Thermal Compression Process Research Articles

Solar driven carbon dioxide Brayton cycle power generation with thermal compression

Solar thermal power generation by and large uses Rankine cycles with organic working fluids or steam when highly concentrated solar source is used. Brayton cycle is seldom used because the work of compression forms a major fraction of turbine output. We investigate removal of this lacuna by adopting thermal compression using the adsorption route. Here we propose a two source operated cycle with the low temperature source used for thermal compression and the high temperature source to increase the inlet temperature of the working fluid to the turbine. We adopt carbon dioxide as the working fluid in view of its excellent heat transfer properties and environmentally friendly disposition. Activated carbon is used as the adsorbent in the thermal compression process. It is shown that, though the First law thermal efficiency does not show the real merit of the cycle, the exergetic efficiency is substantially high even for low side operating pressures in the range of 15–25bar. In particular, where the waste heat is available around 100°C and concentrated solar power is available even at 200–300°C, exergetic efficiencies in excess of 25% can be realised. When other advantages such as dispensing with one whole segment of moving parts (compressor) are taken into account, the running costs of such a cycle can be so low that it would be a viable proposition. However, we appreciate that, large scale use of adsorption compression is associated with huge technological problems for which we propose some remedies.

A Study on Dimensional Stability and Thermal Performance of Superheated Steam Treated and Thermal Compressed Wood

Recently, wood is attracting attention as green building interior decoration material. When wood is used as building interior decoration material, excellent dimensional stability and thermal performance is required. In this study, superheated steam treatment process and thermal compression process were applied to flat sawn Pinus koraiensis wood panel in order to improve dimensional stability and thermal performance. According to results of this study, superheated steam treatment process and thermal compression process improve thermal performance and dimensional stability of wood, especially in tangential direction. The spring back in radial direction reduces the effect of thermal compression on dimensional stability of wood in radial direction.

On the successful fabrication of auxetic polyurethane foams: Materials requirement, processing strategy and conversion mechanism

This study aims to provide fundamental understandings in several issues critical to the fabrication of auxetic polyurethane (PU) foams by thermal compression process: conversion and auxetic structure fixation mechanisms, materials characteristics essential for the successful auxetic conversion, and optimal conditions for auxetic conversion. Three flexible PU foams with similar morphology were selected for the study. First the commonalities as well as the differences between these foams in terms of their chemical composition, microstructure and thermomechanical properties were thoroughly analyzed. This is followed by the auxetic convertibility study of these three foams. Mechanisms for fixing the structure were elucidated and the windows for processing were interpreted in the context of polymer relaxation. Guided by these understandings, a series of auxetic foams were manufactured at a wide range of conditions. The processing conditions agreed very well with those suggested from the mechanistic investigation, validating the proposed auxetic conversion and structure fixation mechanisms. The mechanism was further confirmed by direct observation of the morphology of the fabricated auxetic foams.

High performance thermal conduction of silver microparticles thermos-compressed in three-dimensionally interconnected polystyrene beads

We demonstrate a facile strategy to prepare polymer composite with anomalously increased thermal conductivity based on Ag network and structured polymer matrix. Conventional thermal compression process combined with colloidal type thermoplastic beads as structural matrix enabled efficient interconnected thermal conduction pathways of Ag microparticles, giving rise to extremely high thermal conductivity of 120 W/mK at 70 vol% of Ag particles comparable with one third of the value of pure Ag. The systematic investigation with different types of polymer matrix, such as thermoset epoxy and cross-linked colloidal bead, suggests that appropriate frictional force exerted on Ag particles with polymer matrix during compression is of prime importance for developing Ag conduction pathways. Furthermore, the thermoplastic PS beads matrix also provides sufficient mechanical strength to preserve the networked Ag pathways with firm interfaces.

Three-dimensional carbon nanotubes for high capacity lithium-ion batteries

Carbon nanotubes (CNTs) have been considered as a potential anode material for next generation Lithium-ion batteries (LIBs) due to their high conductivity, flexibility, surface area, and lithium-ion insertion ability. However, the low mass loading and bulk density of carbon nanomaterials hinder their use in large-scale energy storage because their high specific capacity may not scale up linearly with the thickness of the electrode. To address this issue, a novel three-dimensional (3D) architecture is rationally designed by stacking layers of free-standing CNTs with the increased areal density to 34.9 mg cm−2, which is around three-times higher than that of the state-of-the-art graphitic anodes. Furthermore, a thermal compression process renders the bulk density of the multi-stacked 3D CNTs to be increased by 1.85 g cm−3, which yields an excellent volumetric capacity of 465 mAh cm−3 at 0.5C. Our proposed strategy involving the stacking of 3D CNT based layers and post-thermal compression provides a powerful platform for the utilization of carbon nanomaterials in the advanced LIB technology.

Thermodynamic evaluation of high compressible steam flow in vapor compression systems used in desalination processes

In the current study, some thermodynamic aspects of flow stream inside vapor compressors are investigated numerically and the effects of the geometry on compression process are clearly explained. A compressor provides the required energy for distillation process and the driving force for overcoming dynamic pressure losses inside the evaporators. Thermal compression process is frequently used in recent multi-effect desalination units. The basic phenomena within these devices are similar to ejectors and thus might be improved by a thoroughly CFD simulation. An experimental thermal-vapor compressor is investigated in both 2D and 3D approaches to reveal the flow characteristics inside the non-symmetric zones. Variations of some major thermodynamic properties (i.e. velocity, pressure, temperature, and density) are completely investigated within the compressor and useful graphs are produced. Afterwards, the numerical results are compared with experimental ones. Finally, it is shown that the flow deflection in the suction chamber is consequentially declined, which means the non-symmetric geometries have no considerable effect on the overall performance for industrial usages.

Dewatering Performance of Sewage Sludge during the Thermal Compression Process

Sewage sludge proves to be difficult to dewater due to its composition and biological nature, and it is unsuitable for disposal with high moisture content. In the present work, sewage sludge is dewatered by the thermal compression, which shows unique separation advantages of various materials, and the effects of applied temperature and pressure on the dewatering performance are investigated. The filtrate SCOD reveals that higher temperature benefits the disruption of sludge flocs, resulting in the release of organic content. According to the accumulative filtrate volume, higher temperature and pressure facilitate the dewatering process, obtaining sludge cake with lower moisture content.

An in situ fabrication process for highly electrical conductive polyimide/MWCNT composite films using 2,6-diaminoanthraquinone

We present a valuable in situ fabrication process for synthesizing high electrical conductive polyimide/multiwalled carbon nanotube (PI/MWCNT) composite films. The success of this process was achieved the addition of 2,6-diaminoanthraquinone (DAAQ). The DAAQ is not only an excellent dispersion agent to stably disperse pristine MWCNTs in solvent but also a monomer to directly synthesize PI. The strong interaction between DAAQ with MWCNT was verified by FTIR, UV–Vis, Raman, and fluorescence spectra. The highest value of electrical conductivity of 55.6 S/cm are achieved by the PI composite containing 40 wt.% of MWCNT. Moreover, the electrical conductivity of this film further enhanced to 106 S/cm after the thermal compression process. The MWCNT content at the percolation threshold of conductivity is 0.50 wt.% (or 0.32 vol.%) and the critical exponent is equal to 2.52. The developed in situ fabrication process through DAAQ-derived molecules can also be applied to synthesize other polymers requiring diamine structure.

Bending performance of 3-layer beech (Fagus sylvativa L.) and Norway spruce (Picea abies (L.) Karst.) VTC composites bonded with phenol–formaldehyde adhesive and liquefied wood

Low quality beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) were densified with viscoelastic thermal compression (VTC) process to two different degrees of densification, and lamellas were used to manufacture different types of 3-layer VTC composites. Bending properties of 3-layer VTC composites bonded with phenol formaldehyde (PF) adhesive and liquefied wood (LW) were determined and compared to 3-layer composites produced with undensified beech or spruce wood lamellas. Morphology of VTC spruce wood of higher density was analysed with fluorescent microscopic technique. All composites produced with densified beech lamellas and bonded with PF adhesive had significantly higher values of modulus of rupture (MOR) and modulus of elasticity (MOE) than composites produced with undensified lamellas. Densified spruce lamellas contributed to better bending performance of 3-layer VTC composites bonded with PF adhesive to some extent. Furthermore, composites bonded with LW had significantly lower MOR and MOE values compared to composites bonded with PF adhesive. Study of VTC spruce wood microstructure showed that densification caused non-uniform deformation of cell wall structure, in which cell wall fractures were observed.

Preliminary thermoeconomic analysis of combined parabolic trough solar power and desalination plant in port Safaga (Egypt)

The development of society is strongly dependent on water and electricity. There is an increasing water and energy demand driven by population growth and rising industrial and agricultural production. The combination of concentrated solar power (CSP) and desalination processes has a huge potential for producing both energy and water in arid regions suffering from fresh water scarcity and facing the current energy challenge. One of the regions is Middle East and North Africa (MENA), where plans are currently under discussion to make possible large CSP plants developments. The integration of desalination (CSP+D) into solar power plants could make CSP technology even more attractive in such regions. The focus of this study is thermodynamic characterization and an economic evaluation of different configurations for coupling parabolic trough solar power plants and desalination facilities at a MENA location in Egypt chosen as reference for its Southern coast (Port Safaga). The desalination technologies considered for the combination with parabolic trough concentrating solar power plants (PT-CSP), are low temperature multi-effect distillation (LT-MED) and reverse osmosis (RO). Moreover, an additional concept of LT-MED has been evaluated: a LT-MED powered by the steam obtained from a thermal vapor compressor (TVC). In this case, unlike the conventional thermal vapor compression process (TVC-MED), the entrained vapor to be used in the ejector comes from the exhaust steam from the low pressure (LP) turbine instead of an effect of the MED unit. In order to optimize this latter concept (LT-MED-TVC), different configuration schemes have been studied. When thermodynamic efficiencies and costs are analyzed comparing the two more efficient configurations (PT-CSP/RO and PT-CSP/LT-MED), considering 58°C/0.18 bar of exhaust turbine steam conditions and 5.5 kWh/m3 of RO power requirements, initial results are very similar.

Thermally Compressed Poplar Wood (TCW): Physical and Mechanical Properties

Various thermal modifi cation techniques are used to improve some properties of wood materials. Thermally compressed wood (TCW) is obtained by using a hot-press. This study investigates the effect of thermal compression on the density, vertical density profi le (VDP), moisture content (MC), thickness swelling (TS), Janka hardness, and drying characteristics of the poplar wood boards. The experimental boards were cut from poplar wood (Populus spp). The boards with dimensions of 100 mm by 500 mm by 25 mm were thermally compressed at press temperature of either 150 °C or 170 °C, press pressure of either 1 or 2 MPa for 45 minutes in a hot-press. A total of 10 experimental boards were prepared - two boards for each group plus two for control. The results obtained in this study indicated that the density and Janka hardness values increased with the increase of the press pressure. The thermal compression process decreased the thickness of the boards. The thickness reduction in- creased with the increase of the press pressure. An improvement was not seen in the TS values of the samples when compared to those of the untreated samples. This study revealed that the thermal compression technique should be used to improve some properties of poplar wood. In this way better use could be made of low-cost poplar wood.

Microstructure of viscoelastic thermal compressed (VTC) wood using computed microtomography

The paper describes for the first time the analysis of the structure of compressed wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlywood, while the compression of hybrid poplar mainly occurred in the vessels. In both wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlywood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, latewood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir latewood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC densified wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance.

Commercialization Potential of Viscoelastic Thermal Compressed Wood: Insights from the US Forest Products Industry

The increasing demand for forest products and restricted use of natural forests has resulted in a shortage of high-strength wood fiber. The area covered by plantation forests is steadily rising, but the fiber produced by these forests is often unsuitable for high-strength applications. One attempt to combat this problem is the viscoelastic thermal compression (VTC) process, which can dramatically increase the strength and stiffness of any wood species. To advance VTC wood from the concept evaluation stage to the development stage, concept testing interviews were conducted with individuals in the forest products industry. Opinions, ideas, and insights were gathered from interviewees concerning potential applications for VTC wood, as well as advantages and barriers to commercialization. As a whole, interviewees thought the most viable uses for VTC wood were laminated veneer lumber, plywood, concrete forms, transportation components, and flooring. The most frequently mentioned advantages to commercialization included increased mechanical properties and the utilization of a low-value wood species; barriers to commercialization were cost and the forest products industry's resistance to change. Overall, interviewees thought VTC wood would be successful as long as it was not markedly more expensive than similar products.

Experimental results of an activated carbon–HFC 134a adsorption cooling system for thermal management of electronics

Results of performance measurement of a small cooling capacity laboratory model of an adsorption refrigeration system for thermal management of electronics are compiled. This adsorption cooler was built with activated carbon as the adsorbent and HFC 134a as the refrigerant to produce a cooling capacity under 5 W using waste heat up to 90 °C. The thermal compression process is obtained from an ensemble of four solid sorption compressors. Parametric study was conducted with cycle times of 16 and 20 min, heat source temperatures from 73 to 87 °C and cooling loads from 3 to 4.9 W. Overall system performance is analyzed using two indicators, namely, cooling effectiveness and normalized exergetic efficiency.

Fungal decay of viscoelastic thermal compressed (VTC) wood

Low-density hybrid poplar (Populus deltoides × Populus trichocarpa) was densified with the viscoelastic thermal compression (VTC) process to three different degrees of densification (63%, 98%, and 132%). Durability of the VTC treated specimens was assessed by exposure to two white rot fungi (Pleurotus ostreatus and Trametes versicolor) for four or eight weeks. After incubation, mass loss in grams and percentage mass loss were determined. The results showed that VTC densification did not change decay resistance to Pleurotus ostreatus and Trametes versicolor. The mass losses caused by Trametes versicolor were more extensive than those by Pleurotus ostreatus. As expected, longer exposure time resulted in higher mass loss. Furthermore, the degree of densification did not influence susceptibility to fungal degradation.

Study of annealing effects on structural and sorption properties of low energy mechanically alloyed AB 5's

In this work, various AB 5's were mechanically alloyed using a low energy mill until final or completion milling stages were reached. This process leaves micro- and nano-structured materials with highly distorted microstructures. Then, further annealing is needed to obtain an intermetallic suitable for hydrogen thermal compression process. After milling, the samples were annealed and analyzed by X-ray diffraction and Differential Scanning Calorimetry. Hydriding properties were studied using volumetric methods. After annealing at 200 °C for 24 h no changes occur in neither structural nor hydriding properties. For samples annealed at 400 °C, relaxation effects of the structure were observed. It occurs due to the release of strain produced by annealing on the microstructure. It leads to the improvements in both structural and hydriding properties. Strong recrystallization effect was present between 400 and 600 °C. At 600 °C, the main improvements were larger crystallite size, lower strain values and pressure-composition isotherms with well-defined plateaus. Despite this behavior, no evidence of crystallization was observed by Differential Scanning Calorimetry measurements from room temperature up to 500 °C. These topics, the amount of energy supplied during mechanical alloying and the correlation between the structural and sorption properties are discussed according to the governing mechanisms of recrystallization observed in each temperature range. From these results, an improved synthesis-thermal treatment method is outlined.

Phenol–formaldehyde impregnation of densified wood for improved dimensional stability

To produce a highly stable wood-based product with increased mechanical properties, phenol formaldehyde (PF) resin impregnation was combined with the viscoelastic thermal compression (VTC) process. Dimensional stability and bending stiffness were evaluated. Two PF resins with weight average molecular weights of 172 and 780 were studied at three different concentrations, 5, 10 and 20%. After 24-h room temperature water soak and 2-h boil, both PF treatments at all concentration levels showed high levels of dimensional stability compared to non-impregnated VTC processed controls. The higher molecular weight PF provided greater stability with an average thickness swell value of 12% compared to 20 and 37% for the lower molecular weight PF resin treatment and control, respectively. High anti-swelling efficiency values were recorded for both low and high molecular weight resins, implying these modifications were effective at reducing the volumetric swelling which occurred in the unmodified control. PF treatments were also extremely effective at reducing irreversible swelling. The low and high molecular weight resin treatments had 1/5th and 1/7th the irreversible swelling than the unmodified VTC processed controls, respectively. All dimensional stability values improved as resin concentrations increased. Both resin types at all concentration levels reduced Young’s modulus.

Decay and termite resistance, water absorption and swelling of thermally compressed wood panels

This study evaluated decay and termite resistance of thermally compressed pine wood panels under pressure at either 5 or 7 MPa and either 120 or 150 °C for 1 h. Wood specimens from the panels were exposed to laboratory decay resistance tests by using the wood degrading fungi, Gloeophyllum trabeum and Trametes versicolor. The thermal compression process caused increases in density and decreases in thickness of the panels; however, laboratory decay resistance tests revealed that thermally compressed wood was not resistant against the wood degrading fungi tested. More interesting results were found in laboratory termite resistance tests by using the Eastern subterranean termites, Reticulitermes flavipes. As pressure and temperature applied to the specimens increased to 7 MPa and 120 °C, mass losses in the specimens gradually decreased in comparison with control specimens. However, the specimens compressed at 7 MPa and 150 °C showed higher mass losses when compared to the specimens compressed at 7 MPa and 120 °C. The lowest water absorption and swelling rates were seen in the specimens exposed to a pressure of 7 MPa at 120 °C. The thermal compression process at 7 MPa and 150 °C resulted in the highest water absorption and swelling in the specimens.

Activated carbon + HFC 134a based two stage thermal compression adsorption refrigeration using low grade thermal energy sources

A thermodynamic analysis is presented for the two stage thermal compression process for an adsorption refrigeration cycle with HFC-134a as the working fluid and activated carbon as the adsorbent. Three specimens of varying achievable packing densities were evaluated. The influence of evaporating, condensing/adsorption and desorption temperatures was assessed through three performance indicators, namely, the uptake efficiency, the coefficient of performance and the exergetic efficiency. Conditions under which a two stage thermal compression process performs better than the single stage unit are identified. It is concluded that two stage thermal compression will be a viable proposition when the heat source temperature is low or when adsorption characteristics are weak or when adequate packing densities are difficult to realize.

The mechanical properties of densified VTC wood relevant for structural composites

The mechanical properties of densified wood relevant for structural composites were studied. Low density hybrid poplar (Populus deltoides × Populus trichocarpa) was densified using the viscoelastic thermal compression (VTC) process to three different degrees of densification (63, 98, and 132%). The modulus of rupture (MOR) and the modulus of elasticity (MOE) of the control (undensified) wood and of the VTC wood were determined. The bonding performance of the control and VTC wood, using two phenol-formaldehyde (PF) adhesives, was studied. Four different 3-layer composites were also prepared from undensified and VTC wood, and tested in four-point bending. The results showed that the bending properties of the VTC wood (MOR and MOE) were significantly improved due to the increased density. The bonding performance of VTC wood with PF adhesives was comparable with or better than in the case of the control wood. Increased density of the face layers in the 3-layer VTC composites was advantageous for their mechanical performance.