The Experts below are selected from a list of 11097 Experts worldwide ranked by ideXlab platform
Zhifeng Wang - One of the best experts on this subject based on the ideXlab platform.
-
Numerical investigation of the heat transport in a very loose packed granular bed Air Receiver with a non-uniform energy flux distribution
Renewable Energy, 2019Co-Authors: Shengchun Zhang, Zhifeng Wang, Fengwu Bai, Pingrui HuangAbstract:Abstract This study analyzes the heat transfer of the solar energy absorbed by the porous media Receiver to Air where the porous media can reach temperatures up to 1000 °C. The heat transfer was studied numerically for a packed granular bed Air Receiver with a non-uniform energy flux distribution. The conduction is modeled as an effective thermal conductivity with the Ergun equation used to describe the pressure drop. The radiative heat transfer is modeled by a modified P-1 radiative heat transfer model. The local thermal non-equilibrium model is used to relate the Air temperatures to the porous media temperatures. Comparisons with experimental data show that this model can accurately predict the heat transfer in the packed granular bed Air Receiver. The model is used to analyze the effects of flow direction, gas mass flow rate per unit area, particle emissivity, estimated fractional contact area, and particle size. The results illustrate that downward flows, larger gas mass flow rates, higher particle emissivities, larger estimated fractional contact areas, and smaller particle sizes all enhance the heat transport and that the packed bed Receiver outlet Air temperature does not vary much for relatively short term fluctuations of the solar flux.
-
Experimental study of a heat pipe pressurized Air Receiver
SOLARPACES 2018: International Conference on Concentrating Solar Power and Chemical Energy Systems, 2019Co-Authors: Shunzhou Chu, Fengwu Bai, Zhiying Cui, Fuliang Nie, Zhifeng WangAbstract:This study investigated the startup characteristics and thermal performance of a heat pipe pressurized Air Receiver. The heat flux on the Receiver of around 130 kW/m2 was tested to be an appropriat...
-
Thermal analysis of honeycomb ceramic Air Receiver
2017Co-Authors: Zhifeng Wang, Fengwu Bai, Shunzhou Chu, Bei YangAbstract:This study investigated the heat transfer between Air flow and honeycomb ceramic Air Receiver. A one-dimensional model of the Receiver was established considering the distribution of the solar radiation within the channel and the radiative heat transfer between the inner surfaces. The sensitivity studies had been done to explore the influences of the absorber geometric parameters, the incident solar radiation and the Air flow rate on the Receiver steady-state thermal efficiency and outlet Air temperature. The minimal absorber length was analyzed to ensure high thermal efficiency, which is significant for the Receiver design and optimization.
-
dynamic simulation and experimental validation of an open Air Receiver and a thermal energy storage system for solar thermal power plant
Applied Energy, 2016Co-Authors: Qing Li, Zhifeng Wang, Bei Yang, Fengwu Bai, Baligh El Hefni, Sijie Liu, Syuichi Kubo, Hiroaki Kiriki, Mingxu HanAbstract:The transient performance of solar thermal power plants is critical to the system design and optimization. This study numerically investigates the dynamic efficiencies of an open-loop Air Receiver and a thermal energy storage unit. One-dimensional dynamic models of the Air Receiver and thermal energy storage were developed using the Modelica language with a graphical user interface and the Dymola solver to provide comprehensive thermal simulation at low computational cost. An Air Receiver and thermal energy storage experimental platforms were built to validate the simulation models. The simulation results compare well with the experimental data, so the models can be used to predict the variations of Air Receiver and thermal energy storage efficiencies. The models were then combined into a Receiver and thermal energy storage system model with control schemes. The schemes control the Air Receiver outlet Air temperature at relatively stable values while the thermal energy storage automatically switches between charging, discharging and stand-by modes.
-
Experimental study of a single quartz tube solid particle Air Receiver
Solar Energy, 2015Co-Authors: Fangzhou Wang, Tianjian Wang, Qing Li, Zhifeng WangAbstract:Abstract The quartz tube solid particle Air Receiver is a new type of Receiver in which fluidized particles absorb the solar radiation directly and heat the Air effectively, improving the efficiency of solar thermal electricity and reducing costs. In this article, the experiments of the single quartz tube solid particle Air Receiver focus on both cold fluidization and thermal performance. The results of cold fluidization experiment show that when the average diameter of solid particle is between 0.5 mm and 1 mm and initial relative particle packed height is between 0.3 and 0.4, the gas–solid fluidization meets the operating requirements of the Receiver. In the thermal performance testing experiments, the results show that less area in which solid particle absorbs the concentrated sunlight can improve the efficiency of Receiver and stabilize outlet Air temperature. The highest temperature is 867 °C in the thermal performance testing experiment. The results mentioned above provide important reference for improving the performance of the quartz tube solid particle Air Receiver.
Laltu Chandra - One of the best experts on this subject based on the ideXlab platform.
-
a novel approach for modelling fluid flow and heat transfer in an open volumetric Air Receiver using ansys fluent
Solar Energy, 2020Co-Authors: P Sharma, Laltu Chandra, R Shekhar, P S GhoshdastidarAbstract:Abstract Open volumetric Air Receiver (OVAR) has great potential as a source of process heat for metals processing operations. The two major components of OVAR are the porous absorbers and the return Air flow chamber (RAFC). Heat exchange between the “cooler” return Air and the hot curved absorber surface in RAFC is critical as it prevents overheating of absorbers. Unfortunately, modeling of Air flow in the RAFC is conspicuous by its absence. Calculations were performed in ANSYS-FLUENT using the local thermal non-equilibrium model for heat transfer in the porous absorber. Three dimensional flow and heat transfer simulations were carried out in the RAFC. Unfortunately, ANSYS decoupled heat exchange between the absorbers and return Air by splitting the curved absorber surface into real and imaginary surfaces. Decoupling also meant that heat flux had to be specified separately on the absorber and the RAFC, which was a challenge since only the total input solar flux is known. Hence the major contribution of this paper has been to incorporate two innovations in the simulation methodology. One, to couple the absorber and RAFC thermally by mapping the temperature of the real surface to the imaginary surface. Two, the flux used for heating Air in the absorber was calculated iteratively. Limited simulations suggest that in laboratory experiments, relatively inexpensive circumferential (Joule) heating of absorbers can reasonably mimic heating of absorbers by concentrated solar radiation.
-
One-Dimensional Zonal Model for the Unsteady Heat Transfer Analysis in an Open Volumetric Air Receiver
Journal of Thermal Science and Engineering Applications, 2020Co-Authors: Gurveer Singh, Laltu Chandra, Rajiv Shekhar, Vishwa Deepak Kumar, P S GhoshdastidarAbstract: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.
-
on the flow stability in a circular cylinder based open volumetric Air Receiver for solar convective furnace
Energy Procedia, 2018Co-Authors: G P Singh, Laltu ChandraAbstract:Abstract The arid desert regions are considered for installing the concentrated solar thermal based systems owing to the available direct normal irradiance. For process heat applications, like the solar convective furnace that requires an Air temperature of 750 K the open volumetric Air Receiver is preferred. Such innovative concepts are envisaged for achieving high thermal energy conversion efficiency. For the prolonged operation of the solar convective furnace system the stable flow is necessary. On the other hand, the thermally induced flow instability is reported in the open volumetric Air Receivers at a high temperature. This may limit the operating temperature range of a Receiver. In this paper the flow stability analysis in a circular cylinder based open volumetric Air Receiver with the straight pores is presented. The findings allow expecting a stable flow regime in such an absorber pore at a high flux concentration and temperature.
-
thermal and materials perspective on the design of open volumetric Air Receiver for process heat applications
2018Co-Authors: G P Singh, Rajesh Kumar, Ambesh Dixit, Laltu ChandraAbstract:The concentrated solar thermal technologies (CST) are versatile in view of their multi-faceted applications, such as, process heat, cooling, and electricity generation. These are of line and point-focusing types with the later having much higher flux concentration (in Suns). This allows achieving a temperature in excess of 1200 K using, for instance, the open volumetric Air Receiver (OVAR). Such a high temperature is useful for applications, like the one which is developed at IIT Jodhpur, namely the solar convective furnace for heat treatment of aluminum. This requires a temperature of up to 750 K in the first phase of development. Thus, a suitable solar selective coating withstanding such a high temperature and having a thermal conductivity close to the base material for operating in an open atmosphere is desirable. Because of its atmospheric exposure, Air and dust-induced degradation is inevitable, which may lead to its failure. These challenges are to be addressed for adapting such high-temperature CST technologies in arid deserts of India, the Middle-East, and Africa. In view of such challenges, the following details and foreseen developments are discussed in the paper: (a) design of OVAR including various sub-components; (b) flow-stability and the effect of heat-flux distribution on an absorber pore; (c) the developed coating and its characterization for OVAR.
-
experimental and computational investigation of heat transfer in an open volumetric Air Receiver for process heat application
2018Co-Authors: P Sharma, Laltu Chandra, R Shekhar, P S GhoshdastidarAbstract:India receives abundant solar irradiance with an annual average of ~19.97 MJ/m2 per day in Jodhpur only. This solar energy can be harnessed for electricity generation, melting or heat treatment of metals. Use of Air as heat transfer fluid offers significant advantages of being nontoxic, freely available and operating temperature beyond 800 °C. Considering these aspects, as a research initiative, open volumetric Air Receiver (OVAR) is being developed with a peak-power capacity of 4 kWth. The installed testing facility at IIT Jodhpur includes sub systems, which are thermal energy storage (TES), Air–water heat exchanger. In the absence of solar simulator electrical heating is being employed for circumferential (external) heating of the absorbers. In particular, the presented paper presents: (a) Effect of pore diameters (2 and 3 mm) on the average outlet temperature of absorber with porosity (Ɛ) ~52% at \( {\text{POA/MFR}} = 100\;{\text{kJ/kgK}} \), where POA is the equivalent Power-On-Aperture and MFR is mass-flow rate of Air; (b) Efficiency performance curve for absorbers with Ɛ ~ 52%; (c) Modeling of heat transfer in absorber with adopted commercial CFD tool FLUENT including returned Air circulation; (d) Comparison between CFD analyzed and experimentally obtained temperature for absorbers with Ɛ ~ 42, 52, and 62%; (e) Predictions with incident radiation onto the front surface of porous absorber.
R Shekhar - One of the best experts on this subject based on the ideXlab platform.
-
a novel approach for modelling fluid flow and heat transfer in an open volumetric Air Receiver using ansys fluent
Solar Energy, 2020Co-Authors: P Sharma, Laltu Chandra, R Shekhar, P S GhoshdastidarAbstract:Abstract Open volumetric Air Receiver (OVAR) has great potential as a source of process heat for metals processing operations. The two major components of OVAR are the porous absorbers and the return Air flow chamber (RAFC). Heat exchange between the “cooler” return Air and the hot curved absorber surface in RAFC is critical as it prevents overheating of absorbers. Unfortunately, modeling of Air flow in the RAFC is conspicuous by its absence. Calculations were performed in ANSYS-FLUENT using the local thermal non-equilibrium model for heat transfer in the porous absorber. Three dimensional flow and heat transfer simulations were carried out in the RAFC. Unfortunately, ANSYS decoupled heat exchange between the absorbers and return Air by splitting the curved absorber surface into real and imaginary surfaces. Decoupling also meant that heat flux had to be specified separately on the absorber and the RAFC, which was a challenge since only the total input solar flux is known. Hence the major contribution of this paper has been to incorporate two innovations in the simulation methodology. One, to couple the absorber and RAFC thermally by mapping the temperature of the real surface to the imaginary surface. Two, the flux used for heating Air in the absorber was calculated iteratively. Limited simulations suggest that in laboratory experiments, relatively inexpensive circumferential (Joule) heating of absorbers can reasonably mimic heating of absorbers by concentrated solar radiation.
-
experimental and computational investigation of heat transfer in an open volumetric Air Receiver for process heat application
2018Co-Authors: P Sharma, Laltu Chandra, R Shekhar, P S GhoshdastidarAbstract:India receives abundant solar irradiance with an annual average of ~19.97 MJ/m2 per day in Jodhpur only. This solar energy can be harnessed for electricity generation, melting or heat treatment of metals. Use of Air as heat transfer fluid offers significant advantages of being nontoxic, freely available and operating temperature beyond 800 °C. Considering these aspects, as a research initiative, open volumetric Air Receiver (OVAR) is being developed with a peak-power capacity of 4 kWth. The installed testing facility at IIT Jodhpur includes sub systems, which are thermal energy storage (TES), Air–water heat exchanger. In the absence of solar simulator electrical heating is being employed for circumferential (external) heating of the absorbers. In particular, the presented paper presents: (a) Effect of pore diameters (2 and 3 mm) on the average outlet temperature of absorber with porosity (Ɛ) ~52% at \( {\text{POA/MFR}} = 100\;{\text{kJ/kgK}} \), where POA is the equivalent Power-On-Aperture and MFR is mass-flow rate of Air; (b) Efficiency performance curve for absorbers with Ɛ ~ 52%; (c) Modeling of heat transfer in absorber with adopted commercial CFD tool FLUENT including returned Air circulation; (d) Comparison between CFD analyzed and experimentally obtained temperature for absorbers with Ɛ ~ 42, 52, and 62%; (e) Predictions with incident radiation onto the front surface of porous absorber.
-
design of a cyclone separator for cleaning of dust from volumetric Air Receiver
2017Co-Authors: G P Singh, Dheeraj Saini, Laltu Chandra, R ShekharAbstract:Arid regions, like Rajasthan, receive abundant solar energy and are prone to dust/sand storms. Line and point focusing technologies are used for harnessing this energy. At IIT Jodhpur, open porous volumetric Air Receiver based point focusing technology is considered for process heat application. This system uses Air as heat transfer fluid and is expected to achieve a temperature as high as 800 °C. This Receiver on account of volumetric heating, is exposed to a high heat flux, even, up-to 1000 suns (1sun = 1 kW/m2). As this Receiver is open to atmosphere, the dust storms in these regions can block the absorber pores and enter the system. Due to lower thermal conductivity of sand in comparison to absorber material, high temperature gradients and thermal stresses are expected on the absorber. It can result in failure of the system. In view of this the current activity aims at cleaning and collection of the removed dust from pores of Receiver. A 2D2D geometry of cyclone separator is proposed for deposited dust collection. The experiments on collection efficiency and pressure drop are performed and compared with empirical model. Pressure drop is estimated using CFD and experimentally validated for an improved relation for pressure drop coefficient.
-
on the design and evaluation of open volumetric Air Receiver for process heat applications
Solar Energy, 2015Co-Authors: P Sharma, Laltu Chandra, Rakesh Sarma, R Shekhar, P S GhoshdastidarAbstract:Abstract India receives abundant radiant energy from the sun on account of being located at the equatorial solar belt. Especially, an annual global solar radiation of about ⩾2400 kW h/m2 is received in Rajasthan and in northern Gujarat. As a part of research initiative at IIT Jodhpur, heliostat based concentrated solar tower using an open volumetric Air Receiver is being developed for generation of high-temperature process heat, which can be utilized for metal processing operations. This technology includes sub-systems such as thermal energy storage and heat exchangers. In particular, the presented paper describes the design evaluation of an open volumetric Air Receiver. Experiments and computational fluid dynamics tool, ANSYS-FLUENT are used for this purpose. The obtained hot Air (heat transfer fluid) can be employed, for instance, in heat treatment of metal such as Aluminum. The considered design aspects of the open volumetric Air Receiver are as follows: a. Influence of material thermal conductivity on the heat transfer modelling and thermally induced flow instability; b. Thermal–hydraulic analysis of recirculating Air injection system; c. Influence of absorber porosity on the heat transfer using the performed experiments; d. Design and evaluation of the designed mixer-assembly for uniform and non-uniform heating of porous absorber. In this paper, the first section presents order-of-magnitude analysis to quantify the effect of thermal conductivity of the solid on heat transfer process with porous absorbers. The second section deals with analysis of thermally induced flow instability in porous absorbers with the validated and numerically adopted computational fluid dynamics tool, namely, FLUENT using the reported experiment by Fend et al. (2004a). In addition, the effect of thermal conductivity on thermally induced flow instability is presented. The next section presents three-dimensional analysis of the designed mixer-assembly for Receiver using the validated CFD tool FLUENT. For this purpose, analyses are performed with different designs of mixer-plate and for different Receiver geometries. Further, based on the detailed analysis, the injection mechanisms of recirculating Air for circular and square absorber based Receivers are proposed. Finally, a 4kWth experimental facility, which is being commissioned at IIT Jodhpur to test solar thermal sub-systems such as Receiver, heat exchanger, thermal energy storage and experimental evaluation of Receiver components are described. These experiments demonstrate the effect of absorber-porosity, uniform and non-uniform concentrated solar irradiance level on heat transfer with porous absorbers and effectiveness of the selected mixer-assembly design in such a condition.
-
dust deposition mechanism and cleaning strategy for open volumetric Air Receiver based solar tower sub systems
Energy Procedia, 2015Co-Authors: G P Singh, Laltu Chandra, Davinder S Saini, Navneet Kumar Yadav, R Sarma, R ShekharAbstract:Abstract Desert regions like Rajasthan and Gujarat in India receives abundant solar energy. At the same time these regions are blessed with dust or sand. Solar thermal systems are one of the ways to harness this available energy. Open Volumetric Air Receiver based concentrated solar tower systems are being investigated for applications, like, metal processing. The dust deposition on sub-systems like, heliostat, porous Receiver will hinder smooth operation of such a system. Considering this fact, aspects of dust deposition in porous absorber of the Receiver and in heliostat are presented. In this direction, experiments and analyses are performed. This revealed that dust deposition on heliostat will be affected by its location among other parameters. The presented analysis shows the required free-stream Air velocity for cleaning of such a mirror depending on particle size and location. Experiments on dust deposition in a single pore of an absorber, simulated by a thin and long glass tube of 1.3 mm diameter is presented. Furthermore, experiments on dust deposition in one porous absorber reveal its severe consequence. Finally, a strategy for collection of the removed dust particles from these pores is presented to avoid their passage to internals.
P S Ghoshdastidar - One of the best experts on this subject based on the ideXlab platform.
-
a novel approach for modelling fluid flow and heat transfer in an open volumetric Air Receiver using ansys fluent
Solar Energy, 2020Co-Authors: P Sharma, Laltu Chandra, R Shekhar, P S GhoshdastidarAbstract:Abstract Open volumetric Air Receiver (OVAR) has great potential as a source of process heat for metals processing operations. The two major components of OVAR are the porous absorbers and the return Air flow chamber (RAFC). Heat exchange between the “cooler” return Air and the hot curved absorber surface in RAFC is critical as it prevents overheating of absorbers. Unfortunately, modeling of Air flow in the RAFC is conspicuous by its absence. Calculations were performed in ANSYS-FLUENT using the local thermal non-equilibrium model for heat transfer in the porous absorber. Three dimensional flow and heat transfer simulations were carried out in the RAFC. Unfortunately, ANSYS decoupled heat exchange between the absorbers and return Air by splitting the curved absorber surface into real and imaginary surfaces. Decoupling also meant that heat flux had to be specified separately on the absorber and the RAFC, which was a challenge since only the total input solar flux is known. Hence the major contribution of this paper has been to incorporate two innovations in the simulation methodology. One, to couple the absorber and RAFC thermally by mapping the temperature of the real surface to the imaginary surface. Two, the flux used for heating Air in the absorber was calculated iteratively. Limited simulations suggest that in laboratory experiments, relatively inexpensive circumferential (Joule) heating of absorbers can reasonably mimic heating of absorbers by concentrated solar radiation.
-
One-Dimensional Zonal Model for the Unsteady Heat Transfer Analysis in an Open Volumetric Air Receiver
Journal of Thermal Science and Engineering Applications, 2020Co-Authors: Gurveer Singh, Laltu Chandra, Rajiv Shekhar, Vishwa Deepak Kumar, P S GhoshdastidarAbstract: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.
-
experimental and computational investigation of heat transfer in an open volumetric Air Receiver for process heat application
2018Co-Authors: P Sharma, Laltu Chandra, R Shekhar, P S GhoshdastidarAbstract:India receives abundant solar irradiance with an annual average of ~19.97 MJ/m2 per day in Jodhpur only. This solar energy can be harnessed for electricity generation, melting or heat treatment of metals. Use of Air as heat transfer fluid offers significant advantages of being nontoxic, freely available and operating temperature beyond 800 °C. Considering these aspects, as a research initiative, open volumetric Air Receiver (OVAR) is being developed with a peak-power capacity of 4 kWth. The installed testing facility at IIT Jodhpur includes sub systems, which are thermal energy storage (TES), Air–water heat exchanger. In the absence of solar simulator electrical heating is being employed for circumferential (external) heating of the absorbers. In particular, the presented paper presents: (a) Effect of pore diameters (2 and 3 mm) on the average outlet temperature of absorber with porosity (Ɛ) ~52% at \( {\text{POA/MFR}} = 100\;{\text{kJ/kgK}} \), where POA is the equivalent Power-On-Aperture and MFR is mass-flow rate of Air; (b) Efficiency performance curve for absorbers with Ɛ ~ 52%; (c) Modeling of heat transfer in absorber with adopted commercial CFD tool FLUENT including returned Air circulation; (d) Comparison between CFD analyzed and experimentally obtained temperature for absorbers with Ɛ ~ 42, 52, and 62%; (e) Predictions with incident radiation onto the front surface of porous absorber.
-
Experimental and Computational Investigation of Heat Transfer in an Open Volumetric Air Receiver for Process Heat Application
Springer Proceedings in Energy, 2017Co-Authors: P Sharma, Laltu Chandra, Rajiv Shekhar, P S GhoshdastidarAbstract:India receives abundant solar irradiance with an annual average of ~19.97 MJ/m2 per day in Jodhpur only. This solar energy can be harnessed for electricity generation, melting or heat treatment of metals. Use of Air as heat transfer fluid offers significant advantages of being nontoxic, freely available and operating temperature beyond 800 °C. Considering these aspects, as a research initiative, open volumetric Air Receiver (OVAR) is being developed with a peak-power capacity of 4 kWth. The installed testing facility at IIT Jodhpur includes sub systems, which are thermal energy storage (TES), Air–water heat exchanger. In the absence of solar simulator electrical heating is being employed for circumferential (external) heating of the absorbers. In particular, the presented paper presents: (a) Effect of pore diameters (2 and 3 mm) on the average outlet temperature of absorber with porosity (Ɛ) ~52% at \( {\text{POA/MFR}} = 100\;{\text{kJ/kgK}} \), where POA is the equivalent Power-On-Aperture and MFR is mass-flow rate of Air; (b) Efficiency performance curve for absorbers with Ɛ ~ 52%; (c) Modeling of heat transfer in absorber with adopted commercial CFD tool FLUENT including returned Air circulation; (d) Comparison between CFD analyzed and experimentally obtained temperature for absorbers with Ɛ ~ 42, 52, and 62%; (e) Predictions with incident radiation onto the front surface of porous absorber.
-
on the design and evaluation of open volumetric Air Receiver for process heat applications
Solar Energy, 2015Co-Authors: P Sharma, Laltu Chandra, Rakesh Sarma, R Shekhar, P S GhoshdastidarAbstract:Abstract India receives abundant radiant energy from the sun on account of being located at the equatorial solar belt. Especially, an annual global solar radiation of about ⩾2400 kW h/m2 is received in Rajasthan and in northern Gujarat. As a part of research initiative at IIT Jodhpur, heliostat based concentrated solar tower using an open volumetric Air Receiver is being developed for generation of high-temperature process heat, which can be utilized for metal processing operations. This technology includes sub-systems such as thermal energy storage and heat exchangers. In particular, the presented paper describes the design evaluation of an open volumetric Air Receiver. Experiments and computational fluid dynamics tool, ANSYS-FLUENT are used for this purpose. The obtained hot Air (heat transfer fluid) can be employed, for instance, in heat treatment of metal such as Aluminum. The considered design aspects of the open volumetric Air Receiver are as follows: a. Influence of material thermal conductivity on the heat transfer modelling and thermally induced flow instability; b. Thermal–hydraulic analysis of recirculating Air injection system; c. Influence of absorber porosity on the heat transfer using the performed experiments; d. Design and evaluation of the designed mixer-assembly for uniform and non-uniform heating of porous absorber. In this paper, the first section presents order-of-magnitude analysis to quantify the effect of thermal conductivity of the solid on heat transfer process with porous absorbers. The second section deals with analysis of thermally induced flow instability in porous absorbers with the validated and numerically adopted computational fluid dynamics tool, namely, FLUENT using the reported experiment by Fend et al. (2004a). In addition, the effect of thermal conductivity on thermally induced flow instability is presented. The next section presents three-dimensional analysis of the designed mixer-assembly for Receiver using the validated CFD tool FLUENT. For this purpose, analyses are performed with different designs of mixer-plate and for different Receiver geometries. Further, based on the detailed analysis, the injection mechanisms of recirculating Air for circular and square absorber based Receivers are proposed. Finally, a 4kWth experimental facility, which is being commissioned at IIT Jodhpur to test solar thermal sub-systems such as Receiver, heat exchanger, thermal energy storage and experimental evaluation of Receiver components are described. These experiments demonstrate the effect of absorber-porosity, uniform and non-uniform concentrated solar irradiance level on heat transfer with porous absorbers and effectiveness of the selected mixer-assembly design in such a condition.
Zhiyong Wu - One of the best experts on this subject based on the ideXlab platform.
-
fully coupled transient modeling of ceramic foam volumetric solar Air Receiver
Solar Energy, 2013Co-Authors: Zhiyong Wu, Zhifeng WangAbstract:Abstract Ceramic foam is a promising material for the absorber of volumetric solar Air Receiver in concentrated solar thermal power (CSP) plant. The transient behaviors of volumetric solar Air Receiver are crucial to the Receiver’s controllability, and to some extent, the plant’s safety. This study numerically analyzes the transient behaviors of volumetric solar Air Receiver under various working conditions. A fully coupled transient model of the volumetric solar Air Receiver is developed in this paper. The pressure drop of the absorber, the interfacial heat transfer between the flowing fluid and solid, and the radiative heat transfer due to concentrated solar radiation absorption by ceramic foam and the radiation transport inside the media were included together in this transient model. In addition, the temperature fields of the fluid and solid phases were obtained by using the local thermal non-equilibrium model. A comparison of the computed results with experimental data shows that this coupled transient model can be used to predict the performance of volumetric solar Air Receiver. Based on this model, the transient behaviors of the solar Air Receiver under a sudden heat flux, a sudden loss of heat flux, and a step change of heat flux were studied. The results of this study are very helpful in designing and controlling volumetric solar Air Receivers.
-
numerical simulation of convective heat transfer between Air flow and ceramic foams to optimise volumetric solar Air Receiver performances
International Journal of Heat and Mass Transfer, 2011Co-Authors: Zhiyong Wu, Cyril Caliot, Gilles Flamant, Zhifeng WangAbstract:Porous ceramic foams are used to achieve high performance in solar heat recovery systems. Understanding the convective heat transfer between the Air flow and the ceramic foam is of great importance when optimising the volumetric Air Receiver. In this work, the convective heat transfer was numerically studied. The present approach was designed to compute the local convective heat transfer coefficient between the Air flow and a porous ceramic foam. For that purpose, the energy balance and the flow inside the porous ceramic foam were solved. In addition, a detailed geometry of the porous ceramic foam was considered. The ceramic foams were represented by idealised packed tetrakaidecahedron structures. The numerical simulations were based on the three dimensional Reynolds-averaged Navier–Stokes (RANS) equations. A sensitivity study on the heat transfer coefficient was conducted with the porosity, velocity and mean cell size as parameters. Based on the numerical simulation results, a correlation for the volumetric local convective heat transfer coefficient between Air and ceramic foams was developed. The resulting correlation covers a wide range of porosities, velocities, cell sizes and temperatures. The correlation results were compared with experimental data from the literature, and the comparison shows good agreement. The correlation is intended to be used in the design of volumetric solar Air Receivers.
-
experimental and numerical studies of the pressure drop in ceramic foams for volumetric solar Receiver applications
Applied Energy, 2010Co-Authors: Zhiyong Wu, Zhifeng Wang, Cyril Caliot, Gilles Flamant, Jinsong Zhang, Chong TianAbstract:This paper presents experimental and numerical studies of the pressure drop in ceramic foams for solar Air Receiver applications. There are three main aims in this study. The first is to measure the pressure drop in the studied ceramic foams, and to build an empirical model based on the experimental results and a parametric numerical simulation. The second aim is to study flow field characteristics in the ceramic foams, especially in the vicinity of the interface. The third is to study the pressure drop characteristics of two modified structures (by manufacturing holes on the ceramic foams) that are expected to decrease the pressure drop in ceramic foams, but maintain good heat transfer properties. The experimental results from the samples, including two modified structures, along with the simulation results, show that the pressure drop in the ceramic foams follows a modified Darcy relationship. The experimental results also show that the two modified structures dramatically decrease the pressure drop (with pressure drop decreases up to 70% at a superficial velocity of 5 m/s). Based on both the experimental and the simulation results, a generalized model for predicting the pressure drop in ceramic foams was proposed.
