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Chapter 10: Problem 55

What is the modified latent heat of vaporization? For what is it used? How does it differ from the ordinary latent heat of vaporization?

Short Answer

Expert verified
Answer: The main difference between the modified and the ordinary latent heat of vaporization is that the modified latent heat takes into account the specific volume change (expansion or compression) that occurs during the phase transition, while the ordinary latent heat only considers the heat energy added or removed during the transition process.

Step by step solution

01

Definition: Modified Latent Heat of Vaporization

The modified latent heat of vaporization is a corrected value for the ordinary latent heat of vaporization, taking into account the specific volume change during the phase transition process (from liquid to vapor, or vice versa) at a given pressure and temperature. It is used in certain practical applications and calculations, such as in the design of refrigeration systems or heat exchangers.
02

Definition: Ordinary Latent Heat of Vaporization

The ordinary latent heat of vaporization is the amount of heat energy required to convert a unit mass of a substance from its liquid state to its vapor state at a constant temperature and pressure, without changing its temperature.
03

Differences between Modified and Ordinary Latent Heat of Vaporization

The main difference between the modified and the ordinary latent heat of vaporization is that the modified latent heat takes into account the specific volume change (expansion or compression) that occurs during the phase transition, while the ordinary latent heat only considers the heat energy added or removed during the transition process. The modified latent heat is more relevant in practical applications where the effect of specific volume changes on the overall heat transfer process is significant, whereas the ordinary latent heat is more suitable for simple theoretical calculations and analyses.
04

Formulas for Latent Heat of Vaporization

The ordinary latent heat of vaporization (L) can be calculated using the following formula: L = mL_v Where: - L is the ordinary latent heat of vaporization - m is the mass of the substance - L_v is the specific latent heat of vaporization (energy required to convert a unit mass of a substance from liquid to vapor) The modified latent heat of vaporization (L_m) can be calculated using the following formula: L_m = L + p(v_g - v_f) Where: - L_m is the modified latent heat of vaporization - p is the pressure during the phase transition - v_g is the specific volume of the vapor phase - v_f is the specific volume of the liquid phase
05

Applications of Latent Heat of Vaporization

The concept of latent heat of vaporization is important in many practical applications, such as in the design and operation of refrigeration systems, air conditioning systems, heat exchangers, power plants, and other systems involving phase transitions and heat transfer processes. By understanding and taking into account the latent heat of vaporization and its modified form, engineers and scientists can design more efficient and effective systems for various industrial and commercial purposes.

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Most popular questions from this chapter

Saturated ammonia vapor at a pressure of \(1003 \mathrm{kPa}\) is condensed as it flows through a \(25-\mathrm{mm}\) tube. The tube length is \(0.5 \mathrm{~m}\) and the wall temperature is maintained uniform at \(5^{\circ} \mathrm{C}\). If the vapor exits the tube at a flow rate of \(0.002 \mathrm{~kg} / \mathrm{s}\), determine the flow rate of the vapor at the inlet. Assume the Reynolds number of the vapor at the tube inlet is less than 35,000 . Is this a good assumption?

Does the amount of heat absorbed as \(1 \mathrm{~kg}\) of saturated liquid water boils at \(100^{\circ} \mathrm{C}\) have to be equal to the amount of heat released as \(1 \mathrm{~kg}\) of saturated water vapor condenses at \(100^{\circ} \mathrm{C}\) ?

Saturated steam at \(30^{\circ} \mathrm{C}\) condenses on the outside of a 4-cm- outer-diameter, 2-m-long vertical tube. The temperature of the tube is maintained at \(20^{\circ} \mathrm{C}\) by the cooling water. Determine \((a)\) the rate of heat transfer from the steam to the cooling water, \((b)\) the rate of condensation of steam, and \((c)\) the approximate thickness of the liquid film at the bottom of the tube. Assume wavy-laminar flow and that the tube diameter is large, relative to the thickness of the liquid film at the bottom of the tube. Are these good assumptions?

10-59 The Reynolds number for condensate flow is defined as \(\operatorname{Re}=4 \dot{m} / p \mu_{l}\), where \(p\) is the wetted perimeter. Obtain simplified relations for the Reynolds number by expressing \(p\) and \(\dot{m}\) by their equivalence for the following geometries: \((a)\) a vertical plate of height \(L\) and width \(w,(b)\) a tilted plate of height \(L\) and width \(W\) inclined at an angle \(u\) from the vertical, \((c)\) a vertical cylinder of length \(L\) and diameter \(D,(d)\) a horizontal cylinder of length \(L\) and diameter \(D\), and (e) a sphere of diameter \(D\).

Saturated ammonia vapor at \(25^{\circ} \mathrm{C}\) condenses on the outside of a 2 -m-long, 3.2-cm-outer-diameter vertical tube maintained at \(15^{\circ} \mathrm{C}\). Determine \((a)\) the average heat transfer coefficient, \((b)\) the rate of heat transfer, and \((c)\) the rate of condensation of ammonia. Assume turbulent flow and that the tube diameter is large, relative to the thickness of the liquid film at the bottom of the tube. Are these good assumptions?
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