Regeneration Temperature Research Articles

Harvesting freshwater from atmospheric air using thermal energy storage enabled solar air heater

Fresh water resources are scarce worldwide, and prevailing water harvesting systems face limitations of nighttime operations, high regeneration temperature and limited water yield. To address such issues, a novel system that integrates thermal energy storage unit for harvesting fresh water from atmospheric air is built and experimentally investigated under the ambient conditions. The system includes 4.86 m2 both ends open evacuated tube collector solar air heater to produce high regeneration temperature. Additionally, it incorporates a standalone for water vapor condensation. The performance of the system is compared using two different solid desiccant materials based on energy, exergy, environmental and economic analyses. The system using silica gel harvests 3.75 L/day of fresh water at a cost of 0.13 $/L with water harvesting coefficient of 0.76, while from molecular sieve, 3.41 L/day was harvested at 0.15 $/L with water harvesting coefficient of 0.64. From silica gel, the system reported the maximum thermal, overall and exergy efficiencies of 62.22 %, 10.29 % and 2.31 %, respectively, while from molecular sieve it was 59.12 %, 9.53 % and 2.08 %, respectively. The reports of water sample confirm that the harvested water from both the desiccant materials is good and safe for domestic consumption.

Effect of gravity modulation on weakly nonlinear bio-thermal convection in a porous medium layer

Investigating thermal convection within porous media permeated by fluids and micro-organisms stands as a significant inquiry with broad relevance across geophysical and engineering domains. Studying convection within porous media can aid in controlling temperature and nutrient distribution for cell growth and tissue regeneration, as well as the efficiency of biofuel fermentation and production processes. Hence, the primary objective of this study is to investigate the influence of time-periodic gravitational forces on Darcy–Brinkman bio-thermal convection within a porous medium layer. This medium is saturated with a Newtonian fluid that encompasses gyrotactic micro-organisms. The gravity modulation amplitude is assumed to be very small. A weak nonlinear stability analysis is performed to analyze the stationary mode of bioconvection. The heat transport, measured by the Nusselt number, is governed by a non-autonomous Ginzburg–Landau equation. The research explores the influence of several parameters on heat transport, including the Vadaszs number, the modified bioconvective Rayleigh–Darcy number, cell eccentricity, modulation frequency, and modulation amplitude. The results are presented graphically, illustrating the impact of these parameters on heat transfer. The findings reveal that both the Vadaszs number and the modulation amplitude have a positive effect on heat transfer, enhancing the process. On the other hand, an increase in the modified bioconvection Rayleigh–Darcy number and cell eccentricity leads to a decrease in heat transfer. Furthermore, a comparison between the modulated and unmodulated systems indicates that the modulated systems have a more significant influence on the stability problem compared to the unmodulated systems. This highlights the effectiveness of external modulation in controlling heat transport within the system.

Effect of filter material and porosity on the energy storage capacity characteristics of diesel particulate filter thermoelectric conversion mobile energy storage system

The thermal energy generated by the diesel particulate filter (DPF) is converted into electrical energy through the thermoelectric generator (TEG) and stored in a mobile battery power energy storage (MBPE) system. The filter material and porosity directly affect the regeneration temperature of the DPF, which in turn affects the thermoelectric conversion capability of the thermoelectric module (TEM). This study explores the energy storage capacity characteristics for the DPF-TEG of the MBPES system at a regeneration temperature of 923 K. The filter materials considered are cordierite, mullite and SiC with porosities of 0.4, 0.45, 0.5, 0.55, 0.6, 0.65 and 0.7. The maximum output power and thermoelectric conversion efficiency are analyzed. The thermal input power for the SiC filter is approximately 2.4 times and 1.8 times than that of the cordierite filter and the mullite filter. As the porosity increases from 0.4 to 0.7, the output current for the DPF-TEG of the MBPES system with the 3 filter materials ranges from 0.66 A to 2.11 A. The output voltage changes from 50.62 V to 161.98 V. The maximum output power varies from 33.36 W to 341.59 W and the conversion efficiency rises from 0.88% to 2.72%.

Characterization of silica-PEG-CaCl2 composite sorbents in an open thermochemical heat storage reactor

Composite sorbents based on silica, polyethylene glycol (PEG) and containing calcium chloride were successfully synthetized using the sol-gel method. Their heat storage performance was investigated in a lab-scale open fixed-bed reactor. The silica/PEG matrix managed to stabilize hydrated calcium chloride when the salt content was equal to 32 wt% despite partial salt deliquescence. The presence of a crystallized phase CaCl2/PEG resulting from the complexation of the salt by the polymer may indeed prevent salt leakage, which was observed only when the salt content was increased to 42 wt%. Comparative experiments with a PEG-free control sample confirmed that the polymer enhances material stability. With a regeneration temperature of 130 °C, the best performing composite sorbent exhibited an average water sorption capacity of 0.37 gH2O g−1 of dehydrated material and an energy density of 782 kJ kg−1 over four successive sorption cycles at 30 °C and 42 % relative humidity. The dispersion and accessibility of the salt was enhanced after its first dissolution in the reactor. Compared to zeolite 13X, the sorption kinetics of the composite is much slower, resulting in a halved generated power. Still, the mass energy density of the composite is 70 % higher than that of zeolite, which makes it a promising material for heat storage applications with moderate required power outputs.

Servo and Regulatory Response of an Industrial Fluid Catalytic Cracking (FCC) Unit under Fuzzy Logic Supervisory Control

A self-tuning hierarchical controller in which a Fuzzy logic controller supervises the control actions of a conventional PID has been proposed, implemented and presented in this paper. The controller has been applied to a control study of Fluid Catalytic Cracking unit (FCCU) riser temperature, and regenerator temperature respectively. Comparison between the performance of the proposed Fuzzy-PID controller and the conventional PID was made in simulation studies of regulatory and servo performances of the two controller types. Six performance measures: Percent overshoot (OS), settling time (ST), integral absolute error (IAE), integral square error (ISE), integral time absolute error (ITAE) and integral time square error (ITSE) were employed as the tools for performance comparison between the conventional PID and the Fuzzy-PID controller. For the tracking of riser temperature with a set point at 524oC, the performance indicators under PID control gave the following results overshoot (14.5%); settling time (40 seconds) Integral absolute error (8.246), integral square error (3.3); integral time absolute error(1762);integral time square error (43.77) while for the same indicators under Fuzzy-PID control the following values: overshoot (3.3%); settling time (40 seconds) ;Integral absolute error (8.811); integral square error (14.5); integral time absolute error(280),;integral time square error (31.11) .The results allude to the superiority of the fuzzy-PID scheme over the PID scheme in tracking the optimal set point of riser temperature. More so, for tracking the regenerator set point temperature of 746oC, comparative study of step response under the two schemes gave the following results in six performance indicators: overshoot (PID (12.6%) / Fuzzy-PID (6%)); settling time (PID (80 seconds) / Fuzzy-PID (20seconds)); Integral absolute error (PID (14.29) / Fuzzy-PID (8.63)); integral square error (PID(6.713). Fuzzy-PID (4.506)); integral time absolute error(PID(2858)/Fuzzy-PID(305.9)), integral time square error (PID(77.55)/Fuzzy-PID(33.05)) . Moreover, the fuzzy-PID controller also showed superior performance over the conventional PID controller in terms disturbance rejection (regulatory response) of both riser and regenerator temperature. The results from this study suggest that the application of fuzzy-PID scheme to temperature control offers good promise of improved fluid catalytic cracking unit (FCCU) operations.

Numerical simulation of cascaded absorption-two-stage 4-bed adsorption cooling cycles for efficient low-grade heat utilization

Thermal-driven sorption cooling technology was developed to address some pressing challenges including high energy consumption, rising fuel prices, and environmental issues associated with traditional electrical-driven cycles. Nevertheless, this technology needs to be improved in terms of thermal performance and energy efficiency. This study investigates the performance of new cascade single-effect absorption (ABC) and two-stage four-bed adsorption (4ADC) cooling systems powered by low-grade heat source temperatures. Four different configurations are proposed to make proper use of low-temperature heat sources between 45 and 70 °C and improve heat recovery. The use of this temperature range to drive conventional ABC is still considerably lacking in the literature. The ABC does not typically operate below 60 °C. Additionally, the effects of operating conditions on performance are also investigated. The simulation models for both ABC and 4ADC systems are experimentally validated separately and showed excellent agreement. Results showed that the maximum cooling capacity obtained from the proposed system ranges between (5.4–17.1) kW with COP of 0.46–0.47. The COP is found to be relatively insensitive to regeneration temperatures. Increasing the solution pump flow rate increases the system performance by about 25% over the ranges of the regeneration temperature. The proposed configurations provide high energy performance compared with previous related studies. The obtained results proved that the proposed cascade configurations can recover the available low-grade heat source and operate effectively with temperatures between 45 and 70 °C.

Scalable Biomass-Derived Hydrogels for Sustainable Carbon Dioxide Capture.

Carbon capture and sequestration are promising emissions mitigation technologies to counteract ongoing climate change. The aqueous amine scrubbing process is industrially mature but suffers from low energy efficiency and inferior stability. Solid sorbent-based carbon capture systems present a potentially advantageous alternative. However, practical implementation remains challenging due to limited CO2 uptake at dilute concentrations and difficulty in regeneration. Here, we develop sustainable carbon-capture hydrogels (SCCH) with an excellent CO2 uptake of 3.6 mmol g-1 (400 ppm) at room temperature. The biomass gel network consists of konjac glucomannan and hydroxypropyl cellulose, facilitating hierarchically porous structures for active CO2 transport and capture. Precaptured moisture significantly enhances CO2 binding by forming water molecule-stabilized zwitterions to improve the amine utilization efficiency. The thermoresponsive SCCH exhibits a notable advantage of low regeneration temperature at 60 °C, enabling solar-powered regeneration and highlighting the potential for sustainable carbon capture to meet global decarbonization targets.

Performance and mechanism of the functional ionic liquid absorbent with the self-extraction property for CO2 capture

Regarding the bottleneck of high regeneration consumption for the amine absorbents, it was innovatively proposed in this work to construct a novel functional ionic liquid absorbent (3-Dibutylamino-propylamine-imidazole, [DBAPAH][Im]) with the self-extraction property for CO2 capture. The solvent changed from liquid-liquid two-phase to homogeneous as absorption loading increased, and it returned to a two-phase after desorption. The absorption loading of [DBAPAH][Im]-H2O solution for CO2 capture was 1.49 mol mol−1, and its regeneration efficiency was found to be 92.09% for the first regeneration and remained at 81.34% even after six cycles with a low regeneration temperature of 98 °C. It was found that this ionic liquid featured a reversible polarity, for which the polarity of [DBAPAH][Im] was much lower than that of water before absorption. The solvent changed from liquid-liquid phase to homogeneous as absorption loading increased because the polarity of the carbamate product and the Van der Waals interaction between carbamate and water were all increased. After desorption, the ionic liquid resumed with the low polarity and was not miscible in water to form an organic extraction phase, which promoted the rapid separation of the ionic liquid from the main solution and finally achieved the purpose of low temperature regeneration. Due to the coordination between cations and ions, the desorption free energy of the products formed by [DBAPAH][Im] and CO2 was very low (7.56 kJ mol−1). Furthermore, the energy consumption was estimated as 1.83 GJ t−1 CO2, which was much lower than that of benchmark monoethanolamine (MEA; 3.8 GJ t−1 CO2), and finally achieve the purpose of low regeneration temperature and low energy consumption regeneration.

Effect of operating parameters on the performance of rotary desiccant wheel energized by PV/T collectors

The main energy input of a desiccant air conditioning system is the low-quality thermal ener-gy required for regeneration, which can be obtained from waste heat, geothermal resources or solar energy. Regeneration thermal energy can be produced as well as energizing components such as fans, pumps, auxiliary air heaters, and control elements of the system by using pho-tovoltaic-thermal solar collectors (PV/T). In this study, parametric analyzes were performed to investigate the effect of regeneration temperature and air frontal velocity on the tempera-ture and dehumidification performance of a solid silica-gel desiccant wheel and on the wa-ter-cooled PV/T collectors used to provide the regeneration thermal energy. The regeneration temperature was varied between 50 and 70°C, and air frontal velocity between 1.3 and 4.1 m/s. The analyzes show that the dehumidification efficiency increases from 13.94% to 33.04% as regeneration temperature increased from 50°C to 70°C at 1.3 m/s air frontal velocity at which dehumidification efficiency is maximum. At 4.1 m/s air frontal velocity, the required regener-ation thermal energy is maximum and increases from 49.64 kW to 132.48 kW at the same re-generation temperature change. The low regeneration temperature resulted in desirable latent performance and undesirable sensible heat transfer performance in DEW. Finally, considering the whole system, it was concluded that the optimum regeneration air temperature for the performance parameters is 60°C.

High-performance Li4SiO4 sorbents prepared from solid waste for CO2 capture

Li4SiO4 shows great promise for cyclic high-temperature CO2 capture due to its excellent stability, high capacity, and low regeneration temperature. However, the practical application of Li4SiO4 is mainly limited by the high cost of raw materials, particularly lithium resources. Additionally, the heavy use of lithium-ion batteries (LIBs) in developing renewable energy sources raises concerns about the disposal of many waste LIBs. This article synthesized Li4SiO4 sorbent (BR-Li4SiO4) using spent lithium cobalt oxide (LiCoO2) cathodes and rice husk ash for CO2 capture. Meanwhile, we also prepared R-Li4SiO4/P-Li4SiO4 using commercial Li2CO3 and rice husk ash/commercial crystalline SiO2 as a comparison. The results show that the BR-Li4SiO4 sorbent exhibited excellent CO2 capture capacity and cycling stability at 675 °C, maintaining a stable capacity of 0.28 g/g under 100% CO2 after 30 cycles. BR-Li4SiO4 also demonstrated significantly reduced costs and a superior microstructure compared to R-Li4SiO4 and P-Li4SiO4. Furthermore, the impact of a simulated flue gas containing 15% CO2 and 10% H2O on Li4SiO4 adsorption was investigated. It was found that the adsorption of CO2 was decreased at low CO2 concentrations, but the addition of 10% H2O showed a slight enhancement in CO2 adsorption. Under a mixture of 15% CO2 + 10% H2O (balanced with N2), the maximum adsorption capacity of BR-Li4SiO4 was 0.17 g/g, and its optimal adsorption temperature decreased by 50 °C to 625 °C compared to 15% CO2. Therefore, this study will provide valuable insights into the industrial application of Li4SiO4 in CO2 adsorption.

Carbonic anhydrase textile structured packing for efficient CO2 absorption in methyldiethanolamine solvent

AbstractCarbonic anhydrase (CA) is an attractive biodegradable catalyst for CO2 absorption in solvent‐based CO2 capture. However, maintaining the stability of CA as a homogeneous component of the solvents is a challenge. Solvent regeneration temperature typically exceeds the enzyme thermal tolerance, which leads to CA deactivation. To reduce the need for frequent CA replenishment and to avoid inactive CA accumulation in the solvent, this work shows the benefits of an immobilization strategy where CA is fixed in a second‐generation design of textile structured packing (CATSP‐2) modules. The enzyme‐immobilized packing showed 1.5 times better performance in CO2 separation compared with traditional structured packing with a corresponding increased CO2 loading in the rich solvent. The modules exhibited good CA activity retention of ~80% during the tests without any CA replenishment. Applying CATSP‐2 could potentially decrease the packing height and absorber column size for a lower cost per amount of CO2 captured.

Acid-resistant zeolite RHO for deep dehydration

The identification of dehydration materials with hydrophilic properties that are also acid-resistant is highly significant. In this study, we evaluated the performance of zeolite NaCs-RHO (Si/Al = 3) for deep dehydration in comparison to conventional adsorbents zeolite LTA (Si/Al = 1). Water isotherms were measured over the pressure range of 1 × 10−5 to 0.025 bar and temperatures ranging from 30 to 200 °C. The obtained isotherms were described well by a triple-site Langmuir model. Despite exhibiting lower water capacities than LTA, RHO surprisingly maintains comparable working capacities for pressure swing adsorption (PSA), which may be attributed to the unique phase changes occurring during the hydration. Additionally, RHO allows for lower regeneration temperatures compared to LTA. Process simulation further demonstrated that zeolite RHO can meet stringent specifications for deep dehydration in natural gas to cryogenic processing standards, achieving a water content of 0.008 ppm with a regeneration temperature as low as 130 °C. In contrast, 4A failed to achieve the target, resulting in a high water content of 9.2 ppm under the same conditions. Remarkably, RHO displays superior stability in removing water from acidic gases, experiencing only a 5% water capacity loss after 1000 temperature cycles swung between 35 and 400 °C. In comparsion,3A and 4A showed much higher capacity losses of approximately 20 and 50%, respectively, under the identical conditions. 5A performed even worse, losing 30% of its water capacity within 400 cycles. These findings highlight that zeolite RHO is capable of deep dehydration for acidic gases, providing enhanced stability and reducing operating costs. This is particularly advantageous for rapid cycle operations that require numerous cycles.

Influence of the engine drop-to-idle process on regeneration temperature, filtration and morphology characteristics of diesel particulate filters

As emission regulations become more stringent, the durability of diesel aftertreatment system is a concern in addition to its purification capacity. Under extreme circumstances, the engine may drop-to-idle (DTI) sharply, which can cause the diesel particulate filter (DPF) cracking and melting during active regeneration due to the excessive soot combustion heat. This study investigated the regeneration performance of cordierite DPFs during the DTI process, including temperature and emission characteristics. The temperature distribution is nonuniform, with the peak temperature occurring in the middle ring of the DPF monolith’s rear end. As the soot load reached 7 g/L, extensive DPF cracks were observed and the particle number (PN) emission exceeded the regulatory limit. The study also examined the evolution of the DPF's porous wall’s macro morphology and micro pore structure, finding that microcracks formed and the wall surface became rougher. The substrate’s bulk density, average pore diameter, and permeability decreased while the total pore volume, total pore area, tortuosity, and porosity increased. By analyzing temperature, filtration and morphology characteristics, this work provides a recommended soot mass limit (SML) for cordierite DPF, which is essential for developing a reliable regeneration strategy in diesel vehicle control systems. The findings also help with the optimization design of substrate and catalysts for manufacturers in terms of substrate material, filter geometry, cell density and catalyst coating.

Performance Evaluation of Phenol-Resin-Based Adsorbents for Heat Transformation Applications.

Phenol resins (PRs) are considered as relatively inexpensive adsorbents synthesized from agricultural biomass via employing a variety of synthesized procedures. The performance of PR for heat transformation application is not widely investigated. In this regard, the present study aims to evaluate the four PR derivative/refrigerant pairs, namely (i) KOH6-PR/CO2, (ii) SAC-2/HFC, (iii) KOH4-PR/ethanol, and (iv) KOH6-PR/ethanol, for adsorption cooling and adsorption heating applications. Ideal cycle analyses and/or thermodynamic modelling approaches were utilized comprising governing heat and mass balance equations and adsorption equilibrium models. The performance of the AHP system is explored by means of specific cooling energy (SCE), specific heating energy (SHE), and coefficient of performance (COP), both for cooling and heating applications, respectively. It has been realized that KOH6-PR/ethanol could produce a maximum SCE of 1080 kJ/kg/cycle and SHE of 2141 kJ/kg/cycle at a regeneration temperature (Treg) and condenser temperature (Tcond) of 80 °C, and 10 °C, respectively, followed by KOH4-PR/ethanol, SAC-2/HFC-32, and KOH6-PR/CO2. The maximum COP values were estimated to be 1.78 for heating and 0.80 for cooling applications, respectively, at Treg = 80 °C and Tcond = 10 °C. In addition, the study reveals that, corresponding to increase/decrease in condenser/evaporator pressure, both SCE and SHE decrease/increase, respectively; however, this varies in magnitude due to adsorption equilibrium of the studied PR derivative/refrigerant pairs.

Cooling and Heating a Greenhouse in Baghdad by a Solar Assisted Desiccant System

Modeling the microclimate of a greenhouse located in Baghdad under its weather conditions to calculate the heating and cooling loads by computer simulation. Solar collectors with a V-corrugated absorber plate and an auxiliary heat source were used as a heating system. A rotary silica gel desiccant dehumidifier, a sensible heat exchanger, and an evaporative cooler were added to the collectors to form an open-cycle solar assisted desiccant cooling system. A dynamic model was adopted to predict the inside air and the soil surface temperatures of the greenhouse. These temperatures are used to predict the greenhouse heating and cooling loads through an energy balance method which takes into account the soil heat gain. This is not included in conventional methods. The results showed satisfactory agreement with published papers. Also, the results of heating and cooling loads obtained revealed good agreement with those obtained from conventional methods when the soil heat gain is included. Two identical collectors in series of total area of 5.4m2 were employed as a heating system which provides an outlet air temperature of 30 o C at air mass flux of 0.06 kg/s.m2 at midday in January. While, a 65 oC outlet air temperature was achieved for the same mass flux at midday in August. The desiccant cooling system was operated in five operating modes; the ventilation mode and four recirculation modes with 20%, 50%, 70%,and 90% recirculation. The simulation results showed that a regeneration temperature of 60-70 o C is satisfactory for a cool supply air temperature of about 19.5 o C. Also, it was noted that 20-30 % recirculation of return air would result in suitable indoor greenhouse conditions for most periods of system operation. In addition, the coefficient of performance COP of the system was high compared with the conventional vapor compression systems.

Desorption research and energy consumption assessment of a porous liquids impregnated by monoethanolamine (MEA)

Porous liquids (PLs), as new carbon capture materials, have great application potential in gas separation, gas storage, catalysis, etc. Herein, it was reported a new Type 3 porous liquids (T3PLs) based on the rational coupling of MEA-modified porous silica nano-spheres (PSNs) as porous hosts with 2-[2-(dimethylamine) ethoxy]ethanol (DMEE) as the fluid medium. A method was specifically developed to evaluate the regeneration energy of T3PLs. It was found energy consumption followed the order: the sensible energy > solvent evaporation > reaction heat energy for 50 % MEA-PSNs (10 %)/DMEE. Further study revealed that the optimum regeneration temperature of the absorbent was 80 °C and the corresponding regeneration energy was 4.04 GJ/ton CO2, which was much smaller than the regeneration energy of commercial absorbent 5 M MEA (9.54 GJ/ton CO2). The regeneration performance revealed the average absorption rate and the average desorption rate decreasing by only 9.3 % and 11.8 % after nine cycles. All the results indicated the T3PLs in the present work were energy-saving and had potential applications in CO2 capture.

Performance analysis of diesel particulate filter thermoelectric conversion mobile energy storage system under engine conditions of low-speed and light-load

The thermal heat from diesel particulate filter (DPF) can generate electrical energy through the thermoelectric generator (TEG) which can be stored in mobile battery power energy storage system (MBPES). The DPF-TEG of MBPES system is a new technology proposed in this study, which is made up of the DPF system, heat exchanger (HEX), the thermoelectric module (TEM) and the battery. The effects of low-speed and light-load operating conditions on the DPF-TEG of MBPES system were studied. The low regeneration temperatures (823 K, 873 K, 923 K) and the high regeneration temperatures (1606 K, 1696 K, 1786 K) were selected to explore the thermoelectric conversion performance of DPF-TEG of MBPES system. The maximum output power is increased 55% with the velocity change from 6 m/s to 8 m/s at low regeneration temperatures. The DPF-TEG of MBPES system contains the 48 TEMs with external load 19.2 Ω, which can generate the maximum power output of 4.99 w/6 w/7.12 w of 823 K/873 K/923 K, 32.09 w/36.76 w/41.75 w of 1606 K/1696 K/1786 K. The output voltage of the 4 TEMs increased from 0.015837 V to 0.016172 V per 10 K temperature difference. The output power grew from 0.017714 w to 0.08057 w.

Chemical kinetics of two-step thermochemical decomposition of hydrogen sulfide over nickel sulfide

The study develops a multistep reaction mechanism for a two-step thermochemical cycle that produces hydrogen from H2S decomposition, using nickel sulfide as a catalyst. Two mechanisms were investigated: 1) a gas-phase mechanism that occurs without a Ni catalyst to determine the contribution of thermal decomposition to the overall reaction without a catalyst, and 2) a microkinetic model of the catalytic Ni surface phase to examine the key parameters affecting the overall cycling process and H2S conversion efficiency. Both mechanisms were validated using CHEMKIN-Pro software to analyze the experimental data and trends. The study showed that gas-phase H2S conversion was not kinetically significant below 850 °C. The microkinetic model showed that most H2S was transformed into H2 and NiS products when the sulfurization temperature reached 500 °C. Additionally, the site fraction of NiS decreased while the number of free active nickel sites increased as the regeneration temperature increased from 500 °C to 800 °C. A temperature limit of 700 °C was set for the regeneration step due to the agglomeration behavior of nickel sulfide particles.

Theoretical Evaluation of Solar Assisted Desiccant Cooling System for a Small Meeting-Hall

The performance of a solar assisted desiccant cooling system for a meeting-hall located in the College of Engineering/University of Baghdad was evaluated theoretically. The system was composed of four components; a solar air heater, a desiccant dehumidifier, a heat exchanger and an evaporative cooler. A computer simulation was developed by using MATLAB to assess the effect of various design and operating conditions on the performance of the system and its components. The actual weather data on recommended days were used to assess the load variation and the system performance during those days. The radiant time series method (RTS) was used to evaluate the hourly variation of the cooling load. Four operation modes were employed for performance evaluation. A 100 % ventilation mode and 3 recirculation modes, 30 % , 60 % and 100 % recirculation of room air. The concept of variable air volume was employed as a control strategy over the day, by changing the supply airflow rate to match the variation in the cooling load.The results showed that the reduction in moisture content at regeneration temperatures from 55 o C to 75 o C lead to adequate removal of the high latent load in the meeting-hall. Also, the 30 % recirculation of return air resulted in comfortable indoor conditions satisfying the ventilation requirements for most periods of system operation. In addition, the COP of the system was high compared with the conventional vapor compression system. It varied from 1 to 13, when considering solar energy used to regenerate thedesiccant material as free energy.

Study on Preparation and Properties of PNIPAm/PPy Hydrogel Hygroscopic Material for Solid Dehumidification System

Air-conditioning systems account for 40–60% of the energy consumption of buildings, and most of this figure corresponds to the cooling and dehumidification process of air-conditioning units. Compared with traditional compressed air-conditioning systems, solid adsorption dehumidification systems possess good potential to improve indoor air quality and reduce buildings’ energy consumption. However, there are still some problems that prevent the use of solid adsorption dehumidification systems, such as their complexity and high regeneration temperatures. The key to solving the above problem is the discovery of more suitable adsorbents. In this paper, poly N-isopropylacrylamide/polypyrrole (PNIPAm/PPy) hydrogel was selected as the research object, and the performance of the dehumidification material and its potential for application in solid dehumidification systems were studied. It was found that the pore structure of PNIPAm/PPy was relatively complex and that there were abundant pores with uneven pore sizes. The minimum pore size was about 4 μm, while the maximum pore size was about 25 μm, and the pore sizes were mostly distributed between 8 and 20 μm. Abundant and dense pores ensure good hygroscopic and water-releasing properties of the resulting hydrogel. The PPy inside the hydrogel acts as both a hygroscopic and photothermal agent. In an environment with a relative humidity of 90%, 60%, and 50%, the hygroscopic efficiency of PNIPAm/PPy reached 80% in about 75, 100, and 120 min, and the corresponding unit equilibrium hygroscopic capacity values were 3.85 g/g, 3.72 g/g, and 3.71 g/g, respectively. In the initial stage, the moisture absorption increased with the increase in time; then, the increase in moisture absorption decreased. When the temperature was below 40 °C, the hygroscopic performance of PNIPAm/PPy was almost temperature-independent. The PNIPAm/PPy with different thicknesses showed similar moisture absorption efficiency. The lowest desorption temperature of PNIPAm/PPy was 40 °C, which indicates that low-grade energy can be used for material desorption. And the higher the temperature, the faster the desorption rate of PNIPAm/PPy and the higher the desorption amount. It can be seen that the PNIPAm/PPy hydrogel presents good desorption performance and can be used repeatedly.