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Activated carbon signifies extensive carbonized materials of a high degree of porosity and has a wide range of applications. The porous and thermal properties of activated carbon (AC) are primarily...

This paper presents a rigorous exergy analysis of a vapor compression refrigeration system (VCRS) for the AHRI standard cooling operating conditions assessed with a constant cooling load of 50 kW. A comprehensive mathematical model has been developed to evaluate thermodynamic variables of the major components. The analysis is carried out for widely used refrigerants, namely R12, R22, R134a, R152a, R410A; next-generation low GWP refrigerants R32, R1234yf, R1234ze(E); and two natural refrigerants R600a and R744 (CO2). First law analysis and exergetic efficiency at cycle and component level are investigated for all the refrigerants. The results indicate that R600a is the best, followed by R152a, R1234ze(E), and R1234yf in terms of COP, total exergy destruction, and exergetic efficiency. Moreover, the total equivalent warming impact (TEWI), which is the aggregation of direct impact due to refrigerant leakage and indirect impact due to electricity usage, from each system has also been assessed. The lowest and highest amount of TEWI has been found for R600a and R12 systems, respectively. CO2 is an extremely prospective refrigerant for its lower emission, affordability, availability, non-toxicity, non-flammability, and system compactness when the MVRS is driven by electricity from nuclear/renewable sources.

Maxsorb III is the best available microporous activated carbon. The parent Maxsorb III has been modified by pyrolysis in the presence of ammonia carbonate. The adsorption isotherms and kinetics of HFC404A onto the modified Maxsorb III are experimentally measured over 25 °C to 75 °C. Toth and Dubinin-Astakhov models are utilized to fit the experimentally measured data. The isosteric heat of adsorption is calculated by applying the Clausius-Clapeyron equation. The adsorption kinetics of the modified Maxsorb III/HFC404A are fitted using the linear driving force model and Fickian Diffusion equation. Experimental measurements indicate that the modified Maxsorb III has a maximum uptake of 2.65 kg.kg−1 of HFC404A at 25 °C, which is the highest reached value till today. Additionally, the adsorption cooling system efficacy is evaluated under typical operating conditions using the modified Maxsorb III/HFC404A pair. The modified Maxsorb III/HFC404A could achieve a specific cooling power (SCP) of 747 W per kg of adsorbent along with a coefficient of performance (COP) of 0.40. Compared to the parent Maxsorb III/HFC404A pair, the pyrolyzed Maxsorb III/HFC404A pair provides the SCP and COP by a factor of 2.23 and 1.7, respectively, which are are the current benchmark.

This work comes as a part of a series of researches carried out by our team to study and present new materials with distinctive properties suitable for adsorption applications. As we previously studied employment of many Freons within the adsorption cooling systems, this paper expresses a study using HFC404A with activated carbon (Maxorb III). Adsorption of Maxsorb III/HFC404A pair has been estimated experimentally at different temperatures ranging from 25 to 75 °C. Dubinin-Astakhov (D-A) and Toth equations have been fitted with the experimental data to evaluate the adsorption isotherm, while the adsorption kinetic is evaluated by linear driving force model (LDF) and Fickian diffusion (FD) equations. The maximum adsorption capacity is 2.2 kg R404A/kg activated carbon. The numerical values of the activation energy (Ea) and the pre-exponential coefficient (Dso) are evaluated to be 3429.27 kJ/kg and 5.35×10–13, respectively. Transient simulation modeling has been carried out to predict performance of adsorption cooling system under different operating temperatures of Maxsorb III/HFC404A. Optimum recorded coefficient for performance and specific cooling power is 0.23 and 275 W/kg, respectively.

In this study, adsorption characteristics of water vapor onto several silica gel-based composites have been investigated experimentally. Adsorbent samples under investigation are silica gel powder (SGP), 98wt% SGP with 2wt% Polyvinylpyrrolidone (PVP) binder, 93wt% SGP, 2wt% PVP binder with 5wt% EG500 and 93wt% SGP, 2wt% PVP binder with 5wt% EG100. The three composite samples have been named as (S1-PVP), (S2-EG500) and (S3-EG100), respectively. Porous properties and thermal conductivity of S2-EG500 and S3-EG100 have been measured and compared with that of SGP. Experimental results showed that S2-EG500 has higher effect on enhancing the thermal conductivity of the composites where its thermal conductivity reached about 2.8 times that of SGP whilst thermal conductivity of S3-EGP100 is found to be about 2.3 times that of SGP. Adsorption isotherms of composite samples/water pairs have been measured gravimetrically at 30, 50 and 70 °C. The Toth and Dubinin-Astakhov (D-A) equations have been used to fit adsorption uptake measurements, Toth equation shows a better fitting. Isosteric heat of adsorption of the studied pairs have been extracted from the experimental measurements using Clausius-Clapeyron equation. The Linear Driving Force (LDF) model is found to be able to present adsorption kinetics of the studied pairs through a good agreement with the experimental data.

Water scarcity is the biggest survival challenge for the current generation, and atmospheric water condensation can be a solution. This paper presents the results of a numerical and experimental ev...

The present study involves the use of dip nanocoating, one of the passive techniques by the modification of the heater surface to understand the behavior of pool boiling heat transfer characteristi...

The urge to replace hydrofluorocarbons which possess high global warming potentials has taken center stage in the air conditioning industry due to both international and local policies such as the ...

Metal-organic frameworks (MOFs) are emerging as potential adsorbents for adsorption based systems intended for various applications. Aluminum fumarate is one of the promising MOFs for being used as...

Nanofluid preparation and its deposition on metallic surfaces are in wide practice due to their enhancement capability in the pool boiling heat transfer. The effect of zirconia nanoparticles coated...

Porous silica gel (SG) has been extensively used as an adsorbent in adsorption cooling, dehumidification, and desalination applications. Specific heat capacity (Cp) of SG with temperature variation is not experimentally investigated yet. Therefore, this study focuses on the experimental investigation of Cp along with the porous properties of six types of different particle size silica gels. Adsorbed phase Cp of SG is also determined with 10% and 20% water uptake. The experimental Cp is measured within 30 to 100 °C, and the Cp values vary from 0.8 to 1.10 kJ kg–1 K–1 in the measurement temperature range. RD silica gel of the smallest particle size shows the highest Cp values, whereas indicator type silica gel shows the lowest Cp. The Green-Perry model fits well with the experimental Cp data. The porosity analysis shows that RD silica gels of large particle size (D > 0.7 mm) possess the highest surface area (≈ 770 m2/g), and type B silica gels have the largest pore volume (≈ 0.8 cm3/g) along with larger mesopores. A relationship between pore volume and Cp is also reported. The measured data are novel and essential for rigorous performance prediction of adsorption cooling, dehumidification, and desalination systems.

The usage of metal organic frameworks (MOFs) as adsorbent materials for adsorption-based heat transformation applications is gaining popularity among the research society due to their S-shaped water adsorption isotherms. Apart from the S-shaped isotherms, there are other two key features that need to be kept in mind when working with MOF/water pair, namely the equilibrium uptake and the hydrophobic length of the water adsorption isotherms. Therefore, in this study, three different metal organic frameworks, namely MOF–801, aluminum fumarate, and MIL–100(Fe), are synthesized, and water adsorption onto these adsorbents is measured thermogravimetrically. Utilizing the four-step temperature swing adsorption process, the entropy generation in each step is calculated for each pair. Surface properties of the MOFs are measured using the inverse gas chromatography method. We explicitly demonstrated the relation between surface energy components of the adsorbents and their respective water adsorption isotherms. It has been found that the equilibrium uptake is proportional to the surfaces’ work of adhesions, while the hydrophobic length shows a relation with the surface acid-base properties. This information is crucial for designing an optimum MOF adsorbent for an efficient adsorption-based heat transformation application.

The thermodynamic property surfaces such as enthalpy and entropy of an adsorbate + adsorbent systems are essential for designing adsorption-assisted thermal compression, gas storage, separation, and other applications. This paper presents the enthalpy (∆ho) and the entropy (∆so) of the adsorbent-adsorbate system under the barrier of Henry's law region. Hence Henry's law coefficient and Gibbs analogy are applied to formulate the adsorption driving force (∆go). To justify the proposed formulation, the initial adsorption phenomena (at pressure, P → 0) of C2H5OH, CO2, CH4, N2, H2O, R125, R134a, R152a, and R1234yf on graphite/MOFs (such as Zr-MOF-801, Mg-MOF-74, and Al-Fumarate) are considered. It is found that the adsorption driving force is linked with the pore structure of adsorbent materials. We employ experimentally measured isotherms data to calculate the adsorption driving force, ∆go for various adsorbate + activated carbon/MOFs systems. The maximum adsorption driving force is found at the pore widths of 3 Å to 7 Å. The ∆go decreases with higher adsorbent-pore volume and depends on adsorbate molecule size. Employing the proposed driving force concepts, (i) the specific cooing, heating, and COP of the adsorption system, and (ii) the CO2/CH4 storage capacity in the adsorption cell can be projected and analyzed. The adsorption driving force relates to enthalpic and entropic interactions and is useful for the design of adsorbents and the selection of adsorbent-adsorbate pairs for gas storage, separation, and various energy-related applications. Ministry of Education (MOE) The authors acknowledge the financing support from the Ministry of Education (MOE), Singapore (grant reference no. RG 98/17).

Adsorption cooling system using composite adsorbent and high energy density adsorbate (CO2) provides a significant advantage to reduce the system geometry. This study presents the adsorption characteristics of CO2 onto synthesized composites employing graphene nanoplatelets (GNPs) and activated carbon (AC). The influence of GNPs in the composite is investigated in terms of porous properties, thermal conductivity, and CO2 adsorption capacity. The composite 3 (50 wt% AC and 40 wt% H-25) achieves the highest thermal conductivity enhancement which is 23.5 times higher than parent AC powder. The CO2 adsorption uptakes onto different composites are measured gravimetrically at adsorption temperatures 20–70 °C. The measured data are fitted with modified D-A and Toth models. The specific cooling effect (SCE) and coefficient of performance (COP) are estimated for various driving heat source temperatures and two evaporation temperatures of 5 and 10 °C with a fixed adsorption/condenser temperature of 30 °C. AC-GNPs based composites are found suitable for developing compact adsorption cooling systems.

This article discusses a direct approach for assessing irregularly shaped pore distribution of porous materials using Atomic Force Microscopy (AFM). Using the tapping mode, AFM is employed to obtain the surface topographic information of the porous materials commonly used in adsorption applications. Three different types of silica gels, commercially used silica–alumina and acetaminophen samples are investigated using an image processing technique to capture the pore size-related information. Macro and mesopores in a specified region are visualized then quantified and counted using 2-D Fast Fourier Transformation (2D FFT) technique. The results obtained by the AFM technique are then compared with the BET surface area and pore size distribution (NLDFT) extracted from the N2 adsorption isotherms.

The performance of an adsorption system using Maxsorb III + ethanol pair is investigated for practical heat pump applications. An adsorption system using a single bed with a single evaporator/condenser is employed and the performance of the system is assessed for various regeneration temperatures (80 °C, 70 °C and 60 °C). The impact of the adsorption time on the performance of the selected pair is further evaluated. The potential application of the present adsorbent + adsorbate pair is the automobile air-conditioning system where the exhaust waste heat will be recovered to operate the adsorption system. Thus, antifreeze fluid is employed as the heat transfer medium for the adsorber and the evaporator/condenser heat exchanger. A mathematical model is developed to estimate the uptake amount from the experimental data. The sensible heat change (thermal mass), the superheating of the refrigerant in the adsorber, the adsorber heat leak and the heat rejection to the heat transfer medium are accounted for. The uptake amount is further verified using the classical p–T–q diagram. For operation using 30 °C adsorber coolant inlet and 15 °C chilled water inlet, the cooling capacity of the present system ranges from 15 to 35 W for the adsorption times of 600 s and 300 s, respectively. It is observed that the regeneration temperature significantly influences the net uptake of the system. The maximum net uptake is recorded to be about 0.995 kg/kg for the regeneration temperature of 80 °C. The system is further assessed using the ratio of the cooling capacity to the adsorption heat.

In this study, new composite adsorbent with enhanced thermal conductivity and adsorption capacity was synthesized and analyzed comprehensively for the development of compact CO2 based adsorption cooling system. The consolidated composite was prepared employing activated carbon, graphene nanoplatelets and hydroxyl cellulose as a parent adsorbent, thermal conductivity enhancer, and binder, respectively. The surface area and pore volume of the composite were found to be 1778 ± 13 m2 g−1 and 1.014 cm3 g−1, respectively. In addition, the composite showed 233% higher thermal conductivity compared to the parent activated carbon. Adsorption characteristics of CO2 were measured at temperature ranging from 20 to 70 °C and pressures up to 5 MPa. Absolute uptake was evaluated from excess adsorption based on the following two methods: (i) the adsorbed phase volume is equal to the pore volume of the adsorbent; and (ii) the adsorbed phase volume is almost zero under low pressure and/or high temperature conditions. Furthermore, the averaging of above two methods was also taken for avoiding these two extreme assumptions. Obtained absolute adsorption uptake data were fitted with modified Dubinin-Astakhov and Toth models. Results indicated good approximation between data points and models. The average isosteric heats of adsorption estimated using modified D-A and Toth model were found to be 19.742 kJ mol−1 and 19.023 kJ mol−1, respectively. The obtained characteristics of composite adsorbent are prerequisites for designing compact CO2 based adsorption cooling systems.

Made available in DSpace on 2021-06-25T10:20:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-02-01 Boiling heat transfer has been a trending research area for the last several decades due to its excellent heat removal capacity and direct applications in the distillation and pharmaceutical industries. The present investigation focuses on the augmentation of efficiency for the boiling requiring applications, as highlighted earlier. The experimental and numerical investigations study the effect of staggered V-shaped and rectangular grooved copper surfaces on pool boiling, compared with the smooth copper surface in the ZrO2 nanofluid media. The authors adopted fiber laser engraving technology to form the highlighted microstructures. Furthermore, three different concentrations, i.e., 0.001%, 0.005% and 0.01% by volume, were investigated in a medium having equal volumes of distilled water and ethylene glycol. The thermophysical properties of nanofluid and peculiar microstructures enhanced the relative heat transfer coefficient by 41.48%. The wall superheat drastically reduced due to the micro-level convection on the boiling heat transfer promoted by the microstructures. Besides, the numerical results fitted well with the experimental results with a little deviation (MAE = 2.04%). Mechanical Engineering Department National Institute of Technology Agartala Post-Graduation Program in Mechanical Engineering UNESP - São Paulo State University, Av. Brasil 56 UNESP - São Paulo State University, Câmpus of São João da Boa Vista International Institute for Carbon–Neutral Energy Research (WP-I²CNER) Kyushu University, 744 Motooka, Nishi-ku Mechanical Engineering Department Kyushu University, 744 Motooka, Nishi-ku Post-Graduation Program in Mechanical Engineering UNESP - São Paulo State University, Av. Brasil 56 UNESP - São Paulo State University, Câmpus of São João da Boa Vista

Multi-walled carbon nanotubes (MWCNTs) are a contemporary class of nanoparticles that have a prominent thermal, electrical and mechanical properties. There have been numerous studies on the enhancement of thermophysical properties of nanofluids. However, there is only limited research on thermal and stability analysis of MWCNT nanofluids with various kinds of solvents or base fluids, namely propylene glycol, ethanol, ethylene glycol, polyethylene glycol, methanol and water. This paper reports the enhancement of thermophysical properties and stability of MWCNTs with six different base fluids in the presence of sodium dodecyl benzene sulfonate surfactant with a mass concentration of 0.5 wt. Thermal and dispersion stabilities were determined using a thermogravimetric analyzer (TGA) and Zeta potential, along with a visual inspection method to evaluate the agglomeration or sedimentation of MWCNT nanoparticles over a period of one month. Ultraviolet-visible spectroscopy and Fourier transform infrared spectroscopy were utilized to identify the molecular components and light absorption of the formulated nanofluids at their maximum wavenumber (4500 cm-1) and wavelength (800 nm). In addition, thermophysical properties such as thermal conductivity, specific heat capacity, viscosity and density with a peak temperature of 200 C were also experimentally evaluated. The TGA results illustrated that MWCNT/ethylene glycol nanofluid achieved maximum thermal stability at 140 C and it revealed a maximum zeta potential value of -61.8 mV. Thus, ethylene glycol solution was found to be the best base liquid to homogenize with MWCNTs for acquiring an enhanced thermophysical property and a long-term stability. © 2020 IOP Publishing Ltd.

The present study focuses on the synthesis and characterization of new composites comprising of RD silica gel and metal-organic framework (MOF) MIL-100(Fe) to upgrade the performance of the adsorption-based atmospheric water harvesting system. The impact of adding MIL-100(Fe) on the porous properties, thermal conductivity, and water adsorption characteristics of the composites has been experimentally investigated. Furthermore, three performance indicators are introduced to investigate the performance of the system, including net adsorbate uptake (Δq) and the efficiency estimation using two different approaches. Results showed that the maximum increment in the thermal conductivity was found in the composite having the highest concentration of MIL 100(Fe) (69 wt%). Thermodynamic cycles were drawn to show the performance of the composites with heat source temperatures of 50 °C and 70 °C. A composite of 29 % RD silica gel, 69 % MIL 100(Fe), and 2 % PVP showed the highest value of Δq (213.8 % increment over parent RD silica gel). In contrast, the efficiency of the system was enhanced up to 187 % than that of the silica gel-based AWH system.

Significant efforts have been done in order to improve adsorption desalination systems by developing advanced adsorbents. Silica-supported ionic liquid (SIL) has been recently proposed as a promising adsorption material for water desalination due to its relatively high adsorption capacity around 1 kgwater.kgSIL−1. Such achieved performance can be considered as an initial cornerstone that requires further important additional data before reaching a successful practical application. In this paper, experimental measurements of water adsorption kinetics in the SIL named EMIM-AC/Syloid 72FP are presented. The kinetics is interpreted using a linear driving force (LDF) model that shows good harmony with experimental data. Depending on a former study on adsorption isotherms and the current kinetics data, the performance of an adsorption water desalination system (ADS) is predicted using a dynamic lumped parameter model. The results show a bright future for this SIL material in water desalination application with high theoretical pure water production achieving 47 m3 day−1ton−1, 0.85 coefficient of performance with 600 W kgSIL−1 specific cooling power. Furthermore, system working with the EMIM-AC/Syloid 72FP can theoretically be powered by as low as 40 °C heat source.

Solid-gas adsorption has drawn considerable attention utilizing low-grade waste heat and environment-friendly refrigerants for cooling, heating, and air-conditioning. However, low sorption capacity of the adsorbents is a long-standing challenge for achieving highly efficient adsorption heat pumps. This study aims to analyze and compare the performance of green synthesized transitional metal (10% Ni and 10% Co) doped aluminum fumarate metal-organic frameworks as adsorbent materials in an adsorption chiller where water is considered as the refrigerant. Water uptakes on these adsorbents were measured at 303 K, 323 K, and 343 K gravimetrically. It was found that both Ni and Co-doped samples showed higher equilibrium uptake when compared with the parent sample while the adsorption isotherm moved towards the lower pressure region. Additionally, adsorption cycles involving the pressure, temperature, and uptakes (P-T-q diagrams) were drawn to investigate their cyclic performances. The specific cooling effects were also calculated and compared among the associated adsorbent/adsorbate pairs having the adsorption, desorption, evaporator, and condenser temperatures considered as 303 K, 353 K, 288 K, and 308 K, respectively. Additional studies were conducted using the inverse gas chromatography technique to investigate the relation between the surface properties and the water adsorption isotherms.

This research article proposes to develop a waste heat driven single-stage adsorption-based cooling system by selecting CO2 and indigenous coconut shell based activated carbon (CSAC) as the adsorbate/adsorbent pair. The CO2 adsorption isotherms and kinetics of activated carbon are measured at different temperatures (273–368 K) using volumetric method. In order to illustrate adsorption isotherms, experimental data of CO2 uptake is correlated with the Langmuir and Dubinin-Astakhov (D-A) models. On the other hand, Linear Driving Force (LDF) and Fickian Diffusion (FD) models are utilized to explain adsorption kinetics data. Fugacity and pseudosaturation pressure of CO2 plays a significant role in the estimation of high-pressure CO2 adsorption and thermodynamic properties above the critical temperature of CO2, and these parameters are evaluated using adsorption isotherms data. The key thermodynamic properties and kinetics parameters of the assorted pair are estimated using measured adsorption isotherms and kinetics data which are used for the thermodynamic analysis of CO2-CSAC pair based cooling system. The maximum theoretical values of SCE and COP of CO2-CSAC pair are obtained as 12.52 kJ kg−1 and 0.10, respectively at the regeneration temperature of 80 °C along with the evaporator temperature of 15 °C.

An adsorption chiller requires thermal energy to regenerate the adsorbent by desorbing the refrigerant vapor. Minimum desorption temperature is the parameter which defines the lowest possible heat source temperature required for driving adsorption chiller. In this study minimum desorption temperature is evaluated for different types of adsorption isotherms classified by International Union of Pure and Applied Chemistry (IUPAC). For each type, adsorption isotherm model is utilized to estimate the minimum desorption temperature and then compared to the mathematical expression reported in literature derived using Dubinin-Astakhov isotherm model. This allows for critical scrutiny of the universal validity of mathematical expression. It is observed that this expression can estimate the minimum desorption temperature with reasonable accuracy for all isotherm models.

Conventional solar heat-driven single stage two bed chillers demand a large area for installation of solar thermal collector to activate the chiller, but in a highly populated tropical coun...

A combined analytical and experimental study was carried out to analyze the effects of cryogenic cooling on temperature during turning of AZ31C magnesium alloy. Finite element method was employed t...

Air conditioning approach using two separate units for latent heat and sensible heat removal opens up opportunities and challenges for improved efficiency. In such systems, the dehumidification device removes moisture from the air stream usually without condensation whilst the remaining sensible load is handled by a conventional mechanical vapour compression (MVC) machine. This article investigates the thermodynamic feasibility of such hybrid dehumidifier + MVC systems as potential replacements for the conventional MVC devices. We shed some light on the minimum efficacy requirement in terms of COP or simply the breakeven COP for the coupled dehumidification system. Thermodynamic investigation has been conducted using classical Carnot, endoreversible technique and the experimental approaches. The breakeven COPs for a dehumidifier + MVC system where the latter using HFC-R14a, HFC-R32 and HFO-R1234yf as refrigerants have been investigated at assorted outdoor air ratios. Performance enhancement in terms of COP and the cooling capacity at elevated temperatures for sensible cooling are accounted for. It is observed that the breakeven COP for the dehumidification system ranges from 9 to 17 (Carnot approach) and 4.3 to 6.8 (Ideal cycle) in order to be realistically competitive with the current efficiency offered by a MVC system for the both dehumidification and sensible cooling. The life cycle cost (LCC) analysis is further performed to assess the fresh air-handling systems using a conventional MVC system and a dehumidifier + MVC system. The unprecedented improvement in the performance of the MVC systems further raises the ceiling for the breakeven COP of the dehumidification systems.

Several studies have investigated the effect of environmental taxes on economic growth and carbon emissions. However, limited studies have quantitatively identified the connection between environmental taxes and technological innovations. The main focus of this study is to investigate the causal relations between environmental taxes and environment-related technological innovation with a holistic, robust model with significant statistical power. This model consists of panel cointegration analysis considering the cross-sectional dependence, applied to quantify the effects of environmental taxes on environment-related technological innovation in high and middle-income 42 countries from 1995 to 2018. The long-run results suggest that environmental taxes stimulate technological innovation; for example, a 1% increase in environmental taxes was found to increase environment-related technological innovation by 0.57 and 0.78% on average for high and middle-income countries using the CCEMG and AMG techniques, respectively. The policy implications of this study suggest that imposing environmental taxes can accelerate the advancement of environmental-related technologies for reducing carbon emission and sustainable development in high and middle-income nations, with possible applications in a broad range of nations, particularly as an evidence base for developing nations to shorten energy transition timelines.

Accurate simulation and detailed description of the dynamics of the adsorption process play a significant role in forecasting the performance of new materials when used in various adsorption systems, like cooling/heating. The activated carbon (AC) consolidation allows improving the heat transfer rate inside the adsorption/desorption bed and compacting the systems. There are numerous mathematical models in literature for gas adsorption onto granular AC. But for consolidated AC, because of the absence of macropores, most assumptions that work well for granular AC may lead to significant discrepancies. Therefore, the present research proposes a new mathematical model for gas (CO2) adsorption onto consolidated adsorbent, a non-isothermal pore change model. The model takes into account the porosity and permeability changes due to the adsorption. The validation of the developed model is performed via comparison with the results obtained experimentally and numerically using an isothermal model. The effective Knudsen diffusion coefficient for the working pair is evaluated from porosity data. The rate of adsorption or mass transfer coefficient is estimated using the van't Hoff plot. The study results could be applied in the development of waste heat-driven cooling systems employing consolidated composite material as the adsorbent. The proposed mathematical model is also applicable for many other working pairs.

This paper presents an in-depth numerical and thermodynamic study of a two-stage, 2-bed silica gel/water adsorption system for simultaneous generation of cooling power and potable water. The system is air cooled where the ambient temperature remains constant at 36 °C. The first part of this paper investigates the effect of cycle time, chilled water inlet and heat source temperature on system performance viz. specific cooling capacity (SCC), specific daily water production (SDWP) and coefficient of performance (COP). A significant outcome of this study is to show that decrease in heat source temperature not only reduces the specific throughput but also increases the optimum cycle time, whereas COP is relatively insensitive to such alterations. The second part of this paper discusses the estimation of the minimum desorption temperature from the simulated system throughput results as well as from fundamental thermodynamic analysis of a two-stage adsorption cycle. This thermodynamic analysis provides a theoretical limit for minimum desorption temperature and optimal inter-stage pressure for a two-stage adsorption cycle.

The performance of a Mechanical Vapour Compression (MVC) chiller is experimentally investigated under operating conditions suitable for sensible cooling. With the emergence of the energy efficient dehumidification systems, it is possible to decouple the latent load from the MVC chillers which can be operated at higher chilled water temperatures for handling sensible cooling load. In this article, the performance of the chiller is evaluated at the elevated chilled water outlet temperatures (7–17 °C) at various coolant temperatures (28–32 °C) and flow rates (ΔT = 4 and 5 °C) for both full- and part-load conditions. Keeping the performance at the AHRI standard as the baseline condition, the efficacy of the chiller in terms of compression ratio, cooling capacity and COP at aforementioned conditions is quantified experimentally. It is observed that for each one-degree Celsius increase in the chilled water temperature, the COP of the chiller improves by about 3.5% whilst the cooling capacity improvement is about 4%. For operation at 17 °C chilled water outlet temperature, the improvements in COP and cooling capacity are between 37–40% and 40–45%, respectively, compared to the performance at the AHRI standards. The performance of the MVC chiller at the abovementioned operation conditions is mapped on the chiller performance characteristic chart.

Biomasses are renewable resources and suitable precursors for synthesis of activated carbons (ACs). Two biomass sources: (i) Waste Palm Trunk (WPT) and (ii) Mangrove (M) are employed to synthesis activated carbons with huge surface area by chemical activation with potassium hydroxide (KOH). Thermophysical characteristics of the derived activated carbons namely thermal conductivity, particle size distribution, pore size distribution, surface area and pore volume are assessed. The total surface area of WPT-derived AC and mangrove-derived AC are found to be as high as 2927 m 2 g −1 and 2924 m 2 g −1 , respectively. The adsorption capacities of the synthesized biomass-derived ACs for ethanol are evaluated for assorted temperature and pressure conditions. It is observed that WPT-AC shows an ethanol uptake of 1.90 kg kg −1 whilst the M-AC can adsorb up to 1.65 kg kg −1 . The isosteric heat of adsorption associated with the present adsorbents/adsorbate (ACs/ethanol) calculated at different coverages showed only marginal difference. For a typical operating condition of adsorption heat pump, both biomass derived ACs showed similar net ethanol uptake which is significantly higher than the net uptake of commercially prevalent Maxsorb III AC.

The demand for cooling, especially in the developing economies, is rising at a fast rate. Fast-depleting sources of fossil fuel and environmental concerns necessitate looking for alternative cooling solutions. Solar heat driven adsorption based cooling cycles are environmentally friendly due to their use of natural refrigerants and the thermal compression process. In this paper, a performance simulation study of a basic two-bed solar adsorption chiller has been performed through a transient model for two different climatic locations in India. Effect of operating temperatures and cycle time on the chiller performance has been studied. It is observed that the solar hot water temperature obtained in the composite climate of Delhi (28.65°N, 77.25°E) can run the basic adsorption cooling cycle efficiently throughout the year. Whereas, the monsoon months of July and August in the warm and humid climate of Durgapur (23.48°N, 87.32°E) are unable to supply the required driving heat.

Experimental validation of simulated adsorber/desorber beds for sorption cooling applications is essential to obtain reliable results. We have conducted rigorous simulation of the adsorption process occurring in a finned tube adsorber utilizing 2D-axisymmetric geometry. The adsorber uses activated carbon–ethanol as adsorbent–refrigerant pair. It is cooled with water at nearly 30 °C and experiencing a sharp pressure increase of ethanol from 0.95 kPa initially to 6 kPa. The simulated temperatures at adsorbent thicknesses of 0, 1, 5 and 10 mm from tube outer diameter showed an increase in adsorbent temperature up to 20 °C from its initial temperature. They were slightly higher at start of adsorption and were consistent with experimental data at higher flow time. The validated CFD model will serve as a base for evaluating and optimizing activated carbon–ethanol adsorption cooling cycle. It can be extended also to different adsorber designs and other adsorbent–adsorbate pairs.

In this study, the effect of both cryogenic and dry machining of AZ31 magnesium alloy on temperature and surface roughness was examined. Cryogenic machining experiments were conducted by applying liquid nitrogen at the cutting zone. The cutting parameters (cutting speed, depth of cut, and feed rate) were varied, and their effect on the results was identified. It was found that the cryogenic machining was able to reduce the maximum temperature at the machined surface to about 60% as compared with dry machining. A finite element model was developed to predict the temperature distribution at the machined surface. The simulated results showed good agreement with the experimental data. After analyzing the temperature distribution, the model also suggested that the cryogenic-assisted machining removes heat at a faster rate as to that of the dry machining. An arithmetic model using the response surface method was also developed to predict the maximum temperature at the surface during cryogenic and dry machining. The analysis pointed out that the maximum temperature was greatly affected by the cutting speed followed by feed rate and depth of cut. Cryogenic machining leads to better surface finish with up to 56% reduction in surface roughness compared with dry machining.

The integration of building structure with renewable components such as photovoltaic (PV) panel and thermoelectric modules (TEMs), provides new opportunities for exploiting natural energy and minimizing impact on the environment. This paper presents experimental and simulation investigation of a novel thermoelectric air duct system (TE-AD) assisted with photovoltaic (PV) system for space cooling in Malaysian weather condition. The north facing TE-AD system consist of fifteen TEMs assisted by 300 Wp south wall facing PV system for cooling of test room whose volume is 9.45 m3. Both simulation and experimental results were in good agreement and showed that PV assisted TE - AD system when operated at 6 A gives the optimum temperature difference of 6.8 °C with cooling capacity of 517.24 W and COP of 1.15. Combination of the TE-AD and PV system saves 1806.75 kWh/year with an additional benefit of Freon free, highly reliable and less fossil fuel consuming system.

In an attempt to promote research on adsorption cooling systems, novel activated carbon-based composite adsorbents have been studied for thermophysical properties and adsorption characterization with difluoromethane (HFC 32) refrigerant. High surface area activated carbon of type Maxsorb III has been selected as the primary constituent of adsorbent composites, with H25 graphene nanoplatelets (GNPs), 1-Hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide ([HMIM][Tf2N]) ionic liquid, and Polyvinyl alcohol (PVA) binder in varying fractions. The various thermophysical properties such as surface area and porosity, specific heat capacity, and thermal conductivity have been experimentally evaluated. The thermal diffusivities have been measured in two different planes of the composites: parallel and perpendicular to the direction of the compression. It has been observed that the perpendicular plane has significantly higher thermal diffusivities (up to 2.32 times) over the parallel plane of the composites. Besides, a considerable improvement in thermal conductivity of up to 65.6 times is observed over powdered activated carbon. Adsorption uptake characteristics are studied gravimetrically for the composite samples in the temperature range of 30–70°C. Dubinin-Astakhov (D-A) and Toth models are fitted successfully for the adsorption isotherms, with the D-A model seen to offer better fits. Further, the specific and volumetric cooling energies are estimated for the consolidated carbon composites based on the respective D-A adsorption equilibrium parameters and thermophysical properties of the working pairs. Significant enhancements in volumetric cooling energy up to 78% over that of powdered activated carbon are seen for the consolidated composites.

This paper examines the effect of remittance income on energy consumption and the economy between 1976 and 2019 in the four highest remittance recipient nations of South Asia. The detailed analysis explores long-run and directional relationships utilizing stationary tests, the panel cointegration test, dynamic ordinary least square (DOLS), fully modified ordinary least square (FMOLS), and Granger causality tests using a Vector Error Correction Model (VECM). The study reveals the presence of long-run relationships among remittances, energy consumption, GDP and urbanization. Cointegrating regression identifies that remittance income, economic growth and urbanization individually have a positive and significant effect on energy consumption in the long-run. Results showed that a 1% increase in remittance income results in a 0.045% increase in energy consumption. Among nations analyzed, this effect was found to be strongly dominant in case of Bangladesh and Pakistan. The statistically significant and negative coefficient of the error correction term confirms long-run causality from remittance, GDP, and urbanization toward energy consumption. Variance decomposition analysis demonstrated that energy usage is heavily impacted by remittance inflows among studied variables. Policy implications of this study suggest that higher remittance inflows will increase energy consumption in South Asian countries, engendering positive economic growth and sustainable development.

The adsorption rate is an important parameter for accurate performance estimation of adsorbent-refrigerant based adsorption cooling cycles. Here, we have investigated the response of two adsorption kinetics models of activated carbon–ethanol pair by means of CFD simulation. The isothermal assumption used in estimating the diffusion time constant of Fickian diffusion and linear driving force (LDF) models led to divergence and under-estimated adsorption uptakes, respectively. By including the simulated adsorbent temperature profile in fitting of LDF model to experimental data, we assessed the non-isothermal diffusion time constants which were 2.5 to 5 times higher than those evaluated previously with isothermal assumption. The goodness of fitting, evaluated with coefficient of determination (R2), improved and became higher than 0.95 from 0.73 initially. The developed non-isothermal LDF equation allows accurate heat and mass transfer simulations and performance optimization of large scale adsorption/desorption bed employing activated carbon-ethanol pair for adsorption cooling applications.

Environment-friendly adsorption (AD) cycles have gained much attention in cooling industry and its applicability has been extended to desalination recently. AD cycles are operational by low-temperature heat sources such as exhaust gas from processes or renewable energy with temperatures ranging from 55 °C to 85 °C. The cycle is capable of producing two useful effects, namely cooling power and high-grade potable water, simultaneously. This article discusses a low temperature, waste heat-powered adsorption (AD) cycle that produces cooling power at two temperature-levels for both dehumidification and sensible cooling while providing high-grade potable water. The cycle exploits faster kinetics for desorption process with one adsorber bed under regeneration mode while full utilization of the uptake capacity by adsorbent material is achieved employing two-stage adsorption via low-pressure and high-pressure evaporators. Type A++ silica gel with surface area of 863.6 m2/g and pore volume of 0.446 cm3/g is employed as adsorbent material. A comprehensive numerical model for such AD cycle is developed and the performance results are presented using assorted hot water and cooling water inlet temperatures for various cycle time arrangements. The cycle is analyzed in terms of key performance indicators i.e., the specific cooling power (SCP), the coefficient of performance (COP) for both evaporators and the overall system, the specific daily water production (SDWP) and the performance ratio (PR). Further insights into the cycle performance are scrutinized using a Duhring diagram to depict the thermodynamic states of the processes as well as the vapor uptake behavior of adsorbent. In the proposed cycle, the adsorbent materials undergo near saturation conditions due to the pressurization effect from the high pressure evaporator while faster kinetics for desorption process is exploited, subsequently providing higher system COP, notably up to 0.82 at longer cycle time while the COPs for low-pressure and high-pressure evaporators are recorded to be 0.33 and 0.51, respectively.

This study introduces a new adsorbent/refrigerant pair to be used in adsorption cooling applications. Adsorption isotherms and kinetics of Difluoroethane (HFC-152a) onto highly porous activated carbon Maxsorb III at temperatures ranging from 25 to 75°C have been investigated. Experimental data of adsorption uptake have been fitted with Dubinin–Astakhov (D–A) and Toth equations. D–A equation is found to be more suitable than Toth equation for fitting the adsorption uptake. Experimental results showed that Maxsorb III can adsorb up to 1.3 kg of HFC-152a per kg of adsorbent. Experimental data of adsorption kinetics have been fitted with linear driving force (LDF) and Fickian diffusion (FD) models. Both LDF and FD models are found to be able to simulate the adsorption kinetics of the proposed pair. Isosteric heat of adsorption has been estimated considering the real gas case. Pressure–temperature–concentration (P–T–C) diagram of the pair has been also presented.

A combined adsorption and mechanical vapor compression system is a reasonable option to reduce the consumption of fossil fuels for air conditioning by utilizing waste heat. Performance predictions of combined adsorption and mechanical vapor compression systems require detailed dynamic modeling because the transitional characteristics explain the nature of the adsorption system. It is, however, desirable to simplify the model for practical use at engineering stages. Since the mechanical vapor compression system is based on the steady-state thermodynamic cycle, a semi-steady-state modeling of adsorption cycles would be functional for analysis of combined systems. In our study, the analytical solution of transient simulation for adsorption cycles was combined with a steady-state mathematical model of the mechanical vapor compression system. The performance of the combined system was analyzed based on the model developed, taking into account the cycle time of the adsorption cycle. The results show the...

Performance of an adsorption cooling system driven by solar thermal energy was studied under different climatic conditions. The effects of solar collector area, collector slope, hot water temperature and flow rate on the system performance were investigated using the real-time weather data of two cities: Perth, Australia (a representative city in the southern hemisphere) and Amman, Jordan (a representative city in the northern hemisphere). The simulation results showed that the two cities had similar solar radiation during the summer period and that the solar adsorption chiller could reliably provide cooling at a reasonably high system COP. For residential cooling with a total CPC (Compound Parabolic Collector) solar collector area of 36.22 m2, the average system COP was 0.491 for Perth weather conditions and 0.467 for Amman weather conditions, respectively while the cooling capacity was 10.3 kW for Perth and 8.46 kW for Amman, respectively at peak times. Optimum performance occurred when the system run with the CPC collector slope of around 30°, the solar water storage tank volume of 1.4 m3, inlet hot water temperature of 80 °C, and a hot water flow rate of 0.33 kg/s. An economic analysis was further investigated and the results showed that the solar driven adsorption cooling system could reduce the electricity consumption for Perth and Amman cities by 34% and 28%, respectively in comparison to a conventional vapour compression cooling system.