Final answer:
Starting an LPG-fueled engine in cold conditions requires ensuring proper vaporization of the fuel. Cooling a high-pressure gas cylinder to reduce leakage using dry ice is determined by the ideal gas law, and the practicality of this solution depends on various factors. The coefficient of performance for heat pumps and refrigerators indicates their efficiency and is influenced by the temperature difference between reservoirs.
Step-by-step explanation:
LPG Fuel Behaviour in Cold Conditions
The behaviour of LPG (liquefied petroleum gas) in cold conditions, particularly in temperatures ranging from 0 to -40°C, poses challenges for starting air-cooled engines. A typical recipe to start an engine with LPG fuel at -25°C would involve ensuring that the LPG is adequately vaporized for combustion, which may require assistance from a pre-heating system or an engine block heater. Otherwise, the LPG may not vaporize properly due to the low ambient temperatures.
Practicality of Cooling a Tank with Dry Ice
Addressing the questions about the high-pressure gas cylinder cooled to dry ice temperature, we use the ideal gas law to calculate pressures and temperatures. Cooling the tank to -78.5°C (assuming no phase changes or leaks) will lower the pressure according to the proportions dictated by the ideal gas law. The practicality of such cooling depends on factors like the time needed to reach the desired temperature and the safety precautions necessary for handling the gas and the dry ice.
Efficiency of Heat Pumps and Refrigerators
The coefficient of performance (COP) of heat pumps and refrigerators is a measure of their efficiency, relevant for devices operating in cold conditions. For the scenarios provided, calculations based on thermodynamics reveal the theoretical maximum efficiency of each system. The COP is higher when the temperature difference between the hot and cold reservoirs is smaller.