Total Exchanger Research Articles

Exergoeconomic performance optimization for a regenerative closed-cycle gas turbine combined heat and power plant

A combined heat and power plant with regenerative closed-cycle gas turbine is considered. The heat transfer losses, irreversible adiabatic losses and irreversible pressure drop losses are considered in the plant. The expressions of dimensionless profit rate and exergy efficiency are gained. The optimal heat conductance distributions and compressor pressure ratio are derived based on maximum dimensionless profit rate and maximum exergy efficiency objectives, respectively. The results show that the heat conductance distributions and compressor pressure ratio have their optimal values which results in maximum dimensionless profit rate. The curve of maximum dimensionless profit rate and the corresponding exergy efficiency is loop-shaped one. With the increases in heat reservoir temperature ratio τ1, price ratios a and b as well as total heat exchanger inventory UT, the maximum dimensionless profit rate increases. With the decrease in a and increases in τ1, b and UT, the corresponding exergy efficiency increases. The heat reservoir temperature ratio τ2 has its optimal value which leads to double maximum dimensionless profit rate. Moreover, the maximum exergy efficiency performance of the plant is also analyzed. Because the exergoeconomic performance of irreversible regenerative closed-cycle gas turbine cogeneration plant has not been investigated by the researchers before, the exergoeconomic performance optimization is conducted in this paper, and the results obtained can offer new design guidelines for this kind of cogeneration plants.

Selection of working fluid for low enthalpy heat source Organic Rankine Cycle in Dholera, Gujarat, India

Organic Rankine Cycle (ORC) is a technique which can generate electricity by using low to medium enthalpy geothermal water. This paper narrates selection of working fluid which is the most important factor in designing of ORC. In this paper four fluids, R600, R600a, R134a and R245fa were chosen for screening. The screening is done with respect to hot water temperature at generator inlet side and pressure ratio condition. Analysis of working fluid in this paper is done for six parameters namely ORC efficiency, Volumetric Flow Ratio (VFR), Expander Size Parameter (SP), Total heat exchanger utilised area (UA), Network output and Turbine outlet volume flow rate. This analysis were done in order to select the suitable working fluid for ORC integrated with space heating and cooling plant at Dholera. This ORC uses the output water of 75–80 °C obtained from heating side of the space heating and cooling system. As the water temperature which is used in ORC is a low enthalpy it needed a working fluid which can increase the efficiency and exergy of ORC. After screening the results shows that R245fa is a suitable working fluid for ORC integrated with space heating and cooling plant in Dholera, Gujarat, India.

Multicriteria decision-making approach for selecting ventilation heat recovery devices based on the attributes of buildings and the preferences of decision makers

Ventilation heat recovery devices have been increasingly used in energy-efficient buildings. Many factors, such as the attributes of buildings and the economic conditions of decision makers, should be considered in the installation of ventilation heat recovery devices. Thus, decision makers experience a multicriteria decision-making problem. This study presented a method of combining Analytical Hierarchy Process with the Technique for Order of Preference by Similarity to Ideal Solution to provide guidance in selecting ventilation heat recovery devices on the basis of the attributes of buildings and preferences of decision makers. By using residential house, small shop, and small public service center as examples, four types of ventilation heat recovery devices (total, plate sensible, integral heat pipe (R32), integral heat pipe (R717) heat exchangers) were recommended and sequenced under different background requirements through the proposed method. Results showed that the total heat exchanger obtained the highest recommended indicator value in small load application scenario, indicating its suitability. The proposed method can completely consider the attributes of buildings and psychological preferences of decision makers and combine the characteristics of different types of ventilation heat recovery devices. This approach provides scientific and reasonable recommended results in selecting heat recovery devices.

Determining Design Parameters and an Optimal Design Method for Coaxial Geothermal Heat Exchangers Using Verification Experiments and GLHEPro Numerical Analysis

In this study, we investigated the effects that are dependent on the characteristics (length, diameter, type, and flow direction in a pipe) of a coaxial ground heat exchanger, via head loss and pressure drop measurement experiments. We identified that an increase in the length, a decrease in the diameter, and counter-flow generation inside the coaxial ground heat exchanger are the main factors responsible for increases in head loss. To optimize the design of a heat exchanger via numerical analysis using GLHEPro, we performed a sensitivity analysis considering the range of EWT, the number of heat exchangers, and the interval for installation. Based on these results, we calculated a 'Pareto solution' of 3 for the number of heat exchangers, taking into consideration the total heat exchanger length and power consumption conditions. Keywords: Coaxial Ground Heat Exchanger, Head Loss, Pressure Drop, GLHEPro, Sensitivity Analysis, Pareto Solution

Design and analysis of miniature free piston Stirling engine (FPSE) for on-board power production

Free piston Stirling engine integrated with linear alternator has high efficiency, quiet operation, long durability and long life. It is flexible to use any kind of potential heat sources such as chemical energy power sources and solar power. Size, mass and less total heat exchanger area than other power converters makes the FPSE attractive to space power requirements, as soldier borne power sources and cogeneration applications. The step by step design of 100 W power generating FPSE with helium as working fluid is done in the Sage software. To get an output power of 100W, the parental and child components were suitably arranged in the modeling section and then numerically solved in the software (Sage) with various input parameters and the decision variables were optimized to get the desired objective function. The engine uses heater head of 750K at 20 bar mean charge pressure, frequency of 50 Hz and getting overall efficiency of 32%. The design consists of a displacer and a power piston supported on flexure bearings. Non – contacting clearance seals are used between internal volumes. A linear alternator is designed, which converts the piston motion into electricity. Analysis to find the behavior of alternator using FEA is also done.

Optimization of an organic Rankine cycle constrained by the application of compact heat exchangers

Recovering waste heat from the exhaust gases of heavy-duty diesel truck engines by using the organic Rankine cycle can reduce both fuel consumption and greenhouse gas emissions. The design of such systems is constrained by the space available for installation; thus, an optimization procedure is required. In this research work, a two-objective optimization, based on the maximization of power output and minimization of the total heat exchanger surface area, is implemented in the Engineering Equation Solver software package. Application of the developed procedure is illustrated in a case with an exhaust gas temperature of 394.2 °C and mass flow rate of 0.306 kg/s. Configurations both with and without a recuperator are analyzed, and four working fluids (water, ethanol, toluene, and hexamethyldisiloxane) are compared. Of these fluids, ethanol could be recommended as the best when considering the organic Rankine cycle power output and the total area/volume of heat exchangers. For a total surface area of 10 m2 in the case without the recuperator, the power output values for ethanol, water, and toluene are 17.6 kW, 17.2 kW, and 15.8 kW, respectively; with the recuperator, the power output is slightly higher, but the total area of heat exchangers is considerably larger. Again, the best working fluid is ethanol: for a total surface area of heat exchangers of 24 m2, the power output values for ethanol, toluene, and hexamethyldisiloxane are 18 kW, 17.1 kW, and 15.8 kW, respectively. The presented procedure is useful both for the conceptual design of a complete waste heat recovery unit and for the optimization of all heat exchangers.

Development of CFD model for membrane-based energy recovery ventilators

One of the methods of energy recovery in air conditioning systems is the membrane-based heat exchanger. This device uses the energy difference between two airflows (supply and exhaust air). The energy of the airflow is exchanged in the energy recovery system and does not require any external energy. This paper analyzes the numerical study of the new membrane shapes including curvature and circular, using COMSOL Multiphysics. These novel duct structures are used to improve the performance of the membrane-based heat exchanger. The model considers the mechanism of heat and mass transfers for turbulent flow. The flows in these geometries with Reynolds numbers ranging from 100 to 6000 are transitional. The low Reynolds k–w model is used. The cross-flow design is investigated under summer conditions. The flow distribution (velocity contours) is obtained. The friction factor, Nusselt numbers and Sherwood numbers in different Reynolds numbers for each cycle are calculated. The model is validated with available experimental data. After comparing and evaluating the four heat exchangers, it has been made clear that the total heat exchanger with curvature duct is more effective than other heat exchangers.

Application of absorption heat pump and direct-contact total heat exchanger to advanced-recovery flue-gas waste heat for gas boiler

This paper presents a new technology based on a direct-fired absorption heat pump and a direct-contact total heat exchanger. An analysis of existing techniques for heat recovery shows that the limiting factors of condensing heat recovery are return-water temperature and the ability of air to recover heat. In addition, severe corrosion usually exists in indirect-contact heat exchangers where the flue gas and cool water flow. This new technology solves these problems. A 29-MW gas boiler was transformed by the new technology, having been tested throughout an entire heating season. As a result, the exhaust gas of the direct-contact total heat exchanger decreased to 27.4 °C, with an average COPh and COPove,h of approximately 1.69 and 1.57, respectively. The mean heat recovered was 2.67 MW, yielding a heating efficiency increase of 11.54% and a saving in natural gas consumption of 8.75 × 105 Nm3 per year. Testing showed that the NOx reduction rate was 10.48% and the condensation water flow was 3.11 t/h. Hence, this technology achieved excellent results for both energy conservation and emission reduction, thereby proving the feasibility of its large-scale application.

Property of Odor Transfer of Total Heat Exchanger and Wakkanai Siliceous Rotor

Property of Odor Transfer of Total Heat Exchanger and Wakkanai Siliceous Rotor

Optimization of a combined cooling, heating and power system using CO2 as main working fluid driven by gas turbine waste heat

A combined cooling, heating and power system driven by marine gas turbine waste heat is proposed. The proposed CCHP system includes a supercritical CO2 (S-CO2) recompression cycle, two transcritical CO2 (T-CO2) refrigeration cycles and a steam generator. Comprehensive thermodynamic and exergoeconomic analyses are performed for the supercritical CO2 recompression cycle, transcritical CO2 refrigeration cycle and the overall system. Considering the importance of compactness and cost to the ship, the total product unit cost and total heat exchanger area per unit exergy output are proposed as the objective functions of the system optimization. Parametric analyses are conducted to study the effects of key operating parameters including the pressure ratio of air compressor, S-CO2 compressor inlet pressure, pressure ratio of S-CO2 cycle, split ratio of S-CO2 cycle and T-CO2 compressor outlet pressure on the total product unit cost and total heat exchanger area per unit exergy output. The optimum system parameters are obtained through the multi-objective optimization method based on the GA (genetic algorithm). The optimization result shows that the optimum values of total product unit cost and total heat exchanger area per unit exergy output are 10.0526 $/GJ and 0.1755 m2/kW, respectively. The result also indicates that by using the CCHP system, 4.9901 MW of power, 0.584 MW of heat capacity, and 0.627 MW of refrigeration capacity can be recovered from the exhaust gas (with the mass flow rate of 95.6102 kg/s, temperature of 466 °C and the major compositions of nitrogen 74.45%, oxygen 15.74%, carbon dioxide 4.77% and water 5.04% by mass). Furthermore, the superiority of the CCHP system is verified through comparative analyses from the viewpoints of exergoeconomic and compactness.

Exergoeconomic performance analysis and optimisation of an irreversible-closed intercooled regenerated gas turbine cycle

ABSTRACT Based on finite time thermodynamic (FTT) model for a closed irreversible intercooled regenerated (ICR) gas turbine cycle, the analytical expressions of profit rate, power and efficiency are deduced. The dimensionless profit rate can reach its extreme value while the intercooling pressure ratio gradually increases, and the value has an additional maximum, i.e. the double-maximum, while the total pressure ratio gradually increases. The finite time exergoeconomic performance is maximised by optimising four heat conductance allocations with a given total heat exchanger conductance as well as the intercooling pressure ratio. Further optimising the total pressure ratio can make the double-maximum. Some characteristic parameters’ effects on the cycle exergoeconomic performance are analysed.

Modeling, cross-validation, and optimization of a shipboard integrated energy system cooling network

This work presents the modeling, cross-validation, and thermodynamic optimization of a shipboard integrated energy system (IES) cooling network to assess (1) the practicality of a dimensionless graph-based model for scalability; (2) the reliability of different statistical metrics in cross-validation; and (3) the effects of design and operational parameters on the system thermal performance. The IES comprised two 2.5 MW induction motors representing a ship propulsion system which operated at various torques over time resulting in different heat generation profiles. A dimensionless first-law graph-based model was formulated with the lumped capacitance approach, and the unknown physical parameters were estimated using the ant colony optimizer with three different calibration metrics. The validated model was used to distribute the total heat exchanger inventory N optimally across the IES by minimizing the peak system temperature. Subsequently, the study demonstrated the robustness of the optimal heat exchanger area allocation against N and the 20× reduction in N with a tenfold increase in the motor cooling power.

A New Graphical Approach for Heat Exchanger Network Retrofit Considering Capital and Utility Costs

Development of methodologies and tools for heat exchanger network (HEN) retrofit has focused on generating retrofit solutions to address issues of vital importance to industry including energy, economy and sustainability. This work extends the use of the individual stream temperature versus enthalpy plot (STEP) to enable users to select economically feasible retrofit alternative based on capital and utility costs estimation. A new graph known as the heat exchanger area versus enthalpy plot (A vs H plot) is proposed in this work to be used in combination with the STEP diagram to enable visualisation of the area of every heat exchanger in the HEN. Note that, both graphs share the same enthalpy axis. As a result, heat exchange between the stream pairs shown in the STEP diagram can be projected to the A vs H plot. The A vs H plot contains several useful information of the existing HEN which includes the total area and the number of heat exchanger in the HEN. Firstly, retrofit options are generated by using STEP diagram based on the procedure described in a prior work. Users can later use the A vs H plot to select retrofit option which requires the minimum total heat exchanger area or to minimise the total heat exchanger area needed for the retrofit design generated based on the retrofit methodology which is introduced in this work. Capital cost needed for the retrofit options can be estimated based on total area of new heat exchangers added. Application of the combination of A vs H plot with STEP diagram on a literature case study shows that the combined graphical tools are able to provide clear visual insights to assist users identify capital-energy trade off in generating cost-effective retrofit solutions. The retrofit design and area of the individual heat exchangers in the retrofitted HEN are clearly shown in the combined graphical tools to enable users to screen the most economically viable retrofit option prior to performing economic analysis. Application of the new method on a case study shows that the annualised total cost required by the retrofit design after area minimisation is lower than that of the retrofit design before area minimisation by 3.34 %.

Transshipment Type Model for Total Site Heat Integration Using Non-Isothermal Utility Loop

There is a growing interest in developing Total Site Heat Integration methods, since Total Site Heat Integration offers an energy-saving opportunity across multiple plants beyond the traditional intra-plant plant integration. Total Site heat integration can be achieved indirectly by non-isothermal utility loop, such as hot water and thermal oil. The parameters of non-isothermal utility loop, interconnectivity patterns directly determine the energy saving and the capital cost. In this work, a transshipment type Total Site heat exchanger network (HEN) model using non-isothermal utility loop is developed. A new representation method of non-isothermal utility loop is proposed based on transshipment type HEN model to avoid non-linear terms. The model is formulated as a MINLP problem with all linear constraints. The operating cost, capital cost of heat exchangers, pumping and piping cost are holistically considered and optimized. The case study demonstrates the effectiveness of the proposed model.

Thermo-economic analysis based on objective functions of an organic Rankine cycle for waste heat recovery from marine diesel engine

This paper presents the parametric optimization and performance analysis of the organic Rankine cycle (ORC) system for waste heat recovery from marine engine exhaust. The engine exhaust heat under operating conditions has been field-measured and evaluated. The thermo-economic optimization based on multi-objective evaluations is conducted numerically. This study aims to determine the optimal design evaporation temperature and condensation temperature, and to select suitable working fluids. The cooling water loop is taken into accounted for the whole ORC system. The parametric optimization with objective functions is compared. The economic objective function is defined as the ratio of net power output to total heat exchanger area, and the comprehensive objective function is determined as the weight-sum of exergy efficiency and economic objective function. The results show that there is the optimal evaporation temperature under the fixed expansion ratio in the ORC system for achieving the maximum thermal efficiency. The optimal condensation temperature for achieving the maximum economic objective function or comprehensive objective function is determined respectively. The parametric optimization with comprehensive objective function is better. With multi-objective evaluations, R141b performs the most satisfactorily with the maximum net power output of 97 kW, followed by R113 and cyclohexane, and R600a performs the least favorably. The optimized ORC system with R141b under various operating conditions is technically feasible and economically attractive.

Performance investigation of regenerative total heat exchanger with periodic flow

This study proposes a new regenerative type of the periodic total heat exchanger system, which consists of four centrifugal fans and two fixed wheels. The total heat exchanger, which operates periodically to replace the rotation of the fixed wheel in conventional design, can save more energy from motors. The fixed wheels alternately store and release energy using the heat and moisture storage materials of aluminum and silica gel. The operation periods are 2 min, 3 min, 4 min, 6 min, and 8 min. The results show that under the temperature and humidity ratio differences of 10 °C and 4g/kg between indoors and outdoors, the operating period of 3 min has the best performance of sensible heat effectiveness, latent heat effectiveness, and total heat effectiveness. When the temperature and humidity differences increase, the optimal operating period becomes shorter. In order to increase heat effectiveness, adding another high temperature and low moisture air for regeneration in the total heat exchanger increases the latent heat effectiveness, but the sensible heat effectiveness decreases.

Total Site Heat Integration: Utility selection and optimisation using cost and exergy derivative analysis

Abstract This paper presents a new Total Site Heat Integration utility temperature selection and optimisation method that can optimise both non-isothermal (e.g. hot water) and isothermal (e.g. steam) utilities. None of the existing methods addresses both non-isothermal and isothermal utility selection and optimisation incorporated in a single procedure. The optimisation affects heat recovery, the number of heat exchangers in Total Site Heat Exchanger Network, heat transfer area, exergy destruction (ED), Utility Cost (UC), Annualised Capital Cost (CC), and Total Annualised Cost (TC). Three optimisation parameters, UC, ED, and TC have been incorporated into a derivative based optimisation procedure where derivatives are minimised sequentially and iteratively based on the specified approach. The new optimisation procedure has been carried out for three different approaches as the combinations of optimisation parameters based on the created derivative map. The merits of the new method have been illustrated using three case studies. These case studies represent a diverse range of processing types and temperatures. Results for the case studies suggest the best derivative optimisation approach is to first optimise UC in combination with ED and then optimise TC. For this approach, TC reductions between 0.6 and 4.6% for different case studies and scenarios are achieved.

Membrane-type Total Heat Exchanger Performance Simulation with Consideration of Entrance Effects

Membrane-type total heat exchanger (THX) is an air-to-air heat exchanger used to reduce the building energy consumption associated with forced ventilation by recovering both heat and moisture from ventilation air. It contains a heat/moisture exchange core made of a water vapour permeable membrane, supply outdoor air and exhaust indoor air flow through the membrane channels in the core in a crossflow manner and exchange heat and moisture across the membranes. The present work numerically investigates the airflow channel entrance effects on the THX performance. The results show that such effects on the air temperature and humidity distributions are inconspicuous and so are they on the THX effectiveness, it is therefore appropriate to use the constant Nusselt number to evaluate the THX performance.

住宅用全熱交換換気ユニットの有効換気量率測定法に関する研究 : 第2報-各種ユニットへの測定法の適用と換気回路網モデル

住宅用全熱交換換気ユニットの有効換気量率測定法に関する研究 : 第2報-各種ユニットへの測定法の適用と換気回路網モデル

住宅用全熱交換換気ユニットの有効換気量率測定法に関する研究 : 第1報-有効換気量率に及ぼす影響要素

住宅用全熱交換換気ユニットの有効換気量率測定法に関する研究 : 第1報-有効換気量率に及ぼす影響要素