Transient thermal performance prediction method for parabolic through solar collector under fluctuating solar radiation

As the effect of the global warming is becoming noticeable, the importance for environmental sustainability has been raised. Parabolic trough solar thermal collector system, which is one of the solutions to reduce the carbon dioxide emission, is a mature technology for electricity generation. Malaysia is a tropical country with long daytime, which makes suitable for solar thermal applications with parabolic trough solar thermal collectors. However, the high humidity causes the solar radiation to fluctuate. In order to simulate the solar thermal collectors’ performance at an early design stage of solar thermal power generation systems, fast still accurate transient thermal performance prediction methodis required. Although multiple transient thermal simulation methodologies exist, they are not suited especially at an early design stage where quick but reasonably accurate thermal performance prediction is needed because of their long calculation time. In this paper, a transient thermal prediction method is developed to predict exit temperature of parabolic trough collectors under fluctuating solar radiation. The method is governed by simple summation operations and requires much less calculating time than the existing numerical methods. If the radiation heat loss at the parabolic trough collector tube surface is small, the working fluid temperature rise may be approximated as proportional to the receiving heat flux. The fluctuating solar radiation is considered as a series of heat flux pulses applied for a short period of time. The time dependent solar collector exit temperature is approximated by superimposing the exit temperature rise caused by each heat flux pulse. To demonstrate the capabilities of the proposed methodology, the solar collector exit temperature for one-day operation is predicted. The predicted solar collector exit temperature captures the trend of a finite element analysis result well. Still, the largest temperature difference is 38.8K and accuracy is not satisfactory. Currently, the accuracy of the proposed method is being improved. At the same time, its capabilities are being expanded

Prediction methodology for transient thermal response of solar parabolic trough collector under fluctuating solar radiation

Solar parabolic trough collector technology is an effective way to utilize solar thermal energy, which reduces the carbon dioxide emission. Although the weather in Malaysia and other Southeast Asian countries is suited to solar thermal applications for the long daytime that continues all year around. Still, the fluctuation in solar radiation caused by the high humidity must be handled when estimating the thermal performance of the parabolic trough collector application. To perform transient thermal simulation to incorporate the effect from the solar radiation fluctuation, long calculation time and large memory space are required when the existing numerical methods are used. A simple but powerful methodology to predict the time dependent parabolic trough collector tube exit temperature is proposed. In this methodology, the exit working fluid temperature is estimated by superimposing the temperature rise caused by each heat flux pulse that forms the solar radiation. The preliminary results and methodology improvement for more realistic prediction conditions are discussed

On temperature jump condition for turbulent slip flow in a quasi-fully developed region of micro-channel with constant wall temperature

Temperature variation of turbulent slip flows in the quasi-fully developed region of a micro-tube were obtained numerically by solving the energy equation including the substantial derivative of pressure and viscous dissipation terms for the case of constant wall temperature. The fluid was assumed to be an ideal gas with constant density over the cross-section. The turbulent velocity profile was approximated by the three-layer model of Von Kármán. Although the shear work term is not included in the conventional temperature jump boundary condition explicitly, it is verified that the conventional temperature jump boundary condition is valid for a slip flow in a micro-tube with constant wall temperature when both viscous dissipation and substantial derivative of pressure terms are included in the energy equation. The total temperature in the quasi-fully developed region was lower than the wall temperature in the case of Kn ≥ 0.01

Transient thermal prediction methodology for parabolic trough solar collector tube using artificial neural network

The solar radiation fluctuation occurs at practically anywhere on the earth. When a solar thermal power generation system is designed for the areas with considerable solar radiation fluctuation, the collector tube exit temperature becomes more difficult to predict and requires significant calculation time. This paper presents a fast and accurate transient thermal prediction method to predict the parabolic trough collector tube exit temperature. In this work, an artificial neural network (ANN) is combined with the principle of superposition. ANN is used to predict the exit temperature rise caused by a single heat flux pulse in the first step of the proposed methodology, while superposition is used to predict the from multiple heat flux pulses in the second step. Limited cases of conjugate heat transfer analytical results by the finite element method (FEM) are used to train the ANN. The one-day exit fluid temperature from 7 a.m. to 6 p.m. is predicted within 1 min of computational time with mean absolute deviation less than 2 K. The exit fluid temperature of the collector tube for one year operation can be predicted in less than 6 h. Because fluid velocity is included in the input parameters, the proposed methodology is especially useful for flow control simulations where a constant exit temperature is targeted. Through this, the optimum performance of collector tube under multiple radiation conditions can be assessed during an early design phase of parabolic solar trough systems. The predicted results can be used for initial system planning, heat balance analysis, and system design. Since the method shows good prediction capability under the fluctuating solar radiation as well as the stable solar radiation, it is applicable to be used for designing the parabolic trough technology at any weather conditions in the world

Characterization of the feedstock properties of metal injection-molded WC-Co with palm stearin binder system

Feedstock preparation, as well as its characterization, is crucial in the production of highly sintered parts with minimal defect. The hard metal powder - particularly, cemented carbide (WC-Co) used in this study was investigated both physically and thermally to determine its properties before the mixing and injection molding stage. Several analyses were conducted, such as scanning electron microscopy, energy dispersive X-ray diffraction, pycnometer density, critical powder volume percentage (CPVP), as well as thermal tests, such as thermogravimetric analysis and differential scanning calorimetry. On the basis of the CPVP value, the feedstock, consisting of WC-Co powder, was mixed with 60% palm stearin and 40% polyethylene at an optimal powder loading, within 2 to 5% lower than the CPVP value. The CPVP spotted value was 65%. The feedstock optimal value at 61% showed good rheological properties (pseudoplastic behavior) with an n value lower than 1, considerably low activation energy and high moldability index. These preliminary properties of the feedstock serve as a benchmark in designing the schedule for the next whole steps (i.e. injection, debinding and sintering processes)

Ball milling of WC-CO powder as injection molding feedstock

In this paper, an attempt has been made to mill constituent of WC and Co powder towards achieving volumetric percentage of WC (91%) and Co (9%). The ball milling technique was conducted under dry and wet condition using various milling parameters, rotation speed, time and ethanol as milling medium. Electron dispersive spectrometer (EDS) detected the elemental distribution, whilst SEM and particle size analysis was done to study the effect of changes in particle morphology and reduction of particle size. As a conclusion, powder milled by parameter of wet milling by ethanol, speed of rotation at 250 rpm and 90 minutes of milling time exhibits best results in term of volumetric percentage of 91%WC and 9%Co and particle size reduction

Performance of a small-scale solar cogeneration system in the equatorial zone of Malaysia

Solar energy is one of the most promising renewable energy sources in the equatorial zone of Malaysia. The availability of moderate solar energy during the year makes it possible to be used as a heat source for a solar thermal system. In order to determine the potential application of the solar thermal system, a feasibility study of a small-scale solar cogeneration system under measured solar radiation condition is conducted. In this work, the concept design of a 50-kW solar cogeneration system is proposed which consists of a parabolic trough collector with aperture area of 1154 m2, thermal storage system and an Organic Rankine Cycle power conversion system. The performance of the system was simulated using the measured direct normal irradiance during the months of May, June and July in 2018. A net gross electric power of 6373 kWh, 6201 kWh and 5155 kWh were produced with the total monthly available solar energy of 82,809 kWh, 77,592 kWh and 64,239 kWh for May, June and July, respectively. The efficiency of the solar to electric was around 8% and was in good agreement with the findings in the literature. The results for the solar cogeneration system can serve as an evaluation reference for the application of solar thermal system in the moderate solar radiation localities in Malaysia