A model for the quantum Brayton refrigerator that takes the harmonic oscillator system as the working substance is established. Expressions of cooling load, coefficient of performance (COP), and ecological function are derived. With numerical illustrations, the optimal ecological performance is investigated. At the same time, effects of heat leakage and quantum friction are also studied. For the case with the classical approximation, the optimal ecological performance, and effects of heat leakage and quantum friction are also investigated. For both general cases and the case with classical approximation, the results indicate that the ecological function has a maximum. The irreversible losses decrease the ecological performance, while having different effects on the optimal ecological performance. For the case with classical approximation, numerical calculation with friction coefficient μ = 0.02 and heat leakage coefficient C e = 0.01 shows that the cooling load (R E ) at the maximum ecological function is 6.23% smaller than the maximum cooling load (R max ). The COP is also increased by 12.1%, and the exergy loss rate is decreased by 27.6%. Compared with the maximum COP state, the COP (ɛ E ) at the maximum ecological function is 0.55% smaller than the maximum COP (ɛ max ) and that makes 7.63% increase in exergy loss rate, but also makes 6.17% increase in cooling load and 6.20% increase in exergy output rate.

The pilot diesel quantity (m pilot ) has an impact on the liqueified nitrogen gas (LNG)-diesel dual-fuel engine, but it is very difficult for a dual-fuel engine with the traditional injection system to adjust m pilot to meet various operating conditions in practice. In recent years, with great progress in common rail diesel injection technology, m pilot can be adjusted accurately by the electronic control system, which is an advantage for operation with the diesel–LNG dual-fuel. In order to optimize m pilot of the diesel–LNG dual-fuel engine, the combustion and performance of a dual-fuel engine with the m pilot of 5.05 mg/cyc, 5.20 mg/cyc, 5.69 mg/cyc, 6.31 mg/cyc and 6.91 mg/cyc under 50% load at speed of 1600 r/min were analyzed. Experimental results show that, with an increase in m pilot , the maximum in-cylinder pressure, rate of pressure rise, and heat release rate of dual-fuel obviously increase, the crank angles of the maximum value move forward, and the combustion duration becomes shorter. The mean value of peak in-cylinder pressure (p max ) increases obviously while the standard deviation of it decreases, and the distribution of that focuses. The mean value of the crank angle corresponding to p max pressure decreases except for the m pilot of 5.05 mg/cyc, while the standard deviation of that gradually decreases, the distribution of it focuses and moves forward. The brake power increases while the brake-specific fuel consumption (BSFC) decreases, the CO and HC decrease, while the CO 2 , NO x, and smoke density emissions increase.

Calcium chloride hexahydrate (CaCl 2 ·6H 2 O) is an attractive candidate as a phase change material for supplemental cooling in air-cooled thermal power-plant since it has a low-phase transition temperature of 29.3 °C and a relatively large volumetric energy storage density of 289 MJ/m 3 . The volumetric energy storage density is approximately double the energy densities of comparable paraffins with similar melting points. However, calcium chloride hexahydrate often requires high degree of supercooling to initiate solidification and long-term thermal stability has impeded the adoption of calcium chloride hexahydrate in the latent heat thermal energy storage system. There are only a few literatures which report on long-term stability of pure calcium chloride hexahydrate accurately. In this paper, the effects of sodium chloride and strontium chloride in mitigating supercooling in calcium chloride hexahydrate over 1000 melt–freeze cycles and thermal stability at elevated temperatures were studied in large sample size. Since there is not much data available on calcium chloride hexahydrate with nucleating additives, the current data available do not provide an insight into the effects of thermal cycling on supercooling. Therefore, this study also aims to measure the reliability of calcium chloride hexahydrate and report it, in terms of variations in melting temperature, supercooling, energy storage density, and change in mass over 1000 melt–freeze cycles. The results have shown that strontium chloride as heterogenous nucleators reduces supercooling by 2.5 °C and survived up to 1000 melt–freeze cycles (i.e., 2.7 years).

HFO-1336mzz-Z with low global warming potential (GWP) was considered as a promising alternative of HCFC-123, HFC-245fa in air conditioning (AC) and heat pump (HP), respectively. In order to understand the operation performances of HFO-1336mzz-Z and HCFC-123, HFC-245fa in different working conditions, an experimental setup for testing the refrigeration cycle performance was built. The cycle performances of HFO-1336mzz-Z and HCFC-123 in AC conditions, HFO-1336mzz-Z and HFC-245fa in HP conditions were investigated by experiment. It was found in AC conditions, the discharge temperatures for the systems with HFO-1336mzz-Z and HCFC-123 were lower than 115 °C, the cooling capacity of the system with HFO-1336mzz-Z was 27% less than that with HCFC-123 at least, and the coefficient of performance (COP) of the system with HFO-1336mzz-Z was 0.1 lower than that with HCFC-123; in HP conditions, the discharge temperature with HFO-1336mzz-Z was lower than that with HFC-245fa, the former was never over 115 °C while the latter was up to 126 °C, the power input to the compressor with HFO-1336mzz-Z was 20% less than that with HFC-245fa in the same HP conditions, the heating capacity of the system with HFO-1336mzz-Z was 30–40% less than that with HFC-245fa.

A 3D transient numerical model of a ductile iron ladle has been developed to predict the fluid flow and temperature drop during the holding and teeming. The volume of fluid (VOF) multiphase model has been employed to track the interface between the liquid metal and the air. The SST k-ω model has been applied to model the turbulence due to natural convection in the ladle. The temperature evaluation in the refractory lining walls during preheating and teeming is shown. Appropriate boundary conditions are applied for natural convection and radiation to surroundings from all the outer steel surfaces as well as from the top glass wool cover. The heat loss due to radiation from the liquid metal surface to the surrounding walls is also considered in the present model by applying an energy sink term to the cells at the interface. The numerical results of the 780 kg ladle have been compared with the measured temperature drop of the metal using an S-type thermocouple for two ladle cycles and the difference between the measured and predicted temperature at the end of two cycles is 3 °C. Decreasing the ladle capacity to 650 kg for pouring the same amount of metal increased the temperature drop by 11 °C due to increase in surface area to melt volume ratio. Also increasing the refractory thickness for 650 kg ladle increased the temperature drop by 4 °C due to the heat accumulation in the ladle during the cyclic transient heat transfer process.

Low grade waste heat recovery presents an opportunity to utilize typically wasted energy to reduce overall energy consumption and improve system efficiencies. In this work, the technoeconomic performance of a turbocompression cooling system (TCCS) driven by low grade waste heat in the engine coolant of a large marine diesel generator set is investigated. Five different working fluids were examined to better understand the effects of fluid characteristics on system performance: R134a, R245fa, R1234ze(E), R152a, and R600a. A coupled thermodynamic, heat exchanger, and economic simulation was developed to calculate the simple payback period of the waste heat recovery system, which was minimized using a search and find optimization routine with heat exchanger effectiveness as the optimization parameter. A sensitivity study was performed to understand which heat exchanger effectiveness had the largest impact on payback period. Of the five working fluids examined, a TCCS with R152a as the working fluid had the lowest payback period of 1.46 years with an initial investment of $181,846. The R152a system was most sensitive to the two-phase region of the power cycle condenser. The R1234ze(E) system provided the largest return on investment over a ten year lifetime of $1,399,666.

The liquid refrigerant defrosting (LRD) is a defrosting method which leads the liquid refrigerant in the high-pressure reservoir to the frosting evaporator. The refrigeration process is continuous during the defrosting period, which increases the defrosting frequency. Compared with the traditional defrosting method, no large fin spacing should be left to reduce the defrosting frequency. The system can recover all the defrosting cooling capacity to improve the subcooling, so that the indoor air temperature fluctuations are avoided. In order to explore the effect and the rule of the LRD, the defrosting experiments were carried out in different frosting mass under the condition of the cold storage temperature of −20 °C. The defrosting time, temperature rise value, cooling capacity, and compressor power consumption value were calculated at the different frosting mass. Interpolation and applying the curve fitting equation helps to obtain remaining values. The relative humidity was calculated by the frosting mathematical model. Finally, the relationship between the coefficient of performance (COP) and the defrosting cycle (the sum of the defrosting time and the frosting time) was obtained. The experiments and theoretical research showed that the fluctuating value of cold storage temperature was about 5 °C and the defrosting time was about 30 min during the defrosting process. In the case of the relative humidity of 70%, 80%, 90%, the optimum defrosting cycle of the experiment was 16.4, 10.9, 7.5 h and the frosting mass was 2.66, 2.90, 3.22 kg, and the maximum COP was 1.51, 1.48, 1.45.

Condenser performance benefits afforded by dropwise condensation have long been unattainable in steam cycle power plant condensers due to the unavailability of durable and long-lasting hydrophobic surface treatments. However, recent work in superhydrophobic coating technology shows promise that durable coatings, appropriate for use on condenser tubes in steam cycle power generation systems, may soon become a reality. This work presents a nanoscale, vapor phase deposited superhydrophobic coating with improved durability comprised of several layers of rough alumina nanoparticles and catalyzed silica with a finishing layer of perfluorinated silane. This coating was applied to solid, hemicylindrical test surfaces fabricated from several common condenser tube materials used in power generation system condensers: Titanium, Admiralty brass, Cupronickel, and Sea Cure stainless steel as well as 304 stainless steel stock. The development evolution of the coating and its effect on condensation behavior on the above materials are presented. Results show that the performance enhancement, measured in rate of heat transfer spikes corresponding to condensate roll-off events, was best for the titanium surface, which produced 64% more events than the next most active material when coated using the most durable surface treatment tested in this work.

Phase change materials (PCMs) are widely applied in recent decades due to their good thermal performance in energy systems. Their applications are mainly limited by the phase change temperature and latent heat. Many publications are reported around the characteristic improvement of binary organic PCMs. The thermal stability study on organic binary PCMs used in thermal energy storage applications becomes fundamental and meaningful. In this study, thermal stability of three types of organic binary PCMs was experimentally investigated, which are frequently used in building and industry applications. To qualitatively investigate the stability of composite PCMs, differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FT-IR) spectra testing of samples were also conducted. Experimental results showed that the selected composite PCMs, capric acid (CA), and myristic acid (MA), had the best thermal performances, with its phase change temperature unchanged and heat of fusion decreased only 8.88 J/g, or 4.55%, after 2000 thermal cycles. Furthermore, quality ratio of required PCMs as the variation of operation duration was analyzed to quantitatively prepare the materials. The PCMs can successfully operate about 3125 times when prepared as 1.20 times of its calculated value by starting fusion heat. Conclusions of this research work can also be used for guiding the selection and preparation of other energy storage materials.

Exhaust gas heat recovery is one of the interesting thermal management strategies that aim to improve the cold start of the engine and thus reduce its fuel consumption. In this work, an overview of the heat exchanger used as well as the experimental setup and the different tests will be presented first. Then numerical simulations were run to assess and valorize the exhaust gas heat recovery strategy. The application was divided into three parts: an indirect heating of the oil with the coolant as a medium fluid, a direct heating of the oil, and direct heating of the oil and the coolant. Different ideas were tested over five different driving cycles: New European driving cycle (NEDC), worldwide harmonized light duty driving test cycle (WLTC), common Artemis driving cycle (CADC) (urban and highway), and one in-house developed cycle. The simulations were performed over two ambient temperatures. Different configurations were proposed to control the engine's lubricant maximum temperature. Results concerning the temperature profiles as well as the assessment of fuel consumption were stated for each case.

In this study, turbulent natural convection heat transfer during the charge cycle of an isochoric vertically oriented thermal energy storage (TES) tube is studied computationally and analytically. The storage fluids considered in this study (supercritical CO 2 and liquid toluene) cover a wide range of Rayleigh numbers. The volume of the storage tube is constant and the thermal storage happens in an isochoric process. A computational model was utilized to study turbulent natural convection during the charge cycle. The computational results were further utilized to develop a conceptual and dimensionless model that views the thermal storage process as a hot boundary layer that rises along the tube wall and falls in the center to replace the cold fluid in the core. The dimensionless model predicts that the dimensionless mean temperature of the storage fluid and average Nusselt number of natural convection are functions of L/D ratio, Rayleigh number, and Fourier number that are combined to form a buoyancy-Fourier number.

In order to really assess the thermal performance of a wall incorporating phase change material (PCM), a reduced scale cavity has been monitored during two heating cycles. For each cycle, the heat source inside the test cell is switched “on” for 5 h and its setpoint is 38 °C and then switched off for 4 h. The outdoor air temperature is kept constant at a low temperature of 20 °C. Two walls are equipped with a PCM layer at different depths in order to study the optimal PCM location. The two other walls are wooden and glass to model a real building. The comparison between the four walls is made based on the absorbed heat fluxes and outside surface temperatures. The results show that the location of the PCM close to the heat source reaches its melting temperature and then reduces the surface temperature. At this location, the PCM layer stores the major part of the inlet heat flux. It takes 10 h to release the absorbed heat flux. However, the PCM layer, practically, does not have an effect on the surface temperatures and absorbed heat fluxes, when it is placed far from the heat source.

The present work describes a silica gel + water adsorption-based desalination and chiller system, an emerging low cost process of integrating thermal desalination and cooling by utilizing low-grade heat. The cycle employs a combination of flash evaporation and thermal compression of steam in single/two stage to generate the dual effect. The current study aims at simulating a four-bed/stage adsorption system using energy and mass balance along with kinetics of adsorption. The performance of single- and two-stage adsorption systems is compared for ambient temperatures in the range of 25–45 °C and a constant heat source temperature of 85 °C.

This paper explores the effectiveness of phase-change material (PCM) for cooling of a discrete array of heat sources in low form factor channels in the presence of mean flow. The alkane n-Eicosane was chosen as the material for this work. A parametric experimental study was conducted on an array of heaters that simulate the heat dissipating components in a low form factor portable electronic device. The effects of the clearance at the top of the devices, thickness/volume of the PCM, as well as the mean flow velocity were studied under uniform and nonuniform patterns. It was found that the cooling effect of the PCM in the time frame considered reduces with increase in the mean flow Reynolds number due to its delayed melting. Thus, the cooling effect in a natural convection environment is higher compared to one with mean flow. The thickness of the PCM increases its effectiveness for a certain threshold value beyond which we reach a region of diminishing returns. The results are presented as design curves in terms of nondimensional parameters. The use of thin spreader inside the PCM pack improves its cooling effectiveness due to better lateral spreading. However, the cooling time for the n-Eicosane is not negligible and can be a potential challenge under repeated cyclic loads.

Increasing the efficiency of steam power plants is important to reduce their CO2 emissions and can be achieved by increasing steam temperatures beyond 700 °C. Within the present study, the thermal behavior of a steam by-pass valve subject to cyclic operation with 700 °C steam is investigated experimentally and numerically. An innovative numerical approach was applied to predict the valve’s thermal behavior during cyclic operation, which is essential for fatigue life assessment of such a component. Validation of the applied numerical approach has shown good agreement with measurement results, indicating the potential of its application for the valve design process.

The demand for the development of hybrid electric locomotives is increasing due to increased demand and cost of diesel oil, uncertainty in the steady supply of oil, and increased emissions standards. Electrical energy is lost from diesel-electric locomotives in the form of heat during dynamic braking. Using a regenerative braking system can improve the overall efficiency as it can be used later to provide traction force during acceleration. The objective of this study is to evaluate experimentally battery performance considering different discharge and charge rate, and investigate the thermal management requirements and thermal runaway effect of the batteries under a variety of environmental conditions. This was done in an environmental chamber, which controls temperature and humidity. This chamber is also fitted with an external window designed to allow thermal imaging from outside the unit. The batteries were monitored with thermal sensors and a thermal imaging camera while they were run through different load scenarios. Loads were applied using a computerized battery analyzer, which allows control over discharge rates and load cycles. Results indicate high discharge rates, above 1 C, and low operating temperatures, below 20 °C, greatly diminish capacity.

The demand for more fuel efficient vehicles has been growing steadily and will only continue to increase given the volatility in the commodities market for petroleum resources. The internal combustion (IC) engine utilizes approximately one third of the chemical energy released during combustion. The remaining two-thirds are rejected from the engine via the cooling and exhaust systems. Significant improvements in fuel conversion efficiency are possible through the capture and conversion of these waste energy streams. Promising waste heat recovery (WHR) techniques include turbocharging, turbo compounding, Rankine engine compounding, and thermoelectric (TE) generators. These techniques have shown increases in engine thermal efficiencies that range from 2% to 20%, depending on system design, quality of energy recovery, component efficiency, and implementation. The purpose of this paper is to provide a broad review of the advancements in the waste heat recovery methods; thermoelectric generators (TEG) and Rankine cycles for electricity generation, which have occurred over the past 10 yr as these two techniques have been at the forefront of current research for their untapped potential. The various mechanisms and techniques, including thermodynamic analysis, employed in the design of a waste heat recovery system are discussed.

Attaining a reasonable size and weight for a personnel microclimate cooling system for an individual person who operates away from logistical support remains a problem. This work analyzes whether spray cooling the ambient air before it cools the condenser in a small vapor compression cycle is worthwhile in terms of battery weight savings. The analysis specifies essential characteristics of each of the main components of an ideal vapor compression cycle in order to determine equations describing their expected performance. Then, a mathematical technique is used to find balance points for the model system at different ambient air temperatures. The balance points show the decrease in condensing temperature and compressor work that result from a decrease in ambient air temperature. The saved compressor work is converted to battery weight savings and compared to the weight of water required to reduce the air temperature. It is found that the potential battery weight savings do not offset the amount of cooling water required, i.e., spray cooling the air-cooled condenser should not be pursued to decrease system weight.

Cold end in helium liquefiers, where finally the gas is converted to liquid, may have different alternatives in configuration to achieve maximum exergy efficiency. Apart from high exergy efficiency, which also means low specific power consumption, reliability of operation and complexity of equipment design are also some of the concerns for designers. In this work, various cold end configurations are compared at different operating conditions to help arrive at appropriate choices during design and operation. When single Joule–Thomson valve is replaced by more efficient cold ends with expanders, it allows reduction of the number of Brayton stages in precooling section as well as the total heat exchanger size. Cold end with expander and Joule–Thomson valve combination has been found to be a good compromise between reliability, liquid production, specific power consumption, and exergy efficiency. However, for such a configuration, it is important to fix the intermediate pressure at appropriate level so as to avoid liquid formation at the exit of the expander.

A novel approach to propellant pressurization for microscale rocket engines is introduced. The Giffard injector is shown to be a viable alternative to turbomachinery for pressurizing the liquid propellants on board a microrocket, offering a design free of moving parts. Extending the authors’ previous work, the engine performance is computed for several fuel/oxidizer combinations. A large-scope study of the heat transfer throughout the regenerative cooling engine cycle examines the effects of combustion chamber pressure and engine size on performance. A boiler is designed that facilitates the heat transfer required for adequate cooling and is modeled using the effectiveness-number of transfer units method. The computed specific impulse and thrust-to-weight ratio of the design for the propellants considered are roughly 250 s and 2000, respectively. The power density of the proposed injector-pumped design is seen to behave like that of turbopumped microrockets up to a critical nozzle throat diameter of approximately 1 cm, beyond which the advantages of an entirely static structure are outweighed by decreasing performance.