Heat exchanger for thermal control of heat producing devices

A thermal test head assembly comprising:

• a liquid cooled microchannel cold plate assembly thermally coupled to an electrical device under test, having a coolant inlet port and a coolant outlet port,
• at least one chiller fluidly connected to supply coolant to said microchannel cold plate,
• an inlet tube supplying coolant from said chiller to said inlet port,
• an outlet tube returning coolant from said outlet port to said chiller,
• a first control valve fluidically connected in series with said microchannel cold plate,
• a second control valve fluidically connected in parallel with said microchannel cold plate and configured for bypass flow control,
• a control unit constructed and arranged to actuate said first control valve and said second control valve to maintain the temperature of said electrical device under testing at a predetermined set point,
• a first pneumatic actuator having a piston assembly and a second pneumatic actuator having a piston assembly,
• wherein said first control valve and said second control valve are connected in close proximity to said cold plate and constructed and arranged to control flow through said first and second control valves to keep the temperature of said electronic device under testing at the desired setpoint as the power dissipation of the electronic device under testing varies during the test.