Evaporation Rate Model for a Natural Convection Glazed Collector/Regenerator

Abstract

In the present work, a numerical method has been applied to model the water evaporation rate of a glazed collector/regenerator component of an open-cycle absorption refrigeration system. This two-dimensional model calculates local heat and mass-transfer coefficients as part of the solution. The air flow in the glazed channel is driven by the combined buoyancy of both heat and mass transfer (water evaporation). Since the heat and mass-transfer coefficients each depend on both of the driving potentials determined by local conditions in the falling film, a solution of the conjugate problem is required. The resulting nonuniform air-film interface conditions cause the local heat and mass transfer to differ significantly from the uniform boundary condition case. The glazed collector/regenerator is much less sensitive to the ambient temperature and humidity than the unglazed collector. The addition of a glazing over the collector/regenerator provides a significant performance improvement and enhances solution regeneration in a windy humid climate. The glazed collector/regenerator water evaporation rate is higher relative to the unglazed case because the reduction in convective and radiative heat losses increases the absorbent temperature and vapor pressure sufficiently to overcome the concomitant reduction in the mass-transfer coefficient.

Modelling and experimental verification of a solar-powered liquid desiccant cooling system for greenhouse food production in hot climates

“…This is the simplest and cheapest arrangement and therefore considered potentially interesting for the greenhouse application where large areas will be required. Following a survey of theories that have been presented in the literature [5,[7][8][9][10][11][12][13][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], it was decided to adopt the theory of Collier [35] which has already been applied successfully by other researchers [7,11,50]. This approach applies heat and mass balance to a differential control volume at some position x from the inlet of the regenerator to formulate an ordinary differential equation, the solution to which gives an expression for the rate of evaporation per unit area of the surface.…”

Evaluation the Performance of a Horizontal a Prototype Natural Draught Solar Dryer

“…The dryer is covered with ordinary window glass layer of 3 mm thickness which is used as a transparent cover for the solar dryer to reduce the top heat losses. In addition, the glass cover has many operational and performance advantages as reported by Nelson and Wood (1990). The glazing protects the black-coated bed from rain, birds, insects, dust and reduces contamination by other environmental sources.…”

Solar pond powered liquid desiccant evaporative cooling

“…For the natural convection type, the performance can be at the mercy of random wind flow direction. However, studies [126] have indicated that the water evaporation rate can be relatively higher in comparison to the open-type because the reduction in the heat losses can increase the solutions temperature and vapour pressure sufficiently to overcome the associated reduction in the mass-transfer coefficient. Nevertheless, McCormick et al [127] have reported that there exists an optimal glazing height, beyond which the system performance becomes similar to that of the open-type variant.…”