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

2006 ◽  
Vol 128 (3) ◽  
pp. 354-359 ◽  
Author(s):  
Sadasuke Ito ◽  
Minoru Kashima ◽  
Naokatsu Miura
Keyword(s):  
Control System ◽  
Solar Radiation ◽  
Flow Control ◽  
Flow Rate ◽  
Thermal Performance ◽  
Space Heating ◽  
Outlet Temperature ◽  
Unsteady State ◽  
Collector Efficiency ◽  
Unsteady State Analysis

Promotion of the use of renewable energy, such as solar heat, for space heating and drying crops and wood is desired to prevent global warming. High-temperature collection of heat by air collectors producing as much as 50°C in winter for space heating and about 80°C in summer for exchanging heat to circulating water for hot water supply would be appropriate applications. In this study, first, a flow control system for constant outlet temperature was installed in a hot air supply system to examine the feasibility of the control system. After experiments, it was found that the control system could function satisfactory. Second, an unsteady-state analysis was made to predict the thermal performance of a flat-plate collector under a given condition of variable flow rate. The analytical model became simple by the assumptions that the heat capacity of the air in the collector and heat conduction in the flow direction through the air and the materials of the collector could be neglected. The maximum differences in outlet temperature and collector efficiency for constant flow rate between the analysis and the experiment were 1.8°C and 6% of the collector efficiency, respectively, except in the beginning of experiments. The biggest difference in the collector efficiency was 30% at 3:00 P.M., which occurred at the end of one of the experiments. The analytical results generally agreed well with the experimental results even when the flow rate and solar radiation changed greatly as time went on. Transient effects are important to predict outlet temperature for variable solar radiation intensity, wind speed, and flow rate.

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

Solar Energy ◽  
2003 ◽  
Author(s):  
Sadasuke Ito ◽  
Minoru Kashima ◽  
Naokatsu Miura
Keyword(s):  
Control System ◽  
Flow Control ◽  
Air Temperature ◽  
Flow Rate ◽  
Thermal Performance ◽  
Unsteady State ◽  
Solar Radiation Intensity ◽  
Flat Plate Collector ◽  
Unsteady State Analysis ◽  
State Analysis

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.

Modeling and Optimal Control of a Variable-Speed Centrifugal Pump With a Pipeline

2016 ◽  
Author(s):  
Cristian F. Jaimes Saavedra ◽  
Sebastian Roa Prada ◽  
Jessica G. Maradey Lázaro
Keyword(s):  
Mathematical Model ◽  
Control System ◽  
Flow Control ◽  
Flow Rate ◽  
Power Efficiency ◽  
Control Valve ◽  
Operating Point ◽  
Variable Frequency ◽  
Centrifugal Pumps ◽  
Variable Frequency Drive

Pumping processes often require different operating conditions for the same pipeline. The conditions downstream in the pipeline can change in such a way that the pressure at the discharge of the pump may vary, which automatically introduces changes in the flow supplied by the pump into the pipeline due to the head vs flow characteristic curve of the pump. Even under varying pipeline pressure conditions, it may be necessary to keep the flow discharge of the pump constant. The two most commonly used control strategies for flow control with centrifugal pumps are by means of a fixed-speed pump and a control valve at the outlet of the pump, or by means of a variable frequency drive which avoids the need for the control valve. It has been demonstrated that the approach with the fixed-speed pump and the control valve provides poor power efficiency results, so a variable frequency drive is normally the solution of choice in industry applications. The use of a variable frequency drive allows reaching the flow required by the system without changing the physical characteristic of the pump or pipeline, i.e., it is not necessary to shut the system down to replace the impeller of the pump. However, affinity laws of centrifugal pumps dictate that a change in the rotational speed of the impeller shifts the characteristic curves of the pump, not only the flow vs head curve, but also the efficiency curves, among others. Besides, searching for a different operating point by changing the speed of the pump does not necessarily guarantees optimal operating power efficiency. This paper proposes an optimization approach where a compromise is made between flow control and power efficiency by minimizing the error in the flow rate while at the same time maximizing the power efficiency. To accomplish this goal, this paper presents the modeling of the pump and pipeline, and the design of a linear quadratic regulator control for the fluid flow passing through a given pipeline. The fluid under consideration is water. The mathematical model of the overall system is derived by considering the model of an AC motor, the pump and the hydraulic circuit. Then, with the help of the software MATLAB, the controller was designed and implemented with the linearized mathematical model. The actuator of the control system is the variable frequency drive that changes the speed of the impeller to adjust the flow rate to the required operating point under different loading conditions. The results show the behavior of the compensated system with the optimal controller. In practice, the control system must take into account the constraints of the control effort, which means, the frequency of the pump must be kept within safe values to achieve proper functioning of the pumping system.

scholarly journals Experimental Investigation of the Thermal Performance of a Solar Air Heater

2021 ◽  
Vol 9 (2) ◽  
Author(s):  
Abdulghani M. Ramadan ◽  
Khairi Muftah ◽  
Abdul-Rahman Al-Naaji ◽  
Abdul-Baset Al-Soul ◽  
Akram A. Essnid ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Solar Radiation ◽  
Mass Flow ◽  
Thermal Performance ◽  
Operating Conditions ◽  
Space Heating ◽  
Solar Air Heater ◽  
Air Mass ◽  
Incident Solar Radiation ◽  
Air Heater

Solar air heaters are widely used in many low temperature applications such as space heating, crops drying, desalination..etc. It collects solar radiant energy and transforms it into heat through a fluid (air) flowing inside the system. The outside cold air is heated through the system and delivered to the required application. It is simple, economic and clean. In this study, an experimental investigation is carried out using a test-rig installed at the laboratories facility for Center of Solar Energy Research and Studies (CSERS) in Tajoura-Libya equipped with all necessary measuring instruments and devices. The aim of this study is to investigate the effect of process air mass flow rate on the thermal performance of a solar air heater working at different operating conditions under the prevailing conditions of Tajoura-Libya. Experiments were conducted on specified days in August 2019, October 2019 and January, 2020.Results show that there is a noticeable increase in the air temperatures of the solar air heater as incident solar radiation values increase during the day time, especially at afternoon. The maximum average outlet air temperature measured reaches 60 oC which is suitable for space heating and crops drying applications. Useful heat energy collected is directly proportional to the incident solar radiation. Increasing air mass flow rates leads to a corresponding decrease in the temperature at different locations in the solar air heater. Furthermore, the average thermal efficiency values of the solar air heater range from 35% to 65%. Average overall heat loss coefficient values tend to decrease with the day time. Finally, the present study results coincide with literature and show a good agreement.

A Computer-Based Air Flow Control System for Aerosol and Filtration Research

2015 ◽  
Vol 771 ◽  
pp. 137-140 ◽  
Author(s):  
Muhammad Miftahul Munir ◽  
Muhammad Sainal Abidin ◽  
Abdul Rajak ◽  
Khairurrijal
Keyword(s):  
Control System ◽  
Flow Control ◽  
Flow Rate ◽  
Pulse Width Modulation ◽  
Air Flow ◽  
Flow Sensor ◽  
Air Filtration ◽  
Air Filter ◽  
Flow Control System ◽  
Air Flow Control

An airflow control system is one of important parts in the scanning mobility particle sizers system (SMPS) used in the field of aerosol and air filtration. In this paper, the air flow control system that consists of an air filter, a blower, an air flow sensor, a controller, and a computer are reported. A flow rate adjustment was performed by varying the rotation speed of the blower using a pulse width modulation (PWM) technique. The air flow sensor capable of measuring flow rate up to 20 liters / min was used to measure the air flow rate. In order to keep at a certain value of the flow rate, a proportional-integral-derivative (PID) control action was employed in which PID controller were manually tune. The results showed that the desired value of flow rate was quickly achieved with little overshoot was observed in the system output.

Solar Radiation Model Applied to a Low Temperature Evacuated Tubes Solar Collector

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Oscar A. López-Núñez ◽  
J. Arturo Alfaro-Ayala ◽  
J. J. Ramírez-Minguela ◽  
J. Nicolás Flores-Balderas ◽  
J. M. Belman-Flores
Keyword(s):  
Low Temperature ◽  
Solar Radiation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Solar Collector ◽  
Outlet Temperature ◽  
Radiation Model ◽  
Solar Radiation Model ◽  
Evacuated Tubes

A solar radiation model is applied to a low temperature water-in-glass evacuated tubes solar collector to predict its performance via computational fluid dynamics (CFD) numerical simulations. This approach allows obtaining the transmitted, reflected, and absorbed solar radiation flux and the solar heat flux on the surface of the evacuated tubes according to the geographical location, the date, and the hour of a day. Different environmental and operational conditions were used to obtain the outlet temperature of the solar collector; these results were validated against four experimental tests based on an Official Mexican Standard resulting in relative errors between 0.8% and 2.6%. Once the model is validated, two cases for the solar collector were studied: (i) different mass flow rates under a constant solar radiation and (ii) different solar radiation (due to the hour of the day) under a constant mass flow rate to predict its performance and efficiency. For the first case, it was found that the outlet temperature decreases as the mass flow rate increases reaching a steady value for a mass flow rate of 0.1 kg/s (6 l/min), while for the second case, the results showed a corresponding outlet temperature behavior to the solar radiation intensity reaching to a maximum temperature of 36.5 °C at 14:00 h. The CFD numerical study using a solar radiation model is more realistic than the previous reported works leading to overcome a gap in the knowledge of the low temperature evacuated tube solar collectors.

scholarly journals Investigation on The Thermal Performance of Evacuated Glass-Thermal Absorber Tube Collector (EGATC) for Air Heating Application

2021 ◽  
Vol 79 (2) ◽  
pp. 48-64
Author(s):  
Zairul Azrul Zakaria ◽  
Zafri Azran Abdul Majid ◽  
Muhammad Amin Harun ◽  
Ahmad Faris Ismail ◽  
Sany Izan Ihsan ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Thermal Performance ◽  
Glass Tube ◽  
Heating System ◽  
Outlet Temperature ◽  
Water Heating ◽  
Diffuse Solar Radiation ◽  
Air Heating ◽  
Outdoor Experiment ◽  
Flat Plate Collector

Existing design of Heat-Pipe Evacuated Tube Collector (HP ETC) for solar water heating require storage tank and additional heat exchanger required for air heating application which leads to the extra spacing and costing requirement. HP ETC have better thermal performance to produce high outlet temperature than flat plate collector (FPC), especially during diffuse solar radiation. But HP ETC normally focusing on water heating system. Furthermore, HP ETC and FPC installation need to be positioned either to south or north facing to ensure the solar thermal collector absorbs more solar radiation. Meanwhile, HP ETC need to be tilt at the correct angle to maximize the performance of the system. These could lead to design limitation. The aim of this research is to develop the new design of Evacuated Glass-Thermal Absorber Tube Collector namely EGATC for drying application. It was developed from conventional HP ETC evacuated glass tube. In this study comparison result of EGATC and HP ETC performance were evaluated. The three days outdoor experiment proves that the performance of EGATC was better than HP ETC in air heating application which is provide higher outlet temperature. Based on the result, EGATC (Day 1: 50.9 oC, Day 2: 53.9 oC, Day 3: 49.2 oC) performed better with slightly higher temperature at outlet temperature compare with HP ETC (Day 1: 46.7 oC, Day 2: 50.3 oC, Day 3: 46.9 oC). It is concluded that EGATC have better performance in term of temperature different and outlet temperature as compared to HP ETC. EGATC (Day 1: 53.6%, Day 2: 50.6%, Day 3: 49.8%) also have greater efficiency in term of heat storage capability as compared to HP ETC (Day 1: 42.7%, Day 2: 41.6%, Day 3: 41.1%). Regarding energy buffer storage, EGATC have better energy storage compared to HP ETC at sudden weather change such as diffuse solar radiation during clouds. The outlet temperature of EGATC (42.3 oC) was remained slightly higher compared to HP ETC (39.9 oC) at the beginning. The outlet temperature gradually drops slower during discharging period until the end of the experiment for 15 minutes towards outlet temperature 41.1ºC and 37.2ºC for both EGATC and HP ETC with temperature difference 1.2ºC and 2.7ºC respectively.

Performance Analysis of Solar Water Heater in Multipurpose Solar Heating System

2014 ◽  
Vol 592-594 ◽  
pp. 1706-1713
Author(s):  
R. Venkatesh ◽  
W. Christraj
Keyword(s):  
Wind Speed ◽  
Relative Humidity ◽  
Solar Radiation ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Thermal Performance ◽  
Winter Season ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

Of all the renewable sources of energy available, solar thermal energy is the most abundant one and is available in both direct as well as indirect forms. In order to increase the thermal performance of solar collectors, the multipurpose solar collectors were investigated experimentally by the storage tank of the conventional solar water collector is modified as riser tubes and header. It is fitted in the bottom of the solar air heater as an absorber in the normal air heater. The thermal performance of thermosyphon flat plate solar water heater was investigated on both summer and winter seasons. The maximum daily average of 72.05%, 0.0316 kg/sm2and 0.873 m/s were recorded for the relative humidity, mass flow rate and wind speed at summer season respectively. Corresponding figure at for winter was 19.5 % 0.0295 kg/sm2and 0.722 m/s respectively. A minimum daily average of 11.23% and 0.384 m/s for the relative humidity and wind speed respectively. These results show that the mass flow rate obtained was a function of solar radiation and relative humidity. The less humid the ambient air becomes, the higher the heat gained by the system hence higher water flow rate. The maximum value of relative humidity obtained is due to low solar radiation on winter season. The heat removal factor (FR) and collector efficiency factor (Fo) were found to be higher for Multipurpose solar water heater as compared to conventional solar water heaters for summer as well as winter season. These factors for Multipurpose solar water heater were more during summer and winter.

scholarly journals Energy-based performance analysis of a double pass solar air collector integrated to triangular shaped fins

2021 ◽  
Author(s):  
Maytham H. Machi ◽  
Maytham A. Al-Neama ◽  
J. Buzás ◽  
I. Farkas
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Thermal Efficiency ◽  
Outlet Temperature ◽  
Double Pass ◽  
Solar Air Collector ◽  
Collector Efficiency ◽  
Useful Heat ◽  
Air Channels

AbstractIn this paper, the performance of a double pass solar air collector with triangular integrated fins was investigated experimentally at Hungarian University of Agriculture and Life Sciences in Gödöllő, Hungary. The focus of this research is on energy-based performance evaluation. The thermal efficiency of the collector has been compared by testing two collectors that had the same design, with and without fins. The effect of the collector's air mass flow rate on thermal performance was investigated under various environmental situations. The results revealed that the temperature difference is always higher through the finned collector and the higher variation temperature between the inlet and outlet temperature leads to higher useful heat. The daily thermal efficiency of the finned collector was 56.57%, 59.41%, and 61.42%, while for the un-finned collector was 51.04%, 53.28%, and 57.08% for the mass flow rate 0.0081, 0.0101, and 0.0121 kg/s. The finned double pass solar air collector improved the thermal efficiency by 4.3–6.1% over the un-finned one. The efficiency of the finned collector is always higher than the un-finned one regardless of the mass flow rate. The presence of the fins to the top air channels significantly increases collector efficiency, owing to the increased absorbing surface area, which is responsible for increasing the internal thermal convective exchanges. Moreover, it creates a turbulence airflow, meaning that the air will be in good contact with the absorber plate and penetrate all regions, reducing the dead zones contributing to increased heat transfer.

scholarly journals Transient computational fluid dynamics investigations on thermal performance of solar air heater with hollow vertical fins

2018 ◽  
Vol 22 (6 Part A) ◽  
pp. 2389-2399 ◽  
Author(s):  
Duraisamy Jagadeesh ◽  
Ramasamy Venkatachalam ◽  
Gurusamy Nallakumarasamy
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Thermal Performance ◽  
Experimental Work ◽  
Thermal Efficiency ◽  
Solar Air Heater ◽  
Outlet Temperature ◽  
Absorber Plate ◽  
Air Dryer

Evaluation of experimental thermal performance of a single pass solar air dryer is compared with a transient CFD studies is performed. Vertical hollow plates are placed below the absorber plate and compared against the flat solar absorber plate for its performance improvement. Effect of mass-flow rate, the outlet temperature of air is computationally analyzed in comparison with the experimental work, transient boundary conditions for CFD like ambient temperature, solar insolation are taken from the experimental work, and computational results are in good agreement of with experimental results with maximum error percentage of 10%. Thermal efficiency was increased with increase in mass-flow area for without fin configuration, for a specific mass-flow rate thermal efficiency had a good improvement with fin configuration than the without fin configuration.

Preliminary Results of Testing a Solar Air Heater Equipped with Turbulators

2017 ◽  
Author(s):  
Miroslaw Zukowski ◽  
Grzegorz Woroniak
Keyword(s):  
Solar Radiation ◽  
Thermal Performance ◽  
Meteorological Data ◽  
Air Flow ◽  
Solar Air Heater ◽  
Outlet Temperature ◽  
Time Intervals ◽  
Measurement Results ◽  
New Type ◽  
Flow Through

The paper presents the thermal performance of a newly designed device for preheating ventilation air. This new type of a solar air collector is equipped with turbulators to increase heat exchange and eventually to obtain more energy from the Sun. Support elements of this type have not yet been implemented in such heat exchangers. The panel has the following dimensions: width – 0.97 m, length – 1.9 m, thickness – 0.1 m, the area where solar radiation enters the collector – 1.49 m2. Air flow through the exchanger is forced by two radial high flow fans, typically used to cool down servers. The test stand beside the collectors is equipped with an inlet and outlet temperature data recorder and an anemometer to control the air flow rate through the collector. Meteorological data such as solar radiation, wind speed and ambient temperature is obtained from a weather station. The parameters of the working installation have been analysed through the monitoring of measurement variables collected on one-minute time intervals from April to September 2016. The measurement results have been used to determine the thermal performance of the air solar collector of this type. The results of the energy analysis have shown the validity of such an installation.

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