Heat Conduction Lab. The objective of this lab was to learn and understand the principles of heat transfer in a shell and tube heat exchanger. Necessary materials were provided in the lab to investigate the parallel and counter-current flow heat exchange
ENGR 3930U
Heat Transfer
Laboratory #4: Radiation Heat Transfer
By
Ali Akhtar – 100 393 527
Valentin Badea – 100 390 855
Michael Saliba – 100 397 667
Nabeel Pasha – 100 295 606
Curtis Bayens – 100 393 098
November 30th 2011
Abstract
The objective of this lab was to learn and understand the principles of heat transfer in a shell and tube heat exchanger. Necessary materials were provided in the lab to investigate the parallel and counter-current flow heat exchangers. The mechanism behind this instrument makes it possible to represent how heat is being transferred under different mass flow rates and subsequent temperature differentials. The principle behind this very simple instrument was to allow heat transfer from hot water in a pipe to the cold water in the shell as they passed through the heat exchanger in parallel and opposite directions. Calculations of the mean coefficient of the heat transition, based on measurements made at the inlet and outlet of the pipe and the shell, showed that the range of the heat transfer coefficients for Parallel Flow (976.45 - 1484.47 W/K*m2) and Counter Flow (961.89 – 1473.46 W/K*m2) fall in the theoretical range for the overall heat transfer rate for water-to-water heat exchangers (850 - 1700 W/K*m2). It was noted that the mean coefficient of the heat transition showed a linear relationship to the mass flow rate of the hot and cold medium in both Parallel & Counter Flow. The temperature differential for the Parallel & Counter Flow also showed an inversely proportional relationship to the heat transfer rate. The efficiency of the heating and cooling flow in Parallel (91.0% & 109.8%) and Counter Flow (88.7% & 112.6%) were observed to be very favourable but could be improved upon if the physical imperfections in the experimental apparatus are fixed, the heat loss to the environment is negated and the deposition of particulates over time in the pipes and shell are removed. The lab experiment was successful in helping to understand the heat transfer phenomenon under various mass flow rates and temperatures.
Procedure
The procedure outlaid in the lab manual was followed to precision. The procedure steps were carried out once for parallel (uniform) flow and once again for counter flow. [3]
Results
Parallel Flow:
Please refer to Table #6 - #9 for the calculated mass flow rates and heat transfer rates at the hot & cold water inlet and outlet.
Please refer to Table #10 for the calculated exchanged heat fluxes and the mean heat transfer rate.
Please refer to Table #11 for the change in temperature between the inlet and outlet and the log mean temperature calculations.
Please refer to Table #12 for the calculated mean coefficient of heat transition.
Please refer to Table #13 for the mean mass flow rate of inlet & outlet of hot and cold water.
Please refer to Table #14 for the mean mass flow rate of hot and cold water.
Please refer to Table #15 for the calculated efficiency results.
Counter Flow:
Please refer to Table #21 - #24 for the calculated mass flow rates and heat transfer rates at the hot & cold water inlet and outlet.
Please refer to Table #25 for the calculated exchanged heat fluxes and the mean heat transfer rate.
Please refer to Table #26 for the change in temperature between the inlet and outlet and the log mean temperature calculations.
Please refer to Table #27 for the calculated mean coefficient of heat transition.
Please refer to Table #28 for the mean mass flow rate of inlet & outlet of hot and cold water.
Please refer to Table #29 for the mean mass flow rate of hot and cold water.
Please refer to Table #30 for the calculated efficiency results.
Discussion
In an ideal heat exchanger and in general theoretical discussion, it is assumed that as the mass flow rate increases, the heat transfer from a hot medium to a cold medium should increase as well. From the calculations performed and the plots generated, it can be seen that the mean mass flow rates of the hot and cold mediums of the five runs performed (five each for both Parallel and Counter flows) during the lab experiment did not show a linear relationship when compared to the mean coefficient of heat transition (Refer to Figure #1, 2, 5 & 6 – Appendix A). This is primarily due to an experimental error; the inability to maintain a constant mass flow rate for one of the two mediums (hot/cold) caused each plot to generate a rapid rise/plateau relationship (in that the mean coefficient of heat transition increases rapidly with mass flow rate between one set of data points and plateaus on the next set of data points).