Applications Of Forced Convection Engineering Essay

Applications Of essenced Convection Engineering EssayThe experiment was carried out to verify the relationship between Nusselt modus operandi , Reynolds number and Prandtl numerate using the different concepts of convection. Relative discussions and conclusionswere drawn including the various factors affecting the accuracy of the calculated results.The main objective of this experiment was to verify the avocation mania stir relationshipTherefore, the experiment is conducted by an apparatus where hot ait from bullet train is gene wanderd and accrue through dogshit tube. Different values of temperatures and pressure were interpreted and recorded in order to calculate. Besides, graphs plotted and analysed to have a better understanding of convection heat transfer.Thus a Laboratory experiment was conducted where hot propagate from a weed was introduced through a copper tube with the help of a blower. Thermocouples were fixed in placed at various locations along the continuanc e of the copper tube. The different values of temperature and pressure were measured along with the various sections of the tube and other required values were recorded and calculated. Graphs were also plotted with the data obtained and then analysed.INTRODUCTION foment transfer science deals with the time rate of energy transfer and the temperature distribution through the thermal system. It may be follow place in three modes which is conduction, convection and radiation. Theory of convection is presented since this experiment is concerned about convective heat transfer. Convective is the mode of energy transfer between a solid rear and the adjacent liquid or gas that is in motion due to a temperature difference. It involves the combined effects of conduction and peregrine motion.There are ii major type of convective coerce convection is known as fluid motion generated by blowing air over the solid by using external devices such(prenominal)(prenominal) as fans and pumps.The ot her type is natural convection which meant by a phenomenon that occurs in fluid segments and facilitated by the buoyancy effect. It is less efficient than forced convection, due to the absence seizure of fluid motion. Hence, it depends entirely on the strength of the buoyancy effect and the fluid viscosity. Besides, there is no control on the rate of heat transfer.Forced ConvectionForce convection is a mechanism of heat transfer in which fluid motion is generated by an external source deal a pump, fan, suction device, etc. Forced convection is often encountered by engineers designing or analyzing pipe flow, flow over a plate, heat exchanger and so on.Convection heat transfer depends on fluids properties such asDynamic viscosity ()Thermal conductivity (k)Density () peculiar(prenominal) heat (Cp)Velocity (V)Type of fluid flow (Laminar/Turbulent)Newtons law of coolingWhereh = Convection heat transfer (W/(m2.C)A = Heat transfer area= Temperature of solid surface (C)= Temperature of the fluid (C)The convective heat transfer coefficient (h) is dependent upon the somatogenic properties of the fluid and the physical situation.Applications of Forced ConvectionIn a heat transfer analysis, engineers get the swiftness result by performing a fluid flow analysis. The heat transfer results specify temperature distribution for both the fluid and solid components in systems such as fan or heat exchanger. Other applications for forced convection include systems that head at extremely high temperatures for functions for example transporting molten metal or liquefied plastic. Thus, engineers buttocks determine what fluid flow velocity is necessary to affirm the desired temperature distribution and prevent parts of the system from failing. Engineers performing heat transfer analysis can simply click an option to include fluid convection effects and specify the location of the fluid velocity results during setup to yield forced convection heat transfer results.TYPICAL APPLICA TIONSComputer case cooling change/heating system designElectric fan exampleFan- or water-cooled central processing unit (CPU) designHeat exchanger simulationHeat removalHeat sensitivity studiesHeat sink simulationPrinted Circuit Board (PCB) simulationThermal optimizationForced Convection through pipe/TubesIn a flow in tupe, the growth of the boundary layer is limited by the boundary of the tube. The velocity profile in the tube is characterized by a maximum value at the centerline and zero at the boundary.For a condition where the tube surface temperature is constant, the heat transfer rate can be calculated from Newtons cooling law.Reynolds NumberReynolds number can be used to determine type of flow in fluid such as laminar or degenerate flow. Laminar flow occurs at low Reynolds numbers, where viscous forces are dominant. The condition of flow is smooth and constant fluid motion. Meanwhile, turbulent flow occurs at high Reynolds number and is dominated by inactivenessl forces a nd it produce random eddies, vortices and other flow fluctuations.Reynolds number is a dimensionless number. It is the ratio of the inertia forces to the viscous forces in the fluids. Equation for Reynolds Number in pipe or tube is as belowWhere = Fluid density (kg/m3)V = Fluid velocity (m/s)D = Diameter of pipe = The dynamic viscosity of the fluid (Pas or Ns/m) = Kinematic viscosity ( = / ) (m/s)Q = Volumetric flow rate (m/s)A = Pipe cross-sectional area (m2)EXPERIMENT OVERVIEWApparatusFigure 1 Apparatus being usedThe experimental apparatus comprises of a copper pipe, which is supplied with air by a centrifugal blower and heater as figure 1. The test section of the pipe is wound with a heating tape, which is cover with lagging. Six copper constantan thermocouples are brazed into the fence of the test section. Another six thermocouples extend into the pipe to measure the flowing air temperature. In accompaniment five static pressure tapping are positioned in the tube wall. A BS 1042 standard first step and differential manometer measure the air mass flow rate though the pipe.Experimental ProcedureFully close the valve which controlling the air flow rate.Measure the everage intermal diameter (D) of the test section pipe by using a vernier calliper. array the inclination angle of the manometer bundle to 30.Start the blower and turn the valve to the fully open position gradually,Adjust the power input to the heating tape to its maximum valve and allow the apparatus to attain thermal equilibrium.Take down the data and recordPressure lay through the metering chess openingPressure and temperature downstream of the orificeAmmeter and voltmeter readingsTube wall temperature along the interrogatory section blood line temperature along the test section argumentation pressure along the test sectionAmbient temperature and pressure.Repeat the foregoing procedure for another four different flow rate and adjust the heater input to give approximately the same wall te mperature at each flow rate.DATA AND MEASUREMENT TABLEPropertySymbolUnitsValuebarometrical PressurePbmm Hg741.60Diameter of the test section pipeDpm0.038Density of water (Manometers fluid)Kg/m31000 incline of the manometers bundledegree30PropertySymbolUnitsTest12345Pressure drop across orificeHmm H2O685565460360260Pressure drop d/s orifice to atmospherePmm H2O1781521209368Air temperature downstream orificetC3538383839EMF (Voltage) across tapeVVolts230 two hundred165142129Current through tape heaterIAmps7.36.35.55.04.0Flowing air temperaturet1C35.036.938.240.041.4Flowing air temperaturet2C36.137.738.940.641.9Flowing air temperaturet3C43.143.643.444.445.6Flowing air temperaturet4C42.242.442.443.544.6Flowing air temperaturet5C49.648.647.047.348.1Flowing air temperaturet6C63.259.655.754.354.6Tube wall temperaturet7C38.940.040.641.943.0Tube wall temperaturet8C81.2073.665.962.261.2Tube wall temperaturet9C99.889.177.571.569.5Tube wall temperaturet10C105.993.981.374.672.4Tube wall temperatu ret11C106.594.581.875.173.1Tube wall temperaturet12C108.195.582.375.072.5Air static bore-hole pressure (l.sin )P1mm H2O385324255195145Air static estimate pressure (l.sin )P2mm H2O26422317513299Air static gauge pressure (l.sin )P3mm H2O21018114110879Air static gauge pressure (l.sin )P4mm H2O10897815742Air static gauge pressure (l.sin )P5mm H2O2331201614Air static gauge pressure (l.sin )P6mm H2O00000Sample CalculationsBased on 1st set data,Power Input to the tape heaterPower = = (230 x 7.3)/1000 = 1.679Absolute Pressure downstream of the orifice741.60 + (178/13.6)=754.69 mmHgAbsolute Temperature downstream of the orificeT = t + 273 = 365+ 273 = 308 KThe Air quid Flow Rateair =5.66x = = 231.88231.88 Kg/hr = 0.06441 Kg/sec,Since 1 Kg/hr = Kg/sec add up Wall Temperature= (38.9+81.2+99.8+105.9+106.5+108.1)/6 =90.07Average Air Temperature= (35+36.1+43.1+42.2+49.6+63.2)/6 = 44.87The Bulk Mean Air (arithmetic average of mean air) Temperature= (35+63.2)/6 =49.1The Absolute Bulk Mean Air (a rithmetic average of mean air) Temperature49.1+273 =322.10 KThe Properties of Air at TbUsing the tables provided in Fundamentals of Thermal-Fluid Sciences by Yunus A.CengelFrom the table A-18 (Page958), Properties of Air at 1atm pressure at KDensity, = 1.1029 kg/m3Specific Heat Capacity, Cp = 1.006 kJ/(kg.K)Thermal Conductivity, k = 0.0277 kW/(m.K)Dynamic Viscosity, = 1.95 x 10-5 kg/(m.s)Prandtl Number, Pr = 0.7096The Increase in Air Temperature63.2-35 = 28.2The Heat off to Air(231.88/3600) x 1.006 x 28.2 =1.827Where = Heat Transfer to air= Mass flow rate= Specific heat capacity= Increase in air temperatureThe Heat losings1.679-1.827 = -0.148Where = Heat losses= Heat Transfer to airThe Wall/Air Temperature Difference90.07-44.87 = 45.2Where = Wall/Air temperature difference= Average air temperatureThe Heat Transfer Coefficient= ((231.88/3600) x 1.006 x 28.2) / (3.14 x .0382 x 1.69 x 45.2) = 0.199 kW/ (m2 .k)Where= Mass flow rate= Specific heat capacity= Increase in air temperature = Average Diameter of the Copper pipe.= Length of the tube= Wall/Air temperature differenceThe Mean Air Velocity= (4 x (231.88/3600))/ (1.1029 x 3.14 x (0.0382 2) = 50.9575 m/sWhere= Mean air velocity= Mass flow rate= Density= Average Diameter of the Copper pipe.The Reynolds NumberThe Nusselt Number= Nusselt Number= Average Diameter of the Copper pipe.= Thermal conductivityThe Stanton NumberWhereSt = Stanton Number= Nusselt Number= Prandtl numberRe = Reynolds numberThe Pressure Drop across the testing sectionat Tb = 320.1 K= Pressure drop across the testing section= Absolute pressure downstream of orifice.= Barometric PressureThe friction FactorRESULTPowerPowerkW1.6791.2600.9080.7100.516Absolute Pressure downstream of the orificePmm Hg754.69752.78750.42748.44746.60Absolute temperature downstream of the orificeTK308311311311312Pressure drop across the orificeHmm H20685565460360260Air mass flow Rateair231.88209.31188.57166.60141.18Average wall Temperaturetw90.0781.171.5766.7265.28Ave rage air temperaturetair av44.8744.8044.2745.0246.03Bulk Mean air temperaturetb49.148.2546.9547.1548.0Absolute bulk mean air temperatureTbK322.1321.25319.95320.15321.0Density at Tb1.10291.10581.11021.10951.1066Specific Heat Capacity at TbCp1.00601.00601.00601.00601.0060Thermal Conductivity at TbK2.772.762.752.752.76Dynamic Viscosity at Tb1.951.951.941.941.95Prandtl Number at TbPr0.70960.70960.71000.71000.7098Increase in air temperature from t1 to t6t a28.222.717.514.313.2Heat transfer to airairW1.8271.3280.9220.6660.521Heat losseslossesW-0.148-0.068-0.015-0.044-0.005Wall/Air temperature differencet m45.236.327.321.719.25Heat transfer Coefficienth0.1990.1800.1670.1510.133Mean air velocityCm50.957545.87741.16736.39430.922Reynoldss NumberRe110096.35399380.14489994.33079509.22567204.418Nusselt NumberNu274.4249232209.8184.1Stanton NumberSt0.003510.003530.003630.00370.0039Pressure Drop across the testing sectionP1746.421491.591176.73912.57667.08Friction Factorf0.013780.01450.01410.01410.0 143Results piece AExperiment12345Y=ln(Nu x Pr-0.4)5.755.655.585.485.35X=ln(Re0.8)9.299.219.139.038.89Y-X-3.54-3.56-3.55-3.55-3.54Plot BExperiment12345Y=Nu274.4249232209.8184.1X=Re x Pr78124.3770520.1563895.9756451.5547701.69Stanton numberReynolds AnalogyExperiment12345Friction factor0.013780.01450.01410.0140.0143Reynolds Analogy0.006890.007250.007050.0070.00715Stanton number0.003510.003530.003630.03720.0386DISCUSSIONIn order to get more accurate results, there are some suggestions like cleaning the manometer, checking the insulation on the pipe and making sure the valve is closed tightly.An additional way to prove the heat transfer equation is by re-arranging it.Nu = 0.023 x (Re0.8 x Pr 0.4)Substituting in the experimental values into the above equation from section 5.0 returns the following results belowExperiment12345Y=Nu274.4249232209.8184.1X=Re0.8 x Pr0.49415.088674.518014.487258.346344.14Y/X0.0290.02870.02890.02890.029Comparing this to the heat transfer constant, it shows that there is a little difference and which can be negligible.It can also be done by taking the gradient of the line from the plot Nu against (Re0.8 x Pr0.4)as shown below deductionA better understanding of the heat transfer was achieved through conducting the experiment. Theoretical sums and experimental values were found to be approximately similar and the different sources of geological fault have been identified.The main objective of this experiment was to verify the following heat transfer relationshipNu = 0.023 x (Re0.8 x Pr 0.4)Therefore, relation of forced convective heat transfer in pipe is cleared and the objectives were completed.