H893 Bench Top Cooling Tower Droplet Arrester t, Air Outlet Temperatures Orifice Connection for Orifice Differential Pressure -3. CAP Water Distrubution System + Connections For Pressure Drop Across Packing PACKED COLUMN Packing Differential Pressure Transducer H890A Make Up Tank H890C H890D 1kW 5kW Main Switch Switch Switch Temperature Indicator Air Inlet Temperature Damper BASE Fan Air Inlet Water Outlet Temperature Basin Float Valve Heaters 0.5 kW 10kW 50.33 Water Flow Transducer Manometer Recirculation Thermostat Pump Heater Current Sensor Data Logger Duplex Temperature and Sensor Input Figure 2. Diagram of the cooling tower setup used in this lab experiment Table 1: List of temperature locations indicated in Figure 2 Symbol Description T₁ Dry bulb temperature for the inlet of the air-water vapor mixture T₂ Wet bulb temperature for the inlet of the air-water vapor mixture T3 Dry bulb temperature for the outlet of the air-water vapor mixture T4 Wet bulb temperature for the outlet of the air-water vapor mixture T5 T6 Temperature of the liquid water inlet Temperature of the liquid water outlet Here we discuss the path for the water flow. The load tank at the right-hand side of the base of the unit houses two electric resistance heaters. The purpose of these heaters is to simulate the cooling load of the power plant. The heated water is pumped from the load tank through the flow control valve and water flow meter to the top of the water distribution system. After its temperature, T5, is measured, the water is uniformly distributed over the top of the packing. As it spreads over the surfaces of the packing, a large surface area film of liquid water is exposed to the air stream. The liquid flows down through the packing and is cooled by the evaporation of a small fraction of the total flow. The cooled liquid falls to the bottom of the packing deck into the basin. It flows past a point where the water outlet temperature Tε is observed and then back into the cooling load tank. It is reheated in this tank before being re-circulated over the same path. The water level in the load tank will drop due to evaporation of water in the packing section. As the water level decreases, water must be added from the makeup tank to the load tank. Under steady-state conditions, the water leaves the makeup tank at a rate equal to the evaporation rate plus any small airborne liquid droplets discharged with the air exiting at the top of the tower (known as drift loss). Here we discuss the path for the air flow. Air flows over the packing via the fan and the flow rate is controlled by the fan damper. The fan discharges air into the distribution chamber where the air passes a dry and a wet bulb thermometer (T1 and T2, respectively) before it enters the base of the packing. As the air stream flows upward through the packing, the water vapor content of the air increases and the liquid water is cooled. As the air exits the tower, it passes through a droplet arrester, which traps much of the entrained water droplets and returns them to the packing. The air then flows past the dry and wet bulb thermometers (T3 and T4, respectively) and is discharged to the atmosphere through the orifice. A nice feature of the bench-top cooling tower is that the whole process can be observed through the transparent structure. Pre-Laboratory Assessment 1. (50 Points) Create schematics identifying all the important mass and energy transfers occurring in the cooling tower system. Further specify the boundary/interface at which each of these mass/energy transfers is occurring. For example, there is forced convection occurring between the air traveling up the cooling tower and the water traveling down the cooling tower. 2. (30 points) The primary objective of the cooling tower is to maximize heat rejection from the power plant to the cooling water. Consequently, it is important to understand the heat transfer mechanisms in the cooling tower. Write down the heat transfer mode(s) for each of the three questions below. (i) How does heat move from the power plant's condenser to the cooling water loop (note: although our experimental system is “mimicking" this process using heaters, it is important to understand how this would occur in a real system)? (ii) How does heat move from the water to the air inside the cooling tower? (iii) Are there any additional areas in the cooling loop (but outside of the cooling tower) where the water will experience energy transfers (work or heat) and/or heat generation? How/why will these energy transfers and/or heat generations occur? 3. (20 Points) Consider a cooling tower that has a fixed cooling load. Changing cooling tower parameters will certainly alter the overall performance of the cooling tower, but does changing these parameters affect the net amount of energy dissipated to the environment via the cooling tower at steady state? Explain. Operating Procedure & Data Collection Students will be operating the cooling tower setup under the four conditions listed in Table 2. The first condition, A, will likely already be set up and data can be collected immediately. In this scenario, this is the only condition within the entire procedure that will reach steady-state. If condition A is not already set up, follow the procedure as shown below. Note that the suggested waiting periods for each condition should be followed closely; the system after the specific times will not be at steady-state, but this is acceptable for the trends being observed. Condition A B C Table 2: List of Experimental Conditions to Test Water Flow (g/s) 40 20 40 40 Air Flow (Pa) Cooling Load(kW) 120 1 120 1 50 1 120 1.5 1. Study the cooling tower carefully. Identify all the parts, instruments and their locations, controls, water paths, and air paths. Read the descriptions of precautions, warnings and protective devices. 2. Open a LabView file and assign a unique name; this file will store all your temperature, water flow, air flow, and cooling load data. 3. Open the LabView program and observe the temperatures displayed on the screen; match the temperature curves with their corresponding thermocouple. Be sure to keep track of the temperatures critical to measuring the efficiency of the experimental cooling tower setup. 4. Take note of the packing density of the cooling tower setup. 5. Turn on the main power switch on the cooling tower setup; this will begin circulating air and water through the system. 6. Ensure that the wet bulb thermocouples and makeup water tank are filled with distilled water. Throughout the experiment, the makeup water tank may need to be refilled; the wet-bulb thermocouples should not need to be refilled throughout the duration of the experiment. 7. Set the system to condition A as specified in Table 2. Water flow can be adjusted by turning the knob above the rotameter. Air flow can be adjusted by rotating the metal disc covering the intake of the compressor. Heat loading can be adjusted by turning the switches labeled "1 kW" or "0.5kW" on or off. 8. Let the system run for 10 minutes; this will allow most temperature readings to reach steady state. During this step, keep the following in mind: a. Your water flow may fluctuate. Be sure to maintain the desired water flow as set by the condition. The float of the rotameter has a top disk. For the most accurate reading of the water flow rate, look at the bottom lip of the top disk. b. Which temperature has not reached steady-state after 10 minutes? How will this impact the calculated cooling tower efficiency? 9. Begin collecting data by clicking “write” every 10 seconds for 5 minutes. You should end up with 30 data points. 10. Set the system to condition B as specified in Table 2. Required changes from the previous condition are shown in red. 11. Let the system run for 6 minutes. Observe the trends for the critical temperatures. During this step, keep the following in mind: a. Your water flow may fluctuate. Be sure to maintain the desired water flow as set by the condition. The float of the rotameter has a top disk. For the most accurate reading of the water flow rate, look at the bottom lip of the top disk. b. Which temperature has not reached steady-state after 6 minutes? How will this impact the calculated cooling tower efficiency? 12. Begin collecting data by clicking "write" every 10 seconds for 1 minute. You should end up with 6 data points. 13. Set the system to condition C as specified in table 2. Required changes from the previous condition are shown in red. 14. Let the system run for 6 minutes. Observe the trends for the critical temperatures. During this step, keep the following in mind: a. Your water flow may fluctuate. Be sure to maintain the desired water flow as set by the condition. The float of the rotameter has a top disk. For the most accurate reading of the water flow rate, look at the bottom lip of the top disk. b. Which temperature has not reached-steady state after 6 minutes? How will this impact the calculated efficiency? 15. Begin collecting data by clicking "write" every 10 seconds for 1 minute. You should end up with 6 data points. 16. Set the system to condition D as specified in table 2. Required changes from the previous condition are shown in red. 17. Let the system run for 8 minutes. Observe the trends for the critical temperatures. During this step, keep the following in mind: a. Your water flow may fluctuate. Be sure to maintain the desired water flow as set by the condition. The float of the rotameter has a top disk. For the most accurate reading of the water flow rate, look at the bottom lip of the top disk. b. Which temperature has not reached-steady state after 8 minutes? How will this impact the calculated efficiency? 18. Begin collecting data by clicking "write" every 10 seconds for 1 minute. You should end up with 6 data points. 19. Set the system to Condition A before shutting down the entire system. Data and Analysis Deliverables The data and analysis deliverables for this part of the design project will not be submitted at this time. It will instead be submitted alongside the Part 3 results as a Combined Part 2 + 3 Report. A preview of the Part 2 data and analysis deliverable that will be submitted with Part 3 is shown below: Create a main effects plot (See Appendix A) for the experimental results you collected during Part 2 of the experimental design project. Note that when showing air flow in this plot, you will need to convert the pressure units (see Table 2) into mass flow rate units for airflow (see Appendix C). Hence water and air flow in this plot should be evaluated in terms of mass flow rate. The heat load in this plot should be evaluated in terms of kilowatts. For the purposes of creating the main effects plot, please use Condition A as the "default" case (see Table 2 and Appendix C). When creating this main effects plot, you may consider Condition A, B, and D to all have the same air mass flow rate (even though your pressure data for these conditions may be slightly different from one another). Be sure to indicate the total uncertainty in the main effects plot via the inclusion of error bars and as "+" signs in your text/tables. Your analysis should combine the precision and bias uncertainty in the proper manner to yield the total uncertainty. The required cooling tower specifications and relevant bias errors are in Appendix B. Discuss all of the conclusions that can be drawn from this main effects plot. Identify the 2 factors with the strongest influence on the experimental cooling tower efficiency. Your conclusions from the main effects plot should relate your observations to underlying fundamentals in thermodynamics, heat transfer and fluid mechanics, as well as discuss the implications of your uncertainty analysis. Appendix A) Main Effects Plots The data and analysis deliverable asks you to compare the relative effects of multiple factors on a single graph. Comparing these factors in graphical format is more easily visualized by normalizing the factor levels against their minimum value. This normalization process helps eliminate distortions caused by the factor levels having different units and/or widely varying absolute values. An example of this normalization process is shown in the Table 3 and Figure 3 below. This example illustrates the effects of two factors on the kinetic energy of a car. Table 3 illustrates five experiments wherein the factors (mass, m, and velocity, v) are varied and the corresponding response variable is determined (kinetic energy, KE). Similar to the data provided to you in this project, the first experimental case consists of default levels. In the remaining cases, the level of one factor is systematically varied (shown in red) while the other factor is left at the default value. Normalization is conducted by dividing each factor level, L, by the respective minimum factor level, Lmin (see column 4 in the table below): Table 3. Example data for the effect of two factors (mass and velocity) on the response variable (kinetic energy) of a car Response Variable (y-axis) Factors & Corresponding Lvels (x-axis) Case Name Mass (kg) Velocity (m/s) Normalized Level Value for the Factor that is Varied (x- axis) Kinetic Energy (kJ) Default 1500 20 m = v = 20/10 = 2 1500/800 300.0 = 1.875 Slow Velocity 1500 10 v = 10/10 = 1 75.0 Fast Velocity 1500 30 v = 30/10 = 3 675.0 Light Car 800 20 m = 800/800 = 1 160.0 Heavy Car 2500 20 m = 2500/800 = 3.125 500.0