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Internally cooled and heated desiccant-coated heat and mass exchangers (ICHDHMX) driven by low-grade heat are very attractive owing to their energy-saving potential, especially for applications where substantial moisture removal (such as air-conditioning) is a necessity. In this paper, we derive equations for the performance of an ideal ICHDHMX, allowing us to define humidity-ratio effectiveness (εY) and relative-humidity effectiveness (εRH) such that their values approach 1 as the performance approaches that of an ideal ICHDHMX. Besides an equation-based approach, an easy-to-use psychrometric-chart based approach is presented to determine the performance of an ideal ICHDHMX. We invoke conservation principles to ascertain whether or not it is feasible to use the ICHDHMX for a given set of inlet conditions of air and water streams for dehumidification and regeneration. The dimensions of the ICHDHMX can be determined using this methodology, not even requiring knowledge of a tuning parameter unless a precise outlet specific humidity is required. Simulations are conducted for cases involving three incoming hot water temperatures (38, 44 and 50 °C) and several mixing ratios of room return air (25 °C at 0.011 kg/kg dry air) and outdoor air (32 °C at 0.02 kg/kg dry air), typical of warm and humid weather conditions. For all cases, the cool-water inlet is fixed at 30 °C. The results show that even when the dehumidification air-stream humidity is high, if the regeneration air-stream humidity is low (typical of room-exhaust air), the operation of an ICHDHMX is feasible using a low regeneration temperature of only 38 °C. When the regeneration temperature is 50 °C, the exchanger can operate under the complete range of humidity conditions tested. A cooling coefficient of performance up to 9.8 and effectiveness value up to 0.88 is realized, while the fluid power required is generally very low. These findings substantiate the case for commercial adoption of this technology for air-conditioning.

Flow maldistribution compromises thermal and hydraulic performances of heat sinks. The oblique-finned heat sink is a multichannel heat sink comprising parallel (primary) and collinear oblique (secondary) channels and it was reported to suffer from a self-induced flow migration in liquid and air cooling. In this study, a novel tapered inlet/outlet flow manifold was proposed for the planar oblique-finned heat sink. Two heat sink configurations (oblique angles of 30° and 45°) and three flow manifold configurations (of 5%, 10%, and 20% wider flow domains) were investigated. Flow migration characteristics were studied via numerical simulations. Wind tunnel measurements, supported by infrared thermography, were performed to characterize thermal and hydraulic performances on a wide range of air flow rates. The flow manifold was observed to provide a favorable distribution of secondary flows in the spanwise direction of the heat sink. Up to 50% increase in Nusselt number with a negligible increase in pressure drop was observed with the 45° oblique-finned heat sink once the flow manifold was incorporated. 30° oblique angle −10% flow manifold combination provided the lowest heat sink temperature and the most uniform wall temperature. The novel tapered inlet/outlet flow manifold is the first effort reported in the literature to reduce the adverse effects of flow migration through the planar oblique-finned heat sinks.

This paper presents the modeling and optimization of an ejector refrigeration system (ERS). Engineering Equation Solver (EES) has been used for modeling. These models have been validated against published experimental results. Refrigerant R245fa is used as a working fluid. A new analytical model for predicting the optimum (on-design) performance (entrainment ratio) of ejectors is presented. The analytical model of the ejector is validated against two sets of published experimental data and good agreement is established with an average error of 3.4%. The presented ERS model has also been validated with two sets of published experimental results and an average error of 2.9% is obtained. The ERS model is further compared with a model developed in EBSILON (a commercial tool). The results show that for the optimum design of an ERS, the generator pressure increases linearly with heat source temperature while the output (refrigeration effect) increases exponentially. For the case study, the designed ERS produces 1.8 MW of cooling with estimated annual savings of S$0.42 million while operating at 0.3 COP. The presented models can be used for designing ejector and ERS for various applications.