PHYS1630: Thermal Control Systems
Lab #4: Water Cooling (2018F)


The use of flowing water coolant is common with many high-powered devices. In this lab the use of this cooling method will be investigated with a large-frame argon-ion laser (a Coherent Innova-90).

Pre-Lab (Do this before your assigned lab period)

Review the I-90 Operations Manual


I-90 Controls
A Coherent Innova-90 (I-90) laser is used in this experiment (the controls are shown here). This laser runs from a three-phase 208V power source. This supply is rectified with a three-phase bridge rectifier (six diodes) and smoothed to produce a DC voltage of 294V. This DC current then flows through the laser plasma tube at a current selected via the front panel. The total dissipated power which is removed by the cooling water is hence 294V times the DC current through the tube (the cooling water removes heat from the plasma tube as well as the linear passbank current regulator - the current is the same through both and the voltages across each element must sum to 294V).

Water Flow Meter
Water flow is measured in LPM (the flow meter seen here indicates just below 8.0 LPM). Flow is regulated via red valve behind the flowmeter.

Water Flow Temp
Outlet water temperature is measured via the thermometer in the drain trap.

The Experiment

Leave the laser OFF. Start the cooling water and adjust for a flow of 8 lpm (litres per minute). Allow the water to run for ten minutes to achieve a constant temperature - measure it with the thermometer at the water outlet. This will be the inlet temperature.

Start the laser by turning the key on and pressing the ON button (see the SOP for operation details). The laser will start after a one minute delay to preheat the cathode after which the current through the plasma tube will be indicated on the front panel. Adjust the LIGHT control fully clockwise (maximum output) then adjust the CURRENT control for 35A of current. Wait ten minutes for the outlet temperature to stabilize then read the thermometer (This will give the temperature increase at a flow of 8 lpm). Now, decrease the flow rate by carefully closing the water supply valve until the flowmeter reads 7.2 lpm. Once again, wait for the temperature to stabilize then record it. Repeat for flow rates of 6.4 lpm and 5.6 lpm. Do not go below 5.0 lpm or the outlet temperature will climb dangerously high and the power supply will shut off automatically due to an overheat condition. The laser also features an flowswitch interlock for cooling water flow - the lower limit for this flowswitch was purposely lowered to allow low flow rates as used in this experiment but it still has a minimum flow requirement.

For reference, the I-90 Operations Manual lists details such as utility requirements. It also provides a brief overview of operating principles in chapter 7 for the curious.

Lab Report

For this experiment, an abbreviated lab report is required (word processed, never hand-written) with the same format as PHTN1300. Answer each question in the form "4a., 4b., 4c. ..." with each new question (#4, #5, etc) beginning on a new page. Do NOT answer an entire question (e.g. question 4) as a single paragraph without identification of sub-parts ('a', 'b', etc). Submit the lab report in a bound folder NOT simply a pile of loose, stapled papers nor a thick binder!

Each student must submit a unique lab report - no portion other than the results must be shared between lab group members.

  1. The manual for this laser (under "Utility Requirements") specifies a minimum flow rate and a maximum water cooling inlet temperature. Under these conditions what is the maximum output temperature that will be measured? Show all calculations.
  2. The manual also specifies a maximum recommended flow rate. Under these conditions what is the maximum output temperature that will be measured? Show all calculations.