Latent Heats Research Articles

Evaluation of a rough-surface evaporator applied to an absorption heat transformer for water desalination

Abstract The purpose of this work is to evaluate the performance of a rough-textured evaporator applied to a single-stage absorption heat transformer for water desalination (SAHT-WD). The stainless-steel evaporator was subjected to an abrasive material release treatment (sandblast texture) to provide a texture that fosters phase change heat transfer compared to a smooth surface. To determine the performance of the evaporator, the evaluation has been divided into an experimental and a theoretical analysis. The experimental analysis focused on determining the operating conditions that favor the performance of the evaporator and the SAHT-WD. For the theoretical analysis, a mathematical model was developed to predict the wetting efficiency and the heat-transfer coefficients of the evaporator. To quantify the improvement in the performance of the rough-surface evaporator, the experimental results were compared with those reported in a reference work. The results indicate that the sandblasted texture improved the performance of the evaporator as well as that of the SAHT-WD. The results of the mathematical model suggest that the rough tube improved the wetting efficiency of the evaporator.

Polyethylene glycol/polylactic acid block co‐polymers as solid–solid phase change materials

AbstractPhase change materials (PCMs) are promising thermal energy storage materials due to their high specific latent heat. Conventional PCMs typically exploit the solid–liquid (s–l) transition. However, leakage and leaching are common issues for solid–liquid PCMs, which have to be addressed before usage in practical applications. In contrast, solid–solid (s–s) PCMs would naturally overcome these issues due to their inherent form stability and homogeneity. In this study, we report a new type of s–s PCM based on chemically linked polyethylene glycol (PEG, the PCM portion) with polylactic acid (PLA, the support portion) in the form of a block co‐polymer. Solid‐solid latent heat of up to 56 J/g could be achieved, with melting points of between 44 °C and 55 °C. For comparison, PEG was physically mixed into a PLA matrix to form a PEG:PLA composite. However, the composite material saw leakage of up to 9% upon heating, with a corresponding loss in thermal storage capacity. In contrast, the mPEG/PLA block co‐polymers were found to be completely homogeneous and thermally stable even when heated above its phase transition temperature, with no observable leakage, demonstrating the superiority of chemical linking strategies in ensuring form stability.

Analysis on temperature vacuum swing adsorption integrated with heat pump for efficient carbon capture

Carbon capture and storage (CCS) is gathering the momentum to achieve the ultimate target of carbon neutrality. Temperature vacuum swing adsorption (TVSA) has uncovered its superiority due to large working capacity, CO2 purity and recovery rate. However, high energy demand in the regeneration process of adsorbent leads to the loss of net efficiency of coal-fired power plant (CFPP) after retrofitted. This paper initially proposes and evaluates an integrated system which is composed of an adsorption carbon capture unit (ADCCU) and a single-effect absorption heat transformer (SAHT). Then a general concept of sorption carbon capture integrated with heat pump could be introduced. Results indicates that CO2 purity and recovery rate of the integrated system vary from 91.20 % to 92.75 % and from 95.62 % to 98.11 % when flowrate range from 48 NL·min−1 to 60 NL·min−1. Under the condition of 140 °C regeneration temperature of ADCCU and 80 °C generation temperature of SAHT, exergy efficiency of SAHT achieves the maximum value of 85.28 %. Moreover, a vapor compression heat pump (VCHP) system is coupled to provide moderate temperature heat for SAHT when waste heat of CFPP is inadequate. The effect of waste heat and electricity consumed on performance of CFPP is also taken into consideration. When recovery rate is lower than 27 %, performance of the proposed integrated system is more favorable than that using steam evacuated from the turbine. It is demonstrated that heat pump assisted adsorption capture for CFPP may be a promising solution to reduce energy consumption in the near future.

Preparation and characterization of Kevlar nanofiber based composite phase change material with photo/electro-thermal conversion properties

To develop phase change material suitable for multi-energy complementary applications, nanofibrous Kevlar aerogel containing paraffin and then deposited with polypyrrole (PPY-KNF/PF) were fabricated. The structure, morphology and photo/electro-thermal conversion ability of PPY-KNF/PF, especially the effect of confinement on the latent heat storage capacity of composites without PPY (KNF/PF) were investigated. The results showed that PF was induced to the interface of nanofibers, then intercalated into the nanosheets during self-assembly of KNF and formed three-dimensional porous structure. The maximum latent heat of KNF/PF with PF fraction of 78.7 % is 117.2 J·g−1 without leakage. Due to the confinement effect, the actual enthalpies of KNF/PF are all lower than the theoretical latent heats, and the difference between the actual and theoretical values enlarges with the increase of PF percentage. The deposition of PPY has no effect on the structure and morphology of KNF/PF and the PPY-KNF/PF80 displays good shape stability and high latent heat storage ability (101.9 J·g−1). Moreover, the composite was endowed with multi-properties of electrothermal and active photothermal conversion, which makes it more suitable for use in the case of insufficient solar energy. This work demonstrated an effective strategy to fabricate composite PCMs with electro/photo-thermal conversion devoting to energy conversion, storage and complementary utilization.

Thermal properties of lauric acid/high‐density polyethylene form‐stabilized phase change materials doped with hybrid carbon nanofillers

AbstractThe form‐stabilized phase change materials (PCMs) comprised of lauric acid (LA), high‐density polyethylene (HDPE) and graphene nanoplates‐carbon nanofibers (GNP‐CNF) hybrid fillers were synthesized by melt blending method in this work, and the effects of GNP‐CNF mass ratio on thermal properties were investigated. The results from FT‐IR and XRD reveal that LA, HDPE, GNP and CNF were integrated with each other in a physical manner. The LA/HDPE/GNP‐CNF composites possess melting points very close to that of pure LA, with melting latent heats of 113.83–119.84 J/g. Thermal conductivity results indicate that the effect of GNP is better than that of CNF at the same content. The synergistic effect of hybrid carbon fillers can achieve higher thermal conductivity value compared to a single GNP or CNF. The synergistic thermal conductivity improvement mechanism is also analyzed. The sample SN2 (GNP: CNF is 1.7:0.3) exhibits the best thermal conductivity of 0.759 W/(m·K), with 2.73 times that of SN0. It also presents satisfactory thermal stability and reliability, allowing it to have promising applications in thermal energy storage.

Development of a new pumice block with phase change material as a building envelope component

Developed lightweight components of building envelope to improve thermal mass of the building has a crucial role in building sector. There are many studies on this topic around the world. In terms of sustainability, each country focuses on using own local resources and reserves and try to find economic-sustainable solutions. In this context, when examined resources and reserves of our country, it is seen that ranks first in many material reserves. Especially, it is important that Turkey is the second rank in pumice reserves. Pumice is a easily obtainable, healthy economic and lightweight building material. In the literature, it is not found a study improved the thermal mass of the pumice block, which is a lightweight building envelope component. For this reason, this study aims on the production of a new pumice block with phase change material (PCM) as a lightweight building envelope component. PCM improves thermal mass by means of thermal energy storage. The measurement of the thermal mass and physical properties of the building envelope component obtained by adding the phase change material into pumice and discussing the usability of this component in building envelope is a valuable contribution to literature. For this study, four pumice block sample were produced. One of this was reference pumice block without PCM. Others were pumice blocks with PCM at ratios of 5 %, 10 % and 15 %. PCM using block samples is paraffin-based. In the laboratory conditions, the thermal conductivity, specific heat capacity and latent heats of the all samples were measured. Then, using obtained experimental data, an energy simulation is realized to analyze effects on building energy loads of these samples. DesignBuilder was used as energy simulation software and simulations were made on a hypothetical building. In last, the effect of pumice blocks with PCM on the time delay and indoor temperature fluctuations were investigated. In the result of the study, PCM pumice blocks with phase change temperature range at indoor comfort temperatures have been observed to improved up to 6 % in their thermal conductivity and up to 75 % in their specific heat capacity. In hot-humid climates, it is clear that they can provide efficiencies varying between 2 and 7 % during a whole year. Due to their latent heat, it has been observed that they can provide an average of 30 % increase in wall time delay, an approximately 25 % improvement in the effect of indoor temperature fluctuations, and an average of 1.5 °C decrease in indoor maximum temperature.

Structural transitions and magnetocaloric properties of low-cost MnNiSi-based intermetallics

A series of Mn1-xNi1-xFe2xSi0.95Al0.05 MM’X-type compounds (with x = 0.28, 0.3, 0.32 and 0.35) were investigated for their potential as magnetocaloric materials. Structural and magnetic properties were studied by magnetometry, microscopy and X-ray diffraction. Double substitution of Fe in Mn and Ni sites allowed to tune martensitic transition temperatures between low temperature orthorhombic and high temperature hexagonal structures from 373 K in x = 0.28–183 K in x = 0.35 during cooling. Transition temperatures occur around room temperature for x = 0.30 (300 K for cooling transformation) and 0.32 (270 for heating transformation). Isothermal entropy changes of −8, −19 and −26 J/kg.K were calculated for field changes of μ0H = 0–2, 0–5 and 0–7 T for x = 0.30. The values are comparable to those reported for MnNi(SiAl)-based compounds with single site substitutions (Mn and Ni) by Fe. Further analyses show that high magnetic fields are necessary to induce the magnetostructural transition in all studied compounds, which can be attributed to the presence of secondary phases and/or disorder at a local level.

Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic, and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry.

High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular, adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity c_{p}(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a low-temperature ferroelectric nematic phase (N_{F}) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (N_{x}). From the detailed data of h(T) and c_{p}(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (x_{DIO}). The x_{DIO} dependence on the transition temperatures for both transitions could be well described by a quadratic function. Both these transitions were weakly first order. The true latent heat of the N_{x}-N transition of DIO was as low as L=0.0075±0.0005J/g and L=0.23±0.03J/g for the N_{F}-N_{x} transition, which is about twice the previously reported value of 0.115 J/g for the N_{F}-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing x_{DIO}. At all the N_{x}-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the N_{F} to the higher-temperature phase exhibits substantial pretransitional behavior, in particular, in the high-temperature phase. Power-law analysis of c_{p}(T) resulted in an effective critical exponent α=0.88±0.1 for DIO and this value decreased in the mixtures with decreasing x_{DIO} toward α=0.50±0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis.

Thermo-economic assessment of salt hydrate-based thermochemical heat transformer system: Heat upgrade for matching domestic hot water production

Efficient energy storage technology is a crucial step in achieving the broad deployment of renewable energies. Thermochemical heat transformer (THT), which rely on reversible gas–solid reactions, can provide an option for efficient energy storage and heat upgrade. In this article, a pressurisation-assisted sorption THT system driven by low-grade solar thermal energy is proposed to meet the heat demand of domestic hot water (DHW) production, and different temperature rises can be realised by regulating the water vapour pressure. The thermodynamic and economic performances of the THT systems employing ten kinds of salt hydrates are investigated under various operating conditions. The results indicate that most salts-based THT systems enable output temperatures higher than 60 °C. Two-stage pressurisation systems can further elevate the temperature lift but at the cost of thermodynamic performance. SrBr2·6H2O, K2CO3·1.5H2O, and LiOH·H2O are more promising hydrates for the THT system by taking energy density, temperature lift, and thermo-economic performance into account. Compared to the classical TCES cycle, the temperature lifts attained by the above salts-based single-stage and two-stage pressurisation THT systems are 17.6–19.9 °C and 32.2–37.8 °C, respectively. Multi-objective optimisation results suggest that the optimum exergy efficiency for the SrBr2-, K2CO3-, and LiOH-based systems are 82.47%, 55.08%, and 63.97%, and the corresponding levelized energy costs (LECs) are 0.3549, 0.7132, and 0.5721 $/kWh, respectively. The results of this study demonstrate the significant potential of developing such pressurisation-assisted THT system for heat upgradation targeting DHW production.

Energy conservation and recycling transformation of clean energy heating based on artificial intelligence

Energy conservation and recycling transformation of clean energy heating based on artificial intelligence

Energy conservation and recycling transformation of clean energy heating based on artificial intelligence

Energy conservation and recycling transformation of clean energy heating based on artificial intelligence

Prospect of Peak Regulation Capacity Improvement through Flexibility Transformation of Combined Heat and Power Units in Shandong Province

With the high proportion of renewable energy connected to the grid, peak shaving demand surge, which needs to enhance the flexibility of coal power with a larger proportion to support the stable operation of the grid. At present, the capacity of the combined heat and power unit accounts for about 87 % of direct dispatching coal-fired power plants by Shandong power grid. The flexible operation ability of the combined heat and power unit is poor, and its flexible transformation is urgent. This paper summarizes the current relatively mature flexibility transformation technology of combined heat and power unit, including low pressure cylinder zero output transformation (cylinder cutting transformation), bypass load regulation, thermal energy storage and electrical energy storage transformation technology, and puts forward to encourage the flexibility transformation of in-service combined heat and power unit, and actively promote the research and application of the intelligent heating network, the integration of thermal and electricity, and the clean heating construction and clean heating technology.

Carbonized conjugated microporous polymers hollow spheres incorporated with fatty alcohols for ultra-highly efficient energy storage and conversion

With the increasing global instability in the development of the world, the efficient storage and conversion of energy have alerted attention. In this work, a novel conjugated microporous polymer hollow spheres (CMPHS) with a high specific surface (323 m2 g−1) and unique cavity structure are creatively prepared. By treatment with simple carbonization, the resulting carbonized microspheres (CCMPHS) show a high light absorption (80%) and outstanding thermal stability (thermal decomposition at 506 °C). On basis of the abundant micropores distributed on the surface of microspheres, the organic phase change materials (PCMs) i.e., fatty alcohols (tetradecanol (TD), hexadecanol (HD), and octadecanol (OD)), are successfully embedded into CCMPHS to afford a kind of new composite ([email protected]) for energy storage and conversion. The three kinds of [email protected] exhibit high latent heats (220.1 kJ kg−1, 244.6 kJ kg−1, and 228.8 kJ kg−1, respectively.). In terms of energy conversion, the photothermal conversion efficiencies of [email protected] are up to 86.83%, 89.45%, and 85.40% and the electrothermal conversion efficiencies are 83.81%, 81.10%, and 90.50%, which possess one of the highest values among the most of similar composites embed with PCMs reported to dates. Based on the advantages of simple fabrication, easy to scale up, high energy density, and conversion efficiency, the [email protected] are expected to be one of the most promising candidates as efficient PCMs composite for a variety of practical applications such as solar or electric energy harvesting, storage, conversion, and so on.

Heat Transfer Analysis of Generalized Nanofluid with MHD and Ramped Wall Temperature Using Caputo–Fabrizio Derivative Approach

The aim of the present work is to apply the fractional derivative to the heat transformation of a nanofluid along with ramped wall temperature. The flow is analyzed under the effect of magnetohydrodynamic together with heat transfer. A nanofluid under the application of fractional‐order differential equations by Caputo–Fabrizio derivatives with respect to time has the ability to explain the behavior of nanofluid under the influence of memory concept. For the same purpose, Caputo–Fabrizio time‐fractional derivative is applied to investigate the behavior of nanoparticles on the thermal conductivity of a fluid. Appropriate nondimensional variables are engaged in the equation which governs the problem and guides us to obtain the exact solutions for the fields of velocity and temperature. These obtained solutions for the nondimensional set of governing equations are found by extracting them from the governing equations by applying Laplace transform techniques along with Caputo–Fabrizio time‐fractional derivative. The influence of the fractional variable on the velocity, temperature, and Nusselt number is graphically exposed and discussed. The velocity for the state of wall temperature as ramped falls down with the enlarging values of the fractional parameter. Variation in Nusselt number is shown in the tabular form. Solutions are visualized graphically to make an analysis of how the variation is taking place in the physical behavior of the nanofluid flow with respect to the change in distinct physical parameters. The obtained results here will have useful industrial and engineering implementations. It is found that fluid velocity in the flow direction decreases with the increase in the magnetic parameter. The relationship of fractional parameter with the velocity and temperature of the nanofluid is found as direct proportional for a smaller time. However, this direct proportionality converts into inverse proportionality for larger values of time. It is observed that the increase in the nanoparticles volume fraction causes an increase in temperature distribution. It is due to lower specific heat of nanoparticles and its higher thermal conductivity than that of the base fluid.

Analysis of heating transformation of different types of thermal power units

This paper introduces the total heating capacity, total installed capacity, heating area change trend and unit transformation of direct regulating heating units in Shandong power grid in recent years. According to the operation data of condensing pumping units, back pressure heating units and cylinder cutting units in previous heating seasons, the heating and peak shaving performance of different types of cogeneration units of the same type, grade and grade in heating seasons are analyzed, It is convenient for the power grid dispatching department to more reasonably and orderly arrange the unit mediation plan of the province's thermal power plants according to the online situation of new energy and external power. At the same time, it is a reference for power generation enterprises to carry out flexible transformation according to the actual situation of units during the 14th Five Year Plan period, and take into account the low load peak shaving performance of units or the whole plant while increasing heating capacity.

Analysis of Heating Transformation of Nuclear Power Units

Under the current national conditions and policy support, nuclear heating has flourished. Domestic nuclear power units mainly generate electricity, and nuclear heating as a clean energy source is one of the main ways to solve winter heating in the north. This paper first compares and analyzes the two different ways of nuclear heating, then takes the nuclear heating of Haiyang Nuclear Power Station as an example, based on the mature experience of steam extraction heating transformation of thermal power units, makes an economic analysis on the steam extraction transformation of PWR nuclear power units from the characteristics of the thermal system combined with the Spot market, and finally makes an economic evaluation on the Cogeneration nuclear power units.

Express Method for Assessing Optimality of Industrial Heat Exchangers for Adsorption Heat Transformation

In this work, four radiators with different core geometries were tested using a wind tunnel. The values of the global heat transfer coefficient (UA = 5 ÷ 65 W/K) were measured depending on the flow of air and water. The obtained UA values correlate well with the data of sorption experiments described in the literature. The found correlations between the Nusselt and Reynolds numbers made it possible to propose an algorithm for ranging commercial air radiators for the use in adsorption heat transformers. It is shown that the use of a wind tunnel can serve as an effective tool for express assessment of the prospects of using air radiators for adsorption heat conversion without destroying radiators or their direct testing in a complex adsorption installation requiring vacuum maintenance.

Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni49Mn32Ga19 Ferromagnetic Shape Memory Ribbons

In our work, the kinetics of martensitic transformations and the influence of thermal treatments on martensitic transformations, as well as the related magnetic properties of the Ni49Mn32Ga19 ferromagnetic shape memory melt-spun ribbons, have been investigated. Thermal treatments at 673 K for 1, 4 and 8 h can be considered an instrument for fine-tuning the performance parameters of alloys. One-hour thermal treatments promote an improvement in the crystallinity of these otherwise highly textured ribbons, reducing internal defects and stress induced by the melt-spinning technique. Longer thermal treatments induce an important magnetization rise concomitantly with a slight and continuous increase in martensitic temperatures and transformation enthalpy. The activation energy, evaluated from differential scanning calorimeter experimental data with a Friedman model, significantly increases after thermal treatments as a result of the multi-phase coexistence and stabilization of the non-modulated martensitic phase, which increases the reverse martensitic transformation hindrance.

Thermodynamics analysis of a novel absorption heat transformer-driven combined refrigeration and desalination system

Preservation of food and medicines below sub-zero temperatures is the need of the present times. To achieve the required temperature using renewable energy, a waste heat-driven vapour absorption refrigeration system can be implemented. Majority of the available waste heat is available in the low temperature range i.e. between 60–80 °C, which cannot be directly used to provide refrigeration. Therefore, an absorption heat transformer (AHT) is coupled with the VARS (Vapour absorption refrigeration system) system which increases temperature of this waste heat, and the upgraded heat is utilized to produce required refrigeration effect. Further, the rectifiers’ waste heat of the absorption system will be used to power humidification-dehumidification (HDH) desalination cycle. Although all these three components (AHT, VARS, and HDH) have been studied individually, but they have never been combined altogether. This paper presents a mathematical model for the proposed system and its validation against published available literature. The performance parameters such as coefficient of performance, gain output ratio and refrigeration effect of the system is evaluated at different evaporator and desorber temperatures. For 300 kW waste heat at 80 °C, evaporator (VARS) temperature of −10 °C, the system reported 70 kW of refrigeration effect is provided with 20 kg/hr of distillate production rate. An exergy destruction of 82.64 kW has been reported for total input exergy of 142.2 kW, for refrigeration capacity of 157 kW.

Preparation and application of low-temperature binary eutectic lauric acid-stearic acidSiO2 phase change microcapsules

Most phase change materials developed in current research have high phase change temperatures, making them challenging to use in buildings. To solve this problem, the microencapsulated phase change materials (MPCMs) with low eutectic temperature were prepared by interfacial polymerization using binary eutectic of lauric acid (LA) and stearic acid (SA) as the core material and silica as the shell material. And the phosphogypsum-based phase change microcapsules (PG-MPCM) were prepared. Morphology, structure and thermal properties of microcapsules have been investigated. The differential scanning calorimetry (DSC) results indicate that the melting and freezing temperatures of MPCMs prepared under optimal conditions are 27.9 °C and 28.3 °C, and the latent heats of melting and freezing are 170.3 J/g and 155.7 J/g. The thermogravimetry (TG) analysis results confirm that the microcapsules have good thermal stability. There is no significant change in the latent heat of the microcapsules phase change after 300 melting/freezing cycling. The heat storage performance shows that PG-MPCMs have good heat energy storage capacity and temperature regulation ability. In general, the LA-SA/SiO2 microcapsule is suitable as the energy storage material for buildings.