Measuring of isothermal water vapor adsorption/desorption rate using QCM method and its mass transfer resistance of a layer coated with silica-gel micro particles in a moist air

Measuring of isothermal water vapor adsorption/ desorption rate using QCM method and its mass transfer resistance of a layer coated with silica-gel micro particles in a moist air

Significance 

The increase in the future use of adsorption chillers and dehumidification systems will majorly depend on their energy consumption, compaction and general efficiency. Adsorbents are generally coated on heat exchangers to increase their adsorption/desorption rate with enhanced heat transfer. Consequently, researchers have noted the importance of decreasing the vapor transfer resistance in the concentration boundary layer taking into consideration the influence of flow rate on the resistance. This necessitates the need to measure the mass of the adsorbed water vapor which is currently a challenge. To date, several techniques have been devised to measure the amount of the adsorbed vapor and the adsorption rate. However, these methods are limited due to several challenges. As such, researchers have been looking for alternative methods and have identified the quartz crystal microbalance as a promising one.

Dr. Yoshinori Hamamoto, Mr. Takehiro Nakamori, and Professor Hideo Mori from Kyushu University recently used a highly sensitive quartz crystal microbalance to measure the amounts of adsorbed and desorbed water vapor in moist air to a thin layer of the adsorbent. The adsorbent was consolidated with silica-gel microparticles on the quartz crystal coated with thin gold electrodes. The work is published in the International Journal of Refrigeration

Briefly, the authors started by cross-examining the possibility of achieving stable measurements by comparing the data with the catalog date of the desorption equilibrium of silica-gel particles. Additionally, the adsorption/desorption rates were measured taking into account the changes in the surrounding relative humidity conditions. Finally, the influence of the airflow velocity on the mass transfer resistance relative to mass diffusion in the particles and mass transfer in the boundary layer was investigated.

At constant temperatures, the measured relative equilibrium adsorption reproduced the catalog data of the silica gel. The time constants of the reactions reflected the characteristics of the mass transfer resistance of the reactions and the resistance was observed to decrease with the increase in the velocity. Numerical simulations of the temperature change of the layer were conducted during adsorption and desorption reactions. Based on the results, the adsorbents were regarded as isothermal. On the other hand, it was necessary to separate the resistance into diffusion resistance inside the adsorbent and mass transfer resistance in the concentration boundary. Specifically, the resistance through the boundary layer was reported to be negligible at airflow velocity above 0.1 ms-1. Furthermore, these resistances could be predicted by the proposed correlations and fittings parameters.

In summary, the Kyushu University scientists successfully applied the quartz crystal microbalance method to measure the isothermal water vapor adsorption and desorption rate and its mass transfer resistance of a layer in the moist air. In a statement to Advances in Engineering community, Dr. Yoshinori Hamamoto highlighted the importance of the study especially in revolutionizing the future heating and cooling systems.

Measuring of isothermal water vapor adsorption/desorption rate using QCM method and its mass transfer resistance of a layer coated with silica-gel micro particles in a moist air - Advances in Engineering
A QCM sensor with consolidated silica gel particle layer (left hand side), without the layer (right hand side)

About the author

Yoshinori Hamamoto has been an associate professor of Mechanical Engineering at Kyushu University in Japan since 2005. He received his Ph.D. in engineering from Kyushu University in 2001. He worked as a researcher of Japan Science and Technology Agency in 2000, and from 2001 to 2004 worked as an assistant professor of Mechanical System Engineering at Tokyo University of Agriculture and Technology. From 2010 to 2011, he also joined Prof. Khellil Sefiane’s group as a visiting professor at the University of Edinburgh, UK to study heat and mass transfer in the evaporating droplet on a substrate. From 2012 to 2014, he worked as a project leader for research “Smart Energy Utilization Plant Factory”, contributing to agriculture and engineering collaborations, and continues to do so.

His research interests include a thermal energy conversion technology based on a heat and mass transfer of multiphase change process with vapor adsorption phenomena. He is pursuing research that contributes to the development of high-efficiency energy conversion systems such as heat pumps/refrigerators to use waste heat energy and renewable energy rationally.

He has published more than 150 peer-reviewed journal papers, international conference proceedings, reviews, commentary papers and book chapters. Recently, he served as managing guest editor of Heat Transfer Engineering and Applied Thermal Engineering.

Reference

Hamamoto, Y., Nakamori, T., & Mori, H. (2019). Measuring of isothermal water vapor adsorption/desorption rate using QCM method and its mass transfer resistance of a layer coated with silica-gel micro particles in a moist air. International Journal of Refrigeration, 105, 11-18.

Go To International Journal of Refrigeration

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