Omer Comakli

Heat transfer and friction characteristics in decaying swirl flow generated by different radial guide vane swirl generators

In radial guide vane swirl generators, the flow direction must change from the radial direction to the axial direction. This can be achieved either abruptly or by means of a fairing section, and each technique can be used in conjunction with an inserted centre body (deflecting element). This research was conducted to study the effect of the geometry of the deflecting element in the radial guide vane swirl generator on the heat transfer and fluid friction characteristics in decaying swirl flow. The radial guide vane swirl generators used in this investigation had three different configurations related to the deflecting element: the swirl generator with conical deflecting element, with spherical deflecting element and with no deflecting element. These swirl generators were compared with each other by taking into account their heat transfer and friction characteristics. An augmentation up to 150% in Nusselt number relative to that of the fully developed axial flow was obtained with a constant heat flux boundary condition, depending upon the vane angles, Reynolds numbers and type of the swirl generators. It was observed that the swirl generator with no deflecting element gave the highest Nusselt numbers and also gave the highest pressure drop in both the swirl generator and the test pipe. Evaluating the effectiveness of the swirl generators for enhancing heat transfer, it was found that using the swirl generator with no deflecting element may be advantageous in terms of heat transfer enhancement and energy saving in comparison with swirl generators with a deflecting element.

Enhancement of heat transfer by turbulent decaying swirl flow

The heat transfer and friction characteristics of a decaying swirl flow were investigated experimentally. The swirling motion of the air was produced by a radial guide vane swirl generator. The vanes of the swirl generator were designed to be adjustable to obtain different swirl intensities. Different guide vane angles (15, 30, 45, 60 and 75°) were used for the swirling flow experiments. The results were correlated in the form of Nusselt number as a function of Reynolds number, Prandtl number and the vane angle as Nu=0.133Re0.65Pr0.4(1+tan θ)0.406. An augmentation of up to 98% in Nusselt number was obtained in the decaying swirl flow depending upon the Reynolds number and the vane angle. It was found that the performance of swirling flow is higher than corresponding axial flow with high vane angles and relatively low Reynolds numbers.

Solar-assisted heat pump and energy storage for residential heating

In order to investigate the performance of a solar-assisted heat pump system with energy storage for residential heating in the Black Sea region of Turkey, an experimental setup was constructed. This experimental apparatus consisted of flat plate solar collectors with total area of 30 m2, a laboratory building with 75 m2 floor area for heating purpose, a latent heat thermal energy storage tank filled by 1500 kg encapsulated phase change material (PCM), a heat pump with double evaporators (air-sourced and watersourced) and one condenser, a water circulating pump, and measuring equipments. The experimental results were obtained December-May during the heating season of 1992 for the solar-assisted heat pump system used. The experimentally obtained results were used to calculate the collector efficiency, coefficient of performance of heat pump (COP), system COP, storage efficiency, and total energy consumption of the system during the heating season. The mean value of the collector efficiency, heat pump COP, system COP, and storage efficiency were found 70%, 4.5%, 4.0%, and 60%, respectively.

Experimental investigation of two phase flow instabilities in a horizontal in-tube boiling system

This research covers the experimental investigation of two phase flow instabilities in a horizontal in-tube flow boiling system whose test tube is relatively long. All experiments are conducted at constant heat input, system pressure and exit restriction. Steady state characteristics for five inlet temperatures are found and presented in pressure drop versus mass flow rate diagrams. Dynamic instabilities, such as pressure drop type, density wave type and thermal oscillations are found to occur for all the investigated temperatures, and the boundaries for the appearance of these oscillations are found. As a result, the stability boundary moves to lower mass flow rates with decreasing inlet temperature, which means that the system is less stable for higher inlet temperatures. It is found that the periods and amplitudes of the pressure drop type and density wave type of oscillations decreases with decreasing mass flow rate and increases with decreasing inlet temperature. In addition, it is found that the channel length has an important effect on the two phase flow dynamic instabilities.

A THERMODYNAMIC MODEL OF A SOLAR ASSISTED HEAT PUMP SYSTEM WITH ENERGY STORAGE

In this study, a thermodynamic model of a solar assisted heat pump system with energy storage was developed. The model consists of thermodynamic correlations concerning the fundamental equipment in the system such as solar collector, energy storage tank, compressor, condenser and evaporator. Some model parameters of the system were calculated by using experimental results obtained from a pilot plant. Simulation studies were performed to assess the importance of some design factors on the system performance and economy.

R134a and various mixtures of R22/R134a as an alternative to R22 in vapour compression heat pumps

Abstract The performance of an air to water vapor compression heat pump has been investigated experimentally. The main purpose of this study was to investigate the possibilities of using R134a as a working fluid to replace R22 for vapor compression heat pumps. Pure R22, pure R134a and some binary mixtures of R22/R134a were considered as working fluids. The performance of the system was characterized by mixture ratio, COP and evaporator air inlet temperature. Comparisons are made between the pure refrigerants and refrigerant mixtures on the basis of the COP. Experimental results show that the mixture ratio affects the COP significantly, and the COP could be improved by using pure R134a or an appropriate mixture of R134a/R22 instead of pure R22. The maximum COP occurred at a mixture ratio of around 50/50% R134a/R22. For a mass percentage of 50% of R134a, the COP was enhanced by about average 25%.

Determination of optimum working conditions in heat-pumps using nonazeotropic refrigerant mixtures

Abstract The objective of this work is to investigate experimentally the effects of mixture concentrations, source temperature, flow rate of condenser cooling water and air flow rate in the cooling tower on the Coefficient of performance (COP) and η ex (exergetic efficiency) values of vapour compression heat pump systems. The experimental apparatuses consist of a vapour compression heat pump conducting according to the liquid to air principle, refrigerant mixture unit, cooling tower, measuring elements and other auxiliary equipment. Refrigerants R11, R12, R22 and six of their binary mixtures which contain about 25%, 50% and 75% mass fractions of R22 were tested. The experiments were performed in the region of source temperatures from 18 to 28°C and flow rates of condenser cooling water from 500 to 1250 kg/h. Four different air flow rates were chosen in those experiments in the cooling tower. To determine the efficiency of the chosen parameters on the system and optimum working conditions, an experimental design method suggested by Genichi Taguchi was used. In this study, it was observed that the COP and η ex increased with the addition of R22 to the system over R11 and R12 pure refrigerants.

Influence of Refrigerant Properties and Charge Amount on Performance of Reciprocating Compressor in Air Source Heat Pump

AbstractThis article investigates how hydrofluorocarbon (HFC) refrigerant affects compressor operating conditions and system performance using experimental testing under different conditions. In a heat pump or refrigerator cycle, it is necessary to move the fluid in the system to achieve heating or cooling. The compressor is the responsible component in fluid movement and so is a key factor in system power consumption. For this reason, it is essential to discover ways to increase compressor energy efficiency. R404a refrigerant was selected to evaluate the influence of refrigerant on compressor performance. Compressor inlet and discharge temperatures and pressures were measured experimentally. For the tested refrigerant, compressibility factor (Z) and deviation from ideal gas behavior were analyzed cautiously to compute power consumption, isentropic work, coefficient of performance, energy and exergy state, and compressor efficiency. Also analyzed were the influence of condenser water flow rate and the eff...

Experimental investigation of the exergetic efficiency of air-heating flat-plate solar collector with distorted plates

Abstract In order to investigate the effects of new developments of solar collector types on the exergetic efficiency of a solar collector with distorted plates (nonparallel plates), an experimental set up was constructed. This experimental apparatus consists of four types of air-heating flat-plate solar collectors, air circulation fan, measuring elements and other auxiliary equipment. The experiments were made in February, March, April, May, June and July in 1992 under the same ambient air conditions for the four different collector types. The exergetic efficiency of the collectors is calculated by using the experimental data, and comparisons are performed among the different collectors.

Economical evaluation of a cogeneration system for a building complex

In this study, the suitability of using cogeneration system for the Aktürk Building Complex (located in İstanbul) was investigated using electricity and heat consumption data by considering five different cogeneration system capacities (800, 1200, 1400, 2000 and 2600 kW). The different capacities were compared using data of the payback period of investment, amount of net savings, ratio of meeting demand and part-load efficiency of the cogeneration system. Although payback periods of the investment for different capacities are close to each other, 1200 kW capacity cogeneration system is proved to be suitable for the Aktürk Building Complex because it has the shortest payback period (1 year 5 months).