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Conformal cooling is an additive manufacturing-based solution and it is a rapidly developing method for reducing the cooling time of the plastic injection process. The present study investigates the thermal and mechanical performances of the 3D-printed conformal cooling channels using computational analyses and multi-objective optimization. For a real injection mold product, two different conformal cooling channel profiles, which are circular and elongated, are analyzed individually. Their cooling time, temperature non-uniformity, and pressure drop are assessed. Compared to the traditional channels, the cooling time of designed CCCs is reduced in the range of 30-60%. The cooling and fatigue life performances of the elongated channel are analyzed for different channel pathways and cross section areas. As for the circular channel, the coolant temperature, volume flow rate, and channel diameter are selected as the parameters within the ranges of 288.0-298.0 K, 1.0-10.0 L/min, and 2.1-2.5 mm, respectively. According to these parameters, the multi-objective optimization study is performed and the best trade-off point is found at the channel diameter of 2.5 mm, coolant temperature of 297 K, and the flow rate of 1 L/min when all the objectives have equal weights in the optimization problem. Accepted version

Injection molding is widely used in plastic product manufacturing process. The product quality and the cost-effectiveness highly depend on the cooling step in the molding process. Thanks to the development of additive manufacturing techniques, conformal cooling channel (CCC) becomes a promising alternative for channel design. In this paper, three CCCs with different profiles and the same aspect ratio are designed for cooling a plastic product in its manufacturing process. The thermal and mechanical performance is presented by ANSYS Workbench. The simulation results are validated by the experimental data. The cooling performance under different coolant flow rate and different inlet temperature are simulated and compared. The thermal results show that compared with conventional straight channel, the designed CCCs can shorten the cooling time ranging from 10% to 57.1% and the temperature distribution of the plastic product is uniform as well. The mechanical results show that the fatigue life and von Mises stress of the designed CCCs can meet the industrial operating requirement.

The recent developments in the additive manufacturing make easier and more affordable the fabrication of conformal cooling solutions for the injection molding processes compared to the traditional straight-drilled cooling structures. This paper presents four different conformal cooling cavities. Their thermal and mechanical performances are analyzed via computational solutions in the ANSYS environment. Each cavity is supported by lattice structures with unique geometric arrangements. Cooling time is considered as the main assessment criterion for the thermal analyses whereas the von Mises stress and fatigue life are the key criteria for the mechanical simulations. The results are compared with the reference geometry that is a traditional straight-drilled geometry and currently being operated in the real environment. It is seen that the cooling time is decreased in the range of 68.5–74.2%. However, only one of the cavity structures achieves close mechanical performance to the reference geometry; thus, the detailed discussions are also discussed for further studies.

Metal additive manufacturing (MAM) is an effective way to fabricate conformal cooling channels (CCCs), which follow the curves of the plastic product in the mold body of the plastic injection. CCCs have free-curved pathways thanks to the design & manufacturing flexibilities of the MAM process so that they can achieve better cooling performance with shorter cooling time and smaller temperature non-uniformity. On the other hand, the flexibilities of the MAM process bring multiple options for design variables and the high number of design variables make the final design of CCCs complex, high-cost, and time-consuming. Considering this challenge, this study presents the entire process of MAM of CCCs for a target product with eight different design variables, which makes it a product with a high number of design variables, from the initial design to the on-site manufacturing including the steps of computer-aided design & simulations, metamodel, multiobjective optimization, and the printing quality monitoring. The target product has three main objectives that are i) the temperature difference between the maximum and minimum values at the internal wall of the mold, ii) maximum temperature in the mold body, and iii) pressure drop. The optimized product is then printed via direct metal laser sintering (DMLS) machine and the quality check is done via X-ray computed tomography. Ministry of Education (MOE) This study is funded by the Ministry of Education Tier 1 RG154/19.

This study aims to design a complex conformal cooling channel (CCC) structure for an injection mold geometry that has eight different design variables according to multiple main objectives of the maximum temperature at the plastic interface, the difference between the maximum and minimum temperatures at the internal wall, and the pressure drop in the channel. The high number of design variables results in an unaffordable computational load for full factorial design. Hence, we present the hybrid Latin Hypercube (LHC)-Delaunay Triangulation (DT) method to create meta-model data effectively at high dimensions by using 134 different simulations in the MATLAB environment. Since the computational time is a crucial factor, we perform the hybrid LHC-DT approach with four different data simulation set of 1–30, 1–60, 1–90, and 1–134. The multi-dimensional decision-making procedure is completed with multiobjective optimization. The proposed hybrid LHC-DT approach achieves reliable and apparent results for all multiple objectives so that the Pareto frontier of the data set of 1–30 is selected for assessment. According to the data set of 1–30, the optimum values of the temperature difference, maximum temperature, and the pressure drop are found 28.88 K, 361.35 K, and 0.46 bar, respectively.

Vaporizers are the key heat transfer device in the regasification process of liquefied natural gas (LNG), especially for the conventional onshore LNG receiving stations. This paper has proposed a novel intermediate fluid vaporizer by employing multi-stream plate-fin heat exchanger (MPFHE-IFV). Compared to traditional shell-and-tube IFVs, it can not only achieve a higher heat transfer efficiency with more compact structure using MPFHE but also realize the recovery and reuse of LNG cold energy with intermediate fluid. In this ingenious design, the self-evaporating gas of cryogenic liquid is adopted as the intermediate medium of IFV so that the equipment freezing can be effectively avoided under large flow conditions. A thermal-hydraulic design model has been established for MPFHE-IFV to determine the detailed structural dimensions as well as the heat transfer performance, and a corresponding multi-objective optimization algorithm has been adopted to obtain the minimum equipment volume, the optimal channel arrangement and fin structure, the maximum cold energy recovery efficiency and the optimal number of internal cycles. Meanwhile, the transmission process of the cryogenic exergy in MPFHE-IFV has been revealed according to the analysis of the system temperature-entropy diagram. Finally, two experimental cases based on the liquid nitrogen regasification process are conducted to evaluate the practical performance of the novel MPFHE-IFVs using the design and optimization method proposed in this paper. The results indicate that this new type of IFV can reach the highest cold energy recovery efficiency up to 95% within the 8% error range when the heat transfer capacity is 11.5 kW and the heat medium flow rate is near 330 L/h. National Research Foundation (NRF) The funds supported this work include the National Research Foundation of Singapore under the grant NRF2014EWT-EIRP003-014, NRF2013EWT-EIRP004-019, NRF2011NRF-CRP001-090, the Fundamental Research Funds for the Central Universities No. 3132018248 and the National Natural Science Foundation of China No. 51906026, No. 51876019, No. 51779026. Their support is gratefully acknowledged.

National audience; Do people discriminate between co-ethnics and others in cooperative interactions? In an experiment in China, we find that participants in trust games send around 15% more to partners they know to be co-ethnics than to those whose ethnicity they do not know. Re- ceivers’ behavior is determined by amounts received and not by perceived ethnicity. In line with previous literature we find that subjects contribute more to public goods in ethnically homogeneous groups than in mixed groups. We find evidence for a new explanation that is not due to different intrinsic preferences for cooperation with ingroup and outgroup members. Instead, subjects’ willingness to punish in-group members for free-riding is re- duced when out-group members are present. This leads to lower contributions and net earnings in mixed groups. Thus favoritism towards co-ethnics can hurt both those engag- ing in favoritism and those being favored.

The present study proposes a neural network-supported multiobjective optimization procedure for two different conformal cooling channel designs in plastic injection technology. After completing the 3D design of a plastic model, the computational heat transfer & fluid dynamics simulations find the cooling time, temperature uniformity, and pressure drop data, which are the main objectives of the minimization-based multiobjective optimization problem. The performance maps of the objectives are created via i) a classic MATLAB-based interpolation and ii) MATLAB-based neural networks. Then, multiobjective optimization is conducted. The results show that the neural networks can create the performance maps of the cooling time trends with less than 1% error whereas its best trade-off point calculation has nearly 1.1 % deviation. Also, the use of neural networks can decrease the computational time in both simulation and optimization processes.

This paper presents the development of a dynamic model for a newly proposed Absorption-based Liquid Desiccant Regeneration (ALDR) system operating in vacuum condition which can reduce the regeneration temperature to around 20–35 °C. The dynamic model is developed based on the internal and external enthalpy balances and mass balances in the components and it accounts for the dynamic behavior due to the heat and mass transfer process in the components. This approach is simpler as detailed enthalpy at each state point can be avoided. The developed dynamic model is verified using the data obtained from the experimental platform constructed in the laboratory. The dynamic response of the simulation results is in good agreement with the experimental data. This model can predict the relevant parameters such as the temperature, concentration and mass flow of the desiccant solution and temperature of the heating and cooling sources when a step change of inlet water temperature is applied to system. The developed model will be useful for the elaboration of control system in the future. NRF (Natl Research Foundation, S’pore)

Liquid Desiccant Dehumidification Systems (LDDS) have been gaining attention due to its great energy saving potential in buildings. The desiccant regeneration system in LDDS plays a vital role in the system as the major energy consumed is due to the heat energy supplied to regain the concentration of the desiccant solution. The high regeneration temperature prohibits the potential use of low-grade or renewable energy as the heat source in the desiccant regeneration system. Therefore, a desiccant regeneration system operating in vacuum condition was proposed in this work. A novel Absorption-based Liquid Desiccant Regeneration (ALDR) system was developed and studied to validate this approach. A performance prediction model was also developed to predict the regeneration performance of the ALDR system. The model predicted values and the experimental values agreed well with each other with average deviation less than 5.90%. The operating parameters in the proposed ALDR system were also compared with the conventional packed-bed desiccant regeneration system available in literature. The regeneration temperature in LDDS was found to be significantly reduced to around 20–35 °C with the operating vacuum pressure between 1000 Pa and 2000 Pa when regenerating Lithium Bromide solution of 36% mass fraction. This study validated the feasibility of the ALDR system in reducing the regeneration temperature of the desiccant regeneration system. The results also showed that the proposed ALDR system was able to reduce the power consumption by 40.66% compared to the conventional packed-type regenerator from literature. NRF (Natl Research Foundation, S’pore)

In this paper, performance analysis has been conducted to evaluate the regenerator with heat recovery in Liquid Desiccant Dehumidification System (LDDS) under different air mass flow rate. The waste heat of the exhausted regenerating air is recovered by a fixed-plate heat exchanger (FPHE). A hybrid model has been proposed for the heat recovery process and combined with the regenerating heat and mass transfer hybrid model, the heat recovery performance of FPHE and its effects on the regenerating performance have been evaluated. The comparison of the experimental and numerical results show that the numerical computation is accurate and effective for prediction, control and optimization of regenerator with heat recovery. The largest relative error is only 10.03%. With heat recovery, the regenerating performance is improved with high regenerating rate, effectiveness and thermal efficiency. FPHE recovers 16–19% of the waste energy and compared with regenerator without heat recovery, its employment in regenerator contributes to 14–18% energy saving.

This study presents a new desiccant concentration regulation strategy for the dehumidifier of a liquid desiccant air conditioner (LDAC). Starting from the mass balance principle, the proposed strategy supplies the strong solution in an intermittent manner to maintain the required working concentration, and the dehumidification rate is monitored as the feedback to improve the regulation performance. Compared with the conventional method, this new solution transfer strategy avoids the continuously solution exchanging, while allows multiple dehumidifiers to work simultaneously with only one regenerator. A mathematical model emphasizing on the concentration profiles is developed to determine the parameters of the proposed strategy. Simulations and experiments are conducted to evaluate the effectiveness of this strategy in different working conditions. The results prove that the proposed strategy can keep the working concentration at the pre-specified range with less energy consumption during the solution transfer. With this strategy, conventional LDAC can be extended to a mode with multiple dehumidifiers and one regenerator for large-scale applications in buildings.

To evaluate and compare the regenerator of liquid desiccant dehumidification system (LDDS) without and with heat pipe heat exchanger (HPHE), this paper conducts performance analysis by hybrid heat transfer, mass transfer and heat recovery models, and the simulation results are then validated by the experimental results. 4 and 8 rows HPHE are compared to investigate the relationship between heat recovery rate and the additional fan energy consumption caused by the existence of HPHE. Effects of air mass flow rate on the regenerating and heat recovery performance are also discussed. The results show that the numerical computation is effective and accurate and the largest RE is only 10.87%. With heat recovery device, the regenerating performance is in general improved. The model predicted results reveal that the maximal net heat recovery ratios are 25% and 26.5% which contributes to 26.5% and 27% maximal energy saving for 4 and 8 rows, respectively, compared with regenerator without HPHE.

This paper investigates the availability of the numerical model for predicting the performance of regenerator in Liquid Desiccant Dehumidification System (LDDS) with waste heat recovery under different flow rate and inlet temperature of liquid desiccant. Heat pipe heat exchanger (HPHE) is employed as waste heat recovery device in this study. The numerical computation are carried out by combining the hybrid heat transfer, mass transfer and heat recovery models of regenerator with heat recovery. The experimental validation proves the accuracy of the numerical computation and the largest relative error is only 10.46%.

Temperature is a crucial variable to evaluate and measure the energy consumption and efficiency of the Air Conditioning & Mechanical Ventilation System (ACMVS) in the buildings. To ensure the performance and efficiency of the ACMVS, an experimental study of long-term reliability for temperature monitoring to ensure the accuracy of temperature sensor measurement is carried out in this paper. Four experiments were conducted for the influence of temperature measurement under different operating conditions in the ACMVS, which are insertion depth, humidity, tube vibration, and water mixing. Finally, the drift of two types of temperature sensors (RTD and Thermistor) commonly used in industry are compared under the condition of long-term reliability measurement. The results showed that the non-waterproof thermistor installed on the open thermocouple sleeve at least 2/3 of the pipe where the temperature sensor is inserted at 10D away from the water mixing point could provide the best temperature reading.

In the full-volume LNG tank, the leakage of the external heat will increase the internal LNG temperature and aggravate the evaporation of the low-temperature liquid, which may cause delamination and rollover of the LNG in the storage tank, resulting in significant safety hazards. Therefore, this paper analyzes the mechanism of LNG stratification and rollover in storage tanks, establishes the mathematical model of LNG storage tanks, and uses CFD technology, adding the phase change model of LEE by multi-phase flow VOF model. The 2-dimensional transient simulation calculation was carried out in the evolution process of stratification and rollover in LNG storage tanks. The calculation results show that the time of rollover in the LNG storage tank under different working conditions (density difference and heat leakage) is different. Increasing the heat leakage strength of the tank will cause the rollover phenomenon to occur in advance; under the same leakage heat intensity, the LNG of different initial density differences in the tank, the higher the density difference, the easier it is to roll, and the less time is required. Natural convection due to heat leakage is the direct driving force of the rollover phenomenon.

Condition monitoring is critical for the safe usage of Liquefied Natural Gas (LNG). Temperature distribution is an important index of LNG storage and it can reflect the tendency of heat leakage and the situation of evaporation. However, traditional electric sensor may cause explosion due to spark. In this paper, a cryogenic sensor based on fiber Bragg grating (FBG) is developed in which the fiber with pre-tensile force is adhered onto temperature-sensitive metal. The liquefied nitrogen (LN2) is used to test the designed sensor instead of LNG for safety consideration. By setting every 10 K as a testing point from 83 K to 193 K, the experimental investigation reveals that there is a positive linear relation between the reflected wavelength and the testing temperature. By using multiple linear functions to fit experimental data, the maximum measuring error of FBG sensor is less than ±0.35 K, which indicates the usability of this sensor in LNG storage. Finally, an experiment of temperature stratification is performed to validate usability of FBG sensor for LNG monitoring. The results indicate that the designed FBG sensor has enough accuracy to reveal LNG rollover and it has similar dynamic performance with RTD sensor. NRF (Natl Research Foundation, S’pore)

In this paper, a hybrid model for heat pipe heat exchanger used for heat recovery in regenerator of Liquid Desiccant Dehumidification System (LDDS) is developed. The proposed hybrid model starts from the physical governing equations and lumps the complex geometric parameters and fluids’ thermodynamic coefficients as constants since they have very small changes during the process operation. The resulting model has only three unknown parameters which can be determined by Levenberg-Marquardt method. Compared with the existing heat pipe models, the proposed model is very simple, accurate, and does not require iterative computations. A large amount of testing for the heat pipe heat exchanger installed in a pilot LDDS shows that the model is very effective to predict the performance in a wide operating range. The model is expected to find its applications in monitoring, control and optimization of the regenerator heat recovery process of LDDS.

A distributed operating Liquid Desiccant Dehumidification System (LDDS) designed for commercial building applications allows one regenerator to handle multiple dehumidifier units, which provides the potential to apply low-grade energy in a centralized form for desiccant solution regeneration. An online soft sensing model with the Adaptive Network-based Fuzzy Inference Systems (ANFIS) structure is developed to satisfy the operating scheme. The number of input variables is reduced by the regeneration mass transfer model, and the fuzzy interference is optimized by Genetic Algorithm (GA) with a constrained objective function. The accuracy of the soft sensing models with different simplicity levels are validated and compared in case studies. Results show that the proposed soft sensing model is accurate, and the simplification approaches can reduce the size of the model significantly without affecting the predictive accuracy.

The impingement of ethanol droplet train on the heated titanium substrates without or with the titanium oxide nanotube coating has been experimentally investigated in close view. The coating makes the substrate with high wettability. Four distinct but steady hydrodynamic patterns are observed on both two surfaces, namely, liquid aggregation and crown periphery instability; sub-droplet splashing and crown periphery instability; splashing and stable crown; and splashing with stable angle. However, the more wetting nanotube coated substrates push the transition between the patterns to a higher temperature. The quantitatively analysis of spreading length, diameter and height of crown and stable splashing angle further proved the transitions between the hydrodynamic patterns on the two titanium surfaces. The instability at the crown periphery may result from the low surface tension of the working fluids in first and second patterns, while the crown becomes stable on the third pattern. In the fourth pattern, a sharp shift of the splashing angle from decreasing to increasing is found at the surface temperature of 323 ∘C and 404 ∘C for the bare titanium surface and the nanotube coated surface, respectively. The shift could be attributed to the emergence of Leidenfrost effect. It is found that the Leidenfrost point at the droplet train impingement on the nanotube coated surface has been remarkably delayed. Accepted version

This paper investigated a frozen-free and high efficiency cold energy recovery system for cryogenic liquid gasification process. This system comprises three heat exchangers: evaporator, superheater and recuperator. In the evaporator, the cryogenic liquid is heated and vaporized by its own multiple cyclic vapor stream and then the vapor flows into the superheater, where it is further heated by a heat medium. The superheated vapor flows back to the evaporator acting as the first high temperature cyclic stream. In the recuperator, the low temperature cyclic streams from the evaporator are reheated by the heat medium. The last cyclic stream is gas product while the rest cyclic streams return back to evaporator as heating source for the incoming cryogenic liquid. Through cyclic operation by flow arrangement, heat exchanger structure and appropriate flow rate controls, the system prevents the heat medium from freezing and improves the cold energy recovery efficiency. Moreover, the system can achieve different temperature outputs of heat medium for various applications by regulating its flow rate.

In industrial or commercial buildings, the working components and energy sources of a Liquid Desiccant Dehumidification System (LDDS) are usually in different locations, which increases the difficulties of system operation and maintenance. This paper presents a control strategy on the outlet air humidity for a dehumidifier with distributed operating scheme to improve the performance of a large-scale LDDS. A new Fuzzy-PID controller is implemented to fine tune the outlet air humidity by manipulating the solution inlet temperature at a stable desiccant concentration ranges. This Fuzzy-PID controller is developed from a T-S fuzzy model, with varied parameters according to previous and current input and output variables. Control performances of the cooperation between concentration regulation module and General-PID, Cascade-PID or Fuzzy-PID controller have been compared in simulations. Different indices are used to evaluate the control performances of different controllers. The simulation results show that the method proposed in this paper can solve the control issues raised by distributed operation, which is an appropriated choice to be applied in a multiple-terminal LDDS in buildings.

This study represents the development of a mathematical model for a newly proposed Absorption-based Liquid Desiccant Regeneration (ALDR) system operating in vacuum condition. The dynamic model is developed based on the internal and external enthalpy balances and mass balances in generator and condenser in the ALDR system. The relevant governing equations are developed and the dynamic operation is then simulated to study the dynamic performance of the system. The model is able to predict the relevant parameters such as the internal and external temperature in each component, solution concentration, vacuum pressure and thermal power throughout the regeneration process. The approach used is simpler as detailed enthalpy at each state point can be avoided. The rate of evaporation and condensation in the regeneration system is also being focused here. This information will be useful for the elaboration of control system in the future.

In this paper, a hybrid model is proposed for fixed-plate heat exchanger (FPHE) employed as heat recovery device in regenerator of Liquid Desiccant Dehumidification System (LDDS). Starting from the energy balance principles, the developed hybrid model combines the complex geometric dimensions and fluids' thermodynamic properties into constants. The resulting heat recovery model has only three unknown parameters which can be identified by Levenberg-Marquardt method. Compared with the existing heat recovery models, the proposed model is simple yet accurate, and does not need iterative computation. Experimental validation demonstrates the availability of the proposed model in predicting heat recovery performance over a wide working range. The model is expected to be employed in prediction, optimization and performance assessment of the heat recovery process in regenerator of LDDS.

This paper presents a dynamic analysis of an energy efficiency dehumidifier for building applications. This new structured dehumidifier is working with a controllable desiccant concentration, and the dynamic behavior of the heat and mass transfer process inside the dehumidifier becomes rather critical. A model is developed to describe the dynamic behavior of the process air with experimental validation. The numerical results of the dynamic response are clarified to conclude that decreasing the solution inlet temperature has a more significant impact on improving the dehumidification ability than increasing solution mass flow rate. The outcomes provide a comprehensive understanding of the dynamic behavior and the results will benefit the humidity control of the indoor air to improve the living quality of the occupants. NRF (Natl Research Foundation, S’pore) Accepted version

Inlet conditions, including inlet size and location as well as inlet temperature and humidity, have significant effects on the humidity distribution in building room, testing chamber and built environment. This paper presented the investigation of the changes of inlet air temperature, humidity and inlet vent positions on the humidity distribution in the environmental chamber through experimental approach and simulation method. The average relative humidity (RH) and humidity uniformity inside the chamber with different inlet vent positions were investigated. The results show that non-uniformity of the humidity distribution decreases with the increase of the inlet RH value under low inlet temperature conditions while it increases with the increase of the inlet RH value under high inlet temperature conditions. The humidity uniformity is not very good under the lower inlet vent positions. Comparison studies on the humidity uniformity between experimental tests and numerical simulations show that the simulation results agree well with the experimental test results.

In this paper, CFD simulation of evaporative cooling pad, which is one kind of structured packing, has been carried out in Liquid Desiccant Dehumidification System (LDDS). Dry pressure drop and liquid distribution of two types of evaporative cooling pad are simulated and validated by the experimental data and Nusselt formula. For conducting the simulation, micro-scale representative element of evaporative cooling pad is built. VOF model is adopted as multiple phase model. Three turbulence models are compared. By means of CFD simulation comparison, it is found that κ — ω is the most suitable turbulence model for the simulation of structured packing. The liquid distribution pattern inside the packing is uncovered. The influences of flute height of packing are obtained.

This paper reported on a study of using blogs as out-of-class assignments for the development of learners’ writing competence. There were 36 students of English majors from an intact second language (L2) writing class participating in this study. A mixed method design was employed to obtain both quantitative and qualitative data. The results showed that blog-based peer feedback had a statistically significant positive correlation with learners’ motivation, collaboration, and course satisfaction. The findings also revealed that the feedback was conducive to learners’ self-reflection and self-confidence in L2 writing and could give rise to an enhanced L2 writing experience. The study concludes that group collaborative writing via blogging can not only encourage collaboration and self-reflection but also engage learners in noticing and co-construction of knowledge. Pedagogical implications and challenges are addressed and suggestions for future research are advanced.