Florida Institute of Technology College of Engineering Department of Chemical Engineering

Transcription

1 Florida Institute of Technology College of Engineering Department of Chemical Engineering CHE 4115 ChE Process Laboratory II Team Report # 1 Experiment # 3 Experimental Design - Heat Transfer by Convection and Radiation Team D Hani Baatiyyah Nasser Almakhmari Khalid Almansoori Fawaz Alkhaldi Abdullah Kurdi For: Dr. Maria Pozo de Fernandez Experiment performed on: March 1, 2016 Date: March 22, 2016 Team D Grade:

2 I. Introduction Heat is transferred from a region of higher temperature to a region of lower temperature by means of radiation, conduction, and convection. In this experiment heat transfer from the extended surface relies on natural convection and radiation. The convection heat is one of the major modes of heat transfer in the ocean and atmosphere. However, the radiation heat refers to heat transfer by the emission of electromagnetic waves which carry energy away from the emitting body. In many engineering problems a surface losses or receives thermal energy simultaneously by convection and radiation. For example, when a hot body is exposed to its surroundings at a lower temperature, it loses heat both by convection and radiation and the two mechanisms of heat transfer act in parallel. In this experiment, a horizontal cylindrical, made of a metallic, having a diameter d and a length L, is placed inside the oven. Then, the wooden stand used to support the heated cylinder with three glass rods. To determine the total heat transfer rate by convection and radiation the following equations will be used: q = q c + q r = h c A(T s T a ) + Aσ(T 4 S T 4 a ). Where: qc = Heat transfer rates by convention qr = Heat transfer rates by radiation hc = average convection heat transfer coefficient Ts = Surface Temperature of the body Ta = Ambient Temperature σ = Sefan-Boltzman constant of radiation A = Heat transfer area of the body 1

3 The purpose of this experiment is to study experimentally the convection and radiation heat transfer at different heating levels. To Study the convection and radiation heat transfer over a horizontal cylindrical and evaluate the convective heat transfer coefficient and radiation heat transfer coefficient by measuring the temperature distribution along an extended surface. To determine the heat transfer from an extended surface resulting from combined modes of convection and radiation heat transfer of the cylinder. II. Equipment and Experimental Procedure The apparatus needed for this experiment is as follow: o Aluminum cylinder. o Heating Source (Oven) o Weight balance o Caliper o Ruler o Wooden stand o Three glass rods o Stopwatch o Thermocouple 2

4 The following diagram showcases the experimental setting and all elements needed: Figure 1: Experimental Setting in steps The experiment will be conducted using the following procedure: 1) Turn on the Oven, and set the temperature to 200 o C to preheat. 2) Measure and record the mass of the aluminum cylinder. 3) Calculate the surface area of the aluminum cylinder. 4) After the oven reaches the desired temperature, place the aluminum cylinder in the oven and leave it for 15 mins. 5) Measure the interior temperature of the cylinder using the thermocouple, if it did not reach 200 o C, place back in the oven for another 5-10 mins; if it reached 200 o C place it on the wooden stand with the glass rods, and turn off the oven. 6) As soon as the temperature falls down to 190 o C, start measuring the temperature of the surface of the cylinder in 1 minute intervals till the surface temperature reaches 80 o C. 3

5 7) After taking all the measurements, place the cylinder in a small cold water bath to reduce its temperature. 8) Finally, dry the cylinder with paper towels and return all equipment to their storage areas. III. Equipment Parts, Materials, and Reagents A cylinder made of aluminum (Al 6061) with 2.4 cm diameter, and 6.4 cm in length is used. Also, an oven is used to heat the aluminum cylinder up to 200 o C. A wood stand with 20 cm in length, and 10 cm in width is used as an insulation between the lab bench and the hot cylinder to minimize the heat exchange between the bench and the cylinder. Three glass rods are used to separate the cylinder from the wood stand. Those 3 glass rods have length of 20 cm, and diameter of 5 mm. A thermocouple is used to measure the temperature of the cylinder, and a stopwatch is also used to record time. Table 1: Materials of Construction Equipment Cylinder Stand Rods Materials of construction Aluminum Wood Glass Devices: 1) Oven 2) Thermocouple 3) Weight Balance 4) Stopwatch 5) Tongs 6) Gloves 4

6 IV. Safety Considerations In the experiment, the engineers group is dealing with high heat therefore some specific personal protective equipment should be taken to the consideration. Heat resistant gloves are significant while heating the rod metal in the oven. Lab coat and safety goggles should be wore as a normal procedure inside the lab. Since the temperature of the aluminum metal is going to be very hot, it safer for the group members to wear boots. There is no concern about the glass rod gets melted since it has a very high melting temperature might reach up to 1,723 o C, or 3,133 o F. In addition, there also no concern about the wood getting combusted since the auto ignition point of wood is around 300ºC. There is not hazardous disposal materials involved in the experiment. The group should be careful in the procedure of heating up the aluminum cylinder to the needed temperature in the oven. Moreover, the process of handling the heating procedure should be performed carefully due to the high level of heat that is associated with it. 5

7 V. Budget The following Table 2 displays an estimated budget if the items needed would have been bought. The aluminum cylinder was obtained from the FIT machine shop. The glass rods were obtained from the process lab equipment storage, as well as the stopwatch, thermocouple, gloves, and tongs. The oven in the process lab was used as the heating source. Table 2: Price listing of the Items needed for the experiment Item Price Source Dimensions Aluminum Cylinder $ 7.21 Home Depot 0.5 inch Diameter 36 inch Length Glass Rods $ 8.35/rod Home Science Tools 5 mm Diameter 20 cm Length 10 rod pack Wooden Stand $ Home Depot 12 inch Length 12 inch Width 7/8 inch Thickness Total $ VI. Project Timeline First Session: preparing the materials and checking the setup (3/22/2016) Second Session: Performing the experiment and generating the data (3/29/2016) Third Session: Performing the calculations, generating the plots, and discussing the results (4/5/2016) 6

8 VII. Experimental Results Table 3: Dimension of the Aluminum Cylinder Mass of Cylindrical in (g) Diameter in (m) Length of Cylindrical in (m) Radius of Cylindrical (m) Surface Area in (m 2 ) Table 4: Temperature and Time Measurements Time (min) Temperature ( o C) Table 5: Heat Transfer Coefficients The Grashof Number (Gr) 7.0*10-13 The Prandtl Number (Pr) 7.0*10 9 The Nusselt Number (Nu) Average Convection Heat Transfer Coefficient

9 Temperature (oc) Table 6: Heat Transfer Results Heat Transfer By Convection (W) Heat Transfer By Radiation (W) Total Heat Transfer (W) Temperature vs Time Time (min) Figure 2: Temperature measurements as a function of Time 8

10 Change in Temperature ( o C) 10 Change in Temperature vs Time DT = -0.31*t Time (min) Figure 3: Change in Temperature with respect to Time 9

11 VIII. Discussion From Figure 2, it can be noticed that the temperature decreases with increasing time; that proves that the aluminum cylinder was losing heat as time progressed. It can also be concluded that the heat has transferred from the high temperature body to the lower temperature body, in this case the surroundings of the cylinder. It can be concluded from Figure 3 that the temperature change decreases as time progresses; that is expected since the heat of the surroundings is increasing. From Table 6 it can be noticed that the heat transfer due to convection is significantly larger than that due to radiation, which agrees with the expectations of the experiment. The overall heat transfer was found to be W, with convection being the majority. Overall the experiment has met expectations of applying the theory of heat transfer via convection and radiation. Some of the problems that were encountered during the experiment were like the slow display of temperature in the thermocouple, having a relatively large aluminum cylinder made the time of the experiment lengthier than expected. The gloves were bulky relative to the tongs which made handling of the objects challenging. IX. Conclusion In conclusion the experiment proved the concept of heat transfer by convection and radiation. In the experimental results, it was noticed that the temperature change decreases as time progresses. In addition, the convection found to be the major heat transfer in the experiment. 10

12 X. Recommendations Thermocouples should be placed in an effective geometry such as a hole in the middle of the metal that using in the experiment to get better result. Avoid using larger diameter in the metal will also help the thermocouples to get better in touching the metal to get more accurate data. A better insulation material might be used in order to avoid heat transfer to surroundings. Using another shapes or metal in the experiment is recommended for future trials to compare the change of the temperature of the metal depending on the type of metal, and the shape. XI. Material Safety Data Sheet MSDS There are no hazardous chemicals that are used in this experiment. All safety precisions should be taken while conducting the experiment and all lab rules should be enforced at all times. XII. References 1. Art Supplies From Blick. (n.d.) Retrived February 22, "Glass." - Chemistry Encyclopedia. Web. 18 Apr Roncati, Dario. "Iterative Calculation of the Heat Transfer Coefficient."Lisafea.com. Dario Roncati. Web. 18 Apr "Shop for Science Supplies." Home Science Tools. Web. 18 Apr

13 XIII. Sample Calculations Grashof number: Gr = g L3 β (T c T a ) η 2 = ( ) = Where: g = acceleration of gravity = 9.81, m/s2 L = longer side of the fin, m β = air thermal expansion coefficient. For gases, is the reciprocal of the temperature in Kelvin: β = 1 T a, 1/K Tc = Cylinder temperature, C. Ta = Air temperature, C η = air kinematic viscosity, is Prandtl number: Where: P r = µ C p K = = µ = air dynamic viscosity, is cp = air specific heat = 1005 J/(Kg*K) for dry air k = air thermal conductivity = W/(m*K) Rayleigh number: Ra = Gr Pr = ( ) ( ) = Nusselt number: Nu = 0.54 Ra = = Convective heat transfer coefficient: Where: h c = Nu k L = = W m 2 K k = Al-6061 thermal conductivity = 167 W/(m*K) 12

14 Heat transfer Convection: q c = h c A(T s T a ) = ( ) = (W) Where: A = Surface Area in m 2 = Heat transfer Radiation: Where: q r = Aσ(T S 4 T a 4 ) = ( ) ( ) = (W) σ = the Stefan-Boltzmann constant = Total heat transfer: q = q c + q r = = (W) 13

15 XIV. Datasheet Table 7: Dimension of the Aluminum Cylinder Mass of Cylindrical in (g) Diameter in (m) Length of Cylindrical in (m) Table 8: Temperature and Time Measurements Time (min) Temperature ( o C)