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Thermodynamics and Heat Transfer

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Thermodynamics and Heat Transfer

shape Introduction

Thermodynamics and Heat Transfer are both part of thermal engineering. "Thermodynamics" deals with the amount of energy in form of heat or work during a process and only considers the end states in equilibrium. Thermodynamics is that branch of science which studies energy and its manifestations, and provides a framework for converting from one type to the other (i.e. the laws of thermodynamics). Heat transfer, on the other hand, deals with only one type of energy (heat) and how it is transferred from one body to another. "Heat Transfer" deals with the rate of heat transfer thus, thus conveying how long a heat transfer will occur? Heat transfer deals with time and non equilibrium phenomena. Heat can only be transferred when a temperature gradient/difference exists in a body and which indicates a non equilibrium phenomena.
Thermodynamics gives "Why" a process will occur and Heat Transfer gives, "How" a process will occur when it is about transfer of heat. There are three basic ways in which heat is transferred. In fluids, heat is often transferred by convection, in which the motion of the fluid itself carries heat from one place to another. Another way to transfer heat is by conduction, which does not involve any motion of a substance, but rather is a transfer of energy within a substance (or between substances in contact). The third way to transfer energy is by radiation, which involves absorbing or giving off electromagnetic waves. Thermodynamics and Heat Transfer is one of the crucial topics in the technical ability section of various recruitment exams in India.

shape Quiz

Q1. The first law of thermodynamics is the law of
    A. con servation of mass B. con servation of energy C. conservation of momentum D. con servation of h eat Answer: B

Q2. First law of thermodynamics
    A. enables to determine change in internal energy to the system B. does not help to predict whether the system will or not undergo a change C. does not enable to determine change in entropy D. All of the above Answer: D

Q3. Stirling and Ericsson cycles are
    A. reversible cycles B. irreversible cycles C. quasi-static cycles D. semi-reversible cycles Answer: A

Q4. Carnot cycle is
    A. a reversible cycle B. an irreversible cycle C. a semi-reversible cycle D. a quasi static cycle Answer: A

Q5. Chnage in the internal energy of small temperature change DT for ideal gas is expressed by the relation
    A. [latex]U = {C}_{V}X[/latex] B. [latex]U = \frac{{C}_{P}}{{C}_{V}}[/latex] C. [latex] U = {C}_{P} - {C}_{V}[/latex] D. [latex]{C}_{P}X[/latex] - [latex] {C}_{V}X[/latex] Answer: A

Q6. If a heat engine attains 100% thermal efficiency, it violates
    A. zeroth law of thermodynamics B. first law of thermodynamics C. second law of thermodynamics D. law of conservation of energy Answer: C

Q7. A petrol engine theoretically operates on
    A. constant pressure cycle B. con stant volume cycle C. constant temperature1. D.– constant entropy cycle Answer: B

Q8. Which of the following is not an extensive property
    A. entropy B. enthalpy C. internal energy D. density Answer: D

Q9. For reversible adiabatic process, change in entropy is
    A. maximum B. minimum C. zero D. unpredictable Answer: C

Q10. Heat added in a reversible adiabatic process is equal to
    A. [latex]{P}_{1}{V}_{1} log \frac {{V}_{1}}{{V}_{2}}[/latex] B. [latex]{C}_{V} [/latex] C. Zero D. [latex]{C}_{V} ({T}_{2} - {T}_{1})[/latex] Answer: A
Q11. Change in enthalpy in a closed system is equal to heat transferred if the reversible process takes place at constant
    A. pressure B. temperature C. volume D. energy Answer: A

Q12. What are the limitations to the signs of heat exchange from hot and cold reservoirs if a two-temperature machine operates between two negative temperatures?
    A. Heat must be rejected to hot source and abstracted from cold source B. Heat must be abstracted from hot source and rejected to cold source C. Heat must be rejected to both the sour ces D. No limitation Answer: D

Q13. Ericsson cycle consists of the following four processes
    A. two isothermals and two isentropics B. isothermals and two constant volumes C. two isothermals and two constant pressures D. two adiabatics and two constant pressures Answer: C

Q14. Otto cycle consists of following four processes
    A. two isothermals and two isentropics B. two isentropics and two constant volumes C. two insentropics and one constant volume and one constant pressure D. Two isentropics and two constant pressures Answer: B

Q15. The cyclic integral of (dQ/dW) for a process is equal to
    A. positive B. Negative C. zero D. positive or negative depending upon the type of process Answer: C

Q16. Atkinson gas engine has a special feature that
    A. compression and expansion are of equal stroke lengths B. compression is on a short stroke and the expansion on a longer stroke C. isentropic compression is on a longer stroke and the expansion on a short stroke D. it employes shortest compression and expansion strokes Answer: B

QAn actual engine is to be designed having same efficiency as the Carnot cycle. Such a proposition is
    A. feasible B. impossible C. possible D. possible, but with lot of sophistications Answer: B

Q18. The basis for measuring thermodynamic property of temperature is given by
    A. law of thermodynamics B. first law of thermodynamics C. second law of thermodynamics D. third law of thermodynamics Answer: A

Q19. The ideal efficiency of a Stirling cycle with perfect regeneration and operating between two given temperature limits is
    A. equal to Carnot cycle B. less than Carnot cycle C. equal to Brayton cycle D. equal to Joule cycle Answer: A

Q20. Thermal power plant works on
    A. Carnot cycle B. Joule cycle C. Rankine cycle D. Otto cycle Answer: C
Q21. When a process undergoes a complete cycle then the change of entropy will be
    A. +ve value B. -–ve value C. zer o value D. +ve or –ve depending on initial condition Answer: C

Q22. What are the limitations to the signs of heat exchange from hot cold reservoirs if a two-temperature machine operates between two Positive temperatures
    A. heat must be rejected to hot source and abstracted from cold source B. heat must be abstracted from hot source and rejected to cold source C. heat must be rejected to both the sour ces D. heat must be abstracted from both the sources Answer: B

Q23. The ideal efficiency of Joule cycle operating between two given temperature limits is
    A. equal to Joule cycle B. equal to Carnot cycle C. equal to Brayton cycle D. less than Carnot cycle Answer: D

Q24. A Bell-Coleman cycle is a reversed
    A. Carnot cycle B. Otto cycle C. Joule cycle D. Stirling cycle Answer: C

Q25. Diesel cycle consists of following four processes
    A. two isothermals and two isentropics B. two isentropics, one constant volumes C. two isentropics, one constant volume and one constant pressure D. two isentropics and two constant pressures Answer: C

Q26. Which of the following is not a property of thermodynamic system?
    A. Pressure B. Energy C. Heat D. Volumes Answer: C

Q27. Stirling and Ericsson cycles are
    A. irreversible cycles B. quasi – static cycles C. semi – reversible cycles D. reversible cycles Answer: D

Q28. In thermodynamic cycle, heat is rejected at
    A. con stant volume B. constant pressure C. constant enthalpy D. constant temperature Answer: A

Q29. Which of the following cycle consists of three processes?
    A. cycle B. Stirling cycle C. cycle D. None of these Answer: C
Q30. Zeroth law of thermodynamics deals with
    A. concept of temperature B. en thalpy C. entropy D. external and internal energy both Answer: A

Q31. Which of the following gives the correct relation between centigrade and fahrenheit scales? (c = degree centigrade, F = degree Fahrenheit)
    A. C [latex]\frac{5}{9}[/latex](F 32) B. C [latex]\frac{5}{9}[/latex](F -32) C. C [latex]\frac{5}{9}[/latex](F+ 32) D. C [latex]\frac{5}{9}[/latex](F 32) Answer: A

Q32. Properties of substances like pressure, temperature and density in thermodynamic co-ordinates are
    A. Path function B. Point function C. Cyclic function D. Real function Answer: B

Q33. Heat is being supplied to air in a cylinder filled with friction less piston held by a constant weight. The process will be
    A. Isochoric B. Isothermal C. Isobaric D. Adiabatic Answer: C

Q34. Heat and work are
    A. Point function B. System properties C. Path function D. None of these Answer: C

Q35. Which of the following in an irreversible process?
    A. Isothermal process B. Isentrobic process C. Isoparic process D. Isenthalpic process Answer: D

Q36. First Law of thermodynamics depicts the relation between
    A. heat and work B. heat, work and system properties C. various properties of the system D. various ther modynamics processes Answer: B

Q37. If Q = Heat content of a gas, u = Internal energy P = Pressure, V = Volume, T = Temperature then which of the following statement is applicable to perfect gas and is also true for an irreversible process?
    A. dQ = dU + qdV B. Tds = d U + PdV C. dQ = Tds D. dQ = Tds + dU Answer: B

Q38. Plan k's Law deals with
    A. conservation of energy B. con servation of h eat C. con servation of mass D. con version of heat into work Answer: D

Q39. The second Law of thermodynamics defines
    A. Heat B. Entropy C. Enthalpy D. Internal energy Answer: B

Q40. The entropy of the universe is
    A. increasing B. decreasing C. constant D. unpredictable Answer: A
Q41. The changeing entrophy is zero during
    A. Reversible adiabatic process B. Hyperbolic process C. Constant pressure process D. Polytropic process Answer: A

Q42. The ratio of two specific heats of air is equal to
    A. 1.41 B. 2.41 C. 4.14 D. 0.41 Answer: A

Q43. Sensible heat is the needed to
    A. vaporise water into steam B. change the temperature of a liquid or vapour C. convert water into steam and super heat it D. measure dew point temperature Answer: B

Q44. The critical point for water is
    A. 374° C B. 373°C C. 273° C D. 323° C Answer: A

Q45. The capacity of the boiler is defined as
    A. The volume of feed water inside the shell B. The volume of steam space inside the sh ell C. The maximum pressure at which steam can be generated D. Amount of water converted into steam from 100° C to 110° C in one hour. Answer: C

Q46. Maximum heat is lost in boiler due to
    A. Unburnt carbon B. Flue gases C. Incomplete combustion D. Moisture in fuel Answer: B

Q47. The Bell – columan refrigeration cycle uses
    A. Hydrogen as a working fluid B. Air as a working fluid C. carbon di – oxide as a working fluid D. Any inert gas as a working fluid Answer: B

Q48. The refrigeration system works on
    A. First Law of thermodynamics B. Second Law of thermodynamics C. Zeroth Law of therodynomics D. None of these Answer: B

Q49. In a refrigeration system, the refrigerant gain heat
    A. Compressor B. Condenser C. Expansion value D. Evaporator Answer: D

Q50. In actual refrigeration systems, the compressor handles vapour only. This process commonly reflered to as
    A. Gas compression B. Phase compression C. Dry compression D. wet compression Answer: C
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