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# Heat (K / P 1 and 2 cipher 06)

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**26.04.2013**

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Examination number 1 of Heating

(Code 06)

5. Bring the wording of the first law of thermodynamics. On-write an analytical expression of the law for the basic thermodynamic processes

15. What is called the humid air? Give the definition of relative humidity, moisture content and dew point temperature.

Problem number 6

To determine the polytropic exponent of air compression in a single-stage reciprocating compressor, if the pressure increases in the process β = 7,5 times, the gas temperature varies from 20 t1 = t2 = 0C to 120 0C. Identify and process heat, work process change in internal energy and entropy of 1 kg of gas.

Problem number 16

The wet saturated steam having initial parameters t1 = 139 0C and x = 0.94 is compressed during no heat exchange with the environment. The volume of steam decreases ε = 15 times. And determine the state of the steam parameters at the end of the compression process, and changing the specific enthalpy and the work 1 kg of steam in the process. Show process is-diagram.

Problem number 17

What should be the sectional area of \u200b\u200bthe opening of the safety valve of the steam boiler to the sudden termination of the selection of dry saturated steam from it in the amount of G = 5 kg / s absolute pressure does not exceed 1.4 MPa? Atmospheric pressure = 750 mm Hg Loss of pressure on myatie steam heat exchange while passing hole and the velocity of steam inlet valve opening neglected.

Problem number 27

The degree of pressure rise in the compressor of a gas turbine plant (GTP) is λ = 7,8, the temperature of the working fluid (for k = Cp / Cv = 1,4) is equal to the turbine nozzles 800 0C. Ideally, the heat cycle gas turbine is fed at a constant pressure. Identify the basic parameters of the working fluid in the transition points in the cycle, thermal efficiency, specific useful work cycle, as well as changes in specific entropy in heat supply, taking the specific heat of the working fluid does not depend on temperature. The initial parameters of the cycle P1 = 0.1 MPa and t1 = 27 0C. Cycle represented in pv- and TS-coordinates.

Verification work number 2

5. The wall of the heat exchange surface of the steam boiler is washed ML-term side of the hot gases, and the other - the boiling water. Why the surface temperature on the water side is much less different from the water temperature than the temperature of gas?

15. What is the risk of the onset of film boiling regime?

Problem number 6

As steel uninsulated pipe diameter 80h5 mm flowing refrigerant whose temperature t2 = -20 0C. The air temperature in the room where the pipeline passes t1 = 20 0C. The heat transfer coefficient on the air side α1 = 10 W / m2 K, from the refrigerant α2 = 1000 W / m 2 K. By what percentage will decrease the loss of cold, if the pipe covered with a layer of insulation, with thermal conductivity λ2 = 0,14 W / m K and a thickness δ2 = 95 mm.

Problem number 16

A cylindrical channel with a diameter d = 14 mm moving water. Water flow rate G = 850 kg / h = 0.24 kg / s and its inlet temperature t '= 55 0C. At some distance from the entrance of the average cross-section of the water temperature reaches t '' = 95 0C, if the temperature of the inner surface of the channel Tw = 100 0C is constant?

Problem number 17

Find the average heat transfer coefficient in film condensation of dry saturated steam pressure P = 0.6 MPa approximately horizontal tube (diameter d = 0,03 m and a length l = 0,8 m), and having a surface temperature Tw = 50 0C. How many of these handsets will need to condense 500 kg of steam per hour?

Problem number 27

Between two vertical flat plate size 0,5h0,5 m placed an electric heater with a uniform distribution of heat density. Emissivity surfaces ε = 0,85. What should be the capacity of the electric heater to at ambient temperature ti = 0 0 C to keep the temperature of surfaces plates Tw = 120 0 C, if the coefficient of heat transfer