• Energy Research

Abstract In this first part a comprehensive thermophysical characterisation of six activated carbons – based on coconut, peat and stone coal with focus on thermally driven chillers is reported. Pore and surface analysis are performed using N2 and CO2 adsorption. Furthermore the density and heat capacity of the samples is determined. Methanol adsorption measurements for evaporation between −5 °C and 35 °C and driving temperatures up to 130 °C are realized using a thermobalance and evaluated using the Dubinin–Astakhov (DA) approach. Based on the given DA equations, the possible loading lifts for typical applications like 95°-35°-7 °C are calculated. The samples show very attractive maximum loading lifts up to 0.385 g g−1. Furthermore the mass and volume specific cooling enthalpy of 244 kJ kg−1 and 126 kJ dm−3 under realistic conditions demonstrates the good performance of this working pair.

AbstractTwo different composites, one with disordered mesoporous iron silicate matrix and the other with ordered mesoporous matrix together with calcium chloride, are presented. The introduction of CaCl2 in the matrices improves the maximal water sorption capacity. The composite with disordered mesoporous matrix showed a maximal water uptake of 0.58g/g at 5.6kPa, while the composite with ordered mesoporous matrix revealed higher maximal water uptake of 0.88g/g. These composites show good hydrothermal stability after 20 cycles of sorption/desorption between temperatures of 150°C and 40°C and at water vapor pressure of 5.6kPa. After the cycling test no leakage of the salt hydrate from the composites was detected.

This paper presents experimental and theoretical investigations of adsorption characteristics of ethanol onto metal organic framework namely MIL-101Cr. Adsorption isotherms and kinetics of the studied pair have been measured gravimetrically using a magnetic suspension adsorption measurement unit and volumetrically employing a Quantachrome Autosorb iQ MP machine. The present experiments have been conducted within relative pressures between 0.1 and 0.9 and adsorption temperatures ranging from 30 to 70 °C, which are suitable for adsorption cooling applications. Adsorption isotherm data exhibit that 1 kg of MIL-101Cr can adsorb as high as 1.1 kg of ethanol at adsorption temperature of 30 °C, and the Toth equation has been used to fit the experimentally measured data. As of the experimentally measured adsorption uptake rate data, the Fickian diffusion model is found to be suitable. These data are essential for designing a new generation of adsorption chiller.

Abstract In this work a versatile and hydrothermally stable binder based coating with fast adsorption kinetics for the use in thermally driven adsorption chillers, heat pumps and within dehumidification processes is reported. Two different adsorbents, a SAPO-34 with a typical adsorption isotherm favorable for low desorption temperatures and a zeolite Y for higher desorption temperatures were used. The coatings were prepared out of an aqueous dispersion for different binder contents with a minimum of 2.5 wt%. The performance of the coating and the influence of the binder on the equilibrium and dynamic adsorption characteristics were evaluated by means of thermogravimetry and a volumetric pressure jump method. Finally the hydrothermal stability under typical application boundary conditions was evaluated with surprisingly fair stability even for a very low binder content of a 2.5 wt%.

AbstractHeat transformation based on adsorption/desorption of water in microporous adsorbents has been considered for the application as adsorption chiller (ACS), adsorption heat pump (AHP) or thermochemical storage (TCS) since the 1980s. Unfortunately, most of the available adsorbents like zeolites were not optimized for the use in these processes as they originally had been developed for gas separation or catalysis processes. Within the last decade, intensive research on adsorbents yielded in improved and very promising new sorption materials with an enhanced adsorption capacity. This work gives a broad overview on current developments on materials including the new class of metal-organic frameworks for the use in adsorption processes for heat storage and transformation.

Abstract Heat transformation systems such as gas adsorption heat pumps will be one cornerstone in reducing the carbon footprint of the building sector. Their development calls for an increase in power density without sacrificing energy efficiency. For the adsorber component this translates to small ratio of heat exchanger to adsorbent mass. Possibilities to achieve this have been investigated on small scale samples as well as on full scale adsorbers. Different samples and adsorbers with varying adsorbent to metal ratios where produced and characterized using the large pressure jump and large temperature jump method. Under certain conditions it could be shown that in small scale and full scale the power can be kept on a high level while increasing the adsorbent to metal ratio. Here the heat and mass transfer in the coating layer is not limiting the adsorber power.

Abstract This paper describes a simple energy balance model based on static parameters to calculate the COP of an adsorption chiller. The model leads to an analytical equation using basic information about the working pair, the chiller design and the operation temperatures. A set of dimensionless key figures is derived for better understanding of the influence of physical parameters on the COP. These key figures are investigated in this paper. In contrast to absorption chillers, desorption is not an isobaric process in adsorption chillers. The influence of the path is discussed in the limits of isobaric and isothermal desorption. Furthermore, the model is applied to a set of new material data, focussingfocussing on methanol/activated carbon as the working pair. This working pair makes refrigeration below 0 °C feasible. This paper is the second of two articles about the measurement and evaluation of methanol/activated carbon for cooling purposes in adsorption chillers. The first part contains the experimental description and the thermophysical properties of methanol/activated carbon

Zeolite coatings allow for process intensification in various fields. In the zeolite coating process, silicone polymers are well suited as binding agents due to their unique and outstanding properties like thermal stability and water vapor permeability. In this work, selected silicone binders were used to prepare zeolite coatings which were characterized subsequently for their thermal and mechanical properties and pore accessibilities. Thermogravimetrical analysis (TGA) and temperature-controlled diffuse reflection FT-IR spectroscopy (T-DRIFTS) were performed to assess the thermal stability. Cross-cut, bend, and impact tests were used to investigate the mechanical stability of the coatings. The accessibility of the zeolite pores in the coating was quantified by N2 porosimetry. Superior coatings could be obtained using Silres MP50 Binder and Silixan’s W220, which had the least impact on the zeolite micropore volume while Silres REN 50 coatings showed the best mechanical stability and were very temperature ...