mcold=177.28√(V_cold ) (10)
mhot=113.5√(V_hot )(11)
mmix= 210.78√(V_mix )(12)
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Procedure
In this experiment, a total five run were performed, as shown in the Table 1.The Labview program was activated and the data collection rate was set to 5 seconds. First, keep the globe valve closed and control the pressures of the hot and cold streams. The pressures of the streams were measured by orifice and DP/cell. For the first run, the hot water and cold water were set to 0 psig by adjusting globe valve. The temperature of the inlet cold stream was 20.54 °C and hot stream was 52.17°C. The temperatures of the streams were measured by the thermocouple before the streams entered the T-junction. The analogy signals were transferred to OPTO 22 and recorded for every 5 seconds period. The cold stream and hot stream were mixed in the T-junction. At the downstream of the T-junction, three thermocouples were placed to measure the temperature of the mixed streams. The analogy signals were transferred to the OPTO 22 and recorded for every 5 seconds intervals. An orifice and DP/cell was placed before mixed stream poured to drain. After the mixed stream reached the steady state, repeated the whole procedure by increasing the pressure (see Table 1).
Table 1. Pressure setting corresponding flow rates and temperature of hot and cold stream
for five runs.
Run
# Ph
(psig) Pc
(psig) mh
(kg/h) mc
(kg/h) Tc
(°C) Th
(°C)
1
0
0 97.17 154.97 22.14 50.68
2
8
10 139.63 252.48 22.10 50.70
3
13
14 171.56 286.96 22.09 51.00
4
20
18 211.28 302.94 22.12 51.51
5
26
27 239.71 363.30 22.23 50.85
Results and Discussion
The data file contained hot, cold and mixed stream flow rates in Voltsand temperatures in degree Celsius at 5 seconds intervals show in Appendix A andsample calculation and error analysis shown in Appendix B.
Figure 2 show mass flow rates versus time andthe mass flow rates are given as kilogram per hour, and the time is given as second. The mass flow rates were calculated using the calibration Equations (10), (11) and (12). It can be observed that the mass flow rates are increasing 5 times for 5 runs. For every run, the mass flow rates do not change. As there is no reactions occurred in the process, so it can be recognized that these five runs are at steady state.
Figures 2: The measured hot, cold and mixed steam flow rates versus time
Figure 3 shows the cold stream temperature (Tcold), the hot steam temperature (Thot), the mixture steam temperatures measured in 3 different locations (Tmix1 Tmix2 Tmix3). The temperatures are given in degree Celsius and the time are given in second. Those variables are measured by thermocouples and the locations are shown in figure 1. By observing the figure, it can be noticed that the temperatures for each runs are not greatly changed. The hot stream has the highest temperature and cold stream is the lowest temperature. Also, those two steady lines of Thot and Tcold show they are stable streams entering the T-junction.Therefore, these five runs are steady state.
Figures 3:The measured hot, cold and mixed steam temperatures versus time
Table 2 shows a comparison of the measured hot, cold and mixed stream flow rates and the predicted mixed stream flow ratefor all five steady state runs.The predicted mixed stream (Mmix,pred) werecalculated usingthe mass balance equation (3). The error in eachmeasured mass flow rate was calculated by assuming ±4% accuracy for each orifice calibration equation and plustwo times the standard deviation. The error of predicted mixed stream flow ratewas calculated using the technique by Holman (2001). It can be seenthat the predicted mixed stream mass flow rate do not agree with the measured value within their errors. Take run 1 for example. The measured mixture mass flow rate is 183.2±9.4kg/h where the predicted mass flow rate is 252.1±9.5kg/h. They do not agree even considering their errors.Since the experiment is done in good condition and the whole process is steady state as stated before, it can be assumed that the calibration equations to calculate mass for hot, cold and mixed streams are not accurate.Thus, it is necessary to determine which mass flow rate calibration equation is wrong and correct it.
