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Condensation analysis for plate-frame heat exchangers

Description: A theoretical analysis is presented to predict single component and binary-mixture condensation in plate-frame heat exchangers. A thermodynamic property model based on the Peng-Robinson equation of state was developed for the binary-mixture equilibrium and formulated into a performance prediction program. A set of equations was formulated and a calculation algorithm was developed to predict the local rate of heat and mass transfer for binary mixtures. Friction-factor and heat-transfer-coefficient correlations were developed using experimental data obtained with ammonia condensation. The role of the mass-transfer resistance associated with the condensation process were analyzed for a propane/butane mixture using two limiting cases: (1) no liquid-phase mass-transfer resistance, and (2) infinite liquid-phase mass-transfer resistance. The results show that the vapor-phase mass-transfer resistance is the controlling mechanism for binary-mixture condensation.
Date: July 1, 1995
Creator: Arman, B. & Rabas, T.J.
Partner: UNT Libraries Government Documents Department

The effect of the exit condition on the performance of intube condensers

Description: Data collected from the open literature plus some new, unpublished data will be used to show that the exit condition can change the flow regimes, introduce certain types of instabilities, and alter flooding velocities with intube condensation. The major orientations will be considered: horizontal, vertical with vapor downflow, and vertical with vapor upflow (refluxing).
Date: July 1, 1995
Creator: Rabas, T.J. & Arman, B.
Partner: UNT Libraries Government Documents Department

Adsorption analysis of ammonia in an aqueous solution

Description: An analysis is carried out to determine the effects of the diffusional resistance on the rate of the adsorption of ammonia in an aqueous solution. A performance prediction model is developed to calculate the local rate of heat and mass transfer, including physical and thermodynamic property calculations of the mixture. An algorithm is developed for calculating the interfacial conditions. The local heat- and mass-transfer calculation is then incorporated into the performance prediction method for adsorption for a given geometry.
Date: August 1, 1993
Creator: Arman, B. & Panchal, C. B.
Partner: UNT Libraries Government Documents Department

Performance comparisons of enhanced tubes with discrete and wavy disruption shapes

Description: This paper presents comparisons of the friction factors and heat-transfer coefficients obtained with enhanced tubes with transverse discrete and almost transverse wavy two-dimensional disruptions. Both experimental data and numerical predictions were used for the comparisons. For the latter a two-layer turbulence model incorporated in a body-fitted, finite-volume method was used. The disruption shape, discrete or wavy, depends on the manufacturing process. If an extrusion process is used, discrete disruptions (ribs) of various profiles are obtained that are separated from each other by a flat or unaltered inside diameter. If a spirally indenting process is used, a wavy proflie is obtained with a continuously varying inside diameter between two adjacent disruption peaks. These disruptions are transverse or almost transverse to the tube axis and separated by a distance that exceeds the reattachment length. Based on these comparisons, the following conclusions are obtained: (1) the disruption shape is not an important correlating parameter for discrete disruptions, (2) only the friction factor is influenced by the shape for wavy disruptions, and (3) there are major differences between both the friction-factor and heat-transfer performance of discrete and wavy disruptions with the same maximum disruption height and spacing. However, the most important finding is that the groove radius of spirally indented tubes should be increased because of the substantial reduction of the friction factor but only a small decrease in the thermal performance. Additional comparisons of predicted results were made to obtain a fundamental understanding of the influence of these different shapes.
Date: August 1, 1993
Creator: Arman, B. & Rabas, T. J.
Partner: UNT Libraries Government Documents Department

The influence of the Prandtl number on the thermal performance of tubes with the separation and reattachment enhancement mechanism

Description: This paper demonstrates that the heat-transfer performance of an enhanced tube with transverse, rectangular disruptions can be predicted with a numerical modeling method, an accomplishment not previously achieved. This computer code is then used to determine the influence of the Prandtl number. The numerical simulation demonstrated that six distinct regions exist: the three rib surfaces, the upstream and downstream recirculation regions, and the boundary-layer development zone. Three zones dominate the thermal performance: the rib top and downstream faces and the downstream recirculation zone. The thermal performance at the rib region begins to dominate tile overall performance as the Prandtl number becomes large. The contribution from the downstream recirculation zone becomes more important and dominates for low Prandtl number fluids such as air. The Reynolds number dependence at the rib region and the downstream recirculation zone is similar to that for reattaching flows with exponents in the 0.65 to 0.75 range. The location of the maximum in the recirculation moves closer to the rib with increasing Reynolds and Prandtl numbers and is bounded upstream by the location of the maximum wall shear stress and downstream by the reattachment length. The high turbulence level near the surface in this region is responsible for the heat-transfer enhancement.
Date: August 1, 1992
Creator: Rabas, T. J. & Arman, B.
Partner: UNT Libraries Government Documents Department

Disruption shape effects on the performance of enhanced tubes with the separation and reattachment mechanism

Description: A non-orthogonal, body-fitted numerical code is used to determine the thermo-hydraulic performance of enhanced tubes with transverse periodic sine-, semicircle-, arc-, and trapezoid-shaped disruptions. The turbulence closure was achieved with a two-layer turbulence model. It is shown that there is a tradeoff of the heat-transfer and pressure-drop performances when the disruption shape becomes more contoured; that is, both the heat transfer and the pressure drop increase. The local heat transfer is strongly dependent on the shape in the vicinity of the disruption but it is less dependent in the downstream recirculation region and in the boundary layer development zone. With increasing pitch, effect of the shape on the heat-transfer performance becomes less important. The pressure drop is more dependent on the disruption shape and it continues to decrease when the disruptions become less contoured because of the reduced form drag which is by far the major contribution to the total pressure drop. 27 refs.
Date: August 1, 1992
Creator: Arman, B. & Rabas, T. J.
Partner: UNT Libraries Government Documents Department

The influence of the rib width on the performance of tubes with the separation and reattachment enhancement mechanism

Description: This paper presents numerically predicted turbulent heat-transfer and friction-factor results for tubes with transverse, rectangular ribs for different width-to-height ratios. The rib spacing was maintained at values where the separated flow over the rib reattached between adjacent ribs (i.e. the separation and reattachment enhancement mechanism). The mean Nusselt number was found to decrease slightly with an increase in the width to height ratio for low Prandtl number fluids (Pr = 0.71). However, the trend is more complex for higher Prandtl number fluids. The mean Nusselt number can either increase or decrease depending on the magnitude of the Prandtl number and rib spacing. The friction factors decreased with an increase in the width to height ratio and the magnitude of this decrease was somewhat Reynolds number dependent.
Date: January 1, 1992
Creator: Arman, B. & Rabas, T.J.
Partner: UNT Libraries Government Documents Department

The influence of the rib width on the performance of tubes with the separation and reattachment enhancement mechanism

Description: This paper presents numerically predicted turbulent heat-transfer and friction-factor results for tubes with transverse, rectangular ribs for different width-to-height ratios. The rib spacing was maintained at values where the separated flow over the rib reattached between adjacent ribs (i.e. the separation and reattachment enhancement mechanism). The mean Nusselt number was found to decrease slightly with an increase in the width to height ratio for low Prandtl number fluids (Pr = 0.71). However, the trend is more complex for higher Prandtl number fluids. The mean Nusselt number can either increase or decrease depending on the magnitude of the Prandtl number and rib spacing. The friction factors decreased with an increase in the width to height ratio and the magnitude of this decrease was somewhat Reynolds number dependent.
Date: December 1, 1992
Creator: Arman, B. & Rabas, T. J.
Partner: UNT Libraries Government Documents Department

Influence of Prandtl number and effects of disruption shape on the performance of enhanced tubes with the separation and reattachment mechanism

Description: The pressure-drop and heat-transfer performance of an enhanced tube with transverse disruptions can be predicted with a numerical modeling method, an accomplishment not previously achieved. Two computer codes were employed to achieve this goal - an orthogonal code and a nonorthogonal, body-fitted code. The turbulence closure was achieved with a two-layer turbulence model. The orthogonal computer code was used to determine the influence of the Prandti number. The numerical simulations demonstrated that six distinct regions exist and that three zones dominate the thermal performance. The nonorthogonal, body-fitted numerical code was used to determine the thermohydraulic performance of enhanced tubes with transverse, periodic sine-, semicircle-, arc-, and trapezoid-shaped disruptions. The research showed that there was a trade-off between the heat-transfer and pressure-drop performances when the disruption shape becomes more contoured, and that the local heat transfer is strongly dependent on the shape in the vicinity of the disruption, but it is less dependent in the downstream recirculation region and in the boundary-layer development zone.
Date: April 1, 1992
Creator: Arman, B. & Rabas, T. J.
Partner: UNT Libraries Government Documents Department

Disruption shape effects on the performance of enhanced tubes with the separation and reattachment mechanism

Description: A non-orthogonal, body-fitted numerical code is used to determine the thermo-hydraulic performance of enhanced tubes with transverse periodic sine-, semicircle-, arc-, and trapezoid-shaped disruptions. The turbulence closure was achieved with a two-layer turbulence model. It is shown that there is a tradeoff of the heat-transfer and pressure-drop performances when the disruption shape becomes more contoured; that is, both the heat transfer and the pressure drop increase. The local heat transfer is strongly dependent on the shape in the vicinity of the disruption but it is less dependent in the downstream recirculation region and in the boundary layer development zone. With increasing pitch, effect of the shape on the heat-transfer performance becomes less important. The pressure drop is more dependent on the disruption shape and it continues to decrease when the disruptions become less contoured because of the reduced form drag which is by far the major contribution to the total pressure drop. 27 refs.
Date: January 1, 1992
Creator: Arman, B. & Rabas, T. J.
Partner: UNT Libraries Government Documents Department

The influence of the Prandtl number on the thermal performance of tubes with the separation and reattachment enhancement mechanism

Description: This paper demonstrates that the heat-transfer performance of an enhanced tube with transverse, rectangular disruptions can be predicted with a numerical modeling method, an accomplishment not previously achieved. This computer code is then used to determine the influence of the Prandtl number. The numerical simulation demonstrated that six distinct regions exist: the three rib surfaces, the upstream and downstream recirculation regions, and the boundary-layer development zone. Three zones dominate the thermal performance: the rib top and downstream faces and the downstream recirculation zone. The thermal performance at the rib region begins to dominate tile overall performance as the Prandtl number becomes large. The contribution from the downstream recirculation zone becomes more important and dominates for low Prandtl number fluids such as air. The Reynolds number dependence at the rib region and the downstream recirculation zone is similar to that for reattaching flows with exponents in the 0.65 to 0.75 range. The location of the maximum in the recirculation moves closer to the rib with increasing Reynolds and Prandtl numbers and is bounded upstream by the location of the maximum wall shear stress and downstream by the reattachment length. The high turbulence level near the surface in this region is responsible for the heat-transfer enhancement.
Date: January 1, 1992
Creator: Rabas, T. J. & Arman, B.
Partner: UNT Libraries Government Documents Department

Influence of Prandtl number and effects of disruption shape on the performance of enhanced tubes with the separation and reattachment mechanism

Description: The pressure-drop and heat-transfer performance of an enhanced tube with transverse disruptions can be predicted with a numerical modeling method, an accomplishment not previously achieved. Two computer codes were employed to achieve this goal - an orthogonal code and a nonorthogonal, body-fitted code. The turbulence closure was achieved with a two-layer turbulence model. The orthogonal computer code was used to determine the influence of the Prandti number. The numerical simulations demonstrated that six distinct regions exist and that three zones dominate the thermal performance. The nonorthogonal, body-fitted numerical code was used to determine the thermohydraulic performance of enhanced tubes with transverse, periodic sine-, semicircle-, arc-, and trapezoid-shaped disruptions. The research showed that there was a trade-off between the heat-transfer and pressure-drop performances when the disruption shape becomes more contoured, and that the local heat transfer is strongly dependent on the shape in the vicinity of the disruption, but it is less dependent in the downstream recirculation region and in the boundary-layer development zone.
Date: April 1, 1992
Creator: Arman, B. & Rabas, T. J.
Partner: UNT Libraries Government Documents Department

Recovery and separation of high-value plastics from discarded household appliances

Description: Argonne National Laboratory is conducting research to develop a cost- effective and environmentally acceptable process for the separation of high-value plastics from discarded household appliances. The process under development has separated individual high purity (greater than 99.5%) acrylonitrile-butadiene-styrene (ABS) and high- impact polystyrene (HIPS) from commingled plastics generated by appliance-shredding and metal-recovery operations. The process consists of size-reduction steps for the commingled plastics, followed by a series of gravity-separation techniques to separate plastic materials of different densities. Individual plastics of similar densities, such as ABS and HIPS, are further separated by using a chemical solution. By controlling the surface tension, the density, and the temperature of the chemical solution we are able to selectively float/separate plastics that have different surface energies. This separation technique has proven to be highly effective in recovering high-purity plastics materials from discarded household appliances. A conceptual design of a continuous process to recover high-value plastics from discarded appliances is also discussed. In addition to plastics separation research, Argonne National Laboratory is conducting research to develop cost-effective techniques for improving the mechanical properties of plastics recovered from appliances.
Date: March 1996
Creator: Karvelas, D. E.; Jody, B. J.; Poykala, J. A., Jr.; Daniels, E. J. & Arman, B.
Partner: UNT Libraries Government Documents Department