SBIR, Low Cost High Performance State-of-the Art Phased Array Radar Cooling
To: Wayne Liang
Principle Investigator: Martin Pitasi
Submission Date: 21AUG04
Title: Ballistic Missile Innovative Radar and RF Products
Subtitle: Phase 1 Final Report
a. SBIR Topic No. MDA03-052
b. Proposal Number B031-1925
c. Contract No. N00178-04-C-3046
d. Page 7 of the Technical Information Document, No. R-134a, titled “Thermodynamic
Properties of HFC-134a,” published by Dupont SUVA
1. Summary of Results
2. Cooling Cycle Flow Diagrams0
3. System Flow Summary
4. Flow Resistance
5. Load Sensitivity
6. Test Fixture and Instrumentation
7. Heat Exchanger
8. Evaporator Test Results
9. Condenser Test Results
10. Heat Exchanger Test Data and Results
11. Pump Reliability
The goal of this Phase 1 SBIR study is to demonstrate to the Missile Defense Agency (MDA)
that pumped liquid multi-phase cooling (PLMC) technology offers a superior and credible
alternative to conventional single-phase ethylene glycol/water (EGW) systems. The results
show conclusively that a PLMC system designed as a potential replacement for the EGW
system performs equally well. Primary advantages of the PLMC design are its inherent
isothermal cooling, higher reliability, lower hardware and operating costs, smaller package
envelope, and reduced weight.
To enhance and augment Phase Array Radar performance, Raytheon requested (Reference a)
that Thermal Form and Function (TFF) submit a proposal to the MDA SBIR program (Reference
b). As a result of this effort, TFF was awarded a Phase 1 contract (Reference c) to compare the
cooling performances of an existing EGW phase-array cooling platform to a similar PLMC
design. In support of the study, design criteria data was leveraged from an existing Raytheon
EGW cooling platform (Enclosure 1).
PLMC technology was developed in 1998 by Thermal Form & Function for cooling Compaq
Computer’s Alpha Server Division, next-generation, Enterprise Servers. The technology was
driven by design constraints beyond the limits of conventional cooling capabilities. Constraints
included maintaining 32, 200 W computer processor packages at operating junction
temperatures below 85 ºC, reliability and safety, package size and weight, and hardware and
operating cost limits. From these constraints, pumped liquid multi-phase cooling (PLMC)
evolved. The PLMC design consists of commercially available hardware that includes a
refrigerant pump, air- and water-cooled condensers, distribution manifold, separator, reservoir,
and system controls.
To demonstrate the technology a proof-of-concept system packaged in a standard 18” cabinet
was built and tested. The test data and accompanying results confirmed that the PLMC system
met all the design constraints defined by Compaq Computer.
Since 1998, the technology roadmap has successfully evolved from cabinet cooling to rack, 1U,
and blade designs.
The summary of the results is shown in Enclosure 1. Listed are Raytheon’s EGW design
constraint values and corresponding reference items. Adjacent to these values are Thermal
Form and Function’s PLMC R-134a system design results. Both values are compared and
shown as a percentage change.
At a heat load of 54.4 kW and a coolant temperature of 30.0 ºC (86.0 ºF), the PLMC design
requires 8.2 gal/min (gpm) of R-134a coolant. This value is 84% lower than the 50 gpm
specified for the EGW platform. Subsequent reductions of 91% and 98 % are reflected in the
system pressure drop and pump horsepower, respectively. Correspondingly, similar changes in
flow and pressure drop are reflected in the EDA manifold section. The critical manifold
temperature for the PLMC design is 34 ºC or 12 % lower the 38 ºC EGW value.
Chilled water provided for cooling the EGW heat exchanger or PLMC condenser will deliver 50
gpm of water at 15.0 ºC (59.0 ºF) and 20.0 psig.
The R-134a pump advantages include a reduction in horsepower and weight requirements.
Horsepower requirements drop from 10, for the EGW pump, to 0.2 for the R-134a pump or 98%.
Correspondingly, the weight change is from 300lb to 25lb or 92% lower.
The potential of electronics failing due to liquid leakage associated with the ethylene
glycol/water cooling system exists and needs to be considered as having a negative impact on
reliability. However, any R-134a leaks occur in the form of a non-toxic, non-ozone depleting,
inert vapor that has no detrimental effect on electronics. Refrigerant pump hardware reliability is
listed as high and is based on 11 failures of unknown origin over 60 million pump hours of
operation (Enclosure 11). No reliability data exist for the EGW pump. Estimated package
volumes for the PLMC design and the EGW platform are16, 875 in3 (25”L x 15”W x 45”H) and
108,000 in3 (60”L x 30”W x 60”H), respectively. Comparing these results shows that the PLMC
design envelope is 84% smaller than the Raytheon platform. Correspondingly, the PLMC
system weight of 150 lb is 83% lighter than the 874 lb Raytheon platform.
This study assumes that the pumps consume 100 % of the parasitic power. Instrument and
control power is considered negligible and have no impact on the results. Pump specification
indicate that the R-134a pump uses 0.12 kW or 98 % less power than the 7.5 kW needed by the
Hardware costs figures for the Raytheon platform and the PLMC design are $11,340 and
$6500, respectively, or 43% less.
Enclosure 2 details the flow diagrams for the EGW platform and PLMC system design. Figures
1 and 2 show the Raytheon design criteria and PLMC design results, respectively. The EGW
diagram (Figure 1) shows 50 gpm of ethylene glycol/water pumped at 35.0 ºC (95.0 ºF) and
125.0 psig though a water-cooled heat exchanger. The heat exchanger removes 54.4 kW and
reduces the coolant temperature from 35.0 ºC (95.0 ºF) to 30.0 ºC (86.0 ºF). The coolant flows
into the EDA assembly and is uniformly distributed between the manifolds. Approximately 6.3
gpm of coolant passes through each manifold cooling 6.8 kW of EDA power, raising the fluid
temperature from 30.0 ºC to 35.0 ºC. The coolant exits the EDA at 35.0 ºC and 5.0 psig then
flows through the filter prior to entering the pump. Filter and miscellaneous line losses account
for the remaining 5 psig. A reservoir located prior to the filter provides a controlled volume
designed to compensate for any coolant volume change produced by temperature fluctuations.
A motorized valve and temperature sensor control the EGW at 30.0 º C. The valve located in
the water return line of the heat exchanger modulates the flow in response to changes in the
EGW discharge temperature (Figure 1). Reviewing the PLMC cycle (Figure 2) shows 8.2 gpm of
R-134a sub-cooled fluid discharging from the pump at 30.0 ºC (86.0 ºF) and 112.3 psig. The
coolant flows into the EDA assembly and is uniformly distributed between the manifolds.
Approximately 1.0 gpm of coolant passes through each manifold, isothermally cooling 6.8 kW of
EDA power. This design is based on an EDA discharge quality of 50%. The mixture enters the
separator (tube) at 32.0 ºC, 103.4 psig, and 50 % quality. Here gravity causes the saturated
liquid to collect at the tube bottom displacing the saturated vapor. The vapor is condensed to a
sub-cooled liquid leaving the condenser at 28 ºC and 103.4 psig. Prior to the pump both liquids
mix to form a sub-cooled liquid at 30.0 ºC and 103.4 psig. Filter and miscellaneous line losses
account for the remaining 0.5 psig. As in Figure 1 the reservoir compensates for volume
changes due to fluctuation in temperature. In the unlikely event that the R-134a charge is
compromised a sensor located at the top of the bleed line signals a controller to power down the
system. A passive, low cost OEM flow control valve, regulated by pressure, maintains the R-
134a saturation pressure at 103.4 psig or 30 ºC.
Enclosure 3 is a chart showing the system flow summary for R-134a. Included in the chart are
the pump curve, the EDA baseline curve, and EDA design curve. Reviewing the results shows a
system design point (DP) of 9.4 psid at 8.2 gpm (Enclosure1). To achieve the 9.4 psid an
additional 6.3 psid of resistance is added to the 3.1 psid baseline value. The 6.3 psid resistance
is added in the form of manifold metering orifices that augment the flow distribution.
Enclosure 4 details the flow resistance data that characterize the PLMC system design. At the
design flow of 8.2 gpm, Chart 1 shows a corresponding system resistance of 9.4 psid. This
value consists of adding the 6.3 psid metering orifice resistance to the 3.1 psid EDA baseline.
Chart 2 shows both the EGW and R-134a baseline system resistance curves. The R-134a curve
is developed from EGW design criteria of 105 psig at 50 gpm. Extrapolating the R-134a data
from 50 gpm to 8.2 gpm results in a baseline resistance value of 3.1 psid.
Enclosure 5 is a load sensitivity study. Noted in the summary is the design point of 54.4 kW load
and 50 % quality. Typical quality limits for the preferred operating range are 25% and 75%.
The corresponding load limits for this design at 30.0 ºC (86.0 ºF) are 109.6 kW and 37.3 kW,
To supplement the SBIR effort, Raytheon requested that a series of cursory heat exchanger
tests be added. Raytheon supplied two similar aluminum heat exchangers identified by model
numbers C-002 and C-007. Both heat exchangers were designed with off-set aluminum strip
fins. Model C-002 contains 10 fins /inch (fpi) and model C-007, 24 fpi. Enclosure 10 shows the
test data and results used to generate the charts of Enclosures 7 and 8.
Enclosure 6 shows the R-134a test set-up and instrumentation. Inlet and outlet temperatures
were measured at T 8 and T 9 , respectively. Pressure and pressures drop values were measured
at P 2 and ΔP 1 , respectively. Flow rate values were taken from FM4. Two test series designed to
determine the thermal performance of the heat exchangers operating as evaporators and
condensers were performed.
Enclosure 7 is a sketch of the heat exchanger test configuration. It shows a distribution manifold
and off-set strip fin sandwiched between the top and bottom frames. Also shown on the frame
top are the R-134a inlet and exit and the location of the thermocouple holes. Directly above the
top and centered over the fins is a film heater (heat load). Covering the heater is a pad of
thermal insulation used to limit heat losses. Section A-A details the cross section and shows the
thermocouple holes and fin cavities.
Enclosures 8 and 9 summarize the test results for the evaporators and condensers,
respectively. The enclosures combine the thermal and flow resistance results into two charts for
the 10 fpi and 24 fpi heat exchangers. A cursory examination of the thermal resistances show
the 24 fpi heat exchanger values are lower than those of 10 fpi. Also, noted is the negligible
difference in flow resistance values between the two exchangers.
Enclosure 8, Chart 3 and Enclosure 9 Chart 5 summarize the thermal resistant results for the
exchangers tested as evaporators and condensers, respectively. Test results show that Model
C-007, 24fpi consistently has lower thermal resistance than Model C-002 10 fpi design. A
comparison of the evaporator data at an exit quality of 30% shows the 10 fpi value of 0.011 deg
C/W or 43% greater than the 0.006 deg C/W for the 24 fpi. Similarly, for the condenser at 30%
inlet quality, the 10 fpi heat exchanger resistance is 0.011 deg C/W or 50 % greater than the
0.005 deg C/W for the 24 fpi heat exchanger. Enclosure 8, Chart 4 and Enclosure 9, Chart 6
compare the flow resistance of each exchanger tested as evaporators and condensers,
respectively. Reviewing the charts shows little difference between both heat exchangers.
Maximum resistance value for the evaporator is 0.52 psid and occurs at an exit quality of 18%.
Correspondingly, the maximum condenser resistance is 1.4 psid at an inlet quality of 20 %.
Enclosure 10 tabulates the heat exchanges test data and results used in Enclosures 8 and 9.
Ten thermocouples located on the heat exchanges surface between the heater and the fins
(Enclosure 7) provide temperatures data. These values are averaged and subtracted from the
R-134a sink value (R-134a saturated discharge temperature). Note this value is T 9 for the
evaporator and T 8 for the condenser. Correspondingly, the vapor quality is determined from the
heat load, mass flow rate, and the vapor enthalpy. For example, Case no. 100 has an average
surface temperature of 30.4 ºC (Tave) and a saturation temperature of 27.9 ºC (Tsat) or a 2.9
deg C difference. The corresponding load is 203.7 W, thus, the thermal resistance for this case
is 0.0123 deg C/W. Determining the vapor quality requires converting 203.7 w to 695.2 Btuh,
changing the 5.0 gal/hr to an equivalent mass flow rate of 9.9 lb/hr (pph), and obtaining the
vapor enthalpy at 27.9 ºC. Enthalpy data taken from reference d shows a value of 75.9 Btuh/lb.
The vapor quality determined from these values is 0.183 or 18.3 %
Discussion of Results:
The PLMC technology is based on pumping 2 deg C sub-cooled R-134a refrigerant through a
heat exchanger (manifolds) where heat is transferred to the R-134a. The heat added to the R-
134a converts the sub-cooled liquid to a 32 ºC (90 ºF) isothermal mixture of saturated liquid and
vapor, typically known as a quality mixture. More specifically, quality is the weight ratio of the
vapor to the total weight of the mixture. As the mixture exits the heat exchanger it passes into a
long vertical tube called a separator. Here gravity causes the 32.0 ºC saturated liquid to collect
at the tube bottom displacing the vapor. The saturated liquid passes from the separator to a
mixing port upstream of the pump. The displaced vapor (32.0 ºC) passes through the condenser
and exits as a sub-cooled liquid at 28.0 ºC (4.0 deg C of sub-cooling). Combining the fluids at
the mixing port forms a 30.0 ºC sub-cooled liquid. Figure 2 of Enclosure 2 shows the 50%
quality mixture splitting into 41.1 lb/min (ppm) of saturated liquid collecting at the bottom of the
separator and 41.1 ppm of vapor flowing to the condenser.
To prevent condensate from collecting on the external surfaces of the hardware, the R-134a
(coolant) is maintained above the local dew point temperature. A 30.0 ºC (86.0 ºF) value is
specified in the design criteria. A passive low cost OEM control required for maintaining the
coolant temperature also makes it possible to simply change the R-134a operating temperature.
Enclosure 5 addresses the sensitivity of the system to changes in cooling load. The PLMC
operating envelope for a design flow of 8.2 gpm and 30.0 ºC ranges from 109.6 kW to 37.3 kW.
However, the quality changes correspondingly from 25% to 75%. Potential changes to the
pump speed due to line voltage fluctuation or other minor aberrations have no effect on the
cooling performance of the system. However, any changes made in the heat load need to be
followed by changes in the condenser performance.
A specific request to measure the flow resistance of the fins only was made. Initial
measurements were inconclusive. Further investigation concluded that the measured values
were outside the resolution of the available test equipment. A default test that included the
manifold was adopted. Enclosure 8, Chart 4 and Enclosure 9, Chart 6 summarize the flow
resistance results for the heat exchangers. Both charts show that the 10 and 24 fpi flow
resistance values coincide. An explanation of this is found in the heat exchanger distribution
manifold design (Enclosure 7). The manifold governs the heat exchange flow resistance and is
designed with several times the resistance of the fins, thus, making the fin resistance values
The PLMC design results show that a R-134a EDA cooling system is a viable alternative to the
EGW platform. In summary, for the same design constraints as the EGW platform, the PLMC
delivers the same cooling performance at a lower coolant flow rate and subsequently lower
pressure drops. The package envelope and weight are considerably less. Parasitic power
requirement and hardware costs are lower.
Critical to the product development cycle is validating the design by building and testing a proof-
of-concept model. Therefore, it is recommended that a phase 2 SBIR proposal effort be
The PLMC cooling technology provides a new and effective alternative to today’s conventional
design strategies. Visions of the PLMC technology beyond this study are major and complement
the technical challenges of the United States and the world. Adapting the PLMC cooling
technology into future U.S. defense projects will lower parasitic power demands, reduce
package envelope and weight, lower hardware costs, provide isothermal cooling, and widen
operating envelopes. These attributes support the philosophy of a lighter, faster, more effective
military at lower costs.
One major commercial contribution of the PLMC technology is in reducing the amount of waste
energy consumed by the world computer service industries. It is estimated that 40% of the
energy budgeted for cooling computers is used to maintain the computer room environments.
Most of this energy is used to power computer room fans and blowers to augment the cooling
process. By replacing the fans and blowers with the PLMC technology significantly reduce the
40% waste heat. TFF’s current model mounts cold plates to temperature sensitive components.
Manifolds within the cabinet distribute and collect the R-134a coolant. Heat generated by the
component isothermally changes the R-134a from a liquid to a vapor. Conversely, as the vapor
flows through the condenser, heat is transferred to the cooling media (water or air) converting
the vapor back to a liquid. By placing the condenser external to the building, the heat is
transferred outside, thus, eliminating a significant amount of the fan and blower power
Other commercialized avenues targeted for PLMC technology include laser technology, power
and power supplies, astronomy, medicine, and transportation.
SUMMARY OF RESULTS
Reference Items Design Constraints System Design % Change
Cooling Media Single Phase EGW 2 Two Phase R-134a
Quality (%) NA 50 NA
Heat Load (kw) 54.4 54.4 NA
Flow Rate (gpm) 50.0 8.2 -84
Coolant Temperature ( C ) 30.0 30.0 0
Max. Pressure (psig) 125.0 112.3 -10
Pressure Drops (psid) 105.0 9.4 -91
Load (kw) 6.8 6.8 NA
Coolant Temp ( C ) 30 in / 35 out 32 in / 32 out NA
Flow Rate (gpm) 6.3 1.0 -84
Critical Temperatures ( C ) 38.0 34.0 NA
Pressure Drops (psid) 100.0 8.9 -91
Type EGW Vapor NA
Size (Tons) 15.5 15.5 NA
Flow Rate (gpm) 50.0 50.0 NA
Supply Pressure (psig) 20.0 20.0 NA
Supply Temperature ( C ) 15.0 15.0 NA
HP 10.0 0.2 -98
Wt (Lb) 300.0 25.0 -92
Envelope (in) TBD 26quot; x 16quot; x 10quot; TBD
Leakage1 Contamination Potenial None NA
Hardware Reliability (khrs) No Data 50 TBD
Size 60quot;L x 30quot;W x 60quot;H 25quot;L x 15quot;W x 45quot;H -84
Weight (Lb) 874.0 150.0 -83
Power (kw) 7.5 0.1 -98
Hardware $11,340.00 ~ $6500.00 -43
1. Impact on leakage on electrical circuits
2. Single Phase EGW (55/45 by Vol)
3. Water Cooled Heat Exchanger
TEST FIXTURE AND INSTRUMENTATION
0.38”T x 2“W x 4”L
2”x4” Film Heater (Load)
Inlet Thermocouple Locations 10 plc’s) Exit
Distribution 0.10”Tx2.0” W x4.0” L
Manifold Off-Set Strip Fine
0.84”Tx 4.0”W x11.75” L Aluminum
Heat Exchanger Frame (Bottom)
0.84”Tx 4.0”W x11.75” L Aluminum
Heat Exchanger Frame (Top)
Thermocouple Holes Locations (10)
0.05”Tx2” W x11.0”L
Off-Set Fin Cavity (Top)
0.10”Tx2.0” W x4.0” L
Off-Set Strip Fine
0.05”Tx2” W x11.0” L
Off-Set Fin Cavity (Bottom)
PO Box 631
4701 Ridge Road
Cazenovia NY 13035
Phone 315 655 3322 Fax 315 655 4539
August 23, 2001
To: Joe Marsala
From: Walter Joncas
Subject: Refrigerant pump reliability
I will attempt to keep this short and to the point.
After Studies conducted by the National Institute of Standards and Technology (NIST) were
completed and a public report filed The Federal Energy Management Program (FEMP) published
its report in 1995 on the Hy-Save Pump. On the first page of the FEMP report it states that the
Hy-Save Pump was “ultra reliable”. That finding is a result of The US Governments, Pacific
Northwest Laboratory, Richland Washington study of the Hy-Save Pump over a two-year period.
In support of that study an audit of all repair parts sold by Hy-Save for any reason was conducted.
At that point in time 12,500 refrigerant pumps had been installed primarily in refrigeration
systems. Sixty million operating hours is estimated based on 10,000 of the pumps operating at
least 6000 hours per year in a full time refrigeration environment.
A total of 124 impeller / shaft replacements were made during this same time period. Of the 124
impeller / shaft sets replaced, 60 were replaced as a result R&D testing of materials. Forty three
of the Impeller / shaft assemblies were damaged by running dry due to improper piping practice
and or loss of refrigerant through a leak elsewhere in the host system. This caused the bearings to
overheat thus causing failure. The remaining 21 sets showed signs of bearing material
breakdown. At least 10 of those were due to contamination within the system. There were 11
failures of unknown origin. No (of what could be considered normal), worn out impeller bearings
or shafts causing failure were observed.
On a more localized basis, and specific to the pump you are using, the east coast suppliers
(Cazenovia, New York, Gainesville, Florida) have not shipped any replacement parts for the
model 809IND for any reason to any point east of the Mississippi in the past four years with one
exception. The exception is Thermal Form and Function, Manchester MA. Spare parts have been
shipped and inventoried at their location but those parts have not been used. I could not confirm
what was shipped west of the Mississippi in exact terms during this same time period. However I
have strong reason to believe the number was less than three.