Mogaji Taye | Federal University of Technology Akure (original) (raw)
Papers by Mogaji Taye
International Journal of Refrigeration, 2013
This study presents experimental results of heat transfer coefficient and pressure drop during tw... more This study presents experimental results of heat transfer coefficient and pressure drop during two-phase flow of R134a in a horizontal tube containing twisted-tape inserts. The test section is a 2 m long copper tube of 15.9 mm inner diameter. The experiments were performed for tapes with twist ratios of 9 and 14 and a tube without insert. The mass velocity ranged from 75 to 200 kg m2 s1 and the vapor quality from 5 to 95%, for adiabatic condition and for constant heat flux of 10 kW m2. Experimental pressure drop and heat transfer coefficient results are presented, and also an analysis of overall enhancement due to the inserts. The use of twisted-tape inserts is suitable if applied to the high vapor quality region of the evaporator and under high mass velocities.
This paper presents reports on simulation and comparative analysis of single stage vapour compres... more This paper presents reports on simulation and comparative analysis of single stage vapour
compression refrigeration system performance for comparison of refrigerant fluids. A mathematical
model was devised by applying the concept of energy balance in the thermodynamic cycle to the
components of the vapour compression refrigeration system. The developed model implemented in
MATLAB [1] software was used to compare the performance of the system using Hydrocarbons,
R134a and ammonia as refrigerants in place of refrigerants 12 and 22. Simulation data was
generated over a wide range of evaporation and condensation temperatures of −25 to 15ºC and 30
to 60ºC respectively for the selected working fluids considered in this study to observe the
performance of the system in terms of refrigerating effect, coefficient of performance (COP) and
overall efficiency of the system. In the present study, close match of COP and the system overall
efficiency values for R134a, R290 and R600a are observed with that of R12 and R22 counterparts
under the similar operating conditions. Moreover, among the refrigerants simulated in the system
under the similar operating conditions, the system with the use of ammonia yields highest COPs and are of up to 6.3 and 7.5% increment compared with those of R12 and R22 respectively. It can
be concluded that R134a, R290, R600a and ammonia may act as substitutes for R12 and R22
without affecting the energy efficiency of vapour compression refrigeration system, provided the
safety issues are addressed in terms of manufacturing, handling, storage and servicing so as to
prevent flammability and corrosive/toxic natures of both hydrocarbons and ammonia refrigerants
respectively, thus helping to solve the ozone depletion potential (ODP) and global warming
potential (GWP) problems regarding environmental issues.
An evaporative cooling system for the preservation of fresh vegetables was developed for extendin... more An evaporative cooling system for the preservation of fresh vegetables was developed for extending
the shelf life of tomatoes and carrots and its performance was evaluated. It consists of a pyramidal
shaped with total storage space of 0.075 m3, made of galvanized mild steel, stainless steel and internally
insulated with 0.025 m polystyrene foam, a suction fan of 4.3 m/s velocity air flow and 0.5 W (1250 rpm),
cooling pad (Jute) of 0.06 m thickness and water pump with discharge capacity of 3.5 l/min as well as a
power rating of 0.5 W. A water reservoir of capacity 62.5 m3 is linked to the cooling system at the bottom
through a P.V.C. pipe supplying water to keep the cooling pad/mesh continuously wet. Study was
conducted to check the freshness of tomatoes and carrots, and data were observed daily. Results of the
transient performance tests revealed that the evaporative cooling system chamber temperature and
relative humidity depression from ambient air temperature varied over 16-26°C and 33-88% respectively.
Ambient air temperatures and relative humidity during the test periods ranged over 26-32°C and 18-31%
respectively. The shelf life of the vegetable produce inside the evaporative cooling system was
extended by fourteen days relative to ambient storage. Thus, the evaporative cooling system has the
prospect of being used for short term preservation of vegetables soon after harvest and it will be very
useful in a developing economy like Nigeria.
Biodiesel is gradually being accepted worldwide as suitable alternative fuel for diesel engine. R... more Biodiesel is gradually being accepted worldwide as suitable alternative fuel for diesel engine. Rigorous
purification is however required to meet the American Society for Testing and Materials (ASTM) and
European Union (EU) standards for biodiesel because of unfavorable properties and the multitude of
feed stocks with different properties that can be used. Two of such impurities that must be kept within
limits are methanol and glyceride. Egunsi melon oil selected for the study was transesterified using
sodium hydroxide as catalyst and methanol as reagent and then washed with distilled water. The fatty
acid profile, the amount of methanol and glyceride in the oil, (B100) 100% biodiesel and, B10 (10%
biodiesel blend with 90% diesel) and B20 (20% biodiesel blend with 80% diesel) were measured by Gas
chromatography equipped with flame ionization detector. They were also characterized to determine
their suitability for use in diesel engine. The triglycerides, free and total glyceride content of the oil are
all outside the limits, while those of B100, B10, and B20 are within the limits. The measured fuel
properties are also within the limits, hence egunsi melon oil biodiesel and blends can be used as
alternative fuel for diesel engines without major modifications.
The African bush mangos (Irvingia gabonensis) were collected from the wild, dried and the kernels... more The African bush mangos (Irvingia gabonensis) were collected from the wild, dried and the kernels were
split to release the nuts. The oil from the nuts was extracted in a soxhlet extractor that was operated at
60°C using normal hexane as solvent. It gave an oil content of 60% which was mainly triglyceride and
was solid at room temperature. It was heated to 40°C to liquefy it and a methanol molar ratio of 6 to 1
was used along with 4 g/L of sodium hydroxide as catalyst during transesterification to biodiesel.
Chromatography analysis of the biodiesel gave 59% linolenic fatty acid and tests show that the
biodiesel has properties that are within the American society for tests and materials limits for biodiesel.
Of particular significance is the cloud point of -14°C which allows it to be used in cold conditions and a
flash point of 97°C that makes it a safe fuel during storage. The performance characteristic is similar to
that of diesel fuel and the specific fuel consumption is 8% higher than diesel fuel which is consistent
with the difference in their heating values. The oil will thus be a potential source of alternative fuel for
diesel engine.
This paper presents the marketing performance and efficiency of evaporative-preservation cooling ... more This paper presents the marketing performance and efficiency of evaporative-preservation cooling system for fresh tomato as an update of the performance evaluation of the evaporative cooling system developed at the Federal University of Technology Akure, Nigeria. A total of one hundred and five (105) fresh tomato marketers were sampled. Marketing margin analysis was performed to determine the performance of the preserved tomato vegetable during dry season based on their mode of preservation. Shepherd’s efficiency formula result analysis shows that fresh tomato market was efficient with average marketing efficiency of 17.65%. The two-independent samples t-test results (t-value = 74.014) further reveal that profit margin for users of evaporative cooling system is significantly different from users of traditional mode of preservation, at 5% level of significance. However, disaggregated wholesaler’s profit margin of N6,261.6 per month for users of traditional preservation method implies that they are not efficient compared with users of evaporative cooling system averaging N12,381.4 per month. Given the wide tropical variability in temperatures and relative humidity, evaporative cooling system is of economic importance towards commodity marketing development in Ondo State, Nigeria.
This paper presents experimental data for pressure drop and heat transfer coefficient for two-pha... more This paper presents experimental data for pressure drop and heat transfer coefficient for two-phase
flows in tubes containing twisted-tape inserts. Based on these data, an analysis of the heat transfer
enhancement and pressure drop penalty due to the use of twisted-tapes is performed. Experimental
results were obtained for horizontal 12.7 and 15.9 mm ID tubes without and with twisted-tape for twistratios
of 3, 4, 9 and 14. The experiments were performed for R134a as working fluid covering mass
velocities from 75 to 200 kg/m2 s, heat fluxes of 5 and 10 kW/m2 and saturation temperatures of 5 and
15 C. The predictive methods available in the literature were compared against the experimental data
obtained in the present study. In general, it was concluded that the use of reduced twist-ratios values
provide higher overall heat transfer enhancement factors for intermediary vapor quality. Additionally, it
was found that the pressure drop correlation proposed by Kanizawa and Ribatski (2012) is suitable to be
used as a design tool because it predicted 99% of the present database within an error band of ±30%.
This study presents experimental results of heat transfer coefficient and pressure drop during tw... more This study presents experimental results of heat transfer coefficient and pressure drop
during two-phase flow of R134a in a horizontal tube containing twisted-tape inserts. The
test section is a 2 m long copper tube of 15.9 mm inner diameter. The experiments were
performed for tapes with twist ratios of 9 and 14 and a tube without insert. The mass
velocity ranged from 75 to 200 kg m2 s1 and the vapor quality from 5 to 95%, for adiabatic
condition and for constant heat flux of 10 kW m2. Experimental pressure drop and heat
transfer coefficient results are presented, and also an analysis of overall enhancement due
to the inserts. The use of twisted-tape inserts is suitable if applied to the high vapor quality
region of the evaporator and under high mass velocities.
This paper presents an experimental study on heat transfer augmentation during convective boiling... more This paper presents an experimental study on heat transfer augmentation during convective boiling of R134a
inside a 15.9 mm ID horizontal tube containing twisted-tape inserts. The use of twisted-tape inserts is a heat transfer
enhancement technique applied on heat exchangers over more than one century ago. However, the heat transfer
augmentation comes together with pressure drop increment, impacting the pumping power and, consequently, the
system efficiency. Moreover, until now it is not clear when the effects on the heat exchanger efficiency of the heat
transfer enhancement overcomes pressure drop penalties. In the present study, pressure drop and heat transfer
coefficient experiments were performed. Experimental results were obtained during flow boiling of R134a for twistedtape
ratios of 3, 4, 9 and 14, mass velocities ranging from 75 to 200 kg / m2 s, heat flux of 10 kW / m2 and saturation
temperatures of 5 and 15 °C. The results obtained lead to the conclusion that higher heat transfer rates can be
achieved using twisted-tape inserts at the expense of a reasonable pressure drop. In addition, a new correlation to
predict the heat transfer coefficients during two-phase flow inside tubes containing twisted-tape inserts is proposed.
The performance of the correlation can be deemed adequate, considering that it compares well with experimental
results of different authors.
This report presents a study on development and analysis of double effect condensing unit vapour ... more This report presents a study on development and analysis of double effect condensing unit vapour compression refrigeration system (DECU VCR system). The system is composed by two refrigeration cycles working with R134a. Tests under a wide range operating temperature interval conditions were carried out on the developed system. Experimental data was generated to observe the performance of the basic VCR system and DECU VCR system for an important parameters such as condensation (35 to 55°C) and evaporation temperatures (-5 to 15°C). Performance evaluation of the system was characterized in terms of cooling capacity and coefficient of performance (COP). In the present study, both COP and refrigerating effect of the developed system have been found, in general, to be greater than the corresponding basic VCR system values, but the degree of enhancement varies depending on the test conditions. Additionally, by using dedicated subcooling cycle, up to 11 and 11.7 % performance improvement ratio of VCR system are observed at evaporation temperature of 15 oC and condensation temperature of 35 oC respectively. It can be concluded that the use of dedicated sub cooling cycle in VCR system is most efficient and suitable for the betterment of thermal system performance.
International Journal of Refrigeration, 2013
This study presents experimental results of heat transfer coefficient and pressure drop during tw... more This study presents experimental results of heat transfer coefficient and pressure drop during two-phase flow of R134a in a horizontal tube containing twisted-tape inserts. The test section is a 2 m long copper tube of 15.9 mm inner diameter. The experiments were performed for tapes with twist ratios of 9 and 14 and a tube without insert. The mass velocity ranged from 75 to 200 kg m2 s1 and the vapor quality from 5 to 95%, for adiabatic condition and for constant heat flux of 10 kW m2. Experimental pressure drop and heat transfer coefficient results are presented, and also an analysis of overall enhancement due to the inserts. The use of twisted-tape inserts is suitable if applied to the high vapor quality region of the evaporator and under high mass velocities.
This paper presents reports on simulation and comparative analysis of single stage vapour compres... more This paper presents reports on simulation and comparative analysis of single stage vapour
compression refrigeration system performance for comparison of refrigerant fluids. A mathematical
model was devised by applying the concept of energy balance in the thermodynamic cycle to the
components of the vapour compression refrigeration system. The developed model implemented in
MATLAB [1] software was used to compare the performance of the system using Hydrocarbons,
R134a and ammonia as refrigerants in place of refrigerants 12 and 22. Simulation data was
generated over a wide range of evaporation and condensation temperatures of −25 to 15ºC and 30
to 60ºC respectively for the selected working fluids considered in this study to observe the
performance of the system in terms of refrigerating effect, coefficient of performance (COP) and
overall efficiency of the system. In the present study, close match of COP and the system overall
efficiency values for R134a, R290 and R600a are observed with that of R12 and R22 counterparts
under the similar operating conditions. Moreover, among the refrigerants simulated in the system
under the similar operating conditions, the system with the use of ammonia yields highest COPs and are of up to 6.3 and 7.5% increment compared with those of R12 and R22 respectively. It can
be concluded that R134a, R290, R600a and ammonia may act as substitutes for R12 and R22
without affecting the energy efficiency of vapour compression refrigeration system, provided the
safety issues are addressed in terms of manufacturing, handling, storage and servicing so as to
prevent flammability and corrosive/toxic natures of both hydrocarbons and ammonia refrigerants
respectively, thus helping to solve the ozone depletion potential (ODP) and global warming
potential (GWP) problems regarding environmental issues.
An evaporative cooling system for the preservation of fresh vegetables was developed for extendin... more An evaporative cooling system for the preservation of fresh vegetables was developed for extending
the shelf life of tomatoes and carrots and its performance was evaluated. It consists of a pyramidal
shaped with total storage space of 0.075 m3, made of galvanized mild steel, stainless steel and internally
insulated with 0.025 m polystyrene foam, a suction fan of 4.3 m/s velocity air flow and 0.5 W (1250 rpm),
cooling pad (Jute) of 0.06 m thickness and water pump with discharge capacity of 3.5 l/min as well as a
power rating of 0.5 W. A water reservoir of capacity 62.5 m3 is linked to the cooling system at the bottom
through a P.V.C. pipe supplying water to keep the cooling pad/mesh continuously wet. Study was
conducted to check the freshness of tomatoes and carrots, and data were observed daily. Results of the
transient performance tests revealed that the evaporative cooling system chamber temperature and
relative humidity depression from ambient air temperature varied over 16-26°C and 33-88% respectively.
Ambient air temperatures and relative humidity during the test periods ranged over 26-32°C and 18-31%
respectively. The shelf life of the vegetable produce inside the evaporative cooling system was
extended by fourteen days relative to ambient storage. Thus, the evaporative cooling system has the
prospect of being used for short term preservation of vegetables soon after harvest and it will be very
useful in a developing economy like Nigeria.
Biodiesel is gradually being accepted worldwide as suitable alternative fuel for diesel engine. R... more Biodiesel is gradually being accepted worldwide as suitable alternative fuel for diesel engine. Rigorous
purification is however required to meet the American Society for Testing and Materials (ASTM) and
European Union (EU) standards for biodiesel because of unfavorable properties and the multitude of
feed stocks with different properties that can be used. Two of such impurities that must be kept within
limits are methanol and glyceride. Egunsi melon oil selected for the study was transesterified using
sodium hydroxide as catalyst and methanol as reagent and then washed with distilled water. The fatty
acid profile, the amount of methanol and glyceride in the oil, (B100) 100% biodiesel and, B10 (10%
biodiesel blend with 90% diesel) and B20 (20% biodiesel blend with 80% diesel) were measured by Gas
chromatography equipped with flame ionization detector. They were also characterized to determine
their suitability for use in diesel engine. The triglycerides, free and total glyceride content of the oil are
all outside the limits, while those of B100, B10, and B20 are within the limits. The measured fuel
properties are also within the limits, hence egunsi melon oil biodiesel and blends can be used as
alternative fuel for diesel engines without major modifications.
The African bush mangos (Irvingia gabonensis) were collected from the wild, dried and the kernels... more The African bush mangos (Irvingia gabonensis) were collected from the wild, dried and the kernels were
split to release the nuts. The oil from the nuts was extracted in a soxhlet extractor that was operated at
60°C using normal hexane as solvent. It gave an oil content of 60% which was mainly triglyceride and
was solid at room temperature. It was heated to 40°C to liquefy it and a methanol molar ratio of 6 to 1
was used along with 4 g/L of sodium hydroxide as catalyst during transesterification to biodiesel.
Chromatography analysis of the biodiesel gave 59% linolenic fatty acid and tests show that the
biodiesel has properties that are within the American society for tests and materials limits for biodiesel.
Of particular significance is the cloud point of -14°C which allows it to be used in cold conditions and a
flash point of 97°C that makes it a safe fuel during storage. The performance characteristic is similar to
that of diesel fuel and the specific fuel consumption is 8% higher than diesel fuel which is consistent
with the difference in their heating values. The oil will thus be a potential source of alternative fuel for
diesel engine.
This paper presents the marketing performance and efficiency of evaporative-preservation cooling ... more This paper presents the marketing performance and efficiency of evaporative-preservation cooling system for fresh tomato as an update of the performance evaluation of the evaporative cooling system developed at the Federal University of Technology Akure, Nigeria. A total of one hundred and five (105) fresh tomato marketers were sampled. Marketing margin analysis was performed to determine the performance of the preserved tomato vegetable during dry season based on their mode of preservation. Shepherd’s efficiency formula result analysis shows that fresh tomato market was efficient with average marketing efficiency of 17.65%. The two-independent samples t-test results (t-value = 74.014) further reveal that profit margin for users of evaporative cooling system is significantly different from users of traditional mode of preservation, at 5% level of significance. However, disaggregated wholesaler’s profit margin of N6,261.6 per month for users of traditional preservation method implies that they are not efficient compared with users of evaporative cooling system averaging N12,381.4 per month. Given the wide tropical variability in temperatures and relative humidity, evaporative cooling system is of economic importance towards commodity marketing development in Ondo State, Nigeria.
This paper presents experimental data for pressure drop and heat transfer coefficient for two-pha... more This paper presents experimental data for pressure drop and heat transfer coefficient for two-phase
flows in tubes containing twisted-tape inserts. Based on these data, an analysis of the heat transfer
enhancement and pressure drop penalty due to the use of twisted-tapes is performed. Experimental
results were obtained for horizontal 12.7 and 15.9 mm ID tubes without and with twisted-tape for twistratios
of 3, 4, 9 and 14. The experiments were performed for R134a as working fluid covering mass
velocities from 75 to 200 kg/m2 s, heat fluxes of 5 and 10 kW/m2 and saturation temperatures of 5 and
15 C. The predictive methods available in the literature were compared against the experimental data
obtained in the present study. In general, it was concluded that the use of reduced twist-ratios values
provide higher overall heat transfer enhancement factors for intermediary vapor quality. Additionally, it
was found that the pressure drop correlation proposed by Kanizawa and Ribatski (2012) is suitable to be
used as a design tool because it predicted 99% of the present database within an error band of ±30%.
This study presents experimental results of heat transfer coefficient and pressure drop during tw... more This study presents experimental results of heat transfer coefficient and pressure drop
during two-phase flow of R134a in a horizontal tube containing twisted-tape inserts. The
test section is a 2 m long copper tube of 15.9 mm inner diameter. The experiments were
performed for tapes with twist ratios of 9 and 14 and a tube without insert. The mass
velocity ranged from 75 to 200 kg m2 s1 and the vapor quality from 5 to 95%, for adiabatic
condition and for constant heat flux of 10 kW m2. Experimental pressure drop and heat
transfer coefficient results are presented, and also an analysis of overall enhancement due
to the inserts. The use of twisted-tape inserts is suitable if applied to the high vapor quality
region of the evaporator and under high mass velocities.
This paper presents an experimental study on heat transfer augmentation during convective boiling... more This paper presents an experimental study on heat transfer augmentation during convective boiling of R134a
inside a 15.9 mm ID horizontal tube containing twisted-tape inserts. The use of twisted-tape inserts is a heat transfer
enhancement technique applied on heat exchangers over more than one century ago. However, the heat transfer
augmentation comes together with pressure drop increment, impacting the pumping power and, consequently, the
system efficiency. Moreover, until now it is not clear when the effects on the heat exchanger efficiency of the heat
transfer enhancement overcomes pressure drop penalties. In the present study, pressure drop and heat transfer
coefficient experiments were performed. Experimental results were obtained during flow boiling of R134a for twistedtape
ratios of 3, 4, 9 and 14, mass velocities ranging from 75 to 200 kg / m2 s, heat flux of 10 kW / m2 and saturation
temperatures of 5 and 15 °C. The results obtained lead to the conclusion that higher heat transfer rates can be
achieved using twisted-tape inserts at the expense of a reasonable pressure drop. In addition, a new correlation to
predict the heat transfer coefficients during two-phase flow inside tubes containing twisted-tape inserts is proposed.
The performance of the correlation can be deemed adequate, considering that it compares well with experimental
results of different authors.
This report presents a study on development and analysis of double effect condensing unit vapour ... more This report presents a study on development and analysis of double effect condensing unit vapour compression refrigeration system (DECU VCR system). The system is composed by two refrigeration cycles working with R134a. Tests under a wide range operating temperature interval conditions were carried out on the developed system. Experimental data was generated to observe the performance of the basic VCR system and DECU VCR system for an important parameters such as condensation (35 to 55°C) and evaporation temperatures (-5 to 15°C). Performance evaluation of the system was characterized in terms of cooling capacity and coefficient of performance (COP). In the present study, both COP and refrigerating effect of the developed system have been found, in general, to be greater than the corresponding basic VCR system values, but the degree of enhancement varies depending on the test conditions. Additionally, by using dedicated subcooling cycle, up to 11 and 11.7 % performance improvement ratio of VCR system are observed at evaporation temperature of 15 oC and condensation temperature of 35 oC respectively. It can be concluded that the use of dedicated sub cooling cycle in VCR system is most efficient and suitable for the betterment of thermal system performance.