive distillation is an elegant operation to increase conversion and selectivity or to reduce recycle rate. However, additional design interactions arise, which increase the sensitivity to parameter uncertainty. Sensitivity analysis is a powerful tool to assess the process risk arising from incomplete design information and to devise fallback options.In both examples, plant data from similar processes is invaluable to validate designs.

Experimental Investigation of Fin Enhancement for Gas-Cooled Divertor Concepts

The addition of fins to the cooled surface of gas-cooled divertor modules has been proposed as a means to enhance their thermal performance, in the HEMP concept, for example. Such fins enhance heat transfer by significantly increasing the surface area over which convection occurs. However, adding fins also increases pressure losses and manufacturing costs and can adversely affect coolant flow over the cooled surface. More importantly, the high heat transfer coefficients expected with helium (He) cooling may significantly lower the fin efficiency, thereby limiting the extent of heat transfer enhancement to values well below the increase in the area ratio. An experimental investigation was undertaken to quantify the extent of heat transfer enhancement and corresponding pressure loss increase associated with the addition of pin fins to the cooled surface of a modular, helium-cooled, finger-type divertor. Four test cases, including configurations similar to the HEMP and HEMJ concepts, were studied. The results show that the addition of fins to helium jet-cooled finger divertors may not provide enough heat transfer enhancement to justify the associated increases in design complexity and pressure loss. Generalized charts for the thermal performance of helium-cooled divertors have been developed; these allow the designers to estimate the maximum allowable heat flux and corresponding pressure drop for a specified set of operating conditions and maximum operating temperature.

Kinetics of the clogging and optimization of prefilters in a two-stage air cleaning system

The kinetics of the clogging of filters by submicron solid aerosol particles in the diffusion mode of deposition is studied, and a method is developed for optimizing the parameters of a prefilter in a two-stage system of fine air cleaning that consists of a prefilter and a final filter. The relation of the maximum allowable pressure drop to the optimum radius of the fibers, the optimum thickness of the prefilter, and the volume of the particles captured by the system is derived. It is shown that at a fixed radius of the fibers, the dependence of the final pressure drop and the dust holding capacity on the radius of the particles has a maximum that approximately corresponds to the radius of most penetrating particles.

Design and optimization of three-dimensional extrusion dies, using constraint optimization algorithm

Balancing the distribution of flow through a die to achieve a uniform velocity distribution is the primary objective and one of the most difficult tasks of extrusion die design. If the manifold in a Coat-hanger die is not properly designed, the exit velocity distribution may be not uniform; this can affect the thickness across the width of the die. Yet, no procedure is known to optimize the coat hanger die with respect to an even velocity profile at the exit. While optimizing the exit velocity distribution, the constraint optimization algorithm used in this work enforced a limit on the maximum allowable pressure drop in the die; according to this constraint we can control the pressure in the die. The computational approach incorporates three-dimensional finite element simulations software Rem3D ® and includes an optimization algorithm based on the global response surfaces with the Kriging interpolation and SQP algorithm within an adaptive strategy of the search space to allow the location of the global optimum with a fast convergence. The optimization results which represent the best die design are presented according to the imposed constraint on the pressure.