[email protected] Theory The temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment. This procedure is called a Throttling process. This temperature can be described by the “Joule–Thomson effect” or “Joule–Kelvin effect” or “Kelvin–Joule effect” or “Joule–Thomson expansion”.In the Joule experiment, the gas expands in a vacuum and the temperature drop of the system is zero, if the gas were ideal. In this process here is no change in enthalpy from state one to state two, h1 = h2; no work is done, W = 0; and the process is adiabatic, Q = 0. Let’s take an example of a throttling process is an ideal gas flowing through a valve in mid position. We can observe that: Pin > Pout, velin < velout (where P = pressure and vel = velocity). These observations confirm the theory that hin = hout. Remember h = u + PV (v = specific volume), so if pressure decreases then specific volume must increase if enthalpy is to remain constant (assuming u is constant). Because mass flow is constant, the change in specific volume is observed as an increase in gas velocity. The theory also states W = 0. Our observations again confirm this to be true as clearly no "work" has been done by the throttling process. Finally, the theory states that an ideal throttling process is adiabatic. This cannot clearly be proven by observation since a "real" throttling process is not ideal and will have some heat transfer. In this process, steam becomes drier and nearly saturated steam becomes, superheated. As a gas expands, the average distance between molecules grows. Because of intermolecular attractive forces , expansion causes an increase in the potential energy of the gas. If no external work is extracted in the process and no heat is transferred, the total energy of the gas remains the same because of the conservation of energy. The increase in potential energy thus implies a decrease in kinetic energy and therefore in temperature. A second mechanism has the opposite effect. During gas molecule collisions, kinetic energy is temporarily converted into potential energy. As the average intermolecular distance increases, there is a drop in the number of collisions per time unit, which causes a decrease in average potential energy. Again, total energy is conserved, so this leads to an increase in kinetic energy (temperature). Below the Joule–Thomson inversion temperature, the former effect (work done internally against intermolecular attractive forces) dominates, and free expansion causes a decrease in temperature. Above the inversion temperature, gas molecules move faster and so collide more often, and the latter effect (reduced collisions causing a decrease in the average potential energy) dominates: Joule–Thomson expansion causes a temperature increase. There is no need of boiler. the inner chamber and the outer chamber. pressure and temperature of the steam are known. we make use of a separating calorimeter. The steam is made to change direction suddenly. The comparatively dry steam in the inner chamber moves up and then down aging through the annular space between the two chambers and enters the Throttling Calorimeter. When the dryness fraction. THROTTLING CALORIMETER It consists a narrow throat (Orifice). being heavier than the vapor. COMBINED CALORIMETER . As the steam discharges through the metal basket. DRYNESS FACTOR The quality of wet steam is usually defined by its dryness fraction. It is a vessel with a needle valve fitted on the inlet side. For wet steam. When the steam is very wet. to ensure superheat conditions after throttling. the water particles due to their heavier momentum get separated from the steam and collect in the chamber. drop out of suspension and are collected at the bottom of the vessel. The steam is throttled through the needle valve and exhausted to the condenser. In a steam plant it is at times necessary to know the state of the steam. the moisture droplets. then the state of wet steam is fully defined. Pressure and temperature are measured by pressure gauge and thermometer. which has a large number of holes. which communicates with each other through an opening at the top. this entails finding the dryness fraction.SEPARATING CALORIMETER: It consists of two concentric chambers. The steam after throttling process passes through the heat exchanger and condensate is collected. It is a vessel used initially to separate some of the moisture from the steam. Steam Generator is also provided to supply the saturated steam (Max) at 2kg/cm2 pressure. It is defined as ration of mass of dry steam actually present to the mass of wet steam. Collecting the moisture: Collect the suspended moisture from the separating and throttling calorimeter then Weigh it. Dryness Factor Term dryness factor refers to wet steam.0 meter 3 Electricity supply: Single phase 220 V AC and 4 KW 4 Electronic balance say 1 kg 5 Steam table for calculation. Let in sample of wet steam X=Wd/ (Wd+W) . 5. Maintain the pressure: Now slowly open the needle valve.0mx1. Utilities Required 1 Water supply continuous for heat exchanger. 6.Separating calorimeter does not give an accurate result and the throttling calorimeter fails if the steam is not superheated after throttling. 3. 4. which contains it. 2 Space required: 1. 2. maintain the constant gauge pressure. Now at last calculate the dryness factor by the given formulae. Cleaning the setup: Firstly clean the setup and fill your setup with distilled water. Steady state is reached: When steady state is reached note the pressure difference from manometer and Temperature after throttling by thermometer. A combination of separating and throttling calorimeter is therefore found most suitable for accurate measurement of dryness of steam PROCEEDURE 1. Temperature set: Set the temperature of steam generator up to 400 K. A manometer and thermometer are connected with throttling calorimeter to measure the pressure and temperature after throttling process. it will not be superheated. This limits the extent of dryness factor.e. depend on the pressure of the steam in the main steam pipe. After that superheated steam passed through exchanger to condense the steam. A digital temperature controller provided to control the temperature inside the steam generator. If sample of steam which may still wet after passing through the throttle valve i. In others words it may not absolutely dry. It can be reliably measured. Steam from the generator passed from separating calorimeter where most of the water particle gets separated from steam and then passed from separating calorimeter where most of the water particles gets separated from steam and then passed to throttling calorimeter where steam gets superheated. Again in a throttling calorimeter steam after passing through throttle valve must be superheated or at least dry saturated. It is then passed through the throttling calorimeter where superheating takes place without change of total heat. . Wd =Weigh of dry steam in kg W=Weigh of water vapour in suspension Separating and Throttling Calorimeter The steam passing out from a separating calorimeter may still contain some vapours in it. First steam is passed through separating calorimeter where it loses most part of the it’s moisture and become comparatively drier. To overcome the difficulties we make use of combined separating and throttling.Where X= Dryness factor of sample. The temperature and pressure of the steam after throttling are measured by using a thermometer and manometer separately. Description The setup consist of separating and throttling calorimeter. A steam generator is provided at the base of apparatus. 5 120.44 123 130.78 10 36.88 40.20 17.87 159.94 105 136.33 151.45 54.0154 104.19 115.94 20 29.Experimental Setup Experimental Calculation Temperature after throttling : T1 Gauge pressure of Steam Generator : P1 Gauge Pressure before Throttling : P Manometer difference : H Volume of moisture collected : W Volume of dry steam copllected after throttling: W d Observations: T (0C) P (Kpa) T1(0C) P1(KPa) H(mm of Hg) W Wd 120.75 105.9306 .53 64.5 117.91 51. 6645 J/Kg 4) Sensible heat of water at pressure P (From steam table): HW1 = 449961 Joule 5) Latent heat of wet steam entering throttling calorimeter (Steam Table): L1 = 2237790 J/Kg 6) Total heat of dry steam at pressure P2 (Steam table): H2 = 2655180 Joule 7) Saturation temperature at P2 (Steam table): T2 = 99.6*9.61 2) Pressure of superheated steam: P2 = 101.81*18/1000 = 103.Now let me perform calculation for 2nd reading.73 KPa 3) Specific heat of steam: CP = 2081.976 . 1) Dryness fraction of separating calorimeter: X1 = Wd/(W+Wd) = 0.325 + 13.94 0C 8) Dryness fraction from throttling calorimeter: X2 = (H2+Cp(t1-t2)-Hw1)/L1= 0.