Passage
Nitrogen is extremely cold in its liquid phase. It is used in the cryopreservation of small tissue samples and in cryosurgery to freeze and destroy diseased tissues. Liquid nitrogen can be produced from nitrogen gas using the Hampson-Linde cycle (Figure 1) .
Figure 1 Hampson-Linde cycle apparatus used to liquefy nitrogenThe cycle begins by compressing nitrogen gas and forcing it through a coil in an external cooler that contains dry ice. The gas proceeds to a heat exchanger, where it cools further due to the countercurrent heat exchange with colder nitrogen gas returning from a later stage of the cycle; this process is known as regenerative cooling. The gas is subsequently forced through a narrow valve, where it expands and cools significantly upon exiting. As a result, a portion of the gas becomes liquefied.The temperature change of the gas exiting the valve is described by the Joule-Thomson effect, which occurs without heat transfer with the surroundings. Finally, the liquefied nitrogen is collected, and the remaining gas is sent through the regenerative cooler back to the compressor to reenter the cycle. The physical properties of nitrogen are given in Table 1.Table 1 Thermal Properties of Nitrogen

-Which of the following best describes the type of heat transfer that occurs after the compression stage of the Hampson-Linde cycle is completed?

Question

Passage
Nitrogen is extremely cold in its liquid phase. It is used in the cryopreservation of small tissue samples and in cryosurgery to freeze and destroy diseased tissues. Liquid nitrogen can be produced from nitrogen gas using the Hampson-Linde cycle (Figure 1) .

Figure 1 Hampson-Linde cycle apparatus used to liquefy nitrogenThe cycle begins by compressing nitrogen gas and forcing it through a coil in an external cooler that contains dry ice. The gas proceeds to a heat exchanger, where it cools further due to the countercurrent heat exchange with colder nitrogen gas returning from a later stage of the cycle; this process is known as regenerative cooling. The gas is subsequently forced through a narrow valve, where it expands and cools significantly upon exiting. As a result, a portion of the gas becomes liquefied.The temperature change of the gas exiting the valve is described by the Joule-Thomson effect, which occurs without heat transfer with the surroundings. Finally, the liquefied nitrogen is collected, and the remaining gas is sent through the regenerative cooler back to the compressor to reenter the cycle. The physical properties of nitrogen are given in Table 1.Table 1 Thermal Properties of Nitrogen

-Which of the following best describes the type of heat transfer that occurs after the compression stage of the Hampson-Linde cycle is completed?

Quizplus · Accepted Answer

11ecba2d_12fd_56dd_a3bf_23b15d128e9e_MD0008_00 Heat is the energy transferred from one object to another due to their temperature difference, and it always flows from hotter objects to colder objects. Heat can be transferred by three different mechanisms: Conduction is the transfer of heat through direct physical contact. Convection is the transfer of heat through the flow of fluids. Fluids absorb heat from hotter regions and deliver it to colder regions. Radiation is the transfer of heat through electromagnetic radiation, such as infrared light. Radiation heat transfer is significant only for high temperatures. As the nitrogen gas leaves the compressor and flows through the coil of the external cooler, it transfers energy obtained during the compression stage to different sections of the coil. Therefore, the heat transfer that results from the motion of the compressed nitrogen gas is primarily a convective transfer of heat. (Choice A) Although heat is eventually transferred from nitrogen to the dry ice, the dry ice and the nitrogen are not in direct contact; the heat must first move through the coil walls before it can influence the dry ice. (Choice B) Both dry ice and the coil are solids. Therefore, these substances cannot participate in convective heat transfers. (Choice D) Because heat is transferred from hotter objects to colder objects, heat is lost (not gained) by the nitrogen. Educational objective: Heat is energy that flows from high temperatures to low temperatures. Heat can be transferred through direct physical contact (conduction), through the flow of fluids (convection), or through emission of electromagnetic energy (radiation).

Passage Nitrogen Is Extremely Cold in Its Liquid Phase. It Is