Applicability of Heat Mirrors in Reducing Thermal Losses in Concentrating Solar Collectors

2018 ◽  
Vol 10 (6) ◽  
Author(s):  
Vikrant Khullar ◽  
Prashant Mahendra ◽  
Madhup Mittal
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Receiver Design ◽  
Parabolic Trough ◽  
Coated Glass ◽  
Pass Through ◽  
Steady State Heat Transfer ◽  
Glass Envelope

Abstract In the present work, a novel parabolic trough receiver design has been proposed. The proposed design is similar to the conventional receiver design except for the envelope and the annulus part. Here, a certain portion of the conventional glass envelope is coated with Sn-In2O3 and also Sn-In2O3 coated glass baffles are provided in the annulus part to reduce the radiative losses. The optical properties of the coated glass are such that it allows most of the solar irradiance to pass through, but reflects the emitted long wavelength radiations back to the absorber tube. Sn-In2O3 coated glass is referred to as “transparent heat mirror.” Thus, effectively reducing the heat loss area and improving the thermal efficiency of the solar collector. A detailed one-dimensional steady-state heat transfer model has been developed to predict the performance of the proposed receiver design. It was observed that while maintaining the same external conditions (such as ambient/initial temperatures, wind speed, solar insolation, flow rate, and concentration ratio), the heat mirror-based parabolic trough receiver design has about 3–5% higher thermal efficiency as compared to the conventional receiver design. Furthermore, the heat transfer analysis reveals that depending on the spatial incident solar flux distribution, there is an optimum circumferential angle (θ = θoptimum, where θ is the heat mirror circumferential angle) up to which the glass envelope should be coated with Sn-In2O3. For angles higher than the optimum angle, the collector efficiency tends to decrease owing to increase in optical losses.

Applicability of Heat Mirrors in Reducing Thermal Losses in Concentrating Solar Collectors

2016 ◽  
Author(s):  
Prashant Mahendra ◽  
Vikrant Khullar ◽  
Madhup Mittal
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Solar Irradiance ◽  
Solar Collector ◽  
Flux Distribution ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Solar Collectors ◽  
Parabolic Trough ◽  
Glass Envelope

Flux distribution around the parabolic trough receiver being typically non-uniform, only a certain portion of the receiver circumference receives the concentrated solar irradiance. However, radiative and convective losses occur across the entire receiver circumference. This paper attempts to introduce the idea employing transparent heat mirror to effectively reduce the heat loss area and thus improve the thermal efficiency of the solar collector. Transparent heat mirror essentially has high transmissivity in the solar irradiance wavelength band and high reflectivity in the mid-infrared region thus it allows the solar irradiance to pass through but reflects the infrared radiation back to the solar selective metal tube. Practically, this could be realized if certain portion of the conventional low iron glass envelope is coated with Sn-In2O3 so that its acts as a heat mirror. In the present study, a parabolic receiver design employing the aforesaid concept has been proposed. Detailed heat transfer model has been formulated. The results of the model were compared with the experimental results of conventional concentrating parabolic trough solar collectors in the literature. It was observed that while maintaining the same external conditions (such as ambient/initial temperatures, wind speed, solar insolation, flow rate, concentration ratio etc.) the heat mirror-based parabolic trough concentrating solar collector has about 3–12% higher thermal efficiency as compared to the conventional parabolic solar collector. Furthermore, steady state heat transfer analysis reveals that depending on the solar flux distribution there is an optimum circumferential angle (θ = θoptimum, where θ is the heat mirror circumferential angle) up to which the glass envelope should be coated with Sn-In2O3. For angles higher than the optimum angle, the collector efficiency tends to decrease owing to increase in optical losses.

Numerical Simulation on Heat Dissipating Performance of New Pipe with Grid Plate

2012 ◽  
Vol 532-533 ◽  
pp. 417-421
Author(s):  
Chang Li Song ◽  
Jing Ji
Keyword(s):  
Heat Transfer ◽  
Simulation Analysis ◽  
Heat Transfer Analysis ◽  
Finite Element Software ◽  
Grid Plate ◽  
Steady State Heat ◽  
Steady State Heat Transfer ◽  
Energy Conservation Law ◽  
Optimal Diameter ◽  
Selection Of

In order to improve the pipe dissipating area, a kind of new pipe with grid plate is proposed in this paper. Based on the basic principle of heat transfer and energy conservation law, by finite element software ANSYS the simulation analysis of the steady-state heat transfer of the new pipeline is carried out, process of ANSYS modeling, loading and solving is introduced in detail, the distribution of temperature and stress for pipe with a grid plate is given, these can provide the foundation for the selection of the optimal diameter of the grid plate and transient heat transfer analysis of pipe.

Heat Transfer Analysis of a Novel Pressurized Air Receiver for Concentrated Solar Power via Combined Cycles

2009 ◽  
Vol 1 (4) ◽  
Author(s):  
I. Hischier ◽  
D. Hess ◽  
W. Lipiński ◽  
M. Modest ◽  
A. Steinfeld
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Porous Ceramic ◽  
Conservation Equation ◽  
Heat Transfer Analysis ◽  
Operational Parameters ◽  
Small Aperture ◽  
Solar Absorber ◽  
Energy Conservation Equation ◽  
Combined Cycles

A novel design of a high-temperature pressurized solar air receiver for power generation via combined Brayton–Rankine cycles is proposed. It consists of an annular reticulate porous ceramic (RPC) bounded by two concentric cylinders. The inner cylinder, which serves as the solar absorber, has a cavity-type configuration and a small aperture for the access of concentrated solar radiation. Absorbed heat is transferred by conduction, radiation, and convection to the pressurized air flowing across the RPC. A 2D steady-state energy conservation equation coupling the three modes of heat transfer is formulated and solved by the finite volume technique and by applying the Rosseland diffusion, P1, and Monte Carlo radiation methods. Key results include the temperature distribution and thermal efficiency as a function of the geometrical and operational parameters. For a solar concentration ratio of 3000 suns, the outlet air temperature reaches 1000°C at 10 bars, yielding a thermal efficiency of 78%.

Research on Simulation of Operation of DSG Collectors Based on Analysis of Scientific Materials

2011 ◽  
Vol 282-283 ◽  
pp. 710-715 ◽  
Author(s):  
Teng Gao ◽  
Jun Zhao ◽  
Bin Yang ◽  
Fu Wang
Keyword(s):  
Heat Transfer ◽  
Heat Loss ◽  
Energy Balance Equation ◽  
Basic Program ◽  
Transfer Model ◽  
Fluid Temperature ◽  
Steam Generation ◽  
Collector Efficiency ◽  
Steady State Heat Transfer ◽  
Fluid Parameters

In this paper, a direct steam generation (DSG) collector is researched. To determinate the DSG collector efficiency, a simplified heat loss correlation is applied. A one-dimensional steady state heat transfer model and an energy balance equation for DSG collector are developed. A Visual basic program coupled with fluid parameters is compiled to compute fluid temperature, heat transfer coefficient and heat loss along the absorber tube by iterations for given accuracy. The variation trends of many kinds of fluid parameters along the absorber tube are revealed. The effect of length of dry steam region on collector efficiency is accounted for also.

Comparative studies of energy saving polymers and fabrication of high performance transparent polymer by solvent bonding

2018 ◽  
Vol 39 (1) ◽  
pp. 68-75
Author(s):  
S.P. Aadhy ◽  
T. Hema Sinega ◽  
C. Karthikeyan ◽  
S. Akshay ◽  
Mohan Kumar Pitchan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Saving ◽  
High Performance ◽  
Solvent Mixture ◽  
Heat Transfer Analysis ◽  
Compression Moulding ◽  
Lap Shear ◽  
Visible Wavelengths ◽  
Pass Through ◽  
Solvent Bonding

Abstract This work investigates the possibility of using polyetherimide (PEI) as an energy saving alternative to glass, polymethylmethacrylate (PMMA) and polycarbonate (PC) by carrying out heat transfer analysis and suggests vaporized solvent bonding as a viable bonding technique for the fabrication of PEI. By heat transfer analysis using building energy simulation, it is observed that less energy is expended for space-conditioning of a building with windows made of PEI when compared to glass, PMMA and PC. The compression moulding technique is used to mould PEI and fabrication is done using a solvent mixture of dimethyl sulfoxide and tetrahydrofuran in 1:1 ratio. The optical properties of the bonded specimen are studied using UV-visible spectrophotometry and it is found that PEI does not allow UV wavelength radiation to pass through while transmitting visible wavelengths. The mechanical strength of the bond is tested using lap shear tensile strength test and the type of failure is observed to be cohesive from the structure. This is indicative of the fact that using this particular solvent to bond PEI results in the maximum possible strength.

Overall Effectiveness of a Blade Endwall With Jet Impingement and Film Cooling

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Amy Mensch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Jet Impingement ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Convective Cooling ◽  
Impingement Cooling ◽  
Internal Impingement ◽  
The Impact ◽  
Overall Effectiveness

Ever-increasing thermal loads on gas turbine components require improved cooling schemes to extend component life. Engine designers often rely on multiple thermal protection techniques, including internal cooling and external film cooling. A conjugate heat transfer model for the endwall of a seven-blade cascade was developed to examine the impact of both convective cooling and solid conduction through the endwall. Appropriate parameters were scaled to ensure engine-relevant temperatures were reported. External film cooling and internal jet impingement cooling were tested separately and together for their combined effects. Experiments with only film cooling showed high effectiveness around film-cooling holes due to convective cooling within the holes. Internal impingement cooling provided more uniform effectiveness than film cooling, and impingement effectiveness improved markedly with increasing blowing ratio. Combining internal impingement and external film cooling produced overall effectiveness values as high as 0.4. A simplified, one-dimensional heat transfer analysis was used to develop a prediction of the combined overall effectiveness using results from impingement only and film cooling only cases. The analysis resulted in relatively good predictions, which served to reinforce the consistency of the experimental data.

One-Dimensional Zonal Model for the Unsteady Heat Transfer Analysis in an Open Volumetric Air Receiver

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Gurveer Singh ◽  
Vishwa Deepak Kumar ◽  
Laltu Chandra ◽  
R. Shekhar ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Operating Conditions ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
High Heat Flux ◽  
Unsteady Heat Transfer ◽  
Volumetric Heating ◽  
One Dimensional ◽  
Zonal Model

Abstract The open volumetric air receiver (OVAR)-based central solar thermal systems provide air at a temperature > 1000 K. Such a receiver is comprised of porous absorbers, which are exposed to a high heat-flux > 800 Suns (1 Sun = 1 kW/m2). A reliable assessment of heat transfer in an OVAR is necessary to operate such a receiver under transient conditions. Based on a literature review, the need for developing a comprehensive, unsteady, heat transfer model is realized. In this paper, a seven-equations based, one-dimensional, zonal model is deduced. This includes heat transfer in porous absorber, primary-air, return-air, receiver casing, and their detailed interaction. The zonal model is validated with an inhouse experiment showing its predictive capability, for unsteady and steady conditions, within the reported uncertainty of ±7%. The validated model is used for investigating the effect of operating conditions and absorber geometry on the thermal performance of an absorber. Some of the salient observations are (a) the maximum absorber porosity of 70–90% may be preferred for non-volumetric and volumetric-heating conditions, (b) the minimum air-return ratio should be 0.7, and (c) the smallest gap to absorber-length ratio of 0.2 should suffice. Finally, suggestions are provided for extending the model.

Modeling, Testing, and Evaluation of a Building-Integrated Photovoltaic-Thermal Collector

2009 ◽  
Author(s):  
Charles D. Corbin ◽  
Michael J. Brandemuehl
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Low Cost ◽  
Convection Heat Transfer ◽  
Calibration Error ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Electrical Efficiency ◽  
Building Integrated Photovoltaic ◽  
Low Efficiency

The performance of Building-Integrated Photovoltaic-Thermal (BIPV/T) collector is examined in this study. A full scale-test collector is monitored over several weeks in the summer of 2008 and measured data is used to calibrate a heat transfer model implemented in a common scientific computing software package. Following calibration, error between experimental measurements and the calibrated model outputs is within the limits of measurement uncertainty. Collector simulations are constructed to examine thermal efficiency, the effectiveness of the collector as a night-sky radiator, the effect of heat collection on electrical efficiency, the effect of two common exterior convection coefficients on collector performance, and the effect of eliminating the air gap between the PV and absorber surfaces. Overall collector thermal efficiency is relatively low compared to existing collectors. However, the potential low cost of the system could allow larger collector areas to compensate for low efficiency, especially in warm climates. Combined thermal and electrical efficiency can be as high as 34%. Additional analysis also indicates that the predicted thermal performance is highly dependent on the thermal resistance between the PV cells and the absorber plate and is sensitive to assumptions regarding wind-driven convection heat transfer coefficients.

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