3345 -- Evaporator Models for Operation with Dry, Wet, and Frosted Finned Surfaces Part 1: Heat Transfer and Fluid Flow Theory PDF

Evaporator models for operation with dry, wet, and frosted surface conditions require equations for both air-side and refrigerant-side heat transfer coefficients and pressure loss factors. This paper details the heat transfer coefficients, mass transfer coefficients, and pressure loss factors found in the current literature that yielded the best correlation between data simulated by evaporator models developed and data obtained experimentally by the authors. Evaporators operating under wet and frosted surface conditions not only cool the air source but also dehumidify it. Below the freezing temperature of water, frost will form on the evaporator surface. The frost has a thermal resistance, and its accumulation reduces the flow rate of the air source. The thermal resistance of the frost and the air-source flow rate are dependent on the frost density. Equations for the calculation of frost accumulation and its effects on evaporator performance are included. The inclusion of the effects of frost is required for evaporators used in heat pumps.

KEYWORDS: evaporators, heat pumps, heat transfer coefficient, finned tubes, wet, dry, frost, heat flow, fluid flow, calculating, flow rate, thermal resistance.