考电工证试题

考电工证 A, true or false In the same initial and final state, the change in the irreversible process is greater than the change in the reversible process. (x) The reversible process must be a quasi-static process. (?) For the open system, the enthalpy of work represents the total energy transferred by the flow of work. (x) The vapor mass volume of the air suction port is less than the volume of vapor in the vent. (x) The greater the dry x of the wet steam, the farther away the wet vapor from the dry saturated steam line. (x) There is a one-to-one correspondence between the pressure of the refrigerant vapor and the temperature. (x) The lower the temperature of the cold reservoir, the higher the temperature of the hot reservoir, the higher the refrigeration coefficient of the refrigeration cycle. (x) The variable exponent of the constant pressure process is n = 0. (?) 9, the adiabatic process system with the outside world without entropy variation in the process of heat exchange between Δ S = 0. (?) The inner energy of an ideal gas is proportional to the temperature of the gas and the mass. (x) The amount of work done in the heat process is independent of the path through which the process experiences, only the initial and final state functions. (x) The condensation process of gaseous refrigerants in condensers is a constant temperature constant pressure process. (?) The essence of the first law of thermodynamics is the conservation of energy. (?) The efficiency of a reversible engine is higher than that of an irreversible engine. (x) The non-equilibrium system is in an unbalanced state, but its state parameters are determined. (x) The spontaneous process is irreversible, and the spontaneous process is reversible. (x) As long as there is no volume change, the equipment will not do any work. (x) The heat of vaporization of the same industrial substance decreases with the increase of pressure. (?) The physical quantities describing the state of the system are called state parameters. (?) The heat cycle is called the heat cycle by the system, which goes through a series of state changes from a certain state to the initial state. (?) Second, the choice The closed system is the system and the outside (C). (A) no work exchange (B) no heat exchange (C) no mass exchange (D) without any exchange In the case of adiabatic throttling, the following error is (D) (A) the entropy of work increases because of the friction of the adiabatic process (B) the pressure drops because of the sudden narrowing of the flow section and the resistance of the work force to the local resistance (C) the quality of the work is equal to the enthalpy of the throttle (D) the temperature doesn't change because the process is adiabatic The change of dry degree in evaporation of refrigerant in evaporator is (A) (A) x = 0 is increasing to x = 1 (B) x = 0 constant (C) is reduced by x = 1 and x = 0 (D) x = 1 4, A certain mass of an ideal gas, if the pressure is constant, its volume increases (A) Temperature rise (B) temperature decreases (C) temperature invariant (D) temperature has nothing to do with volume In the case of the variable process, when the variable exponent n = k, the process is (D). (A) the process of the constant pressure process (B) constant volume (C) process (D), the process of the constant temperature process (D) For the variable process, the process of presentation when the variable exponent n = 1 is (C) (A) the process of the constant pressure process (B) constant volume (C) process (D), the process of the constant temperature process (D) For the variable process, when the variable exponent n = + -infinity, the process is (B) (A) the process of the constant pressure process (B) constant volume (C) process (D), the process of the constant temperature process (D) The following statement is correct (C) (A) heat can spontaneously transfer from A cold body to A hot object (B) can make a kind of engine, it can get heat from a heat source, make it completely mechanical energy. (C) all the thermal processes are directionality, There are limits to the use of energy (D) the maximum efficiency of a heating machine is 100% 9, quality volume and quality of work (C) (A) the temperature is proportional (B) to inversely proportional (C) to inversely proportional (D) The heating factor of the heating cycle refers to (B) (A) the ratio of the heat absorbed by the cold reservoir to the amount of external work (B) the ratio of the heat released to the hot reservoir to the recycled consumption (C) the ratio of the heat from the cold reservoir to the heat from the hot reservoir (D) the cooling coefficient of the cooling cycle is one less than that of the same heat source The work flow flows through the condenser (A). (A) the heat is released, and the heat is reduced by the enthalpy value of the heat, which increases the enthalpy value (C) to absorb the heat from the outside, the enthalpy value increases (D) because the pressure is constant in the condensation process, so the enthalpy value is constant The temperature of the hot reservoir of a reverse carnot cycle is 28 oC, and the temperature of the cold reservoir is minus 18 oC. The refrigeration coefficient of this refrigeration cycle is () (A) 0.39 (B) 5.5 (C) - 0.39 (D) 6.5 In the case of a cyclic process, the quality of the work is returned to the initial state after a series of state changes, and the parameter changes to (). (A) the change in energy, heat and work is zero (B) the change in internal energy is equal to the difference between the heat added to the system and the external output work, and not equal to 0 (C) the change in energy is greater than 0, and the amount of heat and work varies depending on the situation (D) the change in internal energy is zero, and the external output work is equal to the heat added to the system The absolute temperature is (C) corresponding to the 28oC. (A) -245k (B) 82.4 K (C) 301K (D) 245K On the critical state of industry, the following statement is true (A) (A) for refrigerants, the critical temperature should be well above the ambient temperature (B) when the pressure is above the threshold, only increasing the pressure can make the work from the gas phase to the liquid (C) critical stress is the highest pressure on the job The more the condensation pressure of the refrigeration cycle is closer to the critical pressure, the more efficient the cycle Complete overhaul of the equipment, eliminate potential pitfalls, adjust the equipment to the best state and call it (D). (A) the warranty (B) minor (D) repair (D) When measuring the speed of an centrifugal tachometer, use (D) (A) the round friction head, which reads from the table, is converted (B) the cone friction head, which reads from the table to be converted (C) the round friction head can be read directly from the watch (D) the cone friction head can be read directly from the table To use the ventilation dry wet bulb thermometer, place the instrument in the geodesic environment to make the temperature (C) of the instrument. (A) the temperature of the wet bulb is higher than the temperature of the wet ball (C) is equal to the temperature of the environment (D) equals the dew point temperature of the environment Use atmospheric pressure to consider (B) (A) the effect of temperature (B) on the effect of temperature (C) on the effect of wind speed (D) season Impeller type anemometer for measurement (D) (A) air flow velocity (B) in the air flow rate of the air channel (C) air speed of air flow rate (D) in air conditioning room Third, short answer What are the two streams of fluids? What is the criterion for judging the flow state? Answer: the two kinds of flow of fluid are basically laminar flow and turbulent flow two kinds. The criterion for judging the flow state is the Reynolds number of the fluid, Re Angle 2000 is laminar flow, Re > 2000 is turbulent. What are the measures to reduce the flow resistance? Answer: the main way to reduce the flow resistance is the influence on flow, improve the side wall measures include reducing frictional resistance (reduce the roughness of the pipe wall and using the flexible side wall). Import as smooth and reduce the local resistance (make fluid, the divergent and convergent instead of sudden increase and decrease of the section, circulation reduce turn, handle tee structure arrangement, reasonable cohesion and the arrangement of pipe fittings, pump or fan, try to shorten the pipeline, etc.). What are the basic ways of heat transfer? Under what circumstances? A: there are three basic ways of heat transfer, convection heat and heat transfer. Heat transfer occurs between different parts of the same object's internal temperature or between objects that are directly exposed to different temperatures. Convection heat transfer is the transfer of heat between the fluid and the solid wall. Radiation heat transfer is due to the heat because of (their temperature or thermal motion of microscopic particles) and object excitation radiation of electromagnetic wave to the world and the radiation from each other between the object and the total effect of heat absorption. The properties and applications of freon refrigerants are briefly described. A: freon is the general name of all or part of the hydrogen in saturated hydrocarbons that are substituted by halogen elements, chlorine, chlorine, and bromine. Freon refrigerant is used in all kinds of refrigeration air-conditioning equipment such as refrigerator and air conditioner.