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Heat-pipe Technical Notes

The following tables provide design engineers with as much information as is possible here for the CRS Engineering Standard Range Heat-pipes. (Table 1)  needs to be read in conjunction with (Table 2) and (Table 3), for overall power transmission capabilities.
       
Power Handling Capability
The maximum power transmission ratings stated in (Table 1). opposite are for CRS 5000 ST series and HT series Heat-pipes operating in a horizontal orientation (i.e. virtual zero gravitational influence). The temperature ranges given of + 20°C to + 120°C are mean operating temperatures taken at a mid-measurement point between the heat input and heat output sections arranged at either end.
 
  Table 1
CRS- Series 5000
( Diameter mm )
Maximum Power Handling Capability ( Watts )
@+20°C @+40°C @+60°C @+80°C @+120°C
2.0 9.0 11.0 12.0 13.0 14.0
2.5 12.5 16.0 17.5 19.5 21.5
3.0 16.0 23.5 24.5 26.5 29.0
4.0 22.0 27.5 30.5 32.0 37.0
5.0 50.0 58.0 63.0 65.0 68.0
6.0 72.0 86.0 93.0 98.0 108.0
8.0 90.0 108.0 115.0 122.0 134.0
10.0 112.0 134.0 143.0 152.0 169.0
12.0 148.0 178.0 186.0 197.0 218.0
       
Effects of Gravity upon Capillary Action
The function of a Heat-pipe is dependant upon an effective capillary action system to return the working fluid from the condenser section (Cd) where cooling is applied, to the evaporator section (Ev) where heat input to the Heat-pipe is applied. This function is served by the porous lining wick structure or “wicking system” which is built into the Heat-pipe. Gravity has an important influence on the thermal performance of Heat-pipes. As can be seen in (Table 2)  gravity can be used to advantage to increase the thermal transmission capability to up to twice that of the maximum horizontal position rated value shown in (Table 1). (i.e. provided that the Ev section is below the Cd section). In this orientation, gravity assists the return of the return working fluid.
 
Opposing Effects of Gravity .…
In the opposing mode, i.e. with Ev section high, and driving heat downwards, the Heat-pipe function is now totally dependent upon capillary action for the return the working fluid to the evaporator and to overcome the gravitational restraint. (Table 3)  shows the effects of this, which is to repress the performance capability. In this situation the Heat-pipe capillary pumping capability must work against the static head difference between the Cd and Ev sections. For particular applications where orientational constraints demand Heat-pipes should operate in this mode, CRS engineering can offer Heat-pipes with special anti-gravity wicking systems. These SSX series Heat-pipes use wick structures that develop an increased capillary pumping action over that of the standard series. SSX series Heat-pipes have typically an increased diametrical size for a given value of power handling capability.
 
         
  Photo showing sections of Heat-pipes. (left)
Structures can be of sintered metallic lining and of multi layer woven metallic lining depending upon particular performance characteristics requirements.
         
For more information assistance with thermal solution design, considerations and concepts, consult CRS Engineering Ltd for an appraisal of your application…… see Thermal Solutions Enquiry Check List