Energy Conservation: Heat Transfer Design Considerations Using Thermodynamic Principles

Environmental concerns involving conservation of energy issues gained increasing prominence during and immediately after the OPEC oil embargo of 1973.In addition, global population growth has led to an increasing demand for energy.Although the use of energy has resulted in great benefits, the environmental and human health impact of this energy use has become a concern.One of the keys to reducing and/or eliminating this problem will be achieved through what has come to be referred to as meaningful energy conservation.One of the areas where the aforementioned meaningful energy conservation measures can be realized is in the design and specification of process (operating) conditions for heat exchangers.This can be best accomplished by the inclusion of second law principles in the analysis.The quantity of heat recovered in an exchanger is not alone in influencing size and cost.The law of conservation of energy is defined by many as the first law of thermodynamics.Its application allows calculations of energy relationships associated with various processes.Both a qualitative and quantitative review of entropy and the second law are presented in this paper.This is followed by a section titled "The Heat Exchanger Dilemma" that examines the interrelationship of entropy with heat exchanger design and optimization.The paper concludes with four Illustrative Examples.It is concluded that from a "conservation of energy" perspective, second law considerations mandate its inclusion in heat exchanger applications with appropriate economic considerations.Both the cost of the exchanger and the economic factors associated with the "quality" of the recovered energy must be included in any meaningful optimization study and/or analysis.