You are in:Home/Theses | |

## Dr. Mohamed Reda Aly Abd-Elhamid Salem :: Theses : |

Title | Experimental Study on Convective Heat Transfer and Pressure Drop of Water-Based Nanofluid Inside Shell and Coil Heat Exchanger |

Type | PhD |

Supervisors | K.M. Elshazly, R.Y Sakr; R.K. Ali |

Year | 2014 |

Abstract | The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to the friction factor for fully developed flow through their helically coiled tube (HCT). Nine heat exchangers of counter-flow configuration were constructed with different HCT geometries and tested at different mass flow rates and inlet temperatures of both sides of the heat exchangers. The heat exchangers were geometrically divided into two groups. The first group is fabricated such that the coil torsion (λ) is varied from 0.0442 to 0.1348 with same curvature ratio (δ) of 0.0591. The other group represents another five different HCT-curvature ratios (0.0392≤δ≤0.1194) with same coil torsion (λ=0.0895). Moreover, this work is divided into two main parts according to the fluid type flowing through the HCTs. The first part covers flowing pure water through the two sides of the heat exchanger, while the second part covers flowing gamma- aluminium oxide (Al2O3)/water nanofluid in the HCTs. For all experiments, results showed that the average Nusselt numbers of both sides of the heat exchanger and the overall heat transfer coefficient increase by increasing the mass flow rates and decreasing the inlet temperatures of the fluids in the two sides of the heat exchangers. Also, the HCT-Fanning friction factor (f_c) decreases by increasing the HCT-side mass flow rate and nearly f_c is independent of the HCT-fluid temperature especially at higher HCT-Reynolds number (Re_t). In water experiments, totally 531 test runs were performed on the nine heat exchangers, from which the convection heat transfer coefficients in HCT and shell sides were calculated. For HCTs with the same δ, results showed that the average Nusselt numbers of both sides of the shell and coil heat exchanger and the overall heat transfer coefficient significantly increase by decreasing λ. The increase in the average Nusselt number is of 108.7% to 58.6% for the HCT side and 173.9% to 69.5% for the shell side at lower and higher investigated Reynolds numbers, respectively, when λ decreases from 0.1348 to 0.0442 within the investigated ranges of different parameters. Also, a slight increase of 6.4% in f_c is obtained at lower investigated Re_t when λ decreases from 0.1348 to 0.0442, and this effect diminishes with increasing Re_t. For HCTs with same λ, results showed that the average Nusselt numbers of the two sides of the shell and coil heat exchanger and the overall heat transfer coefficient significantly increase by increasing δ. The increase in the average Nusselt number is of 160.3% to 80.6% for the HCT side and 224.3% to 92.6% for the shell side at lower and higher studied Reynolds numbers, respectively, when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, an average increase of 33.2% to 7.7% in f_c is obtained for this configuration at lower and higher investigated Re_t, respectively. Correlations for the average Nusselt numbers and f_c are obtained within 6471≤Re_t≤62092, 1329≤De≤20927, 2.86≤Pr_t≤4.43, 179≤Re_sh≤1384, 5.23≤Pr_sh≤ 7.54, 0.0392 ≤δ≤0.1194 and 0.0442≤λ≤0.1348. In nanofluid experiments, totally 1080 test runs were performed on the nine heat exchangers, from which the convection heat transfer coefficient in HCT side and f_c were calculated. Al2O3 (40 nm)/water nanofluid with four different nanoparticles volume concentrations (φ) of 0.5, 1, 1.5 and 2% was flowed through the HCTs. For all experiments, results showed that the HCT-average heat transfer coefficient, HCT-average Nusselt number and f_c in addition to the overall heat transfer coefficient of nanofluids are higher than that of the base fluid at same flow condition, and this enhancement goes up with the increase in φ. For HCTs with same δ, at lower and higher Re_t, the average increase in the HCT-average heat transfer coefficient is of 134.1% to 195.7%, respectively, for λ=0.0442 and of 238.9% to 235.4%, respectively, for λ=0.1348 when φ increases from 0 to 2%. While, an average increase in f_c at lower and higher Re_t is of 37.7% to 28%, respectively, for λ=0.0442 and of 36.4% to 26.3%, respectively, for λ=0.1348 when φ increases from 0 to 2%. Furthermore, for HCTs with same λ, at lower and higher Re_t, the average increase in the HCT-average heat transfer coefficient is of 170.1% to 219.9%, respectively, for δ=0.1194 and of 217.3% to 213.8%, respectively, for δ=0.0392 when φ increases from 0 to 2%. While, an average increase in f_c at lower and higher Re_t is of 25.7% to 27.4%, respectively, for δ=0.1194 and of 41.5% to 27.6%, respectively, for δ=0.0392 when φ increases from 0 to 2%. Additionally, same trend was obtained as water experiments for the effect of HCTs geometrical parameters. For HCTs with same δ, results showed that the HCT-average Nusselt number and the overall heat transfer coefficient increase also by decreasing λ. The average increase in the HCT-average Nusselt number at lower and higher Re_t is of 47.8% to 42.1%, respectively, at φ=2% when λ decreases from 0.1348 to 0.0442 with the investigated ranges of different parameters. Also, a slight increase in f_c at lower and higher Re_t of 7.5% to 3.8%, respectively, at φ=2% is obtained when λ decreases from 0.1348 to 0.0442. Moreover, for HCTs with same λ, the HCT-average Nusselt number and the overall heat transfer coefficient increase also by increasing δ. At lower and higher Re_t, the average increase in the HCT-average Nusselt number is of 130.2% to 87.2%, respectively, at φ=2% when δ increases from 0.0392 to 0.1194 with the investigated ranges of different parameters. While, the average increase in f_c is of 18.2% to 7.5% at φ=2% when δ increases from 0.0392 to 0.1194. Another two correlations for the HCT-average Nusselt numbers and friction factor are obtained within 5702≤Re_t≤55101, 1155≤De_t≤18669, 1.92≤Pr_t≤3.9, 0.0392≤δ≤0.1194, 0.0442≤λ≤0.1348 and 0.5%≤φ≤2%. Finally, the thermal performance index was calculated, which measures the ratio between the enhancement ratio in the HCT-average heat transfer coefficient due to using Al2O3/water nanofluid instead pure water relative to the corresponding pressure drop ratio. For all HCTs, results showed that increasing φ, λ and HCT-side inlet temperature and flow rate enhance the thermal performance index. In addition, it was shown that the performance index is more than unity, which states that the enhancement in the heat transfer rate in the HCTs due to using nanofluids is higher than the corresponding increase in the pressure drop. Therefore, this assures the ability of using Al2O3 (40 nm)/water nanofluid in the HCTs with 0.5%≤φ≤2% as a compound heat transfer enhancement technique inside shell and coil heat exchangers instead of using HCTs only. |

Keywords | |

University | Benha University |

Country | Cairo |

Full Paper | - |

Title | Experimental Study on Convective Heat Transfer and Pressure Drop of Water-Based Nanofluid inside Shell and Coil Heat Exchanger |

Type | PhD |

Supervisors | K.M. Elshazly; R.Y. Sakr; R.K. Ali |

Year | 2014 |

Abstract | The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to the friction factor for fully developed flow through their helically coiled tube (HCT). Nine heat exchangers of counter-flow configuration were constructed with different HCT geometries and tested at different mass flow rates and inlet temperatures of both sides of the heat exchangers. The heat exchangers were geometrically divided into two groups. The first group is fabricated such that the coil torsion (λ) is varied from 0.0442 to 0.1348 with same curvature ratio (δ) of 0.0591. The other group represents another five different HCT-curvature ratios (0.0392≤δ≤0.1194) with same coil torsion (λ=0.0895). Moreover, this work is divided into two main parts according to the fluid type flowing through the HCTs. The first part covers flowing pure water through the two sides of the heat exchanger, while the second part covers flowing gamma- aluminium oxide (Al2O3)/water nanofluid in the HCTs. For all experiments, results showed that the average Nusselt numbers of both sides of the heat exchanger and the overall heat transfer coefficient increase by increasing the mass flow rates and decreasing the inlet temperatures of the fluids in the two sides of the heat exchangers. Also, the HCT-Fanning friction factor (f_c) decreases by increasing the HCT-side mass flow rate and nearly f_c is independent of the HCT-fluid temperature especially at higher HCT-Reynolds number (Re_t). In water experiments, totally 531 test runs were performed on the nine heat exchangers, from which the convection heat transfer coefficients in HCT and shell sides were calculated. For HCTs with the same δ, results showed that the average Nusselt numbers of both sides of the shell and coil heat exchanger and the overall heat transfer coefficient significantly increase by decreasing λ. The increase in the average Nusselt number is of 108.7% to 58.6% for the HCT side and 173.9% to 69.5% for the shell side at lower and higher investigated Reynolds numbers, respectively, when λ decreases from 0.1348 to 0.0442 within the investigated ranges of different parameters. Also, a slight increase of 6.4% in f_c is obtained at lower investigated Re_t when λ decreases from 0.1348 to 0.0442, and this effect diminishes with increasing Re_t. For HCTs with same λ, results showed that the average Nusselt numbers of the two sides of the shell and coil heat exchanger and the overall heat transfer coefficient significantly increase by increasing δ. The increase in the average Nusselt number is of 160.3% to 80.6% for the HCT side and 224.3% to 92.6% for the shell side at lower and higher studied Reynolds numbers, respectively, when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, an average increase of 33.2% to 7.7% in f_c is obtained for this configuration at lower and higher investigated Re_t, respectively. Correlations for the average Nusselt numbers and f_c are obtained within 6471≤Re_t≤62092, 1329≤De≤20927, 2.86≤Pr_t≤4.43, 179≤Re_sh≤1384, 5.23≤Pr_sh≤ 7.54, 0.0392 ≤δ≤0.1194 and 0.0442≤λ≤0.1348. In nanofluid experiments, totally 1080 test runs were performed on the nine heat exchangers, from which the convection heat transfer coefficient in HCT side and f_c were calculated. Al2O3 (40 nm)/water nanofluid with four different nanoparticles volume concentrations (φ) of 0.5, 1, 1.5 and 2% was flowed through the HCTs. For all experiments, results showed that the HCT-average heat transfer coefficient, HCT-average Nusselt number and f_c in addition to the overall heat transfer coefficient of nanofluids are higher than that of the base fluid at same flow condition, and this enhancement goes up with the increase in φ. For HCTs with same δ, at lower and higher Re_t, the average increase in the HCT-average heat transfer coefficient is of 134.1% to 195.7%, respectively, for λ=0.0442 and of 238.9% to 235.4%, respectively, for λ=0.1348 when φ increases from 0 to 2%. While, an average increase in f_c at lower and higher Re_t is of 37.7% to 28%, respectively, for λ=0.0442 and of 36.4% to 26.3%, respectively, for λ=0.1348 when φ increases from 0 to 2%. Furthermore, for HCTs with same λ, at lower and higher Re_t, the average increase in the HCT-average heat transfer coefficient is of 170.1% to 219.9%, respectively, for δ=0.1194 and of 217.3% to 213.8%, respectively, for δ=0.0392 when φ increases from 0 to 2%. While, an average increase in f_c at lower and higher Re_t is of 25.7% to 27.4%, respectively, for δ=0.1194 and of 41.5% to 27.6%, respectively, for δ=0.0392 when φ increases from 0 to 2%. Additionally, same trend was obtained as water experiments for the effect of HCTs geometrical parameters. For HCTs with same δ, results showed that the HCT-average Nusselt number and the overall heat transfer coefficient increase also by decreasing λ. The average increase in the HCT-average Nusselt number at lower and higher Re_t is of 47.8% to 42.1%, respectively, at φ=2% when λ decreases from 0.1348 to 0.0442 with the investigated ranges of different parameters. Also, a slight increase in f_c at lower and higher Re_t of 7.5% to 3.8%, respectively, at φ=2% is obtained when λ decreases from 0.1348 to 0.0442. Moreover, for HCTs with same λ, the HCT-average Nusselt number and the overall heat transfer coefficient increase also by increasing δ. At lower and higher Re_t, the average increase in the HCT-average Nusselt number is of 130.2% to 87.2%, respectively, at φ=2% when δ increases from 0.0392 to 0.1194 with the investigated ranges of different parameters. While, the average increase in f_c is of 18.2% to 7.5% at φ=2% when δ increases from 0.0392 to 0.1194. Another two correlations for the HCT-average Nusselt numbers and friction factor are obtained within 5702≤Re_t≤55101, 1155≤De_t≤18669, 1.92≤Pr_t≤3.9, 0.0392≤δ≤0.1194, 0.0442≤λ≤0.1348 and 0.5%≤φ≤2%. Finally, the thermal performance index was calculated, which measures the ratio between the enhancement ratio in the HCT-average heat transfer coefficient due to using Al2O3/water nanofluid instead pure water relative to the corresponding pressure drop ratio. For all HCTs, results showed that increasing φ, λ and HCT-side inlet temperature and flow rate enhance the thermal performance index. In addition, it was shown that the performance index is more than unity, which states that the enhancement in the heat transfer rate in the HCTs due to using nanofluids is higher than the corresponding increase in the pressure drop. Therefore, this assures the ability of using Al2O3 (40 nm)/water nanofluid in the HCTs with 0.5%≤φ≤2% as a compound heat transfer enhancement technique inside shell and coil heat exchangers instead of using HCTs only. |

Keywords | Shell and coil heat exchanger; Nanofluid; curvature; Torsion; Passive |

University | Faculty of Engineering at Shoubra, Benha University |

Country | Cairo |

Full Paper | - |

Title | Thermal Control of Satellites |

Type | MSc |

Supervisors | K.M. Elshazly; M.G. Higazy; A.A. Abdelaziz |

Year | 2011 |

Abstract | The present work is devoted to satellites due to their great importance and wide applications in nearly all fields. A satellite consists of closed vacuum chamber, which contains several electronic components, each of which operates in certain range of temperatures and it performs better and lives longer when its components remain within these temperatures limits. Unfortunately, these satellites in space are exposed to extreme temperature changes from nearly -120℃ in the shade (cold case), to 180℃ in the sun (hot case), which beyond the working ranges of their components. So, the present work is meant to achieve the thermal control of the satellite by developing temperatures analyses for its internal components during its two worst cases at different factors. Throughout this work, a model of a small satellite revolving about the earth in a circular sun-oriented polar orbit is studied with covering the altitude range of that kind of satellites (400 to 1200 km). The present work was carried out using FLUENT® 6.2 Computational Fluid Dynamics (CFD) package. The CFD modeling techniques solved the energy equation in three-dimensional modeling with implicit formulation and steady state conditions. Throughout the investigations, a numerical validation was carried out by preparing a model for an experimental system that was developed by other researcher to simulate the satellite in its orbit. By comparing the results, it was found good agreement between both predictions. In addition, effect of the mesh volumes sizes of the internal components and the medium in-between on their temperatures was studied to attain better and significant predictions of the temperature analyses, from which the best mesh sizes were selected, leading the mesh sizes to exceed 1,000,000 mesh volumes in each case. Through the present study, the effect of the satellite internal components arrangement on their temperatures was studied in hot case. This was through ten different arrangements (800 km, orbit altitude). The main result was that the maximum (max) temperatures of the internal components decreased as these components approached to the radiator. In addition, this study reached to that the best arrangement of the satellite internal components that served their thermal control in hot case could be achieved by attaching the batteries to the inner surface of the radiator, while the input/output (I/O) processor should be attached to the side panel. In addition, the other internal components should be attached to the panel that faces the radiator with attaching the attitude/velocity control electronics (AVCE) near from the I/O processor. In addition, the effect of the emissivity of all surfaces inside the satellite in the two worst cases is studied. The best-obtained arrangement of the satellite internal components, in addition to using the same orbit (800 km altitude) was selected to complete this study in the two worst cases. It was obvious that increasing each surface emissivity leaded its temperature to decrease in hot case, while its effect in cold case differed from component to another. This served the thermal control in hot case, but this study depended on varying the emissivity of the surfaces individually. Therefore, another study of effect of the surfaces emissivity when they have same value in hot case was done. This study reached to selecting the best arrangement for the internal components in addition to increasing the emissivity of all surfaces inside the satellite when they have same emissivity value reduced the components temperature in hot case. Furthermore, it was clear that the thermal control of these components could be achieved passively without using any active thermal control technique through an emissivity range of 0.86 to 0.99 (for small satellite revolving about the earth in circular sun-oriented polar 800 km orbit). In addition, it was clear that achieving the thermal control of the batteries ensures the complete control of the other internal components. In addition, study of the orbit altitude effect on the satellites thermal control was done for the altitude range of the small satellites; 400 to 1200 km. The main result was that increasing the orbit altitude reduced the minimum (min) and max values of the surfaces emissivity with which the thermal control could be achieved in hot case. Furthermore, this study defined an emissivity range of 0.88 to 0.96, which achieved the complete thermal control with using the best arrangement of the internal components in hot case, at any altitude in the range of 400 to 1200 km. In addition, the min emissivity of the surfaces that could achieve the thermal control in hot case according to that orbit altitude was defined in this study through a relation, in which the error value was less than 0.01. Finally, study of the ability to achieve the thermal control of the satellites in cold case with using the obtained results for hot case was done. One of the techniques that were applied to achieve that was thermal louvers. The louvers improved the thermal control but, they did not achieve it completely. Therefore, electrical heaters were used. The results showed that increasing of the surfaces emissivities required heaters of more capacities for all altitudes. Moreover, it was clear that increasing the orbit altitude reduced the min emissivity required to achieve the thermal control in hot case and consequently, the require heater capacity to the thermal control in cold case decreased. Therefore, for an orbit of numerous altitudes that can enable the satellite to do its mission, it should deign the satellite for higher altitudes with using its own min emissivity, which can achieve the thermal control in hot case. |

Keywords | |

University | Benha University |

Country | Egypt |

Full Paper | - |