In the present study, thermal performance of greenhouse solar dryer (GHSD) was analyzed at full load of peppermint leaves for dehydration. The experiments were conducted in both GHSD and sun drying ...processes to compare drying characteristics, thermal properties, and quality assessment of peppermint leaves. The maximum drying cabin temperature attained during the experimentation was 58.3 °C at solar radiation 864W/m2. Initial moisture content of peppermint leaves 81.25% reduced to 11.22% and 22% within 10 h in GHSD and sun drying, respectively. Drying rate was obtained as 0.65 kg water/kg solid.hr and 0.61 kg water/kg solid.hr for GHSD and sun drying process at the end of the experiment. Verma et al. model accurately defined the drying characteristics of peppermint leaves in GHSD and sun drying. Average effective moisture diffusivity (Deff), mass transfer coefficient (hm) and heat transfer coefficient (h) of peppermint leaves were increased by 12.76%, 17.71%, and 64.23%, correspondingly in GHSD compared to sun drying. Activation energy (Ea) of peppermint leaves was computed as 32.25 kJ/mol in GHSD, while in sun drying method, it was 59.68 kJ/mol. Water activity (Aw) peppermint leaves were 0.850, 0.705, 0.385 and 0.850, 0.765, 0.520 at 8, 14, 19 h in GHSD and sun drying.
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•Greenhouse solar dryer (GHSD) was designed and fabricated for peppermint leaves.•Thermal characteristics, drying kinetics, and quality assessment of peppermint leaves were evaluated in GHSD and sun drying.•Verma et al. model was best fit drying model to explain drying behaviour of peppermint leaves in GHSD and sun drying.•Activation energy (Ea) of peppermint leaves was computed as 32.25 kJ/mol and59.68kJ/mol in GHSD and sun drying respectively.
Edible films and coatings gained renewed interest in the food packaging sector with polysaccharide and protein blending being explored as a promising strategy to improve properties of edible films. ...The present work studies composite edible films in different proportions of pectin (P), alginate (A) and whey Protein concentrate (WP) formulated with a simplex centroid mixture design and evaluated for physico-chemical characteristics to understand the effects of individual components on the final film performance. The studied matrices exhibited good film forming capacity, except for whey protein at a certain concentration, with thickness, elastic and optical properties correlated to the initial solution viscosity. A whey protein component in general lowered the viscosity of the initial solutions compared to that of alginate or pectin solutions. Subsequently, a whey protein component lowered the mechanical strength, as well as the affinity for water, as evidenced from an increasing contact angle. The effect of pectin was reflected in the yellowness index, whereas alginate and whey protein affected the opacity of film. Whey protein favored higher opacity, lower gas barrier values and dense structures, resulting from the polysaccharide-protein aggregates. All films displayed however good thermal stability, with degradation onset temperatures higher than 170 °C.
In this paper, a new type of micro combustor is designed to solve the problems of low output performance, insufficient heat source and low quality heat source of combustion-based micro thermoelectric ...systems. The combustor designed in this paper has the opposite intake arrangement, partial porous medium(PM) filling, central raised cavity and multistage sudden expansion structure. The effects of filling ratio of PM, thermal conductivity of PM and input power (Pin) on the thermal characteristics of combustor were investigated by numerical method. The results show that partially filled PM can stabilize the combustion position and shape, and increase the proportion of available energy of the combustor, so as to provide sufficient heat source for the thermoelectric system. The uniformity of combustor plane temperature increases with the increase of PM filling ratio and thermal conductivity. The combustible range of the combustor is 20–140 W. At the same time, at higher Pin, the filling ratio and thermal conductivity of the PM improve the thermal characteristics more obviously, so as to provide high quality heat source for the thermoelectric system. It is clear that strengthening heat transfer capacity, improving temperature uniformity and improving combustion stability are important ways to improve the thermal characteristics of combustor. In addition, the emission performance of the improvement effect is strong. Therefore, this research can be utilized as effective and feasible guidance for researching thermoelectric system and provide useful insights for the research of system heat source, i.e. combustor.
•A new type of micro combustor is designed to improve system performance.•A numerical model is developed to study the characteristics of combustor•Sufficient heat energy and wide combustion range are realized.•Several ways to improve the combustor thermal characteristics are obtained.•The emission performance of micro combustor is improved to some extent.
The use of inorganic phase changing materials (PCMs) in thermal energy stowage systems has become widespread due to the remarkable energy saving capabilities of these substances. In the current ...investigation, the enhancement in energy stowage capability of the calcium chloride hexahydrate (CaCl2·6H2O) had been attempted with the assistance of nano-silica addition. Four different proportion of nano-silica (0.3%, 0.6%, 0.9% and 1.2%) had been employed for this purpose. The thermal characteristics namely, latent content, phase transformation temperatures, and thermal conductivity of the CaCl2·6H2O with the presence of nano-silica had been assessed using DSC and thermal properties analyzer. The results confirmed that the inclusion of nano-silica at 0.6% mass proportion in CaCl2·6H2O would enhance the thermal stowage characteristics in terms of its thermal conductivity to a grander magnitude, without much losing the latent content of the salt hydrate. Whereas, the maximum drop in latent content of 27.1% and 27.51% during heating and cooling was observed at 1.2% fraction of nano-silica in CaCl2·6H2O.
Under the background of “One national network”, the balance between the natural gas supply side and the demand side is prominent. This paper proposes a supply-demand balance method of natural gas ...pipeline network coupled with the hydraulic and thermal characteristics, and decides the transportation scheme through flow rate allocation. This paper designs a two-stage relaxation optimization algorithm, coupled the thermal process into the hydraulic calculation to improve the hydraulic calculation accuracy, making the natural gas transportation scheme more applicable to engineering. The result shows the feasibility of transportation decision-making and the accuracy of hydro thermal calculation of the proposed model through a real case. The relative error of thermal calculation and TGNET is below 2%, and the hydraulic calculation error of coupled thermal can also be within 10%. After optimization, the carbon emissions decrease from 418,100 tons to 260,000 tons, reducing by about 37.81%. This study also analyzes the impact of hydraulic calculation on carbon emissions calculation, and further illustrates the necessity of coupled thermal characteristics in transportation scheme. This study can provide decision support for the transportation operation and help the natural gas pipeline network to meet the dual carbon requirements and achieve sustainable development.
•A flow rate allocation method combining operation process is proposed.•A convex relaxation optimization algorithm is designed for energy consumption calculation.•Two stage relaxation iteration algorithm is designed to couple thermal and hydraulic characteristics.•Carbon emission objective is added to the optimization model for environmental benefit.•An actual case is used to prove the practicability of the method.
•A novel type of lightweight foam concrete was prepared by adding nano-silica aerogel, fiber and ceramist.•A prefabricated foamed concrete wallboard meeting the thermal performance requirement of 65% ...energy saving of residential building structure in the cold region (B region) of China was developed.•The thermal characteristics of the wallboard were tested under steady-state and unsteady-state conditions.
The optimal mix ratio of nano-silica aerogel foam concrete was determined through preliminary design and orthogonal experiment optimization. Based on the design of the size, reinforcement, and interface form of the prefabricated wallboard, a prefabricated foam concrete wallboard which met the requirements for use in the cold region (B region) of China was developed. The dry bulk density, thermal conductivity, compressive strength, and porosity were tested respectively. Besides, the microscopic characteristics of the foam concrete were tested through scanning electron microscopy(SEM). The thermal characteristics of the wallboard were tested under steady-state and unsteady-state conditions. The heat transfer coefficient is 0.5518 W/(m2·K) under steady-state conditions. The test results are that the temperature amplitudes of the inside and outside wall surfaces are 5.2℃ and 0.054℃ respectively, the temperature attenuation multiple and attenuation coefficient are 96.3, 0.0104, The delay time of the wall surface is up to 11.8 h, the heat storage coefficient of the surface is 2.48 W/(m2·K), thermal inertia index is 4.15, tested by using self-designed test device, and the periodic variation of sol–air temperature of Xuzhou area in summer is taken as boundary conditions. It shows that the developed wallboards have good thermal characteristics.
•A TPCT group is used to control the ground temperature for a shallow tunnel section.•A composite heat transfer model is developed for the tunnel with a TPCT group.•The TPCT group can cool down the ...soil layers in the shallow tunnel section.•The research could provide help for applications of TPCTs in other cold regions engineering.
Permafrost is very sensitive to temperature changes. Climate warming would cause the increase of ground temperature and accelerate the degradation of permafrost. One of the important future issues is how to control ground temperature to meet the demand of the engineering stability in permafrost regions under climate warming. In this study, a two-phase closed thermosyphon (TPCT) group is applied to adjust and control the ground temperature for a shallow tunnel section in a permafrost region. A composite heat transfer model, including the air turbulent heat transfer inside the tunnel, the air-TPCT-soil coupled heat transfer for the TPCT group, and the heat conduction with phase change in the soil layers and the tunnel structure layers, is developed for the tunnel with a TPCT group. The numerical results indicate that under the climate warming, the TPCT group can cool down the soil layers in the shallow tunnel section and ensure the thermal stability of the tunnel. Therefore, we conclude that it is an effective method to adjust the ground temperature of permafrost, without active control instrumentation or aid of other external energy. The research results could also provide help for applications of TPCTs in other cold regions engineering.
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