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Heat exchangers are key components in many of the devices seen in our everyday life. They are employed in many applications such as land vehicles, power plants, marine gas turbines, oil refineries, air-conditioning, and domestic water heating. Their operating mechanism depends on providing a flow of thermal energy between two or more mediums of different temperatures. The thermo-economics considerations of such devices have set the need for developing this equipment further, which is very challenging when taking into account the complexity of the operational conditions and expansion limitation of the technology. For such reasons, this work provides a systematic review of the state-of-the-art heat exchanger technology and the progress towards using nanofluids for enhancing their thermal-hydraulic performance. Firstly, the general operational theory of heat exchangers is presented. Then, an in-depth focus on different types of heat exchangers, plate-frame and plate-fin heat exchangers, is presented. Moreover, an introduction to nanofluids developments, thermophysical properties, and their influence on the thermal-hydraulic performance of heat exchangers are also discussed. Thus, the primary purpose of this work is not only to describe the previously published literature, but also to emphasize the important role of nanofluids and how this category of advanced fluids can significantly increase the thermal efficiency of heat exchangers for possible future applications. [ABSTRACT FROM AUTHOR]

The geothermal heat exchanger system is one of the most energy-efficient and environmentally friendly building service systems. In the present study, CuO/water nanofluid was used as the heat transfer fluid to enhance the energy efficiency of the geothermal heat exchangers. A three-dimensional numerical model was employed to investigate the effect of nanoparticle diameter and sphericity on the thermal performance of the geothermal heat exchanger, and it was well validated against the experimental results of nanofluids in the geothermal heat exchangers. The numerical results showed that nanoparticles with a diameter of 5 nm and 50 nm were not recommended for the nanofluids used in the geothermal heat exchangers due to the performance efficiency coefficient lower than 1, and the optimum diameter was 40 nm, which had the highest performance efficiency coefficient (1.004875). Moreover, the spherical particle-based nanofluid was characterized by the 8.55% higher energy efficiency, in comparison to rod-shaped particle-based nanofluid. Therefore, the application of nanofluid in the geothermal heat exchanger can enhance heat transfer, and the proposed optimum particle diameter and sphericity could contribute to higher energy efficiency. [ABSTRACT FROM AUTHOR]

• Combined inverted Brayton – organic Rankine cycle for waste heat recovery. • Pentane as working fluid gives higher system efficiency than toluene and R245fa. • Combined scheme efficiency 10% higher than organic Rankine cycle at high temperatures. • Combined scheme electricity cost 6% lower than of organic Rankine cycle. • Flue gas water condensation non-negligibly affects inverted Brayton cycle performance. Many practical cases with waste heat recovery potential such as exhaust gases of reciprocating engines, cement kilns or heat-treating furnaces, are nowadays often integrated with organic Rankine cycle to convert waste heat to the mechanical power. However, when dealing with high-temperature waste heat, organic Rankine cycle faces efficiency limit due to the physical properties of the working and thermal fluids. That gives room for further enhancement of the waste heat recovery technologies via the investigation of different non-conventional schemes as one of the possible ways. In the present work, a system introducing the combined inverted Brayton plus organic Rankine cycle is under investigation. Aspen Hysys models of both conventional organic Rankine cycle and combined cycle were designed, orienting on waste heat recovery from the heavy-load gas-fueled reciprocating engine exhaust. In this way, the performance of the combined scheme was benchmarked versus the conventional organic Rankine cycle. An assessment of the organic Rankine cycle working fluids was provided, and pentane has shown the best thermodynamic performance. The study on inverted Brayton cycle defined the remarkable effect of the water condensation in the gas duct on the inverted Brayton cycle performance. Finally, both thermodynamic and economic optimizations of the models were conducted, setting the stage for the comparison of solutions. Results have shown the 10% advantage of the combined scheme over organic Rankine cycle in generated power and system efficiency. The levelized-cost-of-energy-based optimization for variable capacity factors has highlighted above 6% advantage of the investigated solution. The analysis of the sensitivity from machines' efficiencies and heat exchangers' pinches has shown that with some sets of parameters, the studied scheme may concede to the organic Rankine cycle. [ABSTRACT FROM AUTHOR]

• Liquid nitrogen maldistribution results in temperature irregularities along microcoolers. • Flow maldistribution in microcoolers is mainly caused by the non-uniform heat load. • Flow maldistribution can be tuned during the cool-down process and operation at 100 K. • Flow maldistribution deteriorates heat exchanger efficiency and microcooler performance. Counter flow heat exchangers (CFHXs) are essential elements of micromachined Joule–Thomson (JT) cryogenic coolers. The performance of CFHXs has a crucial influence on the overall behavior of JT microcoolers. Flow maldistribution, especially those with phase change, can adversely affect the performance of JT microcoolers. However, the underlying mechanisms of flow maldistribution for two-phase flow in JT microcoolers remain unexplored. Here we report the heat triggered switching of two-phase flow maldistribution in the heat exchanger of JT microcoolers by both microscopic observations and temperature measurements. A measure against flow maldistribution is proposed. [ABSTRACT FROM AUTHOR]

The cheese industry has high energy consumption, and improvements to plant efficiency may lead to a reduction of its environmental impact. A survey on a sample of small-medium Italian cheese factories was carried out in order to assess the efficiency of heat recovery of the milk pasteurization equipment for the cheese production. Then, an exergetic analysis to calculate the related exergy loss was carried out together with a cost-benefit analysis to identify the optimized value of the heat efficiency. The exergy loss reduction was determined throughout an exergy analysis that takes into account this last value and the comparison with the previous exergy losses. Finally, the feasibility and the consequent additional reduction of exergy losses were verified, if a cogeneration heat and power (CHP) combined to the pasteurization equipment is assumed. Results show a current heat recovery efficiency of 93.2% in the Italian cheese factories; a close connection between the exergetic losses and the efficiency of the heat recovery exchanger; the optimized recovery efficiency equal to 97.3% obtained from the cost-benefit analysis; a related important exergetic loss reduction of −45% in the heat exchangers, as a second result of the exergetic analysis; a similar reduction of the exergy loss (−42%) of the whole system, as a third result of the exergetic analysis; a total exergy loss reduction of 22.9 kJ kg−1milk, which corresponds to a lower environmental impact due to CO2 reduction; a further reduction of the exergy loss of −10% when the cogeneration heat and power CHP are used. [ABSTRACT FROM AUTHOR]

• Identified the optimal GT pressure ratio requirements for four sCO 2 cascaded cycles. • Pressure ratio of a sCO 2 cycle at maximum efficiency is higher than a steam cycle. • Multi-objective optimisation is done to compare sCO 2 cycles on equivalent basis. • Performance prediction maps were produced to help selecting an optimal GT. • A new sCO 2 cycle is proposed that improves efficiency by 1.4 percentage points. A closed-loop, indirect, supercritical Carbon Dioxide (sCO 2) power cycle is attractive for fossil-fuel, solar thermal and nuclear applications owing to its ability to achieve higher efficiency, and compactness. Commercial Gas Turbines (GT's) are optimised to yield maximum performance with a conventional steam Rankine cycle. In order to explore the full potential of a sCO 2 cycle the whole plant performance needs to be considered. This study analyses the maximum performance and cost of electricity for five sCO 2 cascaded cycles. The plant performance is improved when the GT pressure ratio is considered as a design variable to a GT to optimise the whole plant performance. Results also indicate that each sCO 2 Brayton cycle considered, attained maximum plant efficiency at a different GT pressure ratio. The optimum GT pressure ratio to realise the maximum cost reduction in sCO 2 cycle was higher than the equivalent steam Rankine cycle. Performance maps were developed for four high efficient cascaded sCO 2 cycles to estimate the specific power and net efficiency as a function of GT turbine inlet temperature and pressure ratio. The result of multi-objective optimisation in the thermal and cost (c$/kWh) domains and the Pareto fronts of the different sCO 2 cycles are presented and compared. A novel sCO 2 cycle configuration is proposed that provides ideal-temperature glide at the bottoming cycle heat exchangers and the efficiency of this cycle, integrated with a commercial SGT5-4000F machine in lieu of a triple-pressure steam Rankine cycle, is higher by 1.4 percentage point. [ABSTRACT FROM AUTHOR]

In current work the multi-effect desalination (MED) plant scheme and operation have been studied based on thermodynamic optimization using mathematical calculation and modeling for the main equations related to mass, energy and salinity balance taking in account the synchronized consequence of several constraints on the system execution. The effects of irreversibilities and energy losses are integrated in the study which in turn the results obtained are very close to the real results more than previous studies. The results obtained show that the system performance is meaningfully influenced by heat source flux, stage number, heat exchangers efficiency and feed water temperature and flow rate Then the effects of involved parameters are performed and discussed. Moreover, various 3D results have been displayed involving the effect of more than two parameters in system performance. Therefore, the outputs of this work assist manufacturer for the optimization and design of MED plant. The authenticity and perfection of the numerical solution technique are proved and verified within real results. • Multi-effect desalination (MED) plant scheme and operation have been studied. • The effects of irreversibilities and energy losses are integrated. • Effect of feed water temperature and flow rate was considered. • Perfection of the numerical solution was proved. [ABSTRACT FROM AUTHOR]

• Benefits deriving from MOHC-based nanofluid adoption in ORCs were investigated. • A numerical model for the assessments of the nanofluid benefits was developed. • Semi-empirical correlations for modelling MOHC desorption behaviour were defined. This paper presents an in-depth investigation of the applications of an innovative nanofluid – suspensions of nanoparticles in a base fluid- in the ORC field, based on a new class of nanoparticles – termed Metal-Organic Heat Carriers (MOHCs) – molecularly engineered to reversibly uptake and release the working fluid molecules in which they are suspended. Unlike standard nanoparticles (i.e. Al 2 O 3 , Al, ...), these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption which can be as much as twice the level of the latent heat of vaporization of the pure fluid phase alone. The paper illustrates the development of a numerical model for assessing the MOHC-based nanofluid gain in ORC systems. More specifically, the possible combination of the base fluid R245fa with the nanoparticle MIL101, a robust Metal Organic Heat Carrier, was considered. To properly model the reversible adsorption/desorption process, experimental analyses were carried out to study the uptake of the R245fa in MIL101 at different operating conditions and departing from the experimental results, proper semi-empirical correlations were defined and adopted within the numerical model. The resulting performance of the MIL101/R245fa were compared with those of pure organic fluids, whose cycle was optimized in order to maximize the area-to-power ratio. Promising results were achieved in terms of system efficiency increase and heat exchanger area reduction. [ABSTRACT FROM AUTHOR]

• The 1D model is in good agreement with the CFD model. • Regenerators perform effectively at high speeds. • Heat transfer mechanisms are enhanced at high speeds. • Expressions for the heat transfer coefficient vs Reynolds number were generated. • The efficiency of the designed Vuilleumier machine increases with the speed. A one-dimensional analytical model and a three-dimensional CFD numerical model were used for the investigation of the effect that the rotational speed has on several thermodynamic quantities and the performance of a Vuilleumier machine. The machine, was designed as a combination of two opposing Stirling engines. The one-dimensional program was based on the energy balance at each control volume in order to calculate the energy flow inside the machine and then losses were added. On the other hand, the CFD model utilized fundamental conservation equations at each of the numerous computational cells which resulted to accurate calculations at every dimension. It was able to provide the heat transfer coefficients inside the heat exchangers that were in turn utilized by the analytical model. The pressure drop was computed directly at each space by the numerical model and with equations for flow losses from the bibliography by the analytical model. Pressure drop increased significantly with the speed. The effectiveness of the regenerators was evaluated by an existing analytical model and resulted to reduce drastically with the drop of speed. The effectiveness plays very important role on the efficiency of the machine. Furthermore, there appears to be a discrepancy between the heat flow in the heat exchangers and the wall-gas temperature difference at high speeds which has to be examined according to the oscillatory nature of the gas flow. Heat transfer coefficients were generated in relationship with the Reynolds number for each speed investigated, yielding less thermal resistance when the speed is high. Finally, the change of heat amounts through the four heat exchangers and change of the efficiency of the Vuilleumier machine with the speed, resulted to be similar with experimental data. [ABSTRACT FROM AUTHOR]

• Radiative fins with dynamic geometry can influence heat transfer rates in real time. • Self-irradiation decreases turn-down ratio but increases fin efficiency. • Fin efficiency is greatest for collapsed fins and smallest for extended fins. • A turn-down ratio of three or greater is possible with dynamic radiative fins. Efficient heat transfer is critical in the design and optimization of thermal control systems. Static radiative heat exchangers are often simple and reliable systems but typically cannot be adapted to environmental changes. Adaptable radiative heat exchangers can be adjusted in response to variations in the thermal environment or operating conditions and have the potential for increased efficiency and reduced cost. Dynamic control of a radiative heat exchanger is possible through geometric manipulation of a segmented, self-irradiating fin, consisting of rigid panels that are linked by thermal hinges in an accordion arrangement. In this paper, a numerical model is described to predict the temperature profile and efficiency of a radiative heat exchanger, accounting for conduction and self-irradiation. Governing equations are cast in terms of the conduction-radiation interaction parameter, surface emissivity, actuation angle, and the thermal conductance of the hinges linking the panels. Results indicate that a turn-down ratio (largest possible heat rate divided by smallest possible heat rate) of greater than three is possible for realistic panel geometries and materials. Self-irradiation decreases the turn-down ratio, and there is evidence that an optimal number of rigid panels exists for any combination of panel geometry and device temperature. The maximum efficiency occurs when the plates are in the collapsed position, but the heat rate is at a minimum in this configuration. Finally, the properties and geometry of the plates are shown to have a more significant effect on the turn-down ratio than the properties of the thermal hinges. [ABSTRACT FROM AUTHOR]

Natural gas and electricity together accounted for 82.5% of all residential energy use in Canada in 2013 with nearly half of the average household consumption from natural gas used for heating. Energy demand is projected to grow exponentially due to population increase. In May 2015, Canada submitted its Intended Nationally Determined Contribution to the United Nations Framework Convention on Climate Change which included an economy-wide target to reduce greenhouse gas emissions by 30% below 2005 levels by 2030. As of 2016, Canada is projected to significantly miss its 2020 and 2030 climate target with the set of measures it currently has in place. The projected target for 2020 is 622 mega tons of carbon dioxide equivalent (Mt CO2 eq.) and the projected outcome is 768 Mt CO2 eq. The projected target for 2030 is 524 Mt CO2 eq. and the projected outcome is 815 Mt CO2 eq. This leads to the demand of innovative solutions to reduce fossil fuel usage and to switch to renewable energy. A recent heat extraction system has been developed that combines a typical horizontal ground heat exchanger with a sewage pipe. The heat extraction system is a hollow concrete cylinder with a helical high-density polyethylene pipe embedded within the pipe walls. The high-density polyethylene pipe has an outlet and inlet on each length of pipe which are attached to a heat pump which circulate a heat exchange fluid. As the heat exchange fluid cycles through the system, it extracts heat from the surrounding soil and sewage within the pipe while simultaneously carrying the sewage to a waste treatment plant. A heat pump uses the obtained energy to heat a building in cold weather and cool a building in hot weather. This system has not been studied under transient conditions in an extreme climate. In this study, a numerical model is developed using the finite element solver COMSOL Multiphysics to investigate heat transfer coupled with fluid flow by solving partial differential equations where temperature is the dependent variable. A soil block is initially modelled to simulate a control scenario of ground temperature in order to extract data at specific locations for specific times. Following are multiple simulations which implemented the heat extraction system with various energy demands into the soil block to compare ground temperatures at specific locations. A five year period of sustainability is demonstrated through comparison of temperature differentials of adjacent soil locations to the benchmarks established. The maximum temperature change over the five year period interpreted is 1.8 degrees centigrade at 0.1 meters adjacent to the heat extraction system for 75% energy demand of a bed and breakfast located south of Winnipeg. The system is shown to handle an energy demand of up to 6 typical residential houses in Winnipeg when the sewage temperature is kept constant. [ABSTRACT FROM AUTHOR]

An editorial is presented on the future of vapor compression technology. topics discussed include inherent inefficiency of vapor compression technology; goal of improving energy efficiency that should match the application conditions will yield a larger benefit at lower cost; and advantage of decrease in heat exchanger weight and volume will benefit microchannel technology.

Assessment of suitable locations for a ground source heat pump (GSHP) system based on the groundwater condition of study area is important for its sustainable development. Installation potential of a GSHP system was evaluated for the Aizu Basin, Japan. Firstly, suitability assessment was done for a conventional closed-loop system by preparing a distribution map of heat exchange rates for space heating. Heat exchange rates were higher at the northern and southern areas and lower at the central area, indicating that the northern and southern areas are appropriate for the conventional system. A different type of GSHP system using an artesian well was proposed at the central area because groundwater is flowing in an upward direction and using its heat energy can increase heat exchange rates. Demonstration of this system using an artesian well for space heating resulted in higher heat exchange rates compared to the conventional system. A GSHP system using an artesian well is suitable at the central area, and the conventional one is suitable at the northern and southern areas. Assessment of the installation potential of different types of GSHP system in the same Aizu Basin based on its groundwater condition is unique to this study. It can assist in selecting suitable locations for GSHP system installation and to promote its growth in Japan. [ABSTRACT FROM AUTHOR]

As the dimensions of physical systems approach the nanoscale, the laws of thermodynamics must be reconsidered due to the increased importance of fluctuations and quantum effects. While the statistical mechanics of small classical systems is relatively well understood, the quantum case still poses challenges. Here, we set up a formalism that allows us to calculate the full probability distribution of energy exchanges between a periodically driven quantum system and a thermalized heat reservoir. The formalism combines Floquet theory with a generalized master equation approach. For a driven two-level system and in the long-time limit, we obtain a universal expression for the distribution, providing clear physical insight into the exchanged energy quanta. We illustrate our approach in two analytically solvable cases and discuss the differences in the corresponding distributions. Our predictions could be directly tested in a variety of systems, including optical cavities and solid-state devices. [ABSTRACT FROM AUTHOR]