nN 2 @ 5. Objective Aim Introduction Theory Description Utilities Required Experimental Procedure Observation & Calculation Nomenclature Precautions & Maintenance Instructions Troubleshooting References Block DiagramEXPERIMENTAL WaTER CooLine Tower OsJective: : dynamic conditions, Aw: 241 To calculate the tower characteristic (Tc) of water Cooling tower for various liquid and air flow rates. Intropuction: Water from condensers and heat exchangers is Usually cooled by an air stream in spray Ponds or in cooling towers-using natural draft or forced draft by flow of the air Mechanical draft towers are of the forced draft ‘pe, where the air is blown into the tower by a fan at the bottom. The forced di raft materially reduces the effectiveness of the Water may be cooled by the air as lon temperature of the entering air. Markel’ '9 as its temperature is above the wet bulb Potential difference as the driving force. 's theory is used which is based on enthalpy For mass transfer operation: Each particle of water is assumed to be surrounded by a film of air and the enthalpy difference between the film and the Surrounding air provides the driving force for the cooling process. In the integrated form Markel's equation can be written as: Kav (a)(3) Ts + 0.4(7, ~T,) Ma =Ts -0.4(7, -T) A, Wa =Ts OWT, ~7,) ha=h, +0.4LIG\T, ~T,) hash, +0.4(L/G\T, ~7,) A, 2 ~O4(LIG)\T, ~T,) ~O.4(LIG\T, ~T,) kav i Where “T™ is tower characteristics also called mass transfer coefficient group. ah i Summation of reciprocal of enthalpy difference, enthalpy of air. UG is liquid to air flow ratio, Tharhs ate enthalpy of water, hy, f . y-he are enthalpy of air at wet bulb] temperature. “ The carrying of liquid with the gas stream is termed as liquid ent due to a high rate of air flow, This should be avoided to get better performance. Description: ‘The setup consists of tower which is forced draft countercurrent type. Fan is provided at ‘the bottom of the tower. There is an orificemeter mounted with its taps connected to a manometer to measure the flow rate of air. Butterfly valve is given to control the air flow 3 rate. Nozzles are provided for distribution of water on the packing. Rotameter is given to contml the water flow rate. A water tank atthe Gottom fited with level gauge is proves. Pump is provided for circulation of hot water. Temperature sensors are provided to Measure the dry bulb & wet bulb air temperatures. The cooling tower is packed withae Re Umiuities REQuireD: 6:4 Electrical Supply: Single Phase, 220 V AC, 50 Hz, 5-15 Amp combined socket with earth connection 62 Water Supply 63 Floor Drain Required. 64 Floor area required: 1.2m x 1m ExperIMENTAL PROCEDURE: 7.1 Startinc PRoceDURE: 7.1.1 Close all the valves Vi-Vs._ = 7.1.2 Ensure that switches given on the panel are at OFF position. 7.1.3 Open the valve V; and fill the water. 7.1.4 Connect electric supply to the set up!” 71.5 Set the desired water tempetature in the DTC by operating the increment or decrement and set button of DTC. 7.1.8 Open by pass valve V3 and switch ON the pump. 7.1.7 Switch ON the heater and wait till desired temperature achieves. 7.1.8 Switch ON the blower. 7.1.9 Allow hot water to flow through cooling tower and adjust the flow rate by rotameter and control valve V2. 7.1.10 Allow air to flow through cooling tower and adjust the flow rate by control valve V, provided in pipe line. 7.4.11 At steady state (constant water temperature) record the temperatures. 7.4.12 Record the flow rate of water & manometer reading, 7.1.13 Repeat the experiment for different water & air flow rates. 7.4.14 Repeat the experiment for different water temperature. :7.2 Cosine Proceoure: 72 72 723 72 4 4 2. Switch OFF the pump & blower OsseRVATION & CALCULATION: ‘Switch OFF main power supply. When experiment is over switch OFF the heater Drain the water tank by open the valve Vs, 8.1 Data: Gross sectional area a = 0.0225 mi Diameter of orifice de = 0.026 m Diameter of pipe d, = 0.062 Coefficient of discharge Ca =0.64 ‘Acceleration due to gravity g = 9.81 msec” Density of water pw = 1000 kgim® Density of air pa =1.21 kgim> 8.2 Osservation TaBLe: Ss. th Tz Ts. Ts Ts Ry No. | @C) | (°c) @e) | Pc) | Cc) | (em) 8.3 Catcutations: 4H ARR (ped 100 (* yoM, = «Po (kg/sec) Qe, M = ~""To000%3609 (ka/sec) Gs a (kg/sec m2) is (kg/sec m’) a R= o|~ Ta=Te +010, ~1,) (0) Twa =, + OA(T, ~T,) Cc) tee =T, ~0.4(T,, ~T.) Cc) Tae =T5 OAT, ~T,) (c) » To Calculate the Property of Tye, Water (by) at temperature T, (bya) at temperature Twa, ¥ wt, (Daa) at temperature (haa) at temperature Ty ber (kag ary airy bes ————— (kiig dry airy Ping dry air) | Mee Geingy dry air) x To calculate the Property of air (h, hs 1) at temperature Ts, “— (haikg dy air h, A, +R(T, -T,) (kulkg dry air) hay = My +0.4R(7, 7, (kulkg dry ai) hash +04xR (To ~T.) (kulikg dry ait) ee. ee- a2 id | msec Given | Kilkg dry air | Caiculateg kalo dry air | Caleuateg | ate tistics temperatures | Kikg dry art Calculated | lass transfer coefficient | Kglsec qt | Calculated | || . | | U [Nes ey fvaer ———__#sen? "| Cateuiated | Ma | Mass flowrate ofa | kaise) Saicuos Mw | Mass flow rate of water kgisec | Calculated | Qe | Volumetric flow rate of ar milsec | Calculated | Qu | Flow rate of water LPH) Measured | R | Liquid to air flow ratio * [Cateutated | RiRe_ | Manometer reading em Measured | | T, /Airinlet dry-bulb temperature °C Measured | Th Air inlet wet-bulb temperature °C Measured | Ts [Air outlet dry-bulb temperature C Measured | 14 _ | Air outlet wet bulb temperature °C Measured | Ts Water inlet temperature °C | Measured | Te | Water outlet temperature °C | Measured | ) T, | Tower characteristics . Calculated | Tw-Tws | Characteristics temperatures of water *c Calculated | pa | Density of air im on | —— Pw | Density of water kgim’ Given | aH Head ess mi Calculated | 4h | Summation of reciprocal of enthalpies diference | Kiikg dy a Calculated | aii i fated | Ahr-hh« [Enthalpies difference at characlerstios | kg ary air | Calculates | temperature J = * Symbols are unit less. 10. PRECAUTION & MAINTENANCE INSTRUCTIONS: than 230 10.1 Never run the apparatus if power supply is less than 180 volts and more volts. Il the ON/OFF 10.2 Never switch ON the mains power supply before ensuring that a! Switches given on the panel are at OFF position. ee eefys = he —0.4xR(T, -T,) (kd/kg dry air) Nyy = he = 0.1xR(T; -T.) (kd/kg dry air) Ah, = Pyy — Mor (kJ/kg dry air) Ah, = Fy2 ~ Mee (kulkg dry air) Ay = Fiys — Hes (kJ/kg dry air) (i, = Baa hye (Klaas ry at) CALCULATION TABLE: S.No. Te To plot the graph of 7. vs R. 9. NoMmENCLATURE: Nom Column Heading » Cross section area @ | Area of orifice Area of pipe Coefficient of discharge Diameter of orifice TFaleilated— MALAVIYA NATIONALINSTITUTE OF TECHNOLOGY JAIPUR DEPARTMENT OF CHEMICAL ENGINEERING EXPERIMENT NO 03: LIQUID DIFFUSION FOR AIR- ACETONE SYSTEM (Diffusion of A through non diffusing B) on data JECTIVE: To determine the mass diffusivity of acetone vapor in the air and compare with literature APPARATUS: Stefan tube apparatus, hermometer, stop watch, acetone, THEORY The principles of momentum transfer and heat transfer are applied in most branches of engineering but the application of the principles of mass transfer has traditionally been the province of the chemical engineer. Mass transfer refers to the tendency of a component of a fluid to flow from a region of high concentration to one of low concentrations, Molecular diffusion is the transfer or movement of individual molecules through a fluid by random molecular movements. In the diffusion process. the molecules of interest flow from regions of high concentration to low concentration, Molecular diffusion can occur in both directions with the system, The diffusivity or diffusion coefficient (DAB) is a property of the system. dependent upon the temperature, pressure and nature of the components. Fick’s law: The rate of mass transfer is expressed by Fick’s law which for molecular diffusion in t rection x in a fluid of constant molal density is expressed below. Where: JA = flux of constituent A relative to the average molar velocity in units of moles/m’s DAB = diffusivity of constituent A in solution B in units of m/s. CA = concentration of constituent A in units of moles/m’ The flux of the constituent is the ra © of m ss transfer per unit cross sectional area. The flux can be expressed as JA relative to the average molar velocity or as NA relative to a fixed location in space. For diffusion of A through stagnant B the flux is given by (for gases)3as-Phase Diffusion Coefficient’ 39) Integration of Eq. (2.49) within the above limits gives the working equation for the calculation of Dag. That is, aD fl 1), 8 50) L (t ir} (2.50) Sto be measured in this experiment are the initial pressure in the vessels and the partial pressures of one of the components (say A) in the vessels at the end of the experiment The mutual diffusion coefficient Day can be directly determined from Eq. (2.50). The quantitie 2.5.2 Use of the Stefan Tube This method is suitable if, under the given set of experimental conditions, one of the components (say A) is available as a volatile liquid and the other component (B) is a gas which is not soluble in A. The apparatus is very simple. A vertical glass tube, sealed at the bottom, is joined to a larger diameter horizontal tube to form a tee (T) as shown in Figure 2.12. The liquid A is taken in the narrow vertical tube and the gas B is forced through the horizontal tube Evaporated A diffuses through the mixture of A and B in the vertical tube, reaches the top and is swept away by the flowing stream of B. As B is insoluble in A, i will not diffuse and the situation will conform to diffusion of A through non-diffusing B. The liquid level in the vertical tube will drop very slowly and pseudo-steady state assumption (i.e A diffuses through the tube virtually at steady-state at all time) is reasonable. This means that as the liquid level falls by a small amount, a new steady- State rate of diffusion is established simultaneous y- The drop in the liquid level over a period of tme is noted. P41 = Vapour pressure of liquid 4 Let, at any time 4, the the partial pressure of A at ical tube, pq, be Uhrough this distance z is fusional flux of A Volatile liquid A 251)40 Chapter 2 Molecular Diffusion Wf the fallin the liquid level is dz in a small time di, the number of moles of A that diffuse out is ada(p,/M,). By a material balance over the time di, ade py saNdie —2 M aN, dt Here a is the inner cross-section of the vertical tube, p, and M, are the density (of the liquid) and molecular weight of A respectively If at time f= 0, the liquid level is at zo from the top, and attime f (1c. at the end of the experiment) the liquid Level is at z’, integration of the above equation and rearrangement gives (2.82) ‘The partial pressure of A atthe liquid surface, pq), s equal to its vapour pressure at the prevailing temperature, At the open top of the tube, the partial pressure of A is virtually zero (p, % ‘because A is greatly diluted by the gas B flowing at a high rate. All the quantities being known, Dag can be calculated. 2.5.3 Predictive Equations for the Gas-phase Diffusivity Although experimental diffusivity values for a large number of binary gas mixtures are available, ‘we often come across mixtures for which no experimental data have been reported. In such a case, ‘we take the help of a suitable predictive equation or correlation for the estimation of diffusivity ‘Many such predictive equations—theoretica, semi-empirical or empirical re available. A detailed account of the more important equations and their suitability is given by Poling et al. (2001). ‘A useful and reasonably accurate theoretical equation based on the kinetic theory of gases ‘was suggested independently by Chapman and by Enskog. The diffusion coeffictent Dap strongly depends upon binary interaction parameters of the A-B pair. Chapman and Enskog used the Lennard-Jones potential function (Chapman and Cowling, 1970) given below to calculate the interaction parameters. an f(2)'-(2)] (2.53) potential energy r= distance between the centres of (wo molecules ‘end 6 = Lennard-Jones potential parameters, ‘The Chapman-Enskog equation is given by 1 Das 85810" TY? My + My) + m/s PQ (254) Here absolute temperature, in K My Mp molecular weights of the components A and BMOUID DIFFUSION FOR AI. ACETONE SYSTEM (Diffusion of A through non ifasing 8) EXPERIMENTAL PROCEDURE: The apparatus employed to esti imate the 2.12. mass diffusivity of acetone vapor in air is shown in figure 7 a method involves passing air over the open top ofa graduated tube partially filled with | liquid acetone which is maintained at ambient temperature. Stepwise experimental procedure is as follow : Fill the Acetone up to the certain level in the Stefan tube apparatus. | | Open the air blower valve, regulate at constant air flow rate at the entrance of Stefan tube | eal | The air flow rate is maintained at a rate minimum to sweep away acetone vapour from the top | of this tube, but, at the same time keeping the turbulence at the junction to a minimum. Under these conditions the concentration of acetone vapour at the top of the graduated tube may be taken to be zero and the air above the acetone in the tube can be considered to be | stagnant. Before carrying out the experiment measure the distance from the ‘0’ graduation of the measuring scale to the junction of the tube carrying the stagnant gas. Record this as L. 6. Take the same observation with the time interval of Smin. repeat until 10 successive readings. 7. Perform the same experiment for different at least three set of temperature 8. After the experiment close the air supply and power off the apparatus OBSERVATION TABLE: {SNO] Temperature (O) | Time, § | (Ty- To) RESULT: Diffusivity of acetone into air (experimental and theoretical) values at different temperature is calculated 14ayr» ' Soup In Air Dirrusion APPARATUS f ’ (VaPoRization OF NAPHTHALENE) / ’ i Ve Opsective: » To study the vaporization of naphthalene in air, b 2. Aim: d > e 1 To calculate the mass transfer coefficient for vaporization of naphthalene in air > using a packed bed of spherical particles of naphthalene > 22 Toplot (Shy Sc)? vs Re ona log-log graph and determine the functional relationshi “within the-solidssis, ofmoréimportance=—=—=— THEORY: @ component A (naphthalene) diffusing through non-diffusing B (air) at ambient ‘emperature, with diffusivity coefficient Das in packed bed of sphere particle ‘Then mass transfer coefficient can be calculated by following correlation: Where Re is Reynolds number, Dp, V and v are Particle diameter, velocity of air and kinematics viscosity of air ¢ is schmidt number. sherwood number= a —__ vs (Re) ona log-log paper. ars [we] a Plot the graph of (Sh/Sc)'* @ Nome NCLATURE: 7 Column } Heading z =i rest Setonal sie oFeotma™= _ . Diffusivity: Soetiicient== Diametero| SMOF column= “DS Average diameter of of the sphere k. | Mass transfer Coefficient L Q Flow rate of air Reynolds number | , Se | Schmidt number ® Sherwood number a 5 Ambient temperature V | Velocity of air m/sec Calculated, msec | Given i Kinematics Viscosity of the air | y * Symbols are unitless. 0. Precaution & MAINTENANCE Instructions: 10.1 Air Pressure should be constant during the experiment. 102 Silica gel should be dry. 103 Don't exceed the pressure above 1kg/cm? = Epes Pt Lente Tl ea; wvv wv “, ‘ bieaFy +g. wi bs En Growth 7.2 Closing Procepure: 724° When &Xperiment ig Over remove the balls from Set-up, 7.2.2 Remove the Connection of Compressed air Supply. 8. OBSERVATION & Catcutation: —____ ee oe ee . 8.1 Data: “Tibient temperature T 20°C —y Kinematice Viscosity of the air y = 1.540 meq” ae _ | Average diameter of the sphere Dp = m Diameter of the column D. » aa : Caccutations: | a) my “Ac = =D? (mm?) “4 Q } V= (A F000%60) (m/sec) i wi Re = PDeV v Sc Oo } 3 i i 17 « Re ‘! | 6.4 k, = SPxDyy . 0 Pp ke is mass transfer Coefficient, Description: The equipment is fitted with a Vertical glass $ column with g Mesh near the base of col { to hold the Spherical balls, Spherical ball make a packed bed. Air is all IS of known diameter are filled in the colum bottom of a a Pass through the Silica gel member. Fromi the column, dry air is allow ed to enter in the Packed bed, Rotametel Provided to Measure the flow Fate of air, Utiuities REauirep: Compressed Air Su TAA Pack the glass tube with knor wn number and known diamet Naphthalene balls Up to a height o f about 15 cm, 74.2 Record the average diarneter of the naphthalene ball, 71.3 Connect the air line from the com, pressor to the valve V2 at the base oj column. 7.1.4 Note the ambient temperature, 7.1.5 Open the valve V; and set the flow rate of air. Allow the air to flow through the Packed bed for g fixed time (say 60 7.1.7 Record the flow rate of air. | 718 Repeat the experiment for different flow rate of air