Development of a method for isobaric large temperature jump adsorption experiments

Abstract

Adsorption heat pumps offer the possibility to provide cold from waste heat, and can therefore be an important component for an environmentally friendly and sustainable cooling supply. A new accurate measurement method is developed to evaluate the progress of performance improvement in this area through new material and heat transfer concepts. The new method covers the entire sample range from very small to large sample sizes and also allows measurements in the poorly accessible transition region of medium sample sizes in the range from 1 to 10 g. A comparison with the conventional volumetric method in large temperature jump adsorption experiments is carried out using granular TiAPSO-34 in a flatbed configuration as adsorbent. The sample mass is varied from 300 mg to 1709 mg and the influence on the adsorption rate is compared using the characteristic time constants describing the dynamics of the adsorption reaction. It can be shown that the time constant for the new method is almost constant with a maximum deviation of 9% while the characteristic time constant for the conventional method varies up to 64%. The difference in adsorptive loading per adsorbent varies from 0.193 to 0.197 for the new method and from 0.100 to 0.190 for the conventional method. The new measurement method thus provides significantly more reliable results for the design of adsorption heat pumps than the previous volumetric measurement method. From the experimental results it can also be concluded that the new measurement method can be used in the present case up to sample sizes of 600 g which makes the gravimetric version of the large temperature jump method obsolete in this case.