The paper presents the design and analysis of tray dryer system. The design was done in Solidwork while the analysis and simulation performed using ANSYS FLUENT. ANSYS FLUENT is a Computational Fluid Dynamic (CFD) software in which flow fields and other physics are calculated in detail for various engineering applications. The analysis was done to analyze heat transfer and temperature distribution, ressure, air flow and turbulence. Before generating the product in 3D modeling, the basic data or information of tray dryer system is required such as dimension of dryer equipment, air and heat source supply range, sizing method and etc. Through  his step, the dryer system development and function ability

can be clearly understood by the end of analyzing process is accomplished

Hidayah, Nurul A.

Kamarul, A.M

Widodo, W. Sapto

Wong, C.Y

English

Universiti Teknikal Malaysia Melaka (UTeM) Repository

CFD SIMULATION FOR TRAY DRYER OPTIMIZATIONSapto W.W, Wong C.Y., Kamarul A.M, Nurul Hidayah A.Faculty of Manufacturing Engineering,Universiti Teknikal Malaysia MelakaDurian Tunggal Melaka MalaysiaAbstract –The paper presents the design and analysis of tray dryer system.The design was done in Solidwork while the analysis and simulationperformed using ANSYS FLUENT. ANSYS FLUENT is a ComputationalFluid Dynamic (CFD) software in which flow fields and other physics arecalculated in detail for various engineering applications. The analysis wasdone to analyze heat transfer and temperature distribution, pressure, airflow and turbulence. Before generating the product in 3D modeling, thebasic data or information of tray dryer system is required such as dimensionof dryer equipment, air and heat source supply range, sizing method andetc. Through this step, the dryer system development and function abilitycan be clearly understood by the end of analyzing process is accomplished.Keywords –, CFD, Tray Dryer, Heat Transfer.1.0 INTRODUCTIONTray dryer is an equipment or machine to dry up products which is very useful insmall industrial sector such as food industry or chemical industry. Commonly, a dryersystem consists some form air heater and a fan to pass air over the product to reducemoisture or evaporate the moisture into vapor condition. The drying temperature is setaround 30 degree Celsius to 80 degree Celsius or above. The air enters the bottom ofthe chamber below the trays and then rises, through the trays of product being dried,and exits through the ducting system or opening in the top of chamber. Besides that,this system also reduces back pressure and which is means that the dryer can be buildin cheaper cost by using smaller fan and others low cost material.The drying process depends to the moisture content inside the material and it alsoaffected by the time is taking to reduce the product moisture content. Therefore, dryingprocess is important especially for food industrial, it’s made the food in dry conditionfor the storage purpose, management purpose and manufacture process purpose.However, most of the tray dryers are facing the same problem in design level anddrying process, which is the heat flow in drying chamber uncontrollable and unstable.Although the development of tray dryer is at low cost, the unbalanced heat flowdirectly affected to the production process and labor cost. When the heats are supplyfrom the bottom of dryer, the tray which place near by the heat source is dry faster thanother trays. If need to dry up all the product in once drying cycle, it is impossiblebecause the product which close to the heat source will damage and may affected toothers product quality.The paper focuses on the analysis of heat flow in the dryer system to improve the traydryer system function more effectively by allowing the heat flow easy to run throughthe system and balanced.2.0 BASIC PRINCIPLE OF TRAY DRYER SYSTEMStudy from Devahastin, S. (2000), drying is a complex operation involving transienttransfer of heat and mass along with several rate processes, such as physical orchemical transformations, which, in turn, may cause changes in product quality as wellas the mechanisms of heat and mass transfer. Physical changes that may occur include:shrinkage, puffing, crystallization, glass transitions. In some cases, desirable orundesirable chemical or biochemical reactions may occur leading to changes in color,texture, odor or other properties of the solid product. Drying occurs by effectingvaporization of the liquid by supplying heat to the wet feedstock. As noted earlier, heatmay be supplied by convection (direct dryers), by conduction (contact or indirectdryers), radiation or volumetrically by placing the wet material in a microwave or radiofrequency electromagnetic field. Over 85 percent of industrial dryers are of theconvective type with hot air or direct combustion gases as the drying medium. Over 99percent of the applications involve removal of water. All modes except the dielectric(microwave and radio frequency) supply heat at the boundaries of the drying object sothat the heat must diffuse into the solid primarily by conduction (Devahastin, 2000).The study from Devahastin, S. (2002), the most common dryer for small amount orquantity of product, a batch tray dryer consist stack of tray or several stacks traysplaced in a large insulated chamber in which hot air is circulated with appropriatelydesigned fans and guides vanes. Often, heated air is circulated vertically through thecolumn with a circulating fan (Dalfsen, 1999). These dryers require large amount oflabor to load and unload the product. Typically, the drying times are long (10-60hours). The key to successful operation is the uniform air flow distribution over thetrays as the slowest drying tray decides the residence time required and hence dryercapacity. Warpage of trays can also cause poor distribution of drying air and hencepoor dryer performance (Devahastin, 2000).Figure 1. A Batch Tray Dryer (Devahastin, 2000).2.1 FanBasically, fans can divided in many types and it was depends on the performance andability of fan that can be use in certain specification and requirements. Besides that, fancan be driven by different type of mechanical instruments, electrical device or bothof it to generate energy and air flow which needed to use.2.2 Electric HeaterElectrical heater is an induction heating method which is using the electromagneticinduction to transfer heat to object. This method of heating is of great interest tomaterials and manufacturing industries as it is fast, precise and controllable. However,for this type of heating system may be more expensive, and it is usually preferable toother types of processing methods such as open flame heating or chemical processes. Inmost cases it also is the most efficient and precise heating method in practice today(Butturini, 2002).2.3 Heat Recovery SystemHeat recovery is a system that can give opportunities to increase the quality heatingsystem, productivity of product and also decrease the manufacturing or production cost.Based on the study of Scullion, W. K. (2005), Energy intensive processes such as thoseassociated with the manufacture of tape and label products offer opportunities to reduceoperating costs2.4 Consideration in Sizing Heater and FanThe main purpose of the dryer system is to dry up the work piece or product whichcarrying the moisture or liquid internally or externally. Inside the dryer system, itconsist two main components which is, heater and fan/blower (Devahastin, 2000).Without one of these components, the dryer system will fail to complete the dryingprocess. Basically, at the beginning of the dryer process, heater will start to generate heatuntil certain temperature required, and at the same time, the fan/blower also start tooperate which is set behind the heater and driven by the air flow which is generated bythe fan/blower (Dalfsen, 1999). After that, the heat flow will pass through the workpiece or product and convection process will dry up the product and carry out themoisture or fluid content in the product to the ducting system or direct outlet system(Tanthapanichakoon, 2002). The fan/blower will carry in new or fresh air into the heaterand cycle back the drying process (Adapa, 2004). Base on the design concept, some ofthe dryer designs are using reheat system to save energy and cost.2.5 Insulation of the Drying ChamberAccording to Stephen and Emmanuel, (2009), the development of drying chamberwith different materials is available for insulation, however, to select a suitableinsulating material for installation, it need to consider about the drying temperature,availability and manufacturing costing. Besides that, heat loss from the dryingchamber takes place by conduction, convection and radiation. The heat loss is directlyproportional to the temperature difference between the indoor and outside ambienttemperature (Eltief, 2007). To approximate the thickness of the insulating material, itneeds to identify the heat loss from the chamber of the quantity of heat produced(Kaminski, 2005).Figure 2. Insulation Diagram of Drying Chamber2.6 Heat TransferGenerally, there are three fundamental modes of the heat transfer involved in the dryersystem which is convection, conduction and radiation. All three modes of heat transferare assumed as the steady-state heat transfer and can be expressed as follows:For conduction process,(1)Where,Q = Rate of heat transferk = Thermal conductivity of materialA = Cross section areaT1 = Temperature before transferT2 = Temperature after transferL = LengthFor forced convection which occurs on vertical surface and on cold surface exposed toa hot fluid, the convection heat transfer can be expressed as:Q = hA∆T (2)Where,Q = Rate of heat transferh = Heat transfer coefficientA = Surface area exposed to convection∆T          = Temperature difference between the solid and fluidThe possible radiation that can be emitted(3)Where,Ts = Uniform temperatureTsurr =The absolute temperature of the surrounding surfaceA = The surface area exposed to radiationσ = The Stefan-Boltzmann constant3.0 DESIGN AND MODELING OF TRAY DRYER SYSTEMFigure 3 and figure 4 show the overall design of the tray dryer system which consists ofseveral components. The design will be analyzed and simulated using ANSYSFLUENT.Figure 3 Design of Dryer SystemFigure 4 Exploded View of Dryer SystemZX3.1 ModelingThe actual model was designed in Solidwork and imported into ANSYS FLUENT as ahalf model to reduce the memory space and time required to perform the analysis.Figure 5 Half Model of the Dryer System3.2 Meshing and Boundary ConditionThe model was meshed by using several types of FE model or topology due to thecomplexity of the model i.e. tetrahedral, pyramid and prism elements, as shown intable 1.The boundary condition for the model was applied at the air soured inlet surface asshown in figure 7.Table 1: Volume Mesh Generation StatisticsMesh StatisticsTotal number of nodes 69327Total number of tetrahedral 176056Total number of pyramids 1108Total number of prisms 69456Total number of elements 246620Figure 6 Meshing of the Dryer SystemFigure 7 Boundary Condition3.3 Meshing and Boundary ConditionSome parameters and properties which are required during analysis are shown in table2.Table 2: Physical Parameter and PropertiesNo Physical Parameter Remarks1 Fluid Air2 Density of air 1.127 kg/m33 Specific heat (Cp) 4182 j/kg.k4 Thermal conductivity 0.0242 w/m-k5 Viscosity 1.7894e-05 kg/m-s6 Velocity magnitude (Inlet) 2 m/s7 Temperature (Inlet) 313.15 K8 Gauge Pressure (Room Pressure) 101325 Pa9 Temperature (Room Temperature) 300 K4.0 RESULT AND ANALYSIS4.1 Air FLowAs shown in figure 8, the flow velocity is evenly distributed in each direction and therepresentative flow variables and energy show that the residuals have stagnated and donot change with further iteration. Therefore, the convergence in model is consistent andbalance in time consuming.Air source surfaceFigure 8 Air Flow Rate Result4.2 Turbulence Kinetic EnergyThe turbulence kinetic energy is characterized by measured root means square ofvelocity fluctuations. The lesser the magnitude of the turbulence kinetic energy the morestable of the flow. The maximum value obtained during simulation is 9.00e+01 m2/s2which indicate that the flow is in stable condition.Figure 9 Turbulence Kinetic Energy4.3 Static TemperatureStatic temperature shows that the maximum temperature spreads and distributes evenlyin the drying chamber which means that the drying process is efficient.Figure 10 Static TemperatureStarting Point of AirFlow Velocity inDirection x, y, and zAir Flow in axis-xAir Flow in axis-yAir Flow in axis-z4.3 Static PressureAs shown in figure 11, the static pressure of the drying system is concentrated onexchanger box and the maximum pressure is 4.24e+01 Pa, which is considered verylow. The low static pressure indicates that the humidity of air flow is easily carried inand out to the drying chamber.Figure 11 Static Pressure5.0 CONCLUSIONThe design and analysis .for the tray dryer system is presented and computational fluiddynamic (CFD) for the dryer has been carried out by simulating the realistic conditionto analyze the air flow distribution /convergence, turbulence, temperature distributionand pressure to predict the efficiency of the tray dryer. The result shows that the traydryer system is sufficiently efficient according the measured parameter.6.0 REFERENCESAdapa, P. K. et al. “Performance study of a re-circulating cabinet dryer using ahousehold dehumidifier.”Drying Technology an International Journal, Vol. 20 (8)pp.1673-1689, 2004.Butturini, R. “Fixed-position electric heater.” Consumer product safety commission,United States of American .Devahastin, S.. “Mujumdar’s practical guide to industrial drying principle, equipmentand new develop.”2000.Dalfsen, B. V. “Agriculture building systems handbook: cabinet dryer.”B.C.Ministry ofAgriculture and Food, 1999.Eltief, S. A. et al. “Drying chamber performance of V-groove forced convective solardryer.”Desalination. pp. 151-155, 2007.Jack, B. “Fan noise 2003: fan selection and sizing to reduce inefficiency and lowfrequency noise generation.”International Symposium Senlis. (23-25 September2003 –Texas, United State of American), 2003.Dalfsen, B. V. “Agriculture building systems handbook: cabinet dryer.”B.C.Ministryof Agriculture and Food, 1999.Tanthapanichakoon, W. et al. “Quality and energy efficiency improvement of andindustrial tray dryer.”13th International Drying Symposium - (27-30 August 2002–Beijing, China), Vol. B, pp. 1115-1120.

CFD Simulation for Tray Dryer Optimization

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CFD SIMULATION FOR TRAY DRYER OPTIMIZATION

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