Entransy is a concept developed in recent years to measure the heat transfer ability of an object or a system at a temperature and has been used in heat transfer optimization. In this contribution, the closed system undergoing thermodynamic processes is analyzed from the viewpoint of entransy. Heat entransy flow and work entransy flow are defined with the consideration of heat interaction and work interaction respectively. The entransy balance equation is developed for the thermodynamic cycle and the processes of the Carnot cycle are discussed. In the cycle, the net heat entransy flow is showed to be equal to the net work entransy flow. The difference between heat entransy flow and work entransy flow is discussed. Work entransy flow can be input from low temperature to high temperature and vice versa. Heat entransy flow can only be transferred from high temperature to low temperature spontaneously, leading to entransy dissipation. The entransy balance equation for the closed system with irreversible processes and heat engines is further introduced by defining the irreversible entransy loss. The entransy balance equations are applied to analyzing the heat-work conversion in a system with given heat input. It is shown that reducing the irreversible entransy loss or the entropy generation can improve the heat-work conversion efficiency. For the reversible heating and air conditioning example in which heat from the high temperature heat source is first used to do work and then the work is used to pump more heat from environment into the target room, the change in work entransy flow can be used to measure the cost for the additional heat pumped from environment, but entropy generation is zero and could not be related to the benefit. (C) 2013 Elsevier Ltd. All rights reserved.