Heat and mass transfer in discontinuous system

Another boundary condition suggests that the heat flux at the droplet surface is proportional to the absorbed mass of refrigerant vapor, and we have 

The simultaneous solutions of Eqs. (7.229) to (7.234) describe the mass and heat transport processes between refrigerant vapor and solution droplets at constant pressure and Reynolds numbers smaller than 1. Typical lithium nitrate-ammonia solution properties and ammonia vapor properties are available in Venegas et al. (2004). 

Transport problems in discontinuous (heterogeneous) system discuss the flows of the substance, heat, and electrical energy between two parts of the same system. These parts or phases are uniform and homogeneous. The two parts make up a closed system, although each individual part is an open system, and a substance can be transported from one part to another. There is no chemical reaction taking place in any part. Each part may contain n number of substances. For example, thermal diffusion in a discontinuous system is usually called thermal osmosis. If the parts are in different states of matter, there will be a natural interface. However, if both parts are in liquid or gas phases, then the parts are separated by a porous wall or a semi-permeable membrane. 

The postulate of local thermodynamic equilibrium in a discontinuous system is replaced by the requirement that the intensive properties change very slowly in each part, so that the parts are in thermodynamic equilibrium at every instant. The intensive properties are a function of time only, and they are discontinuous at the interface and may change by jumps. In the following sections, thermomechanical effects and thermoelectricity are summarized. 

Based on these thermodynamic forces, the linear phenomenological equations become 

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