Outlet Temperature Of Heat Exchanger Research Articles

Feasibility investigation on a novel data center cooling system based on cross-seasonal soil cool storage in severe cold area

In response to excessive energy consumption and high carbon emissions associated with the current data center cooling system, the advancement in the utilization of instant free cooling has progressively halted. A novel data center cooling system based on cross-seasonal soil cold storage is proposed，which makes full use of the cold stored in the soil across the seasons and air cold source for realizing the year-round free cooling. A dynamical simulation platform, which describes its operation characteristic, is established to analyze the feasibility. Results indicate that in the typical severe cold area of Harbin, the soil cooling during summer is sufficient to meet the cooling requirements of the data center. The maximum outlet temperature of the ground heat exchanger is only 8.9 °C when releasing cold. The cold energy stored across seasons in the soil can be effectively utilized, achieving a utilization rate of 98.04 %. In Harbin, Changchun, and Shenyang, the cooling capacity stored across seasons accounts for 31.4 %, 32.2 %, and 36.9 % of the total annual cooling capacity of the system, respectively. The annual average coefficient of performance for the system is 13.63, 12.52, and 10.44, respectively. Compared to the cooling system that does not utilize cross-seasonal soil cool storage but achieves efficient use of instant natural cold sources, these values represent an increase of 4.92, 4.02 and 2.62, respectively. Overall, this system demonstrates excellent applicability in severe cold area.

Energy, exergy, exergoeconomic, economic, and environmental analyses and multi-objective optimization of a novel combined cooling and power system with dual-pressure Kalina cycle-absorption refrigeration

A novel combined cooling and power system, the dual-pressure Kalina cycle-absorption refrigeration (DPKC-AR-CCP), is proposed for the cascade utilization of waste heat from high-temperature flue gas and jacket water from internal combustion engines. A pneumatic booster pump unit is employed to increase the inlet pressure of the low-pressure expander, with heat generated during the compression process utilized for preheating the ammonia/water mixture, and exhaust gas from the low-pressure expander is combined with driving gas for absorption refrigeration. By integrating the first and second laws of thermodynamics with the SPECO Methodology, models for energy, exergy, exergoeconomy, economy, and environment of the DPKC-AR-CCP system are developed. A multi-objective optimization model is formulated with maximum exergy efficiency, minimum total exergy cost rate, and maximum annual equivalent carbon dioxide (CO2) emission reduction as objective functions. MATLAB software (combined with REFPROP software) is utilized for simulation and multi-objective optimization. The performance of each component under specific conditions is assessed, and a comparison with the simple absorption refrigeration/Kalina cogeneration system (AR/KC) highlights the advantages of the DPKC-AR-CCP system; an investigation into the effects of different operating parameters on performance is conducted. The results indicate that, under identical operational parameters, the DPKC-AR-CCP system exhibits a substantial increase in net output power (230.2 %), cooling capacity (98.7 %), and exergy efficiency (148.8 %) compared to the simple AR/KC system; payback period is reduced by 64.8 %; and annual equivalent CO2 emissions are decreased by 202.2 %. However, there is an increase in the total exergy cost rate by 90.5 %. The optimal concentration of ammonia/water is determined to be 0.816/0.184, with a heat exchanger outlet temperature of 341.07 K, driving pressure of 0.654 MPa, and low-pressure expander inlet pressure of 5.064 MPa. Correspondingly, the optimal exergy efficiency is 87.2 %, the annual reduction in CO2 emissions is 5.53 × 107 kg, and the total exergy cost rate is 288.48$/h.

An Ejector and Flashbox-Integrated Approach to Flue Gas Waste Heat Recovery: A Novel Systematic Study

In this study, a comprehensive examination was conducted to explore the technology involved in the recovery of waste heat from flue gas emitted by a 1000 MW unit. Traditional methods are constrained in their ability to harness waste heat from flue gas solely for the purpose of generating medium-temperature water. The system being examined not only recovers waste heat but also utilizes it to generate steam, thereby greatly improving resource efficiency. The process entails utilizing the flue gas to heat water to a certain temperature, followed by subjecting it to flash evaporation. This process leads to the generation of low-pressure waste heat steam. Within the steam ejector, the waste heat steam combines with high-pressure motive steam extracted from the source, resulting in the formation of medium-pressure steam. Within the steam ejector, the waste heat steam blends with high-pressure motive steam drawn from the source, forming medium-pressure steam that eventually feeds into the A8 steam extraction pipe (low-pressure turbine pumping pipe). The present study examines the fluctuation patterns in motive steam flow, suction coefficient, waste heat steam volume, and outlet temperature of the flue water heat exchanger when different motive steam sources are used. Additionally, the research calculates the reduction in CO2 emissions, the coal consumption for power supply, and the cost savings in fuel for the retrofitted system. The findings indicate that maximizing energy utilization can be achieved by operating the retrofitted unit at the lowest feasible waste heat steam pressure. The implementation of the new system has resulted in a substantial decrease in coal consumption for power supply. When employing main steam as the extraction steam source, the consumption of coal for power generation decreases in proportion to the decrease in waste heat steam pressure while maintaining a constant unit load. When the waste heat steam pressure reaches 0.0312 MPa, the recorded coal consumption for power generation varies between 289.43 g/kWh at 100% turbine heat acceptance (THA) and 326.94 g/kWh at 30%THA. When comparing this performance with the initial thermal power plant (TPP) unit, it demonstrates reductions of 2.26 g/kWh and 1.52 g/kWh, respectively. After implementing modifications to this 1000 MW unit, it is projected that the annual CO2 emissions can be effectively reduced by 6333.97 tons, resulting in significant cost savings of approximately USD 0.23 million in fuel expenses. This system exhibits considerable potential in terms of emission reduction and provides valuable insights for thermal power plants aiming to decrease unit energy consumption.

Investigating the impact of borehole field data’s input parameters on the forecasting accuracy of multivariate hybrid deep learning models for heating and cooling

Heat pump systems coupled with Borehole heat exchanger (BHEx) are crucial for the efficient and cost-effective heating and cooling of buildings. Accurate performance forecasting of BHEx can help to reduce energy consumption, optimize system design, improve system reliability and ultimately contribute to the sustainability of the built environment. The performance of deep neural networks, including hybrid deep learning algorithms, is dependent on the number and true identification of input parameters used to train the model. While research on the accuracy and selection of individual deep neural networks is well-investigated, the impact of selected input parameters on hybrid algorithm selection and its subsequent influence on multi-step forecasting performance has not been quantified specifically for geothermal heating/cooling systems. The focus of the current work is to investigate and quantify this impact on multivariate hybrid deep learning algorithms for forecasting borehole heat exchanger outlet temperature. In the current work the developed hybrid AI models (LSTM-CNN, GRU-CNN, CNN-LSTM, CNN-GRU) have been trained, validated, and tested using the measured borehole-field data with variable number of input parameters (3,4,5 and 6). The validated AI models are used to forecast 24 h ahead performance of borehole heat exchanger to meet the heating and cooling loads. The most essential input parameters for the data-driven AI models are determined via an importance-level analysis by using Explainable AI techniques of Shapley Additive Explanations (SHAP). The findings show that increasing the number of input parameters has the potential to enhance the multi-step forecasting accuracy of the examined deep learning models. However, it is crucial to note that there is a point where including additional input parameters may not lead to further improvements. Therefore, it is essential to identify the optimal number of input parameters that can maximize the accuracy of the hybrid deep learning models. Moreover, the analysis highlights that depending on the architecture of specific model layers, it is possible to eliminate redundant weather sensors associated with time variables without compromising the accuracy of the hybrid deep learning models.

Application of Feedforward Cascade Compound Control Based on Improved Predictive Functional Control in Heat Exchanger Outlet Temperature System

Aiming at the problems of large delay and poor anti-disturbance ability in the outlet temperature control system of the heat exchanger to optimize the control accuracy of the system and improve the control performance, this paper proposes a control scheme combining predictive functional control with proportional-integral-derivative control. Using the incremental proportional-integral-derivative control algorithm to improve the optimization objective function of the predictive functional control algorithm, a predictive functional control optimization model with a proportional-integral-derivative structure is established. The feedforward compensation control is adopted to eliminate the influence of external disturbances on the heat exchanger temperature control system. Through simulation, the proposed control scheme is compared with the feedforward cascade compound control scheme based on a proportional-integral-derivative main controller. The results show that the scheme has a small over harmonic and strong anti-interference ability. The adaptability and stability of the system are significantly improved, and the exit temperature of the heat exchanger can be effectively controlled.

Experimental study on the influence of inclination on operating characteristics of secondary side passive residual heat removal system

The present work discusses the operating characteristics of the secondary side passive residual heat removal system (PRHRS) of an offshore floating nuclear plant (OFNP). A scaled experimental facility was built on a platform that can be inclined to a certain angle. Experiments were conducted in horizontal and various inclined conditions, and the transient response characteristics and steady-state operating characteristics of the PRHRS were obtained. The experimental results reveal that different inclined directions will change the potential height difference between the cold and heat sources and affect the natural circulation capacity of the system. In general, due to the small inclination of the floating platform in the ocean, the residual heat can be effectively exported by PRHRS. Thermal stratification in the cooling water tank has significant effect on the evolution process of outlet temperature of the passive residual heat removal heat exchanger, and the influence of thermal stratification on the outlet temperature of the heat exchanger decreases under inclined conditions. The research results in this paper can provide some guidance for the design of operating rules of the secondary side PRHRS.

Experiment and Simulation Study on the Heating Performance of Air Conditioners under Variable Working Conditions

In this paper, the performance experiments and simulation studies on air conditioning heating under various fan frequencies were conducted using the air conditioning heating experimental device, and the key factors affecting air conditioning were studied. The experimental study concluded that with the gradual increase of fan frequency, the suction and discharge temperatures of the compressor, the outlet temperature of the heat exchanger, the mass flow of the air duct, and the thermal power consumption showed a gradually increasing trend. From the simulation study, it was found that by simulating the temperature field of the outlet temperature of the heat exchanger under different fan frequencies, and making a relative error with the outlet temperature of the experimental heat exchanger, the relative error is 2.5% at most; while simulating the velocity field of the experimental velocimetry tube flow rate and making a relative error with the experimental velocimetry tube flow rate, the maximum relative error was 1.8%. The research shows that the simulation calculation is highly consistent with the experimental results, which provides a direction and theoretical basis for the study of better air conditioning performance and optimal design.

Numerical simulation of a hybrid system using Peltier thermal switches in magnetic refrigeration

• A 2D transient model of a hybrid magnetic refrigeration system using Peltier modules as the heat switches was established. • The actual transient thermal response of the Peltier modules was considered in the model. • The comparison of the hybrid system with the AMR mode and the Peltier mode was done. • At 4.00 Hz and 0.20 A, the COP and cooling power density of the hybrid system exceeded that of the pure AMR mode. • The influence of operating parameters on the hybrid system performance was evaluated. To overcome the shortcoming of the low cooling power density in the ordinary magnetic refrigerator, a hybrid system using Peltier thermal switches in magnetic refrigeration has been proposed by researchers. In the system, the magnetic material is sandwiched between Peltier modules which are used as the thermal switches to transport the heat to and from the material undergoing the magnetic refrigeration cycle. To analyze the system, a two-dimensional transient model is established by considering the thermal characteristics of the Peltier module, which has not been done before. With the model, the performance of the hybrid system was firstly compared with that using the pure parallel plate active magnetic regenerator (AMR) mode and that using the pure Peltier mode. Compared with pure parallel plate AMR mode, the hybrid system using Peltier thermal switches in magnetic refrigeration can significantly increase the cooling power density at low frequencies (1.60 Hz – 4.00 Hz). In this frequency range, the coefficient of performance (COP) of pure parallel plate AMR mode decreased rapidly with the increase of frequency, while the COP of the hybrid system decreased slowly, and at 4.00 Hz and 0.20 A, the COP of the hybrid exceeded that of the pure parallel plate AMR mode. Compared with pure Peltier mode, the hybrid system can achieve the same cooling power with less power consumption and obtain a higher COP. Furthermore, the influence of operating parameters on the performance of the hybrid system, which included utilization factor, input current, the outlet temperature of the cold-end heat exchanger, frequency, and the number of refrigeration units, was investigated. The results show that, when using Peltier thermal switches, the actual transient thermal response of the Peltier module plays an important role in the hybrid system, which is ignored in previous literature. To achieve efficient operation at high frequency, when using Peltier thermal switches, the thermal response time of the Peltier modules as well as the Joule heating effect, etc, needs to be carefully evaluated.

Analysis of influence factors of casing heat transfer in middle-deep geothermal wells in severe cold region

The medium and deep coaxial casing heat exchange technology uses the fluid circulation inside the casing to improve the deep geothermal energy. Due to the high outlet temperature at the source side， it is a good choice for the heat source of buildings in severe cold areas in winter. We establish a two-dimensional unsteady numerical heat transfer model of fluid-thermal-structure coupling based on standard <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi>κ</mml:mi></mml:math></inline-formula>-<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi>ε</mml:mi></mml:math></inline-formula> model and Simple pressure velocity solution method by analyzing the heat transfer process between coaxial casing and rock mass at source side. According to the climate and stratum characteristics of Changchun City， we analyze the heat transfer performance of heat exchanger and rock and soil mass in full heating cycle by simulation. The results show that due to the cold winter in Changchun City， during the operation of the heat pump， the shallow formation temperature is lower than the fluid temperature at the inlet of the heat exchanger， and the rock and soil within 3.9 m below the ground is a heat source funnel， which gradually changes into a heat sink funnel with the increase of formation depth. In the first week of operation of the heat pump， the outlet temperature and heat exchange of the heat exchanger decrease rapidly and tend to be stable after one month of operation. In the whole operation cycle， the unit time decline of the outlet temperature of the buried pipe becomes smaller and smaller， and the relationship between the change of the outlet temperature and time decreases in the form of a power function with a slow speed. With the increase of thermal conductivity of cementing cement， the heat exchange first increases， and tends to be stable when the thermal conductivity of cementing cement is greater than that of rock and soil. The thermal conductivity of the inner tube increases， the thermal short circuit is serious， and the outlet water temperature and heat exchange of the heat exchanger decrease. When the heat pump unit 24 hours on and off time （start-stop ratio） is 16 h∶8 h， 12 h∶12 h， 8 h∶16 h， respectively， the heat exchanger outlet temperature and heat transfer are irregular， but the overall trend is gradually reduced. The longer the heat pump stops running， the better the temperature recovery of rock and soil body on the source side， and the greater the water outlet temperature and heat transfer when it is turned on again. Through the numerical model， the variation law of influence factors of casing heat exchanger can be obtained. <fig fig-type="abstract-image" id="F1" orientation="portrait" position="float"><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="SP.J.1249-2022-39-1-42/D20AE2D9-DE77-4b51-BEC5-8F4EB83A9A4A-F001.jpg"/></fig>

Corrosion risk analysis of tube-and-shell heat exchangers and design of outlet temperature control system

This study deals with the high-risk shell-and-tube heat exchangers in the effluent system of hydrogenation reaction of the petrochemical industry. The process of hydroprocessing reactor effluent system is simulated in Aspen Plus to study the distribution of corrosive medium in the three phases of oil, gas and water. The least-squares method is utilized to calculate the ammonium salt crystallization temperature. Then, the heat exchanger with risk of ammonium salt crystal corrosion is identified. Dynamic mathematical modeling of the heat exchanger is established to determine the transfer function. A temperature control system with proportional integral derivative (PID) control of the heat exchanger outlet is designed, and fuzzy logic is used to implement self-tuning of PID parameters. After MATLAB simulation, the results show the control system can achieve rapid control of the heat exchanger outlet temperature.

Effects of loss of heat sink transient on flow characteristics in a closed natural circulation system

Flow characteristics during loss of coolant to the heat exchanger (HX) via the secondary loop cold leg of a natural circulation (NC) test facility referred here as loss of heat sink transient (LOHS) in a closed rectangular NC system having a single heated channel at two different heating powers and system pressures has been investigated experimentally. Two LOHS experiments (LOHS-1 and LOHS-2) were conducted in a well dimensioned closed loop NC test facility designed to represent the primary system of a nuclear reactor. Operating conditions were set and maintained at 6.0 kW and 9.0 kW with system pressures of 0.2 MPa and 0.5 MPa respectively for both single-phase and single-to-two-phase flow transition to determine their thermal hydraulic responses at these predetermined parameters. The transients were initiated by closing the cold leg of the secondary loop supplying coolant to the tube-in-shell heat exchanger while NC flow phenomena were monitored at each vital section along the flow map based on the pre-determined inlet operating conditions. LOHS experiment stops when critical heat flux (CHF) occurs or heat exchanger outlet (HXoutlet) temperature rises too high to approximately equal its inlet temperature. Results were acquired using a system-design platform and development environment LabVIEW, programmed in a dedicated computer that was interfaced with the coupled sensors in the measuring devices. Common computational tools which include MATLAB, Ms Excel and Origin software were used for the analysis of the acquired data. Results at the inlet and outlet of heated sections as well as the inlet and outlet of condensers of both tests were analyzed and discussed in details at various flow regimes with the associated phenomena. It is concluded that while stable flow was maintained before transient with slug flow occurring in the heating channel, the system experienced transient stability resulting in steady temperature increase and subsequently drops into an instability region when the transient scenario was activated. In addition, the NC system transited into stable two-phase flow and further loses stability when HXoutlet temperature surges to its inlet value with CHF occurrence. These results are presented to contribute to a more extensive utilization of NC systems and understanding of flow behavior during LOHS in advanced reactors.

A charging time energy fraction method for evaluating the performance of a latent thermal energy storage heat exchanger

• The charging time energy fraction method is developed. • The method allows to predict the outlet as a function of the input conditions. • The method is used to develop a model for a specific heat exchanger. • The predictions are mostly within the measurement uncertainty. Latent thermal energy storage heat exchangers have a large potential in different processes. Implementing such a heat exchanger requires evaluating the performance of the heat exchanger in the conditions of each specific process. Therefore a method to characterize the performance of a latent thermal energy storage design would be a useful tool for designing processes. Characterization methods for heat exchangers such as the effectiveness number of transfer units method are based on the steady-state operation of the heat exchanger. However, latent thermal energy storage heat exchangers do not operate in steady state and therefore the standard methods are not applicable. The present paper develops a novel method to determine the heat transfer fluid outlet state as a function of the initial and input conditions: the charging time energy fraction method. This method is used to characterize and evaluate a latent thermal energy storage channel heat exchanger. For 26 out of 30 calibration and validation experiments, the model predicts the outlet heat transfer fluid temperature within measurement uncertainty (±0.15 °C) during all but the initial 100 s of the charging process. The charging time energy fraction method is according to the authors the first approach to derive a predictive, low computational cost model of the outlet temperature of a latent thermal energy storage heat exchanger from a set of experiments.

Numerical modelling of deep coaxial borehole heat exchangers in the Cheshire Basin, UK

Few deep wells have been drilled in the Cheshire Basin, resulting in high geological and financial risk of geothermal developments. Although the geothermal gradient in the basin can be predicted, the transmissivity of aquifers at depth are unknown. This has led to an investigation of lower risk strategies such as deep coaxial borehole heat exchangers (BHEs) for spatial heating, rather than traditional doublet methods. A model of a deep coaxial BHE was designed within MATLAB using the finite-difference method. The model produces accurate results in comparison to an analytical solution with a fast computational time. Results indicate that under best case geological parameters sustainable heat loads in excess of 298.7 kW can be produced from deep coaxial borehole heat exchangers at a depth of 2.8 km over the duration of a 20 year operational cycle. The thermal gradient and conductivity for this scenario were set at 27 °C/km and 3 W/m°C, respectively.The thermal gradient, depth of borehole, volumetric flow rate and thermal conductivity of the surrounding rock all impact the heat load and outlet temperature of a deep coaxial borehole heat exchanger. The coefficient of system performance decreases with increased volumetric flow rates due to an increase in power consumption within the borehole heat exchanger. For an optimal flow rate of 4 l/s (calculated as the flow rate to produce most net power at the end of a heating season), the coefficient of system performance was 5.29. The thermal performance and efficiency of the system provides confidence that the geothermal resource of the Cheshire Basin has significant potential to be developed via deep coaxial borehole heat exchangers. Additionally, regression analysis was undertaken in this study. These models can be used to predict heat loads and outlet temperatures at the end of a heating season without the need for complex numerical modelling.

EN Energy system efficient performance and energy policy

The 2020 crisis caused by COVID makes the global economy move forward to a new start. In order to achieve strategic goals, the energy sector and the HVAC&amp;R sector forced by faced problems to energy efficiency projects and technologies development and deployment to get fast return on investment and to manage risks for the secure step forward. To meet strategic packet goals global community should redirect investment into the renewables technologies development to integrate them with the energy efficiency projects in the project design phase. On the study of the solar thermal system due to increasing the outlet temperature of ground source heat exchanger it is possible to observe floating increasing COP (opera­ting mode dependence) for the HP system by 4-6%. For getting the greater angles of the collector, the more of the inbound energy can be accumulated and used per annual year. For that reason, collectors intended for the maintenance of HP system, when installing at a large angle. It can reduce the amount of excess heat in the summer season, while the efficiency of the collectors in winter season falling under a smaller angle optimized. The increasing of the COP is caused by reducing of the electrical input to the heat pump cause higher temperature level gain by solar collector. The use of solar thermal collectors bring possibility to reduce borehole depletion. In own turn it can be used for ground heat exchanger regeneration during heat pump stand by. Ukraine can look for the best practices of the sustainable deve­lopment goals worldwide and adopt them by modifying for actual complex tasks due to actual regulations and development new ones to motivate industrial players on the national and global levels for driving sectors development along with the sustainable development scenario

Numerical evaluation of the thermal performance of a near-surface earth-to-air heat exchanger with short-grass ground cover: A parametric study

Abstract High energy consumption and increasing energy cost have encouraged investment in energy efficiency. In hot areas, like the Middle East, the share of space cooling accounts for most of the total energy use in buildings. Earth-to-air heat exchangers represent an energy-efficient and environmentally friendly cooling technique. An earth-to-air heat exchanger buried near the ground surface with short-grass cover, which lowers the soil temperature by evapotranspiration, is an alternative to conventional deep buried types. In this study, a steady three-dimensional numerical model of this earth-to-air heat exchanger was developed by considering the conservation of mass, momentum, energy, and species. Soil temperature and moisture content measurements were used as boundary conditions for the model. In addition, the variations of soil temperature and thermal conductivity with depth were considered in the model. Numerical predictions of temperature matched experimental measurements within ±0.5 °C. Using the validated numerical model, the effect of inlet air temperature, airflow rate, tube length, material, wall thickness, and soil thermal conductivity on the earth-to-air heat exchanger thermal performance was investigated. Increasing the airflow rate and tube length resulted in an asymptotic increase and decrease in the earth-to-air heat exchanger outlet temperature, respectively. By increasing the tube wall thickness from 1 to 10 mm, the outlet temperature for an aluminum tube remained unchanged, while for PE and PVC tubes, the outlet temperature increased by about 1.1 and 2.2 °C, respectively. By increasing the soil thermal conductivity from 1 to 5 W m−1 K−1 the outlet temperature decreased by about 4.4 °C.

The application of thermoelectric and ejector in a CO2 direct-expansion ground source heat pump; energy and exergy analysis

The thermodynamic analysis of a horizontal CO2 direct-expansion ground source heat pump in transcritical cycle was performed to investigate the influence of using thermoelectric sub-cooler and the ejector on the performance parameters of the cycle. A comparative analysis was conducted between the Base cycle and the cycles with ejector and thermoelectric sub-cooler considering the pressure drops in the gas cooler and the ground heat exchanger. The effects of compressor inlet temperature, soil temperature, thermoelectric sub-cooler length, thermoelectric sub-cooler cooling water mass flow rate, and ground heat exchanger outlet temperature on different performance parameters of the cycles were studied. The results demonstrated that the application of ejector exhibits a more stable operation of the cycle and increasing its COP by 16.5% as compared to the Base cycle considering the same ground heat exchanger length. Also, the length of ground heat exchanger is considerably decreased by using the ejector considering the same COP for the Base and EJR cycles. Besides, thermoelectric sub-cooler decreases the irreversibilities of the cycle by generation more power, thereby COP is boosted by 16% as compared to the Base cycle. Furthermore, the major irreversibility in the cycle with thermoelectric and ejector is occurred in the compressor and followed by ejector, ground heat exchanger, gas cooler, thermoelectric sub-cooler, and the expansion valve, respectively.

Simulation Study on Hydrogen-Heating-Power Poly-Generation System based on Solar Driven Supercritical Water Biomass Gasification with Compressed Gas Products as an Energy Storage System

Supercritical water gasification driven by solar energy is a promising way for clean utilization of biomass with high moisture content, but direct discharge of liquid residual causes energy waste and decreases energy efficiency. To reduce energy waste, a poly-generation system for hydrogen-rich gas production coupling heat supply and power generation based on supercritical water gasification of biomass driven by concentrated solar energy was established in this paper, which also provided a novel energy storage method to overcome the shortcomings of solar discontinuity. Thermodynamic model of the system was proposed and life cycle assessment (LCA) of the system was conducted. Influence of different parameters (temperature of 600°C to 800°C, outlet temperature of heat exchanger of 42°C to 56°C, biomass slurry concentration of 5% to 6.5%) on the gasification performance, energy and exergy efficiency, energy distribution and global warming potential (GWP) was discussed. The results indicated that hydrogen yield increased as gasification temperature increased since free radical reaction was enhanced which gas production reaction was classified into. Molar fraction of hydrogen increased as gasification temperature increased and reached 65.6% at 750°C. Energy and exergy efficiency of the system reached 74.84% and 34.87% at 700°C and 600°C respectively and that of gas production was 18.15% at 650°C, which was the highest. Increasing reaction temperature and decreasing biomass slurry concentration were effective ways to decrease GWP. Optimal operating parameter was reaction temperature of 650°C, outlet temperature of heat exchanger of 50°C and biomass concentration of 5%.

Comparison of Static and Dynamic Neural Network Models in Predicting Outlet Temperature of Shell and Tube Heat Exchanger

This paper presents the comparison of static and dynamic neural network (NN), model to predict the exit temperature of the heat exchangers. Feed forward NN was used as a static network while Time delay NN was used for a dynamic network. Experimental data was collected from a shell and tube heat exchanger to provide sufficient data processing, namely training, test and validation data to develop the models. The static and dynamic network models of the heat exchanger have been developed using Matlab. The performances of the models were evaluated by their statistical validity using the correlation co-efficient and the mean squared error. For time series predictions, the dynamic NN has shown better results than the static NN.

Effects of Baffle Width on Heat Transfer to an Immersed Coil Heat Exchanger: Experimental Optimization

Abstract In this work, we investigate the effects of the width of an annular baffle region on natural convection heat transfer to an immersed, coiled heat exchanger in an otherwise quiescent sensible hot water storage tank. In the experiments, the coiled heat exchanger sits in an annular region created by the tank wall and a straight, cylindrical baffle. The width of this baffle region is 1.5, 2, 3, or 4 times the heat exchanger diameter. These experiments are compared to each other and to corresponding control experiments with no baffle. In general, all baffles create considerable benefits over their respective control experiments, consistent with past studies. The considered metrics of heat transfer rate, fraction of energy discharged from the tank, heat exchanger outlet temperature, and heat exchanger effectiveness show that heat transfer is improved slightly by narrowing the baffle region. For example, relative to their respective controls, the energy extracted from the tank after 30 min of discharge in the 1.5D, 2D, 3D, and 4D experiments is 23.3%, 20.8%, 18.1%, and 14.6% higher, respectively. This improvement in natural convection heat transfer as the baffle region narrows is attributed to the increasing thermal stratification observed with increasingly narrow baffle regions.

Methods to Evaluate Heat Transfer Enhancement in an Ultrasonic Heat Exchanger

Several qualitative and quantitative methods to evaluate the performances of an ultrasonically assisted double tube heat exchanger are presented in this work. These methods are theoretically developed and applied to four different fluid-flow configurations: hot and cold fluid interchangeable positions, in parallel-flow (co-flow) or counter-flow and allow estimating heat exchanger outlet temperatures, energetic performances and heating transfer coefficients. Relevance of each method presented with respect to the selected configuration and to the required improvement is discussed. It appears that one method may be more suited than the others to analyze enhancement or thermal behavior induced by ultrasound.