ملخص البحث :

In this research, a study to use direct evaporative cooling supported by a heat exchanger to enhance the performance of conventional air conditioning unit experimentally is presented. Window type air-conditioner unit is implemented in the experiment where the A/C system is modulated to provide a wide range of various weather conditions. The proposed setup simulates severe hot weather condition where the temperature reaches up to 55°C. Several tests are conducted in this investigation and the study addresses four different challenges, namely, COP, cooling capacity, energy saving and the compressor auto-shutdown in very high weather temperature. The experimental results show that using evaporative cooling assist can significantly enhance the system to overcome the previous challenges. The refrigeration capacity is increased in the range of 10-30% whereas the electric demand in a compressor is reduced by 0.12-0.2 for each air temperature degree reduction (for one ton of refrigeration). The air-conditioning unit can run even with the voltage drop of 170 V instead of 220 V which cannot be performed in conventional air condenser.

ملخص البحث :

Research has been undertaken on heat pipe evacuated tube solar collector (HP-ETSC) for hot water applications, which is common in most Middle East regions. The enhancement in thermal performance by using various types of acetone based nanofluids has been explored. This work includes two experimental parts of the gravity-assisted heat pipe (GAHP) installed in evacuated tube solar collector system. The first part is designed to reach the optimal performance conditions for HP-ETSC which is charged with acetone as a working fluid inside the GAHP. Various values of filling ratios (40, 50, 60, 70 and 80%) and tilt angles (30°, 45° and 60°) are considered. The results show that there is an optimal performance at filling ratio equal to 70% and inclination angle equal to 45° when compared with other values during the course of study. This indicates that the importance of fully integrating design process right from the outset of the system design if GAHP is to be installed into an ETSC system to give the maximum possible solar energy benefits of efficient hot water solar collector designs. The main objective of the second experimental investigation is analyzing the impact of the two types of nanofluid (Al2O3 and CuO/acetone-based) on the thermal performance of the HP-ETSC. These two nanofluids are used as working fluid inside the GAHP and two concentration values (0.25% and 0.5% vol.) at the optimal conditions from the first experimental part. On the basis of the present study, it is recommended that HP-ETSC systems should be charged with nanofluids for thermal performance enhancement (20–54%) and efficiency (15–38%).

ملخص البحث :

Mechanical vibration is used to excite a heat pipe evacuated tube solar collector (HP-ETSC), where two (HP-ETSC’s) are built identically to compare the performance of the solar collector with and without applying vibration. A controllable vibration system was designed and manufactured for increased the total collector efficiency. The vibration system consists of a motor with adjustable rotating unbalanced mass and a control circuit. The velocity (frequency) of the motor is controlled by mean of an Arduino circuit that applies the controlling signal in the form of pulses over a certain period of time. The vibration is applied on one of (HP-ETSC’s) and the other is left in static condition under Iraq winter climatic conditions. The enhancement on the thermal performance at different frequency values (2, 4, 6, 8 and 10 Hz) and the three volumetric water flow rates are discussed. Results indicated that the evaporation and condensation heat transfer coefficients increased with vibrational frequencies, and the vibrational frequencies effectiveness depended on the water flow rate and the working conditions. The two heat transfer coefficients, hot water temperature and the total collector effectiveness of the HP-ETSC with controllable vibration system increased by 40%, 20%, and 22% during the test conditions

ملخص البحث :

This paper presents an experimental study to enhance the performance of a small air condition (A/C) system by mean of direct evaporative cooling method. A setup of cooling system is designed to simulate extremely hot weather where the dry bulb temperature (DBT) reaches the vicinity of 55 ◦C which represents the highest possible weather temperature that was recorded during summer. The proposed design utilizing an evaporative cooling cycle where the air flows over wet pads before it goes through the condenser. Four different parameters are considered to be studied, namely coefficient of performance (COP), energy saving, cooling capacity and the compressor auto-shut down in very high weather temperature. The results showed significant enhancement to the entire A/C system performance where the refrigeration capacity is increased in the range of 5% to 7.5% and there is 0.12A to 0.16A electrical current reduction for each temperature degree reduction. Moreover, and the compressor continued working even with a voltage drop of 16% (185 V instead of 220 V) which can help overcoming a serious problem that middle east countries (such Iraq) suffer during summer.

ملخص البحث :

working fluid, where different values of filling ratios and inclination angles are considered. Namely, five values of filling ratios (40, 50, 60, 70 and 80 %) and three inclination angle values (30ᵒ, 45ᵒ and 60ᵒ). The Gravity-assisted wickless heat pipe (GAHP) is made of a copper tube with outer diameter 0.016 m and the dimensions of the evaporator and condenser are 1.15 m and 0.2 m respectively. The core and wall temperatures are measured by means of thermocouples that are located in the center and at the wall of GAHP. This study aims to observe the thermal performance of the HP-ETSC when using different values of working fluid, filling ratio, inclination angle and hot water mass flow rate in Najaf city climate (Iraq: latitude 31 ᵒN and longitude 44 ᵒE) during clear weather days in February 2017. The results show that the optimal filling ratio and inclination angles are 70% and 45ᵒ respectively when compared with other values during the course of study. Hence, in Najaf city ,it is recommended to implement wickless heat pipe evacuated tube so (PDF) Experimental investigation on the performance of evacuated tube solar collector with wickless heat pipe under Iraq climatic conditions. Available from: https://www.researchgate.net/publication/320858661_Experimental_investigation_on_the_performance_of_evacuated_tube_solar_collector_with_wickless_heat_pipe_under_Iraq_climatic_conditions [accessed Jun 24 2021].

ملخص البحث :

Recently, solar and wind are most important sources of renewable energy. Where these resources are practically useable in Iraq, and in order to study the efficacy of implementing these two sources, we present an experimental investigation about the trend of the wind and solar characteristics. A modern new technology weather station is carried out in this work to measure the weather dry bulb temperatures (DBT), solar intensity and wind speed in Najaf city (Iraq 44 ᵒE, 31 ᵒN) over a period of one year from April 2015 to March 2016. The investigation covers Wind speed, solar radiation and dry bulb temperatures (DBT). Meteorological data are illustrated from continuous collecting over one year. Where the results showed that the temperatures distribution in Najaf city has a trend of excessive increase during the summer, it could be the highest in the Middle East. The Same thing is observed regarding the solar energy, where the global radiation recorded the highest level according to the collected data and NASA SSE model. On the other side, the wind speed over one year did not record considerable level and thus, utilizing solar energy in Najaf city is worthy to be considered rather than investing based on wind speed.

ملخص البحث :

Research has been undertaken on thermosyphon heat exchangers (THEs) for coolness recovery in sub-tropical climates conditions to explore the potential for energy savings and humidity control in HVAC systems through using THEs. This work includes an experimental and numerical model of THEs install in HVAC system. The performance of these individual systems was experimentally investigated throughout a wide range of outside design condition DBT (35–50) °C and RH (10–100)%. The outdoor tested parameters were the effect of RH, DBT, type of working fluid charged in THEs (Water, Methanol, Ethanol, Acetone, Butanol and R134a) and the air velocity. The experimental part involves a careful choose of the specification, design and construction of a THEs, an associates conventional chilled water coil, a fan and duct system, and a full range of properly calibrated sensors. The numerical model aims to develop a CFD model to define the flow characteristics (distribution of temperatures, moisture content and air velocity) for a THE in duct flow using momentum, turbulence model κ-ε, moisture content and energy equations in 3D by using FORTRAN code to reach the better results to simulate accurately the influence of adding one or more THEs to the existing HVAC system. This indicates the importance of fully integrating the design process right from the outset of the system design if THEs are to be installed into a HVAC system so as to give the maximum possible energy saving benefits in efficient air handling unit (AHU) designs. On the basis of this study, it is recommended that subtropical HVAC systems should be installed with THEs for dehumidification enhancement (5–20%) and energy saving (5–35%).

ملخص البحث :

An experimental and numerical investigations are conducted on a Two Phase Closed Thermosyphon (TPCT) charged with six working fluids; namely (water, methanol, ethanol, acetone, butanol and R134a) with filling ratios (40, 50, 60, 70 and 100 %). The TPCT is made from a 0.016 m diameter copper tube, which consists of a 0.15 m evaporator, 0.1 m adiabatic and 0.15 m condenser sections, respectively. Thermocouples are located in the core and on the wall of the TPCT. The main objectives of the experimental investigation are to analyze the effect of the working fluid and filling ratio (liquid inventory) under heat inputs (20–120 W) with a fixed condenser cooling temperature of (25 °C) on the thermal performance of the TPCT. The results are compared with a simulation model using finite difference method in three dimensional cylindrical coordinates by using FORTRAN. The correlations of the phase change for the TPCT based on the theory of thermal resistance are used in the evaporator and condenser sections. The agreement between theoretical and experimental results is shown to be accurate within 10 %. The results showed that the maximum heat transport ability is associated with using of water and acetone where it is compared with other fluids under the same range of operating temperatures of 35–50 °C. This is the range between lowest and highest temperatures for the sub-tropical climates.

ملخص البحث :

Research has been undertaken on thermosyphon heat exchangers (THEs) for coolness recovery in sub-tropical climates conditions to explore the potential for energy savings and humidity control in HVAC systems through using THEs. This work includes an experimental and numerical model of THEs install in HVAC system. The performance of these individual systems was experimentally investigated throughout a wide range of outside design condition DBT (35-50) °C and RH (10-100)%. The outdoor tested parameters were the effect of RH, DBT, type of working fluid charged in THEs (Water, Methanol, Ethanol, Acetone, Butanol and R134a) and the air velocity. The experimental part involves a careful choose of the specification, design and construction of a THEs, an associates conventional chilled water coil, a fan and duct system, and a full range of properly calibrated sensors. The numerical model aims to develop a CFD model to define the flow characteristics (distribution of temperatures, moisture content and air velocity) for a THE in duct flow using momentum, turbulence model κ-ε, moisture content and energy equations in 3D by using FORTRAN code to reach the better results to simulate accurately the influence of adding one or more THEs to the existing HVAC system. This indicates the importance of fully integrating the design process right from the outset of the system design if THEs are to be installed into a HVAC system so as to give the maximum possible energy saving benefits in efficient air handling unit (AHU) designs. On the basis of this study, it is recommended that subtropical HVAC systems should be installed with THEs for dehumidification enhancement (5-20%) and energy saving (5-35%).

ملخص البحث :

Mechanical vibration is used to excite a heat pipe evacuated tube solar collector (HP-ETSC), where two (HP-ETSC’s) are built identically to compare the performance of the solar collector with and without applying vibration. A controllable vibration system was designed and manufactured for increased the total collector efficiency. The vibration system consists of a motor with adjustable rotating unbalanced mass and a control circuit. The velocity (frequency) of the motor is controlled by mean of an Arduino circuit that applies the controlling signal in the form of pulses over a certain period of time. The vibration is applied on one of (HP-ETSC’s) and the other is left in static condition under Iraq winter climatic conditions. The enhancement on the thermal performance at different frequency values (2, 4, 6, 8 and 10 Hz) and the three volumetric water flow rates are discussed. Results indicated that the evaporation and condensation heat transfer coefficients increased with vibrational frequencies, and the vibrational frequencies effectiveness depended on the water flow rate and the working conditions. The two heat transfer coefficients, hot water temperature and the total collector effectiveness of the HP-ETSC with controllable vibration system increased by 40%, 20%, and 22% during the test conditions

ملخص البحث :

The research aims to investigate the possibility of enhancing the functionality of a heat pipe evacuated tube collector (HPETC) with a new method of, one or both an evacuated tube (ET) and two separate storage tanks, incorporating nano or micro-enhanced phase change materials as a thermal energy storage system (TESS). In the proposed systems, the (ET) was filled with enhanced medical paraffin wax, while the two separated tanks were filled with enhanced paraffin wax (grade-A). These two types of paraffin wax were enhanced with 5wt% CuO nanoparticle (NP-CuO) or ZnO microparticles (MP-ZnO). In this study, Six tests were carried out to do the investigation. Three tests were done to investigate the effect of the integration of enhanced-PCM in the only (ET) of HPETC. While the other three tests performed to investigate the effect of enhanced-PCM integrated into both (ET) of HPETC and two additional storage tanks. The main advantage of this new system is that it improved solar water heater efficiency by minimizing hot water temperature fluctuations. Thereby, the efficiently thermal isolation of the (ET) and storage tanks and the efficient energy accumulation in PCM which enables the system to supply hot water even when there is no solar radiation at night or in overcast weather. The results showed that the integration of enhanced-paraffin wax with NP-CuO and MP-ZnO in both the (ET) and the separated tanks gives an efficiency improvement range of (36.8-50%) and (25.43-41.4%) respectively, While the integration of enhanced-paraffin wax with NP-CuO and MP-ZnO in the only (ET) led to an increase in the efficiency with a range of (33.8-45.7%) and (23.8-26.7%) respectively, compared with a typical reference collector without PCM. Also, the NP-CuO enhanced paraffin wax integrated with the ET gave a better improvement in the evaporation & condensation coefficients in the evaporator and condenser sections where their values were (401 and 2366.4 W/m2·°C) respectively at a flow rate of 1L/h.

ملخص البحث :

This paper presents an experimental investigation of a new method of phase change materials (PCMs) integration in one or both the evacuated tube (ET) and two separated tanks adjacent to the water tank of heat pipe evacuated tube solar water heater collector (HP/ETC). In this method, the evacuated tube was filled with medical paraffin wax as thermal heat storage, while the two separated tanks were filled with paraffin wax (grade-A). Therefore, owing to the thermal isolation of the evacuated tube and PCM storage tanks, heat is efficiently accumulated and stored for a longer time. The advantage of this new method is that improved overall solar water heater performance by delayed heat release, thereby supplying hot water for a long time at high demand or when low solar intensity. Four HP/ETSCs with gravity assist heat pipe (GAHP) rigs were used for a comparative study. The first HP/ETC was equipped with PCM in its ET and two PCM storage tanks. The second and third HP/ETCs were integrated with PCM in an ET and two PCM storage tanks, respectively. While the fourth HP/ETC was considered a reference as it was left without PCM. Each heat pipe was filled with a 0.7 filling ratio of pure acetone. The tests are carried out with two different rates of water flow (i.e. 1 and 2L/h). The results demonstrate that the integration of PCM in both the ET and the separated tanks gives an efficiency improvement of 55.7%, While the integration of PCM in the ET led to an increase in the efficiency of 49.9%. Whereas the efficiency has been improved with the integration of PCM in the separated tanks by about 36.5%, compared with PCM-free reference collector.

ملخص البحث :

This paper presents an experimental investigation of a new method of phase change materials (PCMs) integration in one or both the evacuated tube (ET) and two separated tanks adjacent to the water tank of heat pipe evacuated tube solar water heater collector (HP/ETC). In this method, the evacuated tube was filled with medical paraffin wax as thermal heat storage, while the two separated tanks were filled with paraffin wax (grade-A). Therefore, owing to the thermal isolation of the evacuated tube and PCM storage tanks, heat is efficiently accumulated and stored for a longer time. The advantage of this new method is that improved overall solar water heater performance by delayed heat release, thereby supplying hot water for a long time at high demand or when low solar intensity. Four HP/ETSCs with gravity assist heat pipe (GAHP) rigs were used for a comparative study. The first HP/ETC was equipped with PCM in its ET and two PCM storage tanks. The second and third HP/ETCs were integrated with PCM in an ET and two PCM storage tanks, respectively. While the fourth HP/ETC was considered a reference as it was left without PCM. Each heat pipe was filled with a 0.7 filling ratio of pure acetone. The tests are carried out with two different rates of water flow (i.e. 1 and 2L/h). The results demonstrate that the integration of PCM in both the ET and the separated tanks gives an efficiency improvement of 55.7%, While the integration of PCM in the ET led to an increase in the efficiency of 49.9%. Whereas the efficiency has been improved with the integration of PCM in the separated tanks by about 36.5%, compared with PCM-free reference collector.

ملخص البحث :

The research aims to investigate the possibility of enhancing the functionality of a heat pipe evacuated tube collector (HPETC) with a new method of, one or both an evacuated tube (ET) and two separate storage tanks, incorporating nano or micro-enhanced phase change materials as a thermal energy storage system (TESS). In the proposed systems, the (ET) was filled with enhanced medical paraffin wax, while the two separated tanks were filled with enhanced paraffin wax (grade-A). These two types of paraffin wax were enhanced with 5wt% CuO nanoparticle (NP-CuO) or ZnO microparticles (MP-ZnO). In this study, Six tests were carried out to do the investigation. Three tests were done to investigate the effect of the integration of enhanced-PCM in the only (ET) of HPETC. While the other three tests performed to investigate the effect of enhanced-PCM integrated into both (ET) of HPETC and two additional storage tanks. The main advantage of this new system is that it improved solar water heater efficiency by minimizing hot water temperature fluctuations. Thereby, the efficiently thermal isolation of the (ET) and storage tanks and the efficient energy accumulation in PCM which enables the system to supply hot water even when there is no solar radiation at night or in overcast weather. The results showed that the integration of enhanced-paraffin wax with NP-CuO and MP-ZnO in both the (ET) and the separated tanks gives an efficiency improvement range of (36.8-50%) and (25.43-41.4%) respectively, While the integration of enhanced-paraffin wax with NP-CuO and MP-ZnO in the only (ET) led to an increase in the efficiency with a range of (33.8-45.7%) and (23.8-26.7%) respectively, compared with a typical reference collector without PCM. Also, the NP-CuO enhanced paraffin wax integrated with the ET gave a better improvement in the evaporation & condensation coefficients in the evaporator and condenser sections where their values were (401 and 2366.4 W/m2·°C) respectively at a flow rate of 1L/h.