Inlet Heat Research Articles

Compound charging and discharging enhancement in multi-PCM system using non-uniform fin distribution

In the present study, a numerical model of a vertical shell and tube latent heat storage system validated with the experimental data is presented. The developed model comprises of three blocks of phase change materials (PCMs) having melting point temperatures (Tm) 360 °C, 335.8 °C and 305.4 °C, respectively. A non-uniform distribution of fins in three PCM blocks is initially employed to study the performance of the single PCM system (Tm=335.8 °C). The effect of inlet heat transfer fluid temperature on the charging and discharging performances of the single PCM and multiple PCM (m-PCM) systems is analysed by varying a Stefan number (Steref) parameter, calculated based on the single PCM system. The charging and discharging times for the m-PCM system are either similar or lesser than the single PCM system for Steref≥1, however, there is an improvement of 21–25% in the specific power charged and discharged by the m-PCM system for all the Sterefvalues (0.5, 1, 1.5 and 2) considered. By employing a compound enhancement technique which is a combination of non-uniform fin-distribution and PCM blocks length ratio optimization for the m-PCM system, 30% and 9% reduction in the charging and discharging time, respectively, over the single PCM system is achieved.

Energy analysis of a solar air heater with an absorber plate made of porous material

In this study, the energy analysis of a solar air heater with an absorber plate made of different obstacles was made. Absorber plate of the solar air heater was created with porous steel wool. Three different absorber plates were used for the experimental study. Complex plate (Type I) was used as the first type of absorber plate, less complex plate (Type II) as the second type absorber plate, and flat plate (Type III) the third type absorber plate. On these plates, which are manufactured as three different absorber plates, steel wools are placed in a complex and less complex way. One absorber plate was left empty. In the experiments, the mass-flow rate of the air passing through the air passage channels was taken as 0.05 kg/s and 0.025 kg/s, and the optimum flow rate was found as 0.05 kg/s. In order to make heater efficiency calculations, heater inlet temperature, outlet temperature, absorber plate temperature, ambient temperature and solar radiation values were measured. Efficiency values for different absorber plate were found between 23% and 74%.

Investigating the Effect of TIG and FSW Joint Design on the Mechanical Properties of the AA5083 Aluminum Alloy in Welding Processes

The 5083 aluminium alloy is one of the alloys of the 5xxx series that is widely used in defence and shipbuilding industries. In this study, the 5083 aluminium alloy plates were evaluated through two friction stir welding and tungsten inert gas welding (TIG) by a double groove weld with a 30° angle and a 2mm gap for TIG and a simple butt weld for FSW. In this study and in addition to examining the samples' mechanical properties, the microstructure changes and the hardness were also reviewed. The results show that the FSW weld has better mechanical properties than the TIG weld due to fast welding speed. However, by preparing the pieces, the mechanical properties of TIG get closer to those of FSW. In the FSW welding in the weld nugget, the grains have a fine and co-axial structure, and an increase in the advance rate will reduce the inlet heat and make the grains smaller. Nevertheless, in TIG welding at high speeds, the grains become more extensive with increased inlet heat.

Cascaded latent thermal energy storage using a charging control method

Several studies have used thermal energy storage systems to store renewable heat energy. Nevertheless, few studies have addressed the charging of renewable heat sources with unsteady temperatures. In this study, a cascaded latent thermal energy storage (CLTES) system utilizing a charging control method (CCM) is proposed for the efficient charging of renewable energy under unsteady temperature conditions. The CCM was used to control the inlet positions of CLTES tanks depending on the inlet temperatures. A CLTES system with a total volume of 834 L (3 × 278 L) was manufactured for the experiment using three tanks and phase change materials (PCM) with three different melting points. To verify the performance of the CCM system, three system types were considered: Single-PCM latent thermal energy storage, CLTES, and CLTES with CCM. The results show that the CCM increased the charged and discharged thermal energy by 33% and 44%, respectively, compared with the reference case under unsteady inlet heat transfer fluid temperature conditions. The results confirm that a multi-tank cascade system utilizing CCM can be used to efficiently charge unsteady renewable thermal energy sources.

A data-driven model for thermodynamic properties of a steam generator under cycling operation

The varying electricity demand from coal power plants due to the intermittent nature of renewable sources leads to load-follow and on/off operations referred to as cycling. Cycling causes transients of properties such as pressure and temperature within various components of the steam generation system.These transients cause increased damage because of fatigue and creep-fatigue interactions shortening the life of components. An algorithm is developed to identify cycling operations from the gross power data. The data-driven model based on artificial neural networks (ANN) is developed using 10 years data from Coal Creek Station power plant located in North Dakota, USA to estimate properties of the steam generator components during cycling operations. The uniqueness of this model is the ability to predict component properties for the cycling as well as base-load operations and is reported for the first time. The ANN model estimates the component properties, for a given gross power profile and initial conditions, as they vary during cycling operations. As a representative example, the ANN estimates are presented for the superheater outlet pressure, reheater inlet temperature, and flue gas temperature at the air heater inlet. The changes in these variables as a function of the gross power over the time duration are compared with measurements to assess the predictive capability of the model. Mean square errors of 4.49E-04 for superheater outlet pressure, 1.62E-03 for reheater inlet temperature, and 4.14E-04 for flue gas temperature at the air heater inlet were observed.

Dynamic Simulation of Hydrogen Iodide Decomposition in Catalytic Multi-Tubular Reactor

Sulfur-Iodine thermochemical cycle process has been considered a promising method to generate hydrogen from water. One of the main limitations of this process lies in the hydrogen iodide decomposer section, which requires substantial amount of heat at high temperature. The present study analyses the heat transfer limitation effect on the performance of hydrogen iodide decomposition in a multi-tubular catalytic reactor by means of dynamic simulation. The extensive numerical simulation shows that the inlet temperature heating medium (Helium gas) should be at least 700°C so to enable at least 90% conversion when the inlet molar fraction of hydrogen iodide is 0.6. Lowering the inlet heating medium will require the reduction in the inlet molar fraction of hydrogen iodide in order to keep the conversion at 90% and above.

Numerical modeling and performance comparison of high-temperature metal hydride reactor equipped with bakery system for solar thermal energy storage

The current study provides an optimal design strategy for the metal hydride reactor for the thermal energy storage system for solar bakery applications. The sensitivity analysis of the annular truncated hollow conical fins type reactor was conducted by using COMSOL Multiphysics 5.3a software. The gravimetric exergy output rate and exergy output of different designs were compared. It was found that the optimal geometric parameters and operating conditions for the annular truncated hollow conical fins type reactor are fin angle (θ)=20°, fin radius (Rf) = 0.07 m, number of fins (Nf)= 32 and fin spacing (Sf) = 0.02 m, fin thickness (thf) = 0.008 m, hydrogen supply pressure (Pin, H2) = 5 MPa and inlet heat transfer fluid velocity (VHTF,in) = 20 m/s. Finally, it was concluded that the Deign IV is the most favorable design, which has a uniform reaction, faster reaction time (15,000 s), and higher values of gravimetric exergy output rate and exergy output (1.23 W/kg, 0.028 kW).

Performance improvement of solar still by using hybrid nanofluids

The biggest shortcoming of conventional solar still is its limited productivity. In this work, improvement of solar still performance using two hybrid nanofluids is examined. Use of hot water and two conventional nanofluids were also utilized to study the improvement of the performance of solar still. Hybrid nanofluids, hot water or conventional nanofluids were linked to the solar system with heat exchanger placed at the bottom of the basin of the solar still. Pure desalinated water yield, the first and the second law efficiencies of the solar still with hybrid nanofluid were observed through modeling. Utilization of heat exchanger with hot water improved the solar still performance. Conventional nanofluids showed better performance than hot water. The best performance is obtained with the use of hybrid nanofluids. The yield, thermal efficiency and exergy efficiency with water–Al2O3–SiO2 hybrid nanofluid resulted in 4.99 kg m−2 day−1, 37.76% and 0.82%, respectively. The basin water depth, nanofluid flow rate, inlet heat exchanger temperature of the nanofluid and nanoparticle concentration played vital role together with solar radiation and ambient temperature to improve the performance.

Analysis and Evaluation of Multi-Energy Cascade Utilization System for Ultra-Supercritical Units

To address the large temperature difference in the air heater (AH) inlet of a traditional exhaust heat utilization system and energy grade mismatch problems during the heat and mass transfer processes, this study proposed a new multi-level waste heat cascade utilization system. Based on a principle of “temperature-to-port and cascade utilization”, this system uses the boiler side high-temperature flue gas and low-temperature air, and the turbine side high-temperature feed water and low-temperature condensate water, to conduct cross heat exchange according to the energy grade matching principle. Combined with a typical 1000 MW coal-fired unit, the heat transfer characteristics and energy-saving benefits of the new system were analyzed. The results showed that the new system has excellent performance: the heat rate decreased by 91 kJ/kWh, coal consumption decreased by 3.3 g/kWh, and power generation efficiency increased to 49.39%.

Solar Thermal Integration With and Without Energy Storage: The Cases of Bioethanol and a Dairy Plant

This paper looks at the resulting combination of working fluid inlet temperature and heat storage capacity as a means for increasing the solar fraction and the number of hours that renewable energy can be supplied to a background process. The portion of the process heat duty that can effectively be supplied from solar thermal energy, or solar fraction, increases with the inlet temperature of the solar field. The increase of inlet temperature is beneficial since it reduces the size of the solar field. The way to achieve higher inlet temperatures is by means of surplus heat that is stored during sunny hour. For further increasing the period of operation beyond sunny hours, thermal storage must be increased. In this work, two case studies are considered and it is found that the integration of solar thermal plants proves to be a cost-effective alternative in energy conservation and pollution reduction. The payback time reveals that doubling the time where the solar system delivers the required temperature is still profitable.

An experimental study of the efficacy of integrating a phase change material into a clay-straw wall in the Drâa-Tafilalet Region (Errachidia Province), Morocco

The objective of this new study is to integrate a Phase Change Material (PCM) into a clay-straw wall in order to reduce the energy consumption of buildings in Morocco's Drâa-Tafilalet Region. The underlying notion is to fully utilize the storage capacity in the walls built with clay and straw. Furthermore, to raise the thermal energy stored in the building envelope, a PCM was integrated into the walls. In this experiment, a reduced-scale cavity with replaceable sidewalls was used to study the thermal transfer taking place in walls. The effect of PCM location was also investigated by considering the reduction in both wall surface temperature and surface heat flux. Both the inner and outer wall layer temperatures were measured, while the heat flux through the walls and the heat stored in the walls were estimated. Results show that by integrating PCM into the clay-straw wall, the surface temperature can be reduced by up to 3 °C. In addition, the location of the PCM adjacent to the heat source considerably lowers the surface temperature, by a value of 1 °C compared to when PCM is placed on the outer wall layer. The peak heat flux of the PCM-integrated wall drops by 31.95% compared to the clay-straw wall without PCM. However, for the clay-straw wall with PCM on the outer layer, the peak heat flux is reduced by 26.5%. Moreover, the PCM-integrated wall stores 14.17 W/m2 on average of the inlet heat flux. On the other hand, the clay-straw wall with PCM on the outer layer and the wall with PCM embedded in the middle are both able to reduce the peak heat flux by 30.41%.

Thermodynamic-CFD analysis of waste heat recovery from homogeneous charge compression ignition (HCCI) engine by Recuperative organic Rankine Cycle (RORC): Effect of operational parameters

Beside the percent of fuel, which is burnt to produce power by combustion, the rest of the fuel energy is waste heat that can be recovered. In the present study, a thermodynamic-computational fluid dynamics (CFD) analysis was performed to recover waste heat from the coolant system (water jacket) in a six-cylinder homogeneous charge compression ignition (HCCI) engine by Recuperative organic Rankine cycle (RORC). The CFD simulations were used to estimate the waste heat at different operating conditions and to investigate the effect of the important parameters including intake temperature, intake pressure, equivalence ratio, and engine speed. Thermodynamic study was performed for the RORC, in which the inlet heat in the evaporator of a cycle was calculated based on the CFD analysis, and then the power produced in RORC was obtained. Results indicate that the improvement in thermal performance of the hybrid system in the HCCI engine can be as high as 27.94%.

Experimental Investigation of Performance and Emissions of Ethanol and n-Butanol Fuel Blends in a Heavy-Duty Diesel Engine

Alcohol fuels are potential alternative fuels for low-temperature combustion concepts in internal combustion engine applications. In this work, 80 vol% of ethanol and 80 vol% of n-butanol are blended with 20 vol% of n-heptane, respectively. These two alcohol fuel blends are investigated in a combustion research unit and a single-cylinder heavy-duty engine to compare the combustion and emission characteristics. The effects of EGR rate and achievable operating load range when using ethanol and n-butanol are the major goals of this investigation. The results show that the ethanol fuel blend requires much higher temperatures to auto-ignite than do the n-butanol blend and diesel. Both alcohol fuel blends show negligible soot emissions in the medium load range when operated with a 40% EGR rate. However, the ethanol fuel blend produces more nucleation mode particles and fewer accumulation mode particles compared to the n-butanol fuel blend under the same operating condition. Furthermore, the particulate size distribution shows that diesel generates more particles with larger particle diameters and thus more soot mass compared to alcohol fuel blends. Still, both alcohol fuel blends can be operated from low to high load with simultaneous reduction of NOx and soot emissions but at the cost of increased HC and CO emissions. The Euro VI-regulated soot mass and particle number are achieved from low to medium-high load for alcohol fuels. Diesel has the great advantage of achieving high combustion efficiency but shows a NOx/soot tradeoff at a high EGR rate. Generally, the ethanol fuel blend yields the lowest gross indicated efficiency in the whole test range compared to diesel and the n-butanol fuel blend due to the necessity of inlet heating, which decreases the thermal efficiency. The n-butanol fuel blend achieves the highest gross indicated efficiency (above 50%) in the medium-high load range.

Biodiesel production integrated with glycerol steam reforming process, solid oxide fuel cell (SOFC) power plant

Process of biodiesel production integrated with glycerol steam reforming process, solid oxide fuel cell power plant, and also the organic Rankine cycle for the simultaneous production of biodiesel and electricity is investigated. In the biodiesel production scenario, biodiesel is obtained from waste cooking oil using acid catalyst coupled with hexane extraction. The glycerol obtained from the above method is subjected to steam reforming process to produce hydrogen. The hydrogen produced is then used as fuel in the solid oxide fuel cell to provide thermal and electrical energy for biodiesel production and reforming processes. In addition, generating extra power will allow biodiesel production to be more economical by injecting it into the electricity network. It also provides the heat duty of organic Rankine cycle. Sensitivity analysis is accomplished on the proposed model to indicate the effects of several parameters on the biodiesel production, glycerol production, power generation, and process efficiency. This study showed that with increasing oil flow rate, total generated power in SOFC, SOFC cycle efficiency, input flow to fuel cell and cell number decreased. Also, with increasing the fuel utilization coefficient, electrical efficiency, cell number, total output power from SOFC and overall thermal efficiency increased. The effect of inlet heat to distillation towers on parameters such as overall thermal efficiency and electrical efficiency and total generated power was also investigated. As main results, solid oxide fuel cell efficiency, Electrical efficiency, and overall thermal efficiency based on LHV are 25.09%, 28.14%, and 85.16%, respectively. Overall, developing a biodiesel production plant by upgrading glycerol to hydrogen through steam reforming and using hydrogen produced in solid oxide fuel cell and employing organic Rankine cycle to generate power is an attractive strategy to make biodiesel production cycles more economical.

Modeling thermal and geometrical effects on non-condensable gas desorption in horizontal-tube bundles of falling film evaporation

Non-condensable gas (NCG) released in the multi-effect distillation associated with a thermal vapor compression (MED-TVC) seawater desalination seriously deteriorates the heat transfer efficiency. Due to the complicated coupled nature between NCG desorption and heat transfer process, little attention has been paid to local NCG desorption conditions which contribute to improving thermal efficiency of MED-TVC. Chemical desorption continuously releases more CO2 than O2 and N2 released by physical desorption. A numerical model, considering heat and mass transfer, flow dynamics and chemical reactions, predicts chemical reaction time, evaporation rate and CO2 desorption rate for varying thermal and geometrical parameters. The predicted CO2 desorption rate is in a good agreement with the running data of a venting system in a reference MED-TVC desalination plant. An increasing evaporation temperature, which results in a decrease in chemical reaction time and element volume, contributes to decreasing a specific CO2 desorption rate. With an increase in inlet heating steam velocity, the specific CO2 desorption rate decreases due to the increasing element volume and decreasing specific evaporation rate. The specific CO2 desorption rate increases with an increase in tube diameter and a decrease in dimensionless tube pitch due to the opposite effects of heat transfer and element volume.

Experimental investigation on the melting and solidification behavior of erythritol in a horizontal shell and multi-finned tube latent heat storage unit

Renewable energy sources are incapable of supplying continuous power due to their intermittent availability. To tackle this, energy storage systems incorporating phase change materials can be utilized. Among the several techniques, shell-and-finned-tube configurations show promising heat transfer performance and have greater engineering applicability. This study experimentally investigated the heat transfer mechanism in a horizontal shell-and-multi-finned-tube energy storage unit. Variation of average temperature and storage effectiveness as well as effects of inlet heat transfer fluid temperature and flow rate on the phase change of erythritol were experimentally investigated. It was found that the effect of inlet temperature was more significant than the flow rate (12–32% and 7–17%, respectively). Moreover, natural convection was found to significantly influence the heat transfer during melting where the melted material initially occupied the upper region of the unit and then moved from top to bottom. The outcomes of the present work help understand the effect of natural convection to be effectively utilized for the design and optimization of such storage configurations.

Second law optimization of heat exchangers in waste heat recovery

This paper numerically investigates the first and second law efficiencies of transient crossflow over tube banks. A significant number of simulations were performed using a commercial computational fluid dynamics (CFD) tool, ANSYS Fluent 18.2, with varying inlet temperature, Reynolds number, pitch ratio (PR), number of inline cylinders, and heat transfer coefficient defining a heat leakage on the system. Numerical results compare favorably with published data in terms of Nusselt number and pressure drop. Five hundred seventy-six simulations were performed, and energy efficiencies ranged from 72% to 99%, while exergy efficiencies ranged from 26% to 70%. No discernable, universal trends were observed across all data sets, but the staggering amount of results spans a wide range of operational characteristics for tube bundle waste heat recovery. To illustrate the insight such data can provide, we consider four sample cases for analysis: well-insulated low-grade heat recovery, poorly insulated low-grade heat recovery, well-insulated high-grade heat recovery, and poorly insulated high-grade heat recovery. Low- and high-grade heat recovery cases were simulated with differing inlet heat transfer fluid (HTF) values, and heat leakage was introduced as a source term in the 2D energy equation. Detailed descriptions of the efficiencies of all cases are described, with references to the immense body of simulation data included in the appendix. Overall, the highest efficiencies of the first and second laws were obtained in domains that have three cylinders and inlet temperature of 500 K and eight cylinders and an inlet temperature of 400 K, respectively. The main findings of this study could be beneficial in designing a highly efficient waste heat recovery system, especially when source temperatures vary.

Performance comparison on wall cooling and heat supply for power generation between fuel- and liquid metal-cooled scramjet

Thermal protection has been one of the main technology limitations for scramjets, due to high-flux combustion heat dissipation. Meanwhile, there is a great demand of high-quality heat source for onboard power generation. This study introduces the concepts of fuel- and liquid metal-cooled scramjet, in which the combustion heat dissipation is transferred by wall coolants to closed power generation system. The performance on wall cooling and heat supply for power generation between these two types of scramjets are compared through the wall temperature distribution, as well as the heat transfer rate and inlet exergy rate of heater. Results indicate that liquid sodium exhibits better on wall cooling than hydrogen, and the decrease percentage of maximum wall temperature is as high as 6.15%. Liquid metal-cooled scramjet provides more heat than fuel-cooled scramjet under identical conditions, but the latter has greater potential of heat supply at high heater inlet temperatures and fuel equivalence ratios. Besides, power generation efficiency has significant influence on the wall temperature distribution for liquid metal-cooled scramjet and the heat transfer rate of heater for fuel-cooled scramjet. This research presents the advantages of liquid metal-cooled scramjet on wall cooling and heat supply.

Numerical investigation on the melting of nanoparticle-enhanced PCM in latent heat energy storage unit with spiral coil heat exchanger

Latent heat storage units are widely used in building heating systems due to its high energy storage density, whereas the practical performances of them are limited by the low thermal conductivities of phase change materials. In this paper, copper nanoparticles were added into paraffin to enhance the heat transfer rate of a latent heat storage unit using a coil heat exchanger. A three-dimensional numerical model was built to simulate the melting process of phase change material, and it was well validated against the experimental data. The simulation results showed that the nanoparticle-enhanced phase change material saved 19.6% of the total melting time consumed by the pure phase change material. In addition, the dispersion of nanoparticles significantly alleviated the temperature non-uniformity in the unit. Moreover, for the unit using nanoparticle-enhanced phase change material, the flow rate of heat transfer fluid was not recommended higher than 0.75 m3/h. The dispersion of nanoparticles could enlarge the optimum heat transfer fluid temperature range to 60–70 °C compared with that of pure phase change material (60–65 °C). Therefore, the application of nanoparticle-enhanced phase change material in the latent heat storage unit can significantly enhance heat transfer, and the proposed optimum inlet heat transfer fluid temperature range could contribute to higher energy efficiency.

Performance assessment of a closed-recuperative-Brayton-cycle based integrated system for power generation and engine cooling of hypersonic vehicle

Hypersonic vehicle is a next generation aircraft/spacecraft with broad applications, but its development is limited by the high-power electricity supply and thermal protection of engine. This study presents an integrated system based on Closed-Recuperative-Brayton-Cycle (CRBC) for power generation and engine cooling, in which combustion heat dissipation is transferred by liquid metal and partly converted into electric power. An integrated system model which consists of a scramjet combustor, wall cooling channels and a CRBC power generator, is established to evaluate system performance. Results indicate that the integrated system can meet the demands of both high power generation and engine thermal protection for hypersonic vehicles. There is an optimal temperature of liquid metal at heater inlet for power generation performance. The peak electric power increases with fuel equivalence ratio. Liquid sodium exhibits excellent heat transfer performance for engine cooling, the mass flowrate of which becomes greater with smaller fuel equivalence ratio. Besides, the influence of power generation on propulsion is not significant. The specific impulse and specific thrust have maximum decrease of about 2% compared to the cases without heat dissipation. This research provides a novel scheme to achieve power generation and engine thermal protection for hypersonic vehicles.