Bed System Research Articles

Long-Term Anaerobic Digestion of Seasonal Fruit and Vegetable Waste Using a Leach-Bed Reactor Coupled to an Upflow Anaerobic Sludge Bed Reactor

Fruit and vegetable waste (FVW) generated locally in open (public or wholesale) markets is a valuable resource and should not be considered as waste. The anaerobic digestion (AD) of FVW can minimize landfill disposal and generate renewable energy, thus decreasing greenhouse gas emissions. Moreover, the digestate after the AD of FVW, devoid of antibiotics and animal fats in manure and food waste, may have a high fertilizing value. In this study, FVW mixtures were composed to mimic the real FVW generated in Mediterranean open markets annually. The first goal was to evaluate the biochemical methane potential (BMP) of different size fractions resulting from FVW grinding. Indeed, the FVW was ground and separated into two size fractions, 0–4 mm and 4–10 mm, respectively. The 0–4 mm fraction exhibited a lower BMP but a higher rate constant than the 4–10 mm fraction. The second goal was to first evaluate the BMP of the lumped fraction of FVW after grinding (0–10 mm) via BMP assays and then feed it to a mesophilic two-stage leaching-bed reactor (LBR)-upflow anaerobic sludge bed (UASB) system for almost one year. The BMP of the FVW ranged between 406 and 429 L kg−1 of volatile solids (VS) independently of the FVW production season. The system received an average organic loading rate (OLR) of 3.1 ± 0.7 g VS L−1 d−1. During operation, the LBR gradually transited from acidogenic to methanogenic, and the overall methane yield of the system increased from 265–278 to 360–375 L kg−1 VS, respectively. The proposed technology does not require water addition or liquid digestate removal. Compared to the continuous stirred tank reactor (CSTR) digester technology, the LBR/UASB system is suitable for the anaerobic digestion of FVW. The results of this study can be further used to upscale the proposed technology and contribute to the societal need for affordable and clean energy included in the Sustainable Development Goals (SDGs).

Growth and yield of rice (<i>Oryza sativa</i>) under different establishment methods and weed management practices in Uttarakhand

An experiment was conducted during the rainy (kharif) seasons of 2021 and 2022 at the Norman E. Borlaug (NEB) Crop Research Centre at Govind Ballabh Pant University of Agriculture and Technology, Pantnagar, Uttarakhand to study the effect of different establishment methods and weed management practices on growth and yield of rice (Oryza sativa L.). The study was carried in a split plot design with 3 replications. In main plot 4 rice establishment methods and in sub plot 4 weed management practices were included. The results revealed that significantly higher grain yield was recorded in mechanical line sowing (S2) over rest of the treatment. According to the pooled data analysis of grain yield the per cent increase in mechanical line sowing (S2) over broadcasting (S1), raised bed system (S3) and semi-dry system (S4) was 23.1%, 17.6% and 8.1%, respectively. Among the different weed management practices grain yield was recorded maximum in W3 (pre emergence herbicide followed by two manual weeding) treatment which showed at par results with W2 (pre emergence followed by post emergence herbicide) treatment. The per cent grain yield increase in pre emergence herbicide followed by two manual weeding (W3) over manual weeding (W1), pre emergence followed by post emergence herbicide (W2) and mechanical weeding (W4) was 19.3%, 0.75% and 31.7%, respectively. Weed density was recorded minimum in mechanical line sowing (S2) and raised bed system (S3). At panicle initiation stage significantly lower weed density was recorded in mechanical line sowing (S2). However, among the weed management practices manual weeding (W1) and pre emergence herbicide followed by two manual weeding (W3) treatments recorded at par. Weed dry weight remain non-significant under different rice establishment methods during active tillering as well as panicle initiation stage.

Modified paddy husk carbon with linked fibrils of FeHO2 using aluminium as the surface regulator for enhanced As (III) removal in fixed bed system

Abstract The As (III) uptake capacity of Fe-impregnated AC greatly depends on the availability of active surface sites of iron oxide. In this context, utilizing aluminium as a surface regulator, we proposed a process to attach linked fibrils of FeHO2 to develop an adsorbent with enhanced As (III) adsorption capacity. The procedure was based on the hydrothermal process using paddy husk-based activated carbon, and both Iron and aluminium ions in the test hydrolysis solution. The exhaust time was observed to rise with increasing dose, falling flow rate, and influent concentration. The CCD optimization result showed that the FeAlPBC was an efficient and cost-effective adsorbent with a maximum response of 1681 min when the independent parameters were retained at 15.0 g FeAlPBC dose, 500 μg/L influent concentrations, 2.0 mL/min flow rate, and a desirability value of 0.986. The experimental results and Thomas and advection-diffusion models were in good agreement. The FeAlPBC samples can be recycled for four cycles with little to no reduction in adsorption capacity. Also, the TCLP test demonstrated that the used FeAlPBC were inert and could be put into landfills without risk. In conclusion, FeAlPBC is a strong contender for removing As (III) from potable water and has a wide range of potential future applications.

Continuous flow degradation of Orange II by a dandelion-like NiCo2O4/NF activated peroxymonosulfate in a fixed-bed system

A novel dandelion-like catalyst, nickel foam supported NiCo2O4 (NiCo2O4/NF), was successfully synthesized and applied to the activation of peroxymonosulfate (PMS) in a fixed bed system for the degradation of Orange II (OII). The physicochemical properties of synthesis catalysts were identified by various characterization methods (SEM, EDS, XRD and XPS), revealing that the dandelion-like NiCo2O4 nanosheets were evenly distributed on the surface of NF. NiCo2O4/NF-250 showed excellent catalytic performance at a hydrothermal reaction time of 8 h, urea/metal ratio of 10:1, and Co/Ni concentration of 10 mM/5 mM. When PMS concentration was 5 mM, reaction temperature was 50 ℃, pH was 7.5, space velocity was 0.236 min−1, the conversion ratios of OII, PMS and COD were 99.8 %, 71.3 %, and 71.4 % at 240 min, respectively. In particular, NiCo2O4/NF still could reach 99.9 % OII conversion and 64.4 % COD conversion in the third cycle. DFT calculations implied that NiCo2O4/NF had excellent PMS activation performance.

Coating of baker’s yeast with a fluidized bed system: Effects of process parameters and storage stability of coated yeast in flour mixtures

In order to prevent the moisture absorption of dried yeast from the flour mixture having a moisture content of 13% (wb), the coating process of dried baker’s yeast was aimed and carried out at different conditions using the palm-gelatin-pectin coating material combination determined previously. At an optimum point, the highest bulk and tapped density, the lowest moisture absorption rate, the highest solubility in water, the highest yeast activity, and the highest bread volume values were targeted. At the optimal point, 50 grams of yeast, 0.25 MPa of nozzle pressure, and 13.09% of coating material to yeast ratio were found to be the best. Dried yeasts coated at optimum process conditions and uncoated yeast were added to the flour mixtures and stored at 25 °C for three months. In addition, the effect of different coating material combinations and exit drying temperatures on the effectiveness of the coating process was examined. The palm-Na caseinate-maltodextrin combination was chosen as an alternative coating based on the analysis results on coated yeasts. In conclusion, the coated yeasts demonstrated protective properties against moisture transfer until the end of the second month.

Process simulation of staging pyrolysis and gasification of biomass in a dual fluidized bed system

Process simulation of staging pyrolysis and gasification of biomass in a dual fluidized bed system

Effects of thermal environment on body temperature rhythm and thermal sensation before and after getting into bed: A laboratory study in Shanghai, China

Body temperature rhythm serves as a crucial bridge connecting thermal environment and sleep rhythm. While previous studies have extensively confirmed the significant effects of thermal environment on sleep process, a quantitative exploration elucidating the relationships between sleeping thermal environment and body temperature rhythm has persistently been absent. This research aimed to investigate the persistent effects of three stable thermal environments (16 °C, 20 °C and 24 °C) on body temperature rhythm and thermal sensation during complete sleep process. In a laboratory with strictly controlled environment, 14 participants underwent a continuous four-day sleep experiment over a two-month period. Throughout three distinct phases (pre-bed sitting, awake lying in bed, and sleep after lights-off), core body temperature at gastro-intestinal tract, as well as skin temperature at nine specific locations, were continuously monitored. Concurrently, regular questionnaires were employed to periodically collect data on participants’ thermal sensation. The data confirmed that (1) three hours after lights-off, core-to-skin temperature gradient consistently fluctuated around 2 °C across three conditions, and this observation may aid in elucidating the physiological significance of sleeping thermal environment; (2) thermal environment before getting into bed exerted a significant influence on body temperature rhythm and can further regulate the duration of sleep onset latency; (3) bedding system significantly diminished the impact of thermal environment on body temperature rhythm, and future bedding microenvironment deserves more attention; and (4) existing methods for sleeping thermal sensation evaluation varying degrees of limitation, and a novel prediction method was proposed. In general, this study provided valuable insights for the design and regulation of bedroom thermal environment from a thermophysiological perspective.

Simulation of Biogas Upgrading by Sorption-Enhanced Methanation with CaO in a Dual Interconnected Fluidized Bed System

In this work, ASPENplus was used to simulate biogas upgrading by sorption-enhanced methanation in a dual interconnected bubbling fluidized bed configuration using inexpensive, abundant, and eco-friendly CaO to remove H2O from the reaction environment. The chemical looping scheme consisted of two reactors: a methanator/hydrator, where the catalytic reactions occurred on a catalyst with 20% Ni supported on alumina as well as the steam removal by CaO, and a regenerator, where the Ca(OH)2 was dehydrated back to CaO. The simulations were carried out to identify possible reactant compositions (H2 and biogas), CaO amount, and the methanation temperature able to produce an outlet gas matching the specifications for direct grid injection. When considering a stoichiometric gas feed ratio at the methanator inlet, the unwanted CaO carbonation worsened the process performance, subtracting CO2 from the desired methanation reaction. However, optimal conditions were found with hydrogen-lean gas feedings, balancing the limited H2 amount with the capture of CO2 due to the sorbent carbonation. Thermodynamic considerations pointed out the possibility of solid carbon formation induced by sorption-enhanced methanation conditions, especially for H2 sub-stoichiometric feedings.

Growth, survival, and morphometric relationships of Crassostrea corteziensis cultivated during the nursery stage in oyster bags at different tidal levels, in Boca de Camichín, Nayarit, Mexico

The optimal tide height at which the intertidal oyster bed system (IOBS) should be installed to cultivate Crassostrea corteziensis in Boca de Camichín (BC), Nayarit, Mexico, during the intermediate grow-out stage (39.3–60.2 mm in shell length) was determined. Temperature, salinity, chlorophyll a (Chla), and turbidity were recorded 3 times a day. A trophic state index (TSI) was calculated with Chla and turbidity data. Three treatments corresponding to tide levels were tested: (1) high level (14 cm above mean sea level [MSL], emersion time [ET] = 56.4% of the total duration of the experiment), (2) intermediate level (MSL, ET = 48.6%), and (3) low level (41 cm below MSL, ET = 32.1%). Gross growth rates and absolute and relative monthly growth rates were calculated to identify periods with highest growth relative to environmental conditions. Finally, the effect of the treatments on the dimensions and weight of the oysters was studied. The results indicate that BC water was mesotrophic in April–June and eutrophic in July–August. The low tide level was the best for IOBS operation, with growth rates of 0.15, 0.10, and 0.07 mm·d–1 in shell length, width, and thickness, respectively, and 0.204 g·d–1 wet weight. Cumulative mortality was lower in the low (18.5%) and intermediate (16.4%) treatments. Shell thickness was significant reduced (P < 0.05) in the high treatment and total wet weight was reduced in the high and intermediate treatments. The results of this study offer a viable and different alternative to the cultivation of C. corteziensis in strings that is currently carried out in Boca de Camichín, Nayarit, Mexico.

Sustainable strategy for converting plastic waste into energy over pyrolysis: A comparative study of fluidized-bed and fixed-bed reactors

This paper proposed a sustainable strategy for converting plastic waste into energy over pyrolysis to address the dual crises of environment and energy. A fluidized-bed reactor was designed for processing three different plastic waste (PP, LDPE and ABS). A product yield and properties from a fluidized bed system were comprehensively analyzed and compared with those from a fixed-bed system. The fluidized-bed reactor well converted ABS and PP wastes into pyrolysis fuel, exhibiting higher medium and low fraction (C5 ∼ C22 of 89.17 % for ABS) as compared to the amount from a fixed bed reactor (84.7 %) whereas LDPE and PP resulted in the similar product yields in the range of C5 ∼ C22 from both reactors. In case of LDPE, the given pyrolysis temperature (520 °C) was not feasible to properly process them into fuels so that dominant heavy oil (∼67.4 %) were produced regardless of the reactor type. GCMS analysis indicated that ABS pyrolysis oil is mainly composed of aromatics, aromatic-N and olefins whereas PP pyrolysis oil mainly includes olefins, paraffins and oxygenated compounds. From the current study, a potential use of a fluidized-bed reactor for pyrolysis was evaluated to overcome the major limitations of conventional pyrolysis process.

Peering into the mechanisms of granulation and CO2 capture on alginate-assisted Li2CaSiO4-decorated Li4SiO4 sorbents

In recent years, high-temperature CO2 capture technology based on Li4SiO4-based sorbents has received widespread attention. However, powder elutriation and low sorption performance of Li4SiO4 hinder its practical application. In this work, these two obstacles have been solved in one step via a novel alginate-assisted route, via which the granulation and performance enhancement of Li4SiO4 sorbents were simultaneously achieved. The obtained Li4SiO4 pellets exhibited good mechanical strength (i.e., anti-attrition ability), demonstrating the suitability for the realistic application in circulating fluidized bed systems. In addition, Li2CaSiO4 phase was formed in the synthesis process and well dispersed in the sorbent. Meanwhile, the produced Li4SiO4 pellets (especially the pellets derived from lithium acetate) were featured with wrinkled surfaces. As a result, Li2CaSiO4-decorated Li4SiO4 sorbents displayed satisfactory CO2 sorption capacity reaching 0.24 g CO2/g sorbent. To clarify the mechanism of Li2CaSiO4 decorating, Li2CaSiO4-Li4SiO4-CO2 sorption model based on the double-shell reaction mechanism was proposed. Following this model, Li2CaSiO4 functioned as a ‘catalyst’ layer that greatly promoting the diffusion of Li+ and O2–, thus improving the cyclic CO2 sorption performance of Li4SiO4 sorbent. In conclusion, two main problems (elutriation and poor sorption performance) of Li4SiO4-based CO2 sorbent have been well mitigated in one step via alginate-assisted technique, which surely helps pave the way for the practical application of Li4SiO4 sorbents for CO2 capture.

Review of Fluidized Bed Technology Application for Adsorption Cooling and Desalination Systems

Adsorption technology utilizes low-temperature renewable and waste heat sources for cost-effective and environmentally friendly cooling and water desalination systems. However, the problem with existing adsorption refrigerators is the low COP. This is caused by poor heat and mass transfer in existing packed bed designs. The solution to this problem lies in the use of fluidized bed technology, which enhances heat and mass transfer mechanisms. Various approaches to the construction and operation of adsorption systems with a fluidized bed of adsorbent can be found in the literature; hence, the aim of the work is to analyze the existing applications of a fluidized bed in adsorption refrigerators and other systems utilizing sorption beds. There are many methods for improving the energy efficiency of adsorption refrigerators. However, the literature suggests that fluidized bed systems have the potential to significantly improve the energy efficiency of adsorption cooling and desalination systems. Based on the review, it was concluded that using fluidization technology in adsorption cooling and desalination systems can be beneficial and represents significant potential for future research.

Chemical looping process for hydrogen and electricity co-production: Design and operational consideration for moving-bed-reducer-based circulating fluidized bed systems

Chemical looping is an economically advantageous technology for reducing carbon emission from energy, fuels, and chemicals conversion systems utilizing a variety of feedstocks including fossil fuels, renewable materials, and industrial and municipal wastes. Its development relies on two key areas of core competency, i.e., metal oxide reaction engineering, and particle science and technology. The reaction kinetics and the transport phenomena in chemical looping reactors are intrinsically twined with the specific system operational conditions, configuration, and their integration. The optimal design and successful operation of chemical looping systems necessitate a comprehensive consideration of both the reaction rates and multiphase flow characteristics within each reactor. In this article, we analyze the impact of particle hydrodynamic characteristics on optimizing the operational conditions of a syngas-fueled chemical looping (SCL) process, which aims to co-produce hydrogen and electricity. Using this SCL process as an illustrative example, we examine how the particle hydrodynamics influence the system performance and efficiency. The outcome of these effects on the system performance is discussed.

Comparison of sub-grid drag laws for modeling fluidized beds with the coarse grain DEM–CFD approach

Fluidized particulate systems can be well described by coupling the discrete element method (DEM) with computational fluid dynamics (CFD). However, the simulations are computationally very demanding. The computational demand is drastically reduced by applying the coarse grain (CG) approach, where several particles are summarized into larger grains. Scaling rules are applied to the dominant forces to obtain precise solutions. However, with growing grain size, an adequate representation of the interaction forces and, thus, representation of sub-grid effects such as bubble and cluster formation in the fluidized particulate system becomes challenging. As a result, particle drag can be overestimated, leading to an increase in average particle height. In this work, limitations of the system-to-grain ratio are identified but also a dependency on system width. To address this issue, sub-grid drag models are often applied to increase the accuracy of simulations. Nonetheless, the sub-grid models tend to have an ad hoc fitting, and thorough testing of the system configurations is often missing. Here, five different sub-grid drag models are compared and tested on fluidized bed systems with different Geldart group particles, fluidization velocity, and system-to-grain diameter ratios.

Three-zone simulated moving bed for the separation of chlorogenic acid and caffeine fractions in the liquid extract of spent coffee grounds

Spent Coffee Grounds (SCG) is an agricultural residue obtained in a large quantity from local cafes in Thailand. In order to handle this waste effectively, the valorization of SCG is essential. SCG consists of beneficial phenolic compounds with antioxidative properties and caffeine, which can be recovered through extraction followed by separation and purification processes. In this work, water extraction of SCG was carried out. The volumetric composition of the liquid extract of SCG was then adjusted with an organic solvent, and the obtained mixture was used as the feed for subsequent separation. For the separation method of the SCG extract, a single chromatographic column was employed to separate a group of phenolic compounds (represented by chlorogenic acid) and a group of contaminants (represented by caffeine). The volumetric composition of the mobile phase was varied to determine the condition suitable for the separation of chlorogenic acid and caffeine in a C18 column. Adsorption parameters were determined and used to formulate the mathematical models describing the adsorption dynamics of those two bioactive compounds in the experimental breakthrough curves of standard solutions and the liquid extract of SCG. Furthermore, the three-zone simulated moving bed system (TZ-SMB) was designed to continuously separate fractions of chlorogenic acid and caffeine in the liquid extract of SCG. The adsorption parameters were employed in the optimization of TZ-SMB operating conditions using triangle theory, conducted via computer simulation. The experimental result of water extraction revealed that the yields of chlorogenic acid and caffeine were 0.292 and 0.583 mg/g dried SCG, respectively, using solid-to-liquid ratio of 1 g: 30 mL and temperature of 75 °C. The separation result in a single chromatographic column showed that the mobile phase consisting of acetonitrile, water, and formic acid (10: 90: 1.5 vol%) provided the linear adsorption isotherms for both chlorogenic acid and caffeine, and the chromatographic peaks of all compounds in the liquid extract of SCG were well separated. The simulated results of TZ-SMB at the optimal point revealed that the flow rates of desorbent, feed, extract product, and raffinate product were 0.626, 0.115, 0.081, and 0.593 mL/min, respectively, with the switching time of 20 min. At this point, the relative purities of caffeine in the extract product and chlorogenic acid in the raffinate product were 99.45 % and 98.88 %, respectively, with the maximum productivity of 0.045 mg/mL⋅h. In addition, for demonstration purposes, the lab-scale TZ-SMB experiment was conducted to show the separation of chlorogenic acid and caffeine in the liquid extract of SCG. The operating point from the triangle separation region was chosen based on the sensitivity of flow rate that ensured the criteria of purity. The experimental results showed that the relative purities of caffeine in extract product and chlorogenic acid in raffinate product were both 100 %, verifying the successful separation.

On the Effect of Volumetric Energy Density on the Characteristics of 3D-Printed Metals and Alloys

Selective Laser Melting (SLM) is a specific 3D printing technique under Additive Manufacturing (AM) metal technologies. SLM is considered to be a precise rapid AM process combined with a powder bed system for producing customized metal products with a tailored microstructure and shape. Differences in the printing parameters can lead to differences in the surface as well as macroscopic mechanical characteristics of the manufactured parts and components. This work aims at quantifying the effect of the Volumetric Energy Density (VED) used in the SLM processing of various metals and alloys. Metallic specimens printed with different VED values were subjected to surface characterization as well as tensile deformation. Their surface roughness, yield stress and toughness were subsequently used to verify a linear relationship between roughness and VED, and a linear behavior between yield stress/toughness and VED was proposed. Predictive models were formulated for estimating the roughness/yield stress/toughness of the produced specimens with respect to the VED used in their production. The models’ predictions will provide insight into the 3D printing parameters, thus minimizing the cost and effort of the 3D printing procedure, in applications where surface quality and strength are important.

Enhanced H2 gas production from steam gasification of a winery waste through CO2 capture by waste concrete fines and use of alkali catalysts

This study focused on production of a high yield of hydrogen as a clean energy source from a winery waste, through steam gasification. The experiments were conducted in a fixed bed system and a thermal analysis-mass spectrometer unit. Quarry dust waste from cement industry was used to capture carbon dioxide emissions and alkali carbonates of K, Li and Na were used as catalysts. Based on the optimum conditions derived in a previous work, the effects of sorbent/biomass ratio, catalyst loading and temperature on conversion, gas composition and quality, cold gas efficiency and yield of high purity hydrogen were investigated. The amount of carbon dioxide captured up to 700 °C was 92–97 % and at 750 °C about 83 %. At Ca/C = 1 the molar fraction of hydrogen in the product gas was 74.8 %. Sodium carbonate exhibited a better overall catalytic activity at a loading of 20 % wt. In this case, hydrogen yield and concentration were 4.7 m3/kgchar and 95.9 %, respectively and char conversion 98.1 % on a dry ash-free basis. The proposed method was proved advantageous for high purity hydrogen gas production and environmental management of wastes.

Effects of the age of raised beds on the physicochemical characteristics of fruit orchard soil in the Vietnamese Mekong Delta.

To grow fruit plants, farmers in the Vietnamese Mekong Delta (VMD) must use raised bed constructions to avoid waterlogging during the rainy season. This study aimed to evaluate the effects of the age of the raised beds on the soil physicochemical properties of longan orchards located in the VMD. Two raised bed systems were evaluated: a young bed constructed 10 years ago and an old bed constructed 42 years ago. Soil samples were collected from five different soil layers (0-20, 20-40, 40-60, 60-80, and 80-100 cm) with four replicates per layer. Soil samples were tested for pH, electrical conductivity (EC), available phosphorus (AP), total nitrogen (TN), soil organic matter (SOM), exchangeable cations (Ca2+, K+, Mg2+, and Na+), cation exchange capacity (CEC), bulk density (BD), soil porosity, available water-holding capacity (AWC), particle composition (sand, silt, and clay), and size. The soil pH was approximately 1.0 units lower in the old bed compared to the young bed at depths of 0-20 and 20-40 cm. The BD was higher in the old bed (0.15 g cm-3) than in the young bed at a soil depth of 0.4 m. SOM, AP, exchangeable cations (Ca2+, Na+, and Mg2+), AWC, and soil porosity were significantly lower in both the topsoil (0-20 cm) and subsoil (20-40 cm) layers in the old bed than in the young bed. In particular, the SOM, AP, AWC, and soil porosity contents in the old bed decreased by 18%, 20%, 15%, and 17%, respectively, compared with those in the young bed at soil depths of 0-40 cm. Therefore, cultivating raised bed soil for a longer period significantly reduced the soil exchangeable cations, porosity, and fertility of the surface and subsurface soils. Based on these results, farmers should use soil conservation practices, such as cover crops, rice straw mulching, and soil amendments in their orchards to mitigate topsoil degradation.

Flow regimes and transitions in an ultra-high temperature gas-solid fluidized bed

Gas-solid fluidized bed reactors are widely used in industrial operations and thus have led to a significant amount of fundamental research over decades. For better design and operation of fluidized bed systems, it is essential to understand the fluidization regime and the related transition conditions. Dr. John R. Grace, a prominent figure and pioneer in fluidization science and technology, has made significant contributions to understanding fluidized bed systems, including fluidization regimes and their transitions. This study is a tribute to his extraordinary legacy, focusing on investigations of fluidization regimes and transitions in a laboratory-scale gas-fluidized bed operating from ambient to 1600 °C. The results indicate that the fluidization regime transitions follow three distinct pathways across different temperature ranges: below 300 °C, from 300 to 1400 °C, and above 1400 °C. These distinctive transitions arise as a result of the varying significances of hydrodynamic and interparticle forces in the fluidized bed of particles investigated.

Use of a residential building’s foundation as Energy Geo-Structures: A case study in the Mediterranean environment

Geothermal energy, a type of renewable energy obtained from the Earth, can be used by Ground Source Heat Pumps (GSHPs) for space heating and cooling. GSHP systems extract/reject heat from/into the earth via a network of pipes or tubes known as Ground Heat Exchangers (GHEs),. GHEs can be horizontal or vertical and come in a variety of forms, including slinky loops and vertical spiral loops for horizontal configurations, and single U-tube, double U-tube in series or parallel, coaxial pipe, and spiral/helical pipe for vertical configurations. Although GSHPs exhibit a higher performance than conventional Air Source Heat Pumps (ASHPs), the systems are less appealing as investments due to their longer payback times and greater upfront costs. A competent design of the GSHP system with the appropriate GHE sizing, including the case of employing the GHEs in the structures foundations, can minimize the initial cost. Such structures are referred to as Thermo-Active Structure systems or Energy Geo-Structures (EGS), which have already found applications as energy piles, barrette piles, diaphragm walls, shallow foundations, retaining walls, embankments, and tunnel linings [1, 2, 3].
 Residential buildings in Cyprus have a higher cooling than heating demand, with an extended payback period for the investment, especially if the system is solely utilized for heating [4]. EGS coupled with a GSHP could offer a substitute to reduce the system’s initial expenses and make it more attractive as an investment. EGS have not yet seen applications in Cyprus, therefore an initial computational analysis utilizing the COMSOL software and relevant data is taken into consideration. To determine the heating and cooling loads, a three-bedroom, two-storey house with a total floor space of 190 m2, with nearly Zero Energy Building (nZEB) characteristics, is used as the typical case for a single detached residential building in Cyprus. The TRNSYS software was used to calculate the heating and cooling loads. In order to analyze the rejected/absorbed energy from the earth, typical foundations were constructed as full sized models in COMSOL (Figure 1). With the exception of pipes, where a 1D solution is employed, the convection diffusion equation for heat transfer is utilized with 3D conservation of heat transfer for an incompressible fluid. A detailed methodology can be found in Aresti et al. [5].
 For the COMSOL compuations, the site ground temperature characteristics and the local ambient temperature were taken into account. Based on the provided loads, the inlet and outlet temperatures were hourly calculated for the highest demand months: February for winter – heating, and July for summer – cooling.
 To assess the potential of using the foundation bed as an alternative to energy piles, a comparison on the performance of the two cases is presented in Figure 2 for both summer and winter conditions. The foundation bed is seen to work in a steady manner, which is highly desired in a system. However, it performs less well, with a lower COP than the energy piles system, which exhibits greater COP values than the foundation bed system both in winter and summer. It remains that both systems exhibit high enough COPs and nearly steady conditions. The COPs vary between 4.4 and 4.8. A yearly simulation (not shown here) yielded a lowest COP value of 4.5.
 The systems were also assessed economically by being compared to a convectional ASHP system. The economic study demonstrated that the suggested foundation systems had relatively short payback times, making them a plausible alternative. More detailed discussion on the results can be found in Aresti et al. [5]. As a future objective, an environmental and Life Cycle Analysis investigation, similar to the one performed by Aresti et al. [6], could provide a deeper insight of the plausibility of using the building foundation as EGS.