Dawit Abay | Mekelle university (original) (raw)
Papers by Dawit Abay
Momona Ethiopian Journal of Science, 2021
Natural convection indirect type solar dryer integrated with reflectors that can be used for dryi... more Natural convection indirect type solar dryer integrated with reflectors that can be used for drying fruits and vegetables was designed, constructed, and evaluated. The study mainly tried to improve the performance of a prototype natural convection indirect solar dryer. The solar dryer was integrated with reflectors and its thermal performance was experimentally analyzed and results were compared with the same dryer without reflectors. The experiments conducted included a no-load test to determine the stagnation temperature that can be reached and drying tests using tomato slices. During the drying test, moisture content at the initial and final stages was measured using a moisture balance instrument. The mass of the tomato slices was measured every two hours to find the drying efficiency. Temperatures were measured using thermocouples located at the absorber plate and at the trays inside the drying cabinet. Solar radiation was also measured using a pyranometer located near the dryer...
IOP Conference Series: Materials Science and Engineering, 2018
World Journal on Educational Technology: Current Issues
Due to the COVID-19 pandemic that affected the world, education has switched to distance educatio... more Due to the COVID-19 pandemic that affected the world, education has switched to distance education. Education has transformed from face-to-face education to distance education. This situation caused educators and administrators who were unprepared to panic. Researchers need to increase research on distance education. In the distance education system, it is the most basic task of the teachers to increase the participation of students in the lessons, to teach the students with different techniques as in face-to-face education and to increase their motivation. It is very important to research and develop the techniques and systems used in distance education. In this context, the aim of this study is to determine the views of university students about the distance education process and to get their suggestions. In this study, the qualitative research method for the research data was used for the views and needs of the students studying at the university about the distance education syst...
An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber i... more An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber is designed, manufactured and tested for its performance. It plays a major role in reducing crop wastage and opens a way to food preservation. The area of the solar collector required to dry a batch of 10 kg of tomato within two days is calculated. The performance of the collector is improved through the use corrugated absorber to create turbulence for air flow and a highly insulating material to minimize heat losses. The thermal performance of the solar dryer is tested under the local weather conditions considering the effect of wind, humidity and cloudiness. The average thermal efficiency of the solar collector is calculated to be 21.5% at air flow rate of 0.0564 kg/s. At the same air flow rate, the maximum daily drying system efficiency is calculated to be 25%. Besides the maximum temperature of the solar dryer attained at the absorber plate is 77°C at 12:00 AM when the solar radiation...
An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber i... more An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber is designed, manufactured and tested for its performance. It plays a major role in reducing crop wastage and opens a way to food preservation. The area of the solar collector required to dry a batch of 10 kg of tomato within two days is calculated. The performance of the collector is improved through the use corrugated absorber to create turbulence for air flow and a highly insulating material to minimize heat losses. The thermal performance of the solar dryer is tested under the local weather conditions considering the effect of wind, humidity and cloudiness. The average thermal efficiency of the solar collector is calculated to be 21.5% at air flow rate of 0.0564 kg/s. At the same air flow rate, the maximum daily drying system efficiency is calculated to be 25%. Besides the maximum temperature of the solar dryer attained at the absorber plate is 77°C at 12:00 AM when the solar radiation intensity reached 1021 W/m² during no load test. Regarding the economical feasible it is analyzed using the common economic parameters such as payback period, net present value and benefit to cost ratio analysis methods. Hence the payback period is about eight months that is someone investing in this solar dryer will return his investment with less than a year. Finally the benefit cost ratio is 11.8 since this ratio is much greater than one the solar dryer it is in the acceptable range.
A wind pump prototype with 3.6 m rotor diameter, 19 m hub height above ground and 0.22 mm recipro... more A wind pump prototype with 3.6 m rotor diameter, 19 m hub height above ground and 0.22 mm reciprocating pump stroke has been developed at the Department of Mechanical Engineering, Mekelle University. The prototype was designed and manufactured locally. Theoretical model based on combined efficiency of the rotor and the reciprocating pump was used to estimate the performance of the wind pump. One year wind speed data collected at 10 m height was extrapolated to the wind pump hub height using wind shear coefficient. The model assumed balanced rotor power and reciprocating pump, hence did not consider the effect of pump size. The theoretical model estimated the average daily discharge to be around 50 m 3 and 30 m 3 at 8 m and 12 m head, respectively. The prototype was tested with the same pump stroke but two different size pumps at two different heads. The pumps were with internal diameter of 55 and 70 mm and the test heads were at 8 and 12 m. Measurement of the flow rate, rotational speed and wind speed were made every 10 minutes during the test period. The data collected were analyzed to find the performance of the wind pump at the two test heads and two pump sizes. The flow rate data was plotted against binned wind speed data to determine the linear fit function. The linear fit function was then used to estimate the flow rate at any wind speed. With the 55 mm pump the measured average daily discharge was 20 and 19 m 3 at 8 m and 12 m head, respectively. With the 70 mm pump the measured average daily discharge was 41 m 3 and 30 m 3 at 8 m and 12 m head, respectively.
Momona Ethiopian Journal of Science, 2021
Natural convection indirect type solar dryer integrated with reflectors that can be used for dryi... more Natural convection indirect type solar dryer integrated with reflectors that can be used for drying fruits and vegetables was designed, constructed, and evaluated. The study mainly tried to improve the performance of a prototype natural convection indirect solar dryer. The solar dryer was integrated with reflectors and its thermal performance was experimentally analyzed and results were compared with the same dryer without reflectors. The experiments conducted included a no-load test to determine the stagnation temperature that can be reached and drying tests using tomato slices. During the drying test, moisture content at the initial and final stages was measured using a moisture balance instrument. The mass of the tomato slices was measured every two hours to find the drying efficiency. Temperatures were measured using thermocouples located at the absorber plate and at the trays inside the drying cabinet. Solar radiation was also measured using a pyranometer located near the dryer...
IOP Conference Series: Materials Science and Engineering, 2018
World Journal on Educational Technology: Current Issues
Due to the COVID-19 pandemic that affected the world, education has switched to distance educatio... more Due to the COVID-19 pandemic that affected the world, education has switched to distance education. Education has transformed from face-to-face education to distance education. This situation caused educators and administrators who were unprepared to panic. Researchers need to increase research on distance education. In the distance education system, it is the most basic task of the teachers to increase the participation of students in the lessons, to teach the students with different techniques as in face-to-face education and to increase their motivation. It is very important to research and develop the techniques and systems used in distance education. In this context, the aim of this study is to determine the views of university students about the distance education process and to get their suggestions. In this study, the qualitative research method for the research data was used for the views and needs of the students studying at the university about the distance education syst...
An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber i... more An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber is designed, manufactured and tested for its performance. It plays a major role in reducing crop wastage and opens a way to food preservation. The area of the solar collector required to dry a batch of 10 kg of tomato within two days is calculated. The performance of the collector is improved through the use corrugated absorber to create turbulence for air flow and a highly insulating material to minimize heat losses. The thermal performance of the solar dryer is tested under the local weather conditions considering the effect of wind, humidity and cloudiness. The average thermal efficiency of the solar collector is calculated to be 21.5% at air flow rate of 0.0564 kg/s. At the same air flow rate, the maximum daily drying system efficiency is calculated to be 25%. Besides the maximum temperature of the solar dryer attained at the absorber plate is 77°C at 12:00 AM when the solar radiation...
An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber i... more An indirect passive convectional solar dryer consisting of a solar air heater and dryer chamber is designed, manufactured and tested for its performance. It plays a major role in reducing crop wastage and opens a way to food preservation. The area of the solar collector required to dry a batch of 10 kg of tomato within two days is calculated. The performance of the collector is improved through the use corrugated absorber to create turbulence for air flow and a highly insulating material to minimize heat losses. The thermal performance of the solar dryer is tested under the local weather conditions considering the effect of wind, humidity and cloudiness. The average thermal efficiency of the solar collector is calculated to be 21.5% at air flow rate of 0.0564 kg/s. At the same air flow rate, the maximum daily drying system efficiency is calculated to be 25%. Besides the maximum temperature of the solar dryer attained at the absorber plate is 77°C at 12:00 AM when the solar radiation intensity reached 1021 W/m² during no load test. Regarding the economical feasible it is analyzed using the common economic parameters such as payback period, net present value and benefit to cost ratio analysis methods. Hence the payback period is about eight months that is someone investing in this solar dryer will return his investment with less than a year. Finally the benefit cost ratio is 11.8 since this ratio is much greater than one the solar dryer it is in the acceptable range.
A wind pump prototype with 3.6 m rotor diameter, 19 m hub height above ground and 0.22 mm recipro... more A wind pump prototype with 3.6 m rotor diameter, 19 m hub height above ground and 0.22 mm reciprocating pump stroke has been developed at the Department of Mechanical Engineering, Mekelle University. The prototype was designed and manufactured locally. Theoretical model based on combined efficiency of the rotor and the reciprocating pump was used to estimate the performance of the wind pump. One year wind speed data collected at 10 m height was extrapolated to the wind pump hub height using wind shear coefficient. The model assumed balanced rotor power and reciprocating pump, hence did not consider the effect of pump size. The theoretical model estimated the average daily discharge to be around 50 m 3 and 30 m 3 at 8 m and 12 m head, respectively. The prototype was tested with the same pump stroke but two different size pumps at two different heads. The pumps were with internal diameter of 55 and 70 mm and the test heads were at 8 and 12 m. Measurement of the flow rate, rotational speed and wind speed were made every 10 minutes during the test period. The data collected were analyzed to find the performance of the wind pump at the two test heads and two pump sizes. The flow rate data was plotted against binned wind speed data to determine the linear fit function. The linear fit function was then used to estimate the flow rate at any wind speed. With the 55 mm pump the measured average daily discharge was 20 and 19 m 3 at 8 m and 12 m head, respectively. With the 70 mm pump the measured average daily discharge was 41 m 3 and 30 m 3 at 8 m and 12 m head, respectively.