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Utilizing electricity from renewable resources is very attractive to decrease the dependence on fossil fuels. As a result, hybrid power systems are gaining more attention. This paper focuses on the optimal design and dynamic simulation of renewable-based, hybrid standalone power systems. The designed system is able to meet the energy need of a building with 5 kW peak electricity demand. Both the technical and economic feasibility of the system was investigated under various climatic conditions of Turkey. Diesel fuel consumption, energy cost and annual CO2 emissions were estimated and compared with the diesel generator-only system. A parametric analysis was also conducted to understand the impact of the capacity of the PV array, wind turbine and the battery on the CO2 emissions and the levelized cost of energy. The system in each location was optimized based on the minimum energy cost and CO2 emissions. (C) 2020 Elsevier Ltd. All rights reserved.

This work presents a thermodynamic evaluation of an operating geothermal ORC power plant. The model is realized by using measured data of AFJET geothermal power plant which has 3MWe net power output capacity. Thermodynamic assessment of the system is conducted to see the energy and exergy efficiencies of each component, and the whole plant. Additionally, a parametric study is conducted to understand the effects of various operating conditions on the system performance. Different from previous studies, daily and annual net power output profile of the plant was investigated with considering ambient temperature fluctuations. Results revealed that net power output can drop as significant as 36% from winter to summer months. Also, between nighttime to daytime, the net power expectation may decrease by 5%. The exergy destruction rate of re-injection process constitutes the most significant part (38.1%) of the total exergy destruction of the plant. The conversion and exergy efficiencies of the system are calculated as 11.24% and 39.03%, respectively. Also, to enhance the performance of the plant, an internal heat recovery system is recommended. The analyses show that the implementation of an internal heat recovery system improves the energy and exergy efficiencies of the plant by 15%.

In this paper, thermal and hydraulic analysis of a dual-separated cooling channel was performed for the cooling applications of different automotive lighting systems. A single LED and multi-LEDs were considered to evaluate the thermal and hydraulic performance as well as the lighting properties of automotive headlights. The detailed hydraulic analysis was theoretically evaluated for developing laminar flow to get higher thermal performance with less pumping power. The theoretical and simulation results for the dual-separated cooling channel were compared and discussed. Unlike the constant properties were used in the current literature, thermal analysis with temperature-dependent properties was performed to estimate Nusselt number preciously for dual-separated cooling channels. The temperature measurements were also performed in the experimental study to compare the numerical results. The light output parameter of the LEDs depends on junction temperature, it was found that the increase in light output by using a dual-separated cooling channel was about 10% for all cases. Otherwise, higher junction temperature values lead to a reduction in operating efficiency. The top copper surface temperature drop was higher than 50%, and the junction temperature had been reduced by 36% to ensure the desired operating conditions of the automotive lighting system.

This article aims to analyze comparatively the performance of a combined refrigeration system consists of an upper section (adsorption chiller) and a lower section (vapor compression chiller (VCC)). The arrangement of the adsorption cooling chiller (ACC) depends on two adsorption beds that use silica gel/water as a working pair. The beds are driven by heat comes from outside heat sources with low-grade temperatures ≤100 °C. Whereas in the bottom section, different types of refrigerants (R410A, R152A, R1234yf, R1270, and R32) have been utilized to be driven by the mechanical compressor. This paper focuses on the evaluation of the refrigerants in VCC and the working pair in ACC by means of coefficient of performance (COP) and energy-saving ratio (ES) in this refrigeration system. The computed results reveal that the refrigerants show the same behavior while calculating the COP of the combined system and the VCC in the combined system, with the high values reached up to 0.5 and 8.8 for R152A, respectively. Meanwhile, the energy-saving reached up to 65.3%. The increase ratio (IR) of the COP of the VCC is also calculated with the highest value reached up to 188%. The effects of the ambient air temperature, the heat source temperature, the cycle time and the evaporation temperature on the system performance and the required mass of adsorbent in the adsorption beds are investigated for the design of ACC-VCC combined system.

In this study a combined computational model of a room with virtual thermal manikin with real dimensions and physiological shape was used to determine heat and mass transfer between human body and environment. Three dimensional fluid flow, temperature and moisture distribution, heat transfer (sensible and latent) between human body and ambient, radiation and convection heat transfer rates on human body surfaces, local and average convection coefficients and skin temperatures were calculated. The radiative heat transfer coefficient predicted for the whole-body was 4.6 W m(-2) K-1, closely matching the generally accepted whole-body value of 4.7 W m(-2) K-.(-1) Similarly, the whole-body natural convection coefficient for the manikin fell within the mid-range of previously published values at 3.8 W m(-2) K-1. Results of calculations were in agreement with available experimental and theoretical data in literature. (C) 2008 Elsevier Ltd. All rights reserved.

In this study, apart from the other studies related to thermal comfort, it is combined that the fundamental equations given in the steady-state energy balance and the empirical relations expressing effects of the thermoregulatory control mechanisms of the body. In the first section of this simulation, body core temperature is calculated by using the equations expressing thermoregulatory control mechanism, the required skin temperature and sweat rate values. Variation of the calculated body core temperature is investigated with the activity level based on required skin temperature and sweat rate values. In the second section of the simulation, heat losses from the body (convection, radiation, evaporation, and respiration) and ratio of the each heat loss mechanism to total heat loss are calculated and discussed in detail.

In industrialized countries about 90% of the time is spent indoors. In indoor, thermal comfort can be basically predicted by the environmental parameters such as temperature, humidity, air velocity and by the personal parameters as activity and clothing resistance. In this study, a mathematical model of thermal interaction between human body and environment was established and the effect of clothing and air velocity was examined under transient conditions. By the developed model, human body has been separated to 16 segments and possible local discomforts are taken into consideration. Using the model, changes in the sensible and latent heat losses, skin temperature and wettedness, thermal comfort indices were calculated. In a hot environment latent heat loss increases by means of sweating. Because of over wetted skin, comfort sense goes worse. Especially, at feet and pelvis skin wettedness reaches maximum level. Sensible and latent heat losses rise and the skin temperature and wettedness decrease with increasing air velocity.

Determination of heat transfer rate and Nusselt number in the thermal entry region in ducts is considered. Alternative relations are derived to calculate the rate of heat transfer and Nusselt number. An approximate equation is proposed for the calculation of mean and local Nusselt number in all range of the axial distance in the thermal entry region in ducts with constant surface temperature. And the use of this correlation is extended to predict mean and local Nusselt number in the thermal entry region in tubes with constant wall heat flux

The human thermal environment can be represented by the air temperature, radiant temperature, air velocity, humidity, clothing and activity. This has implications for health, comfort and performance. An understanding of human thermoregulatory processes facilitates the design and development of improved heating and cooling systems. This study presents a computational model of thermal interactions between a human and the interior environment. The model is based on the heat balance equation for human body with different types of clothing ensembles, combined with empirical equations defining the sweat rate and mean skin temperature. Simulation has been performed by the use of steady state conditions, and two different posture positions, namely sitting and standing, are considered in this study. Results are in good agreement with available experimental data. The parametric studies show that the methodology described can provide an effective means for simulating thermal comfort level.

In an absorption cooling system, simultaneous heat and mass transfer operations take place in the absorber and generator. The performance of an absorber is of paramount importance on the coefficient of performance and the manufacturing cost of an absorption machine. Increasing heat and mass transfer coefficients in an absorber decreases the heat transfer area of the absorber, as a result of this the cost of the system can be reduced. The absorption of water vapor in aqueous solutions of lithium bromide is modelled for a falling-film, vertical-tube absorber. Heat and mass transfer coefficients are determined by calculating temperature and concentration variations at the falling film in the absorber. Then mean Nusselt and Sherwood numbers are determined to see the changes in the heat and mass transfer. Subsequently, a modular computer program has been developed for absorption systems to simulate various cycle configurations and absorber parameters. So, the effect of hot water, chilled water and cooling water inlet temperatures on the coefficients of performance, Nusselt and Sherwood numbers and the surface area of the absorber are studied with the simulation program. The results can be used to optimise the commercial absorption chillers.

This paper describes a combined computational and experimental study of the flow between two contrarotating discs for −1 ≤ Γ ≤ 0 (where Γ is the ratio of the speed of the slower disc to that of the faster one) for the case where there is a superposed radial outflow of air. The computations were conducted using an elliptic solver and a low-Reynolds-number k - ϵ turbulence model, and velocity measurements were made using a laser-Doppler anenometry system. Two basic flow structures can occur: Batchelor-type flow, where there are separate boundary layers on each disc with a rotating core of fluid between, and Stewartson-type flow, where there is virtually no core rotation. The main effect of a superposed flow is to reduce the core rotation and to promote the transition from Batchelor-type flow to Stewartson-type flow. For most of the results, there is good agreement between the computed and measured velocities. Computed moment coefficients show that, for Γ = −1, superposed flow has little effect on C m : an accepted correlation of C m for a free disc should provide a useful estimate for design purposes.