Experimental study of a counter-flow regenerative evaporative cooler

This paper aims to investigate the operational performance and impact factors of a counter-flow regenerative evaporative cooler (REC). This was undertaken through a dedicated experimental process. Temperature, humidity and flow rate of the air flows at the inlet, outlet and exhaust opening of the cooler were tested under various operational conditions, i.e., different inlet air conditions, feed water temperature and evaporation rate were also correspondingly measured. It was found that the wet-bulb effectiveness of the presented cooler ranged from 0.55 to 1.06 with Energy Efficiency Ratio (EER) rated from 2.8 to 15.5. The major experimental results were summarised below: 1) the wet-bulb effectiveness was significantly enhanced through either ways of increasing inlet wet-bulb depression or reducing intake air velocity, or alternatively by increasing working-to-intake air ratio; 2) the cooling capacity and EER of cooler was rapidly increased by means of increasing inlet wet-bulb depression or increasing intake air velocity, or reducing working-to-intake air ratio instead; 3) the effectiveness reduced by less 5% while feed water temperature increased from 18.9 to 23.1°C; 4) apparent acceleration in water evaporation rate was gained from increasing inlet wet-bulb depression or air velocity. The presented cooler showed 31% increase in wet-bulb effectiveness and 40% growth in EER compared to conventional indirect evaporative cooler. The research helped identifying the performance of a new REC with enhanced performance and thus contributed to development of energy efficient air conditioning technologies, which eventually lead to significant energy saving and carbon emissions reduction in air conditioning sector

Energy saving potential of a counter-flow regenerative evaporative cooler for various climates of China: Experiment-based evaluation

© 2017 Recently there has been growing interest in regenerative evaporative coolers (REC), which can reduce the temperature of the supply air to below the wet-bulb of intake air and approach its dew-point. In this paper, we designed, fabricated and experimentally tested a counter-flow REC in laboratory. The REC's core heat and mass exchanger was fabricated using stacked sheets composed of high wicking evaporation (wickability of available materials was measured) and waterproof aluminium materials. The developed REC system has a much higher cooling performance compared to conventional indirect evaporative cooler. However, the decision to use the REC for China buildings depends on a dedicated evaluation of the net energy saved against the capital expended. Such an evaluation requires the hourly-based data on the availability of cooling capacity provided by the REC for various climates. The paper used an experiment-based method to estimate the cooling capacity and energy savings provided by the proposed REC for China's various climates. By using the experimental results and regional hourly-based weather data, the energy saving potential of the REC against an equivalent-sized mechanical air conditioner alone was analysed. The results indicate that, for all selected regions, the REC could reduce 53–100% of cooling load and 13–58% of electrical energy consumption annually

Investigation of a novel dew point indirect evaporative air conditioning system for buildings

This study aims to improve the performance of existing indirect evaporative coolers. A new dew point indirect evaporative cooler with counter-current heat/mass exchanger was developed in this research by optimal design, material selection, numerical simulation, experimental investigations and economic, environmental, regional acceptance analysis. A new dew point heat/mass exchanger using a counter-current flow pattern was designed by numerical simulation in terms of material, structure, geometrical sizes and operating conditions. The numerical results indicate that under a typical cooling design condition, i.e., 35oC dry-bulb/24oC wet-bulb temperatures, the heat exchanger could achieve a wet-bulb effectiveness of approximately 1.4. The results of numerical simulation are consistent with some published test data. Based on the numeric results and the material selection determined from a set of related tests, a prototype dew point heat/mass exchanger and the associated air cooler was designed and constructed in laboratory. Testing was carried out to evaluate the performance of the experiment prototype. The results indicate that the wet-bulb effectiveness of the prototype ranged from 55% to 110% for all test conditions. The power consumption of the prototype ranged from 10 to 50 W with energy efficiency (or COP) rated from 3 to 12. It is also found that the water consumption of the prototype was very small which ranged from 0.2-1.3 litre/h. A comparison between the numerical and experimental results was carried out and the reasons for the discrepancy were analysed. This research also investigates the feasibility, economic and environmental potential of using a dew point cooler in buildings in Europe and China. From the related studies in this thesis, it is concluded that the dew point cooler can achieve a higher performance (in terms of effectiveness and energy efficiency) than the typical indirect evaporative coolers without adding too much cost. It is found that the effectiveness and energy efficiency of the heat/mass exchanger in the cooler are largely dependent upon channel geometries, the intake air velocity, temperature, humidity and the working-to-intake air ratio but less on the feed water temperature. To maximise effectiveness and energy efficiency, it is suggested that 1) the channel height and the length of exchanger should be set below 6 mm and 1-1.2 m respectively; 2) the intake channel air velocity should be controlled to 0.5-1 m/s; and 3) the working-to-intake air ratio should be adjusted to 0.4-0.5. It is also concluded that the dew point system is suitable for most regions with dry, mild and hot climate. It is, however, unsuitable for humid regions where the system is used as a stand-alone unit. Compared to the conventional mechanical compression cooling system, the dew point system has a significantly higher potential in saving energy bills and reducing carbon emission. A project to construct an 8 kW commercial dew point cooler is currently under development with the assistance of a Chinese company. By the optimisation of material, structure and geometries, the cooler is expected to achieve a cooling output of 8 kW at the inlet air of 38oC dry-bulb/ 21oC wet-bulb temperatures, with a wet-bulb effectiveness of 1.02 at 1530 m3/h of supply air flow and 1200 m3/h of discharge air flow, whereas the power input of the unit is about 450 W and the energy efficiency (or COP) at 18.5

Design, fabrication and performance evaluation of a compact regenerative evaporative cooler: towards low energy cooling for buildings

© 2017 Elsevier Ltd The urges of reducing energy use and carbon footprint in buildings have prompted the developments of regenerative evaporative coolers (RECs). However, the physical dimensions of RECs have to be designed enormous in order to deliver a large amount of supply airflow rate and cooling capacity. To tackle the issue, this paper develops a large-scale counter-flow REC with compact heat exchanger through dedicated numerical modelling, optimal design, fabrication and experimentation. Using modified ε-NTU method, a finite element model is established in Engineering Equation Solver environment to optimise the cooler's geometric and operating parameters. Based on modelling predictions, the cooler's experimental prototype was optimally designed and constructed to evaluate operating performance. The experiment results show that the cooler's attained wet-bulb effectiveness ranges from 0.96 to 1.07, the cooling capacity and energy efficiency ratio from 3.9 to 8.5 kW and 10.6 to 19.7 respectively. It can provide sub-wet bulb cooling while operating at high intake channel air velocities of 3.04–3.60 m/s. The superior performance of proposed cooler is disclosed by comparing with different RECs under similar operating conditions. Both the cooler's cooling capacity per unit of volume and per unit of airflow rate are found to be 62–108% and 21.6% higher respectively

Investigation of a novel dew point indirect evaporative air conditioning system for buildings

This study aims to improve the performance of existing indirect evaporative coolers. A new dew point indirect evaporative cooler with counter-current heat/mass exchanger was developed in this research by optimal design, material selection, numerical simulation, experimental investigations and economic, environmental, regional acceptance analysis. A new dew point heat/mass exchanger using a counter-current flow pattern was designed by numerical simulation in terms of material, structure, geometrical sizes and operating conditions. The numerical results indicate that under a typical cooling design condition, i.e., 35oC dry-bulb/24oC wet-bulb temperatures, the heat exchanger could achieve a wet-bulb effectiveness of approximately 1.4. The results of numerical simulation are consistent with some published test data. Based on the numeric results and the material selection determined from a set of related tests, a prototype dew point heat/mass exchanger and the associated air cooler was designed and constructed in laboratory. Testing was carried out to evaluate the performance of the experiment prototype. The results indicate that the wet-bulb effectiveness of the prototype ranged from 55% to 110% for all test conditions. The power consumption of the prototype ranged from 10 to 50 W with energy efficiency (or COP) rated from 3 to 12. It is also found that the water consumption of the prototype was very small which ranged from 0.2-1.3 litre/h. A comparison between the numerical and experimental results was carried out and the reasons for the discrepancy were analysed. This research also investigates the feasibility, economic and environmental potential of using a dew point cooler in buildings in Europe and China. From the related studies in this thesis, it is concluded that the dew point cooler can achieve a higher performance (in terms of effectiveness and energy efficiency) than the typical indirect evaporative coolers without adding too much cost. It is found that the effectiveness and energy efficiency of the heat/mass exchanger in the cooler are largely dependent upon channel geometries, the intake air velocity, temperature, humidity and the working-to-intake air ratio but less on the feed water temperature. To maximise effectiveness and energy efficiency, it is suggested that 1) the channel height and the length of exchanger should be set below 6 mm and 1-1.2 m respectively; 2) the intake channel air velocity should be controlled to 0.5-1 m/s; and 3) the working-to-intake air ratio should be adjusted to 0.4-0.5. It is also concluded that the dew point system is suitable for most regions with dry, mild and hot climate. It is, however, unsuitable for humid regions where the system is used as a stand-alone unit. Compared to the conventional mechanical compression cooling system, the dew point system has a significantly higher potential in saving energy bills and reducing carbon emission. A project to construct an 8 kW commercial dew point cooler is currently under development with the assistance of a Chinese company. By the optimisation of material, structure and geometries, the cooler is expected to achieve a cooling output of 8 kW at the inlet air of 38oC dry-bulb/ 21oC wet-bulb temperatures, with a wet-bulb effectiveness of 1.02 at 1530 m3/h of supply air flow and 1200 m3/h of discharge air flow, whereas the power input of the unit is about 450 W and the energy efficiency (or COP) at 18.5

Investigation of a novel dew point indirect evaporative air conditioning system for buildings

This study aims to improve the performance of existing indirect evaporative coolers. A new dew point indirect evaporative cooler with counter-current heat/mass exchanger was developed in this research by optimal design, material selection, numerical simulation, experimental investigations and economic, environmental, regional acceptance analysis. A new dew point heat/mass exchanger using a counter-current flow pattern was designed by numerical simulation in terms of material, structure, geometrical sizes and operating conditions. The numerical results indicate that under a typical cooling design condition, i.e., 35oC dry-bulb/24oC wet-bulb temperatures, the heat exchanger could achieve a wet-bulb effectiveness of approximately 1.4. The results of numerical simulation are consistent with some published test data. Based on the numeric results and the material selection determined from a set of related tests, a prototype dew point heat/mass exchanger and the associated air cooler was designed and constructed in laboratory. Testing was carried out to evaluate the performance of the experiment prototype. The results indicate that the wet-bulb effectiveness of the prototype ranged from 55% to 110% for all test conditions. The power consumption of the prototype ranged from 10 to 50 W with energy efficiency (or COP) rated from 3 to 12. It is also found that the water consumption of the prototype was very small which ranged from 0.2-1.3 litre/h. A comparison between the numerical and experimental results was carried out and the reasons for the discrepancy were analysed. This research also investigates the feasibility, economic and environmental potential of using a dew point cooler in buildings in Europe and China. From the related studies in this thesis, it is concluded that the dew point cooler can achieve a higher performance (in terms of effectiveness and energy efficiency) than the typical indirect evaporative coolers without adding too much cost. It is found that the effectiveness and energy efficiency of the heat/mass exchanger in the cooler are largely dependent upon channel geometries, the intake air velocity, temperature, humidity and the working-to-intake air ratio but less on the feed water temperature. To maximise effectiveness and energy efficiency, it is suggested that 1) the channel height and the length of exchanger should be set below 6 mm and 1-1.2 m respectively; 2) the intake channel air velocity should be controlled to 0.5-1 m/s; and 3) the working-to-intake air ratio should be adjusted to 0.4-0.5. It is also concluded that the dew point system is suitable for most regions with dry, mild and hot climate. It is, however, unsuitable for humid regions where the system is used as a stand-alone unit. Compared to the conventional mechanical compression cooling system, the dew point system has a significantly higher potential in saving energy bills and reducing carbon emission. A project to construct an 8 kW commercial dew point cooler is currently under development with the assistance of a Chinese company. By the optimisation of material, structure and geometries, the cooler is expected to achieve a cooling output of 8 kW at the inlet air of 38oC dry-bulb/ 21oC wet-bulb temperatures, with a wet-bulb effectiveness of 1.02 at 1530 m3/h of supply air flow and 1200 m3/h of discharge air flow, whereas the power input of the unit is about 450 W and the energy efficiency (or COP) at 18.5.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Comparative study on the sealing performance of packer rubber based on elastic and hyperelastic analyses using various constitutive models

Evaluation of the sealing performance of the packer rubber varies according to specific simulation models. This paper aims at revealing the difference between elastic and hyperelastic analyses using the finite element mothed (FEM). The study extracts the hyperelastic parameters of the neo-Hookean, the Mooney-Rivlin, and the Yeoh models from a uniaxial tensile test. Then, the setting process of a mechanical packer is simulated by elastic and hyperelastic calculations. We compare the deformed configuration and the contact stress given by these models. Our results show that the Yeoh model produces the minimum residual sum of squares (RSS) among the hyperelastic models for hydrogenated nitrile butadiene rubber (HNBR). The mooney-Rivlin model has a negative parameter, making the calculation unstable. The linear elastic model fails to simulate the setting process, while the neo-Hookean model overestimates the contact stress. Despite the similar stress distribution, the nonlinear elastic model provides a 17.8% higher contact stress on average than the Yeoh model. A parametric study based on the Yeoh model points out that the sub-thickness of the packer rubber needs an elaborate design. Reducing the sub-thickness could increase the contact stress but decrease the seal length in the force control mode. From an engineering perspective, this study demonstrates that it needs to pay more attention when selecting an appropriate material model and a sound analysis method to evaluate the sealing performance of an oil packer

Dynamic performance of a façade-based solar loop heat pipe water heating system

This paper reported a dedicated study of a novel façade-based solar loop heat pipe (LHP) water heating system using both theoretical and experimental methods. This system employs a modular panel incorporating a unique loop heat pipe that is able to serve as part of the building façade or a decoration layer of the façade, thus creating a façade integrated, low cost, highly efficient and aesthetically appealing solar water heating structure. Taking into account heat balances occurring in different parts of the system, e.g., solar absorber, heat pipes loop, heat exchanger and storage tank, a dedicated computer model was developed to investigate the dynamic performance of the system. An experimental rig was also established to evaluate the performance of such a prototype system through measurement of various operational parameters, e.g., solar radiation, temperatures and flow rates of the heat pipe fluid and water. Through comparison between the testing and modelling results, the model has been approved to be able to give a reasonable accuracy for predicting the performance of the LHP system. Two types of glass covers, i.e., double glazed/evacuated tubes and single-glazing plate, were applied to the prototype. It was found that for both covers, the heat pipe fluid temperature rose dramatically at the start-up operation and afterwards remained a slow but steady growth; while the water temperature remained a steadily growing trend throughout the operational day. The temperature rise of the circulated water at 1.6. l/min of flow rate was around 13.5 °C in the double-glazed/evacuated tubes based system and 10 °C in the single-glazing based system; correspondingly, their average solar conversion efficiencies were 48.8% and 36%, and the COPs were 14 and 10.5 respectively. In overall, the double-glazed/evacuated tubes based system presented a better performance than the single glazing based one. © 2012 Elsevier Ltd

Cement Integrity Loss due to Interfacial Debonding and Radial Cracking during CO2 Injection

Cement provides zonal isolation and mechanical support, and its integrity is critical to the safety and efficiency of the CO2 injection process for geologic carbon storage. This work focuses on interfacial debonding at wellbore interfaces and radial cracking in cement during CO2 injection. It adopts the definition of the energy release rate (ERR) to characterize the propagation of cracks. Based on the finite element method, the proposed model estimates the ERRs of both types of cracks with practical wellbore configurations and injection parameters. Further parametric studies reveal the effects of cement’s mechanical and thermal properties and the crack geometry on crack propagation. Simulation results show that the ERRs of interfacial and radial cracks would surpass 100 J/m2 with typical cement properties. The cement’s thermal expansion coefficient is the most influential factor on the ERR, followed by its Young’s modulus, Poisson’s ratio, and thermal conductivity. The initial sizes and positions of the cracks are also important parameters for controlling crack propagation. Moreover, non-uniform in situ stresses would accelerate crack propagation at the interfaces. These findings are valuable and could help to optimize cement sheath design in order to ensure the long-term integrity of wells for geological carbon storage