Search

Vapor chambers and heat pipes are often used as standalone heat spreaders for electronics cooling and in other applications. Metal additive manufacturing (AM) techniques have an intrinsic ability to form the porous structures and internal cavities required to fabricate a vapor chamber or a heat pipe. Additive manufacturing techniques thereby have potential for fabricating vapor chambers with complex geometries and locally tailored wick structures to improve performance as well as to monolithically embed vapor chamber heat spreaders within other components. The focus of the present work is to conduct an experimental assessment of the viability of additively manufactured vapor chambers. A direct metal laser sintering (DMLS) technique was used to fabricate a monolithic stainless steel vapor chamber heat spreader with a 39% porous, 0.5-mm thick wick and a 1.5-mm thick internal vapor core. The functionality of the as-printed vapor chamber was evaluated based on characterization of the heat spreading behavior with and without fluid charge. Charging with water decreased the effective thermal resistance of the device while spreading heat from a central hot spot, confirming functionality of the additively manufactured vapor chamber.

Air conditioning (AC) systems demand a significant portion of the total energy consumed by the building sector. Conventional AC based on vapor compression refrigeration (VCR) is neither energy efficient nor environment-friendly due to its method of humidity control and use of refrigerants with global warming potential respectively. Liquid desiccant air conditioning system (LDAS) is a promising alternative to VCR. This review provides a comprehensive overview of the developments in LDAS so far. It explains the principle of operation and classification in detail. The various developments in dehumidifier, regenerator, desiccant material, and mathematical modelling are discussed. The various types of performance parameters, and the design criteria and effect of operating parameters are also detailed. Finally, the climate feasibility, performance control strategies and indoor air quality are explained. This communication will be useful to identify the research gaps to explore new pathways for future research to further improve the efficiency of LDAS.

Air-conditioning (cooling) for buildings is the single largest use of electricity in the United States (U.S.). This drives summer peak electric demand in much of the U.S. Improved air-conditioning technology thus has the greatest potential impact on the electric grid compared to other technologies that use electricity. Thermally-activated technologies (TAT), such as natural gas engine-driven heat pumps (GHP), can provide overall peak load reduction and electric grid relief for summer peak demand. GHP offers an attractive opportunity for commercial building owners to reduce electric demand charges and operating expenses. Engine-driven systems have several potential advantages over conventional single-speed or single-capacity electric motor-driven units. Among them are variable speed operation, high part load efficiency, high temperature waste heat recovery from the engine, and reduced annual operating costs (SCGC 1998). Although gas engine-driven systems have been in use since the 1960s, current research is resulting in better performance, lower maintenance requirements, and longer operating lifetimes. Gas engine-driven systems are typically more expensive to purchase than comparable electric motor-driven systems, but they typically cost less to operate, especially for commercial building applications. Operating cost savings for commercial applications are primarily driven by electric demand charges. GHP operating costs are dominated by fuel costs,more » but also include maintenance costs. The reliability of gas cooling equipment has improved in the last few years and maintenance requirements have decreased (SCGC 1998, Yahagi et al. 2006). Another advantage of the GHP over electric motor-driven is the ability to use the heat rejected from the engine during heating operation. The recovered heat can be used to supplement the vapor compression cycle during heating or to supply other process loads, such as water heating. The use of the engine waste heat results in greater operating efficiency compared to conventional electric motor-driven units (SCGC 1998). In Japan, many hundreds of thousands of natural gas-driven heat pumps have been sold (typically 40,000 systems annually) (Yahagi et al. 2006). The goal of this program is to develop dependable and energy efficient GHPs suitable for U.S. commercial rooftop applications (the single largest commercial product segment). This study describes the laboratory performance evaluation of an integrated 10-ton GHP rooftop unit (a 900cc Daihatsu-Aisin natural gas engine) which uses R410A as the refrigerant (GEDAC No.23). ORNL Thermally-Activated Heat Pump (TAHP) Environmental Chambers were used to evaluate this unit in a controlled laboratory environment.« less