AN EXPERIMENTAL AND ANALYTICAL STUDY OF NEGATIVE HEAT TRANSFER IN LAKES

Negative heat ux is a special type of heat transfer thatis generated by wind or ice on the water surface andtakes place during the day in lakes. The negative heatux produces horizontal,vertical density straticationsthat can generate exchange ow between open waterand covered areas. We conducted an investigation ofthe negative heat transfer generated in the laboratoryby a surface cooling method. We examined the eectiveparameters of the heat ux in surface cooling. Weused mixture of ice,water in a galvanized reservoirto model the cold source producing the negative heatux. Over time, the negative heat ux through the bottomof galvanized reservoir was transferred to the watersurface.Temperature was measured by thermometer probes connectedto a computer,was recorded continuously.The negative ux was then calculated from the temperaturemeasurements at two close depths. We foundthat mass of ice,mass of water, distance betweensurface of water,the galvanized reservoir,waterarea are the important parameters in the negativeheat ux. We also developed an analytical model of theheat transfer in which the tank is assumed to be cooledfrom the surface,has adiabatic conditions at otherboundaries. We used the magnitude of the negative heatux from the experiment in the model,predictedthe temperature at dierent times,depths. The resultsof experimental modeling,analytical solutionare fairly in agreement. The reasons for the dierencebetween the experimental results,the analytical solutionare oscillation of the negative heat ux from theice reservoir,the instability ow generated in the experimenttank below the ice reservoir. The instabilityappears in the form of instability ngers,plunges tothe bottom of the tank due to a lower temperature ofthe cooled surface water relative to the tank temperature.