Junjiro Kai

Phase change stability of CaCl2•6H2O

Abstract A CaCl2·6H2O composition with a slight excess of water was found very stable on repeated phase change (over 1000 cycles) in a heat cycle test (35 ∼ 18°C), using vertical glass tubes of 950 mm height. The mole ratio of water CaCl 2 , n, was 6.11, less than that of the peritectic composition (n = 6.14). Dissolved NaCl had superior nucleating ability to that of common barium salts under certain experimental conditions. This result was attributed to a “memory effect.” The dissolved NaCl decreased the heat of vaporization of water about 15 per cent. NaF had a similar effect to that of NaCl, because NaF powder reacted with CaCl2 in solution yielding NaCl and CaF2. A brief discussion of CaCl2·4H2O formation is presented.

Phase change stability of sodium acetate trihydrate and its mixtures

Abstract Mixtures of NaCH 3 COO·3H 2 O with NaBr·2H 2 O (10 wt%) or NaHCOO·3H 2 O were found very stable on repeated phase change (over 1000 cycles) in a heat cycle test (60 ∼ 30°C), using vertical glass tubes of 950 mm height. On the other hand, NaCH 3 COO·3H 2 O deteriorated rapidly under similar experimental conditions (70 ∼ 40°C), settling anhydrous NaCH 3 COO. Pressed mixture of anhydrous NaCH 3 COO, Na 2 HPO 4 and polyethylene powder was found effective as a nucleating agent. A brief discussion on the heat of fusion of a binary mixture is presented in the appendix.

Mixtures of calcium chloride hexahydrate with some salt hydrates or anhydrous salts as latent heat storage materials

Mixtures of CaCl2·6H2O with some nitrate hydrates [Ca(NO3)2·4H2O and Mg(NO3)2·6H2O] or anhydrous nitrates NH4NO3 and KNO3) were studied as latent heat storage materials for greenhouse purposes. The melting points and the heats of fusion of these mixtures showed no deterioration after thermal heat cycles (30°-10°C, 1000 times). Temperature data of solidification both for vertical and horizontal sample tube settings were given.

Feasibility of trichlorofluoromethane (CCl3F, R11) heptadecahydrate as a heat storage material

Abstract Trichlorofluoromethane (CCl 3 F, R11) heptadecahydrate, which melts at 8.5°C with a heat of fusion of 274 kJ/kg (65.4 cal/g), was investigated as a latent heat storage material. Addition of nonionic surfactant, 2 wt% to water in R11 hydrate, increased the formation rate of the hydrate about 4 times which is sufficient for practical use. Phase separation of R11 was prevented effectively in a gel matrix formed by polyacrylamide (PAA) or gelatin. The PAA gel containing the hydrate-surfactant had an apparent latent heat of fusion of 167–209 kJ/kg (40–50 cal/g), repeating phase change successfully over 100 cycles without deterioration in a heat cycle test (0–20°C, 5 cycles/day). Tetrabutyl ammonium fluoride hydrate [(C 4 H 9 ) 4 NF 34.4 H 2 O] was found effective as a nucleating agent.

Two Figures of Merit for Field Emitters Deduced from Fowler?Nordheim Plots

Two factors are deduced from Fowler–Nordheim plots of field emitters, one from their slopes and the other from their slopes and intercepts. The former factor concerns the work function and local field conversion factor, and the latter concerns the emitting area. These two factors are shown to be useful as figures of merit for field emitters both theoretically and experimentally. The derivation of these two factors and an expression of onset voltage using them are presented. It is illustrated that the onset voltage gives the overall figure of merit for field emitters, whereas the two factors proposed here as figures of merit are useful for further detailed discussions for evaluating field emitters and processes to fabricate them.