Hand Expansion Valves – 2

In the previous blog entry we discussed the use of hand expansion valves (HEV) maintaining a liquid level in a vessel.  In this entry the discussion will center on the HEV being utilized as an expansion device to an evaporator being fed with liquid from a controlled-pressure receiver (CPR).

In this example, the HEV is used to meter the flow of refrigerant into an evaporator.  With this application the time constraint is constant when the evaporator is providing cooling.   Evaporator superheat is not an overriding issue as the CPR system includes a suction accumulator to store excess liquid returning from the evaporators.

Therefore the liquid supply required is 100% of the actual coil capacity, not greater as shown in the example with the liquid make-up requirement.  In this application of a HEV the valve capacity is based on the required mass flow for the cooling load and the pressure differential available (liquid feed pressure – evaporating pressure).  In other words, when the coil is in operation the demand for cooling (liquid refrigerant supply) the hand expansion valve is selected only for that consistent demand.  The HEV selection does not need to be over-sized as in the liquid make-up application.

Again, it is important to select the HEV on the basis of the valve being approximately 50% open.  This provides the ability to adjust the valve performance for minor changes in operation while maintaining the ability to fine-tune the valve setting.

Tags: analysis of refrigeration systems, facility operations, operating issues, System design

This entry was posted on Sunday, October 18th, 2009 at 10:58 am and is filed under ammonia refrigeration components, cold storage warehouse, food processing, industrial refrigeration. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.