Ozgen Acikgoz

Determination of the Effect of Wall Heating Systems on Convective Heat Transfer Coefficient in Buildings

Decreasing energy consumption and advancing thermal comfort are the most important aims of building engineering. Previously reported studies by many researchers have found that different usages of convective heat transfer coefficient (CHTC) correlations in heating system simulations have considerable impacts on calculated heating load in buildings. Hence, correct utilization of CHTCs in real size room enclosures has great importance for both energy consumption and thermal comfort. In this study, a modeled room was numerically heated from one vertical wall and cooled from the opposite wall in order to create a real room simulation. While cooled wall simulate heat losses of the room, heated wall simulates the heat source of enclosure. Effects of heated and cooled wall temperatures and characteristic length on CHTC and Nusselt number in the enclosure were numerically investigated for two (2-D) and three dimensional (3-D) modeling states. CHTCs and Nusselt numbers of a real size room with the dimensions of 6.00 by 2.85 by 6.00 were found with FLUENT CFD and graphics of change were drawn. As result, difference between 2-D and 3-D solutions was found approximately 10%. This was attributed as the effect of air flow pattern effects over other surfaces in the enclosure that can not be counted at 2-D solutions. The change of CHTC at different characteristic lengths was illustrated as well.

Determination of Optimum Velocity for Various Nanofluids Flowing in a Double-Pipe Heat Exchanger

Piping is one of the most important issues in the cost of process factories. It is known that 80% of bought equipment cost or 20% of overhead capital can belong to piping cost in a fluid-process factory. Pipe diameter and therefore flow velocity strongly affect the existing value of the factory regarding the consumed electric energy and fitting cost of pipes, pumps, and valves. We give a detailed cost analysis model for the pure fluids of water, motor oil, glycerin, ammonia, methanol, ethanol, ethylene glycol, and propane and their nanofluid mixtures with Ti and TiO2 particles in liquid phase flowing in the tube side of a double-pipe heat exchanger. Pressure drop and pumping power values increase with flow velocity but total cost values show an arc with it. The clear outcome is that there is a minimum cost value as a result of the analyses for each investigated fluids. Moreover, validation of the model is performed by plotting the calculated items in figures such as total heat transfer coefficient versus Reynolds number, pressure drop versus Reynolds number, and friction factor versus mass flow rate. Characteristics of the trend lines in these figures are seen as they should be.

Numerical Determination of Effects of Wall Temperatures on Nusselt Number and Convective Heat Transfer Coefficient in Real-Size Rooms

A modeled room was numerically heated from a wall and cooled from the opposite wall in order to create a real-room simulation. The cooled wall simulated heat loss of the room, and the heated wall simulated the heat source of enclosure. The effects of heated and cooled wall temperatures on convective heat transfer coefficient (CHTC) and Nusselt number in the enclosure were investigated numerically for two- (2D) and three-dimensional (3D) modeling states. Different hot wall and cold wall temperatures were applied in order to obtain correlations that contained characteristic length in Rayleigh numbers. Results were compared with the results of previously reported correlations that have been suggested for vertical room surfaces in enclosures. In addition, new correlations for Nusselt number and average CHTC for enclosures for isothermal boundary conditions within indicated Rayleigh number ranges were derived through solutions. Average deviations of new correlations obtained for CHTC and Nusselt number from the numerical data were found 0.73% and 1.76% for 2D study, 3.01%and 0.49%for 3D study. It was observed that the difference between the 2D and 3D solutions in terms of CHTC and Nusselt number was approximately 10%.

Exergetic Analysis of a Vertical Ground-Source Heat Pump System with Wall Heating/Cooling

The present study deals with an exergetic analysis and assessment of a Vertical Ground-Source Heat Pump System (VGSHP) combined with a Wall Heating System (WHCS) in a building. This study is an experimental investigation of a real building’s heating system. The system is located at Yildiz Renewable Energy House (YREH) in Yildiz Technical University and fulfills the heating demand of YREH and a living room of the neighboring dormitory. In order to validate an exergetic model, the system is divided into three subsystems: (1) the ground coupling circuit, (2) the refrigerant circuit, and (3) the WHS circuit. The schematic diagram of the constructed experimental system is given in Fig. 26.1. Exergetic model is obtained by applying mass, energy, and exergy equations for each system component. YREH has four rooms, each has 8 m2 floor area, and the neighboring dormitory has a 50 m2 living room. In this study three rooms of YREH and the living room have been heated during heating season. The heating season was assumed to be between 1 January and 31 March. As average results on the heating season, 6.509 kW heat energy was extracted from ground and 5.799 kW was used in the WHS. In this process electrical energy consumption of system components are as follows: compressor 1.711 kW, ground heat exchanger pump 0.092 kW, accumulator tank circulation pump 0.114 kW, and WHS circulation pump 0.108 kW. For heating season, calculated overall system efficiency was 67.36 % while GSHP unit’s efficiency was 85 %. In addition, overall system COP was 2.76, while GSHP unit’s COP was 4.13. Total exergy destruction was found 1.759 kW and largest exergy destruction has occurred in the compressor as 0.714 kW. The exergy efficiency values for the individual components of the system have been found ranging from 58.3 to 98.4 % according to P/F concept. It is expected that the model would be beneficial for evaluating low exergy heating systems which use ground source as a renewable energy.