Abstract Performance of natural draft dry cooling towers is significantly affected when the wind ... more Abstract Performance of natural draft dry cooling towers is significantly affected when the wind velocity is higher than a critical level according to their design and geometry. During this type of conditions, global electricity generation of power plants using especially dry type cooling towers is substantially reduced, up to as high as 40%. In order to decrease the reduction in electricity generation of power plants, it is possible to study on the dimensions of the cooling towers. Additionally, using different types of windbreakers can reduce the effects of unfavorable operating conditions. However, the direction of the wind changes with the seasons although the prevailing wind direction is nearly the same. In this study, internal flat and combination of internal flat–external rounded windbreakers have been analyzed by using the computational fluid dynamics approach. The combination of windbreakers, which is able to move axially around the cooling tower, has been propounded to arrange the flow characteristics during the windy days. The studies on the windbreakers in the literature have been aimed to decrease the negative effects of the wind; however, the design in this study provides also an increase in the air mass flowrate due to the momentum effect of the wind.
Abstract Computational fluid dynamic methods are applied to survey numerical approximations of pa... more Abstract Computational fluid dynamic methods are applied to survey numerical approximations of partial differential equations. In this area, there is a wide range of numerical methodologies, algorithms, schemes, simulation strategies as well as software programs for solution. In most experimental studies, these complicated numerical methods are used to simulate a problem without enough regard to the communication between the problem, advanced software and the nature of the solution methods. In this study, this scientific gap was considered to discuss most used numerical methodologies, their accuracy and the way numerical methods are used to solve engineering problems. In this research, governing equations and formula of numerical methods are introduced; then a 2-D sample object (cylindrical shape) is simulated in the incompressible flow as an example for simulation in CFD program (ANSYS Fluent 16).
Abstract Heat pumps and refrigerators are two systems with different usage, but same working prin... more Abstract Heat pumps and refrigerators are two systems with different usage, but same working principles. Generally, HPs work in steady state condition and specific thermodynamic cycle, but refrigerator or freezer apparatus have variable cycle and work in the unsteady condition. In this study, two different data sources are gathered to analyze thermodynamic differences between two mentioned systems. Initially, an existing heat pump unit is analyzed in different working conditions with different refrigerants and then the unit is converted to a refrigeration device to compare their thermodynamic conditions and treatments. Thermodynamic laws, COP value and efficiency, compressor power consumption, optimum charge amount, and flow rate of secondary fluid are main parameters which are considered to compare heat pump and refrigerator performances by using several refrigerants including R134a, R407c, R22, and R404a. In the case of freezer mode, entropy reduction in compressor and COPL drop to very low values are other substantial issues discussed in this research. It was also revealed that, optimal charge amount of the freezer is 15–25% lower than that of the system when works in HP mode. Experiments showed that, in some cases COP of the heat pump was even more than 100 times greater than that of the freezer.
In this study, an existing laboratory heat pump is converted to a refrigeration unit in order to ... more In this study, an existing laboratory heat pump is converted to a refrigeration unit in order to evaluate efficiency, power consumption, pressure and temperature variations and optimal charge amount of the system in new mode using refrigerant R-407C. Refrigerant charge amount has a key role in the terms of performance, operating cost (regarding to the charge reduction and energy consumption) and environmental concerns in all heat pump and refrigeration systems, which work on the same principles. Heat pump charge amount is the subject of many research, but less studies have been done in the case of refrigerators and freezers where the system works in the transient condition, on the contrary to the heat pump units. Although this study has been devoted to a detailed attempt to examine the possibility of converting the heat pump into the refrigerator, energy aspects of the whole system and the compressor have been analyzed under different working conditions. In the installed setup, the COP value of the system is tested with charge amount between 1 kg and 7 kg, but obtained results show that, this value is so lower than that of heat pump unit due to restricted energy source in cooling chamber.
Abstract The advanced thermal management in the internal combustion engines has a key role in the... more Abstract The advanced thermal management in the internal combustion engines has a key role in the overall performance, which directly effect on the total fuel consumption and engine exhaust emissions. Recently, a number of valuable studies have been carried out to evaluate and improve cooling system performance by using various technologies such as sliding vane rotary pump, ultimate cooling, double temperature circuits, integration, electrically-controlled valves and advanced algorithms for flexible control of the cooling system components, but, in this study an innovative strategy is presented to achieve this purpose. With a novel point of view, air-water mixture is employed to use in the cooling circuit. For this reason, at the point of coolant inlet to the engine, a constant pressure air injection mechanism was established, which can be adjusted at the desired flow rate by computer. The air injection strategy has two significant advantages. In the warm-up stage more air injection into the coolant fluid cause to a rapid heating of engine components by creating air layers around the cylinder. In the after warm-up state, however, air injection is decreased to a specified level for producing turbulence flow only in order to heat transfer enhancement and cooling purposes. Obtained results revealed that the periodic air injection by using special strategy can improve fuel economy and also decrease engine pollutant emissions.
This article investigates how hydrofluorocarbon (HFC) refrigerant affects compressor operating co... more This article investigates how hydrofluorocarbon (HFC) refrigerant affects compressor operating conditions and system performance using experimental testing under different conditions. In a heat pump or refrigerator cycle, it is necessary to move the fluid in the system to achieve heating or cooling. The compressor is the responsible component in fluid movement and so is a key factor in system power consumption. For this reason, it is essential to discover ways to increase compressor energy efficiency. R404a refrigerant was selected to evaluate the influence of refrigerant on compressor performance. Compressor inlet and discharge temperatures and pressures were measured experimentally. For the tested refrigerant, compressibility factor (Z) and deviation from ideal gas behavior were analyzed cautiously to compute power consumption, isentropic work, coefficient of performance, energy and exergy state, and compressor efficiency. Also analyzed were the influence of condenser water flow rate and the effect of evaporator inlet temperature. The study discussed here provided results that can be used to enhance the performance of compressors in heating/cooling systems.
• Effects of wind on the thermo-flow characteristics of cooling towers have been revealed. • Wind... more • Effects of wind on the thermo-flow characteristics of cooling towers have been revealed. • Windbreaker types have been studied to decrease the negative effects of wind. • Results show that it is possible to use the momentum effect of wind. • Movable windbreakers should be used to change the direction according to the wind. A B S T R A C T Performance of natural draft dry cooling towers is significantly affected when the wind velocity is higher than a critical level according to their design and geometry. During this type of conditions, global electricity generation of power plants using especially dry type cooling towers is substantially reduced, up to as high as 40%. In order to decrease the reduction in electricity generation of power plants, it is possible to study on the dimensions of the cooling towers. Additionally, using different types of windbreakers can reduce the effects of unfavorable operating conditions. However, the direction of the wind changes with the seasons although the prevailing wind direction is nearly the same. In this study, internal flat and combination of internal flat–external rounded windbreakers have been analyzed by using the computational fluid dynamics approach. The combination of windbreakers, which is able to move axially around the cooling tower, has been propounded to arrange the flow characteristics during the windy days. The studies on the windbreakers in the literature have been aimed to decrease the negative effects of the wind; however, the design in this study provides also an increase in the air mass flowrate due to the momentum effect of the wind.
Abstract Performance of natural draft dry cooling towers is significantly affected when the wind ... more Abstract Performance of natural draft dry cooling towers is significantly affected when the wind velocity is higher than a critical level according to their design and geometry. During this type of conditions, global electricity generation of power plants using especially dry type cooling towers is substantially reduced, up to as high as 40%. In order to decrease the reduction in electricity generation of power plants, it is possible to study on the dimensions of the cooling towers. Additionally, using different types of windbreakers can reduce the effects of unfavorable operating conditions. However, the direction of the wind changes with the seasons although the prevailing wind direction is nearly the same. In this study, internal flat and combination of internal flat–external rounded windbreakers have been analyzed by using the computational fluid dynamics approach. The combination of windbreakers, which is able to move axially around the cooling tower, has been propounded to arrange the flow characteristics during the windy days. The studies on the windbreakers in the literature have been aimed to decrease the negative effects of the wind; however, the design in this study provides also an increase in the air mass flowrate due to the momentum effect of the wind.
Abstract Computational fluid dynamic methods are applied to survey numerical approximations of pa... more Abstract Computational fluid dynamic methods are applied to survey numerical approximations of partial differential equations. In this area, there is a wide range of numerical methodologies, algorithms, schemes, simulation strategies as well as software programs for solution. In most experimental studies, these complicated numerical methods are used to simulate a problem without enough regard to the communication between the problem, advanced software and the nature of the solution methods. In this study, this scientific gap was considered to discuss most used numerical methodologies, their accuracy and the way numerical methods are used to solve engineering problems. In this research, governing equations and formula of numerical methods are introduced; then a 2-D sample object (cylindrical shape) is simulated in the incompressible flow as an example for simulation in CFD program (ANSYS Fluent 16).
Abstract Heat pumps and refrigerators are two systems with different usage, but same working prin... more Abstract Heat pumps and refrigerators are two systems with different usage, but same working principles. Generally, HPs work in steady state condition and specific thermodynamic cycle, but refrigerator or freezer apparatus have variable cycle and work in the unsteady condition. In this study, two different data sources are gathered to analyze thermodynamic differences between two mentioned systems. Initially, an existing heat pump unit is analyzed in different working conditions with different refrigerants and then the unit is converted to a refrigeration device to compare their thermodynamic conditions and treatments. Thermodynamic laws, COP value and efficiency, compressor power consumption, optimum charge amount, and flow rate of secondary fluid are main parameters which are considered to compare heat pump and refrigerator performances by using several refrigerants including R134a, R407c, R22, and R404a. In the case of freezer mode, entropy reduction in compressor and COPL drop to very low values are other substantial issues discussed in this research. It was also revealed that, optimal charge amount of the freezer is 15–25% lower than that of the system when works in HP mode. Experiments showed that, in some cases COP of the heat pump was even more than 100 times greater than that of the freezer.
In this study, an existing laboratory heat pump is converted to a refrigeration unit in order to ... more In this study, an existing laboratory heat pump is converted to a refrigeration unit in order to evaluate efficiency, power consumption, pressure and temperature variations and optimal charge amount of the system in new mode using refrigerant R-407C. Refrigerant charge amount has a key role in the terms of performance, operating cost (regarding to the charge reduction and energy consumption) and environmental concerns in all heat pump and refrigeration systems, which work on the same principles. Heat pump charge amount is the subject of many research, but less studies have been done in the case of refrigerators and freezers where the system works in the transient condition, on the contrary to the heat pump units. Although this study has been devoted to a detailed attempt to examine the possibility of converting the heat pump into the refrigerator, energy aspects of the whole system and the compressor have been analyzed under different working conditions. In the installed setup, the COP value of the system is tested with charge amount between 1 kg and 7 kg, but obtained results show that, this value is so lower than that of heat pump unit due to restricted energy source in cooling chamber.
Abstract The advanced thermal management in the internal combustion engines has a key role in the... more Abstract The advanced thermal management in the internal combustion engines has a key role in the overall performance, which directly effect on the total fuel consumption and engine exhaust emissions. Recently, a number of valuable studies have been carried out to evaluate and improve cooling system performance by using various technologies such as sliding vane rotary pump, ultimate cooling, double temperature circuits, integration, electrically-controlled valves and advanced algorithms for flexible control of the cooling system components, but, in this study an innovative strategy is presented to achieve this purpose. With a novel point of view, air-water mixture is employed to use in the cooling circuit. For this reason, at the point of coolant inlet to the engine, a constant pressure air injection mechanism was established, which can be adjusted at the desired flow rate by computer. The air injection strategy has two significant advantages. In the warm-up stage more air injection into the coolant fluid cause to a rapid heating of engine components by creating air layers around the cylinder. In the after warm-up state, however, air injection is decreased to a specified level for producing turbulence flow only in order to heat transfer enhancement and cooling purposes. Obtained results revealed that the periodic air injection by using special strategy can improve fuel economy and also decrease engine pollutant emissions.
This article investigates how hydrofluorocarbon (HFC) refrigerant affects compressor operating co... more This article investigates how hydrofluorocarbon (HFC) refrigerant affects compressor operating conditions and system performance using experimental testing under different conditions. In a heat pump or refrigerator cycle, it is necessary to move the fluid in the system to achieve heating or cooling. The compressor is the responsible component in fluid movement and so is a key factor in system power consumption. For this reason, it is essential to discover ways to increase compressor energy efficiency. R404a refrigerant was selected to evaluate the influence of refrigerant on compressor performance. Compressor inlet and discharge temperatures and pressures were measured experimentally. For the tested refrigerant, compressibility factor (Z) and deviation from ideal gas behavior were analyzed cautiously to compute power consumption, isentropic work, coefficient of performance, energy and exergy state, and compressor efficiency. Also analyzed were the influence of condenser water flow rate and the effect of evaporator inlet temperature. The study discussed here provided results that can be used to enhance the performance of compressors in heating/cooling systems.
• Effects of wind on the thermo-flow characteristics of cooling towers have been revealed. • Wind... more • Effects of wind on the thermo-flow characteristics of cooling towers have been revealed. • Windbreaker types have been studied to decrease the negative effects of wind. • Results show that it is possible to use the momentum effect of wind. • Movable windbreakers should be used to change the direction according to the wind. A B S T R A C T Performance of natural draft dry cooling towers is significantly affected when the wind velocity is higher than a critical level according to their design and geometry. During this type of conditions, global electricity generation of power plants using especially dry type cooling towers is substantially reduced, up to as high as 40%. In order to decrease the reduction in electricity generation of power plants, it is possible to study on the dimensions of the cooling towers. Additionally, using different types of windbreakers can reduce the effects of unfavorable operating conditions. However, the direction of the wind changes with the seasons although the prevailing wind direction is nearly the same. In this study, internal flat and combination of internal flat–external rounded windbreakers have been analyzed by using the computational fluid dynamics approach. The combination of windbreakers, which is able to move axially around the cooling tower, has been propounded to arrange the flow characteristics during the windy days. The studies on the windbreakers in the literature have been aimed to decrease the negative effects of the wind; however, the design in this study provides also an increase in the air mass flowrate due to the momentum effect of the wind.
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