Heat exchanger experiment method

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  • 03 Apr, 2021
  • 5 Mins Read

Heat exchanger experiment method

3.2 Apparatus and Materials
Steam from a boiler at 6 barg is dried and reduced to the desired pressure through a pressure reducing valve before entering the shell-side of the VSTC, while cold water is passed on the tube-side for desuperheating and condensing the steam. The vacuum system sets and maintains the desired pressure of the system. Heat is rejected through an air-cooled heat exchanger and a liquid cooled heat exchanger so that the VSTC can be properly controlled and achieve stable operation for the experimental runs.
The VSTC had 11 mountings for thermocouples spaced 100 mm apart evenly along the length of the exchanger. Figure 3.5 shows the schematic details of VSTC used for experiment. The rig was pressure tested using compressed air to find and seal any leaks. Leak detection performed before experimental runs were undertaken whenever a change or replacement carried out with the test facility. Strainer

Strainer is a form of inline screen. The strainer blocks the pipeline debris such as scale, rust, jointing compound, weld metal and other solids in flowing liquids and gases. It contains a mesh, which obstruct these solids, and allowing clean steam to pass through the process. Y-type strainer used for the experiment as shown in Figure 3.7, which is standard, compact, strong and sustained for high pressures. Y-type strainer has two orientation for installation. For steam and gases, horizontal to pipeline, which stops water collecting in pocket. For liquids, pocket should be vertically downwards. Vertically downward orientation prevents drawing debris back to the flow. Due to low dirt holding capacity, Y-type strainers requires regular cleaning, current strainer cleaned at regular interval during experiments. Separator

A VALSTEAM ADCA ENG. S.A. made S16/S baffle steam separator is used. It is the most efficient type of separator over wide range of steam velocities. Figure 3.8 shows the separator that used in the experiment. Steam Trap

An inverted bucket-type steam trap also used to discharge condensed water to the drain without losing dry steam.

Figure 3.9 shows the photo of inverted bucket-type steam trap that was used for the experiment Pressure Reducing Valve

A direct acting DR20 PN-DR pressure-reducing valve (PRV) was used to reduce the pressure of the incoming steam from a nominal 6 barg to the desired pressure (with the aid of the vacuum pump system) and also to control flow of steam.

The PRV has restricting element that provides restricted flow of steam to the system. PRV comes with pressure adjustment handle connected to diaphragm. The movement of diaphragm is use to regulate the pressure. Figure 3.10 shows the PRV used on the experimental rig, the downward pressure on the diaphragm can increase by adjusting the handle position upwards. With no inlet pressure, the spring above the diaphragm pushes it down on the poppet valve, holding it open. Once steam introduced, the open poppet allows flow to the diaphragm and the pressure in the upper chamber increases, the diaphragm pushed upward against the spring, causing the poppet to reduce a flow, finally stopping further increase of pressure (SpiraxSarco, 2007)

3.2.3 Vacuum System

A vacuum system used to reduce the system pressure below atmospheric pressure. The vacuum system included water tank (under vacuum), and a vacuum pump.
Pressure was measured by a vacuum gauge on top of the water tank. A TRMX2571-C-RX single stage liquid ring vacuum pump provides the vacuum in the system. With seal, water provided by a separate tank as seen in the Figure 3.12. The system provided a needle valve to provide precise control the vacuum.

3.2.4 Condensate Handling

On leaving the VSTC, the condensed steam and uncondensed saturated vapour from outlet of the shell-side mixed with cooling water that was entering the tank after dumping heat at plate, and fin and tube heat exchanger after flowing through tubes of the condenser. The arrangement for mixing the condensate/steam mixture into water loop is presented

3.2.5 Insulation

The test rig and steam handling system were insulated by 50 mm fibre glass wool (Figure 3.14). The insulation can withstand high temperature, 450°C.

3.3 Instrumentation and Process Control
3.3.1 Temperature

Fifteen (15) sheathed Class 1 T-type thermocouples used for measuring temperature, at different position of system. Eleven (11) thermocouples were placed along the length of VSTC, at equal distance. The remaining four of thermocouples are placed axially at the steam inlet and condensate outlet, and inlet and outlet of tube-side water respectively.
An Agilent 34970A data logger is used to record thermocouple measurements using 20 channel multiplexer. T-type thermocouples with 3 mm probe diameter embedded in a VSTC with the help of compression fittings (Figure 3.15). The depth of thermocouple probe into the annulus selected to avoid contact with tube wall. Thermocouples were calibrated carefully before actual use for accuracy purpose, based on isothermal check the error associated with thermocouples was 0.2%. All thermocouples calibrated by putting them into boiling water and water/ice mixture before mounting on the system (Figure 3.16). Individual thermocouples were then corrected based on this initial calibration. The maximum thermocouple correction was 0.44°C.

3.3.3 Flow Measurement

Flow meters from Endress Hauser, Promag 50 measured the flowrate entering the tube-side of VSTC, and the condensate coming out from tank, which is equivalent to the total steam mass flowrate (Figure 3.18).

For the experiment, the Promag 50 measured flowrate in L/min. Adjustment of a ball valve at the entry of tube-side of the VSTC controls the cold-water flow rate and a needle valve control the condensate flowrate to the drain exiting the tank. The condensate flow was also logged. Flow meter programed such that it can read flow rate of water for range of 0-5 L/min. using 4-20 mA loop with the logger.

Different heat exchanger equations coded. The Excel-macros workbook contains steam table stored that makes easier to get all properties of steam at different conditions.

3.5 Experimental Procedure

The steps in carrying out the experiments were as follows:

Steam, normal water, and compressed air were used for the experiments.

The boiler was started for steam generation.
The design has been pressure tested and made suitable for vacuum system by isolating from atmosphere and injecting compressed air through the system for leak detection. This step performed at initial stage of building of a rig, and after replacement or change in position of any part of test facility.
A Bench link data logger was switched on and Agilent IO libraries suite was started to ensure the connectivity of all measuring devices like thermocouples, and flowmeter to computer.
At first, the water level in the tank adjusted and initially noted using differential pressure transmitter.
Water flow inside the tubes of VSTC initiated by switching the water pump on.
PID loop initiated by tuning the Altivar 61 variable speed drive, to start the secondary water pump (EBARA I-38023).
The steam trap valve shut off and vacuum pump started. Required vacuum pressure maintained inside the water tank.
After achieving steady state of require pressure in tank, steam introduced to the rig by opening main steam valve. Steam trap valve also adjusted simultaneously to maintain the vacuum established in the system.
The temperature of water in the tank maintained by passing it through plate heat exchanger, and fin and tube heat exchanger driven by fan.
Data acquired from system after the steady state achieved.

Pressure of the system changed through PRV for sets of reading.

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