Recep Yumrutaş

Exergy analysis of vapor compression refrigeration systems

Abstract A computational model based on the exergy analysis is presented for the investigation of the effects of the evaporating and condensing temperatures on the pressure losses, the exergy losses, the second law of efficiency, and the coefficient of performance (COP) of a vapor compression refrigeration cycle. It is found that the evaporating and condensing temperatures have strong effects on the exergy losses in the evaporator and condenser, and on the second law of efficiency and COP of the cycle but little effects on the exergy losses in the compressor and the expansion valve. The second law efficiency and the COP increases, and the total exergy loss decreases with decreasing temperature difference between the evaporator and refrigerated space and between the condenser and outside air.

Analysis of solar aided heat pump systems with seasonal thermal energy storage in surface tanks

Annual periodic performance of a solar assisted ground-coupled heat pump space heating system with seasonal energy storage in a hemispherical surface tank is investigated using analytical and computational methods. The system investigated employs solar energy collection and dumping into a seasonal surface tank throughout the whole year with extraction of thermal energy from the tank for space heating during the winter season. A computational model is presented in this study for the prediction of the annual periodic transient behaviour of the system under investigation. The present computational model is based on a hybrid analytical–numerical procedure which facilitates determination of the annual variation of water temperature in the surface tank, the amounts of solar thermal energy collected during each month and the annual periodic performance of the solar aided space heating system.

A computational model of a heat pump system with a hemispherical surface tank as the ground heat source

A computational model for a space heating system utilising a heat pump with a hemispherical surface tank as the ground heat source is presented. An analytical solution is obtained for the transient temperature field outside a hemispherical surface tank by an application of the Complex Finite Fourier Transform (CFFT) and the Finite Bessel Transform (FBT) techniques. This analytical solution, when utilized with expressions valid for the heat pump work and space heat load, leads to the prediction of the annual variation of water temperature in the surface tank as well as the transient earth temperature field surrounding the surface tank. Monthly and annual heat pump work requirements are predicted and presented.

Investigating thermal performance of an ice rink cooling system with an underground thermal storage tank

This study deals with mathematical modeling and energy analysis of an ice rink cooling system with an underground thermal energy storage tank. The cooling system consists of an ice rink, chiller unit, and spherical thermal energy storage tank. An analytical model is developed for finding thermal performance of the cooling system. The model is based on formulations for transient heat transfer problem outside the thermal energy storage tank, for the energy needs of chiller unit, and for the ice rink. The solution of the thermal energy storage tank problem is obtained using a similarity transformation and Duhamel superposition techniques. Analytical expressions for heat gain of the ice rink and energy consumption of the chiller unit are derived as a function of inside design air, ambient air, and thermal energy storage tank temperatures. An interactive computer program in Matlab based on the analytical model is prepared for finding hourly variation of water temperature in the thermal energy storage tank, coefficient of performance of the chiller, suitable storage tank volume depending on ice rink area, and timespan required to attain an annually periodic operating condition. Results indicate that operation time of span 6–7 years will be obtained periodically for the system during 10 years operating time.

Model-Based Performance Analysis of a Concentrating Parabolic Trough Collector Array

This study presents a comprehensive thermo-mathematical model of a parabolic trough solar collector (PTSC) array which consists of three modules connected in series. A detailed model for the absorbed solar energy falling on the array aperture, the optical efficiency changing with incidence angle, and the useful energy gained by heat transfer fluid (HTF) for a linear with a single-axis tracking motion rotating about a horizontal north–south orientation was programmed in Engineering Equation Solver (EES) based on the actual system parameters. The model comprises steady-state and one-dimensional heat transfer approach using the thermodynamics and the heat transfer relations to evaluate the thermal losses of the receiver (heat collector element) by taking into account the effects of collector dimensions, material properties, and fluid properties. In the performance analysis of the PTSC array, the effects of hourly solar radiation flux, ambient conditions, collector inlet temperature, and mass flow rate of the working fluid were investigated. Typical operating conditions on the 1st day of July at 12:00 solar time exhibited that when the HTF mass flow rate 0.3 kg/s, inlet temperature 150 °C, ambient temperature 39 °C, ambient air velocity 1 m/s and having a 10.26 m2 PTSC aperture area, and 940 W/m2 direct beam radiation incident with 13.98°, the estimated collector array efficiency is about 59.2 %. The model predictions are to be confirmed by the operation of PTSC being installed at Gaziantep.

A Process Heat Application Using Parabolic Trough Collector

A pilot study has been performed based on a heat process application that is designed, installed and tested at Gaziantep University to establish the technical and economic feasibility of high temperature solar-assisted cooking process. The system has been designed to be satisfying the process conditions integrated with parabolic trough solar collector (PTSC). It is primarily consists of the PTSC array, auxiliary heater, plate type heat exchanger, cooking system and water heating tanks. In the operation of the process heat application, the energy required to cook wheat (used as cooking material) has been supplied from solar energy which is transferred to heat transfer fluid (HTF) by heat exchanging units and finally discharged to water in order to produce bulgur. The performance parameters of the sub-systems and the process compatibility have been accomplished depending on the system operation. In addition that the system performance of the high temperature solar heat process has been presented and the recommendations on its improvement have been evaluated by performing an experimental study. As a result that the use of solar energy in process heat application has been projected and its contribution to economics view with respect to conventional cooking systems has been conducted.