Heat Transfer Fluid Outlet Temperature Research Articles

Evaluation of a concentrated solar power-driven system designed for combined production of cooling and hydrogen

The current technique of hydrogen generation and cooling production raises climatic problems, which calls for the investigation of cleaner alternatives. No research has been conducted to propose and analyze a solar thermal power cycle-based water electrolysis for on-site production of hydrogen and the detailed exergy analysis of a series flow double-effect absorption chilling machine employed for large solar cooling. In this regard, a helically coiled tube embedded central receiver is used in the heliostat field for the simultaneous production of solar cooling and green hydrogen to meet the increasing needs of energy and fuel sustainably. The combined system is composed of four sub-systems including a heliostat field, LiBr–H2O operated series-flow double effect absorption refrigeration cycle (DEARC), organic Rankine cycle (ORC), and proton exchange membrane (PEM) electrolyzer. The system was examined from energy and exergy perspectives in the Engineering Equation Solver (EES) using library data of REFPROP for obtaining the thermodynamic properties of working fluids. The results of the thermodynamic model for the combined system are validated. Furthermore, the effect of ambient temperature, solar irradiation, and type of ORC working fluid on the hydrogen and cooling production, and the overall energy and exergy efficiency of the combined system are examined. A computational fluid dynamics simulation applying ANSYS-FLUENT was used to examine how coil curvature ratio and coil torsion affect solar heat transfer fluid (SHTF) pressure and temperature leaving the receiver. The coil curvature ratio affects temperature increase more than coil torsion. Solar heat transfer fluid outlet temperature increases by 36.9 % when the coil curvature ratio increases from 0.063 to 0.095 at direct normal irradiations (DNI) 1200 W/m2, input temperature of 92°C, and coil torsion of 0.032. The response of the cogeneration cycle to varying operating parameters is examined. Application of R141b as the ORC fluid results in a large increase of cooling exergy efficiency from 14.98 % to 63.48 % when the ambient temperature is increased from 15 °C to 45 °C whereas the exergy efficiency of the combined system is marginally improved. The exergy distribution presents for ORC operating on R141b, out of 100 % input solar exergy, 16.42 % is generated as hydrogen exergy and 13.67 % cooling exergy, 66.79 % is the exergy destroyed, and the rest 3.12 % is exergy loss. Exergy analysis is utilized to identify the sources of losses in useful energy within the components of the system considered and provides a more realistic and meaningful assessment than the traditional energy analysis. The results justify a need for the promotion of exergy analysis through policy decisions in the context of the global energy and environment crisis.

Design and performance optimization of a novel zigzag channeled solar photovoltaic thermal system: Numerical investigation and parametric analysis

In order to overcome the drawbacks of traditional photovoltaic thermal systems, including their limited thermal power, low thermal exergy, and heat transfer fluid outlet temperature, it becomes essential to explore the optimal design configuration of the system for maximization both electricity and domestic hot water generation. Therefore, a detailed numerical modeling and comparative performance analysis on a solar photovoltaic thermal collector (PVT) are conducted under two novel structures of the cooling channels. The first system is a reference PVT collector with a classical straight zigzag-plated tube cooling channel (Case A), while the second PVT system proposes an innovative design of flow cooling channel which is divided into three equal zigzag-plated tube sections (Case B). Each section is also split into three double pass tubes and has a separate inlet and outlet in a staggered manner corresponding to the section that precedes and follows it. The two proposed PVT structures are investigated through computational fluid dynamic simulation under solar radiation values ranging from 200 to 1000 W/m2 and coolant flow rates varying between 0.001 and 0.005 kg/s using both water and air as coolant. The obtained results confirm the significant potential of the modified configuration (Case B) that yielded an improvement in the thermal efficiency by 7.23% and 15.75% for water-PVT and air-PVT system, respectively, over the reference PVT system (Case A). Also, the modified configuration (Case B) yielded an enhancement in the electrical efficiency by 4.0% and 4.6% for water-PVT and air-PVT systems, respectively. It can be concluded that dividing the cooling channel area into equally mini zigzag plate tube-shaped sections with multiple reciprocal entrances is regarded a feasible configuration for augmenting the performance of PVT collectors and maintaining a uniform coolant flow and reduced temperature distribution over the entire panel.

Efficient energy generation and thermal storage in a photovoltaic thermal system partially covered by solar cells and integrated with organic phase change materials

To address the limitations of conventional photovoltaic thermal systems (i.e., low thermal power, thermal exergy, and heat transfer fluid outlet temperature), this study proposes a photovoltaic thermal system with a solar thermal collector enhancer (PVT-STE), incorporating phase change materials for simultaneous electricity and thermal power generation and thermal energy storage. The system consists of a water based solar collector with a partially covered absorber plate utilizing photovoltaic cells, while each component is equipped with a thermal storage enclosure filled with phase change materials. The primary objectives of this research encompass the evaluation of the proposed system's performance and the identification of appropriate phase change materials for each component. To gain comprehensive insight into the effects of employing and selecting appropriate phase change materials, the study investigates various configurations under both hot and cold weather conditions of Shanghai, China. Water serves as the heat transfer fluid under real-world operational conditions. The numerical results indicate that, for the given conditions, optimal phase change material selection entails using higher melting temperatures (e.g., RT42) in the STE component and lower melting temperatures (e.g., RT31) in the PVT component. Employing the optimal phase change materials for each component, the system can store 3234 and 1802 kJ/m2 of thermal energy during the charging process in July and November, respectively. Moreover, the proposed system generates almost 1.8 and 2 times more thermal energy per square meter in July and November, respectively, compared to a standalone photovoltaic thermal system coupled with a phase change material.

Unsteady temperature, heat transfer rate and HTF outlet temperature variation during charging of latent thermal energy storage unit

This work reports a detailed numerical study that is aimed to determine the variation of the three principal parameters, temperature of two phase change materials (PCMs), heat transfer rate and heat transfer fluid (HTF) outlet temperature, during charging of latent thermal energy storage unit (LTES). The unit is consisting of a shell-and-tube type. The shell space is filled with two paraffin wax named PCM1 and PCM2. During charging process, hot fluid heats the PCMs, and when PCMs melts, the heat is stored. A mathematical model based on the conservation energy equations was developed and numerically investigated. Numerical results show that, the variation of the three principal parameters goes through three distinct periods. As time progress, the heat transfer rate increases, reaches its maximum value during the first period, and then decreases, until finally it equals zero. The HTF outlet temperature remains constant and is equal to its initial temperature for approximately 200 seconds. During this time period, the heat storage capacity is greater, PCM1 and PCM2 store energy in the sensible form only. The analysis and discussion of results are employed to evaluate the correspondence between the variations of the three parameters in term of charging time.

A big data-handling machine learning model for membrane-based absorber reactors in sorption heat transformers

Membrane-based absorbers have received much attention recently due to their higher absorption rates than conventional absorbers. Several studies have been conducted to analyze membrane-based absorbers’ performance using numerical and analytical modeling. Numerical models are accurate; however, they are computationally expensive. Analytical models are computationally efficient; however, they have limiting assumptions and may exhibit inaccuracy accordingly. This study proposes a novel multi-label, big data-handling machine learning model for membrane-based absorbers used in sorption heat transformers, offering the accuracy of a numerical model with the efficient computation of an analytical model. A comprehensive dataset comprising over one million data points is generated using 2D numerical modeling. The dataset consists of 15 features, input parameters, including operating conditions and geometrical parameters, and four labels, output variables, including absorption rate, outlet concentration, solution outlet temperature, and heat transfer fluid outlet temperature. The Support Vector Regression, Random Forest Regression, and Decision Tree Regression are used and combined to develop the present model. Particle swarm optimization is used to find the optimized hyper-parameters of each model. A map-reduce algorithm is developed to minimize the computational time, and the optimized data chunk number is presented for the highest accuracy and the lowest computational time. The results of the proposed model are validated with experimental data, capturing most data within a relative difference of 15%. The machine learning-based model can predict the four outputs with an accuracy of over 90%. Moreover, it is shown that using the map-reduce algorithm results in a 40-fold decrease in computation time without significantly compromising accuracy.

Thermal performance optimization of rectangular cavity receiver for cross linear concentrating solar power system

ABSTRACT A thermodynamic analysis was performed on a newly developed concentrated solar power (CSP) technology known as the Cross-Linear (CL), which addresses the issue of cosine loss in conventional CSP technology. The analytical model has been developed and validated using experimental data collected at the experimental site situated in Bhopal, India. The analysis was performed under direct normal irradiance of 775 W/m2 with the key objective to determine the optimum inlet condition of the heat transfer fluid (HTF) considering three optimization parameters: HTF outlet temperature, energy, and exergy efficiency of the receiver. Also, the exergy of the solar field is investigated depending on the available solar irradiation throughout the day for three different configurations of the heliostat field. After a comprehensive analysis of the results, the optimal air inlet temperature range was observed to be between 373 and 423 K, and the optimal air mass flow rate was overserved to be 0.0925 kg/s (333 kg/h), which provides energy and exergy efficiency values within 50% to 60% and 28% to 34%, respectively. The maximum electrical exergy efficiency for 30 kW plant capacity is observed to be around 70% at solar noon with a cosine factor of around 0.9 for 4-hour duration.

Numerical investigation of a latent cold storage system using shell-and-tube unit

The use of cold thermal storage systems in low-temperature industrial applications is considered one of the most promising ways of improving energy efficiency and reducing the use of power during peak periods. In this study, the thermal performance of a shell-and-tube cold storage system under realistic operating conditions is investigated numerically. The proposed model is developed based on energy balances and then validated using existing experimental data from the literature. Glycol/water is used as the heat transfer fluid (HTF) and the phase transition phenomena in the phase change material (PCM) is simulated using the enthalpy–porosity approach. The influence of several design and operating parameters, including the HTF mass flow rate, HTF temperature, PCM type, and volume, on the cold storage performance during the crystallization process is presented and analyzed. The numerical results show that increasing the HTF mass flow rate accelerates the PCM crystallization process. However, the delivery periods of constant thermal power and constant HTF outlet temperature are reduced. The HTF inlet temperature has a significant effect on the cold storage performance, and the complete charging period is reduced by approximately 37% when the HTF inlet temperature is reduced from −4 °C to −7 °C. Increasing the number of tubes in the cold storage unit is concluded to significantly improve the thermal performance of the system, and using water/ice as a cold storage medium is more suitable than using the commercial PCMs RT2-HC and RT4-HC. Finally, the proposed numerical model for cold storage systems can be successfully used to design and simulate their realistic operation under different conditions.

Multi-Objective Optimization of a Solar Combined Power Generation and Multi-Cooling System Using CO2 as a Refrigerant

This paper proposes a new combined multi-cooling and power generation system (CMCP) driven by solar energy. Carbon dioxide is used as a refrigerant. A parabolic trough collector (PTC) is employed to collect solar radiation and convert it into thermal energy. The system includes a supercritical CO2 power system for power production and an ejector refrigeration system with two ejectors to provide cooling at two different evaporating temperatures. The CMCP system is simulated hourly with weather conditions for Tunisia. The PTC mathematical model is used to calculate the heat transfer fluid outlet temperature and the performance of the CMCP system on a specific day of the year. A 1D model of an ejector with a constant area is adopted to evaluate the ejector performance. The system’s performance is evaluated by an energetic and exergetic analysis. The importance of the system’s components is determined by an exergoeconomic analysis. The system is modeled using MATLAB software. A genetic algorithm is used for multi-objective optimization to determine the best values and solutions for the system’s design parameters. The optimal energy and exergy efficiencies were found to be 13.7 percent and 37.55 percent, respectively, and the total product unit cost was 31.15 USD/GJ.

Characterization of a latent thermal energy storage heat exchanger using a charging time energy fraction method with a heat loss model

Correlations predicting the transient behavior of latent heat thermal energy storage systems without too many computational efforts are valuable for engineering practices. This characterization of latent heat thermal energy storage systems can be done with the recently developed charging time energy fraction method. This method allows fitting a predictive model for the outlet heat transfer fluid temperature of a latent thermal storage unit as a function of the input condition. The previous application of the method neglected heat transfer to the ambient. The present paper improves the charging time energy fraction method by proposing a heat loss model to the charging time energy fraction model. A finite volume model of a high-temperature thermal battery is used to validate the proposed heat loss model. The improved charging time energy fraction method is then used to characterize a high-temperature thermal battery by calibrating a model on 36 numerical charging experiments. The charging time prediction between energy fractions of 0 and 0.96 deviates maximally 2 % from the measured charging time over all 36 calibration experiments. The deviation increases near the end of the charging process, especially for slower charging experiments. Across the 36 calibration experiments, the worst prediction has an average absolute temperature difference of 0.50 °C with a maximum deviation of 2.58 °C at the very beginning of the charging where fast transients are occurring. The calibrated model is also compared to four numerical validation experiments and four real experiments. Overall it is shown that this low computational cost model with average calculation times of 2–3 ms can accurately predict the heat transfer fluid outlet temperature of latent thermal energy storage heat exchangers.

Dynamic Modeling and Controller Design for a Parabolic Trough Solar Collector

The current study unveils an analytical dynamic model of a parabolic trough solar collector (PTSC) and subsequently presents the process to derive the transfer function of the PTSC system. The presented generalized transfer function derivation can be utilized to relate different operating parameters with the output temperature for any PTSC module. Presented model and derivation are applied on a PTSC module tested by Sandia National Laboratory, USA and a transfer function relating the outlet temperature of heat transfer fluid (HTF) with flowrate is derived. PID controller is designed to maintain the HTF outlet temperature by manipulating the flowrate. Controller tuning is performed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">via</i> nature-inspired algorithms (NIAs) which is rare in the context of the control systems for PTSCs. Two NIAs namely Self-adaptive Differential Evolution (SaDE) and African Vultures Optimization Algorithm (AVOA) were used for tuning with minimization of integral of time-weighted absolute error (ITAE) as an objective. It is concluded that SaDE-PID tuned controller outperforms AVOA-PID tuned controller with lower ITAE and in terms of other controller characteristics. Also, the designed controller is examined on various grounds as transient response characteristics and performance indexes. This completes the investigation of the integrity of the presented model, process, and controller.

Analysis of temperature distribution over pipe surfaces of air-based cavity linear receiver for cross-linear concentration solar power system.

This analysis is based on the computational fluid dynamics (CFD) of the air-based solar cavity linear receiver (CLR) of the cross-linear concentrated solar power plant. In this study, the temperature distribution along the pipe surface is investigated using a small section of a receiver. To study the variation of temperature over the surface of receiver pipes, a CFD model has been developed in Ansys Fluent. The analysis shows the effect of reflected radiation on the temperature variation over the front and back surfaces of the pipes, as well as the effect of this variation on heat transfer fluid (HTF) outlet temperature. The difference in the HTF outlet temperature and heat transfer rate between experimental data and CFD results has been identified. After rigorous examination, it has been observed that the effective range of length for heat absorbing pipe is from 60 to 600mm (outlet) as HTF continues to absorb heat in this range. The average heat transfer rate was observed to be around 14108W. Finally, the effect of variable mass flow rate over thermal efficiency of the receiver has been examined and it has been observed that once the mass flow rate exceeds 0.06kg/s, further increasing the mass flow rate has little effect on improving the thermal efficiency because after an optimum value of mass flow rate would result in increase in heat loss from the pipe's back wall. In the present study, the results of the CFD analysis have been validated with an experimental test data.

Performance of Parabolic Trough Collector with Different Heat Transfer Fluids and Control Operation

Electricity generation from solar energy has become very desirable because it is abundantly available and eco-friendly. Mathematical modeling of various components of a Solar Thermal Power plant (STP) is warranted to predict the optimal and efficient operation of the plant. The efficiency and reliability of STPs are maximized based on different operating strategies. Opting for proper Heat Transfer Fluid (HTF), which is proposed in this paper, helps in reducing operating complexity and lowering procurement cost. The Parabolic Trough Collector (PTC) is the heart of STP, where proper focusing of PTC towards solar radiation is the primary task to maximize the outlet temperature of HTF. This maximum temperature plays a major factor due to diurnal solar radiation variation, and its disturbance nature, with the frequent startup and shutdown of STP, is avoided. In this paper, the PTC component is modeled from the first principle, and, with different HTF, the performance of PTC with constant and quadratic solar disturbances is analyzed along with classical control system designs. Through this, the operator will be able to choose proper HTF and resize the plant components depending on plant location and weather conditions. Furthermore, the thermal energy is collected for therminol oil, molten salt, and water; and its performance with different inputs of solar radiation is analyzed along with closed-loop controllers. Thermal energy extracted by therminol oil, molten salt, and water with constant solar radiation results in 81.7%,73.7% and 18.7%, respectively.

Design and Performance Analyses of Evacuated U-Tube Solar Collector Using Data-Driven Machine Learning Models

Abstract In this study, the implementation of data-driven machine learning (ML) models for design analysis and performance prediction of evacuated U-tube solar collectors (ETSCs) is investigated for the first time. Although evacuated U-tube solar collectors are widely investigated both numerically and experimentally, the implementation of data-driven machine learning models as an efficient predictive tool was not explored for the ETSC. So, to fill this literature gap, seven ML models such as linear regression with repeated K-fold cross-validation (LR), K-nearest neighbors (KNNs), principal component analysis (PCA), partial least-square regression-I (PLSR-I), partial least-square regression-II (PLSR-II), support vector regression (SVR), and stochastic gradient descent regression (SGDR) are employed using three hundred experimental data points and are reported in the literature. The heat transfer fluid outlet temperature (Thtf,o), thermal energy gained by heat transfer fluid (Q˙htf), and ETSC efficiency (ɳETSC) are considered as output/performance parameters. The outcome of the predicted results suggests that the SGDR ML model is superior in predicting all the performance parameters showing R2 values of 0.98, 0.981, and 0.99 for “Thtf,o,” “Q˙htf,” and “ɳETSC,” respectively. Moreover, the KNN ML model showed weaker performance for predicting the output parameters. In addition, it is observed that the SGDR ML model has a low training time of 0.45 s when compared to other ML models. For the given operating range, the predicted optimal performance parameters such as “Thtf,o,” “Q˙htf,” and “ɳETSC” obtained from the SGDR ML model are 45 °C, 0.44 kW, and 71%, respectively. Furthermore, the recommendations and shortcomings associated with the ML models for the design and performance optimization of ETSC are also presented in detail.

Optimization methodology of thermal energy storage systems for domestic water heating applications with different configurations

This paper develops an optimization methodology for the Thermal Energy Storage (TES) tank embedded with Phase Change Materials (PCMs) for domestic water heating applications with respect to the design parameter constraints and tank size. It presents the optimum design conditions for two different TES configurations considering different control strategies for the conventional cascaded system and the multiple entry independent PCM modules. The optimum configurations are determined using adaptive simulated annealing algorithm aimed to enhance the energy content and compare the systems outputs, namely the available energy and the heat transfer fluid outlet temperature at the optimum conditions for the two systems. The present study is conducted during a complete melting and solidification processes. It simultaneously validates the effectiveness of the multiple entry independent PCM modules in satisfying the low and high user requirements of domestic hot water and highlights the reduction in the electric power consumption throughout the year compared to the conventional TES system.

Numerical phase change model considering crystal growth under supercooling

The supercooling of phase change material (PCM) significantly affects the heat release characteristics of heat storage systems. Therefore, accurate numerical modeling of the solidification process is key for studying heat storage. Few models considering the crystal growth of supercooling PCMs have been established; however, their accuracy under slight supercooling conditions is unsatisfactory. In this study, the implicit finite difference method was used to establish a two-dimensional PCM heat transfer model that considers the crystal growth process in detail. The growth rate of the crystallization front was used to control the crystallization start time at each node, and the solidification speed was used to manage the heating process once the crystallization was triggered. The accuracy of the model was verified by the experimental results obtained by melting, cooling, and triggering crystallization in a stable supercooled state and during cooling. Based on the simulations of a concentric tube PCM heat exchanger, the effects of several parameters on the heat release rate were investigated, such as the supercooling degree, the PCM initial temperature, and the inlet temperature of Heat transfer fluid (HTF). The results show that a large supercooling degree will accelerate the heat release rate of the PCM heat exchanger after the crystallization is triggered. An increase in the initial PCM temperature reduces the sharp increase in HTF outlet temperature caused by crystallization; a decrease in HTF inlet temperature also has the same effect. A comparison of various models demonstrated that the use of the crystallization front to calculate the PCM temperature directly causes up to 3% of the heat to be released earlier or later. Moreover, ignoring the crystal growth process causes up to 9% of the heat to be released in advance, and ignoring the supercooling causes an even greater error.

Estimating the state of charge in a latent thermal energy storage heat exchanger based on inlet/outlet and surface measurements

• Estimators for the total and partial stored energy are developed and validated. • The estimator for the heat transfer fluid energy is generally applicable. • A finite volume latent thermal energy storage model is developed and fitted. The performance of latent thermal energy storage (LTES) heat exchangers is related to the stored energy (i.e. state of charge) during the (dis)charging of the energy storage system. Therefore, measuring the stored energy is crucial to understand the behavior of LTES systems. However, technical considerations often oppose the measurability of the stored energy. The present article presents a case where only measurements at the in- and outlet of the heat transfer fluid and on the outer surface of the heat exchanger were possible. Based on this sparse set of measurements, estimators for the stored energy are developed. To test these estimators, a finite volume model of the LTES heat exchanger is made. The finite volume model is fitted by comparing the predicted heat transfer fluid outlet temperature for 36 experiments. The energy estimators are compared to simulation results. The estimators for the stored energy in the heat transfer fluid, metal and phase change material obtain an average deviation of respectively 0.5 %, 3.9 % and 0.6 % with the stored energy predicted by the finite volume model. The estimator for the stored energy in the heat transfer fluid should be applicable to all LTES heat exchangers while the applicability of the estimators for stored energy in the metal and phase change material depend on small temperature differences between surface and interior of the metal and negligible heat losses.

Numerical approach for sizing vertical ground heat exchangers based on constant design load and desired outlet temperature

Vertical ground heat exchangers (GHE), as part of a ground source heat pump system, have been utilized for energy extraction/injection from/to the ground, i.e. a renewable source of energy, in the heating/cooling months to reduce building energy utilization. The current available GHE sizing methods are mostly based on several over-simplified one or two dimensional analyses, which cannot predict its thermal behavior with the accurate and realistic boundary conditions or in series configurations. In this study, thermal performance of vertical GHEs is numerically investigated at a given constant load through solving full transient 3D Navier-Stokes equations inside the U-tubes and the energy equation all over the computational domain, i.e. both fluid and solid parts. There are three interconnected parameters, namely GHE load, the heat transfer fluid outlet temperature, and the GHE depth that influence its thermal performance and consequently, the required investment cost. Therefore, the thermal performance of GHEs is computed for different constant loads at different depths, and it is shown that at each constant load, there is a trade-off between the investment cost and the thermal performance. Furthermore, the GHEs thermal performance in parallel and series configuration is investigated at a fixed depth and different loads. In light of the obtained data, the required size of the GHEs for a test building with an imbalanced energy extraction/injection rate is derived and the thermal performance of the proposed cluster of GHEs is numerically simulated for 20 years.

Effects of geometric and operating parameters on thermal performance of conical cavity receivers using supercritical CO2 as heat transfer fluid

In this paper, a comprehensive optical-thermal numerical model of the conical cavity receiver using supercritical CO2 (S–CO2) as the heat transfer fluid (HTF) is established by combining ray tracing with computational fluid dynamics method, which is verified with published data in the literature. Based on the model, the effects of critical geometric parameters (tube inner diameter, aspect ratio and cone angle ratio) and operating parameters (solar direct normal irradiance (DNI), HTF inlet mass flow rate and inlet temperature) on the thermal performance of the receiver are discussed thoroughly. The results indicate that a decrease in the tube inner diameter is beneficial to improve the optical-thermal performance of the receiver. When the aspect ratio and cone angle ratio are 1.5 and 0.25, respectively, the optical-thermal conversion efficiencies reach their optima, which are 75.13% and 75.30%, respectively. Moreover, for the S–CO2 receiver with optimal geometric parameters, the HTF outlet temperature increases linearly with increasing DNI and inlet temperature. Increasing mass flow rate can improve the optical-thermal conversion efficiency, but once the flow rate exceeds 0.04 kg/s, it has little effect on the efficiency improvement. These results can provide a reference for the design and operation of the S–CO2 conical cavity receiver.

Experimental study on temperature variation of metal hydride reactor incorporating helically coiled heat exchanger during absorption

Incorporating the helically coiled heat exchanger (HCHE) into the metal hydride (MH) reactors is an effective way to improve the hydrogen absorption rate. In the present study, an MH reactor incorporating a HCHE was built to investigate the influences of various operating parameters on the bed temperature and the heat transfer fluid outlet temperature at the hydrogen supply pressure (ps) of 0.8–1.2 MPa, the fluid inlet temperature (Tin) of 20–40 °C, and the fluid flow rate (qf) of 10–50 L h−1. The experimental results show that the increase in the ps and qf can improve the heat transfer performance and accelerate the hydrogen absorption process. Nevertheless, increasing ps makes the temporal variations of the bed temperature and fluid outlet temperature more unevenly, which limits the utilization for the heating system. Furthermore, the recommended fluid velocity (1.0–3.0 m s−1) inside heat exchanger tubes is not suitable for the MH reactor design. Compared with the hydrogen supply at constant pressure, the highest values of the MH bed temperature and the fluid outlet temperature rise are lower at constant flow rate of hydrogen. In addition, the hydrogen absorption process can be controlled by changing the hydrogen flow rate.

Investigation of a Novel Solar Powered Trigeneration System for Simultaneous Production of Electricity, Heating, and Refrigeration Below Freezing

Abstract A solar powered trigeneration system consisting of tower solar collector, Kalina cycle with the heat exchanger, and ejector-absorption refrigeration cycle is proposed to produce refrigeration below freezing, electricity, and process heat, simultaneously. Simulation through computational fluid dynamics using ansys-fluent package is conducted to examine the effect of coil diameter and inlet oil temperature on the pressure and temperature of solar heat transfer fluid. It is found that, for inlet temperature of 92 °C and direct normal irradiations of 850 W/m2, the solar heat transfer fluid outlet temperature increases by 9% when the coil diameter increased from 150 to 400 mm. Trigeneration performance is analyzed after altering hot oil outlet temperature, turbine inlet pressure, and the concentration of ammonia–water basic solution to study their effect on power produced by turbine, refrigeration load, exergy of refrigeration, and efficiencies of trigeneration system. An increase in the concentration of the ammonia–water basic solution is leading toward the significant increase in the turbine power and the elevation of trigeneration system’s energy and exergy efficiencies. Bottoming of the Kalina cycle with ejector-absorption refrigeration cycle shows the distribution of solar energy as energetic output 72.31% and energy lost to environment 27.69%. The solar exergy supplied to the trigeneration system is distributed as follows: 16.23% is the exergy produced, 1.62% is the exergy loss, and 82.15% is the exergy destroyed.