Objectives
This experiment assists you to achieve the following objectives:
- Understand the working principles of a counter-current laminar flow heat exchanger.
- Conduct an energy-balance analysis for a simple heat exchanger.
- Determination of surface heat transfer coefficients on both the oil and water sides, and of the overall heat transfer coefficient.
- Understand the relationship between Nusselt and Graetz numbers for laminar flow in a circular pipe.
- Develop a direct tangible feel for the typical control time constant for heat transfer process control.Experimental procedures
Ensure that the unit has been correctly filled with oil and prepared for use.
(ii) Fully open the oil flow control valve and raise the drain valve in the measuring tank.
(iii) Switch on the power supply and adjust the heater control to its maximum.
(iv) When the oil temperature, ti, reaches about 70°C, turn on the cooling water and adjust the water flow rate to about 15 g/s.
(v) Adjust the heater input to give a steady oil temperature of about 77°C.
(vi) When conditions have stabilized make the observations set out below.
(vii) Partially close the oil control valve and while maintaining the water flow rate. adjust the heater to stabilize the oil temperature. It is important that the adjustment to the heater must be small each time. After every adjustment, allow 20 seconds or slight more for the adjustment to take effect in the system, before making another adjustment.'
(viii) When the system stabilizes, repeat the observation.
Data Analysis
(1) Discuss the energy balance, Q.oil - Q.water, vis-a-vis the experimental condition.
Note that the measurement error for each of the thermocouple reading is about ±1.0°C.
(2) Plot the oil-to-tube and oil-to-water heat transfer coefficients with respect to the mean oil velocity. Explain the observed relationship between the heat transfer coefficients and the mean oil velocity.
(3) Plot the oil Nusselt number with respect to the oil Graetz number. Discuss why is the Nusselt number changing with the Graetz number.
Attachment:- Heat Transfer Lab Experiment.pdf