Flow Control and Unsteady State Analysis on Thermal Performance of Solar Air Collectors

Abstract

Solar air collectors can be used for heating rooms, drying crops and wood, and heating water. In present studies, first, a flow control system for obtaining a constant temperature at the exit of a flat-plate collector was installed in a hot air supply system and the feasibility of the control system was examined. When the flow temperature was lower than the temperature that was set by a digital indicating controller, the fan power was reduced to decrease the flow rate. When the outlet air temperature was higher than the setting temperature, the flow rate was increased. Consequently, the control system worked well to maintain the exit air temperature. Secondly, an unsteady state analysis was made on thermal performance of the collector. In analysis, flow rate variations over time were given as conditions. Validity of this analysis was checked by experimentation. Analytical results agreed well even when solar radiation intensity, wind speed, or flow rate changed abruptly.

Modelling the heat dynamics of a monitored Test Reference Environment for Building Integrated Photovoltaic systems using stochastic differential equations

“…The result is in accordance with several studies on BIPV [3,14]. In this particular case, Ito relation [13] provides the best prediction of the estimated Nusselt numbers for transient and turbulent conditions (R 2 = 0.985). For Re <3000, Candanedo's relation predicts quite correctly the estimated values (R 2 = 0.995).…”

“…11 the estimated Nusselt numbers are compared with values calculated from some of the most typical literature relations [10][11][12][13][14]26] for developing flow in channels with laminar, transient or turbulent regimes. There are only a few relations for developing flow in transient and turbulent regimes [11][12][13] because several authors [25,27] assume that in turbulent flow the entrance effects are not significant and that the flow is fully-developed for the entire channel length. Furthermore, literature relations are normally based on isothermal or isoflux boundary conditions but normally in a BIPV system neither isothermal nor isoflux boundary conditions are fulfilled.…”

“…In addition, other physical inputs and outputs are also considered in the presented models: the angular dependency of the optical properties of the PV module, the electricity production, the effect of PV module inclination over the heat transfer coefficients and the consideration of the ground and sky temperatures for the radiative losses calculations. The estimated convective heat transfer coefficients within the air gap are also compared with the coefficients calculated from [10][11][12][13][14].…”

An outdoor Test Reference Environment for double skin applications of Building Integrated PhotoVoltaic Systems

“…Special attention is paid to the identification of the convective heat transfer exchange coefficients within the air gap. These parameters can be determined with literature correlations [23][24][25][26][27] however, they are difficult to define, especially for laminar flow.…”