Side-on Wind Research Articles

Response surface methodology for characterization of wind effect on combined convective loss from a bicylindrical cavity receiver

To assess the combined convective loss of a bicylindrical cavity receiver, an investigation was conducted using response surface methodology under varying wind directions, speeds, and cavity tilt angles. The study revealed that wind direction has a more substantial influence on the combined Nusselt number than cavity tilt angle. For all wind speeds and cavity tilt angles, the head-on wind direction results in a higher combined convective loss compared to back-on and side-on wind directions. Wind speed significantly affects the combined Nusselt number at higher cavity tilt angles for the back-on and side-on winds, with the effect diminishing at lower tilt angles. Increasing the tilt angle of the cavity leads to a greater change in the combined Nusselt number as wind speed increases. A quadratic model was developed to predict the combined Nusselt number, which achieves reasonable agreement between the predicted and experimental values, with a deviation of up to 12.5%.

Integrated optical and thermal model to investigate the performance of a solar parabolic dish collector coupled with a cavity receiver

The cavity receiver is the most promising type of receiver, which drops the heat loss and converts the incoming concentrated radiation to useful energy. In this work, the coupled optical-thermal investigation is performed for a novel cavity receiver of a 40 m2 parabolic dish collector to estimate the thermal performance. The variation of thermal performance with inclination γ, wind direction ψ, wind speed V, and inlet temperature THTF,i has been discussed. SolTrace and ANSYS® Fluent are used for optical and thermal modeling, respectively. Surface errors, heat flux at each coordinate of the receiver, and the parabolic dish effect have been considered in the study. The text user interface (TUI) over graphical has been adopted in ANSYS® to reduce the computational expenditure for variation of parameters. In thermal modeling, a user-defined function (UDF) is applied for mapping data from SolTrace simulation with 107 rays. Therminol 66, as heat transfer fluid, is used in the receiver coils. The optical performance of 84.15% is achieved at an aiming height of 4.5 m. The thermal performance of 73.11% is obtained as maximum in no-wind conditions for 90° tilt. The worst thermal performance is obtained in side-on wind. Further, the performance has been compared with other models and found to be performing well.

Combined convective loss from a bicylindrical cavity receiver under wind condition: an experimental study

ABSTRACT The solar cavity receiver performance is considerably influenced by wind specifications in the parabolic dish system. This paper performs experiments to study the effects of wind direction and speed on the heat losses from a bicylindrical cavity receiver at different inclinations. A range of wind speeds from 0.3 to 5.7 m/s and the three head-on, back-on, and side-on wind directions for the side-facing and downward-facing cavity situations are examined. The cavity surface temperature distribution shows a jump due to the particular shape of the cavity and the sharp corner between two cylinders. The results show that the head-on wind yields a higher combined convection heat loss in contrast to the back-on and side-on wind directions for all wind speeds and cavity inclinations except 90° (vertically downward-facing) where the effects of wind directions are the same. For the lower side-on wind speeds, increasing cavity inclination results in decreasing combined convective loss, while on the contrary the change in the combined convective loss is very small regardless of the cavity inclination at higher wind speeds above 4 m/s. Moreover, for the back-on wind, comparing to the other wind directions, the combined convective loss is lower. For all wind directions and speeds, the horizontal cavity receiver gives lower forced convective loss compared with the natural convective loss. For the downward-facing cavity, an empirical correlation has been developed for the combined Nusselt number with respect to the Reynolds number, Grashof number, cavity inclination, wind direction, and the absolute temperature ratio. The proposed correlation supports the experimental results by a deviation within ±20%. Moreover, the uncertainty analysis revealed that the relative expanded uncertainty of combined Nusselt number varies between 2.1% and 16.3%, depending upon the cavity inclination, wind speed and direction.

Optical-thermal conversion characteristics of cylindrical receiver with built-in helically coiled tubes

Based on Monte Carlo Ray Trace (MCRT) principle and CFD three-dimensional numerical simulation, the optical-thermal conversion characteristics of cylindrical cavity receiver with built-in helically coiled tubes were explored. The influence of tracking error, two geometric parameters (i.e., tube diameter, aspect ratio), and two operating parameters (i.e. Heat Transfer Fluid (HTF) inlet mass flow rate, wind velocity and direction) were discussed detailedly. The results indicate that the solar radiation heat flux on the outer wall of the coiled tubes is considerably uneven and two heat flux peaks can be observed separately at around Z = 0.05 m and near the bottom of the cavity. When the tube diameter is increased from 8 mm to 18 mm, the optical efficiency, thermal efficiency and optical-thermal conversion efficiency of the receiver are reduced by 0.38%, 0.3%, 1.62%, respectively. There exists an “optimal value” for aspect ratio to maximize the utilization of solar radiation, which is 1.8 under no-wind condition (wind speed V = 0 m/s). The increase of wind speed can obviously enlarge the heat loss and reduce the efficiency, among which the side-on wind has the greatest influence on thermal performance. Once the mass flow rate is greater than 0.03 kg/s, the efficiency improvement is no longer significant.

Thermal losses evaluation of an external rectangular receiver in a windy environment

The efficiency of a CSP plant heavily depends on the performance of the receiver. The receiver is responsible for light-heat conversion in a power generation system. With the objective of numerical evaluation of the thermal losses of an external receiver, a method was developed in the present study. Solar flux was obtained on a north-facing receiver using the “SolarPilot” software, through Monte-Carlo ray tracing technique. Apposite boiling heat transfer coefficients were selected and then applied to obtain the temperature at the surface of the boiling tubes. Numerical simulations were performed to quantify the heat losses in the receiver at different wind velocities. Maximum heat flux and temperature were obtained at the center of the receiver. The results indicated that wind direction and wind velocity have a significant impact on the extent of heat losses. Maximum heat losses occur in the side-on wind direction (i.e., west bound) while losses are minimum in the head-on wind direction (i.e., north bound). Thermal losses through the receiver contribute a sizeable portion to overall energy losses in power tower systems, hence, to attenuate the heat losses a new, yet simple, design is proposed with the addition of wind-blocking walls at the receiver’s periphery. The walls achieve noticeable heat retention in all wind directions, but their role is more prominent in the head-on wind direction. In best case scenario, attaching 1 m wide wind blocking walls resulted in a diminution of about 33 percent of losses in the head-on wind direction at 9 m/s wind velocity. Results obtained are then employed to derive a simplified correlation model to evaluate convective heat losses as a function of wind direction, wind velocity, receiver’s surface area and wind blocking wall width.

The influence of wall temperature distribution on the mixed convective losses from a heated cavity

An experimental investigation is presented of the effects of wind speed (0–9 m/s), yaw angle (0° and 90°), and tilt angle (15° and −90°) on the mixed convective heat losses from a cylindrical cavity heated with different internal wall temperature distributions. The internal wall comprised 16 individually controlled heating elements to allow the distribution of the surface temperature to be well controlled, while the air flow was controlled with a wind tunnel. It is found that temperature distribution has a strong influence on the convective heat losses, with a joint dependence on the wind speed and its direction. For the no-wind and side-on wind conditions, the measured range of the heat losses varied by up to 50% with a change in the wall temperature distribution. However, for high head-on wind speeds, this variation reduced down to ∼20%. In addition, the heat losses from downward tilted were ∼3 times larger than the upward facing heated cavity for high wind speeds (typical of tower-mounted and beam-down configurations, respectively). Also, the measured heat losses were found to be only slightly dependent on wind speed and direction in contrast with the downward tilted cases.

The Wind Test on Heat Loss from Three Coil Cavity Receiver for a Parabolic Dish Collector

The heat loss from cavity receiver in parabolic dish system determines the efficiency and cost effectiveness of the system. A modified three coil solar cavity receiver of inner wall area approximately three times of single coil receiver, is experimentally investigated to study the effect of fluid inlet temperature (Tfi=50°C to 75 °C) and cavity inclination angle (θ = 0° to 90°) on the heat loss from receiver under wind condition for head on wind and side on wind velocity at 3 m/s. Overall it was found that the natural and forced convection total heat loss increases with increase in mean fluid temperature. The combined heat loss decreases sharply with the increase in cavity inclination and observed to be maximum for horizontal position of receiver and minimum with the receiver facing vertically downward for all investigations. The maximum heat lossin wind test (V=3m/s) is 1045 W at θ=0° cavity inclination at mean fluid temperature 68 °C and minimum at 173 W θ=90° at 53°C. Total heat loss from the receiver under wind condition (V=3m/s) is up to 25% higher(1.25 times at 0° inclination) than without wind at mean fluid temperature ~70°C and minimum 19.64 % (1.2 times at 90° inclination) in mean temperature ~50 °C . In horizontal position of the receiver (θ=0°), the totalheat loss by head on wind is about 1.23 times (18% higher ) as compared to side on wind (at fluid mean temperature ~ 70°C). For receiver facing downward (θ=90°), for head-on wind, total heat loss is approximately the same as that for side-on wind.

Experimental investigation of the effects of wind speed and yaw angle on heat losses from a heated cavity

An experimental investigation of the effects of wind speed (0–12 m/s) and yaw angle (0°–90°) on the convective heat losses from a cylindrical cavity heated with a uniform wall temperature, is presented. The cavity is heated with 16 individually controlled copper surface elements, so that both the heat losses and the heat flux distribution can be measured and subjected to a controlled convective environment in the open section of a wind tunnel. It was found that the convective heat losses through the aperture are ∼4 times greater for the head-on wind case than for the side-on wind case, when the inverse of Richardson number (1/Ri) > 77 (wind speed >12 m/s). For the no-wind condition, ≈85% of the heat was lost from the lower half of the surface of the cavity, while for 1/Ri > 43 (wind speed >9 m/s), the heat loss was more uniformly distributed over the surface of the cavity. For head-on-wind conditions and for 1/Ri > 19 (wind speeds >6 m/s), the convective heat losses are ∼2 times greater than for side-wind conditions. The correlations between the mixed (natural and forced) convective heat losses, Nusselt number and Richardson number are also reported.

Numerical investigation on the thermal performance of molten salt cavity receivers with different structures

The geometry of a solar cavity receiver affects the absorption of incident solar energy and the temperature distribution on the absorber tube panels, and hence affects the operation stability and efficiency of the solar receiver. A modified combined computational method was proposed to investigate the thermal performance of the three dimensional (3-D) molten salt cavity models in steady state. This computational method was also used to calculate the thermal performance of the receiver in the Molten-Salt Subsystem/Component Test Experiment (MSS/CTE) in the United States, and the results agree well with published data. Molten salt cavity receivers with different heights were studied. The results show that a too-low or too-high height leads to low thermal efficiency of a receiver. Therefore, appropriate heights shall be chosen to enable receivers achieve relatively high efficiencies and reach low temperatures. The molten salt cavity receivers with different cross-sections in the chosen heights were then studied, to obtain a high-efficiency cavity receiver structure without increasing the inner surface area or the depth of the cavity, under the condition that the molten salt cavity receivers were in the same perimeter of the cross-section, aperture size, cavity height, tube panel and fluid flow layouts but different cavity depths. When only the lengths of the back walls next to the side walls had been increased, the thermal efficiency decreased first and then increased with the depth decreasing, which reached the lowest value when the depth was 2.71m. When the depth of the modified receiver is small enough, its thermal efficiency can be higher than that of the MSEE receiver. When only the lengths of the two walls adjacent to the aperture had been increased, the thermal efficiency increased with the depth decreasing, and was always higher than that of the receiver in the Molten-salt Electric Experiment (MSEE) in the United States. The thermal-efficiency difference between the two arrangements of the side walls decreased with a decrease in the cavity depth. The cross-section of the MSEE receiver is similar to that of the receiver in the molten salt electric experiment by Sandia National Laboratories. Under the condition of side-on wind at a velocity of 8.3m/s, the thermal efficiency of the modified cavity with the minimum depth is 2% higher than that of the MSEE cavity with the maximum depth. The convective heat loss is 3.1% lower, while the radiative and reflective heat losses changed slightly. Therefore, the modified cavity in the present study is capable of achieving a higher efficiency with a less depth.

Experimental and numerical analysis of convective heat losses from spherical cavity receiver of solar concentrator

Spherical cavity receiver of solar concentrator is made up of Cu tubing material having cavity diameter 385 mm to analyze the different heat losses such as conduction, convection and radiation. As the convection loss plays major role in heat loss analysis of cavity receiver, the experimental analysis is carried out to study convective heat loss for the temperature range of 55-75?C at 0?, 15?, 30?, 45?, 60?, and 90? inclination angle of downward facing cavity receiver. The numerical analysis is carried out to study convective heat loss for the low temperature range (55-75?C) as well as high temperature range (150-300 ?C) for no wind condition only. The experimental set-up mainly consists of spherical cavity receiver which is insulated with glass wool insulation to reduce the heat losses from outside surface. The numerical analysis is carried out by using CFD software and the results are compared with the experimental results and found good agreement. The result shows that the convective loss increases with decrease in cavity inclination angle and decreases with decrease in mean cavity receiver temperature. The maximum losses are obtained at 0? inclination angle and the minimum losses are obtained at 90? inclination angle of cavity due to increase in stagnation zone in to the cavity from 0? to 90? inclination. The Nusselt number correlation is developed for the low temperature range 55-75?C based on the experimental data. The analysis is also carried out to study the effect of wind speed and wind direction on convective heat losses. The convective heat losses are studied for two wind speeds (3 m/s and 5 m/s) and four wind directions [? is 0? (Side-on wind), 30?, 60?, and 90? (head-on wind)]. It is found that the convective heat losses for both wind speed are higher than the losses obtained by no wind test. The highest heat losses are found for wind direction ? is 60? with respect to receiver stand and lowest heat losses are found for wind direction ? is 0? (side-on wind). The heat losses obtained for wind direction, ?, is 30? condition are higher than the heat losses obtained for wind direction ? is 0? (side-on wind) condition, while the heat losses obtained by wind direction ? is 90? (head-on wind) condition are less than the heat losses obtained for wind direction, ?, is 60? condition.

Heat loss investigation from spherical cavity receiver of solar concentrator

The heat losses are mainly affects on the performance of cavity receiver of solar concentrator. In this paper, the experimental and numerical study is carried out for different heat losses from spherical cavity receiver of 0.385 m cavity diameter and 0.154 m opening diameter. The total and convection losses are studied experimentally to no wind and wind conditions for the temperature range of 150 °C to 300 °C at 0°, 30°, 45°, 60° and 90° inclination angle of cavity receiver. The experimental set up mainly consists of copper tube material cavity receiver wrapped with nichrome heating coil to heat the cavity and insulated with glasswool insulation. The numerical analysis was carried out with Fluent Computational fluid dynamics (CFD) software, to study connective heat losses for no wind condition only. The numerical results are compared with experimental results and found good agreement with maximum deviation of 12 %. The effect of inclination angle of cavity receiver on total losses & convection losses shows that as the inclination angle increases from 0o to 90o, both losses decreased due to decreased in convective zone into the cavity receiver. The effect of operating temperature of cavity shows that as the temperature of cavity receiver increases, the total and convective losses goes on increasing. The effect of external wind at 2 m/s and 4 m/s in two directions (side-on wind and head-on wind) is also studied experimentally for total and convective heat losses. The result shows that the heat losses are higher for head-on wind condition compared to side-on wind and no wind condition at all inclination angle of cavity receiver. The present results are also compared to the convective losses obtained from the correlations of Stine & Mcdonald and M. Prakash. The convective loss from these correlations shows nearest prediction to both experimental and numerical results.

Effect of wind speed and direction on convective heat losses from solar parabolic dish modified cavity receiver

The performance of solar parabolic dish collector is significantly influenced by heat losses due to wind speed and direction. In this article, investigation of convective heat losses from the modified cavity receiver of solar parabolic dish collector is carried out numerically by considering the wind direction, wind speed, receiver configuration and receiver orientation. The effect of wind on the receiver in various directions (φ=−90° to 90°), wide range of operating wind speeds (V=0–10m/s), receiver inclinations (β=0–90°) and varying surface temperature on convective heat loss from the receiver are studied. Velocity vectors, velocity contours, temperature contours are presented to show the effect of wind on the heat loss from the modified cavity receiver. The forced convection is found to have similar trend of free convection heat loss at lower wind speed. However at higher wind speed, such a pattern is not observed. At lower wind speeds say less than critical wind speed (<2.5m/s), the forced convection heat loss is lower than natural convection heat loss for lower receiver inclinations and wind direction ranging between −90° and 0°. The forced convection heat loss is more significant than free convection heat loss above 5m/s for all φ and β values. For side-on winds, at higher wind speeds above 5m/s, irrespective of receiver inclination, the variation of forced convection heat loss is marginal (less than 5%). The maximum forced convection heat loss occurs for partly open receivers (receiver aperture diameter ratio, RAD=0.4 and 0.6) at φ=0 (side-on wind) for all receiver inclinations and at φ=30° for RAD=0.8 and 1. The receiver inclination has less effect on heat loss from the receiver for V>2.5m/s due to side-on wind. The highest convection heat loss occurs for fully open (RAD=1) receiver as compared to partly open (RAD<1) modified cavity receiver. Nusselt number correlation is proposed to calculate combined convection heat losses from the receiver as a function of receiver inclination, wind direction, wind velocity and aperture diameter ratio.

Combined heat loss analysis of solar parabolic dish – modified cavity receiver for superheated steam generation

In this article, a 3-D numerical modeling is carried out to determine combined convection and surface radiation heat losses from a modified cavity receiver of parabolic dish collector used as mono-tube boiler for sub-cooled, saturated and superheated steam generation conditions. The forced convection heat loss from the modified cavity receiver is estimated using Nusselt number correlation developed for the modified cavity receiver. The effect of receiver inclination (β), operating temperature (Tw), emissivity of the cavity cover (∊), thickness of insulation (tins) on the combined heat losses from the modified cavity receiver is investigated. The boundary conditions for wall temperature and insulation thicknesses are chosen to match the three steam generation conditions. It is found that the natural convection heat losses are higher at β=0° (receiver facing sideward) and lower at β=90° (receiver facing down) whereas the forced convection heat loss is higher at β=90° and lower at β=0°. The variation of radiation heat losses is marginal for all values of β and vary with Tw. The effect of various parameters such as receiver inclination, wind direction (φ), wind speed and diameter ratios on forced convection heat loss from the receiver has also been studied. The forced convection heat loss at lower wind speeds (<2.5m/s) is lower than the natural convection heat losses. The maximum heat losses occur at side-on wind direction (φ=0) followed by head-on wind directions (φ=30–90°) and back-on wind directions (φ=-90° to -30°). The heat losses vary with diameter ratios for different configurations of the receiver. The forced convection heat loss is 1.2–9 times higher than natural convection heat loss for diameter ratio (ratio of cavity diameter to aperture diameter, d/D)=0.4 at 5m/s and receiver inclinations varying from 0° to 90°. Nusselt number correlations have been proposed based on the numerical analysis to estimate the combined convective and radiative heat loss. The present study attempts to estimate natural convection, forced convection and surface radiation heat losses from the modified cavity receiver under various conditions.

Numerical analysis of the influence of inclination angle and wind on the heat losses of cavity receivers for solar thermal power towers

The convective heat losses of cavity receivers for solar thermal power towers are of great importance for the overall efficiency of the whole system. However, the influence of wind on these losses has not been studied sufficiently for large scale cavity receivers with different inclination angles. In this present study the impact of head-on and side-on wind on large cavity receivers with inclination angles in the range of 0° (horizontal cavity) to 90° (vertical cavity) is analyzed numerically. The simulation results are compared to data published in literature. When no wind is present the losses decrease considerably with increasing inclination angle of the receiver. In case of a horizontal receiver wind does not have a huge impact on the losses: they remain constant on a high level. In case of an inclined cavity wind increases the heat losses significantly in most of the cases, although the highest absolute value of the losses occurs for the horizontal receiver exposed to head on wind. In some cases, when wind is flowing parallel to the aperture plane, a reduction of the heat losses is observed. The temperature distribution in the cavity is analyzed in order to explain the impact of wind on the heat losses. Wind in general causes a shrinking of the zone with uniform high temperature in the upper region of the cavity, whereas wind flowing parallel to the aperture plane additionally inhibits hot air from leaving the cavity and therefore leads to an increased temperature in the lower zone.

Thermal performance simulation of a solar cavity receiver under windy conditions

Solar cavity receiver plays a dominant role in the light–heat conversion. Its performance can directly affect the efficiency of the whole power generation system. A combined calculation method for evaluating the thermal performance of the solar cavity receiver is raised in this paper. This method couples the Monte-Carlo method, the correlations of the flow boiling heat transfer, and the calculation of air flow field. And this method can ultimately figure out the surface heat flux inside the cavity, the wall temperature of the boiling tubes, and the heat loss of the solar receiver with an iterative solution. With this method, the thermal performance of a solar cavity receiver, a saturated steam receiver, is simulated under different wind environments. The highest wall temperature of the boiling tubes is about 150 °C higher than the water saturation temperature. And it appears in the upper middle parts of the absorbing panels. Changing the wind angle or velocity can obviously affect the air velocity inside the receiver. The air velocity reaches the maximum value when the wind comes from the side of the receiver (flow angle α = 90°). The heat loss of the solar cavity receiver also reaches a maximum for the side-on wind.

Investigations on heat losses from a solar cavity receiver

Thermal as well as optical losses affect the performance of a solar parabolic dish-cavity receiver system. Convective and radiative heat losses form the major constituents of the thermal losses. In this paper, an experimental and numerical study of the steady state convective losses occurring from a downward facing cylindrical cavity receiver of length 0.5 m, internal diameter of 0.3 m and a wind skirt diameter of 0.5 m is carried out. The experiments are conducted for fluid inlet temperatures between 50 °C and 75 °C and for receiver inclination angles of 0° (side ways facing cavity), 30°, 45°, 60° and 90° (vertically downward facing receiver). The numerical study is performed for fluid inlet temperatures between 50 °C and 300 °C and receiver inclinations of 0°, 45° and 90° using the Fluent CFD software. The experimental and the numerical convective loss estimations agree reasonably well with a maximum deviation of about 14%. It is found that the convective loss increases with mean receiver temperature and decreases with increase in receiver inclination. Nusselt number correlations are proposed for two receiver fluid inlet temperature ranges, 50–75 °C and 100–300 °C, based on the experimental and predicted data respectively. Besides no-wind tests, investigations are also carried out to study the effects of external wind at two different velocities in two directions (head-on and side-on). The wind induced convective losses are generally higher than the no-wind convective loss (varying between 22% and 75% for 1 m/s wind speed and between 30% and 140% for the 3 m/s wind speed) at all receiver inclination angles, the only exception being the loss due to side-on wind at 0° receiver inclination angle. This is because the wind acts as a barrier at the aperture preventing the hot air to flow out of the receiver. The head-on wind causes higher convective loss than the side-on wind. Nusselt number correlations proposed in this work are compared with the existing correlations in the literature. It is found that the correlations available in literature under-predict the convective losses at mean receiver temperatures between 100 °C and 300 °C. This is due to the fact that the correlations are developed for certain receiver geometries having the ratio of aperture diameter to receiver diameter equal to or lesser than one.