Simulation of a transcritical CO 2 heat pump cycle for simultaneous cooling and heating applications J. Sarkar, Souvik Bhattacharyya * , M. Ram Gopal Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India Received 26 May 2004; received in revised form 28 November 2005; accepted 11 December 2005 Available online 28 February 2006 Abstract A steady state simulation model has been developed to evaluate the system performance of a transcritical carbon dioxide heat pump for simultaneous heating and cooling. The simulated results are found to be in reasonable agreement with experimental results reported in the literature. Such a system is suitable, for example, in dairy plants where simultaneous cooling at 4 8C and heating at 73 8C are required. The optimal COP was found to be a function of the compressor speed, the coolant inlet temperature to the evaporator and inlet temperature of the fluid to be heated in the gas cooler and compressor discharge pressure. An optimizing study for the best allocation of the fixed total heat exchanger inventory between the evaporator and the gas cooler based on the heat exchanger area has been carried out. Effect of heat transfer in the heat exchangers on system performance has been presented as well. Finally, a novel nomogram has been developed and it is expected to offer useful guidelines for system design and its optimisation. q 2006 Elsevier Ltd and IIR. All rights reserved. Keywords: Research; Experiment; Growth; Crystal; Frost; Defrosting; Modelling; Plate; Electric field; Alternating current Elimination des cristaux de givre sur une plaque froide: effets des fre ´quences stationnaires et de balayage des champs e ´lectriques Mots cle ´s : Recherche ; Expe ´rimentation ; Croissance ; Cristal ; Givre ; De ´givrage ; Mode ´lisation ; Plaque ; Champ e ´lectrique ; Courant alternatif 1. Introduction A carbon dioxide based vapour compression refriger- ation system was patented in 1850, followed by several decades of its use. However, due to problems arising from its very low critical temperature and high operating pressure, carbon dioxide as a refrigerant was slowly replaced by the synthetic halocarbon refrigerants. Inter- estingly though, with the discovery of the harmful effects of the synthetic refrigerants on environment, there is a renewed interest in natural refrigerants such as carbon dioxide. Lorentzen [1] through his seminal studies has shown that the problem of low critical temperature of carbon dioxide can be effectively overcome by operating the system in the transcritical region. This has led to the development of transcritical carbon dioxide cycles where International Journal of Refrigeration 29 (2006) 735–743 www.elsevier.com/locate/ijrefrig 0140-7007/$35.00 q 2006 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2005.12.006 * Corresponding author. Tel.: C91 3222 282904; fax: C91 3222 255303. E-mail address: souvik@mech.iitkgp.ernet.in (S. Bhattacharyya).