The Experts below are selected from a list of 1947 Experts worldwide ranked by ideXlab platform
Zahid H. Ayub - One of the best experts on this subject based on the ideXlab platform.
-
Comparison of a conventional flooded evaporator with a shell side direct expansion evaporation of ammonia on a plain tube bundle.
2019Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. AyubAbstract:Shell and tube Heat exchangers are widely used in various industrial refrigeration systems. With recent global warming and ozone depletion concerns it is crucial to develop low charge refrigeration systems with environment friendly natural refrigerants such as ammonia. This paper presents a comparative analysis between a conventional shell and tube flooded evaporator and a low charged direct expansion evaporator with ammonia evaporating on shell side of a triangular pitch plain tube bundle. The saturation temperature was varied between -1.7?C and -20?C with Heat Flux Range of 5 to 45 kW/m2. The degree of superHeat for direct expansion case was varied from 2 to 10 K. The Heat transfer coefficient was observed to increase with an increase in saturation temperature and Heat Flux for both flooded and direct expansion case, while for direct expansion case Heat transfer coefficient was observed to decrease with an increase in the degree of exit superHeat.
-
two phase pressure drop and flow boiling Heat transfer in an enhanced dimpled tube with a solid round rod insert
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Gherhardt Ribatski, Tiago Augusto Moreira, Tariq S. KhanAbstract:Abstract An experimental study was conducted on a 19.05 mm (outer diameter) dimpled enhanced tube to evaluate the in-tube two phase Heat transfer and pressure drop performance in an annular section created between the enhanced tube and a solid round PVC rod. The purpose of the study was to understand the effect of forced early transition to annular flow on the pressure drop and Heat transfer coefficient in a horizontal tube. The refrigerant studied was R-134a at a saturation temperature of 5 °C, Heat Flux Range 2.5 to 15 kW m−2, mass Flux from 80 to 200 kg m−2 s−1 and inlet vapor quality of 0.12 to 0.72. Flow pattern and pressure drop results were obtained under adiabatic conditions. Under similar operating conditions the enhanced tube with a rod exhibited three times higher Heat transfer performance versus same size smooth empty tube with lower pressure drop penalty at lower mas Flux.
-
Experimental study of ammonia flooded boiling on a triangular pitch plain tube bundle
Applied Thermal Engineering, 2017Co-Authors: Ahmad Abbas, Zahid H. AyubAbstract:Abstract Flooded ammonia shell and tube Heat exchangers are widely used in refrigeration systems for various fluid cooling applications. Ammonia as a natural refrigerant with zero Ozone Depletion Potential (ODP) and zero Global Warming Potential (GWP) is getting unprecedented attention due to the current potential phase out of hydroflourocarbons (HFC’s). This paper presents the results of an extensive experimental work on boiling of ammonia in a flooded triangular pitch plain tube bundle evaporator with saturation temperature Range of −1.7 to −20 °C and Heat Flux Range of 5–45 kW/m 2 . These Ranges fall well within the practical operating conditions in the real world industrial refrigeration systems. Heat transfer coefficient showed classical behavior of increase with both saturation temperature and Heat Flux. A correlation for outside boiling in a tube bundle was developed and compared with existing general pool boiling correlations and with limited ammonia boiling data on single plain tubes and bundles. A pass to pass bundle performance was also investigated.
-
Shell side direct expansion evaporation of ammonia on a plain tube bundle with exit superHeat effect
International Journal of Refrigeration, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Ahmad Abbas, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract There are no data available on the direct expansion evaporation of refrigerant on the outside of a tube bundle. With the current ozone depletion and global warming issues it is critical to develop systems with low charge refrigerants especially with natural refrigerants such as ammonia which has zero ozone depletion potential (ODP) and zero global warming potential (GWP). This study presents results of an extensive experimental work on direct expansion of ammonia on a triangular pitch plain tube bundle with saturation temperature Range −1.7 to −20 °C, Heat Flux Range 5 to 45 kW m −2 and exit superHeat Range 2 to 10 °C. The test matrix falls well within the practical operating conditions of industrial refrigeration systems. A typical increase in Heat transfer coefficient was observed with saturation temperature and Heat Flux. The effect of exit super Heat on the overall performance of the bundle was also reported. A correlation for outside boiling on a tube bundle in direct expansion mode was developed and compared with existing single tube pool, flooded bundle boiling and spray evaporation studies.
-
Shell side plain tube bundle performance of a multi-pass direct expansion evaporation of ammonia at various degrees of exit superHeat
International Journal of Refrigeration, 2017Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. Ayub, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract This paper presents the experimental results of shell side dry expansion evaporation characteristics of ammonia on a triangular pitch plain tube bundle in a multi pass cross flow configuration evaporator. Heat exchanger had 4 passes with 3 plain tubes in each pass. The average bundle Heat transfer coefficient showed better performance at −1.7 °C versus −20 °C. Heat transfer performance of individual passes were studied at saturation temperature of −1.7 and −20 °C, Heat Flux Range of 5 to 45 kW m −2 and exit superHeat temperature of 2 to 10 °C. Present data suggest that variation in bundle performance is less significant at lower Heat Fluxes with low degree of exit superHeat. Top pass with maximum quality along the bundle height showed the least performance with increase in the degree of exit superHeat.
Ahmad Abbas - One of the best experts on this subject based on the ideXlab platform.
-
Comparison of a conventional flooded evaporator with a shell side direct expansion evaporation of ammonia on a plain tube bundle.
2019Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. AyubAbstract:Shell and tube Heat exchangers are widely used in various industrial refrigeration systems. With recent global warming and ozone depletion concerns it is crucial to develop low charge refrigeration systems with environment friendly natural refrigerants such as ammonia. This paper presents a comparative analysis between a conventional shell and tube flooded evaporator and a low charged direct expansion evaporator with ammonia evaporating on shell side of a triangular pitch plain tube bundle. The saturation temperature was varied between -1.7?C and -20?C with Heat Flux Range of 5 to 45 kW/m2. The degree of superHeat for direct expansion case was varied from 2 to 10 K. The Heat transfer coefficient was observed to increase with an increase in saturation temperature and Heat Flux for both flooded and direct expansion case, while for direct expansion case Heat transfer coefficient was observed to decrease with an increase in the degree of exit superHeat.
-
Experimental study of ammonia flooded boiling on a triangular pitch plain tube bundle
Applied Thermal Engineering, 2017Co-Authors: Ahmad Abbas, Zahid H. AyubAbstract:Abstract Flooded ammonia shell and tube Heat exchangers are widely used in refrigeration systems for various fluid cooling applications. Ammonia as a natural refrigerant with zero Ozone Depletion Potential (ODP) and zero Global Warming Potential (GWP) is getting unprecedented attention due to the current potential phase out of hydroflourocarbons (HFC’s). This paper presents the results of an extensive experimental work on boiling of ammonia in a flooded triangular pitch plain tube bundle evaporator with saturation temperature Range of −1.7 to −20 °C and Heat Flux Range of 5–45 kW/m 2 . These Ranges fall well within the practical operating conditions in the real world industrial refrigeration systems. Heat transfer coefficient showed classical behavior of increase with both saturation temperature and Heat Flux. A correlation for outside boiling in a tube bundle was developed and compared with existing general pool boiling correlations and with limited ammonia boiling data on single plain tubes and bundles. A pass to pass bundle performance was also investigated.
-
Shell side direct expansion evaporation of ammonia on a plain tube bundle with exit superHeat effect
International Journal of Refrigeration, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Ahmad Abbas, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract There are no data available on the direct expansion evaporation of refrigerant on the outside of a tube bundle. With the current ozone depletion and global warming issues it is critical to develop systems with low charge refrigerants especially with natural refrigerants such as ammonia which has zero ozone depletion potential (ODP) and zero global warming potential (GWP). This study presents results of an extensive experimental work on direct expansion of ammonia on a triangular pitch plain tube bundle with saturation temperature Range −1.7 to −20 °C, Heat Flux Range 5 to 45 kW m −2 and exit superHeat Range 2 to 10 °C. The test matrix falls well within the practical operating conditions of industrial refrigeration systems. A typical increase in Heat transfer coefficient was observed with saturation temperature and Heat Flux. The effect of exit super Heat on the overall performance of the bundle was also reported. A correlation for outside boiling on a tube bundle in direct expansion mode was developed and compared with existing single tube pool, flooded bundle boiling and spray evaporation studies.
-
Shell side plain tube bundle performance of a multi-pass direct expansion evaporation of ammonia at various degrees of exit superHeat
International Journal of Refrigeration, 2017Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. Ayub, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract This paper presents the experimental results of shell side dry expansion evaporation characteristics of ammonia on a triangular pitch plain tube bundle in a multi pass cross flow configuration evaporator. Heat exchanger had 4 passes with 3 plain tubes in each pass. The average bundle Heat transfer coefficient showed better performance at −1.7 °C versus −20 °C. Heat transfer performance of individual passes were studied at saturation temperature of −1.7 and −20 °C, Heat Flux Range of 5 to 45 kW m −2 and exit superHeat temperature of 2 to 10 °C. Present data suggest that variation in bundle performance is less significant at lower Heat Fluxes with low degree of exit superHeat. Top pass with maximum quality along the bundle height showed the least performance with increase in the degree of exit superHeat.
Javed A. Chattha - One of the best experts on this subject based on the ideXlab platform.
-
Shell side direct expansion evaporation of ammonia on a plain tube bundle with exit superHeat effect
International Journal of Refrigeration, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Ahmad Abbas, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract There are no data available on the direct expansion evaporation of refrigerant on the outside of a tube bundle. With the current ozone depletion and global warming issues it is critical to develop systems with low charge refrigerants especially with natural refrigerants such as ammonia which has zero ozone depletion potential (ODP) and zero global warming potential (GWP). This study presents results of an extensive experimental work on direct expansion of ammonia on a triangular pitch plain tube bundle with saturation temperature Range −1.7 to −20 °C, Heat Flux Range 5 to 45 kW m −2 and exit superHeat Range 2 to 10 °C. The test matrix falls well within the practical operating conditions of industrial refrigeration systems. A typical increase in Heat transfer coefficient was observed with saturation temperature and Heat Flux. The effect of exit super Heat on the overall performance of the bundle was also reported. A correlation for outside boiling on a tube bundle in direct expansion mode was developed and compared with existing single tube pool, flooded bundle boiling and spray evaporation studies.
-
Shell side plain tube bundle performance of a multi-pass direct expansion evaporation of ammonia at various degrees of exit superHeat
International Journal of Refrigeration, 2017Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. Ayub, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract This paper presents the experimental results of shell side dry expansion evaporation characteristics of ammonia on a triangular pitch plain tube bundle in a multi pass cross flow configuration evaporator. Heat exchanger had 4 passes with 3 plain tubes in each pass. The average bundle Heat transfer coefficient showed better performance at −1.7 °C versus −20 °C. Heat transfer performance of individual passes were studied at saturation temperature of −1.7 and −20 °C, Heat Flux Range of 5 to 45 kW m −2 and exit superHeat temperature of 2 to 10 °C. Present data suggest that variation in bundle performance is less significant at lower Heat Fluxes with low degree of exit superHeat. Top pass with maximum quality along the bundle height showed the least performance with increase in the degree of exit superHeat.
Adnan H. Ayub - One of the best experts on this subject based on the ideXlab platform.
-
Comparison of a conventional flooded evaporator with a shell side direct expansion evaporation of ammonia on a plain tube bundle.
2019Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. AyubAbstract:Shell and tube Heat exchangers are widely used in various industrial refrigeration systems. With recent global warming and ozone depletion concerns it is crucial to develop low charge refrigeration systems with environment friendly natural refrigerants such as ammonia. This paper presents a comparative analysis between a conventional shell and tube flooded evaporator and a low charged direct expansion evaporator with ammonia evaporating on shell side of a triangular pitch plain tube bundle. The saturation temperature was varied between -1.7?C and -20?C with Heat Flux Range of 5 to 45 kW/m2. The degree of superHeat for direct expansion case was varied from 2 to 10 K. The Heat transfer coefficient was observed to increase with an increase in saturation temperature and Heat Flux for both flooded and direct expansion case, while for direct expansion case Heat transfer coefficient was observed to decrease with an increase in the degree of exit superHeat.
-
two phase pressure drop and flow boiling Heat transfer in an enhanced dimpled tube with a solid round rod insert
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Gherhardt Ribatski, Tiago Augusto Moreira, Tariq S. KhanAbstract:Abstract An experimental study was conducted on a 19.05 mm (outer diameter) dimpled enhanced tube to evaluate the in-tube two phase Heat transfer and pressure drop performance in an annular section created between the enhanced tube and a solid round PVC rod. The purpose of the study was to understand the effect of forced early transition to annular flow on the pressure drop and Heat transfer coefficient in a horizontal tube. The refrigerant studied was R-134a at a saturation temperature of 5 °C, Heat Flux Range 2.5 to 15 kW m−2, mass Flux from 80 to 200 kg m−2 s−1 and inlet vapor quality of 0.12 to 0.72. Flow pattern and pressure drop results were obtained under adiabatic conditions. Under similar operating conditions the enhanced tube with a rod exhibited three times higher Heat transfer performance versus same size smooth empty tube with lower pressure drop penalty at lower mas Flux.
-
Shell side direct expansion evaporation of ammonia on a plain tube bundle with exit superHeat effect
International Journal of Refrigeration, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Ahmad Abbas, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract There are no data available on the direct expansion evaporation of refrigerant on the outside of a tube bundle. With the current ozone depletion and global warming issues it is critical to develop systems with low charge refrigerants especially with natural refrigerants such as ammonia which has zero ozone depletion potential (ODP) and zero global warming potential (GWP). This study presents results of an extensive experimental work on direct expansion of ammonia on a triangular pitch plain tube bundle with saturation temperature Range −1.7 to −20 °C, Heat Flux Range 5 to 45 kW m −2 and exit superHeat Range 2 to 10 °C. The test matrix falls well within the practical operating conditions of industrial refrigeration systems. A typical increase in Heat transfer coefficient was observed with saturation temperature and Heat Flux. The effect of exit super Heat on the overall performance of the bundle was also reported. A correlation for outside boiling on a tube bundle in direct expansion mode was developed and compared with existing single tube pool, flooded bundle boiling and spray evaporation studies.
-
Shell side plain tube bundle performance of a multi-pass direct expansion evaporation of ammonia at various degrees of exit superHeat
International Journal of Refrigeration, 2017Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. Ayub, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract This paper presents the experimental results of shell side dry expansion evaporation characteristics of ammonia on a triangular pitch plain tube bundle in a multi pass cross flow configuration evaporator. Heat exchanger had 4 passes with 3 plain tubes in each pass. The average bundle Heat transfer coefficient showed better performance at −1.7 °C versus −20 °C. Heat transfer performance of individual passes were studied at saturation temperature of −1.7 and −20 °C, Heat Flux Range of 5 to 45 kW m −2 and exit superHeat temperature of 2 to 10 °C. Present data suggest that variation in bundle performance is less significant at lower Heat Fluxes with low degree of exit superHeat. Top pass with maximum quality along the bundle height showed the least performance with increase in the degree of exit superHeat.
Tariq S. Khan - One of the best experts on this subject based on the ideXlab platform.
-
two phase pressure drop and flow boiling Heat transfer in an enhanced dimpled tube with a solid round rod insert
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Gherhardt Ribatski, Tiago Augusto Moreira, Tariq S. KhanAbstract:Abstract An experimental study was conducted on a 19.05 mm (outer diameter) dimpled enhanced tube to evaluate the in-tube two phase Heat transfer and pressure drop performance in an annular section created between the enhanced tube and a solid round PVC rod. The purpose of the study was to understand the effect of forced early transition to annular flow on the pressure drop and Heat transfer coefficient in a horizontal tube. The refrigerant studied was R-134a at a saturation temperature of 5 °C, Heat Flux Range 2.5 to 15 kW m−2, mass Flux from 80 to 200 kg m−2 s−1 and inlet vapor quality of 0.12 to 0.72. Flow pattern and pressure drop results were obtained under adiabatic conditions. Under similar operating conditions the enhanced tube with a rod exhibited three times higher Heat transfer performance versus same size smooth empty tube with lower pressure drop penalty at lower mas Flux.
-
Shell side direct expansion evaporation of ammonia on a plain tube bundle with exit superHeat effect
International Journal of Refrigeration, 2017Co-Authors: Zahid H. Ayub, Adnan H. Ayub, Ahmad Abbas, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract There are no data available on the direct expansion evaporation of refrigerant on the outside of a tube bundle. With the current ozone depletion and global warming issues it is critical to develop systems with low charge refrigerants especially with natural refrigerants such as ammonia which has zero ozone depletion potential (ODP) and zero global warming potential (GWP). This study presents results of an extensive experimental work on direct expansion of ammonia on a triangular pitch plain tube bundle with saturation temperature Range −1.7 to −20 °C, Heat Flux Range 5 to 45 kW m −2 and exit superHeat Range 2 to 10 °C. The test matrix falls well within the practical operating conditions of industrial refrigeration systems. A typical increase in Heat transfer coefficient was observed with saturation temperature and Heat Flux. The effect of exit super Heat on the overall performance of the bundle was also reported. A correlation for outside boiling on a tube bundle in direct expansion mode was developed and compared with existing single tube pool, flooded bundle boiling and spray evaporation studies.
-
Shell side plain tube bundle performance of a multi-pass direct expansion evaporation of ammonia at various degrees of exit superHeat
International Journal of Refrigeration, 2017Co-Authors: Ahmad Abbas, Zahid H. Ayub, Adnan H. Ayub, Tariq S. Khan, Javed A. ChatthaAbstract:Abstract This paper presents the experimental results of shell side dry expansion evaporation characteristics of ammonia on a triangular pitch plain tube bundle in a multi pass cross flow configuration evaporator. Heat exchanger had 4 passes with 3 plain tubes in each pass. The average bundle Heat transfer coefficient showed better performance at −1.7 °C versus −20 °C. Heat transfer performance of individual passes were studied at saturation temperature of −1.7 and −20 °C, Heat Flux Range of 5 to 45 kW m −2 and exit superHeat temperature of 2 to 10 °C. Present data suggest that variation in bundle performance is less significant at lower Heat Fluxes with low degree of exit superHeat. Top pass with maximum quality along the bundle height showed the least performance with increase in the degree of exit superHeat.
