Water resource management impacts almost all aspects of the economy, in particular health, food production and security, domestic water supply and sanitation, energy, industry and environmental ...sustainability. For the last several decades, seawater has become an important source of fresh water as it is one of the most abundant resources on earth. Desalination is the process of removal of salts from seawater and is postulated to be a core technology in alleviating this problem. Clathrate hydrate based desalination (HyDesal) is a potential technology for seawater desalination. Salts are excluded from hydrate formation, thereby resulting in solid hydrate and concentrated brine. After separation from brine, the solid hydrate crystals upon dissociation produce pure water. In this work, a detailed review of the literature (both patents and publications) so far on HyDesal is critically evaluated, and prospects and directions to commercialize the HyDesal process are presented. Further, innovation by coupling LNG cold energy with HyDesal can make it economically attractive and can strengthen the energy–water nexus.
Due to the development of the electronic components, concentrator photovoltaic, fuel cell, etc., the cooling requirement of the devices increases rapidly. Due to the higher heat transfer and compact ...design of the microchannel technology, it has been widely considered and investigated to solve the increasing heat flux. Boiling heat transfer is an effective way to dissipate a mass of heat using the latent heat of phase change. Hence, comparing with the single phase liquid flow, flow boiling in microchannel utilizes both advantages of micro scale effect and phase change effect, and can realize a much higher heat flux. Therefore, it becomes a critical way for super high heat dissipation. However, the procedure of the phase change and two phase flow may lead to instability, which can seriously inhibit the heat transfer performance of coolant in microchannel. To tackle with the flow boiling instability, a number of methods were proposed and reported. Therefore, in this paper, to effectively improve the flow boiling in microchannel heat exchanger, the cutting-edge control technologies in this field were reviewed, categorized and summarized, and the future trend of the research was presented.
The utilization of unconventional natural gas is still a great challenge for China due to its distribution locations and small reserves. Thus, liquefying the unconventional natural gas by using ...small-scale LNG plant in skid-mount packages is a good choice with great economic benefits. A novel conceptual design of parallel nitrogen expansion liquefaction process for small-scale plant in skid-mount packages has been proposed. It first designs a process configuration. Then, thermodynamic analysis of the process is conducted. Next, an optimization model with genetic algorithm method is developed to optimize the process. Finally, the flexibilities of the process are tested by two different feed gases. In conclusion, the proposed parallel nitrogen expansion liquefaction process can be used in small-scale LNG plant in skid-mount packages with high exergy efficiency and great economic benefits.
•A novel design of parallel nitrogen expansion liquefaction process is proposed.•Genetic algorithm is applied to optimize the novel process.•The unit energy consumption of optimized process is 0.5163 kWh/Nm3.•The exergy efficiency of the optimized case is 0.3683.•The novel process has a good flexibility for different feed gas conditions.
The high heat flux on the CPV (concentrator photovoltaic) cells may lead to heat dissipation difficulty and high temperature, which will result in the decrease in electricity efficiency or even ...damage of CPV cells. To tackle with this problem, microchannel cooling has attracted increasing attentions recently due to its much higher heat transfer performance. However, the significantly varying solar radiation intensity will cause the sudden variation of heat load on the CPV cells, which may further influence the flow boiling inside the microchannels. Therefore, in this study, the flow characteristics including the pressure drop and flow pattern of deionized water boiling in a single straight microchannel (
D
H
= 400 μm) under sudden heat flux increase were experimentally investigated. The serious pressure drop variation and flow boiling instability properties after the sudden heat flux increase were observed. The study on the influential factors indicates that increasing the mass flux from 411.66 to 720.41 kg m
−2
s
−1
and lowering the inlet temperature from 55 to 45 °C helped weaken fluctuation intensity of pressure drop due to the lower vapor quality. Meanwhile, the detailed flow pattern encountering different levels of heat flux increase were observed using high speed camera, which indicates that much higher heat flux increase leaded to a more rapid bubble generating and phase change phenomenon.
The microchannel heat exchanger is one of the most compact and effective heat exchangers used for cooling devices in building air conditioning system, while application of nanofluids in microchannel ...further enhance its thermal performance due to its much higher thermal conductivity. Considering the continuous rapid increase in energy consumption in the building sector, especially in air conditioning systems, the heat transfer performance of a microchannel with nanofluids should be further enhanced to realize energy savings. This study analyzes the influence of combining nanofluid and flow disturbance structure on the heat transfer enhancement of a microchannel, which is also the noted novelty. A rectangular grooved microchannel (RGMC) is proposed, and its thermal performance using Al2O3/water nanofluids is investigated using the CFD method, with the mixture model to simulate the Al2O3/water nanofluids considering the slip velocity between the base fluid and nanoparticles. The results show that at 1.5 m/s, Nu of RGMC with 2 vol% nanofluids is 38.5% larger than that of smooth microchannel (SMC) with the same nanofluids, and 36.7% larger than that of RGMC with pure water, indicating the much better heat transfer performance of the novel designed RGMC structure. The maximum temperature for RGMC is 5 K lower than SMC with 2 vol% Al2O3/water nanofluid at inlet velocity of 1.5 m/s. Further analysis on the integrated effect between fluid flow and heat transfer shows that the synergy angle β near the center line of RGMC is much lower than that of SMC, representing that the better thermal performance is caused by the flow structured induced by the grooves. Moreover, at 1.5 m/s, βα of SMC with 2 vol% nanofluid is 89.4 Deg, which is 1.66 Deg higher than the βα value of RGMC, while at 0.25 m/s, the βα of two types of microchannel are close to each other. This indicates that the groove structure shows greater enhancement at higher inlet velocity. It is concluded that combining nanofluid and groove structure can significantly enhance heat transfer of the microchannel. The nanofluid enhances heat transfer at lower inlet velocity, while the groove structure enhances it at higher inlet velocity. This study will be helpful for the design of a high-efficiency microchannel heat exchanger that promotes building energy savings.
•Spray falling film of oily wastewater over a horizontal tube was investigated.•VOF model was used to simulate the gas-liquid falling film flow.•The unsteady film and tube temperature distributions ...were analyzed.•The unsteady heat transfer properties were investigated.•The effects of oil content, spray density and tube diameter were studied.
The oil exploit in late-period oilfield usually produce large amount of oily wastewater at moderate and high temperature, the thermal energy of which can be recuperated through a sewage source heat pump (SSHP). Among different kinds of heat recovery facility in SSHP, the spray heat exchanger is a better choice to recover energy from the oily wastewater due to its advantages of simple structure, high heat transfer efficiency and anti-blocking ability. However, the spray falling heat transfer was an unsteady procedure, and the complex properties of oil-water mixer will lead to different heat transfer and flow characteristics in the heat exchanger, which also affect the unsteady heat transfer. Hence, in this paper, a numerical model with VOF method was established to study the unsteady heat transfer properties of oily wastewater spray falling film on a horizontal tube, and the effects of different oil contents, spray densities and tube diameters on the unsteady properties of heat transfer coefficient. The results show that the film temperature and tube temperature were continuously varying with time, and the slight variation in upper part and greater variation in lower part of the tube were observed. A further understanding on the flow field of liquid on the tube revealed the unsteady heat transfer was due to the falling flow instability. Thereafter, the influences of oil content, tube diameter and spray density on the unsteady heat transfer were analyzed. It was found that the decrease in oil content, increase in tube diameter will reduce the fluctuation intensity of heat transfer properties.
•Spray falling film of oily wastewater over a horizontal tube was investigated.•VOF model was used to track the gas-liquid interface of falling film flow.•The effect of different glycerin content on ...heat transfer was investigated.•The effects of spray parameters and tube parameters were studied.•The temperature distribution inside the liquid film was analyzed.
Sewage heat exchanger is the key equipment of oily sewage source heat pump system, which has great influence on its performance. Among many kinds of heat exchangers, the spray heat exchanger has the advantages of simple structure, high heat transfer efficiency, good operability and anti-blocking ability. Therefore, it can be used in a sewage source heat pump to recover energy from the oily wastewater. However, the heat transfer and flow characteristics of oily wastewater spraying in the heat exchanger are different from the ordinary sewage heat pump system. Hence, it’s necessary to investigate the heat transfer of oily wastewater spray falling film on horizontal tube for better application. In this paper, a three-dimensional numerical model was established for a spraying heat exchanger in the oily sewage source heat pump system, and a mixture of water and glycerin was used to simulate the oily wastewater. The VOF model was used to track the liquid-gas interface of oily wastewater spray falling film over a horizontal tube in the heat exchanger, and the effects of different glycerin content, heat flux, spray density, tube diameter, liquid distributor height and spray temperature on the heat transfer coefficient were investigated. To further understand the mechanism of heat transfer inside the film, the temperature distribution inside the liquid film was obtained and analyzed. The results show that: (1) the heat transfer characteristic can be divided into three regions around the tube; (2) the local heat transfer coefficient decreased with increase of glycerin content in the thermal developing region; (3) the local heat transfer coefficient increased with the increase of the spray density and spray temperature, decreased with the increase of the tube diameter and was little affected by heat flux in the thermal developing region, and the increase in the liquid distributor height caused increase of local heat transfer coefficient in the upper part of the tube.
With the application of microdevices in the building engineering, aerospace industry, electronic devices, nuclear energy, and so on, the dissipation of high heat flux has become an urgent problem to ...be solved. Microchannel heat sinks have become an effective means of thermal management for microdevices and enhancements for equipment due to their higher heat transfer and small scale. However, because of the increasing requirements of microdevices for thermal load and temperature control and energy savings, high efficiency heat exchangers, especially microchannels are receiving more and more attention. To further improve the performance of microchannels, optimizing the channel geometry has become a very important passive technology to effectively enhance the heat transfer of the microchannel heat sink. Therefore, in this paper, the microchannel geometry characteristics of previous studies are reviewed, classified and summarized. The review is mainly focused on microchannel geometry features and structural design to strengthen the effect of heat transfer and pressure drop. In addition, the correlation between boiling heat transfer and geometric characteristics of microchannel flow is also presented, and the future research direction of microchannel geometry design is discussed.
In the sewage source heat pump (SSHP) system, which is used to recover the low-level thermal energy in oily sewage, the sewage heat exchanger is an important equipment to determine the heat exchange ...efficiency of the system. In this paper, an oily sewage source heat pump (OSHP) system experimental setup with a spray-type sewage heat exchanger as the evaporator was established. The effects of oil content, spray density and spray temperature on the flow patterns between horizontal tubes and heat flux of tube were investigated and analyzed. It was found that the critical spray density for transformation from droplet flow to column flow was increased to 0.109 kg m
−1
s
−1
for oily sewage, which was much higher than 0.082 kg m
−1
s
−1
of pure water for pure water, indicating that a much higher spray density was needed to maintain a higher heat transfer for oily sewage. With the increase in spray temperature of oily sewage, the critical spray density of flow pattern transformation from droplet flow to column flow was decreased from 0.137 kg m
−1
s
−1
at 46 °C to 0.082 kg m
−1
s
−1
at 65 °C. Besides, oily sewage had obvious lower heat flux than pure water, and the difference was enlarged with the increase in spray density. New heat transfer correlations obtained depending on Re and Pr numbers were proposed, showing more accurate predictions than previously reported models. Corresponding to the falling film flow pattern, a clear dividing between 0.055 and 0.082 kg m
−1
s
−1
for pure water and between 0.082 and 0.109 kg m
−1
s
−1
for oily sewage, for the tube surface temperature distribution for droplet flow and column flow was observed, indicating the significantly high heat transfer for column flow pattern compared with droplet flow.
Among all large-scale natural gas (NG) liquefaction processes, the mixed fluid cascade (MFC) process is recognized as a best-alternative option for the LNG production, mainly due its competitive ...performance. However, from a thermodynamic point of view, the MFC process is still far from its potential maximum energy efficiency due to non-optimal execution of design variables. Therefore, the energy efficiency enhancement of the MFC process remains an ongoing issue. The design optimization after fixing the main configuration of the process is one of the most economic, but challenging exercises during the design stages. In this study, shuffled complex evolution (SCE) is studied to find the optimal design of the MFC process corresponding to minimal energy consumption in refrigeration cycles. The MFC process is simulated using Aspen Hysys® v10 and then coupled with the SCE approach, which is coded in MATLAB® 2019a. The refrigerant composition and operating pressures for each cycle of the MFC process were optimized considering the approach temperature inside the LNG heat exchanger as a constraint. The resulting optimal MFC process saved 19.76% overall compression power and reduced the exergy destruction up to 28.76%. The thermodynamic efficiency (figure of merit) of the SCE-optimized process was 25% higher than that of the published base case. Furthermore, the optimization results also imply that there is a trade-off between the thermodynamic performance improvement and the computational cost (no. of iterations). In conclusion, SCE exhibited potential to improve the performance of highly nonlinear and complex processes such as LNG processes.
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