Secondary Heat Exchanger Research Articles

Investigating the power and efficiency of the 3D model of the concentrated photovoltaic thermoelectric hybrid system and estimating the power consumption of the water pump for cooling

Solar energy is one of the most useful types of renewable energy. Solar cells are being used to convert solar energy into electricity. By focusing the radiation on the cells, more energy is radiated in a smaller area of the cell which is called concentrated photovoltaic (CPV). Due to the concentration of radiation, the temperature of the cell rises which can be converted into electricity through thermoelectric generators (TEG). The present study is a hybrid system of solar cell, thermoelectric generator, and heat exchanger (CPV-TEG). By this survey being created, it was revealed that the combined power produced by the CPV-TEG reaches its maximum value at concentration ratio of 40. This increase continues with the increase in fluid flow rate. however, according to the power consumption of the pump, it was observed that in all types of heat exchangers, an increase in flow rate of more than 8 liters per hour reduces the output power of the system. The replacement of the secondary heat exchanger with the primary one illustrated that the increase of the channels in the exchanger, despite the increase in the power consumption of the pump, causes a very small increase in the output power and efficiency of the system. Moreover, replacing the tertiary heat exchanger instead of the secondary exchanger showed that changing the direction of fluid output increases the power consumption of the pump in high flow rates.

Thermal performance of three-wheel and split-wheel air cycle systems for a civil aircraft environmental control system (ECS)

The conventional approach of regulating cabin temperature and pressure on aircraft is to utilize engine-bleed air through an environmental control system (ECS). The extraction of bleed air from the engine leads to a decrease in thrust and an increase in drag on the ECS ram air duct, resulting in higher fuel consumption. Consequently, the ECS transitioned from being engine-powered to being electrically powered. In this study, the thermodynamic characteristics of three-wheel and split-wheel air cycle systems (ACSs) with a high-pressure water separation system (HPWS) were investigated by developing a parameter decomposition model and an iterative algorithm using MATLAB for a state-of-the-art electrically driven ECS (EECS) on the Boeing 787 Dreamliner. The efficiency of the ACS was assessed by establishing analytical correlations for the coefficient of performance (COP) using relevant literature on endo-reversible thermodynamic model (ETM). By employing these analytical correlations, the thermal performance of both ACSs can be accurately predicted without the need for system modeling and simulation, considering variations in the input variables and operating conditions, such as the temperatures of fresh air and ram air, the ratio of the mass flow rates of ram air and fresh air, and component parameters, including the efficiencies of the primary and secondary heat exchangers and the pressure ratios of the fan and compressor. The implementation of a split-wheel ACS instead of three-wheel ACS in the Boeing 787 EECS led to an improvement in the COP from 0.31 to 0.43, and also resulted in a reduction of 14.35 % in the input power.

CFD investigation on start-up transient of HPR1000 secondary side passive residual heat removal heat exchanger

In advanced pressurized water reactor HPR1000, the secondary side passive residual heat removal heat exchanger (SPRS HX) is a crucial component. It removes the decay heat using boiling and convection heat transfer in the event of accidents. The robust functioning of the SPRS HX significantly influences overall reactor safety. To investigate the thermal hydraulic attributes of SPRS HX, computational fluid dynamics (CFD) is used in this study. The tube region is simulated using the porous media method (PMM). To model the two-phase flow in the tank, the drift flux model (DFM) is employed. The assessment of heat transfer rate from the primary to the secondary sides is conducted by empirical correlations. The governing equations are addressed through the utilization of FLUENT. Specifically, the momentum and energy equations are augmented with additional source terms that account for flow resistance and heat transfer in the tube region. These modifications are enacted through User Defined Functions (UDF). Three-dimensional profiles of the void fraction, fluid temperature and velocity are acquired, allowing for a comprehensive analysis of the heat transfer attributes of tube region.

EXPERIMENTAL AND NUMERICAL STUDY ON EFFECTS OF NEW-GENERATION FINNED HEAT EXCHANGER ON THERMAL PERFORMANCE OF THERMOELECTRIC COOLING SYSTEMS

In this study, an attempt has been made to increase the efficiency of the thermoelectric refrigerator by designinig a new-generation finned heat exchanger. Surface extension, which is one of the most applied passive heat transfer enhancement techniques, was applied for this finned heat exchanger. In this application, the heat absorbed from the cooling room is transferred to the external environment more effectively. In addition, by using an external thermoelectric element (which is installed with the secondary heat exchanger), the heat exchanger cools down faster and the heat is transferred to the environment more quickly. The manufactured cooling system was tested experimentally under different working conditions, including natural and forced convection. The effects of air velocity and applied voltage to the external TE module on thermal performance were examined. Additionally, the external finned heat exchanger has been simulated and heat transfer characteristics have been evaluated using computational fluid dynamics. The lowest and highest COP values have been obtained as 0.003 and 0.011, respectively, when the external TE module has been passive. By providing 12 V for the external TE module, the lowest and highest COP values have been observed as 0.0031 and 0.0042, respectively. In addition, the importance of surface extension applications for the efficient operation of thermoelectric elements has been emphasized.

Optimization of a Reverse-Brayton cycle with inter-cooling and regeneration

A Reverse-Brayton cycle represented by the B787 electrical driven environmental control system is used as the analysis object, including the thermodynamic process of two-stage compression, intercooling, and regeneration. An analytical expression for the thermodynamic performance of the cycle is derived based on the endoreversible thermodynamic analysis model (ETM). Combined with a genetic algorithm, an ETM-based optimization approach (ETM-OA) is proposed. Using this method, it is found that the coefficient of performance is increased by 34.1 % and 48.4 % under two typical flight conditions, respectively, and the corresponding system entropy generation number is reduced by 30.2 % and 51.1 %, respectively. Both ETM-OA and entropy generation analysis show that the electric supercharging module, secondary heat exchanger, and air cycle machine are key components of the system. This study provides a convenient method for obtaining the thermal power conversion mechanism of complex thermal cycles and conducting optimization analysis.

A comprehensive assessment of energetic and exergetic performance for the dehumidification system of a processed pistachio production unit

AbstractThe present study aims to conduct a comprehensive evaluation of the energetic and exergetic performance of a dehumidification system utilized in the processing of raw pistachios. The assessment involved the application of the first and second laws of thermodynamics to calculate the exergy aspects of each component of the system, including input and output exergy rates, output/input exergy efficiency, product/fuel exergy efficiency, exergy destruction rate, exergy loss rate, exergy improvement potential rate, and specific exergy consumption. Furthermore, the effect of variations in reference state temperature on the exergy parameters was also investigated. The results indicated that the pre‐dryer chamber had the highest input exergy rate among all the components of the dehumidification system. The product/fuel exergy efficiency is specified to be 35.10%, 9.47%, and 60.43%, for the electro‐fan, heater, and pre‐dryer chamber, respectively, while their output/input exergy efficiency are 87.87%, 22.10%, and 56.28%, respectively. The values of the exergy destruction rate of these components are 0.83, 147.14, and 1.12 kW whereas the exergy loss rate values are found to be 0.03, 4.12, and 9.24 kW, respectively. The improvement potential rate values of these components are obtained to be 0.10, 117.83, and 4.53 kW, while the amount of specific exergy consumption for the dehumidification system is determined as 481.85 kJ/kg. The study also reveals that the exergy parameters vary with changes in reference state temperature and that the exergy efficiencies decrease linearly as reference state temperature rises. Therefore, the findings of this investigation demonstrate the potential for using exergy analysis as an effective tool to improve the performance of dehumidification systems in industrial settings, specifically in the production of pistachios.Practical applicationsPistachio nut known as green gold because of its high economical value, is one of the popular nuts over the world. Dehumidification system based on drying technology could be used in food industry with many distinct advantages for processing of particulate crops like pistachios. For a comprehensive assessment of this system, analysis of the first and second laws of thermodynamics is applied. Exergy aspect based on the thermodynamic analysis the is an important stage for designing, modeling, optimizing, and performance assessment of the dehumidification system to produce processed pistachio. The results of this study show that the performance of dehumidification system could be improved by incorporating a steam compressor, a secondary heat exchanger, self‐heat recuperation technology, and a pinch method. It is believed that such a study would contribute to the industrial exploitation of pistachio which can provide insight into decreasing energy consumption and reducing capital costs for engineers and factory owners.

Evaluation of Aircraft Environmental Control System Order Degree and Component Centrality

Air cycle systems (ACSs) are primarily used in aircraft environmental control systems (ECSs) to provide a suitable cabin temperature and pressure environment for passengers and avionics. It comprises heat exchangers, compressors, turbines, water separators, and various other components that are interconnected to form an information-transmission network. Traditional research on ACSs has focused primarily on their thermal performance. This study abstracted ACSs into network graphs based on their information-transmission characteristics, determined the weight of each information-transmission route using the fuel weight penalty method, calculated and compared the order degree of different ACSs using the structure entropy method, and measured the importance of each component using centrality for the first time. The results showed that the order degree of the ACSs gradually increased with an increase in the number of wheels in the air cycle machine (ACM), and ACSs with high-pressure water separation had a higher order degree under wet conditions than under dry conditions. Moreover, based on the centrality of each vertex in the graphs, the ACM and secondary heat exchanger in the ACS were fundamentally important and should be focused on during the system design. The methodology proposed in this study provides a theoretical basis for the evaluation of the ACS organizational structure and the design performance of components.

Simultaneous optimization of working fluid and temperature matching for heat pump assisted geothermal cascade heating system

The heat pump assisted geothermal cascade heating system (GCHS) has a promising prospect in space heating. In this paper, considering thermodynamic, economic and environmental performance, the optimal working fluid from four hydrocarbon candidates and temperature-matching for the GCHS are determined simultaneously based on multi-objective optimization and grey relational analysis. The results show that according to the optimal compromise solutions, the GCHS with R600 has the highest thermodynamic performance (COPtot) of 22.58 and the least annual carbon emission (ACE) of 2.80 × 103 ton while R290 has the largest net present value (NPV) about 45.83 × 106 CNY. Additionally, all temperature variables considered generally tend to reach their extreme value except for the temperature lift of middle circulation water in the secondary plate heat exchanger. The optimal working fluid based on comprehensive performance is considered to be R600 with the largest grey relational degree of 0.752. Besides, the global sensitivity analysis on the GCHS with R600 indicates that the pinch point temperature difference of condenser is the most important influential parameter for COPtot with total Sobol index about 0.918 and the geothermal tail water temperature plays a significant role for both NPV and ACE with total Sobol index up to 0.806 and 0.992, respectively.

Investigation of an innovative Canadian well system combined with a frozen water/PCM heat exchanger for air-cooling in hot climate

In recent years, due to many reasons, such as environmental and economic problems, the use of shallow geothermal as a clean energy source has been of great interest inside the scientific community. However, the main targeted application is air cooling and heating in buildings by using a buried pipe in the ground known as Earth to Air Heat Exchanger (EAHE). This system (EAHE) alone cannot fulfill the comfort conditions in countries characterized by hot and cold climates, and an auxiliary system is required. The present work proposes a new hybrid system consisting of coupling the EAHE (primary system) with a concentric two pipes heat exchanger (secondary system). The inner pipe has multiple longitudinal fins filled with frozen water or a mixture of ethylene glycol and water as a phase change material (PCM). The air is cooled when exchanging heat with a frozen PCM in the secondary heat exchanger (Water/PCM HEX). A theoretical investigation of the proposed hybrid system has been carried out. However, transient models have been developed for both heat exchangers, and the nonlinear equations obtained have been solved using numerical methods. The simulation of the behavior of this hybrid system located in Madinah city (Kingdom of Saudi Arabia), presenting a hot climate, has been carried out. The effect of geometrical parameters and operation conditions on the outlet air temperature and the operation period has been investigated. The study results show that the convective heat transfer coefficient is significant in the Water/PCM HEX. As long as its value is low, the cooling is not significant; as shown by decreasing the freezing temperature from 0 °C to −10.71 °C, the gain in the outlet air temperature dropping is <1 °C. When the external pipe diameter has been reduced from 8 to 6 in., the air is cooled down by almost 5 °C. The proposed system presents an attractive cooling solution during peak periods, especially for hot climates less severe than Madinah.

Experimental and numerical study on the heat transfer performance of the radiant floor heating condenser with composite phase change material

• A novel ASHP system integrated with RFHC and CPCM is proposed. • The RFHC system is feasible and has high energy efficiency. • The RFHC system maintains the indoor air temperature stability during defrosting. • A numerical model of the RFHC is established and validated to be credible. • The optimal operating condition and structural scheme are obtained. Traditional hot-water ASHP systems have disadvantage of low energy efficiency due to the requirement of secondary heat exchange. To maintain the stability of indoor air temperature during defrosting, the existing ASHP systems adopt heat exchanger to store heat, which increases the system complexity. To overcome these obstacles, a novel ASHP system integrated with radiant floor heating condenser (RFHC) is proposed, which uses refrigerant as working fluid to exchange heat with indoor environment directly. In addition, the composite phase change material (CPCM) is added in the RFHC for heat storage. Experiments are conducted and results show that compared with traditional ASHP systems, the proposed system has higher energy efficiency and can reduce indoor air temperature fluctuation under defrosting condition. A detailed numerical model of the RFHC is established and validated with the experimental data, and then the impacts of the operating and structural parameters on the heat transfer performance of the RFHC system are investigated. Results show that under the indoor air temperature of test room keeps at 18.0 °C, the optimal operating condition of this system is the condensing temperature with 38.0 °C and the refrigerant mass flow rate with 3.8 kg h −1 . The optimal structural scheme of the RFHC is the copper pipe spacing with 0.25 m and the length of copper pipe with 12.0 m.

Analysis and experimental investigation on the subcooling of liquid oxygen propellant

The isobaric subcooling cryogenic propellants are of higher density, lower vapor pressure and higher sensible cooling capacity over their saturated state, which could bring beneficial impacts on the vehicle weight, engine performance and storage time. Among several subcooling methods, pumping decompression method and heat exchange method are emphatically compared, and three system schemes including subcooling before, during and after loading are illustrated and analyzed. For the target of rapidly obtaining subcooled LO2 below 70 K, the simultaneous subcooling scheme with an atmospheric and a subatmospheric LN2 bath heat exchangers is recommended, where the water-ring vacuum pump is adopted to realize the depressurization. A semi-industry scale experiment facility was designed and built up. Results show that, with conditions of LO2 flow rate ranged from 0.2 L/s to 2.7 L/s, the temperature of LO2 at the outlet of the secondary heat exchanger was always below 70 K, successfully verifying the feasibility and effectiveness of this subcooling system. The minimum subcooling temperature of LO2 was about 66.6 K at around 2.2 L/s (the rated flow rate was designed as 2.0 L/s), indicating the reasonability of the system design. The present study can provide reference for the future applications of the subcooling cryogenic propellants.

Good, Better, Best: How Evolution Optimizes Anatomy and Action

Good, Better, Best: How Evolution Optimizes Anatomy and Action

A novel refrigerant-direct radiant cooling system: Numerical simulation-based evaluation

• A novel refrigerant-direct radiant cooling system is proposed. • The temperature distribution of the RDRC terminal surface is homogenous. • The mathematical and economic models of this terminal are established. • The sequencing of impact factors and the optimal structure are obtained. Split air-conditioners have deficiency in thermal comfort due to draught sensation and fan noise. The existing radiant cooling systems adopt chilled water as circulating medium, resulting in low energy efficiency because of the requirement of secondary heat exchange. To address these problems, a novel refrigerant-direct radiant cooling (RDRC) system is proposed. Experiments are conducted in a climate chamber to evaluate the thermal performance of this system. Results show that the RDRC terminal surface temperature is distributed homogenously and this system has excellent stability. The mathematical and economic models of this terminal are established and the mathematical model is validated with experimental data. The effects of different structural parameters on thermal and economic performances of the RDRC system are investigated, and then this terminal is optimized by orthogonal design method. The cooling capacity for per exterior area is considered as objective function and the initial cost less than 121.1 $ is taken as constraint condition. Results indicate that the fin height of 40.0 mm, the copper pipe diameter of 6.0 mm, the copper pipe spacing of 40.0 mm and the aspect ratio of 0.88 are recommended.

Experimental study and thermo-economic analysis of a novel radiant-convective cooling system

• A novel radiant-convective cooling system is proposed. • The thermal comfort, energy and economic performance are experimentally studied. • The proposed system has better indoor thermal comfort than split air-conditioners. • The proposed system has higher energy efficiency ratio than split air-conditioners. Split air-conditioners have limitations in terms of energy efficiency and local comfortability. Radiant cooling systems (RCSs) cannot be used in most residential buildings, due to its lack of space for a central plant room to achieve secondary heat exchange. To overcome these defects, a novel radiant-convective cooling system with the refrigerant-cooling radiant terminal (RCRT) was proposed, which took the advantages of both split air-conditioners and RCSs. Experiments were conducted in a climate chamber to investigate the thermal comfort performance, energy efficiency ratio and economic performance of the proposed system, in comparison with split air-conditioners. The results indicated that the RCRT cooling system could improve the indoor set temperature from 26°C to 28°C, under the same indoor thermal comfort as split air-conditioners. Additionally, the proposed system had higher energy efficiency ratio than split air-conditioners, and the energy saving potential of this system was 8.4%. The initial cost of the RCRT cooling system was higher than split air-conditioners, however, its life cycle cost was lower. The payback period of using the proposed system to replace split air-conditioners was 2.4 years, indicating that adopting the RCRT cooling system was more economical.

Performance analysis of the refrigerant-cooling radiant terminal: A numerical simulation

• A novel refrigerant-cooling radiant terminal system is proposed. • A numerical model is established to describe the heat transfer characteristics. • The proportions of the sensible, latent and radiant cooling capacity are obtained. • A method using determining the design parameters of this system is provided. • A characteristic equation is proposed to evaluate the cooling performance. The existing radiant cooling systems have the drawback of low energy efficiency due to its secondary heat exchange via chilled water. To overcome this dilemma, a novel refrigerant-cooling radiant terminal (RCRT) system utilizing the refrigerant as direct medium is proposed. A detailed numerical model is established to describe the heat transfer characteristics of this system and validated with the experimental data. The influences of the operating parameters and indoor ambient parameters on thermal performance of the RCRT system are analyzed based on the numerical model. Results show that the proportion of sensible, latent and radiant cooling capacity of this system is 55.5%, 17.3% and 27.2%, respectively, which indicates that natural convection is the main contributor in the heat transfer process. Additionally, a method for design parameters determination of the RCRT system is provided and a simplified characteristic equation is proposed to conveniently evaluate the cooling performance of this system in engineering application. The comparisons of cooling performance are conducted by an assessment index between the RCRT system and other cooling systems. Results show that the cooling capacity per unit projected area of the RCRT system is superior to chilled water radiant cooling systems, while inferior to forced-convection air-conditioning systems.

Development of a Low-Cost Biomass Furnace for Greenhouse Heating

The energy crisis and increasing fossil fuel prices due to increasing demands, controlled supplies, and global political unrest have adversely affected agricultural productivity and farm profitability across the globe and Pakistan is not an exception. To cope with this issue of energy deficiency in agriculture, the best alternate strategy is to take advantage of biomass and solid waste potential. In low-income countries such as Pakistan, the greenhouse heating system mostly relies on fossil fuels such as diesel, gasoline, and LPG. Farmers are reluctant to adopt greenhouse farming due to the continuously rising prices of the fossil fuels. To reduce reliance on fossil fuel energy, the objective of this study was to utilize biomass from crop residues to develop an efficient and economical biomass furnace that could heat greenhouses to protect the crop from seasonal temperature effects. Modifications made to the biomass furnace, such as the incorporation of insulation around the walls of the furnace, providing turbulators in fire tubes, and a secondary heat exchanger (heat recovery system) in the chimney, have increased the thermal efficiency of the biomass furnace by about 21.7%. A drastic reduction in hazardous elements of flue gases was observed due to the addition of a water scrubber smoke filter in the exit line of the flue. The efficiency of the biomass furnace ranged from 50.42% to 54.18%, whereas the heating efficiency of the diesel-fired heater was 71.19%. On the basis of the equal heating value of the fuels, the unit material and operating costs of the biomass furnace for wood, cotton stalks, corn cobs, and cow dung were USD 2.04, 1.86, 1.78, and 2.00 respectively against USD 4.67/h for the diesel heater. The capital and operating costs of the biomass furnace were about 50% and 43.7% of the diesel heater respectively, resulting in a seasonal saving of about 1573 USD. The produced smoke was tested as environmental friendly under the prescribed limits of the National Environmental Quality Standards (NEQS), which shows potential for its large-scale adoption and wider applications.

The efficiency of thermosyphon solar water heating system and traditional solar water heating system

Loop thermosyphon (LT) is typically used for solar water heaters (SHW) to solve the freezing and corrosion issues. The LT – SWH system has a less night time heat loss compared to conventional SWH due to its thermal diode property but a greater heat loss due to the secondary heat exchange. However, the above interactions have rarely had an effect on system performance based on long-term operation [6]. In this paper, the annual results of above two processes, including productive supply day numbers and efficient heat gains and night power losses, was evaluated in this analysis in two separate operating modes on the basis of standard meteorological year data from the City of Fuzhou. Variations of the above variables are addressed with the change in the stated temperature. The results show that the effective delivery days of the LT – SWH system are 139 and 153, respectively, in irregular heating method. The number of days is 168 to 173 in ongoing heating method. The SWH system is predictable to have a higher ratio at nighttime with an annual average of 15.07%, which equates to 6.15% for the LT – SWH system. In fact the LT – SWH method results in a lesser decrease in temperature at night and therefore a smaller raise in the temperature on the following day because of multiple relative heat loss factors running at various hours. The results produced are unpredictable, and lead to an approximately successful heat gain for the same month between November and April. The fixed temperature influences substantially the relative quantities of effective annual supply days and effective annual heat gain, slowly reducing the overall dominance of the LT – SWH method and even changing it as the set temperature increases [12]. This shift is triggered by the biggest daily heat loss leading the domination. In combination with a long static reimbursement time, a conventional SWH system must be substituted by an LT - SWHsystem, particularly when water temperatures are high on demand.

Experimental study on the advective heat flux of a heat exchanger for passive cooling of spent fuel pools by temperature anemometry grid sensor

In commercial nuclear power plants spent fuel assemblies are usually stored in actively cooled water pools. The continuous decay heat release represents a potential risk in case of a station black out scenario. Thus two-phase passive heat removal systems are a key technology to enhance the safety of nuclear power plants. Such systems work only by the energy provided from the heat source, e.g. by the maintenance of a natural convection cooling. A heat transfer loop using air as an unlimited heat sink consists of a primary heat exchanger in the spent fuel pool water and a secondary heat exchanger located in ambient air. Thus the measurement of the heat flux, which gets transferred from the pool to the ambient air, is an important task. If one would measure heat flux, flow rates and temperatures in many positions by help of local probes, the natural flow would get strongly disturbed. For that reason we introduce a heat flux measurement around the secondary heat exchanger located in ambient air, which applies temperature and velocity measurement by an anemometric principle.A 6.5m long flow channel with an electrical heated finned tube heat exchanger was set up at the TOPFLOW facility at HZDR. Since the tubes of a heat exchanger would be tilted in a passive heat removal system, i.e. to allow drainage of the condensed heat transfer medium, different tiled angles were adjusted to 0° (horizontal), 20°,30° and 40°. The frontal velocity was varied between 0.5ms and 4ms and three thermocouples were placed up- and downstream of the heat exchanger respectively. A Temperature Anemometry Grind Sensor (TAGS) was located downstream the heat exchanger. It consists of a wire grid with platinum resistance elements, which are placed in the small sub-channels of a flow straightener to generate laminar flow profiles. Two methods were used to calculate the heat flux: arithmetical average and weighting of the flow area. The results of velocity was compared with the average velocity measured by the volume flow control and out of the velocity and temperature the heat flux was calculated and compared with electrical supplied heat flux. The calculated average velocity measured by the TAGS corresponds well with the velocity measured by the volume flow controller up to approximately 3ms with a maximum deviation of ±5%, but underestimates the velocity measured by the volume flow controller at higher velocities. The heat flux was calculated by five methods, 1.) from the three thermocouples up- and downstream of the heat exchanger, 2.) from the average temperatures measured by the TAGS, 3.) from the weighted temperature measured by the TAGS, 4.) from the average temperature and velocity measured by the TAGS and 5.) from the weighted temperature and velocity measured by the TAGS. In this order the accuracy of methods increases compared to the electrical supplied heat flux. For the last method the maximum deviation was 6.5% for all tilt angles. This measurement concept determines the heat flux without disturbing the flow in the loop.

Assessment of Heat Exchanger Degradation in a Boeing 737-800 Environmental Control System

Abstract There are a number of systems on an aircraft working together, in harmony, to produce safe and trouble free flight. The environmental control system (ECS) is one of these systems, and its failure is a major contributor to unscheduled maintenance, particularly in older aircraft. The ECS is composed of several complex sub-systems and components, but at its heart is the passenger air conditioner (PACK). The PACK is prone to degradation, which can lead to the functional failure of the ECS. Often its degradation is masked by the overall ECS control system and this can, ultimately, result in the ECS shutting down and extensive maintenance being required. There are a number of critical fault modes associated with the PACK, and in this paper, those modes associated with the primary and secondary heat exchangers (SHX) are explored. A robust ECS simulation framework called Simscape ECS simulation under all conditions (SESAC) has previously been implemented, calibrated, and tested against data from healthy systems. Here the simulations are extended to cover degraded components in a representative Boeing 737-800 aircraft PACK model. Fault modes such as blockage and fouling are assessed for the primary and secondary heat exchangers of the PACK. Simulation results, in terms of temperature, pressure, and mass flow at various degradation severities, are presented and discussed. The results highlight the interdependency between the PACK components and the strong association between the primary and secondary heat exchangers performance. The reported simulation methodology and findings serve as a further step towards the goal of formulating a cost-effective ECS fault isolation and diagnostic solution.

Preliminary Analysis and Design of the Energy Conversion System for the Molten Salt Fast Reactor

The unique design features of the molten salt fast reactor (MSFR) should enable higher coolant temperatures than in conventional water reactors, with a significant improvement in the achievable thermodynamic performance. The use of a molten salt as both fuel and coolant, however, poses several advanced heat transfer challenges, such as the design of innovative heat exchangers and energy conversion systems. In this work, we address a preliminary but quantitative analysis of the energy conversion system for the MSFR, based on reference design data from the SAMOFAR H2020-EURATOM project. We consider three main technologies, i.e., the supercritical steam cycle, the closed helium cycle and the helium/steam combined cycle. Preliminary design results are presented for each technology, based on a simplified modelling approach. The considered cycles show promising efficiency improvements, with the best performance being proven by the supercritical steam cycle. The analysis also highlights the critical issue related to the risk of freezing of the molten salts within the secondary heat exchangers, due to the low inlet temperatures of the working fluids. Results show potential incompatibility between the freezing point of molten salts and the temperatures typical of steam cycles, while helium cycles offer the best chances of freezing avoidance. The combined cycle promises intermediate performance in terms of thermodynamic efficiency and thermal compatibility with molten salts comparable with closed helium cycles.