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This study presented an experimental investigation on heat transfer performance of a shell-and-tube heat exchanger with and without circular fins. Particular attention has been paid to the effect of injection flow rate of heat transfer fluid (HTF) on the thermal performance of the heat exchanger. A purposely-designed apparatus was built for experimental observation. Results showed that the application of fins had a great effect on improving phase change heat transfer and the full charging time was significantly reduced. Injection flow rate of HTF was found to have little influence upon the performance of the heat exchanger.

The evaporative cooling is an energy-saving and environmentally-friendly air-conditioning method. A cross-flow regenerative indirect evaporative heat exchanger (IEHX) has been designed and fabricated. In the proposed IEHX, the working air is gradually diverted into the wet channels through the holes distributed along dry channels. This arrangement allows the working air to be pre-cooled before entering the wet channel. The experimental study was carried out to investigate the performance of the IEHX under specific inlet conditions. Measurements have been conducted during steady-state operating conditions. Experimental results have demonstrated that the product air can be gradually cooled along its flow direction by transferring its heat to the working air. In addition, the proposed cross-flow IEHX is able to reduce the air temperature below wet-bulb temperature.

In this paper, a curved wavy channel was proposed to further enhance the thermal performance of the conventional wavy channel. A three-dimensional model of the curved wavy channel was established with defining the overall curvature. The flow behavior and heat transfer in the wavy and curved wavy channels were numerically investigated under various wave amplitudes. The mechanism behind the observed phenomena was revealed by analyzing the synergy between velocity and temperature fields. The results indicated that the Nusselt numbers in curved wavy channels with amplitudes of 0.40 mm and 0.80 mm can be raised by 44.3% and 15.3% compared to those in conventional wavy channels. The parametric study showed that the flow resistance is more sensitive to the wavelength. For a given amplitude, curved wavy channels always show a better field synergy than conventional wavy channels. In addition, an inferior field synergy was observed near the suction side in both types of wavy channels, which indicates that the purposive improvement needs to apply to these locations. This study also found that the field synergy angle has limitations in characterizing the heat transfer intensity in the channel with small wavelengths. This is because that extremely chaotic flow patterns caused by small wavelengths result in a negative dot product of temperature gradient and velocity over a large area.

The application of evaporative cooling technique is getting more and more attention. The aim of the work is to propose a hybrid air-conditioning system. The hybrid system employs an indirect evaporative heat exchanger (IEHX) as a pre-cooling unit that is operated in tandem with conventional air handling unit. The present work has developed a numerical model by considering the pre-cooling effect of the IEHX. The IEHX is able to adopt the room exhaust air as its working air. In addition, the mathematical formulation for the conventional cooling coil has been developed to study the influence of the pre-cooling effect on the chilled water temperature. The calculated results have demonstrated the ability of the evaporative pre-cooling unit to cool and dehumidify the ambient air under humid tropical climates. The chilled water supply temperature can be also raised due the pre-cooling process. Consequently, an improvement on the coefficient of performance for the chiller is achieved. The hybrid system is able to obtain a potential energy saving as a result of the pre-cooling effect and the enhanced efficiency.

This study conducted both experimental and numerical investigations on the solidification behavior in a metal foam composite phase change material (PCM) for cold storage. Volume-average-method was adopted with the help of Forchheimer-Darcy equation to model the fluid flow through porous media. Experimental measurements were performed to validate the analytical model and the numerical method, with good agreement achieved. Local thermal equilibrium and non-equilibrium states were justified numerically and experimentally. Effect of pore morphological parameters (porosity and pore density) upon the solidification features of composite PCM were investigated. For the appliance of composite PCM to cold storage, techno-economic characteristics was also assessed. Results demonstrated that the full solidification time for metal foams with a porosity of 0.93 and 0.97 can be saved 87.5% and 76.7% respectively compared with pure water. It indicated that porosity of metal foam played a dominant role in heat transfer enhancement; while pore density seemed to have little influence on phase change behavior according to the results. Local natural convection in the unsolidified phase caused a remarkable promotion of the interface evolution, and the full solidification time with natural convection considered can be saved by 14.3% compared with pure conduction for the case with the same porosity of 0.97. The economic analyses indicated that using composite PCM was profitable with a short payback period less than 2 years.

A hybrid air-conditioning system has been proposed by integrating an indirect evaporative pre-cooling unit. In the proposed system, the room exhaust air is employed in the indirect evaporative cooler (IEC) to pre-condition the ambient intake air. The mathematical formulation has been judiciously established for the pre-cooling IEC. The validation of the numerical model has been conducted by comparing the simulated results with the experimental data in terms of the outlet temperature and the heat flux along the heat exchanger surface. The pre-cooling performance of the IEC is theoretically investigated for the climate in representative cities selected from five different climate zones. The psychrometric illustration of the air conditioning variation has indicated that the ambient air can be pre-cooled and pre-dehumidified through the IEC. The possibility of water vapor condensation depends on the humidity ratio of the ambient intake air. The simulation result demonstrates the capability of the pre-cooling IEC to fulfill part of the cooling load of the ambient intake air resulting in a marked energy saving potential.

The open-cell metal foam is a porous medium which possesses a true metal skeletal structure. The fully inter-connected pore and ligament structures provide the extreme large fluid-to-solid contact surface area and tortuous coolant flow path inside the metal foam, which could increase dramatically the overall heat transfer rate. The high specific surface area, low density and open-celled nature of a metal foam possesses a combination of properties ideally suited for applications in high heat flux thermal management where conventional materials and products are not adequate. In this research, forced convection in a heated channel filled with open-cell metal foam subjected to oscillating flow has been investigated experimentally and numerically. DOCTOR OF PHILOSOPHY (MAE)

The thermodynamic properties of a working-fluid pair, composed of a refrigerant and an absorbent, greatly influence the performance of an absorption–refrigeration cycle. Particularly important is the solubility of the vaporized refrigerant in the absorbent. Using an isochoric saturation method, solubilities were measured for trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) in 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF6]), and 1-methyl-3-octylimidazolium hexafluorophosphate ([Omim][PF6]) from 283.15 to 343.15 K. Solubilities rise with a decrease in temperature and an increase in pressure. The highest solubility is in [Omim][PF6], followed by [Hmim][PF6], and [Bmim][PF6]. The new data were correlated by the nonrandom two-liquid model and by the Krichevsky–Ilinskays equation; both provide good agreement with the experimental data. Estimates were given for total enthalpy, entropy, and Gibbs energy of dissolution.

Battery thermal management is critical for the success of all electric vehicles due to the effects of extreme temperature on performance, reliability and lifespan of batteries. In this study, the three-dimensional model of a stagger-arranged battery pack was developed to investigate the effects of cooling channel size and air supply strategy on the thermal behavior of battery pack. The thermal resistance model of single irregular air passage was used to validate the numerical scheme. It was found that the appropriate cooling channel size of 1 mm for 18650 lithium-ion battery was achieved based on the three key parameters, namely, the maximum temperature, the space utilization and the energy efficiency factor. The numerical results illustrate that the best cooling performance can be achieved when airflow inlet and outlet are located on the top of battery pack. The cooling energy efficiency β decreases markedly with the increase of battery numbers along horizontal direction. As the ratio of the length of batteries along horizontal direction to battery diameter equals to 36.10, the lowest value of β is still acceptable. The analysis indicates that packing more battery along flow direction is an appropriate solution in terms of battery power density and cooling requirement.

Absorption air conditioning system containing no chlorofluorocarbons is considered environmentally friendly and a competitive alternative to conventional vapor compression air conditioning system. One of the most commonly used refrigeration working pair is LiBr/H2O. This paper experimentally studies the falling film absorption of LiBr/H2O with various kinds of nanoparticles dispersed, such as Cu, Al2O3 and CNT. The results show that the variety, mass fraction and size of nanoparticles, as well as solution flow rate are considered as the key parameters. The smaller the nanoparticles size, the better the effective absorption ratio. The larger the nanoparticles mass fraction, the better the effective absorption ratio. The best enhancement is achieved by adding Cu nanoparticles for all the studied nanoparticles species. The effective absorption ratios for all the studied cases are higher than 1.0, which proves that the dispersed nanoparticles have positive effects on the absorption process.

The deep buried coaxial and horizontally-butted borehole heat exchangers are the two typical wells for geothermal utilization in space heating. The economic indexes, heat extraction performance and environmental impact of the two wells are crucial for actual projects. In this study, the Monte Carlo simulation and sensitivity analysis based on life cycle saving are employed to evaluate the economy of the two borehole heat exchanger systems. The heat extraction considering both performance and economic factors is examined by the levelized cost, while the environmental impact is assessed by the carbon intensity analysis. The results showed that the payback periods of a coaxial borehole heat exchanger system and a horizontally-butted borehole heat exchanger system are 6.7–9.2 years and 9.1–11.7 years respectively, and the life cycle saving of a butted borehole heat exchanger may reach a high value after 25 years of operation. The sensitivity of life cycle saving for both coaxial and horizontally-butted borehole heat exchangers is mainly governed by heating income, discount rate, and non-depreciable initial investment. The heat production capacity of the butted borehole heat exchanger system is 1128–1342 kW, which is twice as much as that of coaxial borehole heat exchanger. From the life cycle perspective, the levelized cost of energy and carbon intensity of the coaxial borehole heat exchanger is $ 8.67–9.35/GJ and 70.43–80.86 g(CO2)/kWh, slightly higher than those of the butted borehole heat exchanger. It can be proved that the two borehole heat exchangers are more in line with the low-carbon policy than the traditional heating methods, and the well construction and operation phase contributes a major carbon emission from the perspective of the life cycle.

Spiral channels are widely used as the core heat exchangers in latent thermal storage units. This study aims to develop a novel spiral channel characterized by wavy sidewalls for high-efficiency convective heat transfer in tube side. The amplitude of the wavy sidewalls is designed to grow from the inlet to the outlet along flow direction. The thermal characteristics in the spiral-wavy channel were numerically investigated under the boundary condition of constant wall temperature, since latent heat storage units mainly work under isothermal condition. The comparison was carried out between a smooth-spiral channel and a spiral-wavy channel in terms of the heat transfer capacity, friction factor, dimensionless temperature distributions and development of boundary layers. At a given heat transfer rate, the required length of the spiral-wavy channel is only 63.5% of that of the smooth-spiral channel, which implies that the energy density and efficiency of a heat storage unit can be improved remarkably. The increase in pressure drop brought by the spiral-wave channel is less important compared with the improvement of thermal performance, suggesting its potential in heat transfer enhancement and energy saving. The present work is expected to motivate the design of compact and high-efficiency heat exchangers for thermal energy storage and extraction.

The lithium ion battery has been widely applied in the fields of electric vehicles and electronic products due to its advantages of high power density, long lifespan and low self-discharging, etc. In this study, two lithium ion batteries are adopted to explore the effects of different thermal conditions on battery’s performance. One of thermal conditions makes battery close to adiabatic condition similar to the thermal condition of battery pack without any thermal management system. Another thermal condition is constant temperature condition employed to simulate the thermal condition of battery pack with thermal management system. The experimental results show that (i) next chargeable capacities of these batteries are dependent on the previous dischargeable capacities for all thermal conditions; (ii) dischargeable capacities of these batteries markedly decrease with the increase of the discharge rates under 20°C constant temperature condition; (iii) dischargeable capacities are independent on discharge rates under close to adiabatic condition because the obvious battery temperature rise can offset the adverse effects of higher discharge rates on battery’s performance. Although higher battery temperature is conductive to weaken or eliminate the adverse effects of higher discharge rates, excessively high temperature can also accelerate battery aging and easily cause battery thermal runaway, which indicates that it is necessary for battery pack with thermal management system to control thermal conditions of batteries.

The sewage flow rate of the urban drainage system is relatively large and generally stable, its sewage temperature range varies relatively lightly and maintains 10~15℃ in winter. The sewage in the drainage system can be the low grade thermal source for building heating and cooling. Sewage source heat pump technology can efficiently extract or discharge the amount of heat from the sewage in the drainage system for building heating or cooling. The field test of the actual operation thermal performance of the sewage source heat pump were carried out and investigated. The sewage source heat pump system were continuously measured for 72 hours. Based on the test datum, the average COP of the heat pump was 4.5. The relationship between energy consumption of system and energy consumption of transportation are analyzed. The analysis shows that the pump of this system cannot match the load change well and the use of variable frequency pump can improve the energy efficiency of the system. Before the use of the sewage source heat pump system, the traditional coal-fired boiler and air-cooled chiller are the heating and cooling system of this building. Compared with the traditional coal-fired boiler and air-cooled chiller, the advantages of sewage source heat pump system in energy saving, economy and environmental protection are analyzed. The results show that: Compared with the original system, direct heat exchange type sewage source heat pump system can save 53% of the primary energy consumption, reduce the annual operating cost by 11%, increase the initial investment by a factor of 14.3%, and the payback period of incremental investment is about 4.7 years. This method not only has better energy saving, saving capital benefit, but also can reduce the local pollutant emission, and has better environmental emission reduction benefits.

This study presented experimental investigations on the thermal performance of a thermal energy storage (TES) unit with coil tubes. A designed test rig was built and the melting heat transfer characteristics (melting front and temperature distribution) inside the TES unit were examined. The effects of charging flow rate on the overall phase change process were examined. The results showed that natural convection accelerated the thermal energy transport in the melt phase in the top region, but weakened the heat transfer in the bottom region; this resulted in the unmelt PCM at the bottom. The melting heat transfer was overall enhanced by the increase in inlet flow rate, indicating that the full charging time can be shortened by a larger flow rate.

This study presented an experimental investigation on solidification behavior of fluid saturated in highly porous open-cell copper foams. Particular attention has been made on the effect of pore parameters (pore density and porosity) on the solidification behavior. A purposely-designed apparatus was built for experimental observations. Results showed that the copper foam had a great effect on solidification and the full solidification time can be saved up to 50%, especially preventing the decrease in solidification rate during the later stage of phase change. The smaller the porosity is, the faster the solidification rate will be. Pore density was found to have little influence upon the solidification rate. In addition, the local natural convection does exist but it has a slight effect on solidification, leading to the slant of the solid-liquid interface.

The polyethylene glycol (PEG-1000) was selected as phase change material (PCM) and the expanded perlite (EP), the granular activated carbon（GAC）, the powdered activated carbon (PAC) and the expanded graphite (EG) were selected as porous adsorption materials. The composite phase change material (CPCM) was prepared by the physical adsorption method. The composite phase change materials compound with the polyethylene glycol and the expanded graphite were picked by comparing and analyzing the adsorption capacity of such four types of porous materials. And then the composite building material for thermal storage mixed with the CPCM and the cement, water-reducer, early strength agent was prepared in the pressure condition of -0.05Mpa and the constant temperature condition of 70℃. Its thermal physical properties, the structural stability and the compression resistance capability of different quality proportion specimens were experimental researched. The results show that such composite building materials with CPCM appears light density, high thermal conductivity, large heat storage capacity and good stability, and its compression resistance capability can satisfy the requirement of ordinary mortar building material.

The ancient architectures of tower buildings type are representative in ancient architectures in Beijing, and compared with other types of ancient architectures, they are characterized by long distance from ground, high height of building itself, and large inner space. For the ancient architectures of tower buildings type, a proposal using floor-type fan coil air-conditioner for control of physical environment is suggested, and simulation calculation for indoor temperature field for one ancient architecture of tower building in Beijing is done using CFD software, with calculation content comprising the indoor temperature field and velocity field when the system is used in summer. The result shows that: adopting floor-type fan coil air-conditioner for summer conditions and adjusting blast amount of fan coil and blasting parameters can make air temperature agreeable and comfortable.

Biomass hot blast stove is one energy source which is aimed to provide clean hot air, it is widespread and has great potential for being generated from biomass. Under the equal condition of heating load between biomass hot blast stove and natural gas blast stove, this paper investigated the economic feasibility and adaptability of a method that using biomass hot blast stove instead of natural gas blast stove. Based on the technological process and the design parameters demand such as air supply temperature, heating capacity, air flow volume of the existed natural gas hot blast stove heating project, the mathematical model and some indexes for evaluating the technical and economic feasibility of the biomass heating way were established, the difference of the technical maturity, initial investment, annual operating cost, operation maintenance, operational risk and allowance policy within the two heating way were comparative analysed, the sensitivity of factors influencing annual total investment of the biomass hot blast stove was analysed. The results show that, the ratio represented by QZs/QZt of annual total investment between biomass hot blast stove and natural gas hot blast stove was only 0.56 under the equal heating load, the sensitivity of factors influencing annual total investment of the biomass hot blast stove was the biomass fuel, and the many problems about biomass hot blast stove like the technology is still immature, operational risk is relatively large, policy direction is unclear, regional differences and other factors were existence. If the operation of the biomass hot blast stove is safety and the biomass fuel of the biomass hot blast stove is plenty, we will recommend using biomass hot blast stove when the ratio of QZs/QZt was less than 1, and using natural gas blast stove when the ratio of QZs/QZt was more then 1.

Fog and haze weather has seriously affected many important aspects of human life and physical fitness. In order to improve air quality, local government has transformed coal-fired heating into clean energy heating in Beijing rural areas. This paper introduces three typical clean energy heating systems which are low temperature air source heat pump (LTASHP), thermal storage heater (TSH) and wall-mounted gas furnace (WGF), researches and tests the practical operation situation of three heating systems in the field. To compare technical and economic feasibility of three heating systems, the paper takes such residence where energy-saving standard of building palisade structure is approximately 50% as the research object, and establishes technical and economic mathematical analysis models, compares primary energy consumption and carbon dioxide emissions of three heating systems. This paper adopts annual cost approach, comprehensively takes into account power capacity increasing tariff and gas pipe network construction fee, and compares initial investment, operation cost and annual cost of three heating systems respectively from the perspective of users and government. The results show that LTASHP is the most energy-saving and its annual cost is lowest in the three heating systems. LTASHP is the most suitable alternative solutions to coal-fired heating in the three heating systems in rural Beijing.

This study focuses on the heat transfer between the vertical concentric tubes buried underground and the medium-deep rock-soil geothermal energy. The numerical simulation based on an in-house FORTRAN computation program was performed to analyze the mechanism of heat exchange underground. The program was shown to predict the test results of outlet water temperature and heat gain very well under the corresponding operating conditions when engineering data of an actual geothermal well were obtained to validate the numerical scheme. The effects of inlet water temperature and flow rate on the heat exchanger performance were also analyzed in detail. The comparison indicated that the present numerical scheme is able to predict the heat transfer performance of extremely long ground-coupled heat exchanger subject to various geothermal conditions.

2,3,3,3-Tetrafluoroprop-1-ene (HFO1234yf) is recently recognized as a new generation refrigerant to replace R134a in automotive air-conditioning system and other refrigeration applications. The knowledge of phase equilibrium property for refrigerant with lubricant oil is therefore interested in these systems. A systematic research program on the phase equilibrium of HFO1234yf with lubricant oils has been carried out in our laboratory, and the purpose is to investigate the influence of the molecular structure of oils, pressure and temperature on the phase behavior of HFO1234yf and lubricant oil system. In this work, the measurements of phase equilibrium for HFO1234yf + pentaerythritol tetrahexanoate (PEC6), HFO1234yf + pentaerythritol tetraheptanoate (PEC7), and HFO1234yf + pentaerythritol tetraoctanoate (PEC8) between 293.15 K and 348.15 K were performed by means of isochoric saturation method. The experimental data were correlated using the PR EOS and HVOS mixing rule combined with Wilson excess free-energy model. The average relative deviations between experimental results and the calculated pressure by the model for HFO1234yf + PEC6, HFO1234yf + PEC7, and HFO1234yf + PEC8 system were 1.23%, 1.19%, and 1.39%, respectively. The maximum relative deviations were 4.04%, 4.34%, and 4.84%, respectively.

This study conducts numerical investigations on melting process in a shell-and-tube latent heat thermal energy storage (LHTES) unit with annular fins. Commercial grade paraffin is employed as the p ...

The radiant cooling air conditioning system has been increasingly prevailed, due to its features of maintaining more comfortable indoor environment with lower energy consumption against the conventional cooling methods. This work explores the effect of heat exchange between human body and surroundings on human thermal comfort subject to the radiant cooling air conditioning system. The widely accepted thermal comfort index, PMV (Predicted Mean Vote), is adopted to evaluate human thermal comfort. To determine the heat loss from human body, the human thermal balance and heat release characteristics are discussed. The test room with various boundary conditions are simulated and analyzed by Airpak. It is found that for sedentary human body subject to the radiant cooling system, the sensible heat loss is approximately linear to the PMV and the value of sensible heat loss for the thermal neutrality (PMV = 0) is a constant. The simplified PMV model is finally achieved based on the results obtained from 594 calculated points. In addition, the relation between the sensible heat loss and the PPD (Predicted Percentage of Dissatisfied) is obtained. The findings from this work could be referenced for thermal comfort evaluation and system design when radiant cooling applies.

We conducted analytical, numerical and experimental investigations on solidification of fluid saturated in highly porous metal foams with open cells. Based on pore-scale thermal equilibrium assumption, an analytical extension of the classical Neumann’s solution was made to predict phase change heat transfer in PCM-foam composites. To explore the heat transfer mechanisms underlying the phase change process and clarify the role of foam insertion, three-dimensional direct numerical simulations on periodically distributed tetrakaidecahedron cells were carried out. Experimental measurements were performed to validate the analytical model and the numerical method, with good agreement achieved. The phase interface was macroscopically flat via experimental visualization but microscopically irregular via pore-scale simulations. Temperature difference between the saturating PCM and metallic ligaments was negligible, so that local thermal equilibrium and one-equation model were applicable especially at low Ste numbers (e.g., 0.22). The present findings provide new insights to cold energy storage design, utilization and economic analysis in HVAC systems.

The reed valve impact is the main reason leads to the valve fatigue failure, the valve noise and energy consumption of the rotary compressor. This paper built up a three dimensional fluid-structure interaction (FSI) model of the dynamic behaviour of the reed valve in a rotary compressor with the rotational speed of 4800 rpm. Then the P-θ diagram inner the cylinder was tested in an experiment to validate the FSI model. By the FSI model, the impact process, the impact stress and the impact velocity respectively for the reed impact against the retainer and the seat were investigated. It was found that for the reed impact against the retainer, the impact occurred at some local spots moving from the neck to the outer edge of the reed head in sequence rather than at all spots on the whole reed head simultaneously. The whole impact process finishes within the rotation angle of 1 o . The highest impact velocity as well as the highest impact stress happens at the outer edge of the reed head. The research results are helpful to the design and failure diagnosis of the reed valve, as well as to energy saving of the rotary compressor.

This is a retrospective investigation of patients with Retinoblastoma (RB) conducted from 2013 to 2016 at the Quanzhou Maternal and Child Health Hospital (China). Demographic and clinical characteristics, treatment outcomes, and risk factors were studied. In total, 436 patients were included in the study. Most of the findings obtained in this study are consistent with other previous reports. The male: female ratio was 1.41:1, and the unilateral: bilateral ratio was 1.51:1. Leukocoria was the most common presenting sign (79.44%), followed by strabismus (12.38%). While, the overall rates of enucleation (15.82%) and mortality (0.92%) were markedly lower than in other reports of RB in Chinese, and most of the patients received conservative therapy. There were signficant differences (p < 0.001) in the age of at first sign and diagnosis, and treatment modalities between patients with bilateral and unilateral RB. The treatment modalities did not show a specific trend over the 3-year study period. Our results suggest that an incorrect initial diagnosis and long lag time may be risk factors for ineffective treatment and a poor prognosis in patients with RB. This was a comprehensive retrospective investigation in which the sample size exceeded most previous retrospective investigations of RB. Our study confirmed that early detection, accurate diagnosis, and active intervention are conducive to control of retention of patients' vision. Fundus examinations, education regarding the early signs of RB, and optimization of the therapeutic strategy of RB may play important roles in ocular health.

This paper proposes a gravity heat pipe exchanger used for cooling the communication base station to replace the traditional air conditioning system during winter and transition seasons. Tests were conducted on a commercial available gravity heat pipe exchanger. The experiment was performed to study the effects of the air flow rate and temperature on the cooling capacity, the heat transfer unit number (NTU) and cooling efficiency of the heat pipe exchanger. The results showed that the larger the air flow rate, the smaller the NTU and the larger the cooling capacity. Based on the analysis of the experimental data, it proved that the gravity heat pipe exchanger could reduce running time and operating cost of air conditioning system. According to the practical applications, the yearly cooling loads of a typical communication base station were further calculated for five typical cities which represent the five climatic zones of China. The results validated that the energy saving by using the gravity heat pipe exchanger is significant. The highest annual electricity-saving rate is achieved by Kunming, about 48.6%, while the lowest annual electricity-saving rate is obtained in Guangzhou, about 18.7% among the five climatic zones. The fitted correlation of cooling capacity in term of outdoor temperature is generic to evaluate approximately the performance of applying the gravity heat pipe exchanger in the actual applications subject to various outdoor temperatures.

Energy losses in district heating pipeline networks can be reduced considerably using insulation materials. In this study, the optimum insulation thickness of direct burial laying used in district heating pipeline networks, energy savings, and payback periods are calculated for various pipe diameters, fuel types and soil depth in the city of Xi’an/China by software MATLAB depending on Life Cycle Cost Analysis (LCCA) method. The results show that optimum insulation thicknesses vary between 0.060 and 0.121 m, energy savings vary between 36.395 $/ m and 194.682 $/m, and payback periods vary between 0.445 and 1.691 years. When the rock wool is used as the insulation material and the soil depth is 1 m, the highest value of energy savings is reached in 500 mm nominal pipe size for fuel-oil fuel type, while the lowest value is obtained in 100 mm for geothermal energy. Therefore, the selection of optimum thickness for different pipes diameters and fuels types is particularly vital for the economic and environmental advantages.

This study presented a pore-scaled numerical simulation on the melting phase change heat transfer of a phase change material (PCM) impregnated in open-cell metal foam. Idealized tetrakaidecahedron was selected as the representing unit cell (UC) to mimic the real foam microstructure and an assembly of tetrakaidecahedron UCs with six lines and three rows was built for computation. Phase change heat transfer in PCM and coupled heat transfer between PCM and metallic ligaments were directly simulated. To address the contribution of natural convection in the melting phase to the overall melting time and pore-scaled melting interface, natural convection in the interstitial fluid was modeled and compared with the conduction-dominated case. Results demonstrated that micro-foam can significantly accelerate the melting phase change rate and further enhancement was observed at pore scale when natural convection in the melting phase was triggered on.

Isobutane (R600a) is widely used in small capacity refrigeration equipment, especially domestic refrigerator. Knowledge of refrigerant absorption in lubricant oil is one of the essential factors for designing refrigeration system and choosing suitable oil. In this work, the liquid mole fractions of R600a in three linear chained pentaerythritol esters (pentaerythritol tetrabutyrate, pentaerythritol tetrahexanoate, and pentaerythritol tetraoctanoate) were measured from 293.15 K to 348.15 K by means of isochoric saturation method. The measured data were modeled using the PR EOS and HVOS mixing rule combined with Wilson excess free-energy model. Average relative deviations between the calculated pressure from the model and measured results for R600a + pentaerythritol tetrabutyrate, R600a + pentaerythritol tetrahexanoate, and R600a + pentaerythritol tetraoctanoate systems were 0.74%, 0.90%, and 0.57%, respectively. Maximum relative deviations were 2.13%, 2.91%, and 2.13%, respectively.

Due to sustainable development, solar energy has drawn much attention and been widely applied in buildings. However, the application of solar energy is limited because of its instability, intermittency and low energy density in winter. In order to use low density and instable solar energy source for heating and improve the utilization efficiency of solar energy, a solar phase change thermal storage (SPCTS) heating system using a radiant-capillary-terminal (RCT) to effectively match the low temperature hot water, a phase change thermal storage (PCTS) to store and continuously utilize the solar energy, and an air source heat pump (ASHP) as an alternate energy, was proposed and set up in this research. Series of experiments were conducted to obtain the relation between the solar radiation utilization rate and the heating supply temperatures, and to evaluate the performance of the RCT module and the indoor thermal environment of the system for its practical application in a residential building in the north-western City of Xi’an, China. The results show that energy saving of the solar heating system can be significantly improved by reducing the supplied water temperature, and the supplied water temperature of the RCT would be no more than 35 °C. The capillary radiation heating can adopt a lower water temperature and create a good thermal comfort environment as well. These results may lead to the development of designing and distributing the solar energy for building heating during winter.

Building energy plays a significant role in total energy consumption in China. It is widely recognized that the insulation performance of the external envelops is a critical factor for energy consumption of building air conditioning system. In this study, the effects of building external wall’s insulation thickness and position on the heating and cooling loads of a commercial building studied for five cities from different climatic zones of China, namely, Harbin, Xi’an, Shanghai, Kunming and Guangzhou, are investigated numerically. The wall’s optimum insulation thicknesses of the building simulated in these cities are determined by the life cycle cost analysis (LCCA) method. Meanwhile, the different positions of insulation layer embedded in the wall are investigated in terms of the time lag and decrement factor. The results show that the increase of insulation thickness has a significant effect on the building heating load, inversely it exhibits a relatively small effect on the building cooling load. The analysis indicates that building energy savings vary from different climatic zones. For a given wall insulation and the same building conditions, the largest building energy savings are achieved in Harbin, and energy savings of other cities follow the order of Xi’an, Shanghai, Kunming and Guangzhou. The variation of building energy savings in Guangzhou is insignificant along with the increase of the insulation thickness. Using expanded polystyrene as insulation layer material, the optimum insulation layers of the building in Harbin, Xi’an, Shanghai, Kunming and Guangzhou are founded to be 80 mm, 60 mm, 40 mm, 40 mm, and 20 mm, respectively.

Latent heat thermal energy storage (LHTES) is a promising way to smooth the discrepancy between energy supply and demand, and it is now becoming increasingly significant in the heating and cooling of buildings. However, the low thermal conductivity of the available PCMs require more efficient configuration of LHTES system in reducing the melting time. In order to evaluate the dynamic thermal performances of LHTES unit in shell and tube heat exchanger, the two-HTF-passage configuration and single-pass configuration are numerically investigated. The results show that the central and annular injection in two-HTF-passage configuration has little influence on the transient melting interface location and temperature in the PCM domain and both can effectively enhance the phase change heat transfer, but the HTF tube injection in single-pass configuration shows a significantly poor performance.

The construction of eco-city is a hot spot nowadays, aiming to build harmony between human and nature. Ecological city is able to deal with the relationship between human and the environment, whose key point is to establish a comfortable outdoor thermal environment. To evaluate the built microclimate environment, a campus area located in Northwest China was selected. Different scenarios with extra greening, high albedo pavement materials, water body and their combinations were numerically analyzed through Universal Thermal Climate Index (UTCI) incorporated in the software ENVI-met V4.0. Results demonstrated that the scenarios with water body or high albedo materials was found to have little contribution to reduce UTCI, while the green scenario significantly reduced the UTCI peak (6.9 C) and also the duration (4.5 hours) of heat stress. The present study may be used as a guide for urban planning and construction for ecological city.

In recent years, a primary concern in the development of electronic technology is high heat dissipation of power devices. The advantages of unique thermal physical properties of graphite foam raise up the possibility of developing pool boiling system with better heat transfer efficiency. A compact thermosyphon was developed with graphite foam insertions to explore how different parameters affect boiling performance. Heater wall temperature, superheat, departure frequency of bubbles, and thermal resistance of the system were analyzed. The results indicated that the boiling performance is affected significantly by thermal conductivity and pore diameter of graphite foam. A proposed heat transfer empirical correlation reflecting the relations between graphite foam micro structures and pool boiling performance of Novec7100 was developed in this paper.

We present numerical models to account for the transient free convection in the melted phase and heat transfer in porous foams filled in cavities with various aspect ratios. A visualization test-bed is set up, allowing for observing the solid-liquid interface and measuring internal temperature distribution. Simulation results are analyzed in terms of the melting rate, flow streamline and phase interface, temperature response, heat storage capacity and heat transfer performance. It is found that for a given aspect ratio, the inclination of the heating surface has a negligible influence on the melting rate, temperature uniformity, temperature response, and energy storage capacity for phase change materials in metal foam. However, for different aspect ratios, the case with a smaller aspect ratio (AR = 0.1) outperforms the one with a bigger ratio (AR = 8.0): a 4.96 and 15.85 times higher temperature uniformity and temperature response are achieved.

A two-dimensional axisymmetric mathematical model was established to describe the pressure-driven water vapor separation in the hollow fiber composite membrane for air dehumidification. The developed transport model considered the permeation in the dense layer and the diffusion in the porous membrane substrate, in which the mass and momentum balance equations were coupled. The predicted results by the simulation model was consistent well with the experimental data. The velocity, pressure and concentration profiles and the mass transfer process in a single hollow fiber membrane were then solved and analyzed in detail, including the effects of feed velocity, feed humidity and transmembrane pressure on the dehumidification performance. The results show that the amount of water vapor separation (outlet humidity) is more sensitive to the medium feed velocity with the separation amount about twice than that of high and low velocities. The separated amount of water vapor by the membrane is less dependent on the feed inlet humidity. And the air dehumidification performance of the membrane could be realized effectively until the transmembrane pressure over a critical value, which is 1.0 bar in this model. The findings deliver an insight into the mass transport in the membrane-based dehumidification process, with the aims to provide a useful reference to the design, process optimization and module development using hollow fiber membrane.

Due to the groundwater migration in the underground aquifer, the heat transfer between ground heat exchangers and surrounding ground changes from heat conduction to the conjugated conduction–convection mode. To investigate the aquifer effects on the ground temperature distribution surrounding the ground heat exchanger, a realistic model was established and numerically solved, including a ground heat exchanger and alternatively stacked aquifer and aquifuge layers. The results show that a variation in groundwater velocity would result in a significant fluctuation in the aquifer temperature field close to the ground heat exchanger, but has less effect on the aquifer temperature field away from the ground heat exchanger. The difference between the initial temperature and local stable ground temperature, and the time for the aquifer to reach the stable temperature are both negatively correlated with the groundwater velocity, and positively correlated with the distance to ground heat exchanger on the downstream. The thermal influence radii are ranging from 7.4 m to 143.0 m in the aquifer layer under tested groundwater velocities ranged from 3.15 m/a to 315 m/a respectively, while the radii of aquifuge layer are about 8.3–8.4 m. There exists a critical velocity that makes the radius of thermal influence in the aquifer layer the same as that in the aquifuge layer. When the groundwater velocity is greater than the critical velocity, the thermal influence radius shows an increasing trend with the increase of aquifer layer thickness, while it shows a reversed trend for the velocity lower than the critical velocity.

Methoxymethane (called dimethyl ether, DME) is recognized as a promising alternative refrigerant. Knowledge of the phase equilibrium behavior of DME-lubricant is essential for selecting a suitable oil. A long-term systematic research program on the phase equilibrium for systems of DME and oils was carried out in our laboratory, making the effort to determine its dependence on the molecular structure of oils, temperature, and pressure. In this article, phase equilibrium data of the DME + pentaerythritol tetraheptanoate system and the DME + pentaerythritol tetranonanoate system were reported from (293.15 to 353.15) K using the isochoric saturation method. Experimental data of phase equilibrium were modeled by the Peng–Robinson (PR) equation of state using the HVOS mixing rule and the NRTL excess-free-energy model. Moreover, the influence of the molecular weight of pentaerythritol esters on the phase equilibrium behavior of DME/ester mixtures was analyzed.

Solidification of distilled water saturated in open-cell metallic foams with graded morphologies was investigated experimentally. Open-cell foams having different morphological properties including porosity, pore density (PPI) and materials for the porous matrix were cut into pieces and stacked up, forming a whole porous layer with gradient morphological features. Systematic measurements of temporal solidification front and full solidification time for distilled water saturated in the morphology gradient foams were carried out. Meanwhile, numerical simulations of solidification in fluid-saturated metallic foams with uniform morphological properties were performed. It was found that the presence of gradient in foam properties affect significantly the solidification rate and full solidification time. The results showed that compared to the single-layered foam with fixed morphology, the stacked foams with properly designed morphology gradient would reduce more effectively the full solidification time, due to the enhanced heat transfer.

The modern development of electric vehicle requires higher power density to be packed into a battery pack. It is always expected that the battery can be arranged as much as possible, however, which leads to the serious thermal management issue due to the heat generation inside the battery packs. As extreme temperature affects performance, reliability, safety and lifespan of batteries, thermal management of battery system is critical to the success of all electric vehicles. The objective of this study is to explore the air cooling capability on the temperature uniformity and hotspots mitigation of a compact battery pack subject to various air flow paths, airflow rates. The numerical results show that the improvement of effective heat transfer areas between air-coolant and battery surfaces is able to obviously lower the maximum temperature and improve the maximum temperature difference in the densely-packed battery box.