che351, (Shuai Li), (1276682), nov-2-2011,Hot and Cold Flow Mixing LAB
Summary
This experimentwas done by mixing hot and cold water in a T-junctionfor five runs. The objectives were to investigate the optimum thermocouple location after the T-junction andby using the mass and energy balance to predict mass flow rates and temperature of the mixed stream after the T-junction and then compare these with the measured values and to investigate the accuracy of the calibration equation.
During the study the average value for mass flow rate in the mixed stream was 330.6 kg/h and the average temperature recorded by the thermocouple place 23 cm from the T-junction was 36.3 °C.  The temperatures given by the thermocouple located at 6 cm from the T-junction, Tmix1, were found to have a higher temperature and standard deviation than the values given by the thermocouples located at 23 and 40 cm from the T-junction (Tmix2 and Tmix3).Average standard deviations for Tmix1, Tmix2, and Tmix3 were 0.96, 0.22 and 0.18 respectively. The values of Tmix2 and Tmix3 agreed within experimental error. For first run, Tmix2=36.0±0.9°C and Tmix3=35.4±0.8 °C. It clearly showed the two streams were not completely mixed at a distance of 6 cm downstream of the T-junction and therefore, the optimum thermocouple should be placed at a minimum of 23 cm from the T-junction. Using mass and energy balances, the predicted mixed stream flow rates and temperatures were calculated;but the predicted values did not agree with the measured values. For the first run, the predicted value was 183.2±9.4kg/h and the measured value was 252.1±9.5 kg/hrespectively.Therefore, calibration equations were assumed to be incorrect. Thenthe predicted temperatures were calculated without cold stream mass values (mcold) produced by the calibration equations. It was found that the new predicted temperatures agreed with the measured values within experimental errors. Take first for example, the new predicted temperature (Tpre,nomcold) was 37.0±1.7°C and the measured value (Tmix2,meas)was 36.0±0.9°C .Thus, the cold stream calibration equation was turned out to be wrong. The corrected cold steam calibration equation was obtained by using a linear regression between the corrected mcold and corresponding volts drop recordings. It was found to be
m ̇_cold=103.67√(V_cold )
 
Table of Contents

Summary i
Introduction 1
Theory 1
Equipment 3
Procedure 3
Results and Discussion 5
Conclusions 11
Nomenclature 12
References 13
Appendix A: Experimental Data A1
Appendix B: Sample Calculations B1

List of Figures

Figure 1. Schematic Diagram 4
Figure 2. The measured hot, cold and mixed steam flow rates versus time 6
Figure 3. The measured hot, cold and mixed steam temperatures versus time 7
  
  
  
Figure 4. Corrected mass flow rate as a function of the square root of the corresponding volt
 10
  
  
  
  
  

List of Tables

Table 1. Pressure setting corresponding flow rates and temperature of hot and cold stream for five runs 5
Table 2. The measured hot, cold and mixed stream flow rates as well as the predicted mixedstream flow rate and their associated errors 8
Table 3. The measured mixed stream temperatures and theirassociated errors and standard deviations 9
Table 4. The measured and predicted stream temperatures and their associatederrors for five steady state runs 10
  

 
Introduction
Material and Energy Balance are often used to determine the outlet variables such as temperatures, concentrations, flow rates, and energy requirements when a new individual process distillation columns, reactors, heat exchangers and cooling towers or multi-unit processes are designed. The copper produce is a typical example of using material and energy balance in the real world. At the beginning, sulfide and oxide ores are mined from the ground through digging or blasting, and after grinding, concentrating, smelting, and electrolytic refining in the industry, pure coppers are produced and cast into wire rod, billets, cakes or ingots, or alloyed with other metals. Material and energy balances are fundamental to the control of processing like concentrating, smelting. Every chemical engineer must be able to use material and energy balances to extract meaningful process information.