INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Res. 2006; 30:1228–1241 Published online 17 May 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/er.1211 SHORT COMMUNICATION Study of thermal aspects in open and greenhouse ponds Bikash Sarkar and G. N. Tiwari n,y Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India SUMMARY In this study, thermal aspects, e.g. convective heat transfer coefficients were evaluated and modelled in open and greenhouse pond systems (natural convection). Values of the constants C and n were determined by linear regression analysis from the experimental data. It was observed that the ranges of the convective heat transfer coefficient were strongly dependent upon D/H (Diameter / Height) ratio of the container. It was also observed that the uninsulated container 5 (D=H ¼ 5:240) and the insulated container 1 (D=H ¼ 0:196) indicate minimum and maximum convective heat transfer coefficient in winter and summer months, respectively. Predicted and experimental values of convective heat transfer coefficients, verified in terms of root mean square of percent deviation, correlation coefficient and error bars (  SD), exhibit fair agreement. The model has been validated for the composite climate of New Delhi. Copyright # 2006 John Wiley & Sons, Ltd. KEY WORDS: greenhouse; convective heat transfer coefficient; energy; evaporation 1. INTRODUCTION Fish ponds, generally, have small water sheds often require the application of heat loss reduction methods and the use of supplemental heat. The heat is most often available in the form of power plant waste heat, geothermal hot water and active or passive greenhouse. In an open and covered pond, exchanges of heat with the atmosphere occur by the way of four mechanisms: (a) conduction, (b) convection, (c) evaporation and (d) radiation. Each of these is influenced by different parameters. The most important mechanisms of heat loss from the pond surface are convection and evaporation. For any pond, convection occurs in two places i.e. at the soil–water interface and water–air interface. Convection is the transfer of heat from one part of a fluid to another part, at a lower temperature by mixing of fluid particles. Heat is transported simultaneously during the process by convection and evaporation. It is dependent upon the local climatic factors such as the wind velocity, the mixing of the water within Received 20 July 2005 Revised 2 February 2006 Accepted 12 February 2006 Copyright # 2006 John Wiley & Sons, Ltd. y E-mail: gntiwari@ces.iitd.ernet.in n Correspondence to: G. N. Tiwari, Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.