Molecular Physics | Thermodynamics Answers

A heat pump cycle delivers energy by heat transfer to a dwelling at a rate of 11.7 kW. The coefficient of performance of the cycle is 2.8. Evaluating electricity at $0.10 per kW ⋅ h, determine the cost of electricity during the heating season when the heat pump operates for 1800 hours.

Steam enters a nozzle at pressure of 6 bar and 2000c with enthalpy 2850 kJ/kg and leaves at a pressure of 1.5 bar. The initial velocity of steam is 50m/s and the exit velocity from nozzle is 650 m/s. The mass flow rate through the nozzle is 1500kg/h, the heat loss from the nozzle is 12000 kJ/hr. Determine the final enthalpy of steam

Air flows steadily through an engine at a constant temperature of 400k. Find the work per kilogram if the exit pressure is one-third the inlet pressure and the inlet pressure is 207 KPa. Assume that the kinetic energy and potential energy variation are negligible.

1. During a steady flow process, the pressure of the working substance drops from 400 to 40 psia, the speed increase s from 300 to 1100 fps, the internal energy of the open system decreases 30 Btu/lb, and specific volume increases from 1.2 to 9 ft^3/lb. no heat is transferred. Sketch the energy diagram. Determine the work per lb. Is it done Or by substance? Determine the work in hp for 11 lb per min.( 1 hp = 42.4 Btu/min).

Water is flowing at a rate of 100 L/s in a 20 cm diameter pipe. How fast is the water flowing in m/s?

A steel railroad track has length of 30m when the temperature is 0 degrees (a) when the temperature is 40 degrees, what is it’s length. (b) if the end of the rail are rigidly clamped at 0.0 degrees so that the expansion is prevented, what is the thermal stress set up if the rail is raised to 40 degrees

Q 4. A 0.5 kg of aluminum cube at 27 ℃ and a 1.0 kg of copper cube at 100 ℃ are placed 

in 2 kg of water at 22 ℃. Assuming no heat loss to the surroundings, calculate the final 

temperature of the mixture.

Specific heat capacities: water 𝑐𝑊 = 4187 𝐽𝑘𝑔−1𝐾

−1

, copper 𝑐𝑐𝑢 = 386 𝐽𝑘𝑔−1𝐾

−1

, 

aluminum 𝑐𝑎𝑙 = 900 𝐽𝑘𝑔−1𝐾

−1

Q 5. A 5 kg of ice cube at −10℃ is mixed with 0.1 kg of water at 80 ℃. There is no heat 

loss to the surrounding. The specific heat capacity of ice is 2.22 𝑘𝐽𝐾

−1𝑘𝑔−1

,The specific 

heat capacity of water is 4.187 𝑘𝐽𝐾

−1𝑘𝑔−1

. The specific latent heat of fusion of ice is 

333 𝑘𝐽 𝑘𝑔−1

.

(a) What is the final physical state of the mixture? (Gas, Liquid or Solid?)

Justify your answer using suitable calculations 

(b) What is the final temperature of the mixture?

A mercury-glass thermometer consists of a glass bulb filled with mercury and a 

narrow glass tube attached to the glass bulb. At 0℃, the bulb is completely filled with the 

mercury and its radius is 5 mm. As the temperature increases the mercury column rise 

through the narrow glass tube whose diameter is 0.3 mm. 

What should be the minimum length of the glass tube so that this thermometer can be 

used to measure the temperatures up to 100 ℃ ?

(Hint: ignore the thermal expansion of the glass tube)

liner expansion coefficient of glass = 3.2 × 10−6 ℃−1

volume expansion coefficient of mercury = 1.82 × 10−4 ℃−1

Assume 2 kg of hydrogen (Item B 28) are initially at 40 atm, 100 K. (a) If the hydrogen changes pressure to 1 atm without a change of temperature, find the changes of enthalpy and entropy. (b) If the hydrogen changes temperature to 35 K with no change of entropy, find the change of pressure and enthalpy.

A nozzle is a device for increasing the velocity of a steadily flowing stream. At the inlet to

a certain nozzle, the enthalpy of the fluid passing is 3000 kJ/kg and the velocity is 60 m/s.

At the discharge end, the enthalpy is 2762 kJ/kg. The nozzle is horizontal and there is

negligible heat loss from it. (a) Find the velocity at exists from the nozzle. (b) If the inlet

area is 0.1 m2 and the specific volume at inlet is 0.187 m3

/kg, find the mass flow rate.

(c) If the specific volume at the nozzle exit is 0.498 m3

/kg, find the exit area of the nozzle.