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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.

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.

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.

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%.

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.

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.

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.

When the outdoor air temperature is low and relative humidity is high, frost will occur and accumulate on the outdoor coil of an ASHP unit, which may decrease the heating performances of the ASHP unit to a large degree. In addition, the defrosting performances of the commonly used defrosting method (reverse cycle defrosting) are poor due to the closed indoor air fan and insufficient energy stored in a conventional indoor coil. On the other hand, the conventional indoor coil based on forced convective heat transfer may cause strong draught sensation and dry eye problem and make users feel less comfortable than radiant heating terminals. Therefore, to improve the system defrosting performances and combine the merits of the conventional indoor coil and those of radiant heating terminals, a novel radiant-convective heating terminal was developed and integrated with an ASHP unit. The frosting and defrosting performances of the novel system were experimentally investigated, and the results showed that the average values of radiant panel surface temperature, outlet air temperature for the novel heating terminal, and system COP were 36.6 °C, 29.4 °C, and 2.78, respectively, during a 66-min frosting period (air temperature is 2.0 °C and relative humidity 84.0%). In addition, the ratio of the radiant heating capacity to natural convective heating capacity to forced convective heating capacity remained at around 1.5:1.0:7.4 during the whole frosting period. Furthermore, the experimental results demonstrated that the novel heating terminal could provide sufficient energy for the defrosting, and some energy could be provided for space heating through radiant and natural convective heat transfer during defrosting. The defrosting and resuming heating periods were 105 and 65 s, respectively.

Data centers undertake transfer, calculation, and store of important information, whose suitable thermal environment is necessary for the safe and reliable operation of information technology (IT) equipment. However, in case of the emergency failure or power outage of the air-conditioning system, the inappropriate thermal environment cannot keep the proper operation of IT equipment. Therefore, a novel cooling system is proposed to maintain the thermal environment of server rooms, in which the liquid nitrogen as refrigerant flows into the spiral finned tube heat exchanger (FTHE) by phase changing to take away indoor heat. The effect of horizontal spacings and heights of the FTHE on the thermal environment are investigated numerically. The results display that the indoor air temperature is divided by FTHE. When the height of FTHE is 2.6~2.9m, the higher the FTHE, the more uniform the indoor temperature distribution. When the FTHE is higher than 3.2 m, the maximum temperature of the heat source is more than 62.6°C, exceeding the temperature tolerance limit. In addition, if space permits, the dislocation layout and the fixed layout can be selected, which perform well in both temperature uniformity and heat source cooling. This investigation provides support for the arrangement of the novel cooling system.

In order to investigate the condensation heat transfer and pressure drop characteristics in tube-side flow of spiral wound heat exchanger (SWHE), a computational model based on two-fluid multiphase model, k-e turbulence model and thermal phase change model was established considering the gravity and surface tension. Also, a calculation formula for mean interfacial length between vapor phase and liquid phase was deduced and the wall contact angle was discussed. Based on the above model, numerical simulations were carried out on the condensation flow and heat transfer for propane upward flow in a spiral pipe. Compared with experimental data, it shows that the errors for the simulation results based on the new model are within ±15% under different operating parameters. Meanwhile, the heat transfer coefficient and frictional pressure drop are mainly influenced by vapor quality, mass flux and saturation pressure while the heat flux almost does not affect them. Comparing with the existing correlations, the improved correlations based on Boyko’s correlation and Fuchs’s correlation have been developed to predict condensation heat transfer coefficients and frictional pressure drop. These results will provide some constructive instructions for the understanding of condensation heat transfer and pressure drop characteristics in the spiral pipe, as well as the design and prediction of condensation heat transfer and pressure drop performance in SWHE.

A study was conducted to investigate the void fraction and pressure drop characteristics of methane/propane under different mass flux, saturation pressure and heat flux in a helically coiled tube, and the effects of distribution ratio (methane/propane) 50/50, 66/34 and 80/20 mole% were also analyzed. The friction pressure drop increased with the mass flux increased. Similarly, with the decrease of saturation pressure, friction pressure drops decreased. For a different distribution ratio, the friction pressure loss increases as the propane component increased in the mixture. Meanwhile, existing correlation models of different forms were used to evaluate the void fraction, and the Ahrens model provided the best accuracy with a MARD (mean absolute relative deviation) of 2.85%. In addition, the existing pressure drop correlations were used to compare with simulated data. Friedel correlation gave a well prediction for non-annular data with a MARD of 16.1%, while Cavallini correlation can well predict annular flow data with a MARD of 16.6%. Finally, considering the influence of flow regime transition, a new frictional pressure drop correlative was proposed, which can predict the data well with MARD of 5.4%.

The fault diagnosis method based on ResNet50 convolutional neural network and migration learning is proposed as a way of improving the gearbox fault diagnosis. Firstly, exporting the normal and faulty data of the gearbox. Then converting the exported data into one-dimensional images to and generate the corresponding training and test sets, train in the model to get accuracy of the test set and training set. After fine adjustment, it is used for gearbox fault diagnosis, compared with the VGG16, ResNet101, and GoogleNet model, the accuracy of ResNet50 is above 86.6%. It has a good prospect of application, and its effect is obviously better than that of other models.

Thermal active building system (TABS) is promising to increase the flexibility of building energy systems. In this research, the thermal characteristics of a ventilated mortar block in the operation mode that the air is directly exhausted are analyzed by models. The block is integrated with phase change material (PCM) and ventilation tubes to increase both heat storage capacity and heat extraction flexibility. The simplified thermal model of the block, which combines the thermal network model and number of transfer unit model (NTU), is established and rearranged in standard state-space form based on the experimental system. The calculation process is also improved. Different modeling methods are compared, and the accuracy of the model is also validated by the testing data of three kinds of ventilated mortar blocks, which have different layers of PCM inside. Furthermore, parametric analysis is also conducted. The results show that for the current operational mode where the air is directly exhausted, the thickness of the mortar block and the diameter of the tube have a dominant impact on the surface and outlet air temperature, while velocity has a lower impact on the outlet air temperature.

Summary Electrochemical CO2 reduction to multi-carbon fuels and chemicals is intriguing but remains a challenge. Here, we report that a combination of Sn doping and creation of oxygen vacancies (VO) can synergistically boost CO2 reduction to C2H4 over CuO nanosheets with an onset potential of −0.7 V (versus reversible hydrogen electrode). The activity and selectivity of CuO can be easily tuned by manipulation of Sn dopant and VO contents. The Faradaic efficiency toward C2H4 formation over Sn-doped CuO(VO) approaches 48.5% ± 1.2%, which maintains stability over 24 h at a mild overpotential, in contrast to a maximum of 26.8% ± 2.2% over pristine CuO. The Sn-doped CuO(VO) catalyst presents an approximately 2.3-fold improvement in C2H4 current compared to undoped CuO at similar overpotentials. Theoretical calculations further show that doping of Vo-enriched CuO surface by Sn lowers the dimerization energy of adsorbed CO intermediate, thereby promoting C–C coupling to yield C2H4.

In order to understand the phenomenon of saturated boiling heat transfer in a vertical rectangular minichannel of the plate-fin heat exchanger (PFHE), the saturated boiling mechanism was investigated by ANSYS CFX based on the model which was validated by the experimental data from literature and the heat transfer correlation by Liu & Winterton's model was improved in terms of the experimental data from literature. The results showed that the deviation between simulation results and experiments is within ±15%. According to the simulation results, the main boiling mechanism is forced convective boiling for saturated boiling heat transfer at high vapor quality while the contribution of nucleate boiling is slight. At the same time, the evaporation of dispersed liquid phase should make the essential contribution to heat transfer. The improved correlation in terms of the experimental data from literature is in good agreement with the simulation results. The deviation between correlation calculations and simulation results is less than ±30%. These results will provide some constructive instructions for the understanding of saturated boiling phenomenon in a vertical rectangular minichannel, and for the design and prediction of heat transfer performance in PFHE.

Adding an energy accumulator to an air source heat pump (ASHP) unit can significantly improve its defrosting performances. However, the added energy accumulator may impact the system performances during heating period, which was rarely investigated in the published studies, especially for multi-split ASHP units (a kind of more and more widely used ASHP unit). In this paper, a comparative study on system performances of a multi-split ASHP unit under frosting condition with different energy accumulator structures and energy storage methods was experimentally carried out. The experimental results showed that the multi-ASHP unit employing fin-tube energy accumulator with serial energy storage method can achieve the longest heating period, which was 3.3%, 13.4%, and 9.4% longer than that employing spiral-tube energy accumulator with serial energy storage method, spiral-tube energy accumulator with parallel energy storage method, and fin-tube energy accumulator with parallel energy storage method, respectively. For spiral-tube energy accumulator using serial energy storage method, using parallel energy storage method, can shorten the energy storage period from 59 to 33 min. For fin-tube energy accumulator using serial energy storage method, using parallel energy storage method can shorten the energy storage period from 33 to 6 min. In addition, compared to serial energy storage method, using parallel energy storage method may significantly reduce the heating capacity, input power and heating COP of the multi-split ASHP unit during the energy storage period.

When used in cold environment, the conventional flat plate solar collectors and all-glass evacuated tube solar collectors will cause various problems, such as large heat loss, low efficiency, freeze and tube-burst, which severely limit their applications. In this paper, a special small-sized parabolic trough solar collector (PTC), which could overcome the shortcomings of conventional solar collectors, was proposed for water heating in cold areas. An experimental platform was developed, and extensive tests were conducted to evaluate the characteristics of the proposed PTC. It was found that the thermal efficiency of the proposed PTC reached about 67% even under the condition of solar radiation of less than 310 W/m 2 , indicating that the PTC could collect solar radiation efficiently. The results also showed that when the fluid temperature was under 100 °C, the thermal efficiency was improved with increased fluid temperature, due to the increase of Reynolds number caused by the great variation of thermophysical parameters of the heat transfer fluid (HTF), which resulted from the increasing fluid temperature. Both the frosting on the reflector and the ambient wind velocity weakened the thermal efficiency greatly. The highest thermal efficiencies were respectively about 26% and 56% under condition of frosting and wind velocity of 5.0 m/s. The comparison test showed the coated double glazing receiver had a longer temperature response delay to the deflected sunlight than that of the uncoated one. The tested PTC system operated normally in low fluid temperature condition, showing great anti-freezing property in cold environment.

Since the temperature of shower drain water (SDW) is relatively high, lots of heat is wasted with the discharge of SDW. Therefore, the recovery of this unutilized heat from SDW shows great potential in improving the building energy efficiency. In this paper, a novel heat pump water heater assisted with SDW for small single family was proposed, which could effectively recover the energy in domestic SDW. To improve its performance, a shower waste heat extraction device (WHED) with water pre-heated loops was designed. A prototype of the system was firstly set up, and then the system performances under different conditions were experimented and discussed. The experimental results showed that approximately 70% of energy could be saved using this novel heat pump water heater, compared with the traditional electric water heater. Furthermore, the COP of the system could be improved observably when using water pre-heated loops. Thus the implementation of this novel heat pump water heater was verified to be capable of reducing energy usage and CO2 emissions significantly.

This paper presents a new design paradigm of ground heat exchanger (GHE), which takes account of uncertainty in the estimation of geothermal properties, including ground thermal conductivity and borehole thermal resistance from a thermal response test (TRT). Some challenges during the TRT parameter estimation process are discussed: A sensitivity analysis to a more accurate solution of the infinite line source model is introduced to identify the parameters to be estimated; a nonlinear least-square method is employed to estimate the selected parameters; and then validated by a traversing method. Afterwards, a case study is conducted to illustrate how the proposed method can be employed to a practical engineering application. The proposed uncertainty design method that provides a quantified margin of design output can be an alternative to traditional deterministic methods that simply add safety factor to expected design value.

Zero energy buildings have attracted more and more attention recently in the world. This research work studied the feasibility of a 12-storey plank-type building achieving zero energy. The study used Software TRNbuild to establish a 12-story residential building, as a reference building, based on DB11/891—2012(Design Standard for Energy Efficiency of Residential Buildings of Beijing). On the one hand, the study does passive building design, including high performance envelope, air-tightness and fresh air heat recovery efficiency, to reduce heating and cooling load. On the other hand, TRNSYS was used to simulate building energy system, such as solar domestic hot water systems (SDHW), unitary air-source heat pump for space heating and cooling, and renewable electricity system-PV. Annual energy consumption of reference buildings (central heating system for heating, ASHP for cooling) is 30.33 kwh/(m2•a) . By contrast, that of NZEBs(ASHP for heating and cooling)is 11.1 kwh/(m2•a), declining by more than half. PV array production on the roof can meets its energy demand. If domestic hot water energy consumption is also included, PV array production on the roof can offer 95.8% of total electricity demand. In general, it's entirely feasible for residential buildings in Beijing to achieve nearly zero energy.

In order to investigate the distribution of PM2.5 in indoor air, a model was established. The distribution of PM2.5 in indoor was simulated in the condition of natural ventilation and air conditioning ventilation with different velocities. The influence of different ventilation methods was analyzed on the distribution of PM2.5 in indoor. The results showed that the PM2.5 was gathered near the inlet, outlet and near the wall in indoor. The distribution of PM2.5 was directly impacted by the ventilation method and the concentration of PM2.5 was lower in natural ventilation than that in air conditioning ventilation.

The purpose of this study was to investigate the effects of wastewater velocity and installation location of a shell-and-tube heat exchanger on particle fouling deposited within the heat exchanger. Three long-term fouling tests with the heat exchanger installed at the shoot-outlet of a pump with varied wastewater flow rates (low, medium, and high), and one test with the heat exchanger installed at the suction-inlet of a pump at a constant (medium) flow rate were conducted. Variation of the heat transfer coefficient and fouling resistance was measured for each test and a sample of the accumulated foulant was collected at the end of each test to determine its particle size distribution. The particle size distribution of the foulant collected from each test case was analyzed and compared to the size distribution of particles in the wastewater. Results suggested that the diameters of particles deposited on the tube surfaces were mainly in the range of 1.5–88 μm. The average particle diameter of fouling was 40.8 μm at a velocity of 0.31 m/s (low), 24.4 μm at a velocity of 0.46 m/s (medium), and 18.6 μm at a velocity of 0.69 m/s (high). Asymptotic fouling resistances were 1.1 × 10−3, 0.59 × 10−3, and 0.22 × 10−3 m2 K/W respectively for the low, medium and high velocities. In addition, negative fouling resistances were observed at the beginning of fouling development with low and medium wastewater velocities. Results also showed that both the asymptotic fouling resistances and the average particle diameter of fouling obtained with the heat exchanger installed at the suction-inlet of pump were larger than that with heat exchanger installed at the shoot-outlet. On average, 71% (by mass) of fouling consisted of ash ingredient.

An experimental and simulation investigation of condensation flow pattern and heat transfer characteristics of zeotropic hydrocarbon mixtures methane/propane and ethane/propane in a helical tube was presented. Flow visualization was conducted to capture flow pattern during flow condensation. The flow mechanisms were categorized into six different flow patterns: slug flow, stratified flow, transition flow, wavy flow, half-annular flow and annular flow. In addition, several existing two-phase flow pattern maps in horizontal tube were compared with the flow pattern data. Then a new flow pattern transition line between annular and non-annular flow pattern was proposed. Based on the flow pattern transition line, the heat transfer data under different flow pattern were compared with the existing heat transfer corrections. Finally, an improved heat transfer correlation was proposed and well coincided with the data with a mean absolute relative deviation (MARD) of 13.8%.

Frost formation on the outdoor coil surface of an air source heat pump (ASHP) unit may occur when it is used for space heating at a low ambient temperature in winter. To reduce the impact of frosting on the operational performance and energy efficiency of ASHPs, a novel non-frosting air-source heat pump (NASHP) system was proposed. The detailed introduction of NASHP prototype was given, and its test rig was developed, as well as its operating principles and modes. Then the characteristics of some conventional dehumidification solutions were compared; the glycerol was selected as spray solution for NASHP system, due to its great influence on the operating performance of the system. The glycerol solutions with different concentration and different mass flow were investigated experimentally, and the best practice by which NASHP system has the most remarkable efficiency was found finally. Such results will provide helpful reference for the potential application of NASHP system and future research work.

When an air source heat pump (ASHP) operates in heating mode, frost can be accumulated on the surface of its finned outdoor coil. Frosting deteriorates the operation and energy efficiency of the ASHP and periodic defrosting becomes necessary. Currently the most widely used standard defrosting method for ASHPs is reverse cycle defrost. On the other hand, electronic expansion valves (EEVs) are commonly used in heat pump/refrigeration systems, including ASHP units, as throttle regulators of refrigerant flow. This paper reports on an experimental investigation of the performance of a reverse cycle defrost operation for a 6.5 kW experimental heating capacity residential ASHP whose outdoor coil had four-parallel refrigerant circuits, and with an EEV as the refrigerant flow throttle regulator. The detailed descriptions of the experimental ASHP unit and the experimental procedures of ASHP are firstly presented. This is followed by reporting the comparative experiments of two control strategies for the EEV to investigate their effects on defrosting performance: the EEV being fully open and the EEV being regulated by a degree of refrigerant superheat (DS) controller. Experimental results revealed that when the EEV was regulated by the DS controller during defrosting, a higher defrosting efficiency and less heat wastage would be resulted in.

Air source heat pump water heater/chiller (ASHPWHC) units, a cooling and heating source for buildings becomes increasingly popular. However, when such a unit is operated as a heating source under low ambient temperature in winter, the formation of frost on the surface of its airside heat exchanger becomes problematic, leading to the degradation of the heat exchanger's performance or even the shutdown of a unit. Therefore it is necessary to have a detailed investigation on the operational characteristic of the airside heat exchanger in an ASHPWHC unit under frosting in order to optimize its structural layout, thus increasing its energy efficiency and operational reliability. This paper first reports on the development of a distributed mathematical model of the airside heat exchanger under frosting in an ASHPWHC unit. The model, firstly seen in open literature, consists of a frosting sub-model and a heat exchanger sub-model. This is followed by an evaluation of operational characteristics of the airside heat exchanger under frosting in an ASHPWHC unit using the model developed. In addition, the impacts of frosting on the operational performance of an ASHPWHC unit were also evaluated. The discussions of optimizing the structural layout of finned tubes used in an airside heat exchanger and improving defrosting control measures are also included in analyzing the simulated results.

A transient three-dimensional volume of fluid (VOF) simulation on condensation of upward flow of wet steam inside a 12 mm i.d. vertical pipe is presented. The effect of gravity and surface tension are taken into account. A uniform wall temperature has been fixed as boundary conditions. The mass flux is 130~6400 kg m−2's−1and the turbulence inside the vapor phase and liquid phase have been handled by Reynolds stress model (RSM). The vapor quality of fluid is 0~0.4. The numerical simulation results show that, in all the simulation conditions, the bubbly flow, slug flow, churn flow, wispy annular flow, and annular flow are observed; in addition, the results of flow pattern are in good agreement with the regime map from Hewitt and Roberts. The typical velocity field characteristic of each flow pattern and the effect of velocity field on heat transfer of condensation are analyzed, indicating that the slug flow and churn flow have obvious local eddy. However, no obvious eddy is observed in other flow patterns and the streamlines are almost parallel to the flow direction. The simulation results of heat transfer coefficients and frictional pressure drop show good agreement with the correlations from existing literatures.

In the heating system, the water ejector can use the “surplus pressure” to pump return water from return pipe instead of using mixing pumps, thus achieving the purpose of energy conservation. The water ejector is normally devised in the design condition, however, it usually does not operate at the design point because the pressure and flow rate of water in water ejector varies with the fluctuation of adjacent heat consumer, which causes the deviation of the indoor air temperature from the designed value. In the present study, the allowed pressure fluctuation of water ejector was investigated under the condition that the indoor air temperature was maintained in a certain range. The experimental results showed that when indoor air temperature was set at °C, the allowed pressure fluctuation range for the water ejector in Harbin was -10%∼20%, and it expanded as the outdoor design temperature increased and/or the supply water temperature of primary network reduced.