عنوان مقاله [English]
Negative heat flux is a special type of heat transfer that is generated by wind or ice on the water surface and takes place during the day in lakes. The negative heat flux produces horizontal and vertical density stratifications that can generate exchange flow between open water and covered areas. We conducted an investigation of the negative heat transfer generated in the laboratory by a surface cooling method. We examined the effective parameters of the heat flux in surface cooling. We used mixture of ice and water in a galvanized reservoir to model the cold source producing the negative heat flux. Over time, the negative heat flux through the bottom of galvanized reservoir was transferred to the water surface. Temperature was measured by thermometer
probes connected to a computer and was recorded continuously. The negative flux was then calculated from the temperature measurements at two close depths. We found that mass of ice and mass of water, distance between surface of water and
the galvanized reservoir, and water area are the important parameters in the negative heat flux. We also developed an analytical model of the heat transfer in which the tank is assumed to be cooled from the surface and has adiabatic conditions at other boundaries. We used the magnitude of the negative heat flux from the experiment in the model and predicted the temperature at different times and depths. The results of experimental modeling and analytical solution are fairly in agreement. The reasons for the difference between the experimental results and the analytical solution are oscillation of the negative heat flux from the ice reservoir and the instability flow generated in the experiment tank below the ice reservoir. The instability appears in the form of instability fingers and plunges to the bottom of the tank due to a lower temperature of the cooled surface water relative to the tank temperature.