Experimental investigation of energy and exergy efficiency of masonry-type solar cooker for animal feed

The performance of a masonry animal feed solar cooker was evaluated in terms of energy and exergy. It is a low-cost cooker made of cement, bricks, glass covers and a mild steel absorber plate. The energy and exergy efficiencies of the animal feed solar cooker were experimentally evaluated. The energy output of this cooker ranges from 1.89 to 49.4 kJ, whereas the exergy output ranges from 0.11 to 2.72 kJ during the same time interval. The energy efficiency of the cooker varies between 1.12% and 29.78%, while the exergy efficiency varies between 0.07% and 1.52 % during the same period.     

Exergy analysis of the solar cylindrical-parabolic cooker

For the first time the simple solar parabolic cooker (SPC), of the cylindrical trough shape, is analysed from the exergy viewpoint. The paper presents the methodology of detailed exergy analysis of the SPC, the distribution of the exergy losses, and, on the example of the cooker surfaces, explains the general problem of how the exergy loss on any radiating surface, should be determined, if the surface absorbs many radiation fluxes of different temperatures. An imagined surface was used in the considerations to close the system of the cooker surfaces. It was shown that optimization is needed, to increase the energy and exergy efficiencies of the cooker.Equations for heat transfer between the three surfaces: cooking pot, reflector and imagined surface making up the system, were derived. The model allowed for theoretical estimation of the energy and exergy losses: unabsorbed insolation, convective and radiative heat transfer to the ambient, and additionally, for the exergy losses: the radiative irreversibilities on the surfaces, and the irreversibility of the useful heat transferred to the water.The exergy efficiency of the SPC, was found to be relatively very low (1%), and to be about 10 times smaller than the respective energy efficiency which is in agreement with experimental data from the literature. The influence of the input parameters (geometrical configuration, emissivities of the surfaces, heat transfer coefficients and temperatures of water and ambience) was determined on the output parameters, the distribution of the energy and exergy losses and the respective efficiencies.     

Comparison of energy and exergy efficiencies of an underground solar thermal storage system

In this experimental study, solar energy was stored daily using the volcanic material with the sensible heat technique. The external heat collection unit consisted of 27 m² of south‐facing solar air collectors mounted at a 55° tilt angle. The dimensions of the packed‐bed heat storage unit were 6 × 2 × 0.6 m deep. The packed‐bed heat storage unit was built under the soil. The heat storage unit was filled with 6480 kg of volcanic material. Energy and exergy analyses were applied in order to evaluate the system efficiency. During the charging periods, the average daily rates of thermal energy and exergy stored in the heat storage unit were 1242 and 36.33 W, respectively. Since the rate of exergy depends on the temperature of the heat transfer fluid and surrounding, the rate of exergy increased as the difference between the inlet and outlet temperatures of the heat transfer fluid increased during the charging periods. It was found that the average daily net energy and exergy efficiencies in the charging periods were 39.7 and 2.03%, respectively. The average daily net energy efficiency of the heat storage system remained nearly constant during the charging periods. The maximum energy and exergy efficiencies of the heat storage system were 52.9 and 4.9%, respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Exergy‐based performance analysis of packed‐bed solar air heaters

This paper presents an experimental investigation of the thermal performance of a solar air heater having its flow channel packed with Raschig rings. The packing improves the heat transfer from the plate to the air flow underneath. The dimensions of the heater are 0.9 m wide and 1.9 m long. The aluminium‐based absorber plate was coated with ordinary black paint. The characteristic diameter of the Raschig rings, made of black polyvinyl chloride (PVC) tube, is 50 mm and the depth of the packed‐bed in flow channel is 60 mm. Energy and exergy analyses were applied for evaluating the efficiency of the packed‐bed solar air heater. The rate of heat recovered from the packed‐bed solar air heater varied between 9.3 and 151.5 W m^?2, while the rate of thermal exergy recovered from the packed‐bed solar air heater varied between 0.04 and 8.77 W m^?2 during the charging period. The net energy efficiency varied from 2.05 to 33.78%, whereas the net exergy efficiency ranged from 0.01 to 2.16%. It was found that the average daily net energy and exergy efficiencies were 17.51 and 0.91%, respectively. The energy and exergy efficiencies of the packed‐bed solar air heater increased as the outlet temperature of heat transfer fluid increased. Copyright © 2004 John Wiley & Sons, Ltd.     

An exergy based test protocol for truncated pyramid type solar box cooker

Developing a test standard/protocol for solar box type cookers has drawn a considerable interest among the researchers throughout the world. Recent publications on solar cookers emphasize the need of introducing the thermal performance indicators determined through exergy analysis. In the present paper, the time variation of instantaneous exergy output and energy output as function of its temperature and also of the instantaneous ambient temperature have been reported for truncated pyramid type solar box cooker and compared with those of box type cooker. Further, variations in the exergy lost with temperature difference have been depicted for the selected water temperature range from 60 °C to 95 °C. Based on this study, quality factor, exergy temperature difference gap product, and heat loss coefficient are determined and are proposed as benchmark parameters of solar cooker’s thermal performance.     

Energy and exergy efficiencies of a hybrid photovoltaic–thermal (PV/T) air collector

In this communication, an attempt has been made to evaluate exergy analysis of a hybrid photovoltaic–thermal (PV/T) parallel plate air collector for cold climatic condition of India (Srinagar). The climatic data of Srinagar for the period of four years (1998–2001) has been obtained from Indian Metrological Department (IMD), Pune, India. Based on the data four climatic conditions have been defined. The performance of a hybrid PV/T parallel plate air collector has been studied for four climatic conditions and then exergy efficiencies have been carried out. It is observed that an instantaneous energy and exergy efficiency of PV/T air heater varies between 55–65 and 12–15%, respectively. These results are very close to the results predicted by Bosanac et al. [Photovoltaic/thermal solar collectors and their potential in Denmark. Final Report, EFP Project, 2003, 1713/00-0014, www.solenergi.dk/rapporter/pvtpotentialindenmark.pdf].     

Energy and exergy utilization efficiencies in the Japanese residential/commercial sectors

Unlike the manufacturing sector, the residential/commercial sectors of Japan struggle to meet their environmental requirements. For instance, their CO₂ emission levels have increased tremendously since 1990. This research estimates energy and ‘exergy (available energy)’ efficiencies in Japan's residential/commercial sectors during the period 1990–2006. Since an exergy analysis reveals ‘available energy losses’, it is an effective tool to achieve sustainable societies. The primary objective of this paper is to examine the potential for advancing the ‘true’ energy efficiency in Japan's residential/commercial sectors—by observing energy and exergy efficiency disparities. The results show large differences between the overall energy and exergy efficiencies in the residential (60.12%, 6.33%)/commercial sectors (51.78%, 5.74%) in 2006. This implies great potential for energy savings in both sectors. Furthermore, this research suggests that the residential sector may face more difficulties than the commercial sector, although the latter appears to be less energy-efficient, according to recent statistics. This is because the disparity between energy and exergy efficiencies has expanded in the residential sector since 2000. This study illustrates the importance of exergy analyses in promoting sustainable energy policies and new adaptation strategies.     

Performance study of solar cooker with modified utensil

A performance study of the box-type solar cooker was made with special emphasis on the shape of lid of the utensils used in a solar cooker. The study revealed that the performance of a solar cooker can be improved if a utensil with a concave shape lid is used instead of a plain lid, generally provided with the solar cooker. The stagnation temperature for a utensil having a concave lid was about 2–7% more than the utensil with a normal lid. The time required for heating the water up to the same temperature in both the utensils was reduced by about 1–13% when a concave shape lid was used.     

Experimental evaluation of energy and exergy efficiency of a seasonal latent heat storage system for greenhouse heating

In the following work, a seasonal thermal energy storage using paraffin wax as a PCM with the latent heat storage technique was attempted to heat the greenhouse of 180 m² floor area. The system consists mainly of five units: (1) flat plate solar air collectors (as heat collection unit), (2) latent heat storage (LHS) unit, (3) experimental greenhouse, (4) heat transfer unit and (5) data acquisition unit. The external heat collection unit consisted of 27 m² of south facing solar air heaters mounted at a 55° tilt angle. The diameter and the total volume of the steel tank used as the latent heat storage unit were 1.7 m and 11.6 m³, respectively. The LHS unit was filled with 6000 kg of paraffin, equivalent to 33.33 kg of PCM per square meter of the greenhouse ground surface area. Energy and exergy analyses were applied in order to evaluate the system efficiency. The rate of heat transferred in the LHS unit ranged from 1.22 to 2.63 kW, whereas the rate of heat stored in the LHS unit was in the range of 0.65–2.1 kW. The average daily rate of thermal exergy transferred and stored in the LHS unit were 111.2 W and 79.9 W, respectively. During the experimental period, it was found that the average net energy and exergy efficiencies were 40.4% and 4.2%, respectively. The effect of the temperature difference of the heat transfer fluid at the inlet and outlet of the LHS unit on the computed values of the energy and exergy efficiency is evaluated during the charging period.     

Experimental study on a small‐scale pumpless organic Rankine cycle with R1233zd(E) as working fluid at low temperature heat source

This paper focuses on the novelty pumpless organic Rankine cycle (ORC) and its choice of working fluids. Based on the selection criteria, the refrigerant of R1233zd(E) is firstly chosen and investigated in the pumpless ORC system. In the system, the feed pump is removed, and the refrigerant flows back and forth between two heat exchangers, which act as the evaporator or condenser, respectively. The impacts of the heating water temperature and loads on the system performance are studied to find out the best operating conditions. The low‐grade heat source is simulated by an electric boiler. The temperature of the heat resource ranges from 80°C to 100°C with the interval of 5°C. The temperature of the cooling water inlet is 10°C and is kept constant. The largest average power output is 127 W under the condition of 100°C heating water with nine loads. Because the cycle efficiency with heating steam temperature of 100°C cannot be determined, the highest energy and exergy efficiencies are 3.5% and 17.1%, respectively, for heating water of 95°C with seven loads. The experimental results show that the energy and exergy efficiencies increase with the increase of the heating temperature. The power and current outputs increase when the loads increase under the condition of the constant heating water temperature, whereas the voltage output decreases meanwhile. The generating time increases when the loads increase. This phenomenon is mainly caused by the increasing evaporating pressure and decreasing condensing pressure when the loads increases.     

Exergy analysis of a passive solar still

This paper presents a steady-state and transient theoretical exergy analysis of a solar still, focused on the exergy destruction in the components of the still: collector plate, brine and glass cover. The analytical approach states an energy balance for each component resulting in three coupled equations where three parameters—solar irradiance, ambient temperature and insulation thickness—are studied. The energy balances are solved to find temperatures of each component; these temperatures are used to compute energy and exergy flows. Results in the steady-state regime show that the irreversibilities produced in the collector account for the largest exergy destruction, up to 615 W/m² for a 935 W/m² solar exergy input, whereas irreversibility rates in the brine and in the glass cover can be neglected. For the same exergy input a collector, brine and solar still exergy efficiency of 12.9%, 6% and 5% are obtained, respectively. The most influential parameter is solar irradiance. During the transient regime, irreversibility rates and still temperatures find a maximum 6 h after dawn when solar irradiance has a maximum value. However, maximum exergy brine efficiency, close to 93%, is found once T_col<T_w (dusk) and the heat capacity of the brine plays an important role in the modeling of collector–brine interaction. Nocturnal distillation is characterized by very low irreversibility rates due to reduced temperature difference between collector and an increase in exergy efficiency towards dawn due to ambient temperature decrease.     

Simulated energy and exergy analyses of the charging of an oil-pebble bed thermal energy storage system for a solar cooker

Energy balance equations are used to model the solar energy capture (SEC) system and the thermal energy storage (TES) system of a proposed indirect solar cooker. An oil-pebble bed is used as the TES material. Energy and exergy analyses are carried out using two different charging methods to predict the performance of the TES system. The first method charges the TES system at a constant flowrate. In the second method, the flowrate is made variable to maintain a constant charging temperature. A Simulink block model is developed to solve the energy balance equations and to perform energy and exergy analyses. Simulation results using the two methods indicate a greater degree of thermal stratification and energy stored when using constant-temperature charging than when using constant-flowrate charging. There are greater initial energy and exergy rates for the constant-flowrate method when the solar radiation is low. Energy efficiencies using both methods are comparable whilst the constant-temperature method results in greater exergy efficiency at higher levels of the solar radiation. Parametric results showing the effect of each charging method on the energy and exergy efficiencies are also presented.     

Performance assessment of a magnesium chloride saturated solar pond

This paper deals with the experimental investigation of a magnesium chloride saturated solar pond and its performance evaluation through energy and exergy efficiencies. The solar pond system is filled with magnesium chloride containing water to form layers with varying densities. A solar pond generally consists of three zones, and the densities of these zones increase from the top convective zone to the bottom storage zone. The incoming solar radiation is absorbed by salty water (with magnesium chloride) which eventually increases the temperature of the storage zone. The high-temperature salty water at the bottom of the solar pond remains much denser than the salty water in the upper layers. Thus, the convective heat losses are prevented by gradient layers. The experimental temperature changes of the solar pond are measured by using thermocouples from August to November. The densities of the layers are also measured and analysed by taking samples from at the same point of the temperature sensors. The energy and exergy content distributions are determined for the heat storage zone and the non-convective zone. The maximum exergy destructions and losses appear to be 79.05 MJ for the heat storage zone and 175.01 MJ for the non-convective zone in August. The energy and exergy efficiencies of the solar pond are defined as a function of solar radiation and temperatures. As a result, the maximum energy and exergy efficiencies are found to be 27.41% and 26.04% for the heat storage zone, 19.71% and 17.45% for the non-convective zone in August, respectively.     

Energetic and exergetic performance evaluation of natural circulation solar water heating systems

This study deals with the energy and exergy analyses of natural circulation solar water heating (SWH) systems. The system comprises of a single glazed flat plate solar collector (FPSC) with absorber plate of 2 m², and a separate insulated well-mixed vertical water storage tank (WST) of 125 liters. The variable heat transfer coefficients, water inlet and outlet temperatures of the FPSC; and temperature of heated water stored in the WST are predicted theoretically for each interval. The daily energy and exergy efficiency of the FPSC, WST and SWH system are estimated to be about 39 and 4.36%, 67 and 38.55%, 27 and 1.01%, respectively. It is found that the water inlet temperature, optical efficiency and the solar radiation strongly influence the performance of the FPSC both energetically and exergetically. It is observed that change in the mass flow rate of water improves the exergy efficiency of the FPSC significantly. FPSC has been identified as a critical component of the system where exergy destruction of 308 W/m² takes place daily as compared to 24 W/m² in the WST against available solar exergy of about 663 W/m².     

Assessment of the energy and exergy utilization efficiencies in the Turkish agricultural sector

This study deals with evaluating the energy and exergy utilization efficiencies in the Turkish agricultural sector over a 12‐year period from 1990 to 2001. In the energy and exergy analyses, two main energy sources, namely fuels and electricity, are taken into consideration, while the sectoral energy and exergy efficiencies are compared for this period. These main energy sources include diesel for tractors and other vehicles, and electricity for pumps. Overall energy utilization efficiencies are obtained to vary between 29.1 and 41.1%, while overall exergy utilization efficiencies are found to range from 27.9 to 37.4% in the analysed years, respectively. It may be concluded that the present technique proposed here may be used as a useful tool in analysing and evaluating the energy and exergy utilization efficiencies, identifying energy efficiency and/or energy conservation opportunities and dictating the energy strategies of countries. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparative study of transparent insulation materials cover systems for integrated-collector-storage solar water heaters

The thermal performance of transparently insulated integrated-collector-storage solar water heaters is investigated theoretically as well as experimentally for a comparative study of cover systems having transparent insulation materials devices placed between the top glazing and the absorber. The data on solar transmittance, heat loss reduction characteristics and solar collector-storage efficiencies of various configurations is generated for the system performance comparisons. These hot water systems exhibit average (diurnal basis) solar collection and storage efficiencies in the range of 20–40% at a collection temperature of 40–50°C. The performance of water heaters with cover system having absorber-perpendicular configuration of TIM excel over absorber-parallel TIM covers. The effect of variation in the temperature of heat collected and cost of cover systems on the performance comparisons is also discussed.     

Energy and exergy analysis of a new solar air heater with latent storage energy

In this paper, we propose a new solar air heater with a packed-bed latent storage energy system using PCM spherical capsules. At daytime, the solar heating system stored the thermal solar energy as sensible and latent heat, however, at night it restored. Some parameters, such as the global solar radiation and the mass flow rate are varied to investigate their effect on the absorbed, used, and recovered heat from the system. An optimization study using the first and second laws of thermodynamics is also carried out to obtain the energy and exergy efficiencies. The experimental study was conducted, designed, and realized in the Research and Technology Center of Energy (CRTEn) in Tunisia. The experimentally obtained results are used to analyze the performance of the system, based on temperature distribution in different parts of the collectors, absorbed, instantaneous stored and used thermal energy. The daily energy efficiency varied between 32% and 45%. While the daily exergy efficiency varied between 13% and 25%. The effect of the mass flow rate of air on the outlet temperature of the solar air heater is examined.     

Performance and parametric investigation of a binary geothermal power plant by exergy

Exergy analysis of a binary geothermal power plant is performed using actual plant data to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy diagram, and compared to the energy diagram. The sites with greater exergy destructions include brine reinjection, heat exchanger and condenser losses. Exergetic efficiencies of major plant components are determined in an attempt to assess their individual performances. The energy and exergy efficiencies of the plant are 4.5% and 21.7%, respectively, based on the energy and exergy of geothermal water at the heat exchanger inlet. The energy and exergy efficiencies are 10.2% and 33.5%, respectively, based on the heat input and exergy input to the binary Rankine cycle. The effects of turbine inlet pressure and temperature and the condenser pressure on the exergy and energy efficiencies, the net power output and the brine reinjection temperature are investigated and the trends are explained.     

A parametric study of polymer membrane electrolyser performance,energy and exergy analyses

In this paper, a mathematical model is developed to study the performance of a polymer membrane electrolyser (PEM) and the effect of different parameters including operating temperature, cathode pressure, membrane thickness, the width and height of channel and current density on the performance and energy and exergy efficiency of PEM electrolyser are investigated. In addition to the resistance overvoltage of components, the concentration overvoltage is modeled using an accurate equation. The model is validated against experimental data. The results indicate that by increasing current density, the voltage of the electrolyser increases, and energy and exergy efficiencies reduce. Increase of temperature from 313 K to 353 K, and decrease of cathode pressure from 40 bar to 1 bar lead to decrease of voltage of the PEM electrolyser by 8.3% and 4.8%, respectively. Moreover, energy and exergy efficiencies increase between 2% and 6% in the range of working temperature and pressure. It is concluded that decrease of membrane thickness, height and width of channel, and increase of exchange current density of the anode and cathode electrodes lead to decrease of voltage of the electrolyser and increase of energy and exergy efficiencies. However, the effect of temperature and cathode pressure and the exchange current densities is greater than the effect of geometric parameters.     

Performance assessment of an integrated PV/T and triple effect cooling system for hydrogen and cooling production

In this paper we study an integrated PV/T absorption system for cooling and hydrogen production based on U.A.E weather data. Effect of average solar radiation for different months, operating time of the electrolyzer, air inlet temperature and area of the PV module on power and rate of heat production, energy and exergy efficiencies, hydrogen production and energetic and exergetic COPs are studied. It is found that the overall energy and exergy efficiency varies greatly from month to month because of the variation of solar radiation and the time for which it is available. The highest energy and exergy efficiencies are obtained for the month of March and their value is 15.6% and 7.9%, respectively. However, the hydrogen production is maximum for the month of August and its value is 9.7 kg because in august, the solar radiation is high and is available for almost 13 h daily. The maximum energetic and exergetic COPs are calculated to be 2.28 and 2.145, respectively and they are obtained in the month of June when solar radiation is high for the specified cooling load of 15 kW.