Thermodynamics

1 January 2017

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

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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.

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 outlet 13 Water-source evaporator water flow meter 10 Condenser water flow meter 11 Main power switch 9 8 Water-heating condenser Electric power meter Condenser liquid receiver Water-source evaporator 19 Inlet of water to be heated

The main components involved in this test are described briefly here. The refrigerant compressor (16) is electrically powered and its power consumption is displayed on a meter (5). Hot, high pressure refrigerant goes from the compressor to the condenser (9), which is of the tube-in-tube type. In the condenser there is heat transfer to the water that is to be heated. The refrigerant condensate from the condenser accumulates in the liquid receiver.

Heat pump test apparatus (Hilton, model R832) 0 Water-source evaporator water inlet 21 Water-source evaporator water outlet thermostatic expansion valve a pressure drop occurs causing part of the refrigerant to become vapour. The mixture of liquid and vapour flows to the air-source evaporator (17) where it receives heat transfer from the air and evaporates to become entirely vapour. The low pressure vapour leaving the evaporator returns to the compressor. Dublin Institute of Technology The water to be heated (19) comes from the cold water supply. It passes through a variable area flow meter (16) before passing through a cooling coil within the compressor.

In this way waste heat from the compressor contributes to the overall water-heating effect. The water then passes through the condenser where the main heating occurs. Thermocouples on the water circuit allow three required temperatures to be displayed on the temperature indicator (3). These are the water inlet temperature, the temperature after passing through the compressor and the final exit temperature. Procedure: 1. Turn on the water supply to the unit and turn on the main switch. 2. Select the air evaporator by pressing the evaporator change over switch down.

Set the condenser gauge pressure to a desired value between 700 and 1100 kN/m2 by adjustment of the condenser cooling water flow rate. 5. Allow time for all of the system parameters to reach a stable condition. Then record the test readings. 6. Repeat steps 4 and 5 until the desired number of tests have been conducted. Results: The main results are the power input, the rate of heat transfer to the water and the coefficient of performance, which is the ratio of the heat output rate to the power input. The waste heat recovered from the compressor can also be calculated. These should be graphed against the exit temperature of the heated water.

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