In this expression, use was made of the condition that AV is invariable with the capillary geometry. Similarly, for the dimensionless capillary width y (= capillary width / distance between neighboring capillaries), one obtains Eqs. (A3) and (A4) show that the optimum capillary height depends on /?, but the optimum capillary width is equal to 0.5 for all /?, i.e. for all PCMs. The functions Eqs. (Al) and (A2) are shown in Fig. Al for LiF with ~ 0.2 for which the heat transfer exhibits a strong maximum at = 0.286. The capillaries for the LiF PCM should therefore be designed with dimensions and yopl as also asssumed in the calculations. It is very fortunate that the heat transfer dictates an optimum dimensionless but not absolute capillary width. This appears plausible. It permits one to choose the absolute capillary width in accordance with the requirements of (a) the physics of the capillary forces and (b) machinability, which must both be satisfied in practice. REFERENCE for Appendix [Al] S. Krause (1990) "Optimierung der Schlitzgeometrie fur maximale Warmeleistung bei Latenwarmespeichem mit Kapillarschlitzen fur die Raumfahrt," Internal Report Nr. 90104, ITT, DLR Stuttgart, Germany, July.
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