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The scarcity of clean water and the lack of sustainable cooling systems are continuously pressing. Although many technologies are well-established, such as vapour compression for refrigeration and reverse osmosis for desalination, they are energy-intensive and conventional refrigeration technology utilising working fluids of long-lasting ozone-depleting and greenhouse effects. Alternatively, adsorption and absorption technologies can meet such demands, and they are the most feasible to utilise the waste and renewable heat abundant in many locations. Therefore, this paper computationally studies the emerging integrated adsorption-absorption system for cooling cum desalination employing transient waste heat sources of various waveform characteristics. A previously validated computational model for the adsorption subsystem was coupled with a thermodynamic model for the absorption subsystem and experimental heat profiles obtained from an internal combustion engine. The energy and exergy analysis of the integrated system utilising the actual heat source from an internal combustion engine and predefined waveforms were undertaken and benchmarked against that operated under steady heat sources. The integrated system operated with a relatively low exergy efficiency in the absorption cycle of up to 15.33%. The adsorption bottoming cycle successfully utilised the heat from the absorption subsystem at a relatively higher exergy efficiency of up to 42.69%. The execution of a transient heat source of sinusoidal waveform enhanced the water production by up to 30% and the cooling of absorption and adsorption subsystems by 24% and 15%, respectively. However, admitting realistic waveforms of an internal combustion engine showed marginal differences compared to the steady heat sources owing to their high frequencies and small amplitudes.

This paper studies the technical, economic, and environmental feasibility of a standalone adsorption cooling system thermally driven by biomass combustion and solar thermal energy. The developed cooling package was benchmarked against a baseline vapour compression refrigeration system, driven by grid electricity and the widely investigated adsorption cooling system driven by solar heat. TRNSYS was utilised to imitate the integrated systems, investigate their performance throughout the year, and optimise their designs by employing the meteorological data for Rwanda and an existing cold room (13 m2 floor area × 2.9 m height) as a case study. The optimisation study for the system revealed that maximum chiller performance (COP = 0.62), minimum biomass daily consumption (36 kg), and desired cold room setting temperature (10 °C) throughout the year can be achieved if the boiler setting temperature, heat storage size, and heating water flow rate are 95.13 °C, 0.01 m3 and 601.25 Kg/h. An optimal PV area/battery size combination of 12 modules / 16 kWh was observed from the economic, environmental, and technical viewpoints.

This work presents a mathematical modelling of a proton-exchange membrane fuel cell (PEMFC) system integrated with a resistive variable load. The model was implemented using MATLAB Simulink software, and it was used to calculate the fuel cell electric current and voltage at various steady-state conditions. The electric current was determined by the intersection of its polarisation curve and applied as an input value for the simulation of the PEM fuel cell performance. The model was validated using a Horizon H-500xp model fuel cell stack system, with the following main components: a 500 W PEM fuel cell, a 12 V at 12 A battery for the start-up, a super-capacitor bank to supply peak loads and a 48 V DC-DC boost converter. The generated power was dissipated by a variable resistive load. The results from the model shows a qualitative agreement with test bench results, with similar trends for stack current and voltage in response to load and hydrogen flow rate variation. The discrepancies ranged from 2% to 6%, depending on the load resistance applied. A controlled current source was utilised to simulate the variation of fan power consumption with stack temperature, ranging from 36.5 W at 23°C to 52 W at 65°C. Both model and experiments showed an overall PEMFC system maximum efficiency of about 48%.

Despite that the Proton Exchange Membrane Fuel Cell (PEMFC) is considered to be an efficient power device; around half of the energy produced from the electrochemical reaction is dissipated as heat due to irreversibility of the cathodic reaction, Ohmic resistance, and mass transport overpotentials. Effective heat removal from the PEMFC, via cooling, is very important to maintain the cell/stack at a uniform operating temperature ensuring the durability of the device as excessive operating temperature may dry out the membrane and reduces the surface area of the catalyst hence lowering the performance of the cell. In addition to cooling, capturing the produced heat and repurposing it using one of the Waste Heat Recovery (WHR) technologies is an effective approach to add a great economic value to the PEMFC power system. Global warming, climate change, and the high cost of energy production are the main drivers to improve the energy efficiency of PEMFC using WHR. This paper presents an overview of the recent progress concerning the cooling strategies and WHR opportunities for PEMFC. The main cooling techniques of PEMFCs are described and evaluated with respect to their advantages and disadvantages. Additionally, the potential pathways for PEMFC-WHR including heating, cooling, and power generation are explored and assessed. Furthermore, the main challenges and the research prospects for the cooling strategies and WHR of PEMFCs are discussed.

In this present study, microwave pre-treatment has been used for sustainable biofuel production from three different biowastes through catalytic aided co-pyrolysis techniques. The experimental investigations have been carried out to develop biofuel at temperature (350-550℃), heating rate (15-50℃/min) and particle size (0.12-0.38mm). The resultant biofuels were characterized using TGA, DTA, FE-SEM, FTIR spectroscopy and NMR spectrum. The pyrolysis process of biomasses without and with catalyst resulted in the yield rate of 29-37% and 39-51% respectively. Moreover, the CaO catalytic co-pyrolysis process of pomegranate peel, groundnut shell and palmcone wastes with a ratio of 50:50 at 0.25mm particle size has resulted in the highest yield rate of 51.6%. The NMR result of bio-oil samples produced hydroxyl group and aliphatics which clearly state the suitability of bio-oils for automotive application. The bio-oil had promising fuel characteristics consisting more energy density (29.1MJ/kg), less oxygen content and free of nitrogen.

This review critically evaluates the latest trends in fuel cell development for portable and stationary fuel cell applications and their integration into the automotive industry. Fast start-up, high efficiency, no toxic emissions into the atmosphere and good modularity are the key advantages of fuel cell applications. Despite the merits associated with fuel cells, the high cost of the technology remains a key factor impeding its widespread commercialization. Therefore, this review presents detailed information into the best operating conditions that yield maximum fuel cell performance. The paper recommends future research geared towards robust fuel cell geometry designs, as this determines the cell losses, and material characterization of the various cell components. When this is done properly, it will support a total reduction in the cost of the cell which in effect will reduce the total cost of the system. Despite the strides made by the fuel cell research community, there is a need for public sensitization as some people have reservations regarding the safety of the technology. This hurdle can be overcome if there is a well-documented risk assessment, which also needs to be considered in future research activities.

This work presents a mathematical modelling of a proton-exchange membrane (PEM) fuel cell system integrated with a resistive variable load. The model was implemented using MATLAB Simulink software based on an H-500xp pinch top PEM fuel cell type, and it is used to calculate the reference fuel cell current at various steady-state conditions. The reference current is the input value for the simulation of the PEM fuel cell performance. The model was validated using a Horizon H500xp model fuel cell stack system, with the following components: a 500 W PEM fuel cell, a 13.5 DC volt battery for the start-up, a super-capacitor bank to supply peak loads and a 48 V DC-DC boost converter. In addition, the generated power is dissipated by a variable resistive load. The results from the model shows a qualitative agreement with test bench results, with similar trends for stack current and voltage in response to load and hydrogen flow rate variation. The discrepancies ranged from 5% to 10%, depending on the load resistance applied. Both model and experiments showed a hydrogen conversion efficiency of 80%.

Cell disruption is an integral part of microalga production process, which improves the release of intracellular products that are essential for biofuel production. In this work, pre-treatment parameters that will enhance the efficiency of lipid production using high-pressure homogenizer on microalgae biomass will be investigated. The high-pressure homogenizer that is considered is a GYB40-10S/GY60-6S; with a pre-treatment pressure of 1000 psi, 2000 psi, and 3000 psi, the number of passes; 1, 2, and 3, a reaction time of 3, 3.5, and 4 h. Pressure and cavitation increase the efficiency of the pre-treatment process of the homogenizer. In addition, homogenization shear force and pressure are the basic significant factors that enhance the efficiency of microalgae cell rupture. Also, the use of modelling to simulate pre-treatment processes (Response Surface Methodology (RSM), Box-Behnken Designs (BBD), and design of experiment (DOE) for process optimization will be adopted in this study. The results clearly demonstrate that high-pressure homogenization pre-treatment can effectively disrupt microalga cell walls to enhance lipid recovery efficiency, with a relatively short extraction time, both that are essential for maintaining a good quality of lipids for biofuel production. A maximum of 18% lipid yields were obtained after 3 h of HPH pre-treatment at 3000 psi.

In the anaerobic digestion of lignocellulosic materials such as waste paper, the accessibility of microorganisms to the fermentable sugars is restricted by their complex structure. A mechanical pretreatment with a Hollander beater was assessed in order to reduce the biomass particle size and to increase the feedstock’ specific surface area available to the microorganisms, and therefore improve the biogas yield. Pretreatment of paper waste for 60 min improves the methane yield by 21%, from a value of 210 ml/gVS corresponding to untreated paper waste to 254 ml/gVS. 30 min pretreatment have no significant effect on the methane yield. A response surface methodology was used to evaluate the effect of the beating time and feedstock/inoculum ratio on the methane yield. An optimum methane yield of 253 ml/gVS was achieved at 55 min of beating pretreatment and a F/I ratio of 0.3.