Solar Heating Process Research Articles

Analysis of a Solar Cookers Box-Type with inner reflectors by using CFD

This work shows the results and evaluation of a solar cooker box-type by using CFD. The values indicate where the highest temperature values happen inside the solar cooker. Also, values for density and airspeed were obtained. These results show where and how density and airspeed have the most important values during the water heating process. The effects of convection as a consequence of the temperature difference can guide possible improvements in future designs of solar cookers since if geometric shapes are used that take advantage of this heat transfer mechanism, the solar heating process can be better.

Thermal behavior of a combi-storage in a solar-ground source heat pump system for a single-family house

Experimental investigations on thermal behavior of a combined solar and ground source heat pump (SGHP) system for a single-family house are presented. The SGHP system was installed at the Lyngby campus of Technical University of Denmark. Detailed experiments were carried out on the system in 2019 under real weather conditions covering domestic hot water (DHW) consumption and space heating (SH) demand. Depending on the contributions of the energy inputs to the combi-storage, five typical daily operation modes are classified. The focus of the investigations is on the dynamic thermal behaviors of the heat storage under different operating conditions. When the combi-storage was primarily heated by solar energy, the inlet stratifier in the storage performed well, ensuring thermal stratification and a good utilization of solar energy. Water temperature in the storage reached up to about 68℃ at the end of the solar heating process. When the combi-storage was primarily heated by the ground heat, the water temperature near the outlet for SH was kept at a temperature range from 26℃ to 31℃ in the heating process to ensure the outlet temperature level of SH, and the water temperature near the outlet for DHW was in the temperature range 47℃∼51℃ in DHW volume. When there was no heat input to the combi-storage, the pre-stored heat can meet the daily heating demand, and the number of days on this mode was up to 9.4% of the total experimental days. The paper gives valuable inputs for researchers and engineers who plan to integrate the combi-storage in a renewable heating system with solar collectors and ground source heat pumps.

A solar reactor for bio-diesel production from Pongamia oil: Studies on transesterfication process parameters and energy efficiency

Abstract Over exploitation of non-renewable energy reserves will lead to increase in price of petroleum fuels. Therefore there is a need for suitable and sustainable substitutes (renewable resource) for conventional fuels. In this study, an efficient and environmental friendly method for production of bio-diesel from Pongamia (Karanja) oil has been developed using a solar reactor. During the experimental study, the maximum temperature attained by the pongamia oil during the transesterification process was 64.1°C. The transesterification reaction was studied by varying different parameters such as reactant flow rate (5-20 LPH), stirring speed (150-450 r·min-1), catalyst loading (0.5 wt% -2 wt%) and methanol to oil ratio (3:1 to 15:1). The maximum biodiesel yield was 83.11% at a flow rate of 5 LPH, stirring speed of 350 rpm, a methanol to oil ratio of 15:1, catalyst loading of 1wt % and reaction time of 270 min. The physical and chemical properties of biodiesel was analyzed as per American Society for Testing Materials (ASTM) standards and it had density of 938 kg·m-3, viscosity (28.7 cSt), acid value (9.45 mg KOH·(g oil)-1) and flash point (215°C). The energy efficiency of solar heating process was determined by comparing the net energy ratio of direct heating process and solar heating process. For solar heating the net energy ratio (NER) was found to be 31.85 against 5.73 for direct heating. Similarly, net energy efficiency index was calculated for 10 kg production scale and was found to be increasing when scaled up which means that the solar heating process is more effective even in scaled up production.

Plasmonic multi-thorny Gold nanostructures for enhanced solar thermal conversion

In this work, thorny Au nanoparticles (NPs) a broadband surface plasmon resonance (SPR) peak were used to enhanced the solar thermal conversion (STC) performance. The SPR peak of the thorny Au NPs can be tuned from 562 nm to 812 nm with the size ranging from 42 to 188 nm, which was controlled by the amount of Ag+ in the growth process and the seed additive amount for optical and morphological evolution of Au NPs. Experiments indicated that the thorny Au NPs can greatly enhance the STC efficiency, the maximal increase of which was 152.0% and 18.5% compared with pure water and quasi-spherical Au NPs respectively. Then, the particle heating model was applied to further confirm that the thorny NP can enhance the solar heating process significantly. Results indicated that the thorny Au NP obtained a higher maximum temperature than that of the spherical Au NP owing to a higher heat resource from the solar radiation in the thorns. In addition, a blended nanofluid with different thorny Au NPs showed a highest STC efficiency in all experimental samples that was as high as 85.8% by broadening its absorption spectra. It indicated that tuning the NP morphology or mixing different NPs could be efficient ways to improve the STC performance.

Exergetic Analysis of Flat-Plate Solar Collector used for Desalination by Humidification-dehumidification

AbstractIn the present work, exergy analysis of flat-plate solar collector is presented in details. Flat-plate solar collector is used for heating saline water, which is the first stage of water desalination process by humidification-dehumidification technique. This stage is considered as the most energy intensive stage. Accordingly, it is important to investigate its performance by using exergy analysis. The exergetic efficiency of solar heating system was examined in different ways to determine the most critical parameters that control the solar heating process. A comparison between both traditional energy (based on the first law of thermodynamics) and exergy analyses (based on the second law of thermodynamics) of a flat-plate solar heater type is carried out to show the importance of such exergy analysis and to show the limitations of conventional energy analysis. Exergy analysis gives a comprehensive and detailed behavior of solar heater performance under different conditions.

Numerically investigating the optical properties of plasmonic metallic nanoparticles for effective solar absorption and heating

Solar heating with plasmonic nanoparticles (NPs) has great potential for application in optical storage, solar thermal collectors, and thermo-photovoltaic technologies. The performance of solar thermal conversion applications depends on the NP parameters. Herein, we present a comparative analysis of the solar absorption properties of noble metallic NPs (Au, Ag, Cu, and Al), to determine suitable parameters for effective solar heating by using the finite-difference time-domain method and the finite-element method. Results show that light absorption plays a major role in the interaction of light with the small NP size, small sphericity, or small dielectric constant of the surrounding environment. Au and Cu NPs have higher solar absorption power and absorption ratio. The NP size has little effect on the peak absorption wavelength. A Au sphere smaller than 30 nm has greater solar absorption ability for the solar heating process when considering the absorption power per unit volume. The solar absorption power first increases rapidly and subsequently decreases slightly with increasing dielectric constant, and can become as high as 0.0045 nW when the dielectric constant is 1.33–2.5 in the calculation samples. The solar scattering power and solar absorption power decrease with increasing sphericity, i.e., ranging from cubic to cylindrical and spherical. Finally, simulation results of NP solar heating show that the Au cube obtains a higher maximum temperature than the Au sphere and Au cylinder, which further verifies that Au NPs with low sphericity can significantly enhance solar heating ability in the simulation cases.

“One-Pot” Solar Fuels

Chemists have always taken great pride in simplifying a complex multistep chemical synthesis into a single step process, in just one reactor. The motivation for doing so, apart from demonstrating synthetic competency and elegance, is the pursuit of green and sustainable solutions to chemical problems, as single step strategies have the inherent advantage of being atomically, energetically and economically efficient, as well as environmentally friendly and responsible.

아크릴 수지를 이용한 차열성 포장의 실내 및 현장 공용성 평가

본 연구에서는 도심지 열섬현상을 완화 시킬 수 있는 아크릴 수지와 차열안료를 혼합한 차열성 포장을 개발하였다. 태양 복사열에 의한 포장체의 온도상승을 모사한 실내 시험으로부터 <TEX>$60^{\circ}C$</TEX>의 포장 온도에서 차열성 포장이 <TEX>$12^{\circ}C$</TEX> 이상의 온도 저감 효과를 나타냈다. 이러한 온도 감소 효과는 차열안료의 배합비가 증가함에 따라 증가하였고, 반면에 점도의 증가로 인하여 작업성은 떨어졌다. 이러한 결과로부터 아크릴 수지 대비 차열안료의 최적혼합비율을 15%로 결정하였다. 차열성 포장의 칸타브로 손실률은 일반 배수성 포장의 손실률 1/4 수준으로 골재 비산 저항성이 우수하게 나타났다. 휠트랙킹 시험결과 차열성 포장의 동적안정도가 일반 배수성 포장에 비해 두 배 증가하였다. 차열성 포장재의 높은 부착력으로 인하여 탈리에 의한 손상 가능성은 낮은 것으로 나타났다. 시험 시공 구간에서의 소음도 측정 시험 결과 일반 배수성 포장에 비하여 평균 3.7dB의 소음저감 효과가 있었고, 미끄럼 저항치는 일반 배수성 포장에 비해서 평균 30% 정도 높아 우수한 미끄럼 저항성을 가지는 것으로 판단된다. 투수 시험 결과 차열성 포장의 투수성은 일반 배수성 포장보다 다소 작았으나 국내 배수성 포장 기준을 만족하는 것으로 나타났다. This study developed a solar radiation reflection pavement, so called a cool pavement, to lessen the urban heat island effect by coating a pavement surface with acrylic resins mixed with light-colored pigments. From a laboratory test, simulating solar heating process in pavements, the cool pavement reduced more than <TEX>$12^{\circ}C$</TEX> of pavement temperature at <TEX>$60^{\circ}C$</TEX> compared to a control porous pavement. With the increase of the mixing ratio of the pigments to acrylic resins, the temperature reduction effect increased, but its workability became worse due to higher viscosity. As a result, an appropriate mixing ratio was determined as 15%. The cool pavement had better durability than the control pavement: One quarter of Catabro loss and twofold dynamic stability. Its adhesion was also higher enough not to be debonded under traffic loading. In-situ noise and friction tests conducted in two field sites showed that the cool pavement reduced its noise level by 3.7dB in average and increased its friction level by 30% compared to the control pavement. The permeability of the cool pavement was little lower than the control pavement, but higher enough to satisfy the minimum requirement for porous pavements.

Solar absorptivity of metallic layers subject to a short-flash of concentrated solar energy. Theoretical-experimental calculation

The paper develops a procedure for the theoretical-experimental calculation of the solar absorption coefficient of metallic layers under the action of a short flash of concentrated solar energy. The knowledge of this coefficient is relevant when the solar thermal processing is used to make a quench in a thin superficial layer of metallic slabs. The experimental data of temperature of the sample are obtained using the SURFSOL experimental device at SOLFACE (High Flux Solar Facilities for Europe), France. In particular, the sensors of temperature are located on its back side as the solar radiation impinges the front irradiated one. The theoretical data are obtained solving the nonlinear inverse transient heat conduction problem using the IHCP1D software based on the well-known function specification method (FSM). It gives transient surface heat fluxes as well as temperatures on the irradiated side of the sample using internal temperature histories. Then a transient radial fin model accounts for the heat diffusion in the radial direction and re-calculates the heat fluxes. Once temperatures and heat flows are known, an estimate of the solar absorption coefficient of the metallic layer (during the flash solar heating process) may be obtained as a function of temperature (AISI 316L steel).

05/00246 Maintenance strategy for a salt gradient solar pond coupled with an evaporation pond: Agha, K. R. et al. Solar Energy, 2004, 77, (1), 95–104

Process simulation has become an accepted tool for the performance, design, and optimization of thermal processes. Solving the mathematical models representing solar heating process units and systems is one of the most tedious and repetitive problems. Nested iterative procedures are usually needed to solve these models. To tackle these problems, several researchers have developed different methods, techniques, and computer programs for the simulation of very wide verity of solar heating process units and systems.It is of interest in this work to characterize and classify these methods, techniques, and programs in order to better understand their relations, types, structures, and procedures.The simulation problems are outlined; the simulation programs are grouped into two main types; special purpose, and general-purpose programs. Sequential and simultaneous computational sequences are illustrated. Simulator structure, program evaluation, and numerical techniques are summarized.By considering the unit and/or system entropy generation as well as the energy and material balances equations, more realistic models can be obtained. Also, rapid development of computer hardware and software will suggest new techniques and programs to be considered. These progress directions are noted.

Sunrise and sunset effects on solar heating in the Jovian thermosphere and ionosphere

We present some calculations on the effects of oblateness on the solar heating process as considered in the Jovian Ionospheric Model by Achilleos et al. (1998). Since Jupiter has significant oblateness we have to use a new approach for the investigation of sunrise/sunset variations in the Jovian ionosphere. We introduce the modified Chapman function ( Che) and point to its importance for the sunrise and sunset time periods where this function significantly deviates from the “classic” Chapman function ( Ch). Because of the dependence of the Che function on latitude and solar declination we have included latitudinal variations in all thermospheric and ionospheric parameters. The Jovian Ionospheric Model assumes plane stratified atmospheric layers. We consider one part of this model, the solar heating, and more precisely take into account the shape of the planetary body. We model it with a rotational ellipsoid and calculate the optical depth parameter, used in evaluation of the neutral volume heating rate due to solar radiation. We use secants for the flat model, the Ch function for spherical model, and the Che function for the ellipsoidal model. We use all other physical inputs of the Jovian Ionospheric Model to explore the effects due to oblateness only. Calculations show that only the modified Chapman function Che can really describe sunrise/sunset and latitudinal variations in the Jovian thermosphere and ionosphere.