Does liquid nitrogen radiate heat

Answer 1

Generally, no. Liquid nitrogen is "too cold" normally to radiate heat, at least compared to surrounding things. Nitrogen liquifies at extremely low temperature, and because it is so cold, it is surrounded by stuff that is a lot warmer. It is generally a heat absorber. There are circumstances where liquid nitrogen will radiate heat. If we conduct an experiment where we cool liquid nitrogen with liquid helium, the liquid nitrogen will radiate heat. And it will become a solid, giving us solid nitrogen (because it changed its state of matter by "freezing" and becoming a solid).

Answer 2

You could put liquid nitrogen in your radiator. But I expect the question you're meaning to ask is 'will my car work if I replace the water in my radiator with liquid nitrogen?' And the answer is no. The way a radiator works is by pumping a liquid round a hot thing that needs to be cooled (for instance, your engine), and back to a big tank with a large surface area (the radiator), where it can cool down again. For this to work, the liquid needs to be liquid at the whole range of temperatures it might encounter during the cycle. Liquid nitrogen doesn't meet this criterion, because it's not even liquid at room temperature. Liquid nitrogen, when introduced into a car's cooling system, would violently expand, much like the water in a steam engine's boiler, or a pressure cooker. The radiator is designed to withstand a certain amount of pressure (which is why you don't take the lid off when it's hot: the pressurised contents would spray out all over you), but probably not the pressure generated by the fluid flash-boiling all at once. So as well as not cooling your engine, it might well blow your radiator up.