Daily Variations of Water Temperature and Useful Heat Accumulation in Flat-Plate Solar Water-Heating Collectors with Cap
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R UNITS AND THEIR APPLICATION
Daily Variations of Water Temperature and Useful Heat Accumulation in Flat-Plate Solar Water-Heating Collectors with Capacitive Solar Radiation Absorbers with Bottom Absorption of Radiation R. R. Avezova, F. Sh. Kasimova, *, and Sh. K. Niyazovb aPhysical–Technical
Institute, Scientific Production Association Physics–Sun, Academy of Sciences of the Republic of Uzbekistan, Tashkent 100084 Uzbekistan b Gulistan State University, Gulistan, 120100 Uzbekistan *e-mail: [email protected]
Received August 5, 2019; revised November 4, 2019; accepted February 7, 2020
Abstract—This study presents the results of numerical experiments conducted for determining the daily variations of water temperature and useful heat in flat-plate solar water-heating collectors (FSWHCs), with capacitive solar radiation absorbers (SRAs) with bottom absorption of radiation. These absorbers are made as rectangular containers 5–7 cm in thickness from translucent plastics. Keywords: capacitive solar water heating collector, useful heat accumulation, capacitive solar radiation absorbers, bottom radiation absorption, water temperature, useful heat flow DOI: 10.3103/S0003701X20040052
INTRODUCTION
η k − theff rd Δτ(i −1) − i ϕсrd twti = twti −1e + 0.5 1 − e (1) qabsi −1 + qabsi × + tambi −1 + tambi , krd where tambi −1 , twti −1 , and qabsi −1 are, respectively, the temperatures of the ambient air, water being heated, and surface density of the flow of the total SR absorbed in the water layer–blackened bottom system of SRAs of FSWHCs of the considered type during daylight timepoint τi −1 ; tambi , twti , and qabsi are the same quantities at daylight timepoint τi ; K rd is the total coefficient of the heat losses of the collector of the considered type per unit frontal surface; and ηtheff is the thermal efficiency factor of the capacitive SRA. That said, daily variations in useful heat accumulation quse can be calculated using the expression from [2, 3], recorded as −
Translucent plastic flat-plate solar water-heating collectors (FSWHCs) with capacitive solar radiation absorbers (SRAs) with bottom absorption of radiation are shallow (with a thickness of no more than 0.1 m) horizontally positioned and thermally insulated rectangular containers with a bottom blackened on the inside [1]. The water being heated is located in a translucent plastic rectangular tank 5–7 cm in thickness, with branch pipes for feeding cold and removing hot (or warm) water. The solar radiation (SR) passing through the upper and lower translucent walls of the tank and the water heated in it is absorbed by the blackened inner surface of the bottom of the collector body and converted to heat and then fed to water for heating. Like in other kinds of SWHCs [1, 2], the task of studying the dynamics of useful thermal energy accumulation in FSWHCs with SRAs with bottom radiation absorption is confined to defining the daily variations in the temperature of the water in their capacitive absorbers.
ηtheff krd Δτ(i −1) − i ϕсrd
quse
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