This paper reviews the recent development of available cold storage materials for air conditioning application. According to the type of storage media and the way a storage medium is used, water and ...ice, salt hydrates and eutectics, paraffin waxes and fatty acids, refrigerant hydrates, microencapsulated phase change materials/slurries and phase change emulsions are separately introduced as suitable energy storage or secondary loop media. Water storage and static ice storage, which are already well-established technologies, have little need for further study. Dynamic ice slurry application is discussed especially for its generation method, relating to the efficiency and reliability of converting water or aqueous solution to ice crystals or ice slurry. Thermal and physicochemical properties of different phase change materials have been summarized including latent heat, thermal conductivity, phase separation, supercooling, and corrosion. Moreover, corresponding solutions for issues of different materials are also discussed. Thermal and hydraulic characteristics of phase change slurries (mainly about clathrate slurries, microencapsulated phase change slurries, and phase change emulsions) are discussed and summarized. In addition, the principle of the sorption cold storage is described and different kinds of working pairs are introduced. Relevant perspectives for commercialization of storage materials are discussed.
► Various kinds of suitable and promising PCMs or PCM slurries are summarized and listed. ► Thermal properties of different PCMs for cold storage are compared in details. ► Phase change slurries are introduced from clathrate slurries, microencapsulated phase change slurries, phase change emulsions. ► Thermal and hydraulic characteristics of phase change slurries are introduced briefly. ► Storage capacities of different sorption working pairs are compared and analyzed.
•Reviewed elastocaloric cooling materials and quantitatively assessed half of them.•Discussed thermodynamic cycle options for elastocaloric cooling.•Reviewed four key aspects of developing a ...successful elastocaloric cooling system.•Summarized the up-to-date development status of elastocaloric cooling prototypes.
Elastocaloric cooling is a new alternative solid-state cooling technology undergoing early stage research and development. This study presents a comprehensive review of key issues related to achieving a successful elastocaloric cooling system. Fundamentals in elastocaloric materials are reviewed. The basic and advanced thermodynamic cycles are presented based on analogy from other solid-state cooling technologies. System integration issues are discussed to characterize the next generation elastocaloric cooling prototype. Knowledge acquired from the elastocaloric heat engines is provided as the basis for the design of cooling system configuration. Commercially available drivers enabling proper compression and tension are also presented. A few performance assessment indices are proposed and discussed as guidelines for design and evaluation of future elastocaloric cooling system. A brief summary of the up-to-date elastocaloric cooling prototypes is presented as well.
This paper reviews the recent development of available cold storage materials for subzero applications. According to the type of a storage medium and the way of the storage medium is used, phase ...change material (PCM) storage and sorption storage are introduced separately. Eutectic water–salt solutions and non-eutectic water–salt solution PCMs are discussed from thermal and physicochemical properties such as fusion heat, thermal conductivity, phase separation, supercooling, corrosion, flammability, etc. Related solutions for issues of such PCMs are offered. Microencapsulated PCMs are introduced as they have an excellent heat transfer performance to the surroundings because of the large surface per volume of the capsules and the excellent cycling stability due to the restricted phase separation in microscopic distances. PCMs with nanoparticle additives are also discussed as they have higher thermal conductivity for better storage process. Absorption and adsorption storages are mainly discussed for their working pairs, heat transfer enhancement and system performance improvement aspects. Relevant perspective technologies are discussed for further work.
► Various kinds of suitable and promising PCMs are summarized and listed for subzero cold storage applications. ► Thermal properties of different PCMs for cold storage are compared in details. ► Storage capacities of different sorption working pairs are compared and analyzed.
Liquefied natural gas (LNG) plants are energy intensive. One way to reduce their energy consumption is to apply optimization methods when designing such plants. In this paper, genetic algorithm (GA) ...from Matlab optimization toolbox was used to optimize a propane pre-cooled mixed refrigerant (C3-MR) LNG plant that was originally designed by Mortazavi et al.
1. GA was chosen because it can reach a global optimum with any problem. A computer model was developed for the LNG plant using HYSYS and verified with the model developed by Mortazavi et al., with good agreement.
The optimization problem has 22 variables and 24 constraints. In order to reduce the complexity of the problem, optimization was carried out in two stages. First, MCR cycle optimization and then Propane cycle optimization were conducted with respective constraints. New refrigerant mixtures were found, with savings in power consumption as high as 13.28%. Propane cycle optimization resulted in a savings of 17.16% in power consumption. The optimized C3-MR LNG plant model consumes 100.78 MW, whereas the baseline consumes 110.84 MW. The optimum composition of refrigerant mixture obtained was compared with two optimized compositions of refrigerant mixtures from the open literature. The resulting power consumption utilizing the literature-referenced mixtures is 6.98% and 13.6% more than this work’s optimum composition of refrigerant mixture.
C3-MR LNG plant optimization was conducted with four pinch temperatures (0.01, 1, 3 and 5 K) that represent different common heat exchangers in LNG applications (e.g., spiral-wound heat exchanger and plate fin heat exchanger). Power savings is increased significantly with a pinch temperature of 1 K as compared to 3 or 5 K, but with little improvement as compared to 0.01 K. This figure can have a significant impact on LNG plants selection.
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►Verified computer model for a propane pre-cooled mixed refrigerant (C3-MR) LNG plant was developed using HYSYS software. The LNG plant model was optimized for minimum power consumption with the help of GA from Matlab software. ►Different optimum composition of refrigerant mixtures were found as a function of the cryogenic heat exchanger’s pinch temperature which represent different heat exchanger type. ►This work optimum composition of refrigerant mixtures was compared with two optimized compositions of refrigerant mixtures from the open literature.
Removal of moisture from the air represents a considerable portion of the air conditioning load in hot and humid regions. It is a common practice to run air conditioning systems at temperatures lower ...than the moist air dew point temperature in order to accomplish dehumidification. Desiccant air conditioners offer a solution to meet the humidity and temperature requirements of buildings via decoupling latent and sensible loads. In this work, the performance of a new desiccant material is investigated experimentally. This desiccant material has a unique S-shape isotherm and can be regenerated using a low temperature heat source. The effects of the process air stream's temperature and humidity, the regeneration temperature, the ventilation mass flow rate, and the desiccant wheel's rotational speed on the cycle performance are investigated. ARI-humid conditions are used as a baseline. The moisture mass balance is maintained within 5% for all conducted tests. The results are presented in terms of the moisture removal rate and latent COPlat (coefficient of performance). The results show a desiccant wheel's COPlat higher than unity when it is coupled with an enthalpy wheel.
•The performance of a new desiccant material is investigated experimentally.•The highest desiccant wheel capacity is obtain at the lowest process air temperature.•A desiccant wheel's COPlat higher than unity is possible when coupled with an enthalpy wheel.•The performance of the tested desiccant wheel does not change much with rotational speed.
The airside thermal resistance of air-to-fluid heat exchangers dominates the overall thermal resistance. On conventional heat exchanger's, fins are required to address such challenges; but their ...benefits are not limitless and are bound mainly by the tube size and shape. The reduction of the tube characteristic length has favorable impact on compactness and heat transfer. Conventional tubes are typically limited to round, elliptical or flat shapes which result in particular thermal-hydraulic characteristics. The current article has three main objectives. First, discuss the importance of fins on typical air-to-fluid heat exchanger's and how they become unattractive at smaller characteristic lengths with numerical analyses to support this argument from different perspectives. Second, present a proof-of-concept design with small finless tubes and a novel shape that can outperform a microchannel heat exchanger. Third, present a comprehensive analysis with shape optimization leveraging automated computational fluid dynamics simulations and approximation assisted optimization techniques. Optimum designs can achieve more than 50% reduction in size, material, and pressure drop compared to the baseline microchannel heat exchanger. The method is validated with the experimental validation of a metal three-dimensional printed prototype of the NTHX-001. The numerical simulations agreed within less than 5% in capacity, 10% in air heat transfer coefficient, and 15% in air pressure drop.
Thermoelastic cooling is a recently proposed, novel solid-state cooling technology. It has the benefit of not using high global warming potential (GWP) refrigerants which are used in vapor ...compression cycles (VCCs). Performance enhancements on a thermoelastic cooling prototype were investigated. A few novel design options aiming to reduce the cyclic loss were proposed. It was found that the maximum temperature lift increased from 6.6 K to 27.8 K when applying the proposed novel designs, corresponding to 0–152 W cooling capacity enhancement evaluated under 10 K water–water system temperature lift. In addition, a multi-objective optimization problem was formulated and solved using the genetic algorithm to maximize the system capacity and coefficient of performance (COP). With all the novel designs, the optimization could further enhance 31% COP, or 21% cooling capacity, corresponding to COP of 4.1 or 184 W maximum cooling capacity.
•Proposed novel designs of the thermoelastic cooling for better performance.•Updated the dynamic system model with novel design options.•Evaluated the performance enhancement when applying these proposed novel designs.•Conducted a multi-objective optimization study using the updated model.
•Drop-in tests of three R410A low-GWP alternative refrigerants were performed.•The results show that R32 and L41a are good replacement candidates for R410A.•Most of the predicted COP and capacity ...results of R32 experiments agree with the measured values.•Varying the compressor size and adding a suction line heat exchanger to the system were investigated.
The environmental impact of high global warming potential (GWP) refrigerants pushed the HVAC&R industry to investigate alternative refrigerants. R410A is a common refrigerant for air conditioning and heat pumping applications, but has a GWP of 2088. Drop-in tests of three R410A low-GWP alternative refrigerants (R32, D2Y60 and L41a) in a 10.55 kW capacity split heat pump unit were performed. The results show that R32 and L41a are good replacement candidates for R410A. A finite volume heat exchanger model and component based vapor compression system simulation tools were validated against the experimental data. Most of the predicted COP and capacity results of R32 experiments lie within 5% of the measured values, which is in good agreement with the experiments. Further investigation was carried out by varying the size of the compressor and adding a suction line heat exchanger to the system to match the capacity to that of R410A.
This article presents the design of elastocaloric cooling system driven by hydraulic actuators. Ni-Ti tubes under axial compressive loading mode are used in the system to provide cooling and heating. ...Those Ni-Ti tubes are enclosed in four identical beds, which are driven by two one-way hydraulic cylinders. Operated under the single-stage reverse Brayton cycle, the system achieves heat transfer and heat recovery by using a sophisticated heat transfer fluid network controlled by solenoid valves. Two novel designs to improve the system's performance based on the lessons learned from the previous studies are applied to this prototype. Preliminary test results of the material's latent heat at a specific fluid flow rate and temperature difference agree well with the results reported in the literature. System coefficient of performance of 11.0 and temperature lift of 24.6 K are estimated based on a dynamic model developed in the previous study.
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