The phenomenon of adsorption known since ancient times is now widely used to convert low-temperature heat. This short review addresses recent results and current tendencies in adsorption heat ...conversion/storage in closed systems, which are the most important according to the author's opinion. The survey is based on literature data, reported mainly in the second decade of this century, and concerns the development of new adsorbents and cycles, improvement of adsorption dynamics, and some other topical issues. The paper aims at highlighting the current progress, research trends and existing gaps of the technology involved.
•The review addresses adsorption heat conversion/storage (AHCS) in closed systems.•It surveys results and tendencies reported mainly in the second decade of the century.•New adsorbents, cycles, heat exchangers, dynamic issues and other topics are involved.•The review aims at highlighting the AHCS current progress, trends and existing gaps.
This paper addresses some thermodynamic aspects of adsorptive heat transformation (AHT) driven by ultralow-temperature (ULT) heat. This non-payable heat is available in abundance from various natural ...thermal sources and as heat wastes from industry, transport and power engineering. The link between the temperature thrush that drives an AHT cycle and the obtained temperature lift is analyzed using the Trouton rule.
It is shown that even if only ULT heat with T ≤ 50 °C is available, it can effectively drive adsorptive cooling cycles and obtain an output temperature sufficient for air-conditioning, ice-making, and freezing. Moreover, heat amplification cycles can be driven by ULT heat with a temperature lower than 20 °C. The Dubinin adsorption potential ΔF is proposed as a quantitative measure of the adsorbent affinity, and the quantitative relationship between the temperature thrush and this potential is found for water as an adsorptive. This link can greatly help in choosing adsorbents optimal for the given AHT conditions.
Adsorptive heat transformation is an emerging technology that can store heat, convert it to heat with another temperature potential, and generate cold. Progress in this field is determined by the ...development of new advanced adsorbents, implementing efficient cycles, and harmonizing the adsorbent with the cycle. The article examines how the fundamental potential theory of adsorption is used to reach these applied goals and highlights the progress resulted from its application to adsorptive heat transformation.
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•Adsorptive heat conversion/storage (AHCS) is commonly used in hot/humid climates.•This review addresses the application of AHCS incold countries.•Which climate is considered cold and ...how it can affect AHCS cycle/unit?•Common and new AHCS incold countries are surveyed for both closed and open systems.•Special attention is paid on new “Heat from Cold” cycle and Ventireg process.
The strategic goal of reducing GHG emissions opens a niche for applying an emerging technology of adsorptive heat conversion/storage (AHCS). Currently, the AHCS technologies are mainly used in countries with a hot and humid climate. However, there are many territories of the Earth with quite a cold weather. The aim of this review has been to survey the application of AHCS incold countries. The thermodynamic indicators of AHCS cycle – the first and second law efficiencies - are briefly described. For obtaining a high first law efficiency, the adsorbate exchange per cycle has to be increased, the inert masses - decreased, and a working fluid with a large latent heat should be used. The SLT efficiency for heat amplification increases at colder ambient. It opens up new possibilities for using AHCS in cold countries.
The issues of which climate is deemed to be cold and how low ambient temperature can affect thermodynamic and dynamic features of the AHCS cycle/unit are considered. Traditional and recently proposed cycles/units are surveyed, and their applicability for cold territories is analyzed for closed and open AHCS systems. Special attention is paid on two new approaches intently proposed for cold climates, namely, a “Heat from Cold” cycle for upgrading the ambient heat temperature and a Ventireg process for regeneration of heat and moisture in ventilation systems. The performed analysis shows the prospects of AHCS technologies for cold countries and outlines the boundaries of their applicability.
The increasing demands for cooling/heating, depletion of fossil fuels, and greenhouse gases emissions promote the development of adsorption heat transformation and storage (AHTS). This emerging ...technology is especially promising for converting low-temperature heat, like environmental, solar, and waste heat. Among the known AHTS applications (cooling, heat pumping, amplification, and storage), the adsorption heat storage and amplification are less developed, thus gaining an increasing attention of the scientific community. The researchers are mainly focused on the developing new cycles for heat storage/amplification and advanced adsorbents specialized for these cycles. In this paper, we review the state-of-the-art in the fields of adsorption heat storage/amplification. The new, recently suggested, cycles (e.g. a “Heat from Cold” cycle for upgrading the ambient heat) will be described and analyzed from both thermodynamic and dynamic points of view. New adsorbents developed for adsorption heat storage/amplification will be presented. Special attention will be paid to the problem how to harmonize the adsorbent with the AHTS cycle under various climatic conditions. The lab-scale units constructed for verification of the cycle feasibility and adsorbent efficiency also are briefly described and analyzed. Finally, the problems and outlooks of adsorption heat storage/amplification will be discussed.
•The state-of-the-art in the field of adsorption heat storage/amplification is reviewed.•The efficiency and dynamics of pressure- and temperature-initiated cycles are compared.•New adsorbents developed for adsorption heat storage/amplification are described.•The problem of harmonization of the adsorbent with the cycle conditions is discussed.
In this paper we proposed and tested a new methodology of studying the kinetics of water vapour sorption/desorption under operating conditions typical for isobaric stages of sorption heat pumps. The ...measurements have been carried out on pellets of composite sorbent SWS-1L (CaCl
2 in silica KSK) placed on a metal plate. Temperature of the plate was changed as it takes place in real sorption heat pumps, while the vapour pressure over the sorbent was maintained almost constant (saturation pressures corresponding to the evaporator temperature of 5
°C and 10
°C and the condenser temperature of 30
°C and 35
°C). Near-exponential behaviour of water uptake on time was found for most of the experimental runs. Characteristic time
τ of isobaric adsorption (desorption) was measured for one layer of loose grains having a size between 1.4
mm and 1.6
mm for different heating/cooling scenarios and boundary conditions of an adsorption heat pump. Maximum specific power estimated from the
τ-values can exceed 1.0
kW/kg of dry adsorbent, that gives proof to the idea of compact adsorption units for energy transformation with loose SWS grains.
Adsorption processes are widely used to convert heat with low- or even ultralow-temperature (ULT) potential. For instance, the adsorptive VentireG process was proposed to regenerate ULT heat and ...moisture in ventilation systems in cold countries. In this paper, a new approach for a deeper analysis of this process is proposed. It is implemented by plotting water adsorption isosters for a specific adsorbent directly on the common psychrometric chart of humid air. Such a combined diagram would allow the states of air and the given adsorbent to be tracked simultaneously.
The merged “psychrometric – isosteric” diagram is plotted for five adsorbents potentially promising for the VentireG process. Their possible application in typical climatic zones of cold countries is analyzed, and the conscious choice of proper adsorbents is made. Composites “salt (CaCl2, LiCl, LiBr) in silica pores” can exchange up to 0.4–0.5 g_H2O/g and ensure low dew point of the outlet air.
In a broader sense, this new combined diagram can be used for analyzing any open adsorption cycles, e.g., for air conditioning, desiccation, water harvesting from the atmosphere, etc.
•Common psychrometric chart of humid air is combined with water adsorption isosters.•It allows simultaneous tracking of the states of humid air and a given adsorbent.•The diagram is used to analyze the VentireG cycle for heat and moisture regeneration.•Composites “salt/silica” exchange 0.4–0.5 g_H2O/g and ensure low dew point of air.•The new diagram can be used for deeper analysis of any open adsorption cycles.
•Dynamics of methanol ad/desorption of commercial carbon ACM-35 is studied.•Dynamics initiated by fast temperature or pressure changes are compared.•Monolayer and multi-layer configurations of carbon ...grains are studied.•For monolayer configuration, the dynamics does not depend on the initiation way.
Despite significant progress made in adsorption heat transformation, still, there is a big room for it's further improving. This work addresses the dynamic study of methanol adsorption and comparison of two ways of the process initiation. The traditional way is due to fast temperature change (TI), and the less studied one is by quick pressure variation (PI). The appropriate temperature/pressure variations were selected similar to those in a new cycle “Heat from Cold” recently suggested for upgrading the ambient heat in cold countries. An activated carbon ACM-35.4, used as a methanol adsorbent, was located on metal support as a thin flat bed of loose grains.
For a monolayer bed configuration, the dynamics is almost identical for the two initiation ways. Both TI and PI kinetic curves are exponential with a characteristic time, which depends on the process boundary conditions rather than the initiation mode. The mathematical model of methanol adsorption on a single spherical carbon grain is developed to explain these results.
The perceptible difference is found for the multi-layer configuration of the carbon bed. The PI adsorption dynamics is faster than the TI one at short adsorption time and equal to it at long time. A possible reason for this difference is discussed.
•The equilibrium and dynamics of methanol adsorption on MIL-101(Cr) are studied.•Methanol adsorption on MIL-101(Cr) grains occurs at “grain size insensitive” mode.•“Grain size sensitive” mode is ...observed for methanol desorption from MIL-101(Cr)•Specific useful heat and heating power reach 385 kJ/kg and 0.65–1.95 kW/kg respectively.•The MIL-101 – methanol working pair is promising for the heat amplification cycle.
Adsorption Heat Transformation (AHT) is one of the most promising solutions for reducing the consumption of fossil fuels and effective environmental protection. The working pair “adsorbent – adsorbate” is a key factor affecting the performance of AHT cycle. This paper addresses the investigation of the adsorption of methanol vapor on MIL-101(Cr), which belongs to a family of porous crystalline solids, Metal – Organic Frameworks. MIL-101(Cr) is shaped with polyvinyl alcohol (PVA) as a binder to form grains. The equilibrium of methanol adsorption on the grains of MIL-101(Cr) is studied and the potential of the MIL-101(Cr) – methanol working pair is estimated for various AHT cycles. The dynamics of methanol adsorption is explored under conditions of a new cycle for upgrading temperature of ambient heat. The main findings of this study are: (i) the addition of PVA does not affect methanol adsorption equilibrium; (ii) the amount of methanol exchanged under typical conditions of the cooling and ambient heat amplification cycles varies from 0.27 to 0.31 g/g; (iii) under conditions of the heat amplification cycle the methanol adsorption on the loose grains of 0.8–1.8 mm size, occurs under the “grain size insensitive mode” when the dynamics of adsorption in the adsorbent beds with the same thickness does not depend on the size of MIL grains. For the desorption runs, the poor mass transfer decelerates the process for the grains of 1.6–1.8 mm size; (iv) the specific useful heat and heating power for heat amplification cycle equal 385 kJ/kg and 0.65–1.95 kW/kg, respectively. The high values of specific heat and heating power illustrate an encouraging potential of the “MIL-101(Cr) – methanol” pair for the ambient heat amplification cycle.
•MgO doped with lithium-potassium nitrate is studied as a thermochemical material.•Its carbonation/decarbonation kinetics as well as cyclic stability are investigated.•The material shows a high ...energy storage density of 1.6 GJ/m3.•The concept of chemical heat pump utilizing the MgO-CO2 pair is discussed.
In this work, the MgO-CO2 working pair has been adapted for thermochemical energy storage (TCES) at medium temperatures by the MgO modification with inorganic salts to promote the TCES dynamics. Brief screening of modifying salts showed that lithium acetate (LiOAc) and mixed lithium-potassium nitrate (Li0.42K0.58NO3) additives could considerably promote the MgO carbonation at P(CO2) ≤10 bar and T ≥300 °C. The de- and re-carbonation kinetics, as well as cycling stability of the doped MgO/MgCO3, was reported to outline possible TCES operating conditions (T = 280 °C–380 °C, P(CO2) = 0–1 bar). The heat storage capacity of the salt-promoted MgO was estimated to be 1.6 GJ/m3. A concept of chemical heat pump utilizing the MgO-CO2 working pair was discussed. The salt-promoted MgO-CO2 working pair was concluded to be promising for TCES.
