Cost Of Heat Exchangers Research Articles

Evaluation of utilizing horizontal directional drilling technology for ground source heat pumps

The drilling cost of Ground Heat Exchangers (GHEs), which increases the capital cost, is one of the main obstacles to their widespread development. Horizontal Directional Drilling (HDD) is a lower cost no-dig drilling technology commonly used for drilling tunnels or for the installation of urban infrastructure such as pipes, cables, etc., using the prescribed underground path. Thus, using HDD technology for horizontal GHE (HGHE) is expected to improve the competitiveness of ground source heat pump (GSHP) systems, since its drilling cost and the requirement of surface land area are significantly smaller than those of conventional excavation.In this research, a horizontal U-shaped hole was drilled as an experimental GHE in Saga City, western Japan. This hole with diameter of 230 mm, length 63 m, and a maximum depth of 8 m was used to place a polyethylene pipe with a 52 mm ID as GHE, inside. The thermal response test (TRT) with a heat load of 35−45 W/m effectively demonstrated the good heat exchange ability of the HGHE due to the larger heat exchange surface and the lack of thermal interference between pipes. The developed numerical model in FEFLOW and based on GHE design as well as the field’s geological condition were validated through the history matching of the heat medium temperatures measured during the TRT. This model was then used to carry out a sensitivity analysis under different design conditions. The results showed that the heat exchange rates were significantly enhanced in larger diameter of GHEs, while the unit heat exchange rates declined in longer lengths of GHE. The deeper installation of GHE was found to be insignificant due to the delayed seasonal change of the ground temperature, not to mention the consequent higher drilling cost. In addition, the effect of groundwater flow indicated that faster groundwater velocities, and in perpendicular direction, show the maximum system improvement.Finally, an economic and comparative study was performed to calculate and compare the merits of HDD with equivalent conventional GSHPs including single and double U-tube, coaxial and slinky GHE. The results of economic analysis showed that HDD technology can reduce GHSP cost up to a maximum of 78 %.

Effects of shell-and-tube heat exchanger arranged forms on the thermo-economic performance of organic Rankine cycle systems using hydrocarbons

Shell-and-tube heat exchangers are crucial and widely used components in organic Rankine cycle (ORC) systems. Heat exchanger arranged forms, namely, the organic fluid flows either inside or outside the tubes, substantially affect the purchased cost and exergy loss of heat exchangers; and thereby considerably influencing the system thermo-economic performance. Based on various heat exchanger arranged forms, the thermo-economic performance of ORC systems may differ remarkably and even result in opposite conclusions, such as in selecting optimal working fluids and ratios of component purchased cost. However, no published studies have focused on this specific issue. Influence degree exerted by the heat exchanger arranged form on the thermo-economic performance of ORC system remains unclear. Selection guidelines for the optimal arranged forms also need to be developed. This study analyzed the effects of heat exchanger arranged forms on the thermo-economic performance of subcritical ORC systems with shell-and-tube heat exchangers. Three common heat exchanger arranged forms were studied. Heat source temperatures are 100–200 °C, and five hydrocarbons are working fluids. Results show that the heat exchanger arranged forms substantially affect the specific investment cost (SIC) of ORC system, and the largest difference in SIC reaches 14.7% among various arranged forms. The optimal working fluid and system parameters, and ratios of component purchased costs also differ remarkably. Optimal heat exchanger arranged form depends on the working fluid and heat source temperature. This study provides the optimal heat exchanger arranged forms for five hydrocarbons at heat source temperatures of 100–200 °C.

Power optimization and economic evaluation of thermoelectric waste heat recovery system around a rotary cement kiln

Cement rotary kiln is the main device utilized for industrial cement production in large scale. The shell temperature can reach several hundred Celsius degrees. Therefore, a thermoelectric waste heat recovery system can be utilized based on its advantages. In this study, an arc shaped absorber is designed and temperature distribution along the absorber circumference is obtained numerically. The calculated temperature is considered as the hot side temperature of thermoelectric generators (TEGs) that recover thermal energy on the absorber. In situations where the heat is free, the metric for designing a thermoelectric system is to reach the maximum power output. In order to reach regional optimal power from parametric design, the absorber length is divided into several sections. For efficient design of the TEG in each section, effect of significant parameters such as leg length and fill factor of the TEG and thermal resistance of the heat sink are studied. Effect of variation of the temperature and velocity magnitudes of the air next to the heat sinks is considered on thermal resistance and performance of the pin-fin heat sinks along the absorber. β-phase zinc antimonide (Zn4Sb3) and magnesium tin silicide (Mg2SiSn) are chosen as the p- and n-leg thermoelectric materials of the TEGs, respectively, because of their relatively high performance over the considered range of operating temperature. The results show that, staggered arrangement of the pin-fins is more effective for higher power generation and system performance compared to in-line arrangement of the fins. Moreover, by evaluation of the results, maximum matched power output in each section versus the fill factor and leg length can be determined in this study. The results show that, low fill factors between 0.05 and 0.2 can provide relatively a same maximum power as high fill factors. Furthermore, an economic evaluation is carried out to find optimal design of the TEG device for highest power generation and lowest investment cost. Various parameters of the cost function, such as cost of the bulk raw material (CB), manufacturing cost associated with processing bulk material (CM,B), areal manufacturing cost (CM,A), heat exchanger cost (CH-EX), balance of the system cost (CBoS) and the installation cost (CI) are taken into account in this study. The results show dominant parameter in the system cost is the heat sink.

Reliability and reliability-based sensitivity analysis of shell and tube heat exchangers using Monte Carlo Simulation

In the present work, the reliability-based sensitivity analysis of a shell and tube heat exchanger has been investigated. Four optimum heat exchanger layouts have been selected among the available layouts in literature as case studies (which optimized based on the GA, PSO, ICA and BBO algorithms). A computer code has been developed based on the Bell-Dellawar method for the hydraulic and thermal modeling of heat exchanger. The shell and tube side inlet flow temperatures, mass flow rates, fouling resistance and the reduction of inner tubes diameter due to sedimentation are considered as uncertain parameters. The Monte Carlo Simulation (MCS) as the most accurate simulation method has been applied to determine the safety level of different layouts. The total cost of heat exchangers are reported 55.1 k€, 53.2 k€, 54.4 k€ and 50.6 k€ for the GA, PSO, ICA and BBO layout respectively, while the corresponding failure probabilities for these cases are 17.2%, 24.9%, 11.6% and 18.2%. The contribution of different parameters on the system failure has been determined. The contribution of shell side mass flow rate, hot and cold flow inlet temperature uncertainties on the system failure are 38–41%, 22–27% and 18–23% respectively for different layouts. Finally, appropriate ranges for variation of operating conditions are determined by using the sensitivity analysis. The present study shows the importance of reliability analysis in the real world applications which opening a new approach for heat exchanger design.

Flow Boiling over Tube Bundles with Combination of Plain and Coated Tubes

The present Paper focuses on studying the effect of the number of coated tubes in a tube bundle under flow boiling heat transfer. The coated tubes are prepared by creating a porous layer of copper using plasma spraying of copper powder on stainless steel tubes. The experimental results in terms of heat transfer coefficients are presented for different configurations of tube bundles by varying the number of coated tubes. The operating parameters are heat flux (), mass flux (), and pitch-to-diameter ratio (1.25, 1.6, and 1.95). The results show that using coated tubes only in the lower portion of the horizontal tube bundle is beneficial during vertical crossflow of liquid. The performances of two rows coated, three rows coated, and all five rows coated are found to be comparable to each other. The number of rows of coated tubes that should be used for a tube bundle depends on the degree of enhancement and configuration of tube bundle. The result is useful in reducing the cost of shell and tube heat exchangers by using the optimized number of coated tubes in the tube bundle during flow boiling heat transfer.

Thermoelectric System Economics: Where the Laws of Thermoelectrics, Thermodynamics, Heat Transfer and Economics Intersect

ABSTRACTThermoelectric technology has key benefits and strengths in many terrestrial energy recovery applications. Thermoelectric system cost is a key factor governing final decisions on the use of thermoelectric energy recovery systems in all terrestrial applications; thus cost being just as important as power density or efficiency for the adoption of waste energy recovery (WER) thermoelectric generators (TEG). New integrated cost analysis / thermoelectric analysis approaches have now shown key relationships and interdependencies between overall TEG system costs, including TE material costs, manufacturing costs, and specifically heat exchanger costs; and the TE performance design metrics such as TE material properties, TE device design parameters, heat exchanger performance metrics such as hot-side and cold-side conductances and UA values, and hot side heat flux in achieving optimal TEG WER designs. These new approaches have led to a new thermoelectric system economics paradigm that strongly influences TEG cost and performance decisions. While prior work provided foundations for the latest cost scaling analysis / TE performance analysis, this new work offers new insights and understandings and provides the basis for new thermoelectric system economics. Optimum TEG system cost conditions can now be tied directly to the TE materials, TEG design parameters, and heat exchanger design parameters through critical non-dimensional analysis. The non-dimensional analysis and metrics show the TEG system cost and performance interdependencies and intercouplings in one unifying and cohesive relationship. Prior work by T.J. Hendricks, S.K. Yee, and S. LeBlanc, J of Electronic Mater, 45, (3), 1751-1761, 2015 has shown that the system design that minimizes cost (e.g., the G [$/W] value) can be close to designs that maximize power, but these design regimes are not necessarily aligned with high system conversion efficiency or high specific power. Key sensitivities and interrelationships between critical cost metrics and critical TE performance and design metrics in the new thermoelectric system economics paradigm are explored. Quantitative data showing these sensitivities and their implications on TEG system design in terrestrial WER applications are presented. Critical non-dimensional parameter mapping has shown where heat exchanger cost- dominated conditions, TE material or manufacturing cost-dominated conditions, and combinations of cost conditions control and drive the overall TEG cost and performance. This new cost-performance paradigm shows the required pathways and challenges to achieving TEG system costs of $1 -$3/Welec.

Total costs of shell and tube heat exchangers with concentric helical tube coils

The paper deals with the manufacturing costs of shell and tube heat exchangers with concentric helical tube coils. The most common correlations for calculating prices of shell and tube heat exchangers found in accessible literature were tested using the market data for a comparison and they have shown significant deviations. A new correlation for estimating prices of heat exchangers with concentric helical tubes (when the shell is made of carbon steel and the helical tube of copper) was determined in the following form: Cin = 614?S0.627/hts

New Paradigms in Defining Optimum Cost Conditions in Thermoelectric Energy Recovery Designs

Cost is just as important as power density or efficiency for the adoption of waste heat recovery (WHR) thermoelectric generators (TEG). Prior work [1] has shown that the system design that minimizes cost (e.g., the G [$/W] value) can be close to the designs that maximize power, but these design regimes are not necessarily aligned with high system conversion efficiency or power density. Recent work [2–5] further explores the impact of heat exchanger conditions on the optimum TEG fill factors and cost scaling of a waste heat recovery thermoelectric generator with a detailed treatment of the hot side exhaust heat exchanger. The cost scaling analysis considers the overall TEG system costs, including TE material costs, manufacturing costs, and specifically heat exchanger costs; and the performance analysis accounts for heat lost to the environment and updated relationships between the optimum hot-side and cold-side conductances that maximize power output. The optimum fill factor, Fopt, to minimize TEG energy recovery system costs is strongly dependent on the heat leakage fraction, σ, the mass flow rate of the exhaust, the hot-side heat exchanger effectiveness, heat exchanger UAu, and interfacial heat flux [1]. A more rigorous analysis and conclusion for the optimum fill factor was recently introduced and characterized at the 14th European Conference on Thermoelectrics [5] in 2016. A new, more comprehensive relationship for Fopt has created an updated, more rigorous relationship for the optimum cost, Gopt, relationship for thermoelectric energy recovery systems. These new [Gopt, Fopt] relationships are explored and characterized to show the inherent design complexities. The heat exchanger costs can often dominate the TEG cost equation and it is critical to fully understand the tradeoff between heat exchanger performance, TEG manufacturing and material costs, optimum TEG fill factors, and TE performance to establish potentially optimum design points within the cost-performance design space. This work explores and characterizes new design tradeoffs and new cost minimization relationships within this cost-performance design space for a typical thermoelectric energy recovery system application where the interplay between optimum TEG fill factors, TE device design parameters, and heat exchanger design parameters can impact system footprint, volume, and mass in weight-sensitive applications. This work shows how heat exchanger UAu, interfacial heat flux, and Fopt govern cost minimization and create and control cost regimes within the overall cost-performance design domain. This shift of emphasis acknowledging the interdependence of optimum TE fill factors, heat exchanger performance, and interfacial heat flux has significant implications on thermoelectric WHR system designs, their performance, and their operation.

Система теплопостачання з використанням скидного тепла трансформатора

The task is to use the waste heat of powerful electric transformers for hot water supply in residential and industrial buildings. The high heat of transformers is of low-temperature and therefore requires heaters. The thermal scheme of the hot water supply system with electric transformer and heater - heat pump and electric heater is considered. In the scheme, the heat from the transformer is transmitted to oil, from oil to the heat in the oil-heat exchanger is transferred to water, from water to the evaporator of the heat pump installation (HPI) is transferred to the freon and from the freon to the water of the hot water system is transmitted in the condenser of the HPI. After the HPI condenser, water is heated in the electric heater and is supplied to the consumer. The thermal capacity of the transformer and the temperature of hot water supplied to the consumer are known. The temperature of the water supplied to the heater after the HPI condenser is unknown. According to the criterion of quality of variants with different water temperatures, the total cost of equipment of the scheme of hot water supply system is accepted. The method of determination of the total reduced costs of the hot water supply system with regeneration of waste heat of the transformer is offered. Costs for the hot water supply system are defined as the sum of the costs of heat exchangers, pumps and their consumed electricity, the costs of HPI and consumed electricity of its compressor, the cost of the heater and the consumption of electricity. A computer program for determining the total reduced costs of a hot water supply system with regeneration of the transformer discharge heat has been developed. The results of calculations of the total reduced costs for hot water system options are presented. The variants without HPI with heating of water in the electric heater, with heating of water in HPI and heating it in the electric heater are investigated. The HPI thermal capacities and the compressor drive electrical capacities at different water temperatures from the condensers were determined using the well-known FKW Cycle program. The comparative analysis of the obtained results is performed and it is shown that the cumulative cited costs for the variant of HPI are lower than the cumulative cited costs of the variant without HPI, that the nature of change of the cumulative reduced costs when the temperature of the heated in HPI of water is the same for a wide range of specific costs of HPI and electricity. The lowest total costs shown correspond to the lowest water heating in the HPI and, accordingly, the highest heating in the electric heater.

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.

Thermo-economic evaluations of dual pressure organic Rankine cycle (DPORC) driven by geothermal heat source

The thermo-economic evaluation of the dual pressure organic Rankine cycle system was presented based on the geothermal heat sources ranging from 100 to 180 °C. Two kinds of heat exchangers were selected to form four specific configuration layouts. The comparison between single and dual pressure systems was carried out. Moreover, the influence of economic parameters on cycle performance was analyzed. The electricity production cost (EPC), payback period (ppd), and saving-to-investment ratio are among the crucial considerations when the two stage evaporating pressures and pinch point temperatures are selected as independent variables. The results indicate that the dual pressure system possesses optimal EPC with the variation of low-evaporating pressure and the configuration layouts of type-FF and type-FP perform better. The cost of heat exchangers accounts for the largest proportion in the total cost of the system, followed by the expander. It can also be found that, for R1233zd, the average increasing rate of 20.87% in Wnet brings no economic benefits to the dual pressure system because the EPC also increases 12.98% averagely compared to the single pressure system. In addition, the impact of the annual loan interest rate, on-grid electricity price, and carbon tax of the system economic performance was discussed.

Dynamic modelling and simulation of a slinky-coil horizontal ground heat exchanger using Modelica

Ground source heat pumps are attractive alternatives for both conventional heating and cooling systems because of their higher energy efficiencies. A ground source heat pump system consists of a conventional heat pump coupled with a ground heat exchanger where water or a water-antifreeze mixture exchanges heat with the ground. Several major design options are available for ground heat exchangers, which are classified by layout to open and closed loops. Closed loop tubing can be installed horizontally as a loop field in trenches or vertically as a series of long U-shapes in wells. Slinky-coil horizontal ground heat exchangers are a compromise between vertical ground heat exchangers and conventional horizontal ground heat exchangers. They combine the relatively small installation cost of conventional horizontal ground heat exchangers and the high heat exchange capacity of vertical ground heat exchangers. These traits make a slinky-coil horizontal ground heat exchanger a suitable alternative for space heating in areas with limitations on land space usage. However, caused by a lack of appropriate dimensioning tools, these systems are often undersized or overdesigned. In this research, the feasibility of modelling and simulation of slinky-coil geothermal heat exchangers in the modelling language Modelica has been demonstrated. A model of a slinky-coil horizontal ground heat exchanger has been developed to simulate the performance of such systems. The model includes a ground heat exchanger and a soil cell. The ground heat exchanger has been modelled in two levels of detail, one with coil-like pipes and one with thin plates instead of pipes. In order to be able to assess the validity of the model, it has been developed based on a field test in Japan, and simulated under the same conditions. Reasonably good agreement has been obtained between the numerical predictions and published experimental measurements, which demonstrates the reliability and accuracy of the model.

Heat Exchanger Performance Impacts on Optimum Cost Conditions in Thermoelectric Energy Recovery Designs

Cost is just as important as power density or efficiency for the adoption of waste heat recovery thermoelectric generators (TEG). Prior work [1] has shown that the system design that minimizes cost (e.g., the $/W value) can be close to the designs that maximize the system’s efficiency or power density, however, it is important to understand the relationship between those designs to optimize TEG performance-cost compromises. Expanding on recent work [1, 2, 3] the impact of heat exchanger conditions on the optimum TEG fill factors and cost scaling of a waste heat recovery thermoelectric generator with a detailed treatment of the hot side exhaust heat exchanger has been investigated further. The effect of the heat lost to the environment and updated relationships between the hot-side and cold-side conductances [4] that maximize power output are considered. The optimum fill factor to minimize TEG energy recovery system costs is strongly dependent on the heat leakage fraction, σ, the mass flow rate of the exhaust, the hot-side heat exchanger effectiveness, heat exchanger UAh, and heat flux. These relationships are explored and characterized for typical exhaust gas-flow conditions to show the inherent design complexities. The heat exchanger costs often dominate the TEG cost equation and it is critical to fully understand the tradeoff between heat exchanger performance, optimum TEG fill factors, and cost to establish potentially optimum design points within the cost-performance design space. This work will explore the design tradeoffs and relationships within the cost-efficiency-power density design space for a typical thermoelectric energy recovery system application. The interplay between optimum TEG fill factors and heat exchanger design can impact system footprint, volume, and mass in weight-sensitive applications. Less-effective, low-cost heat exchangers may outperform higher cost alternatives from a market adoption perspective. This shift of emphasis acknowledging the interdependence of optimum TEG fill factors and heat exchanger performance has significant implications on thermoelectric waste heat recovery systems designs and their operation. In addition, preferred TEG design regimes exist that accommodate reasonable compromises in TE performance and cost. This effort highlights how the optimum fill factor–heat exchanger performance relations couple to these optimum TEG performance-cost domains based on TEG-system-level analyses and provides a focus for future system research and development efforts.

Novel pinch point method based exergetic optimisation of subcritical organic Rankine cycle for waste heat recovery

A new pinch point design methodology for subcritical organic Rankine cycle (ORC) is proposed to predict pinch point locations in both evaporator and condenser, and optimise working fluid mass flow rate to get maximum heat recovery and exergetic efficiency for given heat source and heat sink conditions. Selected working fluids have been compared based on different performance parameters for various heat source conditions. The present method seems to be better than previous pinch point design methods as it optimises the cycle by considering both source and sink. At optimum operation, ammonia is best in terms of lower mass flow rate and turbine size, toluene is best in terms of lowest heat exchanger size and cost, whereas, R-1233zd and isopentane are best in terms of higher power output and heat recovery, exergy and entrancy efficiencies. Contour plots are presented as well to select optimum design parameters for available heat source and sink.

Numerical and experimental analysis on shell side thermo-hydraulic performance of shell and tube heat exchanger with continuous helical FRP baffles

The present work deals with the numerical and experimental investigation of heat and fluid flow in shell and tube heat exchanger with continuous helical baffles on shell side. Seven helix angles, namely 10°, 19°, 21°, 25°, 30°, 38°, and 50° are investigated numerically by modeling a full length continuous helical baffled shell-and-tube heat exchanger for different mass flow rates and inlet temperature conditions. Results revealed that the larger helix angles (30°, 38° and 50°) adds to lower heat transfer and lower pressure drop, and smaller helix angles (10°, 19°and 21°) resulted in higher heat transfer as well as higher pressure drop. The experiments were carried out on shell and tube heat exchanger for helical baffles with 25° helix angle and results were compared with segmental baffles. New baffle material, FRP (Fiber Reinforced Plastic) is introduced on the shell side of the proposed heat exchanger. For material comparison between FRP and stainless steel, the deviation of heat transfer coefficient is 8–10%, which can serve as a potential replacement for conventional baffle material, thereby reducing the capital and operating cost of the tubular heat exchanger.

Optimum waste heat recovery from diesel engines: Thermo-economic assessment of nanofluid-based systems using a robust evolutionary approach

Nearly 30% of the input energy to a diesel engine is wasted through the exhaust gas; thus, considerable attention has been directed toward developing efficient heat recovery systems for these engines. Given the demonstrated ability of nanofluids to boost the heat transfer rate of heat exchangers, these heat transfer fluids merit consideration for use in diesel exhaust heat recovery systems. In this study, the effects of employing nanofluids on the optimum design of these systems are investigated. An existing heat diesel engine exhaust heat recovery system is modeled to work with Al2O3/water and a modified imperialist competitive algorithm is employed for the optimization. Seven variables consisting of five heat exchanger geometric characteristics together with nanoparticle volume fraction and coolant mass flow rate are considered as design variables. The heat exchanger cost and charging rate of the storage tank are optimization objectives, while the greenhouse gas savings of the heat recovery system are assessed for measuring the environmental impact of the energy recovery. The results indicate that the proposed approach can overcome the challenge of finding the near-optimal design of this complex system and using nanofluids enhances the performance of the heat recovery heat exchanger.

Mathematical modelling and optimization of a liquid separation condenser-based organic Rankine cycle used in waste heat utilization

The organic Rankine cycle (ORC) is a promising method of generating power that utilizes low-enthalpy renewable energy and industrial waste heat. Given that the exergy loss and capital investment cost of heat exchangers account for a large proportion of the components in the ORC, research on the development of novel heat exchangers and configuration optimization coupling with other components and cycle parameters is essential to improve the ORC performance. In this study, an innovative liquid separation condenser (LSC) is incorporated into a waste heat-driven ORC system. A non-convex mixed integer non-linear programming model is formulated to simultaneously optimize the component configurations and system parameters of the LSC-based ORC. The objective is to minimize the electricity production cost of the ORC. The pressure drops of the heat exchangers are directly incorporated into the cycle model instead of ignoring them or constraining them by upper bounds. The physical property parameters of the working fluid are regressed using the Refprop 9.0 database to ensure the optimization of cycle operating variables. A case study is presented to test the proposed methodology and the formulated model. The results achieved using the simultaneous optimization method are compared with the results achieved using the sequential optimization method. The optimization results of the LSC-based ORC are also compared with those of the parallel flow condenser-based ORC. Then the influences of the key structure variables on the optimization results are studied. Finally, a sensitivity analysis of heat source parameters and environmental parameters on the optimization results are conducted.

Simultaneous synthesis of non-isothermal water networks integrated with process streams

This paper is an extension of our previous study [1] and addresses simultaneous synthesis of non-isothermal water networks heat-integrated with hot and cold process streams. Hence, the scope of heat integration is expanded by enabling heat integration of process streams such as waste gas streams and reactor feed and effluent streams simultaneously with the water network's hot and cold streams. A recently proposed superstructure [2] for the synthesis of non-isothermal water networks is extended in order to enable additional heat integration options with process streams. The model and solution strategy are modified in order to enable achieving the solution of the problem within the reasonable computational time. Pseudo heat exchanger cost was introduced in order to find heat exchange matches. They are used as constraints within the mixed-integer nonlinear programming (MINLP) model that simultaneously addresses the synthesis problem. The objective function of the proposed model accounts for operating costs, including fresh water, utilities and treatment operating cost, and investment costs of heat exchangers and treatment units. The results indicate that by solving a unified network, rather than stand-alone non-isothermal water network and separate process heat exchange network, additional savings in utilities consumption and total annualised cost can be achieved.

Heat Transfer Enhancement and Optimization of Lean/Rich Solvent Cross Exchanger for Amine Scrubbing

The lean/rich amine cross exchanger is one of the cost centers in the amine scrubbing process, and accounts for 20–30% of the capital cost. To minimize the cross exchanger cost, shortcut methods that determine optimum LMTD and fluid velocity were developed. The optimum LMTD is a function of heat transfer coefficient, temperature change and the capital cost of heat exchanger. A greater LMTD should be used to prevent excessive capital cost when the number of heat transfer units (NTU) is large and the heat transfer coefficient is small. The heat transfer performance can be enhanced by increasing pressure drop and reducing solvent viscosity. The corrugation angle is the primary design geometry for plate-and-frame exchanger (PHE). Based on the empirical correlations for PHE, the heat transfer coefficient at 60° is almost double that at 30°; however, the pressure drop at a large corrugation angle is also greater. The dependence of the pressure drop per unit length on the heat transfer coefficient is 0.35–0.40, which implies that the heat transfer coefficient will increase 30% by doubling the pressure drop per unit length. The cost associated with the optimization of the cross exchanger has been developed as a function of the fluid velocity, the physical properties, the exponents of the empirical correlations and the pricing parameters. The optimum velocity is independent of the solvent rate, the temperature change of the cross exchanger, and the cross exchanger LMTD. To stay at optimum fluid velocity, the plate number needs to increase as the solvent rate increases while the plate length will increase as the NTU increases. Viscous solvent will result in a lower optimum velocity since it causes higher pressure drop. Typical optimum fluid velocity is at 0.32–0.42 m/s for 8 m PZ. It is worthwhile to utilize higher fluid velocity and pressure drop when the heat transfer can be effectively enhanced by turbulence.

Multi-objective thermal design optimization of plate frame heat exchangers through Global Best Algorithm

This study deals with thermal design of plate frame heat exchangers based on Global Best Algorithm. By utilizing some basic perturbation schemes adopted from Differential Search and Differential Evolution, Global Best Algorithm aims to obtain optimum solution of any optimization problem with intensifying on exploitiation of the promising solutions rather than exploring of the unvisited paths of the search domain. Firstly, optimization performance of the proposed algorithm has been benchmarked against variety of well-known optimization algorithms by means of 16 different highly challenging optimization test functions. Then, the proposed method is put into practice to acquire the optimal values of the design variables those optimize the considered problem objectives including overall heat transfer coefficient, total cost and weight of the plate frame heat exchangers seperately as well as simultaneously. Considerable improvement in objective function values is observed as compared to preliminary design in single objective manner. Pareto frontier is constructed for dual and triple objective and best optimal solution among the curve is selected by means of the widely-known decision making methods of LINMAP, TOPSIS, and Shannon’s entropy theory. Optimal results obtained from each decision making theory are compared with respect to their corresponding deviation indexes and the best one is preferred. A sensitivity analysis is then performed to study the variational influences of some design parameters on the considered objective functions. It is observed that selected design variables has a signficant effect on problem objectives.