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The spiral tube heat exchange is widely used in large-scale liquefaction process. However, the research on the friction pressure drop of the two-phase flow in the spiral tube is limited, especially for the offshore sloshing condition. In this paper, an experimental system is designed and built, and the effects of sloshing form (roll, pitch, heave), sloshing period (5-15s), mass flux (200-800 kg/(m2·s)), vapor quality (0.3-0.9) and operating pressure (2-4 MPa) on friction pressure drop of methane/ethane (C1/C2) mixture in spiral tube are studied. The result shows that the growth rate of time-averaged friction pressure drop during condensation under sloshing condition is less than 0, which indicates that sloshing will lead to drag reduction. And under the three sloshing parameters, the growth rate of time-averaged friction pressure drop of C1/C2 is reduced by-5.99%%, 5.97% and -6.70% respectively.

The core of building energy allocation is to reduce the power load and power consumption through the reasonable allocation of energy equipment, so as to reduce the capacity of the supply side and save investment. In this way, the configuration of energy schemes in data center is conducted in this paper. According to the results of load forecasting, the energy supply scheme of each building in the planning area is determined, including ground source heat pump (GSHP) system, solar water heating system and heat pipe air conditioning system. In addition, feasibility analysis and economic analysis of each configuration scheme are carried out, and the relatively reasonable scheme is selected. It is found that GSHP system can be used in canteen building, solar hot water system can be used as auxiliary for apartment buildings and joint operation of heat pipe air conditioning unit and traditional machine room air conditioning unit is the most economical for data room. Through the research of this paper, a feasible method for the reasonable allocation of energy is provided in the data center planning stage.

The maldistribution of working medium restricts the heat transfer performance of the spiral-wound heat exchangers (SWHEs), especially when the heat exchangers are applied in floating production storage and offloading platform. Therefore, the maldistribution in the SWHEs needs to be studied under sloshing conditions. In the investigation, a novel distributor named “disc distributor” is designed and its distribution characteristic is analysed under sloshing conditions experimentally. The impacts of sloshing amplitude, sloshing periods, mass flow rate and structural parameters on flow uniformity are discussed. The results show that based on steady condition the augmentation of the sloshing amplitude makes the liquid uniformity deteriorate by 14.2–56.0%, and the enlargement of the sloshing period improves the liquid flow uniformity by 12.8–28.3%. The elevation of the mass flow rate promotes the flow uniformity by 23.8–27.0% and 13.9–32.4% under steady and sloshing conditions, respectively. The variation of hole diameter exacerbates distribution performance of the distributor by 5.3–18.4% and 2.5–22.3% under steady and sloshing conditions separately. Heave condition always has less influence on the flow uniformity of the distributor than other sloshing conditions.

Spiral-wound heat exchanger (SWHE) is important equipment for industry, and it is suitable for floating production storage off-loading (FPSO). However, two-phase mixture maldistribution always restricts the heat transfer capacity of SWHE in FPSO. Few studies have focused on the maldistribution of SWHE. According to this, an experimental device was fabricated to evaluate the maldistribution of a novel distributor on the sloshing platform. The effects of vapor qualities and mass flow rates were analyzed at the range of 0.106–0.702 and 608.5–1491.6 kg h−1, respectively. The following conclusions are drawn: With the augmentation of vapor quality, the gas–liquid uniformity deteriorates after optimizing under steady and sloshing conditions. Heave condition improves gas and liquid flow uniformity by 2.9–11.0% and 1.7–3.7% separately, and pitch condition improves the gas flow uniformity by 0.5–3.7%, and roll condition lowers the liquid flow uniformity by 2.0–7.2% in the variation of vapor quality. It is also proved that the flow uniformity achieves better performance with the increasing mass flow rate under steady, heave and pitch conditions. Heave condition improves the distribution characteristic by 4.4–8.7% for the gas phase and 2.0–9.5% for the liquid phase, and pitch condition elevates the gas flow uniformity by 3.1–7.7%. Under the roll condition, the distribution performance of the experimental model changes worse after better and obtains the best performance at the mass flow rate of 1183.8 kg/h. At large mass flow rates, gas entering into liquid space under roll condition can bring the structural problem. Increasing the tube diameter and making the upper baffle tilt from shell to center barrel are beneficial to keep the distributor structure safe.

The existing gearbox fault diagnosis models often need a lot of fault data and corresponding tags to complete the model training, but the actual fault data is often less and unevenly distributed. Aiming at the situation that the gearbox fault data is scarce and unevenly distributed, this paper proposes a fault diagnosis method based on the Deep Convolution Generative Adversarial Network (DCGAN). First, the original vibration signals collected in the early stage are processed through data processing to form a sample data set and input into the DCGAN model for confrontation training, and virtual samples with real sample characteristics are generated to expand the sample data set. Then, the convolution neural network model is constructed to complete the fault diagnosis and get the results. The results show that the model trained by this method is more accurate when generating a large amount of data, and the diagnostic effect is significantly better.

The non-uniformity of gas–liquid mixture is a critical issue which leads to the heat transfer deterioration of spiral-wound heat exchangers (SWHEs). Two-phase mass flow rate and the content of gas are important parameters as well as structural parameters which have prominent influences on flow distribution uniformity of SWHE shell side. In order to investigate the influences of these parameters, an experimental test system was built using water and air as mediums and a novel distributor named “tubes distributor” was designed. The effects of mass flow rate and the content of gas on two-phase distribution performance were analyzed, where the mass flow rate ranged from 28.4 to 171.9 kg·h−1 and the content of gas changed from 0.2 to 0.8, respectively. The results showed that the mixture mass flow rate considerably influenced the liquid distribution than that of gas phase and the larger mass flow rate exhibited the better distribution uniformity of two-phase flow. It was also found that the tubes distributor had the better two-phase uniformity when the content of gas was around 0.4. Tube diameter played an important role in the distribution of gas phase and slit width was more significant for the uniformity of liquid phase.

This work investigated comprehensively the impacts of non-ideal optical factors, including incident angle, sunshape and optical errors on the performance of the parabolic trough collector (PTC). Each optical factor was defined based on their geometrical principles. It was revealed that the heat flux distribution distorted by optical factors was the main cause of changing performance of the PTC. The temperature distribution was completely dependent on the heat flux distribution. The incident angle caused cosine loss and end loss, which respectively reduced the effective incident solar radiation and produced a near-zero heat flux section at one end of the absorber. Based on the effective incident solar radiation, the collector efficiency was reduced by 41.11% with the incident angle increasing from 0° to 60°. Larger circumsolar ratios produced more uniform circumferential temperature distribution, while reduced greatly the collector efficiency. The specularity error and tracking error affected slightly the receiver's safety, while the slope error reduced obviously the threat to the receiver. When specularity error was small enough (

A model based on ASNYS CFX was established to explore the pressure drop and heat transfer characteristics of condensation flow with hydrocarbon mixtures in a spiral pipe under static and heaving conditions, whose deviations are within ±15% compared to experimental ones. It considered the effects of motion parameters, operating parameters and structural parameters on frictional pressure drop and heat transfer coefficient for three hydrocarbon mixtures. The ranges of mass flux, vapor quality, heat flux, saturation pressure, hydraulic diameter, curvature diameter and inclination angle were 200–800 kg/(m2·s), 0.3–0.9, 10–20 kW/m2, 2–4 MPa, 6–14 mm, 1.6–2.4 m and 6–14°, respectively. The results demonstrate that methane/ethane mixture has the best heat transfer and the smallest pressure drop among three mixtures. At static condition, as the vapor quality and mass flux increase and the saturation pressure and hydraulic diameter decrease, there are evident increases in heat transfer and pressure drop, whereas the impacts of curvature diameter, inclination angle and heat flux on them are insignificant. Meanwhile, the heaving motion affects pressure drop and heat transfer and makes it show better overall heat transfer performances, where the comprehensive heat transfer factors (CHFs) of 83.33% data points are more than 1. Further, the heaving effects increase with the increasing heaving amplitude and the decreasing heaving cycle.

Enhancing the heat transfer in the absorber tube improves effectively both the thermal efficiency and the structural safety of the parabolic trough receiver (PTR). This study proposed a novel unilateral spiral ribbed PTR (USR-PTR) for enhancing the heat transfer inside the absorber. The flow and heat transfer performance of the proposed USR-PTR was studied numerically using CFD tool coupled with Monte Carlo Ray Tracing (MCRT). A detailed comparison between the USR-PTR and the conventional straight and smooth PTR (CSS-PTR) was conducted in terms of both thermal and hydraulic performance, revealing that fluid disturbance, rotational flow and local longitudinal vortexes induced by the discontinuous spiral ribs are the three main causes of heat transfer enhancement in the USR-PTR. In most cases of the discussed flow rates, the overall performance of the USR-PTR is better than that of the CSS-PTR. The circumferential temperature difference of the USR-PTR can be reduced by up to 25% compared to the CSS-PTR. The structural parameters of the spiral rib influence greatly the performance of the USR-PTR. It is revealed that the improvement of the overall performance of the USR-PTR by changing individually the rib structural parameters, including pitch interval, rib height, corner radius and spiral angle, can be up to 12.5%, 9.8%, 10.8% and 30.1% respectively.

Spiral-wound heat exchangers (SWHEs) are the important equipment for the industry development, however, the non-uniformity of flow medium in the shell side seriously decreases their heat transfer performance. The maldistribution is more critical when SWHEs are used in the floating production storage & offloading system (FPSO) and this restricts the application of SWHEs in the FPSO system. To make SWHEs more suitable for the FPSO, it is necessary to study their distribution performance of gas-liquid mixture under sloshing conditions. A novel distributor named “tubes distributor” was designed and a gas-liquid two-phase experimental bench was built to process the investigation via air and water as the mediums. The influence of sloshing amplitude, sloshing period and sloshing form was investigated. The results show that the increase of heave amplitude makes the two-phase distribution performance better which is in contrast with that in roll condition. At the same time, the increasing pitch angle results in the better gas uniformity and worse liquid uniformity. Different from sloshing amplitude, the longer sloshing periods lead to the worse two-phase distribution uniformity. It is also got that roll condition can provide the worse two-phase distribution performance under complex practical offshore sloshing condition than the experimental condition.

In this paper, the coupled lattice Boltzmann BGK method (CLBGK) is applied to simulate the 2D enclosure Rayleigh–Benardconvection (RBC) filled with air at Rayleigh number Ra =7.5 × 104 ∼ 10 9. Based on these results, the pair of character frequencies with their corresponding oscillatory structures is achieved. The present study indicates that the time–dimensionless frequency (f*) of a specific oscillatory structure has a regular change with the increase of Ra. Three f* ∼ Ra trends are clearly confirmed respectively in laminar states, transitional states, and turbulent states, which can be summarized as f* ∼ Ra −1/6 in laminar and transitional states, and f* ∼ Ra 2∕7 in turbulent states, where the former one corresponds to the natural property of RBC and the latter one well matches the scale law of Nu ∼ Ra 2∕7 . With the guidance of these conclusions, a set of auxiliary RBC experiments are performed and obtain the similar f* ∼ Ra trends, which proves the reliability of LBM in the spectral research of RBC.

In recent decades, multi-split air source heat pump (M-ASHP) unit has been widely used for space heating. Similar to the split-ASHP unit, frost would accumulate on its outdoor coil surface under frosting condition, which significantly deteriorates its heating performance. In the previous study, a novel reverse-cycle defrosting method based on phase change energy storage was developed and investigated, and the study demonstrated that the novel defrosting method could significantly improve defrosting performance. To provide guidelines for designing the M-ASHP units with phase change energy storage, it is necessary to investigate the characteristics of heating and energy storage for M-ASHP units, which is presented in this paper. Experimental results showed that there was no frost on outdoor coil when only the indoor unit with heating capacity of 7.1 kW was turned on under frosting condition. In addition, the energy storage period increased as the number of operating indoor unit increased, namely the load rate. Furthermore, the optimal starting time of the energy storage operation was around 10 min after the start-up of M-ASHP unit. Even though, compared with the conventional heating mode with three turned-on indoor units, the energy storage mode shortened the heating period by 8 min and decreased the average heating capacity and COP by 4.4% and 1.9%, respectively. The above negative impacts of energy storage operation on the heating performance of the M-ASHP unit could be neglected by considering its positive impacts on defrosting performance, for a periodic heating-defrosting condition.

In order to explore tube-side heat transfer characteristics in the spiral wound heat exchange (SWHE) used in liquid natural gas (LNG) plants, the study on zeotropic hydrocarbon mixtures condensation heat transfer in a helical pipe is proposed. Firstly, based on two-fluid model and thermal phase change model, a numerical method coupling with empirical correlations is established to predict condensation heat transfer for zeotropic mixtures, in which the mixed effects are taken into account. Meanwhile, the rationality of the above methods is verified based on existing experimental results. Then, the effects of refrigerant components and operating parameters on flow patterns, heat transfer coefficients and heat and mass transfer resistance are discussed as the ranges of mass flux, saturation pressure and vapor quality are 200–800 kg/(m2·s), 2–4MPa and 0.15–0.90, respectively. It can be found that the predicted results coincide with the experimental ones, with deviations within ±15%. For different zeotropic hydrocarbon mixtures, as the vapor quality increases, the stratified flow, half-annular flow and annular flow appears in turn. The condensation heat transfer coefficients are always smaller than film heat transfer coefficients owing to the existence of heat and mass transfer resistance in vapor core. Besides, both film and condensation heat transfer coefficients increase with the increase of vapor quality and mass flux, while decrease with the rise in saturation pressure. Further, heat and mass transfer resistances increase as the vapor quality and saturation pressure increase and the mass flux decreases. In addition, compared to methane/ethane/propane/nitrogen (65/25/5/5, mole%) mixture, the averaged heat transfer performance for methane/ethane (90/10, mole%) mixture improves by 19.55%, whereas, the average heat and mass transfer resistance decreases by 53.51%. This study is helpful for understanding the zeotropic mixtures condensation in tubes and gives some suggestions for the choice of refrigerant components used in LNG SWHE, to design more effective SWHE.

There were very limited modeling studies are around a phase change material based double-spiral coiled heat exchanger, due to the difficulties of model development and the lack of mature simulation tools. When a phase change material based double-spiral coiled heat exchanger applied in an air source heat pump for defrosting, its model development becomes more complicated. To solve this fundamental problem, a mathematical model for such heat exchanger was developed, as well as the numerical solution method proposed. To improve the convergence and the speed of numerical simulation of the phase change material’s heat transfer process, both of special treatments in space and time were conducted. According to the circular shape boundary, an implicit solution method was used to reduce the number of grids so that computation became convenient. Heat storage and release processes of this model were finally experimentally validated in a specially built heat pump system during frosting and defrosting, respectively. The deviation conditions are demonstrated acceptable with the mean average temperature differences at the small range of −0.71–1.64 °C. Potential uses and limitations of the modeling work are also further discussed. Contribution of this work are meaningful for the optimization of heat pump and any other systems, where applied a phase change material based heat exchanger.

In Rayleigh-Benard convection (RBC), it has been confirmed that the enlargement of the corner vortexes directly causes the reversals of mean wind in transient states. But when and how the size of corner vortexes start to increase are still unclear. In this paper, both experiments and simulations (Lattice Boltzmann Method) are applied to the research on corner-vortex enlargement in 2D square RBC cells filled with air (Pr = 0.7, Ra = 104–108). The results show that the dominant frequencies of RBC are divided into three levels with the increasing Ra. The wind reversals caused by corner-vortex enlargement are confirmed in transient states where the three frequency levels coexist. And obvious frequency-jump from the lower level to the higher level is detected before the corner vortexes grow up, which is absent in the cases without reversals. Further analysis based on the temperature contours ascribes these three frequency levels to different temperature-structure motions. And it is observed that the periodic change of corner-vortex volume dynamically keeps balance with the pulsating flow featuring these frequencies from the opposite conductive walls. In transient states, when the pulsating flow jumps into a new frequency, the previous heat balance inside the corner vortexes is broken, which immediately triggers the size enlargement of the corner vortexes.

In order to explore condensation flow and heat transfer characteristics in the tube side of spiral wound heat exchange (SWHE) used in floating liquefied natural gas (FLNG) field, a model was established to simulate methane condensation upward flow in a spiral pipe at different sloshing conditions, such as heave, roll and pitch conditions. The simulated results coincide with experiment ones, and the deviations are within ±15%. The effects of various parameters on frictional pressure drop and heat transfer coefficient were discussed in pipes with curvature ratio of 0.003–0.007. The ranges of Reynolds numbers in vapor and liquid flows are respectively 154,944–697,251 and 18,190–127,331. It was found that at static conditions, both frictional pressure drop and heat transfer coefficient increase with the increase of mass flux and the decrease of saturation pressure and hydraulic diameter; with the increase of vapor quality, the heat transfer coefficient first increases and then decreases whereas the frictional pressure drop continuously increases; the effects of curvature diameter are slight. Meanwhile, in most cases, the sloshing motions can cause a remarkable heat transfer enhancement as well as a small decrease of frictional pressure drop. Further, the effects of heaving motion on flow and heat transfer are more obvious than the others, with the average drag reduction and heat transfer augmentation of 1.51% and 15.70%, respectively. These results are helpful for the understanding condensation characteristics in the spiral pipe at sloshing conditions, and for the design of SWHE used in FLNG field.

Recently, the authors have published a paper which provided the frost distribution and growth along the airflow direction of finned tube heat exchangers (FTHXs), and demonstrated that some frost was accumulated on the edge of windward fins at a given frosting condition. As a follow-up to the work reported in the previous paper, in the current paper, the effects of frosting conditions on frost distribution and growth characteristics of FTHXs with different fin pitches were experimentally investigated. The results showed that the protruded thickness of frost on the edge of windward fins and the ratio of the frost mass on the edge of windward fins to that on the entire FTHX were both increased with the increases in air temperature (Ta) and relative humidity (RHa), but decreased with an increase in initial air face velocity (va). In addition, the effects of RHa on the mass ratio were more significant than those of Ta and va. Furthermore, the averaged frost density on the edge of windward fins was increased with an increase in RHa; and that on the surfaces of fins and tubes was increased with an increase in va, but decreased with an increase in RHa.

Gas-liquid two-phase maldistribution is an important problem for plate-fin heat exchangers (PFHEs), which has hampered the application of PFHEs in offshore natural gas liquefaction. In order to efficiently use PFHEs in the field of offshore natural gas exploration, it is necessary to study the two-phase distribution performance of PFHEs under sloshing conditions. In this paper, the experimental bench of gas-liquid distribution was built and the distribution characteristics of distributor in PFHEs referred to as liquid-injected seal was investigated under sloshing conditions using air and water as mediums. The effects of vapor quality (0.2–0.4) and mass flow rate (647–1310 kg/h) under sloshing conditions were analyzed. The results showed that by increasing vapor quality, the gas distribution performance in the distributor changed more significantly than the liquid one and the liquid distribution performance at low vapor qualities cases strongly depended on sloshing conditions. It was also proved that the gas-liquid distribution performance of liquid-injected seal enhanced with the increase of mass flow rate, and its sloshing resistance was increased as well.

With the increase in data traffic, high energy consumption of cooling systems in data centers are rising continually and rapidly. Thus planning energy is more and more important to minimize resources consuming. The equipment in data room can produce vast amount of heat which must be removed, and waste heat recovery is an effective means of saving energy. In this paper, a simulation of the annual dynamic air conditioning load of buildings was conducted through Designer's Simulation Toolkit (DeST) to get the cooling and heat load index, and a data center in Harbin was taken as a case study to evaluate the energy-saving effect. The results indicated that the annual cumulative cooling load was far greater than the annual cumulative heat load, so it has great potential for heat recovery. Then a system that made use of waste heat from data rooms to serve subsidiary buildings was proposed. It could fully satisfy the heat demand in data centers when equipment in data rooms all run. Meanwhile, the heat recovery system has a better economic viability when compare with the air source heat pump system. Therefore, using the heat recovery system can improve the energy efficiency and realize the energy saving.

In this paper, the condensation heat transfer of hydrocarbon mixtures refrigerant (methane/propane) flowing in a helical tube with 10 mm hydraulic diameter was investigated by experiments and numerical simulations. The experiments were conducted at mass flux of 200–400 kg/(m2·s), saturation pressure of 0–4Mpa and heat flux of 4.8–5 kW/m2. Also, the effects of mass flux, vapor quality, and saturation pressure on heat transfer coefficient were studied. It was observed that the heat transfer coefficients increased with the increase of mass flux and vapor quality, while the heat transfer coefficients generally decreased as the saturation pressure increased. Meanwhile, annular flow(half-annular flow, annular flow) and Non-annular flow patterns (slug flow, stratified flow, wavy flow, transition flow) were observed during the condensation of methane/propane mixtures refrigerant. And a new flow pattern transition line for hydrocarbon refrigerants condensation process was proposed. The condensation heat transfer coefficient data were compared with several existing correlations, and a modified heat transfer correlation for different flow patterns was proposed, which predicted the results well with a mean absolute error of 10.03%.

A numerical model of condensation heat transfer and frictional pressure drop in a circular tube was developed and validated. In order to facilitate the model validation, the physical model was built according to the experiment condition in the existing literature. In the numerical models proposed in this work, the following models were involved: volume of fluid (VOF) multiphase model, Lee’s phase change model and Reynolds Stress turbulence model. The importance of boundary-layer mesh size was analyzed, and the effects of entrainment, turbulent Prandtl number and gas-liquid interface turbulence damping on the simulation results of heat transfer coefficient (HTC) and frictional pressure drop (FPD) were evaluated and modified. The numerical model was validated with Neeraas’s experimental data and Steiner's correlation results at various mass fluxes, vapor qualities, pressures and fluids. The simulation results of void fraction showed good agreement with Steiner's correlation; the HTC and FPD showed good agreement with Neeraas’s experimental data, which indicated the model developed in this work has good universality and accuracy.

Helical tube has been widely used in liquefied natural gas (LNG) liquefying applications. However, studies on the heat transfer performance of hydrocarbon mixture refrigerant in a helical tube have rarely been conducted. In this paper, condensation heat transfer characteristics of hydrocarbon mixture refrigerant in a helical tube were investigated numerically. The tests were conducted at saturation pressure of 2–4 MPa, mass flux of 100–400 kg/(m2·s) and vapor quality 0–1. The numerical model was well verified by experimental data. And the effects of different structural parameters (tube diameter, helix angle and curvature diameter) and operating parameters (mass flux, heat flux and saturation pressure) on the heat transfer of hydrocarbons refrigeration were considered. The results showed that the tube diameter and mass flux had significant effect on condensation heat transfer coefficient. Meanwhile, stratified flow, half-annular flow and annular flow were observed during the condensation of methane/propane mixtures refrigerant by simulations, and a new flow pattern transition line for hydrocarbon refrigerants condensation process was proposed. Finally, the simulation results were compared with several well-known condensation heat transfer correlations. The research results will provide some constructive instructions for more effective design of LNG heat exchanger.

Fouling deposit is a common issue on the heat transfer surface caused by the impurity of working water. Many researchers conducted experimental test to study the relationship between the fouling thermal resistance and operating parameters, such as water quality, tube geometry, and liquid velocity, targeting at developing the accurate correlation of fouling thermal resistance on heat transfer tubes. The accurate test of fouling thermal resistance is critical for investigators. In fouling test, with the fouling deposit on the internal surface, both the liquid (water) velocity through the tube and the heat flux of the test tube deviated automatically. Although testers usually tried to adjust the water velocity and heat flux back to the original point, it is hard to be realized, thus the water velocity and heat flux deviated somehow inevitably. In fact, the variations of water velocity and heat flux would cause the change of overall thermal resistance of test tubes, which should be separated from the change caused by fouling deposit. This process could be named as “decoupling”. This paper analyzed the effect of deviations of water velocity and heat flux on the test results of fouling resistance quantitatively based on experimental test, and a decoupling method and formulas were developed. One set of accelerated fouling test was conducted and result shows the fouling resistance with decoupling and non-decoupling had a maximum difference of 0.000002124 m2 K/W for tube 1, and 0.000002363 m2 K/W for Tube 2, 0.000001316 m2 K/W for tube 3.

Coil-wound heat exchangers (CWHEs) have been widely used in natural gas liquefaction plants nowadays. But few studies on the condensation heat transfer and frictional pressure drop of mixed hydrocarbon refrigerants inside the tubes of CWHEs have been conducted under practical conditions. In this study, numerical simulations were carried out to investigate the condensation flow and heat transfer characteristics of mixed hydrocarbon refrigerants inside the tubes of liquefied natural gas (LNG) CWHEs under practical operating conditions. A combinational numerical method based on computational fluid dynamics (CFD) simulation and modified Silver method was proposed to predict the condensation heat transfer coefficients of mixtures. The numerical results showed good agreement with experimental data and calculation results by the empirical correlation in the literature. The relative errors of void fraction, heat transfer coefficient and frictional pressure drop were predicted within ±5%, ±15% and ±15% respectively. The simulation results indicated that the heat transfer coefficients of mixed refrigerants varied slightly with the increase of vapor quality, but significantly with the increase of mass flux. And the frictional pressure drop increased with the increase of both vapor quality and mass flux. This study is instructive to the design and optimization of CWHEs used for natural gas liquefaction process.

In this paper, the condensation heat transfer and pressure drop characteristics for hydrocarbon mixture upward flow in smooth and enhanced spiral pipes were numerically investigated. The numerical model was established and verified by experimental results in literatures. It discussed the influence of geometrical parameters on condensation heat transfer and pressure drop in three kinds of enhanced spiral pipes, which contained square corrugated pipe, sinusoidal corrugated pipe and spiral grooved pipe. The results indicate that in enhanced spiral pipes, both frictional pressure drop and heat transfer coefficient increase with the rise in corrugation (groove) height and the decrease of corrugation (groove) pitch. Meanwhile, compared to the smooth pipe, the augmentation on heat transfer for square corrugated, sinusoidal corrugated and spiral grooved pipes are 0.934–2.052, 1.103–2.216 and 1.206–1.804 times, respectively, while the increase of frictional pressure drop are 1.805–10.930, 1.272–7.176 and 0.851–3.587 times, respectively. Besides, the comprehensive heat transfer enhancement factor (CHF) was introduced to evaluate the overall heat transfer performance of enhanced pipes. It is found that as the corrugation (groove) height increases, the CHF increases in square and sinusoidal corrugated pipes but decreases in spiral grooved pipe; at the meantime, with the increase of corrugation (groove) pitch, the CHF first decreases and then increases in square and sinusoidal corrugated pipes while first increases and then decreases in spiral grooved pipe. The average CHFs for all square corrugated pipes, sinusoidal corrugated pipes and spiral grooved pipes are 0.872, 1.083 and 1.275, respectively. Moreover, the spiral grooved pipe with the relative groove height and pitch of 0.03535 and 5.0 shows the best overall heat transfer performance among others, whose average CHF can reach to 1.413. These results provide some instructions for the application of enhanced spiral tube in the design of spiral wound heat exchange (SWHE).

A model was established to explore the shell-side heat transfer characteristic of saturated boiling in spiral wound heat exchanger (SWHE), which was used for liquefied natural gas (LNG). The saturated boiling mechanism was investigated by ANSYS CFX based on the model which was validated by the experimental data, and the correlations for shell-side heat transfer coefficient of SWHE were improved, where mass flux G, heat flux q and vapor quality x were 40–100 kg / ( m 2 · s ) , 2,000–8,000 W / m 2 and 0.3–0.9, respectively. The results show that the deviations between simulation results and experimental data are within ± 13 % . According to the simulation results, the main boiling mechanism for shell-side saturated boiling heat transfer is forced convective, and the contribution of nucleate boiling contribution is slight (less than 0.77 % ). At the same time, the improved correlations are in good accuracy, the deviations between correlation calculation results and simulation results are within ± 25 % .

Spiral wound heat exchanges (SWHE) has been the most widely used in large-scale liquid natural gas (LNG) plants. However, few studies have been focused on the condensation heat transfer and pressure drop for hydrocarbon mixture refrigerant in SWHE tube side. In this paper, the condensation heat transfer and pressure drop characteristics for ethane/propane mixture upward flow in a spiral pipe were numerically investigated. The numerical model was established and verified based on the existing experimental results and new flow pattern observation experiments. It discussed the variation trends of void fraction, frictional pressure drop, heat transfer coefficient and heat and mass transfer resistance with various parameters, such as, vapor quality, mass flux, heat flux, saturation pressure and inclination angle. Comparing with the existing correlations, the results showed that Steiner’s correlation, modified Fuchs’s correlation, Boyko’s correlation could better predict the void fraction, frictional pressure drop, film heat transfer coefficient with mean absolute deviation of 6.08%, 10.67% and 13.06%, respectively. Meanwhile, modified Silver approach was used to modify the mixed effects of ethane/propane mixture on heat transfer. The study provides some constructive instructions to understand the condensation of zeotropic mixtures in the spiral pipe, and is helpful in designing more effective SWHE.

In order to explore the shell-side flow and heat transfer characteristics for spiral wound heat exchanger (SWHE) in floating liquefied natural gas (FLNG), a model was established to simulate the flow and heat transfer of shell-side superheated vapor flow under rolling working conditions. The effects of rolling parameters and working parameters were investigated. By comparing, the deviations between simulation results and experimental data were generally within ± 10 % . Under static working conditions, both frictional pressure drop gradient and heat transfer coefficient increased with the increasing mass flux, which were consistent with the predictions of calculation correlations. After that, an improved heat transfer correlation was proposed with an error of ± 5 % . Meanwhile, rolling motions can affect the shell-side flow and heat transfer characteristics of superheated vapor flow and lead them to show obvious periodicity. The influence of rolling period was smaller than that of rolling amplitude, and 90 % of the working conditions in FLNG SWHE can lead to the enhancement of heat transfer from −0.5 % to 2.6 % . These results can provide some instructions in the design and efficient running for FLNG SWHE.

A new algorithm for obtaining the critical tube diameter and intercept factor of parabolic trough solar collectors (PTCs) under the condition of tube alignment error has been developed theoretically, which, compared with the Monte Carlo Ray Tracing (MCRT) method, reduces the computing time remarkably. The results produced by the proposed method comply very well with the results obtained by MCRT. The critical tube diameters for different alignment errors can be precisely calculated using the algorithm, which can also be used to explain well the variation of optical efficiency. Effects of structural parameters on the optical performance are also discussed comprehensively. It is revealed that the offset direction that is perpendicular to the focus-edge connection line is most likely to cause rays-escaping. There exists an aperture width range (and also focal length range) in which the optical efficiency decreases with increasing offset angle, which is contrary to the conclusion presented in previous literature that the effects of X-direction offset (a = 0°) is greater than that in Y-direction (a = 90°). The proposed algorithm establishes the foundation for further geometric study on the coupling effects of multi-errors on PTCs’ performance, and can also be used for quick calculation and analysis in practice.

The maldistribuiton of gas-liquid mixtures has serious influences on the heat-transfer characteristics of plate-fin heat exchangers (PFHEs) and restricts the development of PFHEs in the floating liquefied natural gas (FLNG) field. To efficiently use PFHEs for FLNG, it is necessary to investigate the gas-liquid distribution at the entrance of PFHEs under sloshing conditions. In this study, an experimental gas-liquid distribution system was built, and the distribution characteristics of a PFHE distributor were investigated under sloshing conditions using air and water as mediums. The influence of sloshing form, sloshing amplitude, and sloshing period on the gas-liquid distribution is discussed with flow ratio m∗k and standard deviation STDk as the distribution index. The results showed that in the experimental condition the non-uniformity of two-phase mixture under sloshing conditions increase by 1.25–18.03% on the basis of steady condition with the increase of sloshing amplitudes and decrease with the increasing sloshing periods. The variation range of two-phase uniformity under mixed sloshing conditions is 14.8–27.9% on the basis of steady condition. These results provide constructive instructions for the design and safe operation of PFHEs in the FLNG field.

Spiral-wound heat exchanger (SWHE) is under sloshing working conditions when it is used on floating liquefied natural gas (FLNG), which can remarkably influence the efficiency of liquefaction and the stability of operation. In this paper, a numerical method for realizing the sloshing of SWHE shell side with different degrees of freedom (DOFs) was successfully proposed based on ANSYS software. The sloshing simulations were carried out, and the effects of sloshing motions on the shell-side flow and heat transfer characteristics were analyzed. By comparing, the uncertainty of simulation result was within ±10%. As a result, the shell-side flow and heat transfer characteristics were obviously influenced by sloshing motions and showed periodicity. The effects of pitching and heaving were more significant than that of rolling, and the effect of sloshing period was smaller than that of sloshing amplitude. At the same time, the fluctuations’ regularity of two-phase flow and heat transfer characteristics decreased with the increasing vapor quality.