doi: 10.3850/978-981-08-7614-2_IMPRES045

ABSTRACT

R134a (1, 1, 1, 2 tetrafluro ethane) – DMAC (N, N Dimethyl Acetamide) vapour absorption refrigeration system can be used for sub zero temperature cooling applications and where ammonia cannot be used. This system needs rectification of vapour from generator and also draining of residual R134a-DMAC liquid from evaporator. As such, due to comparatively low latent heat of vaporisation to vapour specific heat ratio of R134a, liquid vapour heat exchanger (LVHX) is required and the residual liquid further enhances its prominence in sub-cooling the incoming condensate thereby in improving the system COP. In this paper LVHX is analysed in detail by varying operating parameters like rectifier efficiency and cooling and generator temperatures. Thermal capacity of the cold stream (vapour and residual liquid) changes continuously due to progressive phase change of the residual liquid. Depending on rectifier efficiency the maximum temperature difference shifts from one end of LVHX to the other, while at certain efficiencies it occurs within the heat exchanger indicating that normal design procedure would lead to an over estimated design. The prominence of LVHX increases with decrease in both rectifier efficiency and evaporator temperature.

Keywords: Adsorbed phase, Entropy, Heat of adsorption, Thermodynamic formulation.

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