Multi-stream Plate-fin Heat Exchangers Research Articles

Multivariate multi-objective collaborative optimization of pumped thermal-liquid air energy storage

Pumped thermal-liquid air energy storage (PTLAES) is a novel energy storage system with high efficiency and energy density that eliminates large volumes of cold storage. In this study, three different configurations of PTLAES systems with direct and indirect thermal energy storage were proposed. The “adaptive segmentation-based temperature transfer matrix” method was developed to capture the heat transfer characteristics of multi-stream plate-fin heat exchangers (MPFHEs), which is the key component of the system. To determine the upper limit of the techno-economic performance of the system, single/multi-objective optimization was performed with up to 35 decision variables. Additionally, the “Pareto efficiency” concept was defined to quantify the goodness of a point compared to the Pareto front. The results showed that the irreversible heat transfer and pressure drop in MPFHEs contribute 20.6 %–44.3 % of the total exergy destruction. Therefore, the design of MPFHEs significantly impacts the system performance. Multivariate multi-objective collaborative optimization can significantly improve the optimization results. PTLAES with closed loop indirect thermal energy storage was determined to have the best overall performance, achieving round-trip efficiency of 63.3–70.1 %, levelized cost of storage (LCOS) of 0.162–0.181 $/kWh, and energy density of 122–161 kWh/m3. The optimized PTLAES system can achieve lower LCOS than lithium-ion batteries when the discharge duration exceeds 3.5 h. Furthermore, it was shown that key criteria including round-trip efficiency, LCOS, and energy density can be traded off over a broad design space of different system configurations, parameter combinations, and material choices. This research demonstrated that PTLAES is a promising choice for long-duration energy storage and provided guidance for the design and techno-economic optimization of PTLAES systems.

Modeling and Design of a Multistream Plate-Fin Heat Exchanger in the Air Separation Units by Pinch Technology

Recent years have seen considerable advancement in cryogenic technology. Air separation devices have used the cold box with heat exchanger plate-fin (PFHE) in numerous applications. Cryogenic technologies are used in many industrial processes to recover heat and reduce energy consumption. The multistream plate-fin heat exchanger (MSPFHE) is heavily utilized in the air separation plant’s (ASU) design. The plate-fin heat exchanger, one of the most important applications in the cryogenic industry, is the focus of the current investigation. The air entering this operation has been cooled by utilizing energy from streams originating from the distillation tower in the air separation unit (ASU) to reduce energy usage. The project aims to develop and create a multistream plate-fin heat exchanger (MSPFHE) that may be used in the cold box of an air separation unit practically and without limitations. The pinch technique, a method based on the usage of composite curves, was used in the creation of MSPFHE. With pinch technology, it is possible to divide a multistream exchanger into block portions that represent enthalpy intervals and identify the entry and departure sites for the streams. The correlations used in the MSPFHE thermal design model were first modeled and compared to earlier models as part of this effort. This model has been turned into MATLAB code and utilized in two case studies to yield acceptable results during the sizing step. Calculations of thermodynamic properties, heat transfer, pressure drop, choice of fin type, and final heat exchanger size were all part of the design of the MSPFHE. Finally, based on the software’s ability to reproduce the identical environmental conditions nature produces, the case study results have been validated using Aspen EDR. These findings were matched to findings from the literature and determined to be reliable and consistent.

An investigation of multistream plate-fin heat exchanger modelling and design: a review

Abstract In line with population expansion and industrial development, the world’s energy consumption has been rising gradually over the past three decades. As a result, methods for energy conservation have been sought. One of the most common strategies is heat recovery, which is efficient and cost-effective to the extent possible. Heat recovery is not just about saving energy for primary consumption; it is also about lowering emissions and protecting the environment. In this respect, one of the most important strategies for heat recovery is to develop heat exchangers and exploit the energy associated with many of the processes’ output products in order to use it in new processes. Many researchers working in the field of heat engineering are now looking into novel heat transfer techniques. Use of the heat exchanger as a compact is one of these ways that might be considered. The current review therefore concentrates on the design of plate-fin heat exchangers (PFHE) and multi-stream plate-fin heat exchangers (MSPFHE) based on various models. The current review offers some suggestions for upcoming studies on improving heat transfer and minimizing power use.

Study on multi-stream plate fin heat exchanger coupled with ortho-para hydrogen conversion based on distributed parameter model

The distributed parameter model is used to simulate full domain of multi-stream CFPFHE (catalyst filled plate fin heat exchanger). The heat transfer due to the extended catalyst surface area, the ortho-para hydrogen conversion heat and the flow resistance in porous catalyst are integrated in the model. The results show that increasing the mass flow of fluid channel filled with catalyst not only decreases HEPUP (heat exchange amount per unit pump power), but also weakens efficiency of o-p conversion. For example, when the mass flow of fluid A (in which catalyst is filled) increases from 0.06 kg/s to 0.084 kg/s, the pump power increases by 34.6%, and the HEPUP and the average outlet para-hydrogen decreases by 30.9% and 7.0% respectively. In addition, A deviation parameter ϕ is defined to qualitatively describe the degree of inlet maldistribution. Although no catalyst filled in fluid C channel, the effect of ϕC on the outlet para-hydrogen mass fraction is obvious. With ϕC increasing from 0 to 1.5, the outlet para-hydrogen mass fraction in the layer numbered by 42 (middle layer of fluid A) increases by 6.8%, decreases by 11.9% and 11.9% respectively, in the layer numbered by 6 (upmost layer of fluid A) and 76 (downmost layer of fluid A). The increase of inlet maldistribution of fluid C prevents the potential of catalyst filled in up and down layers of fluid A from being fully utilized.

Numerical investigation of turbulent nanofluid flow behavior in a multi-stream plate-fin heat exchanger with a novel design of fractal fins

Plate heat exchangers are widely used in various industries. This study considers using a novel design of fractal shape fins with a new structure on the performance of multi-stream plate-fin heat exchangers for the first time, which has not been studied by researchers before. The numerical study is done with a 3D finite volume method. The effect of using Oil/MWCNT nanofluid and using various configurations of fractal fins with different attack angles ranging from 30 degrees to 100 degrees with the range of Reynolds number of 10,000–40,000, have been studied in the current research. These changing parameters have a significant impact on the flow field and heat transfer in the heat exchanger. The results of this study show that increasing the angle of attack of fractal fins creates more flow deflection and higher fluid mixing. The rise of the Reynolds number creates stronger vortexes as the flow passes over the fins, thereby it can augment the fluid mixing in the areas which are close to the finned. As the Reynolds number rises, the growth of the thermal boundary layer diminished. It can also be seen that as the fluid impacts the fractal fins at higher angles of attack, the temperature distribution becomes more uniform in the heat exchanger. Increasing the Reynolds number from 10,000 to 40,000 increases the heat transfers up to 63 %. At the constant Reynolds numbers, increasing the fraction of solid nanoparticle volume up to 4 % in the cooling fluid augment the heat transfer rate by 48 % compared to the base fluid. Increasing the fluid velocity results the amplification of longitudinal vortex formation. Therefore, the pressure loss is higher at the increased Reynolds numbers. At the lower Reynolds numbers, the pumping power has a weaker dependency on the nanofluids concentration. Increasing the angle of attack of fractal fins increases the pumping power by 50 % compared with the angle of attack of 30 degrees. Increasing the fractal fin angle of attack compared with 30 degrees increases friction by 45–85 %. Changes in the Colburn factor show that considering all parameters that increase heat transfer, the Colburn factor increases by 23–42 % compared with the base scenario with Re = 10,000 and angle of attack = 30 degrees.

Design of the Multistream Plate-Fin Heat Exchanger in the Air Separation Units

Design of the Multistream Plate-Fin Heat Exchanger in the Air Separation Units

Geometric optimization of thermo-hydraulic performance of multistream plate fin heat exchangers in two-stage condensation cycle: Thermodynamic and operating cost analyses

LNG is an energy carrier with growing importance, but LNG cryogenic cycles are energy-intensive. Because the thermo-hydraulic performance of heat exchangers affects the operation and energy consumption of a compressor. The optimization of heat exchangers is key to improving the energy efficiency of a cryogenic plant. In this work, the screening analysis and optimization procedures are performed for a two-stage condensation plant to enhance the Coefficient of Performance (COP) as the operating performance criterion. Five geometric design categories of applied fins, such as fin type, fin height, fin thickness, fin frequency, and the number of layers of MPFHEs (Multistream Plate Fin Heat Exchanger) are selected as input parameters for the optimization process. Then, a thermodynamic analysis including the second law analysis and capital and operating costs assessment are carried out to show the improvements of applied optimization in the mentioned objectives. The results of the optimization procedure have indicated a considerable improvement in the COP of up to 13.7% and significant mitigation in total power consumption of up to 11.8 MW. Furthermore, the optimal configuration of heat exchangers presents an increase in exergy efficiency of up to 4.1%, a saving in exergy destruction of 10.2 MW and up to 8.6 M USD/year in the operating cost when compared with conventional cases.

Passage Arrangement Optimization of Plate-Fin Heat Exchanger under Uncertain Operating Conditions

As the total flow rate and passage number increase, the quality of the passage arrangement has an important influence on the thermal efficiency of a multi-stream plate-fin heat exchanger (PFHE). The operating conditions are uncertain due to changes in environmental and product requirements, which affect the design of passage arrangements. If this influence is not considered enough in design, it will lead to the loss of heat transfer efficiency of the PFHE. Therefore, an optimization design method for passage arrangement is developed considering the influences of uncertain operating conditions. First, the uncertain operating conditions of the PFHE are represented using probability density functions of mass flow rates and temperature. Next, the optimization goals are chosen through the correlation calculation between the passage arrangement and the heat transfer indexes by the integral-mean temperature difference method. The particle swarm optimization algorithm is adaptively improved for the passage arrangement calculation. Then, the result under uncertain operating conditions is compared with the result under a single condition. The total heat transfer rate is increased, and the dimensionless mean square error of the cumulative heat load is decreased, so the method of designing the passage arrangement under uncertain operating conditions is effective.

A Framework for Multi-Objective Optimization of Plate-Fin Heat Exchangers Using a Detailed Three-Dimensional Simulation Model

The design of a multi-stream plate-fin heat exchanger is a highly integrated task with multiple opposing objectives and many degrees of freedom. This work shows how it can be fully or partially automated by the combination of a detailed three-dimensional simulation model and an optimization routine. The desired task is formulated as the target of a multi-objective optimization and solved using a genetic algorithm. The workflow is presented using a cryogenic plate-fin heat exchanger with four process streams. The design is optimized towards high efficiency, low pressure drop, and low unit weight by adjusting the outer geometry, the inlet and outlet distributor configuration, and the detailed stream geometry. A detailed analysis of the Pareto-set gives a good overview of possible solutions, and the optimization routine can automatically find a feasible design with a reasonable tradeoff between the objectives. All elements of the framework are implemented in open source software. A highlight of this research is that a very comprehensive and detailed simulation model is employed in the optimization framework. Thus, the presented method can be easily adjusted to fit the needs of other engineering tasks.

A new multiscale modeling framework for investigating thermally-induced flow maldistribution in multi-stream plate-fin heat exchangers

Multi-stream Plate-fin heat exchangers (MSPFHEs) are among the most efficient heat exchangers in energy-based industries. They should be carefully designed to have maximum effectiveness and to avoid wasting energy. Flow maldistribution could significantly degrade the performance of heat exchangers. This study presents a novel modeling framework to capture the thermally-induced maldistribution in two-phase MSPFHEs. The developed model is used to show how thermally-induced flow maldistribution affects the performance of the heat exchanger, and some possible modifications are investigated to reduce its consequences. Our case study results show that thermally-induced maldistribution decreases the total heat transfer by 10.8%. Heat leakage helps to induce less flow near the leakage region, so it can be managed to overcome the initial thermally-induced flow. Moreover, thermally-induced maldistribution affects a limited region along the heat exchanger height direction. So, thermal performance deterioration decreases with increasing the number of layers for each stream. Nevertheless, increasing the heat exchanger length increases the degraded region in the heat exchanger. Thus, increasing the core length is not a good way to counteract the thermal performance deterioration caused by thermally-induced maldistribution. It is also found that an optimum layer arrangement could help to eliminate the thermally-induced maldistribution in the heat exchanger.

Exergy efficiency design for multi-stream plate-fin heat exchangers based on entropy generation assessment

The fundamental concepts of energy, entropy and exergy are progressively introduced for deepening. Furthermore, the state corresponding to the designated exergy is creatively defined as the referential assessment benchmark so as to asymptotically reckon the optimal rigorous operation decisions. Inspired by bionics design, the different types of lateral perforated fins and wavy fins are designed for various application scenarios. The temperature, T-Q diagram, entropy generation, dimensionless entropy generation, exergy loss and exergy efficiency within either stream or system hierarchy are observed to evaluate the adjustable design portfolio, for trade-off between benefits and costs. The proposed entropy generation assessment (EGA) is verified by physical experiment under different Reynolds number. The results prove that, the net cost of multi-stream plate-fin heat exchangers (MPFHE) is reduced from 20,813 $/kW to 19,072 $/kW after using EGA by −8.36%, while maintaining exergy efficiency. Therefore, EGA herein has important perspicacity for energy availability utilisation and operating economical assessment among heat exchange fields.

Exergy efficiency design for multi-stream plate-fin heat exchangers based on entropy generation assessment

The fundamental concepts of energy, entropy and exergy are progressively introduced for deepening. Furthermore, the state corresponding to the designated exergy is creatively defined as the referential assessment benchmark so as to asymptotically reckon the optimal rigorous operation decisions. Inspired by bionics design, the different types of lateral perforated fins and wavy fins are designed for various application scenarios. The temperature, T-Q diagram, entropy generation, dimensionless entropy generation, exergy loss and exergy efficiency within either stream or system hierarchy are observed to evaluate the adjustable design portfolio, for trade-off between benefits and costs. The proposed entropy generation assessment (EGA) is verified by physical experiment under different Reynolds number. The results prove that, the net cost of multi-stream plate-fin heat exchangers (MPFHE) is reduced from 20,813 $/kW to 19,072 $/kW after using EGA by −8.36%, while maintaining exergy efficiency. Therefore, EGA herein has important perspicacity for energy availability utilisation and operating economical assessment among heat exchange fields.

COP optimization of propane pre-cooling cycle by optimal Fin design of heat exchangers: Efficiency and sustainability improvement

The demand for LNG (liquefied natural gas) increases each year, and relevant studies have been developed in order to reduce both power consumption and greenhouse gas emissions of LNG plants. Multistream plate-fin heat exchangers (MPFHE) are widely used in these plants due to their large heat transfer surface area per unit volume for multi-phase flows. The thermal-hydraulic performance of heat exchangers also impacts on compressor shaft work of liquefaction plants. In this study, an automated optimization procedure is performed for commonly used MPFHE in a three-stage propane pre-cooling cycle to maximize the coefficient of performance (COP) of liquefaction plants. Four geometric input parameters (fin type, fin height, fin thickness, and fin frequency) have been selected for the optimization. The optimal heat exchangers and operating conditions of the entire refrigeration cycle and their feasibility are taken into account. The optimal fin designs of the heat exchangers affect the cycle operating conditions, which results in COP improvements of 18.9%, 2.5%, and 9.4%, and ranging from 7% to 32% of mitigation in CO2 emission when compared to the literature cases. Compared with the baseline case, the COP is improved by 9.4%, compressor shaft power is reduced by 7.1% (about 11.2 MW), heat transfer is augmented by 1.5% (3.8 MW), and CO2 emission is reduced by 6.3 t/h, which result in more efficient and sustainable LNG production.

A general multi-scale modeling framework for two-phase simulation of multi-stream plate-fin heat exchangers

Compact heat exchangers are among the vital components used in various industries. In this study, a general framework has been developed with a multi-scale point of view for three-dimensional simulation of multi-stream plate-fin heat exchangers. The most important features in the MSPFHEs simulation, such as phase change phenomena, multi-component mixtures, multiple streams, transversal, lateral and longitudinal conduction, non-uniformity of inlet flow, variable fluid properties, and heat leakage are simultaneously considered in this model. The modular form of the model structure has facilitated layer-by-layer simulation of cross flow heat exchangers as well as parallel flow ones. Our model has been successfully validated with numerical and experimental case studies. Periodic boundary conditions are developed for simulating heat exchangers with a high number of layers to reduce the computational cost. The results for a challenging six-stream test case show that when the number of layers for each stream is more than 15, results converge to the periodic boundary condition case. The total simulation time is decreased by 98.1% for a heat exchanger with 40 repeating unit cells. Liquefied natural gas production has been decreased by 5.8% due to the non-uniformity of natural gas at the entrance of the six-stream test case. Fluid temperature, and vapor quality distributions for a multi-component two-phase cross-flow MSPFHE have been presented. A dead zone is observed in the results of the cross-flow heat exchanger that does not have a significant contribution to the heat exchange. Results show that the total heat exchange between streams has been decreased by 8.5% in comparison to the parallel-flow ones.

Design and optimization of natural gas liquefaction process using brazed plate heat exchangers based on the modified single mixed refrigerant process

The multi-stream plate-fin heat exchangers (PFHEs) are widely used as the core heat transfer equipment in small-scale natural gas liquefaction processes. However, the PFHEs have disadvantages such as the strict pre-treatment standard and the complicated engineering and transportation. The brazed plate heat exchangers (BPHEs) have been suggested to replace the PFHEs to overcome such disadvantages. In this paper, the methodology for transforming PFHE processes into BPHE processes was introduced and a novel liquefaction process using BPHEs was proposed based on the modified single mixed refrigerant process. The key parameters of the new process were optimized by using the genetic algorithm, and the optimal operating conditions were compared with the base case. The results showed that the specific energy consumption (SEC) of the optimized case was 10.3% lower than that of the base case, while it was slightly higher than the SEC of the original PFHE process. Additionally, the exergy losses of the major equipment in the process were analyzed. The exergy losses were reduced by 7.6%, 19.5%, 29.5% and 15.3% respectively for the compressors, the heat exchangers, the Joule-Thompson valves and the water coolers in the optimized case. The total exergy loss was lower by 14.7% after the optimization.

Multi-objective optimization design and performance evaluation of a novel multi-stream intermediate fluid vaporizer with cold energy recovery

Vaporizers are the key heat transfer device in the regasification process of liquefied natural gas (LNG), especially for the conventional onshore LNG receiving stations. This paper has proposed a novel intermediate fluid vaporizer by employing multi-stream plate-fin heat exchanger (MPFHE-IFV). Compared to traditional shell-and-tube IFVs, it can not only achieve a higher heat transfer efficiency with more compact structure using MPFHE but also realize the recovery and reuse of LNG cold energy with intermediate fluid. In this ingenious design, the self-evaporating gas of cryogenic liquid is adopted as the intermediate medium of IFV so that the equipment freezing can be effectively avoided under large flow conditions. A thermal-hydraulic design model has been established for MPFHE-IFV to determine the detailed structural dimensions as well as the heat transfer performance, and a corresponding multi-objective optimization algorithm has been adopted to obtain the minimum equipment volume, the optimal channel arrangement and fin structure, the maximum cold energy recovery efficiency and the optimal number of internal cycles. Meanwhile, the transmission process of the cryogenic exergy in MPFHE-IFV has been revealed according to the analysis of the system temperature-entropy diagram. Finally, two experimental cases based on the liquid nitrogen regasification process are conducted to evaluate the practical performance of the novel MPFHE-IFVs using the design and optimization method proposed in this paper. The results indicate that this new type of IFV can reach the highest cold energy recovery efficiency up to 95% within the 8% error range when the heat transfer capacity is 11.5 kW and the heat medium flow rate is near 330 L/h.

A quasi-three-dimensional thermal model for multi-stream plate fin heat exchangers

In this study, a novel pseudo-three-dimensional model is developed to find out both fluid and solid temperature distributions in multi-stream plate fin heat exchangers. In this simulation algorithm, heat exchangers can be in either parallel flow or cross flow configuration. The model considerations include: heat leakage of cap plates and side plates, conduction throughout the solid matrix of the heat exchanger, variable physical properties, and inlet mass flow rate maldistribution. Using the computational code, the effects of different factors such as: the number of layers, mass flow variation, inlet mass flow rate maldistribution, and stacking pattern on the thermal performance of the heat exchanger have been investigated. The results of this investigation show that when the number of layers for each stream is small, a linear nonuniformity in the mass flow rate of a hot stream has a more destructive effect on the thermal performance than that in a cold stream. Moreover, the heat transfer rate of the heat exchanger is more sensitive to mass flow deviation of cold streams than that of hot streams. In the present research, when the number of unit cells are higher than 15, periodic boundary conditions can be applied to reduce the computational cost.

Thermal performance evaluation method of multistream plate fin heat exchanger

Multistream plate fin heat exchangers (MSPFHEs) are vital components of large cryogenic systems. A computer program is developed for layer by layer analysis of thermal performance of MSPFHEs and is validated against the published experimental results. Cross layer conduction between the streams in non-adjacent layers and heat transfer between the streams in consecutive layers are computed using analytical formulation. This avoids the need of fin discretisation along its height. Heat exchanger is discretised along the flow direction to take care of the effects of axial heat conduction and material property variation. Finite difference method (FDM) is used to convert the energy balance equations into a system of linear algebraic equations, which are solved iteratively. The developed computational method is found to be of adequate accuracy, capturing all the effects and can be used for MSPFHE design for cryogenic systems.

Impacts of thermos-physical properties on plate-fin multi-stream heat exchanger design in cryogenic process for CO2 capture

Oxy-fuel combustion is one of the most promising technologies for CO2 capture for power plants. In oxy-fuel combustion plants, cryogenic process can be applied for CO2 purification because the main impurities in flue gas are non-condensable gases. The multi-stream plate-fin heat exchanger is one of the most important components in the CO2 cryogenic system. In-depth understanding of the impacts of property on the heat exchanger is of importance for appropriate design. In order to investigate the impacts of properties on sizing the heat exchanger and to further identify the key properties to be prioritized for the property model development, this paper presented the design procedure for the plate-fin multi-stream heat exchanger for the CO2 cryogenic process. Sensitivity study was conducted to analyze the impacts of thermos-physical properties including density, viscosity, heat capacity and thermal conductivity. The results show that thermal conductivity has the most significant impact and hence, developing a more accurate thermal conductivity model is more important for the heat exchanger design. In addition, even though viscosity has less significant impact compared to other properties, the larger deviation range of current viscosity models may lead to higher uncertainties in volume design and annual capital cost of heat exchanger.

In-field Performance Evaluation of a Large Size Multistream Plate Fin Heat Exchanger Installed in a Helium Liquefier

A large size multistream plate fin heat exchanger (MSPFHE) is developed for an in-house-developed modified Claude cycle-based helium liquefier. The development of this heat exchanger, including thermal sizing and mechanical design, is described in this article. A pressure drop analysis is also carried out to compute the pressure drops across various components of the MSPFHE. The MSPFHE, after fabrication, pressure and leak testing, is integrated with the rest of the process equipment and piping of the developed helium liquefier cold box. Experiments are conducted to evaluate the performance of the developed MSPFHE under different modes of operations of the helium liquefier. Experimental results are compared with the computed predictions based on the two-dimensional numerical model as well as the commercial software Aspen MUSETM and reported in this article. Good agreement between the computed and measured performances is observed during the field testing of the MSPFHE.