Experiment 2 - Energy Balance and Overall Efficiency Objective To perform an energy balance across a Shell and Tube Heat Exchanger and calculate the Overall Efficiency at different fluid flowrates.

MCE 431 - Thermal Science Lab Method By measuring the changes in temperature of the two separate fluid streams in a shell and tube heat exchanger and calculating the heat energy transferred to/from each stream to determine the Overall Efficiency. Equipment Required As Exercise A. Equipment set-up If using the results from Exercise A then the equipment is not required. If previous results are not available refer to the Set-up and Procedure sections of Exercise A. Theory/Background Note: For this demonstration the heat exchanger is configured for countercurrent flow (the two fluid streams flowing in opposite directions). Therefore: ahot Mass flowrate (qm)= Volume flowrate (qv) x Density of fluid (p) (kg/s) Heat power (Q) = Mass flowrate (qm) x specific heat (Cp) x change in temperature (AT) (W) Overall Efficiency T41 Heat power emitted from hot fluid Qe = qmn. Cph (T1 - T2) (W) Heat power absorbed by cold fluid Qa = qmc. Cpc (T4 - T3) (W) Heat power lost (or gained) Q₁ = Qe - Qa (W) M = T3 ↑ a cold x 100 (%) 4 MCE 431- Thermal Science Lab Theoretically Qe and Qa should be equal. In practice these differ due to heat losses or gains to/from the environment. Note: In this exercise the cold fluid is circulated through the outer shell, if the average cold fluid temperature is above the ambient air temperature then heat will be lost to the surroundings resulting in n<100%. If the average cold fluid temperature is below the ambient temperature, then heat will be gained resulting in n>100%. Procedure Use the results obtained from Exercise A. Results and Calculations The software records all sensor outputs and also calculates several derived figures, and presents the recorded data in tabular form. The following columns are relevant to this exercise, and are suggested as suitable column headings if recording values manually: Hot fluid volume flowrate Hot fluid inlet temperature Hot fluid outlet temperature Cold fluid volume flowrate qVhot (m³/s) Multiply Fhot (litres/min) by 1.667x10-5 T1 Specific heat of hot fluid Specific heat of cold fluid Density of hot fluid Density of cold fluid T2 qVcold Cold fluid inlet temperature T3 Cold fluid outlet temperature T4 You should also estimate and record the experimental errors for these measurements. For each set of readings, the software calculates the average hot fluid temperature (from T1 and T2) and the average cold fluid temperature (from T3 and T4) and then automatically provides values for the following variables. If recording data manually, calculate these values and obtain the variables from the Reference Tables section 14.3: Cph Cpc Ph Po (°C) (°C) (m³/s) Multiply Foold (litres/min) by 1.667x10-5 5 (°C) (°C) kJ/kg°K (From table 1) kJ/kg°K (From table 1) kg/m³ (From table 2) kg/m³ (From table 2) MCE 431 - Thermal Science Lab For each set of readings, the relevant derived results are calculated and presented with the following headings: Mass flowrate (hot fluid) Mass flowrate (cold fluid) Heat power emitted Heat power absorbed Heat power lost Overall Efficiency qmn qmc Qa 6 Q4 M (kg/s) (kg/s) These values should be calculated manually if not using the software. A graph may be plotted of the results. The software graph facility may be used for this. Estimate the cumulative influence of the experimental errors on your calculated values for Qe, Qa, Qf and n. Conclusions Explain any difference between Qe and Qa in your results. Comment on the effects of the increase in the cold fluid flowrate. Exercise C should be carried out on completion of this exercise. (W) (W) (%) Compare the heat power emitted from/absorbed by the two fluid streams at the different flowrates.