Thermodynamics

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Objective: to show the relationship between pressure and temperature of saturated steam

Apparatus: a Marcet boiler (Figure 1) is used. It is provided with a pressure gauge, a digital thermometer and a safety valve. An aneroid barometer is used to determine atmospheric pressure. 1 2 3 Drain valve Heater Overflow

Variation of saturation temperature with pressure

Thermodynamics Laboratory Manual

Marcet boiler

4 5

6 7 8 9

Temperature sensor Pressure relief valve Filler opening with plug Pressure gauge Master switch Boiler with insulating jacket

11 Temperature display

10 Heater switch

The drain valve (1) can be used to drain the vessel. An electric heater (2) is bolted into the floor of the boiler in such a way that the heating element protrudes from below into the boiler. A pressure gauge (8) is fitted to provide a direct indication of the boiler pressure. There is also a Pt-100 temperature sensor (4) to measure the boiler temperature, and a safety valve (5) to prevent excess pressure build-up in the boiler. If the Safety valve is activated, the excess pressure is discharged to the rear of the unit via a drain pipe. The boiler temperature can be read from the digital display (11) fitted into the switch box. The unit is switched on at the master switch (9). The additional 8 Thermo_Lab_Manual_BE_Year_2_r008.docx

The main element of the apparatus is the stainless steel steam boiler (7). It has a mineral wool insulating jacket. The filler opening (6) is used to pour water into the boiler. The overflow valve (3), closed off by means of a knob, is used to ensure the vessel is filled to the correct level.

Figure 1 Marcet boiler apparatus (from Gunt AG manual, model WL204)

Procedure: The boiler must be filled before the unit is run for the first time. Subsequently the level should be checked routinely after a certain number of experiments have been performed Bring the water to its boiling point with the overflow valve opened. When steam is seen coming from the overflow valve it should be closed. This is to ensure that there is no air in the boiler. With the valve shut the boiler is further heated and the boiler pressure is raised to 15 bar. Temperatures corresponding to the various pressures are recorded at 0.5 bar intervals up to 15 bar. Results: The results obtained in this experiment are approximate. Compare the results obtained in the experiment to the values given in the standard steam tables. Plot the average saturation temperature against absolute pressure for the experimental results and on the same graph plot the values obtained from the steam tables, as given below. Table 1 Saturation temperature versus pressure for water. (data generated from ASME Fortran property routines, 1993) ps/[bar] 0.90 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 ts/[°C] 96.71 99.63 104.8 109.3 113.3 116.9 120.2 127.4 133.5 138.9 143.6 ps/[bar] 4.50 5.00 6.00 7.00 8.00 9.00 10.00 12.00 14.00 16.00 18.00 ts/[°C] 147.9 151.8 158.8 165.0 170.4 175.4 179.9 188.0 195.0 201.4 207.1

heater switch (10) can be used to switch the heater on and off as required during the experiment.

Dublin Institute of Technology

9

Objective: to determine the power input, heat output and coefficient of performance of an air-to-water heat pump.

Apparatus: a Hilton air and water heat pump test stand, Figure 1, is used. The unit has two evaporators and a change over switch that allows one or the other to be selected. One evaporator takes heat from ambient air while the other takes heat from flowing water. In this test the air-source evaporator is used.

Power Input, Heat Output and C.O.P.

Thermodynamics Laboratory Manual

Heat Pump

1 2 3 7 4 5 6

Temperature indicator Evaporator pressure Temperature selector

High pressure cut-out switch Condenser pressure

12 Evaporator change over switch 14 Thermostatic expansion valve 15 Refrigerant flow meter 16 Compressor 17 Air-source evaporator 18 Heated-water...
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