Heat of fusion, latent

The latent heat of fusion of a solid, denoted, Lp and expressed in J.kg is the heat required per unit mass of solid to melt it. For instance, in order to melt ice or to freeze water, 340 kj/kg (146 Btu/lb) must be supplied or removed. 

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Several recent patents describe improvements in the basic belt process. In one case a higher soHds polymerization is achieved by cooling the starting monomer until some monomer crystallizes and then introducing the resulting monomer slurry onto the belt as above. The latent heat of fusion of the monomer crystals absorbs some of the heat of polymerization, which otherwise limits the soHds content of the polymerization (87). In another patent a concave belt is described which becomes flat near the end. This change leads to improved release of polymer (88). 

A man of weight 100 kg standing on skis 2 m long and 0.10 m wide slides on the 2° mountain slope, at 0°C. Calculate the work done against friction when the ski slides a distance equal to its own length. Hence calculate the average thickness of the water film beneath each ski. (The latent heat of fusion of ice is 330 MJ m °.)... 

The solidification speed of salol is about 2.3 mm mim at 10°C. Using eqn. (6.15) estimate the energy barrier q that must be crossed by molecules moving from liquid sites to solid sites. The melting point of salol is 43°C and its latent heat of fusion is 3.2 x 10 ° J molecule F Assume that the molecular diameter is about 1 nm. 

Polymer compounds vary considerably in the amount of heat required to bring them up to processing temperatures. These differences arise not so much as a result of differing processing temperatures but because of different specific heats. Crystalline polymers additionally have a latent heat of fusion of the crystalline structure which has to be taken into account. 

Extrusion blow moulding of bottles has been successfully accomplished in reeent years by attention to the points mentioned above. It is to be noted here that UP VC has a much lower average specific heat between the proeessing temperature and room temperature than polyethylene and, being essentially amorphous, no latent heat of fusion. This leads to much less heat needing to be removed on cooling of mouldings and very short cycle times are possible. 

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