Int. J. Mech. Eng. & Rob. Res. 2014 Mukund Y Pande and Atul Patil, 2014 Research Paper ISSN 2278 0149 www.ijmerr.com Vol. 3, No. 4, October 2014 2014 IJMERR. All Rights Reserved COMPUTATIONAL FLUID DYNAMICS ON DIFFERENT PASSAGES OVER A PLATE COIL EVAPORATOR FOR 40 LITER STORAGE TYPE WATER COOLER Mukund Y Pande 1 * and Atul Patil 1 *Corresponding Author: Mukund Y Pande pande21mukund@gmail.com By using ANSYS Fluent 14.5 In computational Fluid Dynamics (CFD) analysis, Dimpled Plate coil evaporator with different passage likes six passages and eight passages are simulated using the appropriate boundary conditions and fluid properties specified to the system with suitable assumptions. The process in solving simulation consists of modeling and meshing the basic geometry of the Dimpled plate coil evaporator using CFD package ANSYS 14.5. The objective of the project is to study the temperature field of the coil using ANSYS software tools. The temperature contours was plotted using ANSYS 14.5 for different passages of Dimpled plate coil evaporator. Different Dimpled plate coil evaporator passages configurations is analyzed using CFD software for validation of experimental values determined the output temperature of Plate coil evaporator to improving the coefficient of performance of the System. Keywords: Bonded coil Evaporator, Plate coil evaporator (PHE), Dimpled plate and Computational Fluid Dynamics (CFD) INTRODUCTION Dimpled surface is shown in Figure 1. This surface is machine punched and swaged, prior to welding, to increase the flow area in the passage. As compared with other two surfaces concept dimpled surfaces are successfully employed in many industries. Most common example is bulk milk cooler used in dairy industry. Over the last decade, numerical and experimental work in channel flow has shown that flow over dimpled surfaces develop vortex like structures inside and in the wake area of the dimples, increasing the overall drag due to inertial and viscous effects in the fluid. However, dimples also increase the surface heat transfer coefficient without a substantial rise in drag penalties observed in other heat 1 Deprtment of Mechanical Engineering, Godavari College of Engineering, Maharashtra India. 16
Figure 1: Dimpled Surface transfer enhancement devices such as rib tabulators and pin fins. Fluid motion inside dimples is self-organized: it is induced by the presence of the dimple with no physically protruding part projecting into the flow or deflecting it to create the vortices; therefore, dimples lack the pressure loss associated with form drag. Heat transfer is enhanced because vortex structures promote mixing, drawing cold fluid from outside the thermal boundary layer into contact with the wall and ejecting hot fluid from the near wall area into the stream, thus enhancing the overall convective heat transfer. When a dimpled wall is used in channel flow, dimple geometry play a key role in the heat transfer and drag coefficients. The optimum configuration should provide the higher heat transfer improvement with less drag for a specific application. As of today, there exists no road map to determine the optimum dimple configuration. During the last few years, studies on turbulent flow over dimpled walls have provided some insight into the application of this technology for turbine blade and jet impingement cooling. However, application of dimples in laminar flow was scarcely explored. Microelectronic cooling and micro fluids, where the flow regime is mostly laminar, are two potential fields of application for dimple technology. Surface dimples produce substantial surface heat transfer augmentations with relatively small pressure drop penalties in internal passages. As such, arrays of surface dimples are useful for a variety of practical applications, such as electronics cooling, heat exchangers, turbine blade internal cooling passages, micro-scale passages, bio-medical devices, and combustion chamber liners. Of several early studies (mostly conducted in Russia), Murzin et al. (1986) describe the flow over and within shallow spherical depressions and conclude that this flow is mostly symmetric, with stable re-circulatory flows inside of the depressions. Kesarev and Kozlov (2003) present distributions of local heat transfer coefficients inside of a single hemispherical cavity and indicate that the convective heat transfer from the cavity is higher, especially on the downstream portion, than that from the surface of a plane circle of the same diameter as the cavity diameter. Afanasyev et al. (1993) experimentally studied the heat transfer enhancement mechanism for flows in a dimpled channel with several different shapes. Enhancements of 30 40%, with pressure losses that are not increased appreciably relative to a smooth surface, are reported. Terekhov et al. (1995) present experimental measurements of flow structure, pressure fields, and heat transfer in a channel with a single dimple on one surface. According to the authors, pressure losses increase (compared to a smooth wall) with an increase of cavity depth and decrease as the Reynolds number increases. Cavity heat transfer enhancements 17
are also noted, especially for shallow holes, mainly as a result of an increase in heat transfer area and the changes to flow structure produced by the dimple. LITERATURE REVIEW Xiao et al. The present study provides the systematic set of data which illustrate the effects of an array of dimples on local and spatially averaged surface Nusselt number distributions, as well as on friction factors in channels with laminar flow. Trends of spatiallyaveraged Nusselt numbers and friction factors are provided as they vary with dimple depth, channel height, Reynolds number and the use of protrusions on the opposite channel wall. When compared with turbulent flow results, the present laminar data illustrate changes due to the absence of turbulence transport. For example, in contrast to turbulent flows, the present laminar flow data show that there is no overall benefit from the use of a top wall with protrusions. In addition, spatiallyaveraged Nusselt number ratios and friction factor ratios measured on a deep dimpled surface with a smooth top wall show trends which are opposite from ones observed in turbulent flows, since lower laminar heat transfer augmentations are present for smaller channel heights when compared at the same Reynolds number. Derya Burcu Ozkan et al. examine parameter affecting the frost formation on the evaporator of a refrigerator and the structure of frost. Air velocity both at the air inlet and outlet channels of the evaporator were performed, and the effect of the air velocity on frost formation was examine. In this experiment parameter affecting on frost formation on the evaporator and structure of the frost were examined and frost thickness on the chosen fin was measured. In this experiment the compressor of the refrigerator operated at 100% load and cooling was carried out for 5 h. N. Xiao et al. The present study provides the systematic set of data which illustrate the effects of an array of dimples on local and spatially averaged surface Nusselt number distributions, as well as on friction factors in channels with laminar flow. Trends of spatiallyaveraged Nusselt numbers and friction factors are provided as they vary with dimple depth, channel height, Reynolds number and the use of protrusions on the opposite channel wall. When compared with turbulent flow results, the present laminar data illustrate changes due to the absence of turbulence transport. For example, in contrast to turbulent flows, the present laminar flow data show that there is no overall benefit from the use of a top wall with protrusions. In addition, spatiallyaveraged Nusselt number ratios and friction factor ratios measured on a deep dimpled surface with a smooth top wall show trends which are opposite from ones observed in turbulent flows, since lower laminar heat transfer augmentations are present for smaller channel heights when compared at the same Reynolds number. The present investigation leads to the following conclusions a. As the dimple depth increases, higher magnitude of stream wise vorticity, vortex circulation and Reynolds normal stress are obtained, which implies strong vortices and increasing turbulence transport associated with increase of the depth of the dimples. 18
b. The maximum heat transfer rates are obtained downstream of the dimples. The minimum heat transfer rates occur along the row containing the dimples. Silva et al. In present study, numerical and experimental work was performed to determine the effect of dimpled surfaces on the convective heat transfer in the channel flow under a laminar regime with the Reynolds number (based on the channel height) between 500 and 1000. This study identified the bestperformance dimple geometry and conducted experiments to validate the numerical results. The following findings/conclusions can be drawn from the work done CFD MODELING CFD is a sophisticated computationally-based design and analysis technique. CFD software gives you the power to simulate flows of gases and liquids, heat and mass transfer, moving bodies, multiphase physics, chemical reaction, fluid-structure interaction and acoustics through computer modeling. This software can also build a virtual prototype of the system or device before can be apply to real-world physics and chemistry to the model, and the software will provide with images and data, which predict the performance of that design. Computational fluid dynamics (CFD) is useful in a wide variety of applications and use in industry. CFD is one of the branches of fluid mechanics that uses numerical methods and algorithm can be used to solve and analyses problems that involve fluid flows and also simulate the flow over a piping, vehicle or machinery. Computers are used to perform the millions of calculations required to simulate the interaction of fluids and gases with the complex surfaces used in engineering. More accurate codes that can accurately and quickly simulate even complex scenarios such as supersonic and turbulent flows are ongoing research. Onwards the aerospace industry has integrated CFD techniques into the design, R&D and manufacture of aircraft and jet engines. More recently the methods have been applied to the design of internal combustion engine, combustion chambers of gas turbine and furnaces. Furthermore, motor vehicle manufactures now routinely predict drag forces, under bonnet air flows and surrounding car environment with CFD. Increasingly CFD is becoming a vital component in the design of industrial products and processes. Figure 2: Overview of Modeling Process CFD PROCEDURE For numerical analysis in CFD, it requires five stages such as: a. Geometry creation 19
b. Grid generation c. Flow specification d. Calculation and numerical solution e. Results Based on control volume method, 3-D analysis of fluid flow and dimpled plate has been done on ANSYS FLUENT 14.5 software. All the above mentioned processes are done using the three CFD tools which are preprocessor, solver and post-processor. Mesh Generation The mesh of the model is shown in Figures 5 and 6. It depicts that the domain was meshed with rectangular cells. Grid independence was studied by doing different simulation with taking different no cells. Figure 5: Meshing of 6 Passage of Dimple Plate Evaporator Geometry Creation A 3-d model of Dimpled Plate Evaporator has been created using design modeler of ANSYS as shown in Figures 3 and 4. Figure 3: 6 Passage of Dimple Plate Evaporator Figure 6: Meshing of 8 Passage of Dimple Plate Evaporator Figure 4: 8 Passage of Dimple Plate Evaporator The assumptions used in this model were 1. The flow was steady and incompressible. The fluid density was constant throughout the computational domain. 20
2. R-134 a was the working fluid. The fluid properties constant throughout the computational domain. 3. The effect of heat conduction through the tube material is small. Relaxation Factors Mass flow rate was given at the inlet whereas static temperature was given at inlet for velocity inlet and pressure outlet boundary condition and static pressure was given at the inlet as well as at the output for pressure inlet and pressure outlet boundary condition. The input parameters were indirectly taken from the Reynolds number value. Table 1 : Relaxation Table in ANSYS FLUENT 14.5 Pressure Momentum Energy Density Body Force 0.3 0.7 1 1 1 Table 2: Comparison of Exit Static Temperature with Experimental Value No. of Passages Experimental Values CFD Analysis Value INLET OUTLET INLET OUTLET 6- Passage Dimpled plate Evaporator 275 282 275 285.079 8- Passage Dimpled plate Evaporator 284 298 284 296.744 Figure 7: Contour of Temperature Distribution for 6-passage 21
Figure 8: Contour of Temperature Distribution for 8-passage CONCLUSION The Static temperature at out let of a dimpled plate can be visualized from the contour diagrams of temperature distribution which have been plotted using ANSYS FLUENT 14.5. from above table static outlet temperature of 6 and 8 passages of dimpled plate evaporator is validated and by using this different passage improve the coefficient of performance (COP) of the system as generally used in storage type water cooler. REFERENCES 1. Afanasyev et al. (1993) Experimentally studied the heat transfer enhancement mechanism for flows in a dimpled channel with several different shapes Therm Fluid Sci Vol. 7, pp. 1 8. 2. Apu Roy and D H Das, CFD analysis of shell and finned tube heat exchngerfor waste heat recovery application, International Journal of Mechanical & Industrial Engineering, Vol. 1, No.1, pp. 77-83. 3. Flavio C C G, Raquel Y M, Jorge A W G and Carmen C T (2006), Experimental and numerical heat transfer in a plate heat exchanger, Vol. 61, No. 21, pp. 7133-7138. 4. Jader R Barbosa Jr., Chirstan J L Hermes and Claudio Melo (2010), CFD Analysis of tube fin No Frost Evaporator, International Journal of Emerging Trends in Engineering and Development, Vol. 1, No. 3. 5. Kesarev and Kozlov (2003) Present distributions of local heat transfer coefficients inside of a single hemispherical cavity Turbo Expo 2003, Vol. 5. 22
6. Murzin V N, Stoklitskii S A and Pchebotarev A (1986), Creation of solitary vortices in a flowaround shallow spherical depressions, Soviet Technical Physical Letters, Vol. 12, No. 11, pp. 547 549. 7. N Xiao, Q Zhang, P M Ligrani and R Mongia (2009), Thermal performance of dimpled surfaces in laminar flows International Journal of Heat and Mass Transfer, Vol. 52, pp. 2009 2017. 8. Piotr A Domanski, David Yashar and Minsung Kim (2005), Performance of finned tube evaporator optimized for different refrigerants and effect on system efficiency, International Journal of Refrigeration, Vol. 28, pp. 820-827. 9. Terekhov et al (1995). Flow Structure and Heat Transfer on a Surface With a Unit Hole Depression Russ, J. Eng. Thermophys, Vol. 5, pp. 11-33. 23