Expansion Across a Valve

Check the initial guess box and set this to IF . Press the Calculate button 

What is the new temperature if the outlet pressure is reduced to 3100 psia  

Hint You may need to use an initial guess to get the iteration to converge (try 50°F). 

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Extraction of nicotine from tobacco using supercritical fluid is carried out in a manner quite similar to the decaffeination of roasted coffee described in U.S. 3,843,824. Tobacco is first contacted with dry supercritical CO2 which extracts the aroma constituents. The C02-aroma stream is expanded to subcritical conditions via expansion across a valve the aromas precipitate from soludon. The CO2 vapor is recompressed, is adjusted in temperature to supercritical conditions via heat exchangers, and is recycled to the extractor via a compressor. The aromas extracdon step condnues until the aroma constituents are removed from the tobacco. 

By measuring the temperature change accompanying a differential volume change in a free expansion across a valve and separately in a reversible adiabatic expansion, the two derivatives cT/dV)H and [cT/dV)s can be experimentally evaluated. 

The simplest continuous-distillation process is the adiabatic single-stage equihbrium-flash process pictured in Fig. 13-25. Feed temperature and the pressure drop across the valve are adjusted to vaporize the feed to the desired extent, while the drum provides disengaging space to allow the vapor to separate from the liquid. The expansion across the valve is at constant enthalpy, and this facd can be used to calculate To (or T to give a desired To). 

The air feed is first compressed and heat of compression is removed from the stream by intercooling, aftercooling and direct water quench. The elevated pressure airstream is purified to remove water and other impurities and it is then expanded to a lower pressure to generate the reduced temperature necessary for liquefaction. Expansion takes place either across a valve (Joule-Thompson expansion) or through a turboexpander producing useful work. The compression, cooling and subsequent expansion of the air feed stream constitutes the refrigeration cycle. 

One of the classic examples in thermodynamics is the expansion of a fluid across a valve (or a porous plug), which is a constant enthalpy process. The process is shown in Figure 1. The specification of this process is given the temperature and the pressure of the inlet (state 1) and the pressure at the outlet (state 2), calculate the temperature of the outlet stream. Since this is an isenthalpic process, we also know that ... 

Systems are normally designed to work satisfactorily during maximum amhient conditions, and the condenser will he sized for this. In colder weather, the condensing temperature and pressure will fall and the resulting lower pressure difference across a thermostatic expansion valve may lead to malfunction. A drop of pressure difference to half the normal figure may reduce mass flow helow that required, and it will he necessary to prevent the condenser pressure from falling too low. 

Expansion cooling You would suspect that when we depressure gas it would cool, if the gas gets hotter upon compression. Except for pure hydrogen, that is correct. Steam, air, and fuel gas all cool when we let the pressure down across a control valve. 

The retention data described by Equation 2 are corrected from ambient conditions to the prevailing temperature and pressure conditions within the sorbent column. Use of the expansion valve at the end of the chromatographic column resulted in a negligible pressure drop across the sorbent bed, thereby simplifying the pressure correction factor used in the retention volume computations (23, 39). 

Calculate the horsepower (HP) needed to process a 8500-acfm gas stream from an incinerator. The pressure drop across the various pieces of process equipment has been estimated to be 8.4 in. H2O. The pressure loss for duct work, elbows, valves, and so on, and expansion-contraction tosses are estimated at 5.8 in. H2O. Assume an overall fan-motor efficiency of 58%. 

When the bottoms product is a good refrigerant, the scheme in Fig. 17.10c is a possible candidate for reducing energy consumption. Bottoms liquid is flashed across the expansion valve to a pressure corresponding to a saturation temperature of the distillate. The overhead condenser then doubles as the reboiler. 

Process 1 Finite stepwise irreversible expansion. From the initial conditions, we want to expand the methane to 1.1 bar. To create a pressure imbalance across the piston, we vent the air chamber. In this first example, air is removed by cycling the ball valve open and shut three times. During each cycle enough air is vented to reduce P by 0.1 bar. The vent line is so large that each drop in Pgj t is nearly instantaneous. Between each cycle the system is given time to reestablish equilibrium, as indicated by steady readings on the pressxue gauges and the position indicator. 

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