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Chapter 11: Problem 138

Describe the cardiovascular counter-current mechanism in the human body.

Short Answer

Expert verified
Answer: The primary purpose of the cardiovascular counter-current mechanism is to maintain and regulate body temperature efficiently by conserving heat and minimizing heat loss to the environment. This is achieved by transferring heat from warmer blood to cooler blood in close proximity within the blood vessels.

Step by step solution

01

Introduction to Counter-Current Mechanism

The cardiovascular counter-current mechanism is a biological system present in the human body that helps maintain and regulate body temperature efficiently. This mechanism is crucial for conserving heat and minimizing heat loss to the environment.
02

Purpose of Counter-Current Mechanism

The primary purpose of the cardiovascular counter-current mechanism is to maintain and regulate body temperature in a way that conserves heat and minimizes heat loss to the environment. This is achieved by transferring heat from warmer blood to cooler blood in close proximity within the blood vessels.
03

Components of the Counter-Current Mechanism

The key components of the cardiovascular counter-current mechanism are the blood vessels, specifically arteries and veins. Arteries carry warm blood from the heart to the extremities and other parts of the body, while veins carry cooler blood back to the heart.
04

Functioning of the Counter-Current Mechanism

The counter-current mechanism functions through the close physical proximity of arteries and veins. When warm blood flows from the heart through the arteries towards the extremities (such as hands and feet), it comes into close contact with the veins carrying cooler blood back to the heart. As these blood vessels are in close proximity, heat from the warmer arterial blood gets transferred to the cooler venous blood, effectively pre-warming it before it reaches the heart. This exchange of heat helps to conserve overall body heat and minimize heat loss.
05

Counter-Current Mechanism in Different Conditions

The efficiency of the counter-current mechanism varies depending on the environmental temperature and the individual's level of activity. For example, the mechanism is more efficient in warmer environments as there is less need for heat conservation. Conversely, when the body is exposed to cold environments or when a person is engaging in physical activity, the counter-current system becomes more active to conserve heat and maintain body temperature.
06

Importance of the Counter-Current Mechanism

The cardiovascular counter-current mechanism plays a crucial role in the human body by ensuring an efficient regulation of body temperature. By conserving heat and minimizing heat loss, this system helps maintain an optimal internal environment for the proper functioning of various body processes and overall survival.

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Most popular questions from this chapter

Write an essay on the static and dynamic types of regenerative heat exchangers and compile information about the manufacturers of such heat exchangers. Choose a few models by different manufacturers and compare their costs and performance.

The condenser of a room air conditioner is designed to reject heat at a rate of \(15,000 \mathrm{~kJ} / \mathrm{h}\) from refrigerant-134a as the refrigerant is condensed at a temperature of \(40^{\circ} \mathrm{C}\). Air \(\left(c_{p}=1005 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\right)\) flows across the finned condenser coils, entering at \(25^{\circ} \mathrm{C}\) and leaving at \(35^{\circ} \mathrm{C}\). If the overall heat transfer coefficient based on the refrigerant side is \(150 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\), determine the heat transfer area on the refrigerant side.

In a 1-shell and 2-tube heat exchanger, cold water with inlet temperature of \(20^{\circ} \mathrm{C}\) is heated by hot water supplied at the inlet at \(80^{\circ} \mathrm{C}\). The cold and hot water flow rates are \(5000 \mathrm{~kg} / \mathrm{h}\) and \(10,000 \mathrm{~kg} / \mathrm{h}\), respectively. If the shelland-tube heat exchanger has a \(U A_{s}\) value of \(11,600 \mathrm{~W} / \mathrm{K}\), determine the cold water and hot water outlet temperatures. Assume \(c_{p c}=4178 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\) and \(c_{p h}=4188 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\).

Water \(\left(c_{p}=4180 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\right)\) enters the \(2.5\)-cm-internaldiameter tube of a double-pipe counter-flow heat exchanger at \(17^{\circ} \mathrm{C}\) at a rate of \(1.8 \mathrm{~kg} / \mathrm{s}\). Water is heated by steam condensing at \(120^{\circ} \mathrm{C}\left(h_{f g}=2203 \mathrm{~kJ} / \mathrm{kg}\right)\) in the shell. If the overall heat transfer coefficient of the heat exchanger is \(700 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\), determine the length of the tube required in order to heat the water to \(80^{\circ} \mathrm{C}\) using ( \(a\) ) the LMTD method and \((b)\) the \(\varepsilon-\mathrm{NTU}\) method.

A performance test is being conducted on a double pipe counter flow heat exchanger that carries engine oil and water at a flow rate of \(2.5 \mathrm{~kg} / \mathrm{s}\) and \(1.75 \mathrm{~kg} / \mathrm{s}\), respectively. Since the heat exchanger has been in service over a long period of time it is suspected that the fouling might have developed inside the heat exchanger that might have affected the overall heat transfer coefficient. The test to be carried out is such that, for a designed value of the overall heat transfer coefficient of \(450 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) and a surface area of \(7.5 \mathrm{~m}^{2}\), the oil must be heated from \(25^{\circ} \mathrm{C}\) to \(55^{\circ} \mathrm{C}\) by passing hot water at \(100^{\circ} \mathrm{C}\left(c_{p}=4206 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\right)\) at the flow rates mentioned above. Determine if the fouling has affected the overall heat transfer coefficient. If yes, then what is the magnitude of the fouling resistance?
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