Heat Transfer from Stream to Water - Research Paper Example

Oct 09, Dr. David Bell Abdulmajed Alnahwae Heat Transfer from stream to water ______________________________________________________________________________ GRADE Data analysis: 5 Other technical content: 30 Technical writing: 48 TOTAL 83 SUMMARY This experiment comprises two parts: the Corning Heat Exchanger and then Heating Liquids contained in Tank Storage. The aim of both experiments is to evaluate the overall external heat exchanger transfer coefficient (Uo) at some diverse rates of water circulation, as well as to ascertain whether the hypothesis that the flow rates are directly proportional to the overall heat transfer coefficient is valid or not. Experimental data was collected and compared with predicted values. In general, the recorded results were acceptable. In addition, the temperature plots against flow rates were scientifically right. Results showed that, as the flow rates increases the overall heat transfer coefficient increases. BACKGROUND AND METHODS Heating Liquids in Tank Storage The experiment comprises a water stirred tank, a centrifugal pump that pushes the water from the tank to a heat exchanger tube, and an external shell that later directs the water back to the original tank. It also contains a stirrer that ensures the tank’s temperature is fixed. The experiment main source of heat is steam condensation that enters the heat exchanger shell side through stream inlet. A water drain valve is used to drain water out of the tank and hence, the turning the tank cold. One of the essential sections of this experiment is a thermocouple that is linked to a computer via an analog/digital converter. The purpose of the thermocouple is to measure the temperature of water getting in and out of the heat exchanger. The thermocouple also measures the stream in our condensate. Additionally, an orifice meter is employed to weigh the water flow rate when the heat exchanger is used. A computer installed with the appropriate programs, is also important to provide the time against temperature data, which will assist the student to analyze the obtained results. Figure 1, 2, and 3 shows the Heated Tank assembly and connection, with figure showing the entire Heated Tank whose capacity is roughly 30 gallons and should be about 31 inches deep. .Corning Heat Exchanger The foremost section of the experiment is the heat exchanger. Water is supplied in the shell region as the steam is supplied in the tube region of the heat exchanger. A computer, as previously employed in the initial stage of the experiment initial, is also employed in the second stage of the experiment. A rotameter is regarded as major component of the experiment because it measures the water flow rate in the corning cap heat exchanger. Figure 4 and 5 shows the experiment’s corning heat exchanger assembly and connection. Heating Liquids in Tank Storage instruments . Corning Heat Exchanger: Figure 5: Water inlet and drain for the Corning heat exchanger. There are a number of important equations, which are used to obtain the overall heat transfer coefficient. The equations used to calculate experimental and predicted values for heat transfer coefficient. For instance, Eq1, as outlined below is the tank experiment equation for perfect mixing. Eq1 Where: =steam temperature, taken as the average of the inlet steam temperature and the outlet steam (or condensate) temperature. T = tank temperature, a function of time W = water circulation rate, mass/time ρ = water density V = water volume t = time Additionally, Bell argues that the Eq2 outlined below can be used for the ideal in the tank.1 Eq2 Where: = overall heat transfer coefficient (based on Ao) = heat transfer area based on the tube outside diameter = heat capacity of water After plotting the left part of the Eq1 versus time, we will obtain a straight line governed by the equation below. Eq3 One of the complex issues which make the report very technical is the comparison of the experiment values of all variables to the forecasted value. Bell prefers the use of the equation Eq4 below so as to determine the predicted value.2 Eq4 Where: = outside tube diameter = inside tube diameter = heat transfer coefficient due to fouling on the inside tube surface = water-to-metal heat transfer coefficient on the inside tube surface = copper tube thermal conductivity (use 232 Btu/hr-ft-F) While fouling is insignificant, Bell prefers the utilization of Eqn. 5 to evaluate the heat transfer coefficient Uo predicted value.3 Eq5 For = 2,000 Btu/hr-ft2-F. To evaluate hi in equation 5, the utilization of equation 9 and 8 is required to evaluate Nu, and later the value of hi can be determined by use of Eq7 Eq6 Eq7 Where Nu = the Nusselt number k = thermal conductivity of water. Eq8 Where: Re is the Reynolds number v = average linear water velocity, length/time μ = water viscosity Eq9 Where: Pr is the Prandtl number. Eq1 and Eq 2 are used to calculate the overall heat transfer coefficient for the data gained from the experiment. However, Eq3 to Eq9 are used to calculate predicted values. PROCEDURE Heating Liquids in tank Storage The closure of tank drain valve took place. The tank was then filled with chilly tap water. The stirrer was then turned on and positioned at maximum speed. The pump was initiated and adjustment of water control valve was done in order to attain around 40 lb/min. The stream inlet valve was then opened. Computerized data collecting process was initiated immediately after stream inlet valve was opened. This processe was stopped after the tank attained a temperature reading of 130F. The stream, stirrer and pumps were then stopped. The opening of the drain tank valve was done so as to cool the tank. This procedure was repeated at different flow rate of 70 lb/min rather than 40 lb/min. The students are then required to evaluate the external heat exchanger general heat transfer coefficient at two varying water circulation rates. Corning Heat Exchanger At the initial stage, the heated tank experiment program was opened. The water drain valve was then closed. The water flow rate was then set to 2 gpm, after which, the opening of the stream valve took place. After the stabilization of the temperature, the temperature value was recorded. This procedure was repeated for 4, 6, 8 and 10 gpm rates of water flow. Results and Discussion Table 1 and 2, Illustrate the slope values and the overall heat transfer coefficient from the data evaluated from the experiment for three weeks. The K values can be obtained from the tables as well. . Table 1: Calculation of overall heat transfer coefficient for 40 lb. /min     K Uo Uo (Btu/ft2-hr-F) slopeweek1 0.0313 1.241534519 6.773846933 406.43 slopeweek2 0.0287 1.21711485 6.15187657 369.11 slopeweek3 0.0304 1.232971432 6.557148459 393.43 Table 2: Calculation of over-all heat transfer coefficient for 70 lb. /min     K Uo Uo (Btu/ft2-hr-F) slopeweek1 0.0321 1.128680947 6.632600055 397.96 slopeweek2 0.0347 1.140568817 7.206684803 432.40 slopeweek3 0.0355 1.144277167 7.384543237 443.07 Figures 6 and 7 are plots of the 40 lb. /min and 70 lb. /min heat tank data versus time in minutes. The figures presented the data for three weeks of experimental and as well as the values of the slope. Figure 6: Plot show relationship verses time for 40 lb. /min Figure 7: Plot show relationship verses time for 70 lb. /min Equation 1 was applies to measure heating liquids temperature and the graph slopes of the experiments were used for comparison and trend analysis. Table 3 shows the average and standard division values for overall heat transfer of tank 40 lb/min and tank 70 lb/min Table 3: Average and standard deviation values for the overall heat transfer coefficient of tank 40 lb/min and 70 lb/min. Tank Average Standard Deviation  (lb/min) (Btu/ft2-min-F) (Btu/ft2-min-F) 40 390 15.47 70 424 19.25 Tables 4 and 5 show the calculation for percentage error between the experimental and predicted values for overall heat transfer coefficient for the 40 lb. /min and 70 lb. /min flow rates of water Table 4: shows the percentage error between the experimental and predicted values for overall heat transfer coefficient for the 40 lb. /min flow rate of water.   Uo Experimental Uo Predicted Week 1 6.773846933 5.990673695 Week 2 6.15187657 5.990673695 Week 3 6.557148459 6.03714974 Average 6.494290654 6.00616571 SD 0.315713653 0.026832957 % Error 8%   Table 5: shows the percentage error between the experimental and predicted values for overall heat transfer coefficient for the 70lb. /min flow rate of water.   Uo Experimental Uo Predicted Week 1 6.632600055 8.491565558 Week 2 7.206684803 8.491713674 Week 3 7.384543237 8.491713674 Average 7.074609 8.491664 SD 0.392985 0.000086 % Error 20%   The basic motive of the experiment was covered by analyzing the comparison between experimental data and predicted data. Hence we were comfortable to find out causes of errors between the two of them. There is an error of 8% and 20% in the calculations for 40 lb. /min and 70 lb. /min of water. It shows that as the flow rate increase the error increase. The table 6 below outlines the Calculations for the overall heat transfer coefficient for the corning exchanger Table 6: Calculations for the overall heat transfer coefficient for the corning exchanger. Flow Rate U1 U2 U3 Average Standard Deviation GPM (BTU/ft2-hr-˚F) (BTU/ft2-hr-˚F) (BTU/ft2-hr-˚F) (BTU/ft2-hr-˚F) (BTU/ft2-hr-˚F) 2 128.106 132.636 129.346 130.029 1.912 4 248.938 258.959 259.795 255.897 4.933 6 310.498 325.899 338.864 325.087 11.595 8 339.018 358.368 354.011 350.465 8.288 10.0 196.226 153.092 366.728 238.682 92.239 A plot of the values that in table 6 for flow rate versus overall heat transfer coefficient for three weeks shows in figure 8 Figure 8: plot for overall heat transfer coefficient verses water flow rate for three weeks The result from the data is that the overall heat transfer coefficient for 40 lb. /min flow rate was 6.49 U(Btu/ft2-hr-0F) and for 70 lb./min was 7.07 U(Btu/ft2-hr-0F) hence it proves the hypothesis that as the flow rate increase the overall heat transfer coefficients increase. The same results are found on corning heat exchanger. Bibliography Bell, David. Heat Transfer from Steam to Water. Laramie, WY, 2014. Read More