Reducing the energy consumption of domestic refrigeration appliances has been a key research focus over the past decade. This study presents an innovative approach that integrates phase change materials (PCMs) in household refrigerators to enhance energy efficiency while optimizing storage space utilization. Unlike prior studies, this study comprehensively analyzes the combined effects of PCM placement, five types of PCM, and distribution, filling a critical gap in the literature. A combined vertical and horizontal PCM configuration was implemented, and its impact on the temperature distribution inside the compartments was analyzed using computational fluid dynamics (CFD) simulations in ANSYS FLUENT. This study evaluated multiple PCM materials, including water, eutectic solutions and commercial PCMs such as Caproic Acid, E3, and Puretemp-2, to identify the most effective materials for thermal stability. This study further explored the impact of various PCMs, revealing diverse cooling patterns and identifying Caproic Acid and E3 as superior choices for stabilizing temperatures within compartments. E3 displayed a slightly better result than Caproic Acid. Conversely, water as a PCM performed poorly. A constant PCM volume was considered for each case, taking only 6.6% of the compartment’s volume. Notably, the results demonstrate a maximum temperature reduction of 8.1% in the top compartment and 5.1% in the bottom compartment during compressor off-cycles, resulting in a 42% reduction in refrigeration load. These findings highlight the potential of PCM integration as a viable approach for enhancing refrigerator energy efficiency while maintaining optimal cooling performance.

A typical commercial two-bed adsorption chiller using silica gel as adsorbent and water as adsorbate is simulated in the current study. Each of the two beds goes through four processes in one cycle, namely, adsorption, mass recovery, heat recovery, and desorption. A transient lumped analytical model is developed, and the governing equations are solved using the MATLAB® platform. The thermophysical properties of the refrigerant are collected from REFPROP®, which is integrated within the MATLAB® codes. The simulation model is validated with the test results of a commercial chiller manufactured by Bry-Air (Asia) Pvt. Ltd. The cooling capacity of the chiller is 40 ton of refrigeration, and in this study, the simulation results are in good agreement with the test results provided by the manufacturer. The simulation model is then utilized in the present investigation to predict the performance of a typical commercial chiller under various working conditions. The recovery times, the temperatures of hot water, cooling water, and chilled water are varied, and their impacts on the cooling capacity and COP of the chiller are analyzed. The optimum recovery durations are reported for different temperatures, and their effects on the bed uptakes are investigated. The model can be used as an effective means to determine the optimal cycle time with necessary recovery durations for a specific cooling load, with a view to providing the maximum efficiency under specified operating conditions.

The dynamic uptake of adsorbate onto the porous adsorbent plays a crucial role in determining the performance of the adsorption-based cooling system. Therefore, it is imperative to know the kinetics parameters of an adsorbate - adsorbent pair to design a system to be operated at variable working conditions. The kinetics models of adsorption, used to simulate the adsorption rate of different pairs, are derived and presented in this paper. Besides, the limitations and advantages of the models are also mentioned. Moreover, the dynamic performance of different adsorption pairs is analyzed, and the values of kinetics parameters, determined through experimental procedures and fitting of kinetics models, are also summarized. It is opined that during the initial unsaturated condition of adsorption, the semi-infinite model can be preferred to determine the diffusion time constant. The modification of different models, e.g., Langmuir and linear driving force models, can significantly overcome the drawbacks of the models, as shown by several researchers. However, research may be carried out to investigate different models' fitting errors from a statistical perspective. Furthermore, to evaluate the dynamic performance of different adsorbates, a lot of research needs to be done, specifically, on the adsorption of the newly developed environment-friendly refrigerants, onto the promising composite adsorbents possessing high thermal conductivity and significantly improved adsorption uptakes.

Computational fluid dynamics (CFD) is one of the promising methods that can precisely predict non-uniform air flow and contaminant distribution in indoor environments. The overarching objective of this study was to develop a mathematical model for describing the photocatalytic oxidation (PCO) reaction mechanism of gas phase toluene with titanium dioxide (TiO 2 )-bound indoor building materials. This mathematical model was developed based on Langmuir-Hinshelwood type kinetics and for the integration with CFD simulations as a wall surface boundary condition. The effects of gas phase toluene concentration, illuminance and humidity on the toluene oxidation reaction were considered with locally TiO 2 -doped building materials. Especially, humidity dependence was explicitly integrated as a competitive adsorption model between toluene and water vapour. Moreover, surface compositions of TiO 2 and the substrate (ceramic tile in this study), and the physical adsorption properties of those materials, were modelled and integrated into the mathematical model. A 0.02 m 3 chamber experiment and adsorption isotherm measurements were conducted to identify the model parameters. CFD analysis was carried out according to experimental scenarios, and an optimization procedure for the model parameters was proposed for their application as the boundary conditions in the CFD analysis.

This study experimentally investigated the effect of adsorbent height on adsorption dynamics for carbon dioxide gas (CO2) adsorption onto commercially available highly porous activated carbon powder, named as Maxsorb III. The experiments were conducted using a magnetic suspension adsorption measurement unit. Three different heights of the Maxsorb III adsorbent were used in the experiments. Experimental data were reported for adsorption temperatures of 30 degrees C and 70 degrees C and for 2 different pressure steps. It had been observed that the adsorption rate strongly depended on the height of the adsorbent. This signifies that the kinetic parameters obtained by the similar experimental measurements may not be directly applicable in designing an adsorption heat exchanger. The lower height of the adsorbent provided faster adsorption kinetics. Key performance parameter, such as the specific cooling capacity for an adsorption refrigeration system was also calculated from the experimental data. The results of the present study suggested that the adsorbent height needs to be considered while using kinetics parameters in designing adsorption heat exchanger.

Adsorption heat transformation (AHT) systems can play a major role in protecting our environment by decreasing the usage of fossil fuels and utilizing natural and alternative working fluids. The adsorption isotherm is the most important feature in characterizing an AHT system. There are eight types of International Union of Pure and Applied Chemistry (IUPAC) classified adsorption isotherms for different “adsorbent-adsorbate” pairs with numerous empirical or semi-empirical mathematical models to fit them. Researchers face difficulties in choosing the best isotherm model to describe their experimental findings as there are several models for a single type of adsorption isotherm. This study presents the optimal models for all eight types of isotherms employing several useful statistical approaches such as average error; confidence interval (CI), information criterion (ICs), and proportion tests using bootstrap sampling. Isotherm data of 13 working pairs (which include all eight types of IUPAC isotherms) for AHT applications are extracted from literature and fitted with appropriate models using two error functions. It was found that modified Brunauer–Emmet–Teller (BET) for Type-I(a) and Type-II; Tóth for Type-I(b); GAB for Type-III; Ng et al. model for Type-IV(a) and Type-IV(b); Sun and Chakraborty model for Type-V; and Yahia et al. model for Type-VI are the most appropriate as they ensure less information loss compared to other models. Moreover; the findings are affirmed using selection probability; overall; and pairwise proportion tests. The present findings are important in the rigorous analysis of isotherm data.

In this study, new composite adsorbent with enhanced thermal conductivity and adsorption capacity was synthesized and analyzed comprehensively for the development of compact CO2 based adsorption cooling system. The consolidated composite was prepared employing activated carbon, graphene nanoplatelets and hydroxyl cellulose as a parent adsorbent, thermal conductivity enhancer, and binder, respectively. The surface area and pore volume of the composite were found to be 1778 +/- 13 m(2)g(-1) and 1.014 cm(3)g(-1), respectively. In addition, the composite showed 233% higher thermal conductivity compared to the parent activated carbon. Adsorption characteristics of CO2 were measured at temperature ranging from 20 to 70 degrees C and pressures up to 5 MPa. Absolute uptake was evaluated from excess adsorption based on the following two methods: (i) the adsorbed phase volume is equal to the pore volume of the adsorbent; and (ii) the adsorbed phase volume is almost zero under low pressure and/or high temperature conditions. Furthermore, the averaging of above two methods was also taken for avoiding these two extreme assumptions. Obtained absolute adsorption uptake data were fitted with modified Dubinin-Astakhov and Toth models. Results indicated good approximation between data points and models. The average isosteric heats of adsorption estimated using modified D-A and T6th model were found to be 19.742 kJ mol(-1) and 19.023 kJ mol(-1), respectively. The obtained characteristics of composite adsorbent are prerequisites for designing compact CO2 based adsorption cooling systems. (C) 2019 Elsevier Ltd and IIR. All rights reserved.

Adsorption based cooling systems are gaining considerable attention since it can utilize low grade thermal energy, which otherwise could go as a waste. Heat sources possessing a temperature of as low as 60 degrees C can drive an adsorption chiller and that temperature requirement is even lower in the case of multi-stage adsorption cooling systems. A typical flat plate solar collector can provide hot water having a temperature of 65 degrees C inmost of the countries in the Asian region. The temperature of evacuated tube collectors' water outlet can reach above 95 degrees C. In order to make use of such collectors, in conjunction with other auxiliary heat sources, for providing heat to power an adsorption chiller, it is imperative to have a proper mathematical model. This can aid in designing the network and predicting the performance of the whole system, prior to installation. This chapter focuses on the modelling of a system that incorporates flat plate collectors, evacuated tube collectors and a thermally powered adsorption chiller. Here, mathematical equations to calculate the efficiency of flat plate and evacuated tube collectors are presented; processes that are involved in a typical two bed adsorption cooling system are explained in brief, and a mathematical model of an adsorption chiller, that employs mass and heat recovery schemes is developed. Finally, the simulation results of the model are presented, and the performance of the chiller is investigated to demonstrate a clear understanding of its operation.

Adsorption heat exchanger comprises of the adsorbent granules/particles packed in between heat exchanging surfaces. The refrigerant vapor flow as well as heat transfer occurs through the adsorbent column. A 2-dimensional transient CFD study is employed to simulate the adsorption dynamics of ethanol vapor on loosely packed activated carbon. The adsorbent chosen for this study is activated carbon and the refrigerant is ethanol. In this paper, the efficacy of the refrigerant vapor transport through the porous adsorbent bed is studied in terms of flow resistance and thermal diffusion along with the mass diffusion through adsorbent particles. Three heat exchanging domains with same area but different aspect ratios (fin height to fin pitch ratio) along with two particle sizes are evaluated. The dynamic uptake predicted by this CFD study shows strong dependency on flow resistance of porous media for smaller particle size whereas a weak dependency on thermal and intra-particle mass diffusion is observed for larger particles. Furthermore, a comparison on the adsorption dynamics predicted by the present CFD study and the lumped kinetics model is carried out to determine the validity of the lumped model with respect to the adsorber geometry and particle size. (C) 2018 Elsevier Ltd. All rights reserved.

An adsorption chiller requires thermal energy to regenerate the adsorbent by desorbing the refrigerant vapor. Minimum desorption temperature is the parameter which defines the lowest possible heat source temperature required for driving adsorption chiller. In this study minimum desorption temperature is evaluated for different types of adsorption isotherms classified by International Union of Pure and Applied Chemistry (IUPAC). For each type, adsorption isotherm model is utilized to estimate the minimum desorption temperature and then compared to the mathematical expression reported in literature derived using Dubinin-Astakhov isotherm model. This allows for critical scrutiny of the universal validity of mathematical expression. It is observed that this expression can estimate the minimum desorption temperature with reasonable accuracy for all isotherm models. (C) 2018 Elsevier Ltd. All rights reserved.

Singapore is located at the equator, with abundant supply of solar radiation, relatively high ambient temperature and relative humidity throughout the year.The meteorological conditions of Singapore are favourable for efficient operation of solar energy based systems.Solar assisted heat pump systems are built on the roof-top of National University of Singapore's Faculty of Engineering.The objectives of this study include the design and performance evaluation of a solar assisted heat-pump system for water desalination, water heating and drying of clothes.Using MATLAB programming language, a 2-dimensional simulation model has been developed to conduct parametric studies on the system.The system shows good prospect to be implemented in both industrial and residential applications and would give new opportunities in replacing conventional energy sources with green renewable energy.