Operating limits heat pipe capillary limit

Figure 12.36 illustrates the relationship between the static liquid and static vapor pressures in an operating heat pipe. As shown, the capillary pressure gradient across a liquid-vapor interface is equal to the pressure difference between the liquid and vapor phases at any given axial position. For a heat pipe to function properly, the net capillary pressure difference between the wet and dry points, identified in Fig. 12.36, must be greater than the summation of all the pressure losses occurring throughout the liquid and vapor flow paths. This relationship, referred to as the capillary limitation, can be expressed mathematically as... 

Microheat pipes are subjected to the same operating limits as the conventional heat pipe. The capillary limitation is the most important operating limit of the microheat pipe. 

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