scholarly journals Effects of Absorber Emissivity on Thermal Performance of a Solar Cavity Receiver

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Jiabin Fang ◽  
Nan Tu ◽  
Jinjia Wei
Keyword(s):  
Heat Loss ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Radiative Heat ◽  
Slight Effect ◽  
Radiative Heat Loss ◽  
Total Heat Loss ◽  
Convective Heat Loss ◽  
Performance Curves ◽  
Variation Tendency

Solar cavity receiver is a key component to realize the light-heat conversion in tower-type solar power system. It usually has an aperture for concentrated sunlight coming in, and the heat loss is unavoidable because of this aperture. Generally, in order to improve the thermal efficiency, a layer of coating having high absorptivity for sunlight would be covered on the surface of the absorber tubes inside the cavity receiver. As a result, it is necessary to investigate the effects of the emissivity of absorber tubes on the thermal performance of the receiver. In the present work, the thermal performances of the receiver with different absorber emissivity were numerically simulated. The results showed that the thermal efficiency increases and the total heat loss decreases with increasing emissivity of absorber tubes. However, the thermal efficiency increases by only 1.6% when the emissivity of tubes varies from 0.2 to 0.8. Therefore, the change of absorber emissivity has slight effect on the thermal performance of the receiver. The reason for variation tendency of performance curves was also carefully analyzed. It was found that the temperature reduction of the cavity walls causes the decrease of the radiative heat loss and the convective heat loss.

scholarly journals Optimizing solar dish performance using analytical flux distribution in focal region

2020 ◽  
Vol 9 (1) ◽  
pp. 63-67
Author(s):  
Dany Iman Santoso ◽  
Bambang Antoko ◽  
Djatmiko Ichsani
Keyword(s):  
Heat Loss ◽  
Thermal Efficiency ◽  
Flux Distribution ◽  
Radiative Heat ◽  
Total Heat ◽  
Focal Region ◽  
Radiative Heat Loss ◽  
Total Heat Loss ◽  
Image Characteristics ◽  
Parabolic Dish

In this paper, thermal performance analysis of 4 m2 solar dish collector is presented.The focal image characteristics of the solar dish are determined to propose the suitable design of a receiver. A flat plate was used for the receiver to measure flux distribution in the focal region. The measurement had been done in the midday. Intercept factor based on this distribution had been calculated and was obtained to calculate thermal efficiency after total heat loss was described. From the experiment, total heat loss was formed by conductive and radiative in the receiver. The results showed that the increase in total heat loss followed the increase in receiver temperature and it caused a decrease in thermal efficiency. On the peak of the measurement or in midday, receiver temperature can achieve 138°C and it gave around 1200-Watt heat loss and it was dominated by radiative heat loss for around 80%. The thermal efficiency of the system due to flux distribution measurement in the focal region was above 70% and it was classified as high average but we needed to cover this flux up so it did not lose a lot of heat. Cavity aperture would keep around 20% total heat loss and it minimized radiative heat loss from the flux. The design of cavity aperture was the next discussion to insulate thermal heat reflection of the parabolic dish system from high radiative heat loss.©2020. CBIORE-IJRED. All rights reserved

Mechanisms of thermal stability during flight in the honeybee apis mellifera

1999 ◽  
Vol 202 (11) ◽  
pp. 1523-1533 ◽  
Author(s):  
S.P. Roberts ◽  
J.F. Harrison
Keyword(s):  
Thermal Stability ◽  
Heat Loss ◽  
Heat Production ◽  
Radiative Heat ◽  
Carbon Dioxide Production ◽  
Metabolic Heat Production ◽  
Evaporative Heat Loss ◽  
Radiative Heat Loss ◽  
Convective Heat Loss ◽  
Metabolic Heat

Thermoregulation of the thorax allows honeybees (Apis mellifera) to maintain the flight muscle temperatures necessary to meet the power requirements for flight and to remain active outside the hive across a wide range of air temperatures (Ta). To determine the heat-exchange pathways through which flying honeybees achieve thermal stability, we measured body temperatures and rates of carbon dioxide production and water vapor loss between Ta values of 21 and 45 degrees C for honeybees flying in a respirometry chamber. Body temperatures were not significantly affected by continuous flight duration in the respirometer, indicating that flying bees were at thermal equilibrium. Thorax temperatures (Tth) during flight were relatively stable, with a slope of Tth on Ta of 0.39. Metabolic heat production, calculated from rates of carbon dioxide production, decreased linearly by 43 % as Ta rose from 21 to 45 degrees C. Evaporative heat loss increased nonlinearly by over sevenfold, with evaporation rising rapidly at Ta values above 33 degrees C. At Ta values above 43 degrees C, head temperature dropped below Ta by approximately 1–2 degrees C, indicating that substantial evaporation from the head was occurring at very high Ta values. The water flux of flying honeybees was positive at Ta values below 31 degrees C, but increasingly negative at higher Ta values. At all Ta values, flying honeybees experienced a net radiative heat loss. Since the honeybees were in thermal equilibrium, convective heat loss was calculated as the amount of heat necessary to balance metabolic heat gain against evaporative and radiative heat loss. Convective heat loss decreased strongly as Ta rose because of the decrease in the elevation of body temperature above Ta rather than the variation in the convection coefficient. In conclusion, variation in metabolic heat production is the dominant mechanism of maintaining thermal stability during flight between Ta values of 21 and 33 degrees C, but variations in metabolic heat production and evaporative heat loss are equally important to the prevention of overheating during flight at Ta values between 33 and 45 degrees C.

Numerical Investigation of the Tube Layout Effects on the Heat Losses of Solar Cavity Receiver

2017 ◽  
Vol 10 (1) ◽  
Author(s):  
Jiabin Fang ◽  
Nan Tu ◽  
Jinjia Wei ◽  
Tao Fang ◽  
Xuancheng Du
Keyword(s):  
Heat Loss ◽  
Convective Heat ◽  
Radiative Heat ◽  
Calculation Model ◽  
Heat Losses ◽  
Radiative Heat Loss ◽  
Water Steam ◽  
Convective Heat Loss ◽  
Circulation Mode ◽  
Lower Heat

The effects of tube layout on the heat losses of solar cavity receiver were numerically investigated. Two typical tube layouts were analyzed. For the first tube layout, only the active surfaces of cavity were covered with tubes. For the second tube layout, both the active cavity walls and the passive cavity walls were covered with tubes. Besides, the effects of water–steam circulation mode on the heat losses were further studied for the second tube layout. The absorber tubes on passive surfaces were considered as the boiling section for one water–steam circulation mode and as the preheating section for the other one, respectively. The thermal performance of the cavity receiver with each tube layout was evaluated according to the previous calculation model. The results show that the passive surfaces appear to have much lower heat flux than the active ones. However, the temperature of those surfaces can reach a quite high value of about 520 °C in the first tube layout, which causes a large amount of radiative and convective heat losses. By contrast, the temperature of passive surfaces decreases by about 200–300 °C in the second tube layout, which leads to a 38.2–70.3% drop in convective heat loss and a 67.7–87.7% drop in radiative heat loss of the passive surfaces. The thermal efficiency of the receiver can be raised from 82.9% to 87.7% in the present work.

Effect of radiative heat loss on steady hypersonic flow past a blunt body

1967 ◽  
Vol 29 (3) ◽  
pp. 485-494 ◽  
Author(s):  
M. I. G. Bloor
Keyword(s):  
Numerical Solution ◽  
Heat Loss ◽  
Blunt Body ◽  
Radiative Heat ◽  
Constant Density ◽  
Axially Symmetric ◽  
Radiative Heat Loss ◽  
Stagnation Region ◽  
Expansion Procedure ◽  
Axis Of Symmetry

Using the grey gas approximation, the effect of radiative heat loss on axially symmetric flows is studied. Using an expansion procedure about the axis of symmetry, a numerical solution for the stagnation region is found taking the shock to be spherical. The results of this calculation are compared with the results of Lighthill's non-radiative constant density solution.

scholarly journals Analysis of MHD Forced Convective Flow of Variable Fluid Properties over a Saturated Porous Medium with Thermal Radiation Effect

2016 ◽  
Vol 9 ◽  
pp. 47-65 ◽  
Author(s):  
Kolawole Sunday Adegbie ◽  
Adeyemi Isaiah Fagbade
Keyword(s):  
Porous Medium ◽  
Heat Loss ◽  
Convective Flow ◽  
Radiative Heat ◽  
Saturated Porous Medium ◽  
Fluid Velocity ◽  
Radiative Heat Loss ◽  
Variable Fluid Properties ◽  
Fluid Properties ◽  
Forced Convective Flow

The present paper addresses the problem of MHD forced convective flow in a fluid saturated porous medium with Brinkman-Forchheimer model, which is an important physical phenomena in engineering applications. The paper extends the previous models to account for effects of variable fluid properties on the forced convective flow through a porous medium in the presence of radiative heat loss using bivariate spectral relaxation method (BSRM). The dynamic viscosity and thermal conductivity of the newtonian fluid are assumed to vary linearly respectively, with temperature whereas the contribution of thermal radiative heat loss is based on Rosseland diffussion approximation. The flow model is described and expressed in form of a highly coupled nonlinear system of partial differential equations. The method of solution BSRM as proposed by Motsa [25] seeks to decouple the original system of PDEs to form a sequence of equations that can be solved in a computationally efficient manner. BSRM is an approach that applies spectral collocation independently in all underlying independent variable is executed to obtain approximate solutions of the problem. The proposed algorithm is supposed to be a very accurate, convergent and very effective in generating numerical results. The results obtained show a significant effects of the flow control parameters on the fluid velocity and temperature respectively. Consequently, the wall shear stress and local heat transfer rate of the present paper are compared with the available results in literatures. Remarkable impacts and a good agreement are found.

Cavity receiver thermal performance analysis based on total heat loss coefficient and efficiency factor

2018 ◽  
Vol 42 (6) ◽  
pp. 2284-2289 ◽  
Author(s):  
Qiangqiang Zhang ◽  
Xin Li ◽  
Zhifeng Wang ◽  
Zhi Li ◽  
Hong Liu ◽  
...  
Keyword(s):  
Performance Analysis ◽  
Heat Loss ◽  
Thermal Performance ◽  
Efficiency Factor ◽  
Loss Coefficient ◽  
Total Heat ◽  
Total Heat Loss
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