Evaporator for orc cycle with recirculating heat carring water – computational model

The following paper presents an ORC installation including an evaporator with recirculation (heat carrying water exiting the evaporator is redirected to its inlet). It covers the calculations of inlet/outlet temperature of the evaporator taking into account a variant recirculation coefficient. Formulas for heat transfer between heat carrying water and working fluid inside evaporator are also included in this paper. The calculations are based on properly defined average specific heat. The analysis shows that the system performance depends on heat carrying water inlet temperature, on heat carrying water flow rate and the recirculation coefficient.

The analysis also shows that the heat

2.ORC POWER PLANT WITH RECIR-CULATING HEAT CARRYING WATER
In a power plant with single ORC loop it is possible to select a proper working fluid. Currently, there is a variety of substances that can serve as working fluid: natural pure substances (butane, izobutane, propane), synthetic pure substances and blends [1][2][3][4][5][6][7][8][14][15][16]. Utilization of organic substance allows to achieve better working conditions comparing to the water (for the same pressure and temperature). The main advantage of those substances over the water is low evaporation temperature (for some of them even below 100°C).
A scheme of a single loop ORC power plant with recirculating heat carrying water evaporator is presented in Fig. 2

3.A METHOD FOR MODELLING OF RECIRCULATING HEAT CARRYING WATER EVAPORATOR
In order to determine the recirculating water temperature, the energy balance equation for node A is used: (4) or after rearrangements the formula (4) takes the following form: After introducing another average specific heat and average specific heat s c from (2a) into (4a), it can be rewritten to the following form: ( ) ( ).
After proper rearrangements, the temperature or recirculating water can be calculated according to the following formula: To derive the formula for water temperature at evaporator outlet, it is necessary to make an energy balance for section b (Fig. 3): that after substituting (3) takes the following form: After using the definition of average specific heat the (7a) can be transformed into a formula for water temperature : Using the formulas (6) and (9a) that allow to calculate water temperature at evaporator inlet and outlet, z s T 1 and z s T 2 , respectively, it is possible to evaluate the temperature difference : where: . were calculated using specific enthalpy h′ for saturated water available in REFPROP 9 software [9]: The results of average specific heat calculations are presented in tables 1-6. They served as a base for average specific heat charts ) .     Scientific and research interests include: renewable energy sources (with ORC), geothermal heat plants, heat management, ventilation and air conditioning, heat exchange and heat exchangers. His specialty is thermal technology, especially heat transfer, has a significant scientific output, including authorship or co-authorship of 5 monographs, 6 didactic scripts, 5 patents, 3 patent applications and over 450 original scientific publications in major national and international scientific journals and conference materials. He promoted 11 doctors, 4 of whom received a postdoctoral degree and 3 are titular professors. He is a reviewer of 17 habilitation dissertations and 27 doctoral dissertations from Poland and abroad. He made 10 opinions for awarding the title of professor and a dozen for the position of full professor. Promoter of over 250 diploma theses. Organizer and co-organizer of national and international symposia and conferences, including: Heat Transfer and Renewable Sources of Energy. From January 1, 2003, Professor Władysław Nowak is retired, still working actively in the field of science and playing an important role in the activity and development of the parent unit, which is the Department of Heat Engineering.