Tuncay Yilmaz

Analysis of variable-base heating and cooling degree-days for Turkey

The degree-day method is one of the well-known and the simplest methods used in the Heating, Ventilating and Air-Conditioning industry to estimate heating and cooling energy requirements. In this study, the heating and cooling degree-days for Turkey are determined by using long-term recent measured data. Five different base temperatures ranging from 14 to 22°C are chosen in the calculation of heating degree-days. In the case of cooling degree-days, 6 different base temperatures in the range 18 to 28°C are used. Yearly heating and cooling degree-days are given both in tabular form and as counter maps for all the provinces of Turkey (78 weather stations).

Optimum shape and dimensions of ducts for convective heat transfer in laminar flow at constant wall temperature

One knows that a certain geometry exists for a given pressure loss in a duct, where maximum heat transfer occurs. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in different duct shapes for laminar flow conditions. Simple equations which enable calculation of these optimum values for all Pr numbers and for all shapes of duct cross-sectional areas have been derived.

Irreversibility analysis of cross flow heat exchangers

Abstract In this paper, a cross flow plate type heat exchanger, operating with unmixed fluids, was analysed with balanced cross flow. For this aim, a cross flow plate type heat exchanger was developed and manufactured in the laboratory. The heat exchanger was tested with an applicable experimental set up, and temperatures, velocity of the air and the pressure losses occurring in the system were measured so that the effectiveness of the heat exchanger has been determined. The minimum entropy generation number has been taken into consideration with respect to the second law of thermodynamics for the heat exchanger in this analysis. The minimum entropy generation number depends on parameters such as optimum flow path length, dimensionless mass velocity, dimensionless heat transfer area and dimensionless heat transfer volume. The variations between the entropy generation number and these parameters were analysed for the manufactured heat exchanger and introduced with their graphics.

General equation for heat transfer for laminar flow in ducts of arbitrary cross-sections

Abstract This paper presents the general equations for heat transfer calculations for constant wall temperature in laminar developed flow in ducts of arbitrary cross sections. The results obtained from these equations compare well with the theoretically-calculated values available in the literature for circular, rectangular, triangular, elliptical and parallel plate ducts. The maximum and minimum deviations by these comparisons are −8.7 and +8.0% respectively.

New outdoor cooling design data for Turkey

In this study, new outdoor design conditions for space heating were determined for 78 locations within Turkey according to the format recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. (ASHRAE). Dry-bulb temperature corresponding to 99%, 99.6% and 97.5% annual cumulative frequency of occurrence, the mean and standard deviation of the annual minimum dry-bulb temperatures were obtained. These calculations used hourly data measured during at least 13 years. The current heating design conditions used in the calculation of space heating load in Turkey were analyzed based on their frequency levels. Comparison of the existing space heating design data with the data obtained in this study revealed that the current space heating design temperatures are generally stringent and provide total protection.

Bin weather data for Turkey

One of the well-known and simple steady-state methods used to predict heating and cooling energy consumption of buildings is the bin method that requires reliable and detailed bin data. In this study, the bin data for Turkey are determined by using long-term measured data. The bin data for dry-bulb temperature from -36 °C to 45 °C with 3 °C increments are calculated in six daily 4-h shifts for 78 provinces of Turkey.

Second-law and experimental analysis of a cross-flow heat exchanger

This article presents a cross-flow plate-type heat exchanger that has been studied and manufactured in laboratory conditions because of its effective use in waste heat recovery systems. This new heat exchanger was tested with an applicable experimental setup, considering temperatures, velocity of the air, and the pressure losses occurring in the system. These variables were measured and the efficiency of the system was determined. The irreversibility of the heat exchanger was taken into consideration, while the design of the heat exchanger was such that the minimum entropy generation number was analyzed with respect to the second law of thermodynamics in the cross-flow heat exchanger. The minimum entropy generation number depends on the parameters called the optimum flow path length and dimensionless mass velocity. Variations of the entropy generation number with these parameters are analyzed.

Design of Regenerative Heat Exchangers

Rotary regenerators are used widely for energy recovery, both in industrial and air-conditioning applications, because of the advantages they have over other types of heat exchangers. In this study, a mathematical model for the design of rotary regenerators is presented. The method is valid for all kinds of channel geometries that form the matrix of a rotary regenerator and can be used for all rotational speeds. The validity of the method is tested with the experimental and numerical results available for rotational speeds between 0.05 and 7 rev/min. A good agreement between the model and the experimental numerical results is obtained. The method presented can therefore be recommended for the safe design of rotary regenerators.

Development of an Artificial Neural Network Model for the Prediction of the Performance of a Silica-gel Desiccant Wheel

This work presents mathematical equations derived from Artificial Neural Networks (ANNs) for the estimation of dry bulb temperature and specific humidity at the outlet of a desiccant wheel to predict useful data for designers and engineers. The neural network model comprises five inputs and two output neurons that define the outlet conditions (dry bulb temperature and specific humidity) of a desiccant wheel. The results obtained by the ANN model are compared with the actual data by using input variables. The results show that the mean absolute percentage errors for dry bulb temperature and specific humidity are found to be 0.80% and 1.56% respectively; and the correlation coefficient (R) values obtained are approximately 0.986 for both output variables. The root mean square errors, which is another significant point in this study, are found to be 0.54% and 0.18% for dry bulb temperature and specific humidity respectively.

Computer simulation of two-phase flow thermosyphon solar water heating system

Abstract A two-phase flow thermosyphon solar water heating system is modelled theoretically. In the model, non-homogenous two-phase flow and heat transfer in the collector and condenser are considered, and variation of the properties of the working fluid and water with temperature are taken into account. Numerical calculations are carried out for the refrigerant R-11. The temperatures in the system, the heating and boiling section of the collector, the recirculating mass flow rate of the working fluid and the efficiency of the heating system are presented. The influences of solar insolation, water temperature and the collector tube on the efficiency of the system and on the recirculating mass flow rate are discussed.