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Adel O. Sharif - One of the best experts on this subject based on the ideXlab platform.

  • Measuring the Overall Volumetric Heat Transfer Coefficient in a Vapor-Liquid–Liquid Three-Phase Direct Contact Heat Exchanger
    Heat Transfer Engineering, 2017
    Co-Authors: Hameed B. Mahood, Rex B. Thorpe, Alasdair N. Campbell, Adel O. Sharif
    Abstract:

    An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct Contact Condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct Contact condensation height. Pentane vapour at three different initial temperatures (40°C, 43.5°C and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.

  • HEAT TRANSFER MODELLING OF TWO-PHASE BUBBLES SWARM CONDENSING IN THREE-PHASE DIRECT-Contact Condenser
    Thermal Science, 2016
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Sami Al-ailbi, Ali Hossini, Rex B. Thorpe
    Abstract:

    An analytical model for the convective heat transfer coefficient and the two-phase bubble size of a three-phase direct Contact heat exchanger was developed. Until the present, there has only been a theoretical model available that deals with a single two-phase bubble and a bubble train condensation in an immiscible liquid. However, to understand the actual heat transfer process within the three-phase direct Contact Condenser, characteristic models are required. A quasi - steady energy equation in a spherical coordinate system with a potential flow assumption and a cell model configuration has been simplified and solved analytically. The convective heat transfer in terms of Nu number has been derived, and it was found to be a function to Pe number and a system void fraction. In addition, the two-phase bubble size relates to the system void fraction and has been developed by solving a simple energy balance equation and using the derived convective heat transfer coefficient expression. Furthermore, the model correlates well with previous experimental data and theoretical results.

  • Heat transfer measurement in a three-phase direct-Contact Condenser under flooding conditions
    Applied Thermal Engineering, 2016
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    Abstract The transient temperature distribution and volumetric heat transfer coefficient during the inception of flooding in a three-phase bubble type direct Contact Condenser have been experimentally investigated. The flooding mechanism and the factors affecting the onset of flooding of the three-phase direct Contact column are not considered. A short Perspex column of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. Pentane vapour with initial temperatures of 40 °C, 43.5 °C and 47.5 °C was the dispersed phase and tap water at a constant temperature (19 °C) was the continuous phase. Only 48 cm of the column was used as the active height and different mass flow rates of both phases were used. The experimental results showed that the instantaneous temperature distribution along the direct Contact column tends to be uniform when the direct Contact column is working under flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the dispersed mass flow rate is increased towards the flooding limit and remains constant along the column height. In addition, the dispersed phase mass flow rate that leads to flooding increased with increasing mass flow rate of the continuous phase. The initial temperature of the dispersed phase did not have a considerable effect on the flooding inception limit under the present experimental conditions.

  • Flooding Limitations in a Three-Phase Direct Contact Condenser for the Utilisation of Low-Grade Energy Sources for Desalination and Power Generation Application
    Qatar Foundation Annual Research Conference Proceedings Volume 2016 Issue 1, 2016
    Co-Authors: Adel O. Sharif, Hameed B. Mahood Al-muhammedawi, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    The continuing enhancement of energy recovery cycles that exploit low grade energy resources requires an efficient heat absorption and rejection system. Implementation of a conventional surface type heat exchanger, evaporator or Condenser has many disadvantages. The low efficiency, fouling, corrosion problems, high cost and high heat transfer resistance are the most important shortcomings that emerge as a result of the metallic barriers involved. On the other hand, a direct Contact heat transfer device offers a high heat transfer area and reduces or eliminates fouling and corrosion problems. They can also work with very low temperature differences and subsequently can enhance the cycle efficiency. Direct Contact heat exchangers clearly have many advantages over surface type heat exchangers and can also be efficiently used in places where the surface heat exchanger cannot be. Accordingly, direct Contact heat exchanger can be found in different applications, such as water desalination and power generation from geothermal brine. Water desalination utilising direct Contact heat exchangers can be achieved by two general methods: direct Contact freezing-melting and direct Contact evaporation- condensation. The former is based on the ability to remove water from a solution by freezing it out as crystalline ice. The ice or crystal should contain only pure water; therefore the partial freezing separates the fresh water from brine. The ice melts at another stage to produce distilled water. Direct Contact freezing exploits the concept of direct Contact evaporation of a low boiling point working fluid by absorbing heat from surrounding continuous fluid (water). The heat absorbed by the working fluid; which causes the water to freeze, is equivalent to the energy required to melt the ice. The working fluid used must have a low boiling point and a high freezing point along with other properties mentioned above. Refrigerants such as carbon dioxide and butane are widely used as a working fluid. For second application, the most common application of direct Contact heat exchangers is in the generation of electricity from hot geothermal brine, utilising low boiling point fluids and the conventional Rankine cycle. The first plant utilising a spray column, which produces 500 k. We was designed by Barber-Nichols Engineering and installed at the East Mesa Geothermal Field in the U.S. in 1980. The spray column was 12 m in length and 1 m diameter. Hot brine is flashed to remove the non-condensable gases before entering the spray column from the top, while the isopentane liquid is injected in to the bottom of the column through a suitable distributer. Direct Contact counter-current heat transfer between the two fluids takes place throughout the column height. According to the density difference, isopentane drops/bubbles rise upward with brine falling down and exiting the column at the bottom after being cooled down. On the other hand, isopentane heats up as a result of absorbing heat from the brine, and leaves the column as a superheated vapour from the top of the column. Isopentane vapour expands through a turbine to produce electricity, is liquefied in a Condenser, and sent back to the direct Contact heat exchanger again. For a bubble type three-phase direct Contact Condenser, it is widely reported that its performance is characterised by a volumetric heat transfer coefficient, which is directly proportional to the holdup ratio in the column. It is both economical and practical for the bubble type direct Contact Condenser to operate at the maximum possible holdup ratio. This, of course, increases the possibility of flooding, which considerably impairs the performance of the column. Flooding can be either defined as the case when the continuous phase is completely held up by the dispersed phase or the dispersed phase is swept backward by the continuous phase. Two mechanisms could lead to the inception of flooding in the three direct Contact columns, depending on the critical velocity of each individual phase. The critical velocity can be defined as a maximum velocity that can be achieved by a given direct Contact system and it is a function of the bubble size, the flow rate and the physical properties of the phases. The first mechanism depends on the reduction in the dispersed phase (bubbles) upward velocity due to the interactions within a swarm of two-phase bubbles. The two-phase bubbles move closer together when the dispersed phase flow rate increases, which results in a further dispersed phase slowing. Bubbles are swept down and drain out with the continuous phase from the bottom of the column. Therefore, the danger from this form of flooding form is the increased loss of the working fluid. The second scenario assumes that the continuous phase is swept upwards because of a high dispersed phase flow rate. This occurs when the dispersed phase velocity passes the critical velocity. The result of this flooding type lies in a change of geometry and makes the heat transfer relationships available invalid. Accordingly, flooding can be defined as the case when the continuous phase is completely held up by the dispersed phase or the dispersed phase is swept backward by the continuous phase. As the first time, experiments to study the limitation of flooding inception of three-phase direct Contact Condenser have been carried out in a counter-current small diameter vertical Condenser. The total column height was 70 cm and 4 cm diameter. Only 48 cm has been used as an active three-phase direct Contact Condenser height. Vapour pentane with three different initial temperatures (40°, 43.5° and 47.5°) and water with a constant temperature (19°) have been used as a dispersed phase and a continuous phase respectively. Five different continuous phase mass flow rate and four different dispersed phase mass flow rate have been tested throughout the experiments. The experimental results showed that the effect of dispersed phase initial temperature on flooding inception to be insignificant at low continuous phase velocity (v_L^(*1/2).

  • Heat Transfer Measurements in a Three-Phase Direct Contact Condenser for Energy Production and Water Desalination
    2015
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    An experimental investigation of heat exchange in a three-phase direct Contact Condenser was carried out using a 70-cm-high Perspex tube with a 4-cm inner diameter. The active direct Contact Condenser comprised 48 cm. Pentane vapour at three initial temperatures (40℃,43.5℃, and 47.5℃) and water at a constant temperature (19℃) were used as the dispersed and continuous phases, respectively, with different mass flow rate ratios. The results showed that the continuous phase outlet temperature increased with increasing mass flow rate ratio. On the contrary, the continuous phase temperature decreased with increases in the continuous mass flow rate. The initial temperature of the dispersed phase slightly affected the direct Contact Condenser output, which confirms a latent phase effect in this type of heat exchanger.

Hameed B. Mahood - One of the best experts on this subject based on the ideXlab platform.

  • Convective heat transfer measurements in a vapour-liquid-liquid three-phase direct Contact heat exchanger
    Heat and Mass Transfer, 2018
    Co-Authors: Hameed B. Mahood, Alasdair N. Campbell, Ali Sh. Baqir, A. O. Sharif, R. B. Thorpe
    Abstract:

    Energy usage is increasing around the world due to the continued development of technology, and population growth. Solar energy is a promising low-grade energy resource that can be harvested and utilised in different applications, such solar heater systems, which are used in both domestic and industrial settings. However, the implementation of an efficient energy conversion system or heat exchanger would enhance such low-grade energy processes. The direct Contact heat exchanger could be the right choice due to its ability to efficiently transfer significant amounts of heat, simple design, and low cost. In this work, the heat transfer associated with the direct Contact condensation of pentane vapour bubbles in a three-phase direct Contact Condenser is investigated experimentally. Such a Condenser could be used in a cycle with a solar water heater and heat recovery systems. The experiments on the steady state operation of the three-phase direct Contact Condenser were carried out using a short Perspex tube of 70 cm in total height and an internal diameter of 4 cm. Only a height of 48 cm was active as the direct Contact Condenser. Pentane vapour, (the dispersed phase) with three different initial temperatures (40^° C , 43.5^° C and 47.5^° C ) was directly Contacted with water (the continuous phase) at 19^° C . The experimental results showed that the total heat transfer rate per unit volume along the direct Contact Condenser gradually decreased upon moving higher up the Condenser. Additionally, the heat transfer rate increases with increasing mass flow rate ratio, but no significant effect on the heat transfer rate of varying the initial temperature of the dispersed phase was seen. Furthermore, both the outlet temperature of the continuous phase and the void fraction were positively correlated with the total heat transfer rate per unit volume, with no considerable effect of the initial temperature difference between the dispersed and continuous phases.

  • Measuring the Overall Volumetric Heat Transfer Coefficient in a Vapor-Liquid–Liquid Three-Phase Direct Contact Heat Exchanger
    Heat Transfer Engineering, 2017
    Co-Authors: Hameed B. Mahood, Rex B. Thorpe, Alasdair N. Campbell, Adel O. Sharif
    Abstract:

    An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct Contact Condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct Contact condensation height. Pentane vapour at three different initial temperatures (40°C, 43.5°C and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.

  • HEAT TRANSFER MODELLING OF TWO-PHASE BUBBLES SWARM CONDENSING IN THREE-PHASE DIRECT-Contact Condenser
    Thermal Science, 2016
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Sami Al-ailbi, Ali Hossini, Rex B. Thorpe
    Abstract:

    An analytical model for the convective heat transfer coefficient and the two-phase bubble size of a three-phase direct Contact heat exchanger was developed. Until the present, there has only been a theoretical model available that deals with a single two-phase bubble and a bubble train condensation in an immiscible liquid. However, to understand the actual heat transfer process within the three-phase direct Contact Condenser, characteristic models are required. A quasi - steady energy equation in a spherical coordinate system with a potential flow assumption and a cell model configuration has been simplified and solved analytically. The convective heat transfer in terms of Nu number has been derived, and it was found to be a function to Pe number and a system void fraction. In addition, the two-phase bubble size relates to the system void fraction and has been developed by solving a simple energy balance equation and using the derived convective heat transfer coefficient expression. Furthermore, the model correlates well with previous experimental data and theoretical results.

  • Heat transfer measurement in a three-phase direct-Contact Condenser under flooding conditions
    Applied Thermal Engineering, 2016
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    Abstract The transient temperature distribution and volumetric heat transfer coefficient during the inception of flooding in a three-phase bubble type direct Contact Condenser have been experimentally investigated. The flooding mechanism and the factors affecting the onset of flooding of the three-phase direct Contact column are not considered. A short Perspex column of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. Pentane vapour with initial temperatures of 40 °C, 43.5 °C and 47.5 °C was the dispersed phase and tap water at a constant temperature (19 °C) was the continuous phase. Only 48 cm of the column was used as the active height and different mass flow rates of both phases were used. The experimental results showed that the instantaneous temperature distribution along the direct Contact column tends to be uniform when the direct Contact column is working under flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the dispersed mass flow rate is increased towards the flooding limit and remains constant along the column height. In addition, the dispersed phase mass flow rate that leads to flooding increased with increasing mass flow rate of the continuous phase. The initial temperature of the dispersed phase did not have a considerable effect on the flooding inception limit under the present experimental conditions.

  • Heat Transfer Measurements in a Three-Phase Direct Contact Condenser for Energy Production and Water Desalination
    2015
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    An experimental investigation of heat exchange in a three-phase direct Contact Condenser was carried out using a 70-cm-high Perspex tube with a 4-cm inner diameter. The active direct Contact Condenser comprised 48 cm. Pentane vapour at three initial temperatures (40℃,43.5℃, and 47.5℃) and water at a constant temperature (19℃) were used as the dispersed and continuous phases, respectively, with different mass flow rate ratios. The results showed that the continuous phase outlet temperature increased with increasing mass flow rate ratio. On the contrary, the continuous phase temperature decreased with increases in the continuous mass flow rate. The initial temperature of the dispersed phase slightly affected the direct Contact Condenser output, which confirms a latent phase effect in this type of heat exchanger.

Rex B. Thorpe - One of the best experts on this subject based on the ideXlab platform.

  • Measuring the Overall Volumetric Heat Transfer Coefficient in a Vapor-Liquid–Liquid Three-Phase Direct Contact Heat Exchanger
    Heat Transfer Engineering, 2017
    Co-Authors: Hameed B. Mahood, Rex B. Thorpe, Alasdair N. Campbell, Adel O. Sharif
    Abstract:

    An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct Contact Condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct Contact condensation height. Pentane vapour at three different initial temperatures (40°C, 43.5°C and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.

  • HEAT TRANSFER MODELLING OF TWO-PHASE BUBBLES SWARM CONDENSING IN THREE-PHASE DIRECT-Contact Condenser
    Thermal Science, 2016
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Sami Al-ailbi, Ali Hossini, Rex B. Thorpe
    Abstract:

    An analytical model for the convective heat transfer coefficient and the two-phase bubble size of a three-phase direct Contact heat exchanger was developed. Until the present, there has only been a theoretical model available that deals with a single two-phase bubble and a bubble train condensation in an immiscible liquid. However, to understand the actual heat transfer process within the three-phase direct Contact Condenser, characteristic models are required. A quasi - steady energy equation in a spherical coordinate system with a potential flow assumption and a cell model configuration has been simplified and solved analytically. The convective heat transfer in terms of Nu number has been derived, and it was found to be a function to Pe number and a system void fraction. In addition, the two-phase bubble size relates to the system void fraction and has been developed by solving a simple energy balance equation and using the derived convective heat transfer coefficient expression. Furthermore, the model correlates well with previous experimental data and theoretical results.

  • Heat transfer measurement in a three-phase direct-Contact Condenser under flooding conditions
    Applied Thermal Engineering, 2016
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    Abstract The transient temperature distribution and volumetric heat transfer coefficient during the inception of flooding in a three-phase bubble type direct Contact Condenser have been experimentally investigated. The flooding mechanism and the factors affecting the onset of flooding of the three-phase direct Contact column are not considered. A short Perspex column of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. Pentane vapour with initial temperatures of 40 °C, 43.5 °C and 47.5 °C was the dispersed phase and tap water at a constant temperature (19 °C) was the continuous phase. Only 48 cm of the column was used as the active height and different mass flow rates of both phases were used. The experimental results showed that the instantaneous temperature distribution along the direct Contact column tends to be uniform when the direct Contact column is working under flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the dispersed mass flow rate is increased towards the flooding limit and remains constant along the column height. In addition, the dispersed phase mass flow rate that leads to flooding increased with increasing mass flow rate of the continuous phase. The initial temperature of the dispersed phase did not have a considerable effect on the flooding inception limit under the present experimental conditions.

  • Flooding Limitations in a Three-Phase Direct Contact Condenser for the Utilisation of Low-Grade Energy Sources for Desalination and Power Generation Application
    Qatar Foundation Annual Research Conference Proceedings Volume 2016 Issue 1, 2016
    Co-Authors: Adel O. Sharif, Hameed B. Mahood Al-muhammedawi, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    The continuing enhancement of energy recovery cycles that exploit low grade energy resources requires an efficient heat absorption and rejection system. Implementation of a conventional surface type heat exchanger, evaporator or Condenser has many disadvantages. The low efficiency, fouling, corrosion problems, high cost and high heat transfer resistance are the most important shortcomings that emerge as a result of the metallic barriers involved. On the other hand, a direct Contact heat transfer device offers a high heat transfer area and reduces or eliminates fouling and corrosion problems. They can also work with very low temperature differences and subsequently can enhance the cycle efficiency. Direct Contact heat exchangers clearly have many advantages over surface type heat exchangers and can also be efficiently used in places where the surface heat exchanger cannot be. Accordingly, direct Contact heat exchanger can be found in different applications, such as water desalination and power generation from geothermal brine. Water desalination utilising direct Contact heat exchangers can be achieved by two general methods: direct Contact freezing-melting and direct Contact evaporation- condensation. The former is based on the ability to remove water from a solution by freezing it out as crystalline ice. The ice or crystal should contain only pure water; therefore the partial freezing separates the fresh water from brine. The ice melts at another stage to produce distilled water. Direct Contact freezing exploits the concept of direct Contact evaporation of a low boiling point working fluid by absorbing heat from surrounding continuous fluid (water). The heat absorbed by the working fluid; which causes the water to freeze, is equivalent to the energy required to melt the ice. The working fluid used must have a low boiling point and a high freezing point along with other properties mentioned above. Refrigerants such as carbon dioxide and butane are widely used as a working fluid. For second application, the most common application of direct Contact heat exchangers is in the generation of electricity from hot geothermal brine, utilising low boiling point fluids and the conventional Rankine cycle. The first plant utilising a spray column, which produces 500 k. We was designed by Barber-Nichols Engineering and installed at the East Mesa Geothermal Field in the U.S. in 1980. The spray column was 12 m in length and 1 m diameter. Hot brine is flashed to remove the non-condensable gases before entering the spray column from the top, while the isopentane liquid is injected in to the bottom of the column through a suitable distributer. Direct Contact counter-current heat transfer between the two fluids takes place throughout the column height. According to the density difference, isopentane drops/bubbles rise upward with brine falling down and exiting the column at the bottom after being cooled down. On the other hand, isopentane heats up as a result of absorbing heat from the brine, and leaves the column as a superheated vapour from the top of the column. Isopentane vapour expands through a turbine to produce electricity, is liquefied in a Condenser, and sent back to the direct Contact heat exchanger again. For a bubble type three-phase direct Contact Condenser, it is widely reported that its performance is characterised by a volumetric heat transfer coefficient, which is directly proportional to the holdup ratio in the column. It is both economical and practical for the bubble type direct Contact Condenser to operate at the maximum possible holdup ratio. This, of course, increases the possibility of flooding, which considerably impairs the performance of the column. Flooding can be either defined as the case when the continuous phase is completely held up by the dispersed phase or the dispersed phase is swept backward by the continuous phase. Two mechanisms could lead to the inception of flooding in the three direct Contact columns, depending on the critical velocity of each individual phase. The critical velocity can be defined as a maximum velocity that can be achieved by a given direct Contact system and it is a function of the bubble size, the flow rate and the physical properties of the phases. The first mechanism depends on the reduction in the dispersed phase (bubbles) upward velocity due to the interactions within a swarm of two-phase bubbles. The two-phase bubbles move closer together when the dispersed phase flow rate increases, which results in a further dispersed phase slowing. Bubbles are swept down and drain out with the continuous phase from the bottom of the column. Therefore, the danger from this form of flooding form is the increased loss of the working fluid. The second scenario assumes that the continuous phase is swept upwards because of a high dispersed phase flow rate. This occurs when the dispersed phase velocity passes the critical velocity. The result of this flooding type lies in a change of geometry and makes the heat transfer relationships available invalid. Accordingly, flooding can be defined as the case when the continuous phase is completely held up by the dispersed phase or the dispersed phase is swept backward by the continuous phase. As the first time, experiments to study the limitation of flooding inception of three-phase direct Contact Condenser have been carried out in a counter-current small diameter vertical Condenser. The total column height was 70 cm and 4 cm diameter. Only 48 cm has been used as an active three-phase direct Contact Condenser height. Vapour pentane with three different initial temperatures (40°, 43.5° and 47.5°) and water with a constant temperature (19°) have been used as a dispersed phase and a continuous phase respectively. Five different continuous phase mass flow rate and four different dispersed phase mass flow rate have been tested throughout the experiments. The experimental results showed that the effect of dispersed phase initial temperature on flooding inception to be insignificant at low continuous phase velocity (v_L^(*1/2).

  • Heat Transfer Measurements in a Three-Phase Direct Contact Condenser for Energy Production and Water Desalination
    2015
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    An experimental investigation of heat exchange in a three-phase direct Contact Condenser was carried out using a 70-cm-high Perspex tube with a 4-cm inner diameter. The active direct Contact Condenser comprised 48 cm. Pentane vapour at three initial temperatures (40℃,43.5℃, and 47.5℃) and water at a constant temperature (19℃) were used as the dispersed and continuous phases, respectively, with different mass flow rate ratios. The results showed that the continuous phase outlet temperature increased with increasing mass flow rate ratio. On the contrary, the continuous phase temperature decreased with increases in the continuous mass flow rate. The initial temperature of the dispersed phase slightly affected the direct Contact Condenser output, which confirms a latent phase effect in this type of heat exchanger.

Alasdair N. Campbell - One of the best experts on this subject based on the ideXlab platform.

  • Convective heat transfer measurements in a vapour-liquid-liquid three-phase direct Contact heat exchanger
    Heat and Mass Transfer, 2018
    Co-Authors: Hameed B. Mahood, Alasdair N. Campbell, Ali Sh. Baqir, A. O. Sharif, R. B. Thorpe
    Abstract:

    Energy usage is increasing around the world due to the continued development of technology, and population growth. Solar energy is a promising low-grade energy resource that can be harvested and utilised in different applications, such solar heater systems, which are used in both domestic and industrial settings. However, the implementation of an efficient energy conversion system or heat exchanger would enhance such low-grade energy processes. The direct Contact heat exchanger could be the right choice due to its ability to efficiently transfer significant amounts of heat, simple design, and low cost. In this work, the heat transfer associated with the direct Contact condensation of pentane vapour bubbles in a three-phase direct Contact Condenser is investigated experimentally. Such a Condenser could be used in a cycle with a solar water heater and heat recovery systems. The experiments on the steady state operation of the three-phase direct Contact Condenser were carried out using a short Perspex tube of 70 cm in total height and an internal diameter of 4 cm. Only a height of 48 cm was active as the direct Contact Condenser. Pentane vapour, (the dispersed phase) with three different initial temperatures (40^° C , 43.5^° C and 47.5^° C ) was directly Contacted with water (the continuous phase) at 19^° C . The experimental results showed that the total heat transfer rate per unit volume along the direct Contact Condenser gradually decreased upon moving higher up the Condenser. Additionally, the heat transfer rate increases with increasing mass flow rate ratio, but no significant effect on the heat transfer rate of varying the initial temperature of the dispersed phase was seen. Furthermore, both the outlet temperature of the continuous phase and the void fraction were positively correlated with the total heat transfer rate per unit volume, with no considerable effect of the initial temperature difference between the dispersed and continuous phases.

  • Measuring the Overall Volumetric Heat Transfer Coefficient in a Vapor-Liquid–Liquid Three-Phase Direct Contact Heat Exchanger
    Heat Transfer Engineering, 2017
    Co-Authors: Hameed B. Mahood, Rex B. Thorpe, Alasdair N. Campbell, Adel O. Sharif
    Abstract:

    An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct Contact Condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct Contact condensation height. Pentane vapour at three different initial temperatures (40°C, 43.5°C and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.

  • Heat transfer measurement in a three-phase direct-Contact Condenser under flooding conditions
    Applied Thermal Engineering, 2016
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    Abstract The transient temperature distribution and volumetric heat transfer coefficient during the inception of flooding in a three-phase bubble type direct Contact Condenser have been experimentally investigated. The flooding mechanism and the factors affecting the onset of flooding of the three-phase direct Contact column are not considered. A short Perspex column of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. Pentane vapour with initial temperatures of 40 °C, 43.5 °C and 47.5 °C was the dispersed phase and tap water at a constant temperature (19 °C) was the continuous phase. Only 48 cm of the column was used as the active height and different mass flow rates of both phases were used. The experimental results showed that the instantaneous temperature distribution along the direct Contact column tends to be uniform when the direct Contact column is working under flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the dispersed mass flow rate is increased towards the flooding limit and remains constant along the column height. In addition, the dispersed phase mass flow rate that leads to flooding increased with increasing mass flow rate of the continuous phase. The initial temperature of the dispersed phase did not have a considerable effect on the flooding inception limit under the present experimental conditions.

  • Flooding Limitations in a Three-Phase Direct Contact Condenser for the Utilisation of Low-Grade Energy Sources for Desalination and Power Generation Application
    Qatar Foundation Annual Research Conference Proceedings Volume 2016 Issue 1, 2016
    Co-Authors: Adel O. Sharif, Hameed B. Mahood Al-muhammedawi, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    The continuing enhancement of energy recovery cycles that exploit low grade energy resources requires an efficient heat absorption and rejection system. Implementation of a conventional surface type heat exchanger, evaporator or Condenser has many disadvantages. The low efficiency, fouling, corrosion problems, high cost and high heat transfer resistance are the most important shortcomings that emerge as a result of the metallic barriers involved. On the other hand, a direct Contact heat transfer device offers a high heat transfer area and reduces or eliminates fouling and corrosion problems. They can also work with very low temperature differences and subsequently can enhance the cycle efficiency. Direct Contact heat exchangers clearly have many advantages over surface type heat exchangers and can also be efficiently used in places where the surface heat exchanger cannot be. Accordingly, direct Contact heat exchanger can be found in different applications, such as water desalination and power generation from geothermal brine. Water desalination utilising direct Contact heat exchangers can be achieved by two general methods: direct Contact freezing-melting and direct Contact evaporation- condensation. The former is based on the ability to remove water from a solution by freezing it out as crystalline ice. The ice or crystal should contain only pure water; therefore the partial freezing separates the fresh water from brine. The ice melts at another stage to produce distilled water. Direct Contact freezing exploits the concept of direct Contact evaporation of a low boiling point working fluid by absorbing heat from surrounding continuous fluid (water). The heat absorbed by the working fluid; which causes the water to freeze, is equivalent to the energy required to melt the ice. The working fluid used must have a low boiling point and a high freezing point along with other properties mentioned above. Refrigerants such as carbon dioxide and butane are widely used as a working fluid. For second application, the most common application of direct Contact heat exchangers is in the generation of electricity from hot geothermal brine, utilising low boiling point fluids and the conventional Rankine cycle. The first plant utilising a spray column, which produces 500 k. We was designed by Barber-Nichols Engineering and installed at the East Mesa Geothermal Field in the U.S. in 1980. The spray column was 12 m in length and 1 m diameter. Hot brine is flashed to remove the non-condensable gases before entering the spray column from the top, while the isopentane liquid is injected in to the bottom of the column through a suitable distributer. Direct Contact counter-current heat transfer between the two fluids takes place throughout the column height. According to the density difference, isopentane drops/bubbles rise upward with brine falling down and exiting the column at the bottom after being cooled down. On the other hand, isopentane heats up as a result of absorbing heat from the brine, and leaves the column as a superheated vapour from the top of the column. Isopentane vapour expands through a turbine to produce electricity, is liquefied in a Condenser, and sent back to the direct Contact heat exchanger again. For a bubble type three-phase direct Contact Condenser, it is widely reported that its performance is characterised by a volumetric heat transfer coefficient, which is directly proportional to the holdup ratio in the column. It is both economical and practical for the bubble type direct Contact Condenser to operate at the maximum possible holdup ratio. This, of course, increases the possibility of flooding, which considerably impairs the performance of the column. Flooding can be either defined as the case when the continuous phase is completely held up by the dispersed phase or the dispersed phase is swept backward by the continuous phase. Two mechanisms could lead to the inception of flooding in the three direct Contact columns, depending on the critical velocity of each individual phase. The critical velocity can be defined as a maximum velocity that can be achieved by a given direct Contact system and it is a function of the bubble size, the flow rate and the physical properties of the phases. The first mechanism depends on the reduction in the dispersed phase (bubbles) upward velocity due to the interactions within a swarm of two-phase bubbles. The two-phase bubbles move closer together when the dispersed phase flow rate increases, which results in a further dispersed phase slowing. Bubbles are swept down and drain out with the continuous phase from the bottom of the column. Therefore, the danger from this form of flooding form is the increased loss of the working fluid. The second scenario assumes that the continuous phase is swept upwards because of a high dispersed phase flow rate. This occurs when the dispersed phase velocity passes the critical velocity. The result of this flooding type lies in a change of geometry and makes the heat transfer relationships available invalid. Accordingly, flooding can be defined as the case when the continuous phase is completely held up by the dispersed phase or the dispersed phase is swept backward by the continuous phase. As the first time, experiments to study the limitation of flooding inception of three-phase direct Contact Condenser have been carried out in a counter-current small diameter vertical Condenser. The total column height was 70 cm and 4 cm diameter. Only 48 cm has been used as an active three-phase direct Contact Condenser height. Vapour pentane with three different initial temperatures (40°, 43.5° and 47.5°) and water with a constant temperature (19°) have been used as a dispersed phase and a continuous phase respectively. Five different continuous phase mass flow rate and four different dispersed phase mass flow rate have been tested throughout the experiments. The experimental results showed that the effect of dispersed phase initial temperature on flooding inception to be insignificant at low continuous phase velocity (v_L^(*1/2).

  • Heat Transfer Measurements in a Three-Phase Direct Contact Condenser for Energy Production and Water Desalination
    2015
    Co-Authors: Hameed B. Mahood, Adel O. Sharif, Alasdair N. Campbell, Rex B. Thorpe
    Abstract:

    An experimental investigation of heat exchange in a three-phase direct Contact Condenser was carried out using a 70-cm-high Perspex tube with a 4-cm inner diameter. The active direct Contact Condenser comprised 48 cm. Pentane vapour at three initial temperatures (40℃,43.5℃, and 47.5℃) and water at a constant temperature (19℃) were used as the dispersed and continuous phases, respectively, with different mass flow rate ratios. The results showed that the continuous phase outlet temperature increased with increasing mass flow rate ratio. On the contrary, the continuous phase temperature decreased with increases in the continuous mass flow rate. The initial temperature of the dispersed phase slightly affected the direct Contact Condenser output, which confirms a latent phase effect in this type of heat exchanger.

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  • MODELING OF INTERFACIAL TRANSPORT PROCESSES IN A DIRECT-Contact Condenser FOR METAL RECOVERY
    Numerical Heat Transfer Part A-applications, 1998
    Co-Authors: Hasmet Turkoglu, Bakhtier Farouk, Lei Yang
    Abstract:

    A three-dimensional computational fluid dynamic model has been developed to investigate the efficiency of a direct-Contact metal recovery Condenser as a function of the operating conditions ( droplet diameters, droplet injection rate) and overall Condenser dimensions. The Eulerian-Lagrangian approach is used to model the Condenser, where liquid zinc droplets are injected into a zinc vapor laden gas stream so that zinc vapor can directly condense on the droplets. The results show that there exists an optimum droplet injection rate that maximizes Condenser efficiency