Diffusion absorption refrigeration systems for thermally-driven cooling from low-temperature heat sources

Diffusion absorption refrigeration (DAR) is a small-scale cooling technology that can be driven purely by thermal energy without the need for electrical or mechanical inputs. In this work, a detailed experimental evaluation was undertaken of two newly-proposed DAR units, aimed at solar-driven cooling applications in warm climates, especially in arid and semi-arid regions. Firstly, a detailed experimental evaluation was undertaken of a DAR unit with a nominal cooling capacity of 100 W. Electrical heaters were used to provide the thermal input which was varied in the range 150-700 W, resulting in heat source temperatures of 175-215 C at the generator. Tests were performed with the DAR system configured with the default manufacturer's settings (22 bar charge pressure and 30 % ammonia concentration). The measured cooling output (to air) across the range of generator heat inputs was found to be in the range of 24-108 W, while the coefficient of performance (COP) was in the range of 0.11-0.26. The maximum COP was obtained at a generator heat input of 300 W. Results were compared to performance predictions from a steady-state thermodynamic model of the DAR cycle, showing a reasonable level of agreement at the nominal design point of the system, but considerable deviations at part-load/off-design conditions. Temperature measurements from the experimental apparatus were used to evaluate assumptions in the estimation of the model state point parameters and examine their influence on the predicted system performance. Temporal variations in the heat-input power and temperature strongly affect the performance of DAR chillers. In particular, the instantaneous cooling power delivered by a DAR unit powered by an intermittent heat source such as solar heat directly depends on the dynamics of start-up and shutdown processes. Therefore, the dynamic performance of an 80 W thermally-driven DAR system using ammonia-water (NH3-H2O) as a working fluid and charged with hydrogen (H2) as an auxiliary gas was investigated. The cooling temperature was set to 5 C. The (electrical) heat-supply power (200 W to 700 W), charge pressure (15 bar, 18 bar, and 21 bar at a 200 W heat input), and mixture concentration (25%, 30%, and 38% at a 200 W heat input) were varied and their effects on the system start-up time were investigated experimentally. The start-up time decreased with increasing heat-input power, and increased with increasing charge pressure, but in both cases, the system COP reduced by 30%. Furthermore, it was found that reducing the charge pressure and increasing the refrigerant concentration led to COP improvements. Further to this, a simple mathematical model was developed for the DAR performance when this receives a transient thermal input. Performance maps were generated according to the operating temperature of the system (5 C for refrigeration and 23 C for air-conditioning) at three charge-pressure levels (15 bar, 18 bar, and 21 bar) and three refrigerant concentration levels (25 %, 30 %, and 38 %) which can be used to select the desirable properties of a DAR system according to application. The best DAR performance for constant heat sources was achieved when the charge-pressure was set to 18 bar and the refrigerant concentration to 38 % (COP of 0.350 for HVAC and 0.22 for refrigeration purposes). For intermittent heat sources such as a solar input, a typical day with maximum solar irradiance of 650 W/m2 is selected as a case study and cooling demand of 452 Wh for air-conditioning purposes is considered between 11:45 to 16:15. The system uses evacuated tube collectors to heat up the generator. The adjustable parameters (21 bar of charge pressure and the refrigerant concentration of 38 %) are selected based on the availability of the solar energy. The system performance was best with a 3.7 m2 solar array, a COP of 0.25 at which point the system covers 420 Wh of the cooling demand. A comparison of a DAR system with a vapour-compression refrigeration (VCR) unit when both receive input energy from the sun. Whereas the DAR system has to store some part or all of the solar energy in the form of cold (ice) for the use overnight, some VCR scenarios store the PV electricity into a battery array. The analysis shows that the DAR system can compete with VCR systems in terms of the levelised cost of cooling, which is 0.32 $US and that is 0.16$US less than the VCR best scenario. However, the DAR systems need more space to be installed because of their significant solar array areas. Apart from occupied space, DAR systems are more profitable than VCR systems when both cooling systems are totally driven by solar energy.Open Acces

Growth inhibition and apoptosis induction of Scutellaria luteo-coerulea Bornm. & Sint. on leukemia cancer cell lines K562 and HL-60

Objective: Scutellaria (Lamiaceae) has been implicated for medicinal purposes both in modern and traditional medicine. Some species of the genus Scutellaria has extensively been studied for anticancer activity. Scutellaria luteo-coerulea (S. luteo-coerulea) is one of the Iranian species of the genus Scutellaria. Materials and Methods: In the present study, cytotoxic and apoptogenic properties of CH2Cl2, EtOAc, n-BuOH, and H2O fractions of S. luteo-coerulea were investigated on K562. Moreover, HL-60. DNA fragmentation in apoptotic cells were determined by propidium iodide (PI) staining (sub-G1 peak). Results: Scutellaria luteo-coerulea inhibited the growth of malignant cells in a dose-dependent manner. Among solvent fractions of S. luteo-coerulea, the CH2Cl2 fraction was found to be the most cytotoxic one among others. Sub-G1 peak in flow cytometry histogram of treated cells suggested the induction of apoptosis in S. luteo-coerulea. Conclusion: Scutellaria luteo-coerulea could be a novel candidate for further analytical elucidation in respect to fine major components responsible for the cytotoxic effect of the plant also clinical evaluations

Experimental investigation of an ammonia-water-hydrogen diffusion absorption refrigerator

Diffusion absorption refrigeration (DAR) is a small-scale cooling technology that can be driven purely by thermal energy without the need for electrical or mechanical inputs. In this work, a detailed experimental evaluation was undertaken of a newly-proposed DAR unit with a nominal cooling capacity of 100¿W, aimed at solar-driven cooling applications in warm climates. Electrical cartridge heaters were used to provide the thermal input which was varied in the range 150–700¿W, resulting in heat source temperatures of 175–215¿ measured at the generator. The cooling output during steady-state operation was determined from the power consumed by an electric heater used to maintain constant air temperature in an insulated box constructed around the evaporator. Tests were performed with the DAR system configured with the default manufacturer’s settings (22¿bar charge pressure and 30% ammonia concentration). The measured cooling output (to air) across the range of generator heat inputs was 24–108¿W, while the coefficient of performance (COP) range was 0.11–0.26. The maximum COP was obtained at a generator heat input of 300¿W. Results were compared to performance predictions from a steady-state thermodynamic model of the DAR cycle, showing a reasonable level of agreement at the nominal design point of the system, but noteworthy deviations at part-load/off-design conditions. Temperature measurements from the experimental apparatus were used to evaluate assumptions used in the estimation of the model state point parameters and examine their influence on the predicted system performancePeer Reviewe

Dynamic Modelling and Experimental Validation of a Pneumatic Radial Piston Motor

A pneumatic radial piston motor is studied in this paper in order to establish a dynamic modelling and simulation method. As a result of using geometric parameters, the piston cylinder volume change was calculated, and the heat transfer equation, thermodynamic energy balance equation, and motion equation were combined in order to create a complete model of the piston cylinder. With the aid of compressed air, several experimental tests were conducted, and the results of rotational speed with varying inlet pressure were fed into the simulation to determine one of the critical unknown parameters, such as the overall friction coefficient of the system. For the studied piston motor, this coefficient was 0.0625 Nm. Computer simulations can be used to adjust design parameters in order to reach a higher rotation speed by using an accurate model. As a result, better efficiency and performance present several opportunities that would not be possible when running experimental tests in a lab. The mathematical model yielded higher rotational speeds of 50 RPM on average, with an increased piston diameter of 1.775 mm; by increasing the diameter of the cylinder to 25.8 mm, it was possible to achieve faster rotational speeds. The performed precise simulation could be used for further motor design and optimisation, and performance estimates under a broader range of operational conditions. Simulations should be conducted on multiple sets of experimental test results to determine the correct overall value for each motor. In addition to guiding the design and optimisation of the motor, simulations could also predict its performance under a broader range of operating conditions by utilising effective parameters such as geometrical characteristics, flow conditions, and motion equations

Experimentally Validated Modelling of an Oscillating Diaphragm Compressor for Chemisorption Energy Technology Applications

This study presents a detailed dynamic modelling and generic simulation method of an oscillating diaphragm compressor for chemisorption energy technology applications. The geometric models of the compressor were developed step by step, including the diaphragm movement, compressor dimensions, chamber areas and volumes and so on. The detailed mathematical model representing the geometry and kinematics of the diaphragm compressor was combined with the motion equation, heat transfer equation and energy balance equation to complete the compressor modelling. This combination enables the novel compressor model to simultaneously handle the simulation of momentum and energy balance of the diagram compressor. Furthermore, an experimental apparatus was set up to investigate and validate the present modelling and the simulation method. The performance of the compressor was experimentally evaluated in terms of the mass flow rate of the compressor at various compression ratios. Additionally, the effects of different parameters such as the inlet temperature and ambient temperature at various compressor ratios on the compressor performance were investigated. It was found reducing the inlet temperature from 40 to 5 °C at a constant pressure results in the enhancement of the compressor flow rate up to 14.7%. The compressor model proposed and developed in this study is shown to be not only able to accurately deal with the complexity of the dynamic behaviour of the compressor working flow but is also capable of effectively representing diaphragm compressors for analysis and optimisation purposes in various applications