Zap Pak Heat Pack

To begin the product design process, the team would probably seek to identify a salt with the following properties (1) capable of remaining dissolved in a supersaturated solution at 

For a hand warmer, select a suitable salt and estimate by an energy balance a salt and water mixture that could achieve a temperature rise of 20°C under adiabatic conditions. An article by de Nevers (1991) discusses the hand warmer and the energy balance. 

patent literature, which is readily accessible on the Internet at www.uspto.gov, suggests several possible salts, including sodium acetate, sodium thiosulfate, calcium nitrate, and lead acetate. These are all hydrated at ambient temperatures with high solubility and relatively high heats of crystallization, as shown by the following data taken from Mullin (1993)  

NaCjHjOj 3H2O Na2S203 5H2O Ca(N0,)2 4H2O Pb(C2H302)2 3H2O 

Assume that upon the completion of crystallization at 40°C, we have a solution containing 100 g of water (MW =18) and the equilibrium solubility of sodium acetate (MW = 82), or 65.5 g of sodium acetate from the above table. Let the solid crystals at 40°C be a g of solid crystalline trihydrate of sodium acetate (MW = 136). For a thermod3mamic path, take crystallization at 20°C, but with the 40°C solubility, followed by heating the crystaUine solids and the solution to 40°C. Therefore, specific heats are needed for the solid and the solution. In the absence of data for the trihydrate of sodium acetate, Kopp s rule (Felder and Rousseau, 2000) is applied with atomic heat capacities in cal/mol-°C of 1.8 for C, 2.3 for H, 4.0 for 0, 9.8 for water of crystallization, and 6.2 for all other atoms in the four salts. Thus, for NaC2H302 3H2O, 

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For therapeutic, health, and fitness piuposes, until recently, hot-water containers to heat body parts and ice bags to cool body parts dominated the market. Now, a number of new products have been developed, principally thanks to advances in the ease of manufacture of leak-proof polymer containers. These include two hand warmers carried in the palm (1) the GRABBER MYCOAL Hand Warmer made in Japan and distributed by GRABBER Warmers of Grand Rapids, Michigan, and (2) the Zap Pak Heat Pack made and distributed by Prism Enterprises in San Antonio, Texas. The former produces heat by a chemical reaction, but can only be used once. The latter produces heat by crystallization and can be regenerated. 

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