Notre Dame University – Louaize Faculty of Engineering Department of Mechanical Engineering Fall 2023 MEN 376- Thermo/Fluid Laboratory Forced and Free Convection H112P – Free and Forced Convection from flat, finned, and pinned plates. Lab Report #2 Forced and Free Convection Prepared by: Lea Doueihy ID#20182434 Fouad Roumieh ID#20197079 Submitted to: Dr. Sylvie Melki Set Up and Procedure 1- Experimental Set Up The H112P unit and the Heat Transfer Service Unit H112 will be used in this experiment to examine how heat is exchanged from diverse surfaces under both free and forced convection. The experimental unit, as seen in Figure 1, is made up of several parts that have been given reference numbers. Figure 1: Schematic diagram of the machine Figure 2: The lab set up of the plate and the power input machine. The H112P apparatus for examining free and forced convection consists of a vertical duct with a central opening to hold typical heat exchanger surfaces, which are fastened using sliding clamps. The equipment is attached to a bench and is used to study both free and forced convection. Three heated plates—a flat plate, a finned plate, and a pinned plate—shown in figures 3, 4, and 5 will be used in this lab report. Temperature sensors and electric heaters are installed on each plate. Figure 3: Flat plate Figure 4: Finned plate Figure 5: Pinned plate A wind velocity sensor, a hot wire anemometer, and thermocouples were used in this experiment to detect the wind velocity and temperature of the air and plates at various positions in a channel. A hot wire anemometer is positioned in the middle of the duct to monitor the rate of cooling, which reflects the wind speed, and a variable velocity wind tunnel is also part of the setup. A digital velocity meter shows the wind speed, which is adjustable by changing the wind tunnel's voltage, frequency, and intake air throttle. The plates become more effective heat exchangers as wind speed increases since it takes them longer to heat up and reach a greater temperature. To examine how hot air rises from the surface and up the channel as a result of temperature variations that affect density, the fan switch on the H112P console can be turned off. Another method for evaluating forced convection is to use a variable-speed fan to push air over the surface and into the channel. Thermocouples, which detect the temperature via the probe and provide a signal to a read-out device that shows the temperature digitally, are used to monitor the temperature of the air and plates at various positions in the channel. On the console screens, the heat power, voltage, and amps are also displayed. Overall, this experiment offers useful information about how temperature and wind speed affect the efficiency of heat exchangers in ducts. The variable velocity wind tunnel and fan offer a variety of testing environments, and the wind velocity sensor and thermocouples are efficient instruments for monitoring these variations. The findings of this experiment can be utilized to improve the layout and functionality of heat exchangers in a variety of settings, including electronics, engines, and heating and cooling systems. Figure 6: The H112P Console displaying the temperature. Thermocouples are used to measure temperature to keep track of the temperatures of the various kinds of plates during the experiment. For the pinned and finned plates, four extra thermocouples are employed to measure the temperature of the extended surface (T2-T5), whereas for the flat plate, just the temperature of the heater surface (T1) is continually monitored and shown on the screen. T1 additionally keeps track of the temperature of the surrounding air for the finned and pinned plates. The flat plate, however, doesn't need any extra surface thermocouples. At the bottom of the duct, a temperature sensor measures the temperature of the air moving through it, and all temperature data are shown as digital values on a screen. 2- Experimental Procedure With the aim of comparing the time required for each heated plate to attain a particular temperature and determining which is a superior heat exchanger, the experiment will be carried out on three distinct heated plates: Flat, Finned, and Pinned plates. All three plates will be subjected to the same working circumstances, such as the same starting temperature, same wind speed, and same wattage, to guarantee a fair comparison. Four sensors (2, 3, 4, and 5) will measure the temperature of the expanded surface at various locations, while sensor (1) will gauge the surrounding air's temperature. Since sensor 5 is the furthest from the heat source, its temperature readings will be lower than those of the other sensors. Three distinct heat exchanger surfaces will be examined in the experiment to examine both forced and free convection. Only forced convection will be carried out during the lab time since free convection takes hours to complete and stabilize. This is so because forced convection transfers heat more quickly than natural convection. The main switch and fan will be switched off before the device is first hooked into the power. The two toggle clamps on the sides will be closed to secure the heated plate when it has been fitted and fastened to the duct's central aperture. Before continuing with the experiment, make sure the plate is securely fastened and that each thermocouple is inserted into the appropriate socket on the H112P console. The heater at the intake will operate at a desired temperature after the main switch and heater switch on the instrument console are both turned on. To avoid varying the wind speed's valve position between the three tests, the wind speed will be set at a low value that will be maintained for all three plates. The initial temperature readings (T1 through T5) will be logged, and at regular 3-minute intervals, the evolution of temperature changes across the various thermocouple sensors will be read and recorded. The stopwatch will be paused, the heater will be turned off, the wind speed will not change, and the plate will be left to cool before being detached once the temperature reaches the desired temperature of 40°C. For the additional plates, the same experimental process will be used while maintaining the same conditions and being constant throughout the experiment. The time it takes for each convection plate to achieve the desired temperature will be compared after testing all three plates. This comparison will serve as a direct evaluation of each plate's performance and will show how much heat is exchanged between the plates and the air. The temperatures from the first measurement can be used as beginning values if one forgets to record the initial temperature circumstances. As a result, the instant the convective plates meet the designated beginning conditions, the timer and data collection for the remaining plates will start. And ultimately, we may conclude that the heat exchanger that takes the longest to heat up is the good one. References 1. Kiefer Paul James Stuart, M. C. (2012). Principles of Engineering Thermodynamics (8th ed.) 2. Lab # 2 Free and Forced Convection from Different Plates.pdf
