Experimental investigation on hygroscopic kinetics and regeneration behavior of silica gel-modified molecular sieve composite desiccant

ABSTRACTIn this article, the regeneration of various saturated desiccant (wet basis) such as silica gel, activated alumina, molecular sieve, and novel composite desiccant using Scheffler solar concentrator (SSC) has been proposed. The regeneration performance is greatly affected by solar radiation, surface temperature of desiccant, wind velocity, and initial moisture content. SSC having aperture area of 1.54 m2 is used for regeneration of 0.620 kg sample of each desiccants. During the investigation, it has been found that silica gel has maximum moisture content (dry basis), i.e. 0.2944 followed by molecular sieve, novel composite, and activated alumina having moisture content 0.2205, 0.19, and 0.0671, respectively. The maximum regeneration rate of 0.07440 kg/hr is achieved in novel composite and maximum weight loss percentage of 22.74% is achieved in silica gel. Regeneration time taken by silica gel, activated alumina, molecular sieve, and novel composite desiccant are 160, 90, 140, and 110 min, respectively.

A solar-powered composite desiccant cooling system has been experimentally investigated. It consists of evacuated tube solar water heater, composite desiccant bed heat exchanger (CDBHE), direct evaporative cooling unit and cooling tower. The composite desiccant material has been synthesized by using iron mesh and jute layer impregnated with calcium chloride solution, and this composite desiccant is placed in shell- and tube-type heat exchanger to make CDBHE. In this desiccant cooling system, the evacuated tube solar water heater is used to produce required hot water for regeneration of composite desiccant material. A cooling tower is used to produce cooling water which is pumped into CDBHE during dehumidification process to remove heat of adsorption. Direct evaporative cooling unit is used to cool the outlet process air of CDBHE. It has been found that the average dehumidification rate increases by 54.1 % when using circulating cooling water. The COPth of desiccant cooling system has been found to be 0.46 with a cooling capacity of 353.8 W.

This work compares the performance of simple silica gel desiccant wheel (SG) and composite desiccant (CD) wheels using parabolic trough solar collector (PTSC) as a heat source. The adsorption rate (AR) and regeneration rate (RR) were checked experimentally. From experimental investigations, it was observed that CD wheel having composition silica gel-lithium chloride-molecular sieve (SG-LiCl-MS) has enabled more AR and RR. It was observed that the percentage improvement in adsorption rate (PIAR) is 35%, 43.6%, and 85.5%, the percentage improvement in (PIRR) is 5.7%, 7.1%, and 14.4% for CD wheel made from SG-MS, SG-LiCl, and SG-LiCl-MS, respectively. The same wheel showed wheel effectiveness in adsorption sector of 0.234 and wheel effectiveness in regeneration sector of 2.366.

Indoor comfort has become a major factor with advancements in science and technology. This also leads to an increase in greenhouse gases as well as energy consumption. Desiccant-coated heat exchangers are one of the common solutions to these risks and to lower energy usage. In the present work, the capability of a solid composite desiccant blend prepared from coconut shell-based activated carbon and bio char was studied. Aluminum plates have been coated with the prepared solid desiccants. Desiccant-coated heat exchangers were cooled by the cerium oxide nanofluid passing through the pipes connected along the length of the heat exchanger. Air was blown through the plates where dehumidification occurs due to the vapor pressure difference between the air and the desiccant-coated plate. The experiments were conducted by varying the air velocity, water flow rate, and nanoparticle concentration. The nanoparticle volume fraction varied from 0.05% to 0.3%. Different performance parameters such as the moisture removal rate, dehumidification efficiency, cooling capacity, and coefficient of performance (COP) were calculated. Results showed that the performance parameters were enhanced with an increase in the water flow rate as well as the air flow rate. Furthermore, it was seen that with the addition and increase in nanoparticle concentration, the moisture removal rate and dehumidification efficiency were enhanced. In comparison to no addition of nanoparticles, a 0.3% addition of nanoparticles demonstrated a maximum increase in MRR of 53% and dehumidification efficiency of 57%. A maximum reduction of 6.1% in the dehumidification area was achieved by using 0.3% nanoparticles with water. It is recommended to use nanofluids for dehumidification using solid desiccants, which can enhance the performance without having negative influence on the environment.

Thermal environment in buildings in hot climate is conditioned for comfort by air-conditioning that is energy intensive. Presently, most air-conditioning systems in Thailand and other countries in Southeast Asia use electricity-driven vapor compression systems to cool down the air to the set-point temperature. However, latent load due to condensation of air humidity forms a large part of the air-conditioning load. This paper presents the results of experiments on a dehumidifier constructed from a water-to-air heat exchanger coated with a composite desiccant of large-pore mesoporous silica gel and LiCl, regenerated by low-temperature hot water. Moisture removal capacity (MRC), dehumidification capacity (DC), thermal coefficient of performance (COPth), and an equivalent air conditioning load of dehumidification (EALD) are comparative quantitative parameters derived from experimental results and are studied in this research. The composite desiccant requires low-temperature water for regeneration and offers a higher rate of vapor adsorption and desorption that leads to a shorter required desiccant dehumidification cycle time. The results demonstrate that the dehumidifier is able to effectively reduce moisture in ventilation air and substantially reduces the cooling load of air-conditioning.

In this paper, the air dehumidification performance of MIL-101(Cr) and MIL-101(Cr)-SO3H used for solid desiccant air conditioning (SDAC) system is experimental investigated, and compared with conventional desiccant materials including silica gel, molecular sieve and activated carbon. The results show that the moisture saturated adsorption capacity of MIL-101(Cr) is 1206–1392 mg/g at 25.0–33.5 °C/95%RH which is 4–6 times of the conventional adsorbents. MIL-101(Cr) presented an S-shaped isotherm with steep point between 30% and 50%RH which provide the possibility for low temperature regeneration. The water vapor desorption measurement results show that MIL-101(Cr) could have 96.3% (93.5%) desorption rate at 45 °C/15.95%RH (45 °C/30.60%RH) after saturated adsorption at 33.5 °C/58.0%RH. The modified material MIL-101(Cr)-SO3H didn’t show better moisture adsorption and desorption performance than MIL-101(Cr) at moderate relative humidity range but higher moisture adsorption capacity at low relative humidity cases. Its saturated adsorption capacity for moisture is 2–3 times of traditional adsorbents. MIL-101(Cr) has shown excellent moisture adsorption capacity and low-temperature regeneration property which makes it be a potential option for SDAC system optimization.

Experimental investigation on suppression effect of molecular sieve powders on asphalt fume

Regeneration of composite desiccant dehumidifier by parabolic trough solar collector: An experimental investigation

All-solid-state lithium metal batteries (LMBs) are currently one of the best candidates for realizing the yearning high-energy-density batteries with high safety. However, even polyethylene oxide (PEO), the most popular polymeric solid-state electrolyte (SSE) with the largest ionic conductivity in the category so far, has significant challenges due to the safety issues of lithium dendrites, and the insufficient ionic conductivity. Herein, molecular sieve (MS) is integrated into the PEO as an inert filler with the liquid metal (LM) as a functional module, forming an "LM-MS-PEO" composite as both SSE with enhanced ionic conductivity, and protection layer against lithium dendrites. As demonstrated by theoretical and experimental investigations, LM released from MS can be uniformly and efficiently distributed in PEO, which could avoid agglomeration, enable the effective blocking of lithium dendrites, and regulate the mass transport of Li ions, thus achieving even deposition of lithium during charge/discharge. Moreover, MS could reduce the crystallinity of PEO, improve lithium-ion conductivity, and reduce operating temperature. Benefiting from the introduction of the functional MS/LM, the LM-MS-PEO electrolyte exhibits fourfold higher lithium ionic conductivity than the pristine PEO at 40°C, while the as-assembled all-solid-state LMBs have four to five times longer stable cycle life.

In this article, various desiccants such as silica gel, molecular sieve 13X, and activated alumina have been regenerated using a novel heated surface plate. No experiment for the regeneration of desiccant has been done with the use of a hot surface plate heated by the heat pipe vacuum tube collector. A novel apparatus SHPPCP (solar heat pipe powered copper plate) based on heat pipe vacuum or evacuated tube collector (ETC) has been made. SHPPCP contains a surface plate, which is an open box of copper and this open box is attached to heat pipes. The Heat pipe is made of copper and used to extract heat from ETC. Desiccants regenerate by taking heat from the surface plate. The average temperature range for regeneration was 65–105°C during the experiment. The different parameters like humidity ratio, surface plate temperature, regeneration rate, solar intensity, and so on, have been discussed to get the performance of a desiccant. Silica gel among other desiccants has shown better adsorption rate and regeneration rate. The maximum regeneration rates of silica gel, activated alumina, and molecular sieve are 0.0936 kg/h, 0.072638 kg/hr, and 0.051348 kg/hr, respectively, and the minimum regeneration rates of silica gel, activated alumina, and molecular sieve are 0.0936 kg/h, 0.072638 kg/hr, and 0.051348 kg/hr, respectively.

Experimental investigation on cryogenic hydrogen adsorption of molecular sieves

Experimental performance and energy efficiency investigation of composite superabsorbent polymer and potassium formate coated heat exchangers

Experimental Investigation and Modeling of Adsorption of Carbon Dioxide on 5A Molecular Sieve for Helium Purification of High-temperature Gas-cooled Reactor

Experimental investigation on hydrogen adsorption performance of composite adsorbent in the tank with high vacuum multilayer insulation

Desiccant cooling system is a suitable alternative option for conventional cooling system in humid climates. It is an environmental protection technique for cooling buildings. This study has investigated the effect of supply/regeneration section area ratio on the performance of desiccant wheels in hot and humid climates, using Silica Gel (WSG) and Molecular Sieve (LT3) desiccants. To this end, some parameters such as outlet air humidity ratio, process removed moisture, process outlet temperature, reactivation outlet temperature and reactivation outlet moisture have been examined as a function of rotational speed and inlet air humidity ratio in 1:3, 1:2 and 1:1 split. In this study, desiccant materials are regenerated using a constant regeneration temperature of 80 °C, wheel rotation speed range of 4–12 RPH (revolutions per hour) and variable humidity. The results show that a rise in area ratio causes an increase in process removed moisture, process outlet temperature, reactivation outlet temperature and a drop in reactivation outlet moisture and outlet humidity ratio of process air.