Hot Heat Exchanger Research Articles

Numerical assessment of stability behaviour in supercritical CO2 based NCLS configured with heater, heat exchanger and isothermal wall as heat source

Three-dimensional numerical analysis is presented in this study to assess the transient and stability behaviour of supercritical CO2 (sCO2) based NCLs configured with three different types of heat sources, i.e., heater, a hot heat exchanger (HHX) and isothermal wall (ISO) at the source, and a cold heat exchanger (CHX) at the sink in all three NCLs. Unsteady threedimensional conservation equations (mass, momentum and energy equations) are solved to assess the transient and stability behaviour of sCO2 mass flow rate, temperature and velocity as a function of time. Further, the effect of pressure on sCO2 mass flow rate is also assessed to compare the loops performance. Performance of the loop has been studied for various heat inputs at the source by keeping constant mass flow rate and temperature at the sink. It is observed that for any boundary condition at the source, the loop experiences some initial disturbances or instabilities before reaching the steady-state. However, the time needed to attain a steady-state varies with the nature of heat input employed at the source. Results show a higher magnitude of instabilities in the Heater-CHX loop than HHX-CHX and ISO-CHX loops, and these instabilities mitigate at a faster rate in the ISO- CHX loop at all levels of heat input and operating pressure of the loop. It is also observed that as loop fluid operating pressure increases, the instability of the system decreases and the loop fluid mass flow rate increases. Further, the Nusselt number in the Heater-CHX loop is more than other loops because of its high turbulent kinetic energy. The findings of this study are validated with the published experimental and numerical data and found a good agreement.

Investigations on nonlinear processes of a Gifford-McMahon type orifice pulse tube refrigerator

The target of this investigation is to illustrate the nonlinear fluid flow, heat transfer, and vortex formation phenomena in an orifice pulse tube refrigerator by numerical simulation. Numerical results confirm that jet streaming is generated at the low-temperature end of the pulse tube in between the junction of U-shaped tube and pulse tube. The primary vortex, which is generated due to the minor loss, continuously grows because of velocity change and eventually leads to the formation of secondary eddy. Consequently, flow straighteners have been adopted at the hot side of the regenerator, hot heat exchanger, and both sides of U-shaped tube. It is noticed that, jet streaming has been suppressed at the cold end of the pulse tube. Nevertheless, the streaming effect generated due to the oscillating flow of the gas parcels within the pulse tube, and third type of streaming have not been suppressed with the flow-straightener. Additionally, the numerical simulation shows different gas flow behaviors within the pulse tube that occurs due to the oscillating pressure pulse. An experimental investigation is conducted to compare experimental results with the numerical results and a valid agreement is observed between them.

Multi objective ecological optimization of an irreversible Stirling cryogenic refrigerator cycle

The primary objective of the current study is to demonstrate the multi-objective, ecological optimization of an irreversible Stirling cycle-based cryogenic refrigerator. The novelty of the work lies in the ecological optimization of the system, where irreversibilities are considered during the study and the thermal reservoirs have finite energy. The heat source and heat sink exchange energy with the working fluid and respective thermodynamic processes are carried out. The aim is to maximize the ecological objective function and the ecological coefficient of performance, and the effect of design variables on the objective function is investigated. The heat sink capacitance rate, temperature ratio, heat source, and sink capacitance rates, and effectiveness of the hot and cold side heat exchangers are regarded as the design variables. A heat transfer search algorithm is used to optimize the objective functions, and multiple optimal solutions are presented using the Pareto optimal curve. The multi-criteria decision technique TOPSIS is employed to select the ideal solution. For an ideal point selected through TOPSIS, the system works at an optimum ECF and ECOP of 787 W and 5.9, respectively. The ECOP of the system for the current study is 1.81 times and 4.03 times higher than the existing literature. However, the maximum ECF of 1797 W or maximum ECOP of 17.2 can be obtained for the given constraints of design variables.

Thermoelectric generator for high temperature geothermal anomalies: Experimental development and field operation

In the current climate and energy context, it is important to develop technologies that permit increase the use of renewable sources such as geothermal energy. Enhancing the use of this renewable source is particularly important in some places, due to its availability and the enormous dependence on fossil fuels, as is the case of the Canary Islands. This work proposes the use of thermoelectric generators with heat exchangers working by phase change to transform the heat from the shallow high temperature geothermal anomalies on the island of Lanzarote directly into electricity, since the use of conventional geothermal power plants would not be possible because they would damage the protected environment. To bring this proposal to reality, this work has succeeded in developing and field-installing a geothermal thermoelectric generator that operates without moving parts thanks to its phase-change heat exchangers. This robust generator do not require maintenance nor auxiliary consumption, and produces a minimal environmental impact, it is noiseless, and the use of water as working fluid makes it completely harmless.The developed device consists of a thermosyphon as hot side heat exchanger, thermoelectric modules and cold side heat exchangers also based in phase change. Tests were carried out in the laboratory at various heat source temperatures and varying the number of thermoelectric modules. It was determined that installing more modules decreases the efficiency per module (from 4.83% with 4 modules to 4.59% with 8 modules at a temperature difference between sources of 235 °C), but for the number of modules tested the total power increases, so the field installation was carried out with 8 modules. After the good results in the laboratory, it was satisfactorily installed at Timanfaya National Park (Lanzarote, Spain) in a borehole with gases at 465 °C. This generator presents a maximum output power of 36 W (4.5 W per module), and is generating 286.94 kWh per year, demonstrating the great potential of the developed thermoelectric generators to build a larger-scale renewable installation.

Performance analysis and exergy assessment of an inertance pulse tube cryocooler

The world is facing the problems of the energy crisis. Thermal analysis and energy conservation of the engineering devices help to improve their performance. This paper conducted an experimental investigation for the performance analysis and exergy assessment of an Inertance Pulse Tube Cryocooler (IPTC) that uses working fluid -helium operated between 80 K cold end side temperature and room temperature.The variation of the different performance parameters like the effect of charge pressure, pulse tube volume, pulse tube length, etc., and its effect on the refrigerating effect isdescribed graphically. Exergy analysis involves the use and concepts of energy andexergy balances, enthalpy, entropy, and exergy calculations at various stages in thesystem. Exergy analysis identifies the zones of key exergy destruction that occurs insidethe system, which afterward can be subjected to its minimization to amend the systemperformance. The actual exergy efficiency value calculated for the overall system is 21.30 %. The decreasing order of exergy efficiency among the different components is acompressor (38.79 %), a hot end heat exchanger (6.19 %), regenerator, pulse tube andinertance tube (6 %), and cold end heat exchanger (2.70 %).

CLASSIFICATION OF LOCAL EXERGETIC LOSSES IN HEAT RECOVERY SYSTEMS OF DIFFERENT TYPES

The results of classification and analysis of local exergy losses in heat recovery systems of various types are presented. The combined heat recovery system of a boiler plant, designed for heating water and blast air, as well as heat recovery systems with anti-corrosion methods for protecting gas exhaust tracts, are considered. On the examples of these systems, a classification of local exergy losses was carried out and their type and place in heat recovery systems were established. For research, a complex methodology was used, combining structural-variant methods of exergy analysis with methods for presenting exergy balances in matrix form. Structural diagrams of heat recovery systems are presented and exergy equations are obtained for calculating exergy losses in places of localization. For a combined heat recovery system, a comparative analysis of local exergy losses was carried out. It has been established that the smallest exergy losses are observed in the hot air heat exchanger and in the gas heater. The total contribution to the total exergy losses of the pumping system and the piping system is quite significant for all boiler power values. With an increase in boiler power from 30 to 70% of the installed power, there is a slight increase in exergy losses in the heat recovery system and in the hot water heat recovery unit. In this section, the main exergy losses are in the pumping system and in the pipeline system. With a further increase in the power of the boiler, the exergy losses in the heat recovery system and in the hot water heat recovery unit begin to increase more significantly. In this case, the main exergy losses fall on the hot water heat exchanger. It is concluded that the optimal mode of operation of the installation is carried out at the boiler power, which is 50 ... 60% of its installed power.

Effects of Compressor Frequency on Performance of Inertance Tube Pulse Tube Refrigerator: A Numerical Study

Pulse-tube refrigerators are considered as the mainstream elements in cryogenic plants. Normally, the efficacy of the inertance tube pulse tube refrigerator (ITPTR) is considered to be the highest among other pulse-tube refrigerators. In the current study, the mechanical performance of ITPTR system is numerically investigated to identify the impact of compressor frequency. The finite volume approach (FVM) is utilized to model the whole ITPTR with the specified boundary conditions using a commercial program ANSYS. The modelled ITPTR includes an inertance tube, reservoir, pulse-tube, cold heat exchangers, after cooler, regenerator, compressor and hot heat exchangers. These coupled systems that are simulated in a steady-state to reveal the performance and cooling rate. It has been discovered that the compressor’s frequency has a significant impact on the ITPTR’s performance and cooling rate. In four distinct ways, the compressor’s frequency has been changed from 10 Hz to 100 Hz. When the compressor runs at 20 Hz, the rate of cooling is determined to be at its highest.

Heat Transfer Analysis and Performance Investigation of Generator Thermoelectric Applied in LPG Stove Waste Heat Recovery

A thermoelectric generator (TEG) can convert heat from LPG gas stoves into electricity. The application of this conversion technology consists of three major components: a hot side heat exchanger, a TEG, and a cold side heat exchanger. This study investigates the effects of TEG cold surface cooling system variations on heat transfer and the thermoelectric generator module's electric performance when applied to convert liquefied petroleum gas (LPG) stove waste heat. Four thermoelectric generator modules are placed outside the plate and connected in series to take advantage of the waste heat. Three different cooling systems are used to cool the thermoelectric generator module's cold surface: a heatsink, a heatsink with a fan, and a water block cooling system. Measurement and data retrieval are performed using the temperature and electrical output from the TEG module. Temperature and electrical output from the thermoelectric generator module are measured and data retrieved, while the heat transfer that occurs in the cooling system is calculated using the formulation. The results indicate that the cooling system's heat absorption capacity increases by more than 300% when the heatsink with a fan is used. When compared to a heatsink with a fan cooling system (i.e., 47.09 J/s), using a water block as a cooling system can increase heat absorption by 27% or a value of 60.00 J/s. Based on the performance of the thermoelectric generator module in generating electricity, it is clear that when comparing an air-cooling system to a water block-based cooler, the water block-based cooler produces more power. Water cooling is the optimal method for obtaining a high-power output from the TEG module when this conversion technology is applied to convert LPG stove waste heat to electrical energy.

Design and experimental study of an outdoor portable thermoelectric air-conditioning system

This study aims to identify suitable microclimate cooling systems to reduce heat stress and improve human thermal comfort. A portable thermoelectric air conditioner was developed for local cooling of the human body. Effects of core components thermoelectric refrigerators (TECs), hot end heat dissipation, intake flow and cold end heat exchangers on TEAC performance. It is shown that, remarkably, this operating voltage can be distinguished from the optimal voltage for the maximum operational performance of TEAC. When the TECs operating voltage is 4V, the maximum COP is 2.2, and the best operating voltage is 10V, the maximum cooling capacity is 26.7 W (COP=0.92). Simulation data show that the area of the diffuser can effectively control the contact between the air and the cooling surface with an error of less than 10% compared to the experimental results. The fans and radiators attached to the hot side of the TEM play an important role in keeping the temperature difference on the hot side of the TECs as small as possible, by dissipating the heat generated on the hot side of the TEM to the external environment. In addition, the experimental refrigeration capacity is greater than 26.7 W and the new system has ultra-quiet operation at large refrigeration capacity, which has promising potential for advanced refrigeration, building air conditioning, ventilation systems and other applications. • Thermalelecrtic air conditioner (TEAC) can achieve a cooling capacity of 26.7W and a cooling coefficient of 0.92, enabling local cooling of the human body. • The maximum cooling capacity of thermoelectric refrigerator varies nonlinearly with the surface area and height of thermoelectric leg. • The increase of cooling capacity decreases with the increase of intake flow rate. • Increasing the strength of heat dissipation at the hot end of the thermoelectric cooler has a larger effect on the TEAC cooling capacity than on the cooling coefficient.

Design and optimization of heat exchanger in coaxial pulse tube cryocooler working above 100 K

The coaxial pulse tube cryocooler (PTC) has the advantages of without moving parts at the cold end, compactness and high-efficiency, it shows great application potential in many fields. The present work numerically and experimentally investigated a coaxial PTC working at temperature range from 90 K to 260 K. To improve its efficiency, the exergy analysis method was used to study the distribution of available energy loss in the coaxial PTC. To reduce one of the main available energy losses coming from the heat exchanger, three types of heat exchanger, slit, circular hole (CH) and copper mesh (CM), were analyzed and optimized based on the law of conservation of energy. Finally, two different cold end and hot end heat exchangers are designed respectively in the experiment. The results show the optimized pulse tube cooler can supply 50 W cooling power at 185.3 K with 200 W input power. To the best of our knowledge, its relative Carnot efficiency (16% at 165 K) lies one of the best results in the world. The experimental results also show that the refrigeration efficiency of the present PTC could be much improved by optimizing its operating parameter. In summary, the present PTC can work efficiently at a wide temperature range from 90 K to 260 K, which shows great potential candidate for small refrigerators such as vaccine preservation, organ freezing transportation and outdoor preservation of wildlife samples.

Waste heat recovery of a wind turbine for poly-generation purpose: Feasibility analysis, environmental impact assessment, and parametric optimization

World energy markets are gradually shifting in favor of wind-based power plants. A decrease in global warming can be attributed to the reduction of dependence on fossil fuels as a result of wind energy. In this regard, utilizing the waste heat from the generator of a wind turbine has recently been considered and only a few studies have been done about it. This shortage has made clear the need for further studies. In the present research, a novel poly-generation system is introduced based on the waste heat recovery of a wind turbine to fill this research gap because the waste energy of a wind turbine has not been utilized for the poly-generation purpose. A novel power-cooling production absorption cycle and a domestic hot water heat exchanger are utilized for this purpose. Also, the produced power in the absorption cycle is sent to a reverse osmosis desalination unit for freshwater production. The considered system is comprehensively studied from energy, exergy, environmental, and exergo-economic standpoints. In the average wind speed of 10 m/s, the exergy efficiency, unit cost of products, reduction in CO2 emission rate, and payback period are seen to be 36.76%, 20.25 $/GJ, 2452801 kg/year, and 2.301 years, which shows its performance is better than the previous studies based on the waste heat recovery of a single wind turbine.

Synthesis of utility supply chain network and industrial symbioses for heat integration

This paper presents a method for integrating the periodic heat demand of sets of co-located process plants with a biomass-based utility supply chain network. The methodology adopted involves generating a composite superstructure, which combines the supply chain model and the multi-period interplant stage-wise superstructure model. Supply nodes in the supply chain are linked to the central utility hub through a set of transportation/energy transmission options, while the utility hub is linked to a set of co-located process plants through fluid transmission pipelines. The developed model was applied to a hypothetical case study involving three co-located process plants. The solution generated involves the use of biomass, transported by truck. For hot utility generation at the utility hub, corn stover is used in all seasons (63.4% of the total feedstock), glycerol in seasons 1 and 3 (27.1% of the total feedstock) and wood only in season 1 (9.5% of the total feedstock). In terms of hot utilities generated from the selected feedstocks, only high- and low-pressure steam were selected. Of the 14 heat exchangers selected, 3 involve interplant heat exchange at the utility hub, 2 are hot utility heat exchangers, 1 is cold utility exchanger and 8 are intra-plant heat exchangers. The developed method illustrates how seasonality in availability of bio-based renewable energy sources and the periodicity of process plants operating parameters influence the heat demand of co-located process plants.

Waste heat recovery of two solar-driven supercritical CO2 Brayton cycles: Exergoeconomic analysis, comparative study, and monthly performance

The waste heat from a supercritical Brayton cycle has a great potential to be recovered. However, there is a lack of research regarding the utilization of these cycles in multi-generation systems. In addition, different multi-generation systems based on supercritical Brayton cycles have not been compared in the literature. In the present study, two multi-generation configurations based on two supercritical Brayton cycles, namely regenerative (configuration 1) and recompression (configuration 2), are proposed and compared from thermodynamic and exergoeconomic standpoints. In both configurations, an organic Rankine cycle, a domestic hot water heat exchanger, and an LiCl-H2O absorption refrigeration system are employed to convert the waste heat of the two supercritical Brayton cycles into useful energy. Meanwhile, a thermoelectric generator is used instead of a condenser for efficient waste energy recovery of the organic Rankine cycle. The generated electricity by the organic Rankine cycle and thermoelectric generator is used to generate hydrogen in a proton exchange membrane electrolyzer. In addition, a direct integration method is employed to integrate the two supercritical Brayton cycles with a solar power tower as the heat source. The final results regarding the net output power, exergy efficiency, and economic performances of the two configurations reveal the superiority of configuration 2 over configuration 1. Net output power and exergy efficiency of configuration 2 are 6.55 MW and 4.06% points higher than configuration 1. Moreover, total cost rate and unit cost of products for configuration 2 are 0.4 $s-1 and 10.03 $GJ-1 lower than configuration 1. On the other hand, cooling, heating, and hydrogen rates of configuration 1 are respectively 2.93 MW, 4.23 MW, and 2.84 kgh-1 higher than configuration 2. Moreover, the monthly analysis of the two systems for Dhahran city (26.3°N/50.2°E) as a case study indicates that the best thermodynamic performance of the systems is achievable in February, June, and July.

Comprehensive Review on Solar Stills—Latest Developments and Overview

This up-to-date and comprehensive literature study provides a rich overview of recent developments in several solar still types. This review examines a large number of theoretical, experimental, and computational studies connected to the single-slope, double-slope, solar still with a condenser, hybrid, and other limited types of solar stills. To make the work more relevant to readers, the authors provide a panoramic view of solar still varieties as well as a complete overview of the most recently published review papers in the solar stills field. The most important conclusions drawn from prior research are carefully discussed and outlined in a useful table to give interested researchers a good road map of many various sorts of solar stills and encourage them to pursue new research avenues in this field. The foremost key results of the evaluated work are presented in a table for readers’ convenience. The results indicated that the absorption in the basin was improved by adding charcoal, matt, sponge, jute and cotton clothes, dye, wick, porous or energy-storing material, black rubber, and floating absorber sheet. Moreover, the productivity of solar stills was significantly improved by using the inclined external flat-plate reflector, combined stills, condenser, sun tracking system, reflectors, greenhouse, hot water tank, solar collector, heat exchanger, and solar pond. Further, heat loss was minimized by re-utilizing the latent heat of condensation, cover cooling, and increasing the insulation thickness.

Digital twin driven life-cycle operation optimization for combined cooling heating and power-cold energy recovery (CCHP-CER) system

Natural gas is expected to be the dominant fossil fuel in the coming decades. Improving the sustainability of natural gas usage is imperative to achieving a low-carbon society. This study proposes a combined cooling, heating, and power incorporating cold energy recovery (CCHP-CER) system to utilize both heat and cold energies of liquified natural gas (LNG) in a cascade way. The system is comprised of four subsystems, namely, gas turbine, water-lithium bromide absorption chiller, hot water heat exchanger, and cold energy recovery unit. A digital twin approach is applied to this system for real-time and life-cycle operational optimization. The cascade forward neural network (CFNN) is employed to construct the virtual representation while a parameter-free intelligent algorithm is adopted to seek the optimal operating parameters. Key results from this study revealed that incorporating the cold energy recovery (CER) unit produces additional electricity and cooling effect, bringing a 0.72 % improvement in the average daily primary energy saving rate (PESR). The digital twin-based optimization process updates the optimal operation parameters in time when the system suffers degradation. Consequently, the degradation performance is alleviated by the living parameters. Compared to static model-based optimization, the digital twin-based optimization improves the daily PESR by 2.23 %, 0.35 %, and 1.53 % during respective winter, summer, and transition days, particularly when the compressor and turbine of the gas turbine suffer degraded efficiency of −2 %.

Heat transfer analysis cabinet-type ERK solar dryer machine for drying agricultural products

The Cabinet-type ERK solar dryer is manufactured by a temperature distribution process so that the temperature inside the appliance is well distributed. The cabinet-type ERK solar dryer comprises several components to maintain the water content, including a drying oven, air blower, heat-resistant pipe, hot water pump, thermostat, heat exchanger, and heater. These tools are used to convert heat radiation into conduction or convection so that the dried agricultural products' water content is relatively low. The data needed to show the quality of the tool include temperature on temperature received by the wall (Tw), absorbent plate (Tp) and room temperature (Tr). And as for other supporting data including the environmental air/ ambient temperature (Ta) and solar irradiation (I) for optimal tool usage time.
 The experiment results for 5.5 hours, as many as 23 measurements with time interval 15 minutes, obtained a relatively unchanged temperature distribution. During that time, the average temperature received by the wall (Tw) was 41.26 °C, while the middle plate temperature (Tp) was 40.65 °C and room temperature (Tr) was 40.71 °C. Thus, the temperature in the Cabinet-type ERK solar dryer is well distributed. The distribution percentage between wall temperature and plate temperature is 98.52 %, while wall temperature and room temperature are 98.67 %. The result indicates that the Cabinet-type ERK solar dryer is potential as a drying device for agricultural commodities. It is hoped that the Cabinet-type ERK solar dryer will be an alternative to a drying system that can improve the quality of agricultural commodities for farmers in Indonesia

Influence of foamed metal core flow heat transfer enhancement on the performance of thermoelectric generators with different power generation characteristics

• Core flow heat transfer enhancement with foamed metal has been studied by experiment. • The effect of different PPI of the foamed metal has been analyzed. • The effect of different filling rate of the foamed metal has been analyzed. • PEC and OP are used to analyze the performance of enhancing heat transfer at core flow. With the development of science and technology, how to recycle the waste heat of high-temperature exhaust gas discharged from daily life and industry has become the focus of attention of the scientific community. Using thermoelectric generation technology to recover and utilize the waste heat of high-temperature gas of this part can effectively improve the efficiency of energy utilization. The thermoelectric generator (TEG) is modified by inserting the foamed metal copper (FMC) at the core flow field of the heat exchanger tube to enhance the heat transfer, and the heat exchange capacity of the heat exchanger can be effectively improved, so that the power generation efficiency of the TEG can also be effectively improved. At the same time, the core flow filling method can also reduce the increased amplitude of the back pressure of the TEG. Therefore, in this article, experiments have been conducted to investigate the effect of improved heat transfer of FMC at the core flow field on the performance of TEG with different power generation characteristics. We first evaluate the effect of different enhanced heat transfer conditions on the heat transfer capacity of TEG hot end heat exchanger with the Performance Evaluation Comprehensive (PEC) evaluation method. The results showed that the enhanced heat transfer by the FMC at the core flow field can significantly improve the heat transfer capacity of the heat exchanger. Then we use the Overall Performance (OP) evaluation method to evaluate the effect of TEG on its performance under different enhanced heat transfer conditions. The results showed that the power generation of the TEG filled with FMC at the core flow field is higher than that of the unfilled TEG, and the filling of FMC with a high filling rate and high pore density can significantly improve the power output and power generation efficiency of the TEG. However, by evaluating the TEG filled with FMC at the core flow field through the OP evaluation method, it was found that the use of FMC with a low filling rate and low pore density can better improve the overall performance of TEG.

Analysis of a scheme of reliable and safe heat supply of residential buildings with independent connection of the heating system

The scheme of heat supply of residential buildings with independent connection to external heating systems is considered, providing reliability of heat supply and required comfort in indoor premises in case of cold snaps after the official end of the heating season or before its beginning through supplying water from the return main of the heating system after the hot water heat exchangers. It is established that an additional decrease in the temperature of the return network water that occurs in this mode allows in most cases to carry out its primary heating in the lower heater of the condensing turbine without a concomitant increase in fuel consumption and thereby increase the coefficient of its use at the CHPP. The parameters of the main points of the thermodynamic Rankine cycle for the option under consideration are determined through the example of a T-100-130 turbine, a flow diagram of heat carriers is constructed, and calculations are carried out to determine the most important technical and economic indicators of the heat-generating plant of the CHPP in the climatic conditions of Moscow. It is proved that when all heat consumers are connected to the heat network according to the scheme under consideration, the maximum share of usefully used condensation heat under transition conditions for primary heating of supercooled return network water to the level corresponding to the temperature schedule can amount to almost a half, if the structure of the energy balance of consumers corresponds to the one characteristic for residential buildings. It is noted that the implementation of the proposed design of heat points allows to increase the efficiency of the CHPP and (or) the heat supply organization by obtaining additional revenue for the heat extracted from the network wastewater after the hot water heaters, without increasing fuel costs and with minimal capital costs for additional equipment (pump, regulator, frequency-controlled drive).

Contribution to research on ground heat storages as part of building energy systems using RES

Contribution to research on ground heat storages as part of building energy systems using RES

Design Optimization of Tubular Heat Exchangers for a Free-Piston Stirling Engine Based on Improved Quasi-Steady Flow Thermodynamic Model Predictions

This paper presents the design optimization of a heat exchanger for a free-piston Stirling engine (FPSE) through an improved quasi-steady flow (iQSF) model and a central composite design. To optimize the tubular hot heat exchanger (HHX) design, a design set of central composite designs for the design factors of the HHX was constructed and the brake power and efficiency were predicted through the iQSF model. The iQSF model is improved because it adds various heat and power losses based on the QSF model and applies a heat transfer model that simulates the oscillating flow condition of an actual Stirling engine. Based on experimental results from the RE-1000, an FPSE developed by Sunpower, the iQSF model significantly improves the prediction error of the indicated power from 66.9 to 24.9% compared to the existing QSF model. For design optimization of the HHX, the inner diameter and the number of tubes with the highest brake power and efficiency were determined using a regression model, and the tube length was determined using the iQSF model. Finally, the brake output and efficiency of FPSE with the optimized HHX were predicted to be 7.4 kW and 36.4%, respectively, through the iQSF analysis results.