Experimental determination of the overall heat loss coefficient for energy requirement of greenhouse heating

2005 ◽  
Vol 29 (10) ◽  
pp. 937-944 ◽  
Author(s):  
H. Huseyin Ozturk
Keyword(s):  
Experimental Determination ◽  
Heat Loss ◽  
Energy Requirement ◽  
Loss Coefficient ◽  
Overall Heat Loss Coefficient

Analytical and Experimental Investigation to Determine the Variation of Hottel–Whillier–Bliss Constants for a Scaled Forced Circulation Flat-Plate Solar Water Heater

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
U. C. Arunachala ◽  
M. Siddhartha Bhatt ◽  
L. K. Sreepathi
Keyword(s):  
Mass Flow Rate ◽  
Heat Loss ◽  
Mass Flow ◽  
Flow Rate ◽  
Loss Coefficient ◽  
Absorber Plate ◽  
Forced Circulation ◽  
Solar Water ◽  
Scale Thickness ◽  
Overall Heat Loss Coefficient

Fixed tilt flat-plate solar thermal collectors, popularly known as solar water heaters, still remain as one of the most interesting technologies for utilization of solar energy. The system performance deteriorates due to scaling because of the continuous use of hard water as feed water. The present study deals with the experimental and analytical approach to determine the variation of Hottel–Whillier–Bliss (H–W–B) constants (which compactly represent the efficiency characteristics of a solar water heater) due to variation in solar power input and degree of scaling in case of forced circulation system (FCS) without considering the variation of input power to the circulating pump. Indoor tests are performed with a copper tube to investigate the flow characteristics. This forms a part of conventional FCS, in place of the usual nine-fin tube array in a full-fledged collector. In indoor tests, electrical heating is favored to simulate solar radiation level. Various energy parameters are determined and compared by incorporating the developed numerical code FLATSCALE. Variation between experimental and analytical mass flow rate, overall heat loss coefficient, and H–W–B constants with simulated solar radiation level is plotted. In scaled condition, the drop in instantaneous efficiency is due to both scale thickness and reduced water flow rate. Scale thickness acts as an additional thermal conductive resistance between absorber plate and flowing water. Overall heat loss coefficient increases as absorber plate temperature is high during reduced flow rate. The maximum deviation observed is 21.68% in mass flow rate, 14.64% in absorber plate mean temperature, 7.86% in overall heat loss coefficient, and 12.04% in instantaneous efficiency. Compared to a clean tube, a highly scaled tube of 3.7 mm scale thickness indicates a drop of 4.76% in instantaneous efficiency and 40.28% in mass flow rate. It is concluded that the growth of scale in FCS does not affect the instantaneous efficiency significantly because of the margin in heat carrying capacity of water in spite of high drop in the flow rate.

scholarly journals Pengaruh Overall Heat Loss Coefficient Terhadap Hasil Output solar still

2019 ◽  
Vol 3 ◽  
pp. 59
Author(s):  
Regita Septia Cahyani ◽  
Dan Mugisidi ◽  
Rifky Rifky ◽  
Oktarina Heriyani
Keyword(s):  
Heat Loss ◽  
Loss Coefficient ◽  
Solar Still ◽  
Overall Heat Loss Coefficient

Penelitian ini bertujuan untuk mengetahui pengaruh koefisien kehilangan panas keseluruhan terhadap hasil output yang terjadi pada solar still. Penelitian ini menggunakan material stainless still tebal 1,6 mm dan kaca penutup tebal 3mm dengan kemiringan terhadap alat solar still 30 ̊. Pengujian dilakukan mulai pukul 08.00 WIB sampai 17.00 WIB selama 3 hari, dengan beberapa parameter yang di ukur seperti suhu kaca bawah (Tgi), suhu air (Tw), kecepatan angin (v), intensitas radiasi matahari (I(t)s) yang terdapat dalam sistem alat solar still. Dari hasil pengujian yang dilakukan overall heat loss coefficient  tertinggi yaitu sebesar 50,7 W/m2.K.. Semakin tinggi coefficient top heat loss sangat mempengaruhi coefficient heat loss overall sehingga hasil output tidak mengalami kenaikan.

scholarly journals Influence of Initial and Boundary Conditions on the Accuracy of the QUB Method to Determine the Overall Heat Loss Coefficient of a Building

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 284 ◽  
Author(s):  
Naveed Ahmad ◽  
Christian Ghiaus ◽  
Thimothée Thiery
Keyword(s):  
Experimental Data ◽  
Temperature Distribution ◽  
Solar Radiation ◽  
Boundary Conditions ◽  
Heat Loss ◽  
Initial Conditions ◽  
Loss Coefficient ◽  
Heating Power ◽  
Initial Power ◽  
Overall Heat Loss Coefficient

The quick U-building (QUB) method is used to measure the overall heat loss coefficient of buildings during one to two nights by applying heating power and by measuring the indoor and the outdoor temperatures. In this paper, the numerical model of a real house, previously validated on experimental data, is used to conduct several numerical QUB experiments. The results show that, to some extent, the accuracy of QUB method depends on the boundary conditions (solar radiation), initial conditions (initial power and temperature distribution in the walls) and on the design of QUB experiment (heating power and duration). QUB method shows robustness to variation in the value of the overall heat loss coefficient for which the experiment was designed and in the variation of optimum power for the QUB experiments. The variations in the QUB method results are smaller on cloudy than on sunny days, the error being reduced from about 10% to about 7%. A correction is proposed for the solar radiation absorbed by the wall that contributes to the evolution of air temperature during the heating phase.

Thermal performance assessment of a cylindrical box solar cooker fitted with decahedron outer reflector

2021 ◽  
pp. 0958305X2110707
Author(s):  
B C Anilkumar ◽  
Ranjith Maniyeri ◽  
S Anish
Keyword(s):  
Heat Loss ◽  
Figure Of Merit ◽  
Average Energy ◽  
Loss Coefficient ◽  
Ease Of Use ◽  
Superior Performance ◽  
Renewable Energy Resources ◽  
Minimum Entropy ◽  
Optical Efficiency ◽  
Overall Heat Loss Coefficient

One of the important issues humankind globally faces in recent years is the scarcity of non-renewable energy resources. Solar energy is considered safe and renewable, which can fulfil the demand and supply chain requirements. Solar box cookers (SBCs) are popular in domestic cooking due to their ease of use and handling. The prime objective of the present work is to develop and test the performance of a cylindrical SBC fitted with decahedron-shaped reflector (CSBC-FDR). The CSBC is designed using minimum entropy generation (MEG) method. Through experiments, we observed that absorber plate attains peak temperature of about 138°C–150°C with the aid of decahedron reflector. The first figure of merit (F1) is found to be 0.13, indicating better optical efficiency and low heat loss coefficient for the SBC. The second figure of merit (F2) is obtained as 0.39, which indicates good heat exchange efficiency (F') and less heat capacity for cooker's interior. The average energy efficiency, exergy efficiency, and standardized cooking power values are 21.93%, 3.04%, and 25.28W, respectively. These results show that the present CSBC-FDR is able to cook food in a shorter period with better efficiency. The experimental and numerical values of overall heat loss coefficient of the developed SBC are in close agreement. The experimentally assessed performance parameters reveal superior performance of the present cylindrical SBC in comparison with many conventional rectangular and trapezoidal box solar cookers.

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