Apparent Heat Research Articles

Fabrication and Performance of 300-mm Wafer-Scale Silicon Microchannel Cooler

This paper describes the design, fabrication, and thermal performance of 300 mm diameter wafer-scale Si microchannel coolers that demonstrated a junction temperature rise of less than 18°C when dissipating about 14 kW of power. A thermal test wafer, which included hot-spot regions to mimic high-power compute cores, was attached to the wafer-scale microchannel cooler with Pb-Sn solder. Glass manifold layers were attached to the microchannel wafer using a frit material. The average apparent heat transfer coefficient, h <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">app</sub> , was about 104,000 W/(K-m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ).

Experimental study on diesel spray combustion and heat transfer characteristics with multiple injection strategies by means of rapid compression and expansion machine

A comprehensive investigation was carried out to understand diesel spray combustion processes and heat transfer by applying multiple injection strategies. Experiments were conducted under different injection pressure conditions ranging from 30 MPa to 180 MPa, and the results clarified the capability of high injection pressure to facilitate spray evaporation and distribution in detail. It also demonstrated that the local heat flux at the piston lip started to increase earlier, followed by the upper lip and lower lip resulting from the spray/wall interaction and mixture development. In addition, the heat flux at the chamber head showed the highest value and longest duration, which was primarily related to the initial location where the high-temperature flame appeared. Furthermore, combining the spray combustion images acquired from diffused backlight illumination (DBI) and the apparent heat release rate (AHRR) by analyzing the in-cylinder pressure, the results clarified the effect of high injection pressure on reducing the heat transfer and soot formation by improving the combustion performance.

Condensation of NH3/H2O with mass concentrations of 80%-96%: Experimental study in a plate heat exchanger

High concentration NH3/H2O is suitable for Kalina cycles used for the recovery of low grade heat. Plate heat exchangers (PHEs) are compact and reduce the charge of working fluid. This paper investigates the condensation of NH3/H2O with NH3 mass concentrations of 80%-96%. The vapor and liquid concentrations are close to equilibrium state, which are different from normal absorbers. The apparent heat transfer coefficients (HTCs) and frictional pressure drop are presented, covering the mass fluxes of 32–86 kgm−2s−1, the averaged vapor qualities of 0.08–0.65 and the saturated pressure of 610 to 780 kPa. Larger mass fluxes noticeably increase the apparent HTCs and frictional pressure drop. At the mass concentrations of 96%, 91% and 88%, higher vapor qualities increase the apparent HTCs for large mass fluxes. The apparent HTCs decrease slightly with vapor qualities for 80% mass concentration. The experimental results are compared with those of pure NH3. The flow patterns of high concentration NH3/H2O are considered as full film flow and partial film flow, which are the same as for NH3. The mass transfer resistance deteriorates the heat transfer especially for partial film flow, which happens at small liquid mass fluxes. The mass transfer resistance has negligible influences on frictional pressure drop.

PMMA nano-encapsulated phase change material colloids for heat management applications

Phase Change Materials (PCM) emulsions or micro-nano-encapsulated into organic and inorganic shells have attracted scientific interest for their potential to enhance the thermal capacity and the efficiency of heat transfer liquids. In this work, RT21HC, a commercial PCM with transition temperature at 21 °C, has been successfully nano-encapsulated into Poly(methyl-methacrylate) (PMMA) shells by an emulsion polymerization process after the selection of proper surfactant and synthesis parameters, in order to obtain complete encapsulation and stable colloidal dispersions. Water-based colloidal dispersions containing 10 wt% PCM were obtained and characterized from point of view of microstructure, colloidal stability, rheological properties, apparent heat capacity and thermal diffusivity, in order to show the potential of these colloidal dispersions as advanced heat management fluids. With the aim to mitigate the phenomenon of PCM crystallization supercooling that is caused by nano-confinement and is cause of apparent thermal capacity loss, the effect of incorporation into the nano-capsules of two fatty esters, two fatty alcohols and a fatty acid as nucleating agents, has also been studied.

Distinct magnetic relaxation behaviors in nitronyl nitroxide-based cocrystalline supramolecular system with DyIII-O-H⋯O-N hydrogen bond

The self-assembly of Dy(hfac)3·2H2O, Co(hfac)2·2H2O or Mn(hfac)2·2H2O (hfac = hexafiuoroacetylacetonate) with NITPh-triazole radical (NITPh-triazole = 2-[2-(1H-1,2,4-triazol-1-yl)phenyl]-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) produces two 2p-3d-4f compounds of formula {[Dy(hfac)3(H2O)2][Co2(hfac)4(NITPh-triazole)2]2.CH2Cl2}n (1) and {[Dy(hfac)3(H2O)2][Mn2(hfac)4(NITPh-triazole)2]2}n (2) featuring extraordinary intermolecular hydrogen bonds between coordinated H2O molecules and uncoordinated NO groups linking into a supramolecular one-dimensional chain. Notably, the LnIII-O-H⋯O-N hydrogen bond bridge has been rarely observed in nitronyl nitroxide-metal system. Magnetic performance and heat capacity of both 2p-3d-4f compounds are detected. Interestingly, 1 and 2 both show apparent double peaks of χ′′ signals with two-step magnetic relaxation processes. Furthermore, the effective barrier of 1 is obviously higher than 2. As far as we know, employing unusual intermolecular LnIII-O-H⋯O-N hydrogen bond, it is the first to obtain supramolecular 2p-3d-4f one-dimensional heterospin materials with apparent slow magnetic relaxation and heat capacity behaviors.

A multidimensional numeric study on smoldering-driven pyrolysis of waste polypropylene

The ex-situ smoldering driven pyrolysis reactor can simultaneously remediate the organically contaminated soil/sand and valorize the plastic waste to value-added fuels. This study establishes a multidimensional model to investigate the pyrolysis of polypropylene driven by self-sustained smoldering. The melting and decomposing processes during the pyrolysis of polypropylene have been simulated using the modified apparent heat capacity method and lumped kinetic model. Using a porous structure with high thermal conductivity in the pyrolysis domain proved to be a practical approach to address the non-uniform temperature distribution and low heating rate of plastics during pyrolysis. The research focus of this study is to obtain high-quality plastic pyrolysis liquid (oil, C6–C24) within a reasonable operating time (duration of the plastic pyrolysis process). Also, the operating conditions (Darcy air velocity, initial char concentration, and PP content) determine the yield of pyrolysis products by regulating the temperature and vapor residence time. Therefore, the sensitivity analyses of pyrolysis duration and oil yield to operating conditions have been performed. It is also found that the interface wall (between smoldering and pyrolysis chambers) heat transfer coefficient determines the smoldering chamber's thermal performance. This study provides new insights into the valorization of waste plastics and the remediation of contaminated soil/sand.

Impact of Low Reactivity Fuel Type and Energy Substitution on Dual Fuel Combustion at Different Injection Timings

Dual fuel combustion leverages a high-reactivity fuel (HRF) to ignite a premixed low reactivity fuel (LRF)–air mixture to achieve high efficiencies and low engine-out emissions. The difference in the relative amounts of these fuels and in-cylinder fuel reactivity stratification profoundly impacts dual fuel combustion. The effect of increasing LRF energy substitution on dual fuel combustion at various fixed HRF (diesel) quantities was experimentally studied for two different LRFs (natural gas and propane) on a heavy-duty single cylinder engine at a constant intake pressure of 1.5 bar and injection pressure of 500 bar. Further, this effect was studied for three different HRF start of injection (SOI) timings of 310 CAD (50° BTDC), 330 CAD (30° BTDC), and 350 CAD (10° BTDC). For 310 CAD SOI, increasing the LRF substitution at a fixed HRF resulted in higher loads, peak cylinder pressures, and peak apparent heat release rates (AHRR). The onset of low temperature heat release (LTHR) was advanced as the LR fuel flowrate increased at a given pilot quantity for diesel–NG but remained constant for diesel–propane dual fuel combustion at these SOIs due to the impact of propane on the temperature at which the onset of LTHR occurs. The indicated fuel conversion efficiency (IFCE) ranged from 35% at 4 bar IMEPg to 47% at 9 bar IMEPg with NG as the LRF and from 35% at 3 bar IMEPg to 51% at 8 bar IMEPg with propane as the LRF. For 330 CAD SOI, the HC and CO emissions decreased at a higher fixed HRF quantity and an increasing LRF substitution. However, this was accompanied by significantly higher oxides of nitrogen (NOx) emissions for both NG and propane as LRFs. For 350 CAD SOI, increasing the LRF substitution at constant HRF consistently led to a higher second stage AHRR, whereas the first stage AHRR remained relatively unchanged for both NG and propane as LRFs. This was accompanied by higher IFCE for all fixed HRF quantities as LRF substitution was increased. For all SOIs studied, the HC and CO emissions were substantially lower and combustion stability was significantly improved as the LRF substitution (and consequently, the load) was increased. To the best of the authors’ knowledge, the present work is unique in that it involves the first systematic experimental study of the impact of LRF energy substitution at fixed HRF quantities over a range of SOIs, providing comparative results for two different LRFs (NG and propane) on the same engine platform.

An experimental and computational analysis of combustion heat release transformation in dual fuel combustion

Dual fuel (DF) diesel-methane combustion, which employs a high-reactivity fuel (diesel) to ignite a low-reactivity fuel (methane), is a widely studied combustion strategy for internal combustion engines, with significant potential for engine-out emissions reductions without the need for major hardware modifications. A phenomenon, which has been reported in the DF literature, but not explained fully, is the transformation of the shape of the apparent heat release rate (AHRR) curve as the start of injection (SOI) of diesel is advanced beyond a certain threshold; coincidentally, this AHRR transformation is usually accompanied by a sharp decrease in engine-out emissions of oxides of nitrogen (NOx). The goal of the present work is to establish the underlying physical reason(s) that cause the AHRR transformation. The AHRR transformation was observed on a single cylinder research engine (SCRE) at an indicated mean effective pressure (IMEP) of 5 bar at a speed of 1500 rev/min. The transformation occurred over a range of SOIs from 330 to 320 crank angle degrees (CAD). While the 330 CAD SOI exhibited a typical two-stage AHRR curve, with a clearly definable first-stage peak followed by a second-stage AHRR with little-to-no low temperature heat release (LTHR) present and high engine-out NOx, the 320 CAD SOI exhibited a single-stage, Gaussian-like AHRR curve, with noticeable LTHR and at least one order-of-magnitude lower NOx emissions. Leveraging analysis of experimental data and three-dimensional computational fluid dynamic simulations, the authors show that the AHRR transformation is impacted mainly by differences in local equivalence ratio distributions within the cylinder at ignition onset for different diesel SOIs.

Heat capacity of cytisine – the drug for smoking cessation

The characterization of cytisine (CYT) and its blends with poly(lactic acid) was performed using thermal analysis, elemental analysis, infrared spectroscopy, and powder X-ray diffractometry. The heat capacities, total enthalpy, and phase transitions of CYT were established from 1.8 to 448.15 K (−271.35 – 175 °C) by advanced thermal analysis. Data were obtained using a Quantum Design Physical Property Measurement System (PPMS) and a differential scanning calorimetry (DSC). The low-temperature heat capacity of the crystalline CYT in the range of 1.8 to 300 K (−271.35 – 26.86 °C) was measured by PPMS and fitted to a theoretical model in the low temperature region below 11 K (−262.15 °C), to orthogonal polynomials in the middle range 5 K <T < 60 K (−268.15 °C < t < −213.15 °C) and to the Debye and Einstein functions in the high range of temperature above 60 K (−213.15 °C). The liquid heat capacity was calculated based on the approximated linear regression data above the molten state of the experimental heat capacity of CYT obtained by the standard DSC measurements, and it was expressed as Cpliquid = 0.0838T + 346.78 J·K−1·mol−1. The calculated heat capacity in the solid state was extended to a higher temperature and was used, together with liquid heat capacity, as the reference baselines for the advanced thermal analysis of CYT. The PPMS and DSC/TMDSC methods are complementary methods for thermal analysis of cytisine. The PPMS method allowed determination of the equilibrium heat capacity in the solid state, which together with the equilibrium heat capacity in the liquid state allowed to analyze of the experimental apparent heat capacity of cytisine obtained based on DSC. The melting temperature and the total heat of fusion of crystalline material were established as 431.8 K (158.65 °C) and 26.5 kJ·mol−1, respectively. The solid and liquid heat capacities and transition parameters of CYT were applied to calculate total enthalpies for fully amorphous and crystalline states. Analyses of DSC and X-ray confirmed the presence of the solid-solid transition linking with not so far described a polymorphism phenomenon of CYT. Based on the thermogravimetric analysis the temperature of degradation of CYT was determined as 460.5 K (187.35 °C). Also, a preliminary thermal analysis of the blends of cytisine and poly(lactic acid) as a new candidate for drug delivery system was presented.

Advances in material phase change modelling approach for EU-DEMO limiter’s plasma-facing components

Within the EU-DEMO first wall protection framework, work on limiter’s plasma-facing component design has started under plasma disruptive events (Richiusa et al., 2022). Starting from the rationale behind the TARTIFL&TTE software (Richiusa et al., 2022), this companion paper describes the progress on the engineering modelling of the plasma-facing material phase change under high heat flux, with the aid of COMSOL Multiphysics® software. The aim is to develop a reliable technique which can be used by designers for predicting how much of the solid armour undergoes phase change. This helps satisfy requirements for actively cooled components, such as at which armour depth safely locating the cooling system, and if its design can safely handle the heat transfer in the resulting component configuration after the disruption is extinguished. A few changes to the driving idea in Richiusa et al. (2022) will be also highlighted.The multiphysics software allows us to implement a 1D model which can be extended to 2D/3D geometries subjected to both uniform and non-uniform heat flux. It also offers the capability of conjugated heat transfer in solids and liquids by coupling the two different domains. Although this multiphysics approach is also investigated, no effort in melting layer motion modelling is done. Therefore, the equivalent way of validating this approach while reducing its computational time is working with one single solid domain, within which any liquid phase changes are tracked by an apparent heat capacity formulation. The vapour domain is not modelled. The material removal due to the evaporative mass flux is modelled by means of moving mesh frames which push the recessing liquid interface backwards according to gas kinetics-driven boundary conditions. The melt pool is not removed during the transient. Mass balance considerations drive the liquid-to-vapour interface velocity.The 3D Multiphisics implementation (3D-TARTIFL&TTE), is here supported by a benchmark activity and an application to the limiter’s plasma-facing armour, whose preferred chosen thickness is 20 mm.

Thermal-seepage coupled numerical simulation methodology for the artificial ground freezing process

This paper proposes a thermal-seepage coupled numerical simulation methodology for the artificial ground freezing (AGF) process using measured soil freezing characteristic curve (SFCC). Firstly, the relation equation between pore ice content and temperature is established based on the measured SFCC, and a thermal-seepage coupled simulation method of AGF is proposed. After that, the performance of the proposed method was investigated based on soil column and large-scale model tests. Finally, the proposed method is compared with the traditional apparent heat capacity method. The results show that: (1) By introducing SFCC, the relation equation between pore ice content and temperature can be established with a clear physical meaning and a direct parameter determination process; (2) The proposed method can reasonably simulate the thermal and hydraulic field of AGF with or without seepage; (3) Compared with the traditional apparent heat capacity method, the proposed method has a conform to physical essence of phase transition and potential heat release and shows comprehensive improvement in theoretical basis, calculation accuracy, robustness and efficiency. Overall, the research results can provide a further understanding and improvement for numerical simulation in AGF.

Advantages and risks of using ore-coal briquettes in blast furnaces

Reducing carbon consumption, and, consequently, CO2 emissions during iron smelting in blast furnaces is a priority for improving the technology of blast furnace smelting. In the literature, the question of the influence of the development of direct reduction of iron on the consumption of carbon as a source of reducing gas and a source of heat has been considered. In this case, the development of direct reduction in the lower zone of the furnace at temperatures above 900 °C is considered. However, direct (solid-phase) reduction can be implemented in the upper zone of a blast furnace when using ore-coal briquettes in the charge. It is shown that the solid-phase reduction reactions can proceed at temperatures above 700 °C in the upper zone of a blast furnace during the reduction of Fe3O4 and FeO. At the same time, the apparent heat capacity of the charge increases and the temperature of the top gas decreases, which is confirmed by data on the operation of blast furnaces of NLMK PJSC, which use ore-coal briquettes. The raw materials for the production of briquettes are iron ore concentrate, sludge, blast furnace dust, aspiration dust. A bentonite and a ce-ment are used as a binder. The briquettes contain 40‒42% iron and 10‒15% carbon. The theoretical analysis and statistical processing of data on the operation of blast furnaces led to the conclusion that the solid-phase reduction of iron oxides actively proceeds at temperatures below 900 °C. The results of experimental heats showed the use of briquettes allows to reduce the specific consumption of coke and the total carbon consumption of fuel. The prospects for the use of the briquettes are associated with an increase in their mechanical properties. The use of ore coal briquettes obtained from a concentrate with an iron content of 65‒68% will reduce the rate of fuel carbon and CO2 emissions.

Development and Validation of a CFD Combustion Model for Natural Gas Engines Operating with Different Piston Bowls

Nowadays, an accurate and precise description of the combustion phase is essential in spark-ignition (SI) engines to drastically reduce pollutant and greenhouse gas (GHG) emissions and increase thermal efficiency. To this end, computational fluid dynamics (CFD) can be used to study the different phenomena involved, such as the ignition of the charge, combustion development, and pollutant formation. In this work, a validation of a CFD methodology based on the flame area model (FAM) was carried out to model the combustion process in light-duty SI engines fueled with natural gas. A simplified spherical kernel approach was used to model the ignition phase, whereas turbulent flame propagation was described through two variables. A zero-dimensional evolution of the flame kernel radius was used in combination with the Herweg and Maly formulation to take the laminar-to-turbulent flame transition into account. To estimate the chemical composition of burnt gas, two different approaches were considered—one was based on tabulated kinetics, and the other was based on chemical equilibrium. Assessment of the combustion model was first performed by using different operating points of a light-duty SI engine fueled with natural gas and by using the original piston. The results were validated by using experimental data on the in-cylinder pressure, apparent heat release rate, and pollutant emissions. Afterward, two other different piston bowl geometries were investigated to study the main differences between one solution and the others. The results showed that no important improvements in terms of combustion efficiency were obtained by using the new piston bowl shapes, which was mainly due to the very low (+4%) or null increase in turbulent kinetic energy during the compression stroke and due to the higher heat losses (+20%) associated with the increased surface area of the new piston geometries.

Self-assembly of MXene-decorated stearic acid/ionic liquid phase change material emulsion for effective photo-thermal conversion and storage

As a typical latent functionally thermal fluid with large energy storage capacity and good liquidity, phase change material emulsion (PCME) plays a broad and important role in solar energy utilization. However, the high-temperature instability and supercooling problems of PCME limit its practical application. The ionic liquid (IL)-based PCME allows for the possibility of being used as a heat transfer fluid (HTF) under more extreme temperature conditions. In this work, stearic acid (SA)/IL PCME, prepared by one-step self-assembly of MXene nanosheets at the SA/IL interface, can effectively absorb and convert solar energy into thermal energy. Furthermore, MXene-decorated SA/IL PCMEs have good high-temperature stability, little supercooling degree (0.9–3.1 °C), and large energy storage capacity. The maximum apparent specific heat capacity and average absorbance of the MXene-decorated SA/IL PCME are 4.5 and 303.1 times higher than those of IL, respectively. Under 2 sun irradiation, the 0.05–20 wt% MXene-decorated SA/IL PCME achieves high photo-thermal conversion efficiencies (91.3% at 68.9 °C, 39.4% at 115.1 °C) due to its large energy storage capacity and excellent optical absorption property. The simple interfacial self-assembly provides a promising strategy to prepare high-performance SA/IL PCME used as a novel HTF for medium-temperature solar energy utilization systems.

Numerical modeling of phase prediction and geometry evolution of micro-drilling using single pulse laser

Due to high production capability, long laser pulses are preferred over ultrashort pulses during Laser-based machining. To reduce metallurgical defects, viz. heat-affected zone, recast layer, and micro-cracks, it is essential to analyze the causes of these defects and to derive the remedies. Generally, an extensive experimental investigation is carried out for the same. The experimental analysis is time-consuming, tedious, and requires high capital investment. Therefore, in this work, a two-dimensional axisymmetric transient finite element method (FEM) based numerical model of Laser-material interaction was developed to explore the temperature evolution, phase change, and geometry evolution with the help of coupled heat transfer and deformed mesh. The heat transfer module was implemented by considering the phase change using the apparent heat capacity method. The model was duly validated for the evolution and geometry of the Laser-drilled hole. The model was found in agreement with the experimental results, with a percentage deviation of 12% in the prediction of the responses. The numerical model will help to predict the temperate evolution and hydrodynamic behavior of the material during the laser-material interaction. This, in turn, will help to mitigate the metallurgical defects.

On the interpretation of the unusual behavior of aqueous-organic mixtures in concentration regions with intersecting isotherms of heat capacity properties

Based on our own and some literature results, we have carried out a detailed analysis of concentration regions of the aqueous-organic mixture in which the temperature dependences of both excess molar heat capacity, CpE, and apparent molar heat capacity of each component, Cp,ϕ,i, are intersected. It is established that the ∂CpE/∂T and ∂Cp,ϕ,w/∂Tderivatives (W is water) for the {(W + hexamethylphosphoramide (HMPA)} and {(W + tert‑butanol (t-BuOH)} mixtures intersect in a rather narrow concentration interval between (0.30 and 0.35) and (0.35 and 0.40) mole fractions of the organic component, respectively. This fact we have interpreted as evidence that the decisive role in the mutually overlapping heat-capacity contributions to CpEresulting in such a situation plays the abnormal change in the isobaric molar heat capacity of W (Cp,w), which has a minimum at T ≈ 308 K, when the temperature increases.

Predicting the Temperature Evolution during Nanomilling of Drug Suspensions via a Semi-Theoretical Lumped-Parameter Model.

Although temperature can significantly affect the stability and degradation of drug nanosuspensions, temperature evolution during the production of drug nanoparticles via wet stirred media milling, also known as nanomilling, has not been studied extensively. This study aims to establish both descriptive and predictive capabilities of a semi-theoretical lumped parameter model (LPM) for temperature evolution. In the experiments, the mill was operated at various stirrer speeds, bead loadings, and bead sizes, while the temperature evolution at the mill outlet was recorded. The LPM was formulated and fitted to the experimental temperature profiles in the training runs, and its parameters, i.e., the apparent heat generation rate Qgen and the apparent overall heat transfer coefficient times surface area UA, were estimated. For the test runs, these parameters were predicted as a function of the process parameters via a power law (PL) model and machine learning (ML) model. The LPM augmented with the PL and ML models was used to predict the temperature evolution in the test runs. The LPM predictions were also compared with those of an enthalpy balance model (EBM) developed recently. The LPM had a fitting capability with a root-mean-squared error (RMSE) lower than 0.9 °C, and a prediction capability, when augmented with the PL and ML models, with an RMSE lower than 4.1 and 2.1 °C, respectively. Overall, the LPM augmented with the PL model had both good descriptive and predictive capability, whereas the one with the ML model had a comparable predictive capability. Despite being simple, with two parameters and obviating the need for sophisticated numerical techniques for its solution, the semi-theoretical LPM generally predicts the temperature evolution similarly or slightly better than the EBM. Hence, this study has provided a validated, simple model for pharmaceutical engineers to simulate the temperature evolution during the nanomilling process, which will help to set proper process controls for thermally labile drugs.

Fast differential scanning calorimetry to mimic additive manufacturing processing: specific heat capacity analysis of aluminium alloys

Eutectic AlSi12, commonly used in casting and in additive manufacturing, is investigated with Fast Differential Scanning Calorimetry to determine the impact of different cooling rates from the liquid state upon the apparent specific heat capacity on subsequent heating. A heat flow correction strategy is developed and refined for the reliable and precise measurement of sample heat flow using chip sensors and assessed by the evaluation of results on pure (99.999%) aluminium. That strategy is then applied to the study of the AlSi12 eutectic alloy, and rate-dependent perturbations in the measured apparent specific heat capacity are discussed in terms of Si supersaturation and precipitation. Several cooling rates were implemented from − 100 to − 30,000 K s−1, and subsequent heating ranged from + 1000 to + 30,000 K s−1. After rapid cooling, a drop in AlSi12 apparent specific heat capacity is found on heating above ~ 400 °C; even at rates of + 10,000 K s−1, a result which has high relevance in metal additive manufacturing where similarly fast temperature cycles are involved. The Literature data, temperature modulated DSC and CALPHAD simulations on the heat capacity of AlSi12 are used to provide comparative context to the results from Fast Differential Scanning Calorimetry.

Simulation of Phase Change Material Absorbers for Passive Cooling of Solar Systems

One of the main challenges that face the reliable use of photovoltaic solar systems in hot arid regions is the prevailing high temperatures during the day. To overcome this issue, Phase Change Materials (PCM) are used for passive cooling providing different options to attain sufficient thermal management solutions for different applications. Passive cooling can be achieved by adjusting a heat sink to the solar PV module. This can be realized by attaching a PCM layer or sensible heat storage to the backside of PV panels. Few studies have reported on simplified modeling and numerical procedures using the apparent heat capacity formulation and volume averaging technique as a robust approach to solving such sophisticated problems with minimal computational efforts, high accuracy, and in a short period of time. However, there is still a need to bridge the large-scale gap between the macroscale within the PCM layer, with a moving melting front, and the length scale of PV modules. Hence, this work focuses on modeling and simulating PCM-Matrix Absorbers (PCM-MA) that consist of fibrous aluminum cellular structure filled with PCM for passive thermal management of PV panels using apparent heat capacity formulation and homogenization based on volume averaging technique. COMSOL Multiphysics FEM software was used for the numerical simulation of the phase change problem by using a Smoothed Heaviside step function to overcome the singularity of PCM challenge that arises with sharp melting temperatures. To validate the proposed model, it has been compared with a benchmark analytical solution for an ice melting problem, i.e., the Stefan problem, in a semi-finite slab, i.e., Neumann’s solution under the same assumptions and boundary conditions. The specific characteristics of phase change and evolution of melting front with time, heat capacity change with the temperature at different times, and with locations along the slab height are presented. As the phase change is modeled to take place over a mushy region, i.e., a narrow temperature interval rather than a sharp melting point, the results show a good coincidence of the heat capacity profile and its peak at different times and locations. The validated model can be used for the optimization of PCM-MA for any specific geographical location and other applications such as the passive cooling of buildings with PCM integrated with the outer envelope. To this end, the results of the simulation in this work are shown to be in agreement with those obtained from the analytical solution.

Thermodynamic modeling of MDEA(aq)-NH3(aq)-K2CO3(aq)-CO2(aq) using the Extended UNIQUAC model

The development of advanced processes for carbon dioxide capture requires reliable thermodynamic models to ensure accurate process design. This work presents an optimized parameter set of the Extended UNIQUAC model for advanced mixed solvent solutions containing CO2-MDEA-NH3-K2CO3 in water. The model was parameterized using vapor–liquid equilibrium, pure component saturation pressure, excess enthalpy, heat of absorption, molar heat capacity, apparent molar heat capacity, and solid–liquid equilibrium. These thermal and equilibrium properties cover temperatures between 253.6K to 600K and pressures up to 75.6bar. The current model represents an extension of previous versions that were suitable for modeling aqueous NH3 and K2CO3 solutions. This parametrization accounts for molecular interactions between MDEA and these two components, which allows for the design of advanced capture processes. This paper demonstrates that the new model parameters are valid within the range of operational conditions typically found in CO2 capture processes.