Muhsin Kilic

Evaluating thermal environments for sitting and standing posture

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.

Evaluation of Heat Transfer Characteristics in an Automobile Cabin with a Virtual Manikin During Heating Period

In this study, a three-dimensional transient numerical analysis was performed inside the automobile cabin during heating period. A three-dimensional vehicle cabin including glazing surfaces was modeled by using the real dimensions of a car. A virtual manikin with real dimensions and physiological shape was added to the model of the vehicle cabin. It was assumed that the manikin surfaces were subjected to either constant heat flux or constant temperature. Three-dimensional fluid flow, temperature distribution, and heat transfer characteristics inside the cabin were calculated. Experimental measurements were also conducted. Comparisons of the results were presented and discussed. The results of numerical calculations were in good agreement with the experimental and theoretical data in the literature.

Transient numerical analysis of airflow and heat transfer in a vehicle cabin during heating period

This paper describes a three-dimensional transient numerical analysis to determine the airflow and heat transfer characteristics inside the vehicle cabin during a heating period. A three-dimensional vehicle cabin including glazed surfaces and pertinent physical and thermal properties of the enclosure was modelled by using the real dimensions of a car. A virtual manikin was added to the model of the vehicle cabin to determine the heat transfer between the human body and the vehicle cabin ambient. The analysis takes into account all the possible thermal load of the cabin. Governing equations were solved by an implicit, time marching finite volume numerical scheme under varying inlet boundary conditions of the vehicle air conditioning system. The results of numerical calculations were in good agreement with the available experimental and theoretical data in the literature.

THE EFFECT OF INPUT TEMPERATURES ON THE ABSORBER PARAMETERS

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.

Computation of Flow Between Two Discs Rotating at Different Speeds

Discs rotating at different speeds are found in the internal cooling-air systems of most gas turbines. Defining Γ as the ratio of the rotational speed of the slower disc to that of the faster one then Γ = −1, 0 and +1 represents the three important cases of contra-rotating discs, rotor-stator systems and co-rotating discs, respectively. A finite-volume, axisymmetric, elliptic, multigrid solver, employing a low-Reynolds-number k-e turbulence model, is used for the fluid-dynamics computations in these systems. The complete Γ region, −1 ≤ Γ ≤ +1, is considered for rotational Reynolds numbers of up to Reφ = 1.25 × 106 , and the effect of a radial outflow of cooling air is also included for nondimensional flow rates of up to Cw = 9720. As Γ → −1, Stewartson-flow occurs with radial outflow in boundary layers on both discs and between which is a core of nonrotating fluid. For Γ ≈ 0, Batchelor-flow occurs, with radial outflow in the boundary layer on the faster disc, inflow on the slower one, and between which is a core of rotating fluid. As Γ → +1, Ekman-layer flow dominates with nonentraining boundary layers on both discs and a rotating core between. Where available, measured velocity distributions are in good agreement with the computed values.Copyright

Computation of Flow Between Two Disks Rotating at Different Speeds

Disks rotating at different speeds are found in the internal cooling-air systems of most gas turbines. Defining r as the ratio of the rotational speed of the slower disk to that of the faster one then Γ=-1, 0 and +1 represents the three important cases of contra-rotating disks, rotor-stator systems and co-rotating disks, respectively. A finite-volume, axisymmetric, elliptic, multigrid solver, employing a low-Reynolds-number k-e turbulence model, is used for the fluid-dynamics computations in these systems. The complete Γ region, -1≤Γ≤+1, is considered for rotational Reynolds numbers of up to Re Φ =1.25×10 6 , and the effect of a radial outflow of cooling air is also included for nondimensional flow rates of up to C w =9720. As Γ→-1, Stewartson-flow occurs with radial outflow in boundary layers on both disks and between which is a core of nonrotating fluid. For Γ0, Batchelor-flow occurs, with radial outflow in the boundary layer on the faster disk, inflow on the slower one and between which is a core of rotating fluid. As Γ→+1, Ekman-layer flow dominates with nonentraining boundary layers on both disks and a rotating core between. Where available, measured velocity distributions are in good agreement with the computed values.

Flow and convective heat transfer in cylindrical reversed flow combustion chambers

This paper presents a computational study of the flow and convective heat transfer in cylindrical reversed flow combustion chambers. The computations are performed using an elliptic solver incorporates the {kappa}-{epsilon} turbulence model. Heat production by combustion is simulated by adding heat generation source terms in the energy equation. And it is assumed that heat generation occurs only a section of the furnace. A number of different inlet conditions with different geometries are considered, and the changes of flow structure, temperature distribution, convective heat flux rate are presented and compared. The results show that, in general, heat transfer in the reversed flow combustion chamber can be improved by properly chosen geometry for the required output.

Investigation of Humidity Effects on the Thermal Comfort and Heat Balance of the Body

Humidity, one of the most confusing of all climatic parameters in assessing the indoor climate, affects comfort in a number of ways both directly and indirectly, and the avenues by which humidity affects comfort are not completely known. The aim of this study is to comprehend the effects of humidity on thermal interaction between the human body and its environment, and thermal sensation. In this chapter, the effect of humidity on heat and water balance of human body, and in turn on body temperatures and thermal sensation, is investigated. A mathematical model of heat and mass interaction between the human body and the surrounding environment has been established, and the effect of air humidity has been examined under various relative humidity levels by means of using the empirical relations that express thermoregulatory control mechanisms. In the numerical model, human body has been separated into 16 sedentary segments, and possible local discomforts have been taken into consideration. Using the model, changes in the sensible and latent heat losses, body temperatures, skin wettedness, and thermal comfort indices have been calculated and results have been discussed explicitly.

Influence of environmental temperature on exergetic parameters of a combined cycle power plant

Ambient conditions have significant effect on combined cycle power plants (CCPPs). Parameters-like efficiencies, fuel consumption, power production and even operation cost differ according to the ambient conditions that depend on the climate that cannot be changed. Therefore, deciding the location of the plant wisely would bring more efficient and profitable. In this paper, exergy analysis based on the second law of thermodynamics, considering environmental temperature variations, are performed for a cogeneration power plant. Mathematical model of analyse is introduced. Magnitudes of the variation of irreversibility, reversible power, power production and specific fuel consumption (SFC) are evaluated for the combined cycle. The results indicated that, decrease of environmental temperature augments the energy performance of the combined cycle form about 53% to 56% and improves the exergetic performance from about 51% to 56%. However, the augmentation via temperature decrease is not continuous. It is shown that the environmental temperature decrease causes a reduction about 5% in the SFC.

Evaluation of windshield defogging process in an automobile

The defogging process on a windshield is one of the important concerns in the automotive industry for driver safety and certification. Therefore, the simulation of the windshield defogging process provides a very effective and useful tool for the designers to obtain a more efficient and rapid defogging process. In this paper, an experimental and numerical study is presented for the windshield defogging process of an automobile. A computational fluid dynamics (CFDs) tool was used to perform the relevant three dimensional (3-D) transient simulations. Both droplet and wall film models are employed for comparison of the demisted area on a windshield in the numerical calculations. The 3-D fluid flow, temperature distribution and heat transfer characteristics of the interior surfaces of the automobile cabin are also considered. It is shown that the results of the simulations are in a good agreement with the experimental data presented in this study.