We are building a Vapor Compression Refrigeration Unit to cool a simulated, scaled-up electronic chip (cold plate with heater assembly on surface). We are trying to determine the best expansion valve to use from the condenser to the evaporator. We are hoping for any easily operated and easily integrated component. Some members believe that a manual valve with 30-40 turns would be the way to go. We are not sure if we have the means to integrate and maintain a thermostatic expansion valve. What would you recommend? The evaporator load is under 600W. Mass flow is 0.0036 kg/s.

Much more detail would be required to give a definative answer.

There are several options to use as a metering device in your VCRU.
1) hand expansion valve (what you are suggesting)
2) Capillary tube
3) automatic expansion valve
4) Thermostatic expansion valve
5) Electric or electronic expansion valves.

All of the above are used in OEM refrigeration equipment depending on a large variety of system parameters including but not restricted to the following.
initial first cost
stability of load
refrigerant type
evaporator temperature range
skill of the design personal
skill of the construction personal
longevity of the equipment.
etc etc etc....

My personal opinion would be ....
For typical system, with a normal operating ambient and a somewhat variable load, using a non-exotic commercial refrigerant,(excluding ammonia), in a standard temperature range (-20 to +50