Hot water expands so it is less dense than room temperature water. Cold water contracts so it is denser than room temperature water. The red hot water rises and the blue cold water sinks. So when we mix hot water with cold water there will be a transfer or thermal energy from hot to cold, or a flow of heat from hot to cold. It takes about 4,186 Joules to heat up 1 kilogram of water by 1°C. This odd sensation is called paradoxical cold and is caused by the temperature receptors in the skin. There are separate, specific receptors that respond to decreases or increases in skin temperature.

"Hot water expands so it is less dense than room temperature water. Cold water contracts so it is more dense than room temperature water. The red hot water rises and the blue cold water sinks."

Dr Sundus F Hantoosh thank you for your contribution to the discussion

I agree with Rana Hamza Shakil that density and Temperature are inversely related at constant Pressure. Initially, hot water has a lower density and cold water has a higher density. Due to the density differences, hot water floats above cold water. Due to temperature differences heat transfer takes place within the mixture from hot water to cold water. The great ocean conveyor moves water around the globe. Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface. Cold water has a higher density than warm water. The water will cool down until both temperature water becomes the same temperature. Because the hot water will heat the cold water up and the cold water will cool the hot water down until they have the same temperature. There is more energy in the hot water than the cold water. Hot water expands so it is less dense than room temperature water. Cold water contracts so it is denser than room temperature water. The red hot water rises and the blue cold water sinks.When fluids (liquids and gases) are heated, they expand and therefore become less dense. Any object or substance that is less dense than a fluid will float in that fluid, so hot water rises (floats) in colder water. For most temperatures, the density of water decreases as the temperature increases. So over time, as water cools we will develop a "hot top” the surface of the water will be warmer than the average temperature of the water, or the water at the bottom of the container.