STANDARD OPERATING PROCEDURE AND SAFETY GUIDE FOR FORCED CONVECTION HEAT TRANSFER APPARATUS (Located in Rm. H-19 Head Hall)

Transcription

1 STANDARD OPERATING PROCEDURE AND SAFETY GUIDE FOR FORCED CONVECTION HEAT TRANSFER APPARATUS (Located in Rm. H-19 Head Hall) Prepared May 16, 2010

2 Table of Contents 1. Scope Objective Regulations Apparatus Overview and objective Apparatus overview Hazards and control evaluation Possible fire event Ventilation Kinetic, thermal & accoustic Electrical Hot air General, physical & equipment concerns Access Training Personal equipment Operation Qualified personnel Experiment preparation Lab instructions Operating procedure Inspections Operational & Periodic inspections Typical test...22 Appendix A: Experiment field notes sheet...23 Appendix B: Experiment calculation method...26 ii

3 H-19, Head Hall floor plan Figure 1: H-19, Head hall floor plan 3

4 1. Scope 1.1 Objective This standard operating procedure is intended to provide operating instructions and safety information for the Department of Mechanical Engineering s forced convection heat transfer experiment apparatus located in H-19, Head Hall. This document is intended as a guideline and supplement to proper training that must be provided by qualified personnel before the apparatus is operated. The aim of this document is to ensure that safe work practices have been developed for the forced convection heat transfer experimental work. This SOP is primarily concerned with the procedure, hazards involved in the experiment and safety precautions that must be taken to avoid injuries. 1.2 Regulations This document has been developed in accordance with the Environmental Health and Safety Office of the University of New Brunswick. 2. Apparatus Overview and Objective: 2.1 Apparatus overview The experimental apparatus consists of an electrically powered fan. The fan forces air through a long pipe which has an orifice plate mounted in it. The orifice plate determines the flow rate of air from the fan, by measuring the pressure difference across the orifice plate. The pressure difference across the orifice plate is measured by the pressure transducer assembly at the rear of apparatus, which is then displayed on the digital display of the apparatus. There is a gradual reduction in pipe diameter before the test section. The test section has an internal coiled heater along its length to provide heat to the test section. This resistive heating wire coil is powered by an electrical source via a cable. The heating power is controlled by Variac which can deliver variable power to the coiled heater. There is a small Variac transformer unit located at the bottom of Variac, which varies the voltage and current to the resistive heating wire element. The heating power signal is sensed by the watt transducer from transformer unit. It measures the heating power by sensing the voltage and current and it outputs a voltage that corresponds to the power consumption. The output signal in mv is then 4

5 amplified by the amplifier which can then be displayed on a digital display in watts. There are two analog displays which reveal the voltage and current to the coiled heater as well when varied by the Variac. An power indicator of consisting of a red light indicates the ON/OFF status of coiled heater. The coiled heater is properly insulated in between Mica layer/plaster case and fiber glass lagging. The test section is a 1.25 inch, inside diameter of copper tubing having a wall thickness of inches. The coiled heater in the test section is insulated from the tube between the Mica layer/plaster case and the fiber glass lagging layer. There are seven thermocouples placed along the test section to measure the surface temperature of the copper tube test section and the temperature of air in test section. They are connected to a Temperature indicator dial. The dial can be rotated to determine the desired temperature which will be displayed on digital display of apparatus. The exit section of the test section pipe has a radial temperature and pressure measuring device, which measure the exit temperature and the pressure of the air. The exit pressure is measured by a Pitot tube relative to atmospheric pressure and can be read from the U-tube manometer of the apparatus. The manometer is filled with red gauge oil of a specific gravity of The amount of air entering the fan can be controlled by the threaded damper on the fan inlet. The exit temperature is measured by a thermocouple via temperature transducer assembly and is displayed on digital display of apparatus. The temperature transducer assembly is in the electrical box of apparatus. All the temperatures can be read on the digital display by altering the dial on the apparatus. There is rotating dial that causes the transverse motion of Pitot tube and thermocouple assembly. Two turns of the rotating dial transverses the assembly 0.10 of an inch. Please see Figures 2, 3, 4, 5 & 6 for description of components of the apparatus. The apparatus is used to develop a practical understanding of forced convection heat transfer for the students. After completing this experiment, the students are able to determine the convective heat transfer coefficient and friction factor of air forced through the pipe and evaluate the Reynolds analogy. The students are also able to measure the radial velocity and temperature profile of air in the internal pipe flow for this apparatus. For complete details on Lab work for students and theory behind the forced convection heat transfer experiment, please refer to Appendix B. 5

6 Figure 2: Apparatus component overview 6

7 Figure 3: apparatus components overview 7

8 Figure 4: Apparatus component overview 8

9 Figure 5: Apparatus component overview 9

10 Figure 6: Apparatus component overview 10

11 Please see the schematic Figures 7 & 8 below of the apparatus to completely understand the apparatus: Figure 7: Apparatus schematic Figure 8: Test section length and position of 7 thermocouples 11

12 3. Hazards and Controls Evaluation:- 3.1 Possible fire event In the event of fire, evacuate the room immediately. Pull the nearest fire alarm (located outside room H-17, see H-19 floor plan in figure 1). Should you return to attempt to extinguish the fire, do not do so alone. Make one attempt only and if unsuccessful leave immediately. If successful stay at the scene and have someone alert Security (ph. # 4830) and the Environmental Health and Safety Office (ph. # 5075). Please refer to Figure 1 (H-19, Head hall floor plan) to see the locations of fire extinguisher, fire alarm pull station and phone. 3.2 Ventilation There are no ventilation fans in room H-19 for room ventilation. However, when the forced convection heat transfer apparatus is in operation, the front door of room H-19 is kept open to introduce fresh air in the room and exhaust the hot air leaving the test section of apparatus. There is also an air conditioner in the room which should be utilized for lab cooling while the apparatus is in operation. 3.3 Kinetic, Thermal and Acoustic The only moving part associated with the apparatus is a Variac (see Figure 2) and it doesn t pose any kinetic threat if handled carefully. The air fan is well protected. The test section consists of a coiled heater and is insulated such that the apparatus doesn t pose any thermal threat. If however, any of the electrical components of the apparatus overheat and cause the apparatus to become hot or produce smoke then TURN OFF the apparatus immediately by pressing the Stop button (Red button) on digital display (see Figure 2 and Figure 10) of apparatus. This will turn off the fan which will automatically turn off the coiled heater. Press the coiled heater power switch to off as well as all the digital display power switches to ensure that there is no power supply to the apparatus. Notify the Lab technician/instructor immediately. In the case of apparatus switch failure when powering off the electrical components, follow the lock-out/tag-out procedure instructions to locate the main electric supply of the apparatus and cut off the main disconnect electrical supply. All the wires and cables of the apparatus are well insulated 12

13 so there is no usual threat associated with wires overheating, however the apparatus should be checked regularly for bare and damaged wires. 13

14 Figure 9: Apparatus test section insulation layers 14

15 Figure 10: Apparatus electrical component Power ON/OFF push buttons The apparatus fan is slightly noisy but it does not pose any acoustic threat. If continuous fan noise makes the user/operator feel uncomfortable, then the user can wear ear plugs. Furthermore, if there is any other equipment being 15

16 operated in H-19 room while using the forced convection heat transfer apparatus and it requires hearing protection then disposable earplugs shall be worn by students, instructors and all other room occupants. Instructors are responsible for relaying this information onto all involved. To see the location of the earplugs in room H-19, please refer to Figure 1 (H-19 Head hall floor plan). 3.4 Electrical There is no electrical hazard associated with the apparatus if the apparatus is handled carefully and instructions are followed. But in case of emergency shut off, first shut off all the power switches (see figure 10) on digital display, starting from the coiled heater switch. If this does not work, and trouble still continues then follow the lock out/tag out procedure poster instructions to locate the main electric supply of the apparatus and cut off the main electric supply. The apparatus should be checked regularly for bare or cut electrical wires every time before operating it to prevent the user from electrical threats. 3.5 Hot Air The only fluid associated with this experiment is air and the hot air exhausting the apparatus is not hot and fast enough to be a hazard. 3.6 General, physical and equipment concerns The apparatus is associated with low pressures and moderate temperatures. The pressure is not high enough to be considered as a threat. The temperature hazard is taken care of by the fiber glass lagging insulation over the coiled heater. If at any time during the experiment startup, operation or shutdown, the apparatus behaves different than normal like there are strange noises, smoke, smell, vibrations, elevated temperatures, elevated pressures, vacuum or air leaks of any kind, immediately switch off the apparatus and notify the lab attendant/technician. 3.7 Access H-19 Laboratory room has restricted access because of the LASER usage in room. There is a red LASER warning light (see figure 1) which is illuminated if LASER is in use in room H-19. However, before starting this experiment it is ensured that there is no LASER usage in progress in room H-19. Furthermore, all personal in the H-19 laboratory should be preauthorized by the faculty in charge or under the supervision of authorized 16

17 personal (lab technician or teacher assistant). No person other than the faculty in charge or specifically authorized personal are permitted to make alterations to, or run experiments with the forced convection heat transfer apparatus. 3.8 Training All individuals using the apparatus shall be required to receive training in the proper operation and maintenance of the apparatus and its controls. Training will include such topics as the complete operation and controls of the apparatus. Training programs shall be administered by qualified personnel at UNB. 3.9 Personal Protective Equipment Following personal protective equipment is a good option while doing the experiment: Ear plugs 4. Operation 4.1 Qualified Personal These notes in the operation section will provide a guideline to the individual that has been trained by a qualified personal to operate the forced convection heat transfer apparatus. Only after the individual has been trained and feels confident with the apparatus operation and shutdown procedures should he attempt to operate the apparatus using these notes. Do not proceed if you are not properly trained or are unsure in any manner of the safety operation and safety concerns. 4.2 Experiment preparation/startup Following steps should be carried out to prepare for the experiment:- Ensure that the system s physical integrity is not compromised (cut electrical cable, bare wires, twisted or pierced pipes and air leak/pipe cracks etc.) Make sure that the electrical box (see figure 6) at the front side of apparatus is closed Press the start button (green button see figure 10) to start the fan of apparatus. Then turn on the coiled heater by lifting up the heater ON switch (see figure 10). A red light indicator beside the 17

18 switch will light up when the heater is powered ON. Then adjust the voltage control to a maximum of 3 amperes using the Variac and analog display (see figure 2). This must be done at least an hour before starting the actual experiment Establish the required airflow by adjusting the fan inlet damper and monitoring the orifice pressure drop Figure 11: Check system s physical integrity Let the apparatus run for atleast an hour before noting down the actual experiment readings. In this way the apparatus will reach steady state equilibrium and will give accurate measurement of air s temperature 18

19 and pressure at different positions in the pipe and apparatus test section as desired by the operator/user 4.3 Lab Instructions Instructor Responsibilities: The apparatus (SOP) should be read and understood. This document provides all the necessary information regarding the apparatus startup procedure, operation, hazards involved & safety precautions to be taken while using this apparatus. The lab instructor shall remain in the room while the experiment is in progress. After the full students group has assembled and before any explanation has begun the instructor should relay all safety precautions and hazards as outlined in section 3. Inform them that they must contact the instructor should any problems or concerns arise during the experiment. Make the group aware of the fire extinguisher locations, fire alarm pull stations, phone and exits. Any student from the group missing his any personal protective equipment should not be allowed by the instructor to enter the laboratory H-19 and proceed with the experiment Data/Instruments Locations and Functions Please refer to figure 12 to see the location of data display units and their functions Test length pressure drop display- (displays the pressure drop across test section in Pascal) Orifice plate pressure change display- (displays the pressure change across Orifice plate of apparatus in Pascal) Fan pressure display- ( displays the fan pressure of the air flowing through pipe in KPa) Temperature display- (displays all the temperatures in apparatus by using a dial). Rotate the dial to get the desired thermocouple temperature displayed in C # 1-7 Copper wall, #9 After Orifice and #10 Exit Temperature Coiled heater power display (displays the power consumed by coiled heater in watts) Voltage and current analog displays (display the voltage and current input to the coiled heater) U- tube manometer (see figure 2)- (displays the head difference to measure the air exit pressure relative to atmospheric pressure) in cm of specific gravity Oil 19

20 Figure 12: Data locations and functions 4.4 Operating Procedure Experiment procedure After preparing for the experiment and following all the steps mentioned in section 4.2 to prepare for this experiment, follow the following steps to complete the experiment:- For the axial temperature profile part of the experiment, read and note down the following from the digital display unit a) Test section pressure drop 20

21 b) Orifice plate pressure drop c) Fan pressure d) Coiled heater power e) Air temperature at the inlet (room temperature 21 C) f) Temperatures at the seven thermocouples in test section After 5 minutes interval each, note down 3 more sets of same readings for axial temperature profile For the radial temperature and pressure profile part of the experiment, when the first reading of the U-tube manometer height difference is noted down (pitot tube and thermocouple assembly on extreme left position), the exit temperature is not recorded as the position of the thermocouple assembly is such that it is outside of the tube s diameter The rotating dial (see figure 3) is rotated to transverse the pitot tube and thermocouple assembly. The exit temperature and pressure of the air at different positions is recorded, but for the last reading (Pitot tube and thermocouple assembly on extreme right position) the exit pressure is not recorded as it is now outside of the tube s diameter. please see schematic figure 13 to understand the radial profile part of the experiment It should be noted that the first pitot tube pressure measurement will correspond to the second thermocouple temperature measurement as you traverse right. In other words the temperature recorded aligns with the previously recorded pressure Figure 13: Side view of the exit of test section 21

22 4.4.2 Shutdown Shut off the coiled heater first by pressing down the power switch (see figure 10) of coiled heater Let the apparatus fan run for next minutes to remove the remaining heat from the pipe Shut off the fan by pressing the red press button (see figure 10) and switch off all the digital display buttons Before leaving the lab, ensure that there is no object left on the apparatus test bench and all the switches are powered off. Also clean the bench with a piece of cloth 5.0 Inspection Inspections at regular intervals will be performed on the apparatus to ensure that the apparatus is kept in a safe and well maintained condition. The inspection includes the checking of any cracks in pipe, regular check for bare & cut electrical wires in the apparatus. 5.1 Periodic & Operational Inspections Visual inspections are the responsibility of the person who is conducting experiments on a regular basis with the forced convection heat transfer apparatus and should be carried out each time before operating the apparatus. A complete periodic inspection of the apparatus shall be performed by the person who is conducting experiments on a regular basis with this apparatus but will alert the faculty in charge in case of any deficiencies in the apparatus. The deficiencies such as those listed below shall be examined during both the periodic & operational inspection and the faculty in charge will determine if the deficiencies will affect the safe operation of the apparatus. a. zero error associated with the pressure transducers (see figure 14) b. Function, digital display and warning labels c. Worn, cut or bare electrical wires d. crack, air leak and worn/corroded pipe e. test section insulation and pierced pipes 22

23 Figure 14: Pressure transducer assembly (removing zero error) 6.0 Typical Tests The actual test procedure will be outlined in the lab script as issued by the professor. A typical test includes recording the temperature and pressure from the digital display unit and U-tube manometer for the axial temperature profile and radial temperature and pressure profile. A typical field notes sheet that can be used for doing this experiment is in Appendix A. 23

24 Appendix A 24

25 25

26 26

27 Appendix B 27