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A numerical model by coupling Monte Carlo Ray Tracing (MCRT) and Computational Fluid Dynamics (CFD) was built to explore the convective heat loss of a cylindrical receiver with built-in coiled tube. Noted that the non-uniform heat flux boundary of the receiver was obtained by optical simulation and the effect of existence of the dish concentrator was taken into account. The variation of flow field and convective heat loss with inclination α, wind direction φ, wind velocity V were analyzed in detail. The results indicate that the presence of concentrator in a windy environment can significantly interfere with the air flow thus affecting the convective heat loss of receiver, and such effect gradually weakens with the increase of α. Except for the case of φ = -90° and 0°≤α ≤ 17°, the convective heat loss with concentrator is always less than that without concentrator. The effect of φ on convective heat loss is complicated and has a great relationship with both V and α. In most cases except for φ = 0°, the convective heat loss takes on a trend of first decreasing and then increasing with varying α. Additionally, a Nusselt number correlation for predicting the convective heat loss of receiver under the effect of dish concentrator was proposed.

A novel dual-channel photovoltaic/thermal (PV/T) system featured by a nanofluid-based spectrum-splitting top channel and an S-shaped bottom channel (Model A) was proposed. The temperature uniformity of PV panel and performance of Model A under different structural and operational parameters were discussed through 3-D numerical simulation. To quantitatively reflect the temperature uniformity of PV panel, two evaluation criteria were presented. The performance of Model A was compared with that of PV/T system with two rectangular channels above/below PV panel (Model B) and PV/T system only with an S-shaped channel below PV panel (Model C). The results illustrate that mass flow rate has the greatest influence on temperature uniformity, whilst the influence of inlet temperature and wind velocity is much lesser. The optimal values of the optical nanofluid thickness and mass flow rate are 10 mm and 0.008 kg/s, at which the total energy efficiency and overall exergy efficiency reaching maximum of 86.97% and 13.80% respectively. The temperature uniformity of PV panel in Model A is better than Model B and Model C, besides, the total energy efficiency of Model A is 0.2% and 3.17% higher than those of Model B and Model C in a certain condition.

Photocatalytic (PC)-Trombe wall with dual functions of space heating and air purification has a promising way in solar architecture integration. In this paper, a two-dimensional numerical model on air purification and thermal performance of PC-Trombe was established based on relevant experiments in literature. The coupling relations and sequence among the low Reynolds number k-e model, Langmuri-Hinshelwood kinetics, natural convection heat transfer and convection-diffusion equations were established and used to solve multiple physical fields coupling. The numerical results were in good agreement with the experimental data in related literature. The effects of environmental factors, geometric structures and operating conditions on the thermal efficiency and formaldehyde degradation rate of PC-Trombe wall were investigated. The results show that the thermal efficiency increases with increasing solar radiation and ambient temperature, but it is opposite for inlet temperature of air and ambient wind velocity. However, the thermal efficiency increases first and then decreases as the channel width increases, the maximum thermal efficiency is 52.98% when the width is 0.04 m. For the air purification rate, all factors also show the trend of increasing first and decreasing afterward, there is a maximum air purification rate of 2.91 μg/s when the channel width is 0.05 m.

Background Overseas study trips can enhance healthcare students’ intercultural communication competence. An opportunity to immerse in the new culture enables them to develop their ability to offer services to people from different countries. However, the role that open-mindedness (i.e., a personality trait) can play in this process has not been explored. Methods The present study adopted a mixed-method design to identify how open-mindedness trait affected this overseas learning process. Thirty-two undergraduate healthcare students in Australia took part in the study. Questionnaires, which measured socio-demographic information, intercultural communication competence and open-mindedness trait were administered to the participants before and after their overseas trip. Half of the participants (n = 16) were interviewed after the overseas trip. Results The correlational analysis showed that the open-mindedness trait was correlated with cultural skills, a component of intercultural communication competence, but not significant with the other three components. Three themes emerging from the qualitative data indicated that the open-mindedness trait affected students’ cultural exposure. This trait enabled participants to be actively involved in the immersion in the local culture. They were willing to learn from peer fellows, and keen to embrace novel challenges. Conclusion It is concluded that open-mindedness trait is vital for increasing cultural immersion, and hence promote intercultural communication skills.

In present work, a comprehensive simulation method coupled with Monte Carlo Ray Tracing (MCRT) method and Finite Volume Method (FVM) is employed to simulate the complex photo-thermal conversion of PDC system. The whole photo-thermal conversion process is divided into two sub-processes, namely PartⅠ receiver walls absorb solar energy as thermal energy, and PartⅡ receiver walls convey thermal energy to heat transfer fluid (HTF) and ambient air. PartⅠ (optical performance) is evaluated by MCRT and the solar flux distribution on walls is obtained. PartⅡ (thermal performance) is solved by FVM model in which the solar flux on walls is treated as a source term. It is shown that the legitimate adjustment of receiver position, rim angle, tilt angle and emissivity will increase photo-thermal conversion efficiency by 2.6%, 2.4%, 8% and 1.8% respectively. Appropriate mass flow rate in this work is chosen as 0.02 kg/s for insuring high outlet temperature with higher photo-thermal efficiency as possible. In addition, photo-thermal conversion efficiency will largely rise up 8% for every 0.1 growing of absorptivity. These results would enrich the literature archive tremendously and be needed for better solar power generation engineering design.

An investigation on the effect of cooling channel position on heat transfer characteristics and thermoelectric performance of air-cooled PV/T systems has been conducted numerically. Two design positions, cooling channels above PV panel (case1) and below PV panel (case2), were considered. It is found that the effect of internal radiation in the cooling channel on the system performance is greater for case1 in comparison to case2, while an opposite behavior is presented for the cooling effect on PV panels. Except for the effect of air inlet temperature, the magnitude and variation trend of the convective Nusselt number on PV panels are almost the same for two case systems. A maximum total exergy efficiency is obtained at the air inlet temperature of 298.15 K for case1 system and 295.65 K for case2 system. From the perspective of the amount of supplied energy, the case1 system is preferred. Detailed analysis focusing on the quality of energy should be carried out to determine the merits of case1 and case2 systems.

An axisymmetric 2-D mathematical model was established and the volume of fluid +method was adopted to numerically investigate the condensation heat transfer process of alkali metal in the alkali metal thermal to electric converter (AMTEC) porous wick condenser. The steady-state physical fields of working medium were obtained and the impacts of some relevant parameters including geometrical and operational parameters on condensation heat transfer characteristics were discussed. The results show that the thickness of the liquid sodium increases along the radial direction. The temperature distribution in liquid phase is approximately linear. The condensation rate at the phasechange interface decreases along the radial direction, and the cold end heat flux, q, increases initially and then decreases along the radial direction. The porous wick condenser has very limited self-adaptive ability once the mass flow rate, M , exceeds in some critical value. In addition, there is a corresponding T for a certain M to ensure the w in stable phase-change interface. The performance of AMTEC can be enhanced by reducing the distance between artery and cell wall.

The flow state undergoes a series of transitions with varing inclination of the shallow enclosure constituted in the glass-covered PV-T system. Based on this fact, a three-dimensional unsteady numerical model has been established to investigate the flow mechanism. The surface radiation and PV operating characteristic were taken into consideration. The critical tilt angle from steady to unsteady state was determined under different heating conditions and initial conditions. With the decreasing of inclination, main features including spectrum amplitude, velocity distribution and temperature contours were specified in three flow states. Results show that in general, the critical tilt angle is a positive function of total input heat flux qt, the exception is the radiation uncoupled case of qt = 100 W/m2. When the reduction step size for inclination is fixed at only 1°, the derived critical tilt angle may be hysteretic. From the velocity contours, transverse roll in steady flow presents the dominant state. While during the transition process, the longitudinal flow is developed and superposed on the main flow step by step until the chaotic flow forms. In this state, continuous spectrum appears instead of several dominant frequencies observed in the periodic flow.

Under no-wind condition, heat dissipation in partitioned and non-partitioned rectangular enclosures formed by quartz glass cover and base plate made of composite stone was experimentally investigated. Internal and external combined heat transfer coefficients hin and hex of enclosure, total thermal resistance Rtot of heat dissipation and correlations of average radiative and convective heat loss Nusselt numbers outside the glass cover were obtained and discussed. Also, the impacts of the gradient parameter k and magnitude of heat flux and tilt angle were compared. Results show that the local temperature differences (tl − ta) on the base plate and glass cover change in the same trend, while the impacts of partitions on average temperature on glass cover is greater than that on base plate. Compared with non-partitioned condition, hex is decreased and hin is increased, meanwhile, Rtot is higher when tilt angle θ

In this paper, a new AMTEC/TAR hybrid system was proposed to utilize condensation heat of the alkali metal thermal to electric converter (AMTEC) as heat source for the triple-effect absorption refrigeration (TAR). Based on the first and second laws of thermodynamics, a theoretical analysis has been undertaken to evaluate the performance of the hybrid system. Meanwhile, the effects of the electrode current density, the condenser temperature in AMTEC, the pressure of medium pressure generator, and the temperatures of absorber, medium pressure generator and low pressure generator on the performance of the hybrid system were investigated and discussed. The results show that the AMTEC condensation heat can be effectively utilized by the TAR. When the evaporation temperature of AMTEC is 1200 K, the maximum value of exergetic efficiency of hybrid system is 42.7%, the input heat flow rate is 166.4 kW, and the output electric power and cooling load are 48.8 kW and 110.2 kW, respectively. The maximum exergy destruction rate is generally from the heat loss of AMTEC, but when the electrode current density is relatively high or the temperature of AMTEC evaporator is relatively low, the maximum exergy destruction rate comes out of the BASE.

A numerical model, whose computation domain contains the glazed shallow cavity and surrounding wind field, has been proposed to investigate the characteristics of heat dissipation from photovoltaic cells within the glazed cavity to the windy environment. To reflect the actual working characteristics, both the photoelectric conversion characteristic and surface radiation were considered. The temperature distribution of PV cells particularly the hot spot temperature has been displayed to reveal the effect of tilt angle (α) and wind velocity (v). Then a thorough analysis was presented in virtue of visualized results, convection Nusselt number inside the cavity (Nucin) and total heat loss coefficient (Ut). Meanwhile, efforts were also performed to compare the partitioned and non-partitioned cavities. Results show that hot spot position at α = 15° has the obvious diversity due to the variation of wind velocity. Unlike the increased Nucin, total heat loss coefficient of PV cells at v = 5 m/s decreases when the tilt angle shifts from 15° to 30°. Further, it is found that hot spot temperature difference between the three cells shrinks in the partitioned cavity, and the partition indeed contributes to the improvement of PV cells temperature uniformity, which plays a positive role in the protection of PV cell property.

A three-dimensional numerical model of water-cooled PV/T system with cooling channel above PV panel was built to analyze the influences of mass flow rate, cooling channel height, inlet water temperature and solar radiation intensity on heat transfer characteristics of cooling channel and performance of system. The Nusselt numbers of bottom and top surfaces of cooling channel were calculated, and the energy and exergy efficiencies of PV/T system were obtained. Results show that the Nusselt numbers of bottom and top surfaces perform opposite trend along the flow direction, and the convection heat transfer of bottom surface is better than that of top surface for almost all of cases. There is opposite direction of heat transfer within a certain distance from the entrance when inlet temperature of cooling medium is less than ambient temperature. As for system performance, both thermal efficiency and thermal exergy efficiency have greater variation amplitude when compared with electric efficiency and electric exergy efficiency respectively. The overall exergy efficiency of system achieves maximum at the mass flow rate of 0.003 kg/s and cooling channel height of 5 mm. Besides, the performance between the present system and traditional system was compared and some different conclusions have been drawn.

To utilize heat from round shaped heat sources or heat sinks effectively, a segmented annular thermoelectric generator was proposed. Each leg is composed of two materials with different optimum operating temperatures jointed in series. Based upon a developed theoretical model, the influences of annular shape parameter, height ratios of high temperature segment to leg in p- and n-type legs, temperature ratio and load ratio on the performance of segmented annular thermoelectric generator were studied. A finite element method was adopted to consider the Thomson effect and temperature-dependence of materials. Performance comparisons with simply non-segmented annular thermoelectric generators were conducted. For application security, the interface temperatures were analyzed. Results show that compared to a simply non-segmented annular thermoelectric generator, the superiority of segmented annular thermoelectric generator becomes visible with rising temperature ratio. As the annular shape parameter increases, the power rises firstly and then declines, and the optimal annular shape parameter is around 1.0, but not strictly equal to 1.0. Besides, the optimal ranges of height ratios in p- and n-type legs for higher performance are identified. The current study demonstrates the potential of segmented annular thermoelectric generator from the perspectives of performance and practicability.

Porous wick evaporator is an important power source of alkali metal thermal to electric converter (AMTEC) available for different kinds of energy sources including renewable energy. A bayonet tube structure is adopted in porous wick evaporator which is based on the principle of capillary pumped loop (CPL). The phase change heat transfer characteristics in the evaporator were numerically studied and the impact of the bayonet tube was investigated. The working fluid temperatures on two feature lines were selected to analyze the effect of bayonet tube on temperature of porous wick evaporator. The results show that for the evaporator using alkali metal as working fluid, a stable vapor-liquid interface is maintained at wick-groove interface. The bayonet tube divides the working fluid flow in porous wick into two parts, and the temperature change rule inside the bayonet tube is different from that outside the bayonet tube. The bayonet tube structure in the evaporator causes the temperature distribution in liquid channel to become more uniform and the maximum temperature to be decreased. The fluid temperature in the evaporator, especially in the liquid channel, can effectively be affected by the thermal resistance per unit area, length and diameter of bayonet tube. These parameters for bayonet tube must be limited within acceptable ranges in a specific operating condition, and there are optimum values to guarantee the best performance of the evaporator.

Based on the sparseness of research on the multi-droplet impact coupled with the anisotropy induced by cylindrical surface, in this paper, the hydrodynamics and heat transfer of multiple droplets successively impacting on cylindrical surface are deeply studied with three dimensional numerical simulation method. The comparison of single, two and even three droplets impacting on the heated cylindrical surface is carried out, and the effect of vertical space between successive droplets is discussed. Moreover, the influence of cylinder diameter on the hydrodynamics and heat transfer of multi-droplet impact is analyzed in detail. The results show that, the combination of multi-droplet interaction and anisotropy induced by cylindrical surface greatly affects the global heat flow, heat transfer coefficient, temperature distribution of liquid-vapor interface. By decreasing the vertical space between successive droplets impacting on the heated cylindrical surface, the heat transfer performance is obviously improved. Increasing the cylinder diameter boosts the heat transfer performance, but once the cylinder diameter augments to a certain value, the change of cylinder diameter no longer has an effect on the heat transfer performance, which is very close to the flat surface situation.

The maximum spreading length of liquid film after droplets impacting on cylindrical surfaces reflects one of the important aspects in the dynamic behaviors. In this paper, the parametric influence on the maximum spreading lengths in circumferential and axial directions, and the relationship between two maximum spreading lengths, were studied by the numerical simulation and theoretical analysis methods, respectively. The results show that, both of the apparent contact angle and Weber number have a crucial influence on the maximum spreading length of liquid film, but for the effect of cylinder diameter, when the cylinder diameter is much larger than the droplet's, the change of cylinder diameter does not affect the maximum spreading lengths in both directions significantly. In addition, an acceptable relationship between the maximum circumferential and axial spreading lengths has been obtained from the established theoretical analysis model. By comparison of the calculated results from the relationship with simulated and experimental data, the deviation is within ±25.8%.

A solar thermoelectric generation system characterized by Fresnel lens, cavity receiver and heat pipe, i.e., FCH-STGS, was proposed. To analyze the performance of FCH-STGS accurately, a comprehensive theoretical model was built, where a finite element method was employed to consider the Thomson effect and temperature-dependence of thermoelectric materials. With this model, the influences of emissivity of ceramic plate and environment factors such as solar irradiation, optical concentration ratio, wind speed, wind incident angle, system tilt angle and ambient temperature were discussed. Results show that the FCH-STGS has the potential to reach the output power and efficiency of 45.73 W and 3.289%. Both output power and efficiency of FCH-STGS can be improved by decreasing the emissivity of ceramic plate or ambient temperature, or increasing the total solar irradiation (product of solar irradiation and optical concentration ratio). However, the efficiency reduces slightly when the total solar irradiation exceeds a certain value. As the wind speed increases, both output power and efficiency rise firstly and then fall. Due to the high thermal efficiency of cavity (exceeding 85%), the effects of wind incident angle and system tilt angle are approximately negligible. Compared with the previous STGSs, the FCH-STGS is excellent in the perspectives of performance, economy and practicability.

A general mathematical model of the AMTEC/TEG hybrid system consisting of alkali metal thermal electric converter (AMTEC) and thermoelectric generator (TEG) has been developed, in which the load parameters and main geometric parameters were considered. Instead of specifying some parameters, the evaporating temperature and condensing temperature of the AMTEC as well as the operating temperature of the TEG subsystem were determined by solving energy balance equations. Results show that electrode current density has a quite noticeable influence on both AMTEC subsystem and TEG subsystem. The maximum conversion efficiencies for AMTEC and AMTEC/TEG are 27.42% and 31.33%, respectively. Besides, it is interesting to note that the optimal value of the ratio of thermoelectric module area to electrode area is always near 0.2 regardless of the ratio of evaporator heat transfer area to electrode area. The length of thermoelectric arms l and the ratio of the thermoelectric couple area to the total area of the thermoelectric module b are critical factors, b ≥ 0.55 and l ≤ 11 mm should be satisfied to obtain a compact and low-cost system.

For a round shaped heat source or heat sink, annular thermoelectric couples (ATCs) are designed to remove the contact thermal resistance induced by geometrical mismatching. In this study, the performance (power and efficiency) of ATCs subjected to a constant heat flux condition, which is often encountered in the utilization of solar energy and radiant heat, was assessed by a developed theoretical model. A finite element method was used to incorporate the temperature-dependence of thermoelectric materials and Thomson effect. The effect of annular shape parameter S r , a parameter characterizing the geometric feature of ATCs, was particularly stressed. Also the influences of external load, heat flux, heat transfer capability at the cold junction and leg height were analyzed. The performance comparisons with the condition of constant temperature were conducted. Results show that the influence of S r is not affected by other parameters. Contrary to a constant temperature condition, the performance enhances with S r deviating from 1 (i.e., flat-plate thermoelectric couple), and the power increases with an increase of leg height. The external load maximizing the performance is larger than the internal electrical resistance. The larger the heat flux is, the better the performance is. As the heat transfer capability at the cold junction increases, the performance reduces, first sharply and then leveling off. Since the performance of ATCs is superior to FTCs and the undesired contact thermal resistance can be eliminated by the use of ATCs, the potential of ATCs is demonstrated.

Taking isoflux upward-facing cylindrical cavities as object, the effect of aperture size on free convection and radiation heat transfer was studied experimentally and numerically. The influences of tilt angle and heat flux under different aperture sizes were also tested. The reliability of experiment was confirmed by experimental uncertainty analysis and reproducibility. The results indicate that the larger the aperture size is, the lower the temperature of cavity surfaces is and the stronger the free convection and radiation heat transfer are. The effect of aperture size on free convection heat transfer is of more significance for the cavities with small aperture size, while the behavior is opposite to its effect on radiation heat transfer. Aperture size has no influence on the variation trends of free convection and radiation heat transfer Nusselt numbers ( Nu c and Nu r ) with tilt angle and heat flux. To facilitate engineering applications, some suggestions and empirical correlations with high prediction accuracy were proposed.

Summary A concentrated solar-driven thermionic-thermoelectric hybrid generator composed of solar heat collector, thermionic generator (TIG), thermoelectric generator (TEG), and radiator is introduced in this paper. A theoretical model of thermoelectric conversion performance for the hybrid generator is built up based on the heat source of the concentrated solar radiation rather than isothermal heat source. Based on the model, the impacts of related parameters on the internal temperature distributions, output power, and efficiency have been discussed. Moreover, the optimal operating conditions of the TIG-TEG hybrid device at its maximum output power and efficiency have been determined. Results show that when cascading the TEG with the TIG, there is very little change of the TIG cathode temperature in most conditions, namely, TC ≈ TC′. Meanwhile, the anode temperature becomes higher, and the TEG cold end temperature T2 is close to the anode temperature TA′ for the single TIG system, ie, TA > TA′ ≈ T2. In theory, the optimal concentrated solar radiation I0 for the maximum output power Pmax and the maximum efficiency ηmax differs, which are I0,P = 2.5 × 106 W/m2 and I0,η = 2 × 106 W/m2, respectively, whereas the output power and efficiency of the TIG-TEG hybrid system simultaneously reach their maximum values when the optimal TIG anode temperature TA,opt = 1025 K, the optimal TIG output voltage Vopt = 2 V, and the optimal ratio of load resistance to internal resistance (R2/R)opt = 2. However, in practice, the parameter values of I0, ΦA, and TA should be strictly controlled under 1.8 × 106 W/m2, 1.4 eV, and 660 K, respectively. Generally, the maximum output power and efficiency of the hybrid TIG-TEG system are, respectively, 35% and 4% higher than that of the single TIG.

Due to the negative correlation between PV cell temperature and its efficiency, study on convection heat transfer from PV panel under real windy condition seems essential. Then a 3D numerical model has been established to investigate the impact of PV tilt angle, wind condition and different heat flux boundary conditions. To reveal the influence of photoelectric conversion characteristic on convection heat transfer, two boundary conditions, i.e., constant heat flux and heat flux varying with temperature are adopted and compared. Velocity vector field, temperature and velocity contours are also provided for detailed analysis. Within the studied range of tilt angle α , it is interesting to find there exists a minimum Nu c , and the corresponding α shifts to a larger value with increasing wind velocity. As wind direction varies, a decrease in Nu c is discovered at first, and then a rising tendency is followed. In addition, as wind velocity is relatively lower, higher heat flux enhances Nu c at random α , especially for the case of α ≥ 45°. Finally, a novel empirical correlation about convection Nusselt number incorporating the factors of tilt angle, wind direction and wind velocity is put forward.

With annual net profit of system as the objective function, the thermo-economic performance comparison between subcritical organic Rankine cycle (ORC) and LiBr absorption refrigerating cycle under different local electricity or cooling price and heat source conditions was conducted. Results show that, the thermo-economic performance of LiBr absorption refrigerating cycle and ORC using zeotropic mixture as working fluid are better than that of ORC using pure working fluid at any heat source temperature Tgi, heat source mass flow rate mg, local electricity price Se or cooling price Sc. There exist critical Tgi (Tgi,cr), critical mg (mg,cr) and critical Se (Se,cr) at which the economic benefit of ORC using zeotropic working fluid and refrigeration cycle is equal. If Tgi (or mg or Se) is lower than Tgi,cr (or mg,cr or Se,cr), the refrigeration cycle is prior, on the contrary, the ORC using zeotropic working fluid is preferential. The Tgi,cr, mg,cr and Se,cr are all increasing with the augment of the ratio of Sc to Se.

By using theoretical analysis method, effects of different parameters on condensation heat transfer characteristics of porous wick condenser of alkali metal thermal to electric converter (AMTEC) are discussed. The results show that, along the radius direction r of the condenser, the condensate film thickness δ ( r ) increases gradually, and the Nusselt number Nu ( r ) decreases. With increasing of the permeability K or decreasing of the effective thermal conductivity λ e and the heat transfer temperature difference Δ T , the condensate film thickness δ ( r ) decreases significantly, and the Nusselt number Nu ( r ) increases. However, the BASE tube temperature T B and condensate film temperature T S have little impact on condensation heat transfer characteristics, which indicates that for AMTEC condenser, the latent heat releasing dominates the total heat transfer while the radiation heat transfer almost has no influence.

Flow and heat transfer characteristics of alkali metal liquid in a pipe with inscribed regular polygon porous media are numerically investigated under local thermodynamic equilibrium condition. The effects of filling ways including inscribed regular polygon filling way and segmented inscribed square filling way under different Darcy number (10-6≤Da≤10) are analyzed. The results show that, the velocity near the wall is violently changed by inserting partially filled porous media due to the high resistance of porous media. For inscribed regular polygon filling way, the PEC value of inscribed square is the maximum, which makes it optimal for heat transfer enhancement. For segmented inscribed square filling way, the average Nusselt number increases as the filled ratio increases while decreases as the unit length increases. Owning to the dominant role of the entrance effect, the smaller the unit length is, the larger the PEC is. The PEC of 5:5 segmented filling way is found superior to other filling ways, possibly because the heat transfer enhancement and flow resistance control reach an excellent balance for that case.

In this paper, the mechanism and parameters affecting the contact time of droplet impacting on the solid surface were studied by incorporating numerical simulation method and water spring theory. An empirical correlation of dimensionless contact time was obtained and an exploring idea with the application of wettability-controlled surface was proposed to control the contact time. The results show that, the water spring theory can be extended to the situation of droplet impacting on cylindrical surface. And the introduction of surface wettability makes this theory more adaptive. The increase of Weber number or decrease of cylinder diameter augments the anisotropy and reduces the contact time effectively. And the surface wettability has the greatest effect on the contact time. The surface wettability or anisotropy caused by geometric modification can be introduced in the surface center as much as possible to control the contact time.

By establishing wind tunnel and employing electrical heating method, the heat transfer characteristics of flat plate were investigated under environmental wind condition. Both the uniform and linear heat flux boundary conditions were adopted for comparison purpose. Besides, the impacts of heat flux qwm, tilt angle α and wind incidence angle θ on heat transfer were explored in cases of windward and leeward facing positions. The local convection heat transfer coefficient hcx and average convection Nusselt number Nucm were obtained. The results show that, when α is small, there are two maximum values of hcx under linear heat flux boundary condition. As for Nucm, differences between the two boundary conditions seem indistinctive. At windward orientation, Nucm is not sensitive to α. While for leeward orientation, Nucm has a rapid decline progress with the increasing α, which indicates the tilt angle α is an important parameter to affect the heat transfer of plate. Finally, new correlations of Nucm have...

The critical cavity tilt angle is defined to mark the stability of free convection heat transfer shifting from steadiness to unsteadiness with the cavity rotating from sideward to vertical upward. In this article, taking a cylindrical cavity subjected to constant heat flux as object, experiments were firstly performed to show the possible reason why the unsteady free convection heat transfer was not discovered in previous experimental studies. Afterwards, on the basis of three-dimensional steady and unsteady simulation models, the concept of critical cavity tilt angle was proved and its magnitude was determined. For the compromising of computation cost and accuracy, the verified steady state model was employed to analyze the effects of aperture ratio and heat flux on critical cavity tilt angle. Also the importance of selecting appropriate monitoring parameters was detailed. Results show that in general, the critical cavity tilt angle increases with decreasing aperture ratio or increasing heat flux for partially open cavities. Remarkable differences may occur among scenarios having different monitoring parameters. Hence, to identify the critical cavity tilt angle accurately, more parameters, especially those inside the cavity should be taken into account.

Considering the thermodynamic and economic constraints simultaneously, the critical external heat source conditions available for sub-ORC systems with pure or zeotropic mixture working fluids are clarified. The critical external heat source conditions include the maximum allowed heat source temperature T gi,max, the minimum allowed heat source temperature T gi,min and the minimum allowed heat source mass flow rate m g,min. The results show that, no matter using pure working fluid or zeotropic mixture working fluid, the maximum allowed heat source temperature T gi,max increases linearly with the increasing of its critical temperature T cr. For the pure working fluid, the minimum allowed heat source temperature T gi,min is not sensitive to the variation of T cr. While, for the zeotropic mixture working fluid, the minimum allowed heat source temperature T gi,min firstly falls down, then rises up along with the increasing of T cr. An increase in mass flow rate of heat source causes enlarged range of heat source temperature available. And the minimum allowed heat source mass flow rate m g,min reduces sharply with the increase of heat source temperature.

Cavity receivers play a key role in the utilization of solar energy, and the convective heat losses in them can directly affect their efficiency. Yet the effect of wind on convective heat losses has not been investigated extensively. In this paper, taking an isothermal upward-facing cylindrical cavity as object, the combined convective heat loss under windy condition was studied by three-dimensional numerical model. The influences of surface temperature, cavity tilt angle, wind incident angle and wind speed were analyzed. The results were compared with those in no-windy condition. To facilitate engineering applications, empirical correlations for predicting combined convective heat loss were developed. Results show that the combined convective heat loss increases with increasing surface temperature. With the disturbance of wind, the effect of cavity tilt angle becomes complicated and is related to wind condition. For almost all of cases, as wind speed increases from zero, the combined convective heat loss is initially dropped and then increased, i.e., a minimum is observed. And the minimum is even below that in no-windy condition. The wind incident angle for maximizing combined convective heat loss is not fixed and can be affected by cavity tilt angle and wind speed.

To make more effective use of photovoltaic waste heat, a novel photovoltaic-hydrophilic modified tubular seawater desalination system was proposed in this paper. Based on the first and second laws of thermodynamics, energy analysis and exergy analysis models of the system were established. The influences of operation and structure parameters on system performance, heat and exergy losses of each component and performance comparisons among different solar tubular seawater desalination systems were analyzed and discussed. The results manifest that freshwater yield rate, thermal efficiency, energy efficiency and exergy efficiency are enhanced by raising the mass flow rate of working medium and heating pipe length; particularly when the length is small, the increase of heating pipe length can significantly elevate system performance. Moreover, 69.2% of the whole system's heat losses and 90.6% of the whole system's total exergy losses are attributed to the PV module. Compared with other solar tubular seawater desalination systems, the photovoltaic-hydrophilic modified tubular seawater desalination system proposed in this paper has the highest average energy efficiency and exergy efficiency, which are 32.6%, 10.4% respectively. Meanwhile, the photovoltaic thermal collector can provide up to 49.1 W of electricity to maintain the operation of system without consuming extra energy.

In this paper, the impacts of inclination angle, wind incidence angle, wind velocity and light intensity on the thermal characteristics and output performance of photovoltaic (PV) panel were studied experimentally under linear light source and windy conditions. The results demonstrate that there is a hot spot on the PV panel and the critical inclination angle that the hot spot occurs is speculated to be between 45° and 50°. The size (area), position and temperature of hot spot are affected by operating parameters. The laws of parametric influence on convective heat dissipation Nusselt number Nuc are different from those on the output performance in some ways. Nuc and output efficiency reach maximums at wind incidence angle of 90° and a certain light intensity related to wind velocity, respectively. For a PV panel with rated output power PPV,s of 40 W and rated output efficiency ηPV,s of 15.38% under standard conditions, the actual output power PPV and efficiency ηPV of PV panel under linear light source and within the range of experimental parameters in this paper degrade to 9.53%–48.45% of PPV,s and 62.16%–87.0% of ηPV,s, respectively. Finally, an empirical correlation of Nuc was proposed by incorporating different operating parameters.

Solar parabolic trough collector (PTC) always operates under non-designed conditions in actual situation. Some errors such as slope error, tracking error and installation error strongly affect the absorber tube's deformation and thermal stress performance. Based on the optical-thermal-stress coupling principle, a numerical analysis on the influence of different errors on deformation and thermal stress of absorber tube was carried out by coupling MCRT-FVM-FEM. The results show that the maximum deflection always occurs in the middle of absorber tube, and lower slope error and higher positive y-direction (vertical direction) installation error can greatly increase the deflection of absorber tube. Tracking error and x-direction (horizontal direction) installation error have little impact on the maximum deflection, but can remarkably increase the maximum equivalent stress as slope error is 0 mrad. Due to the occurrence of tracking error and x-direction installation error, the absorber tube's bending direction changes and it's equivalent stress distribution becomes asymmetric. The maximum equivalent stress descends with enlarged tracking error when slope error is greater than 3 mrad. While slope error is more than 6 mrad, the maximum equivalent stress is hardly affected by x-direction installation error. Under the condition of slope error, increasing y-direction installation error from 0 mm to 15 mm elevates the maximum equivalent stress.